Aetna considers genetic testing medically necessary to establish a molecular diagnosis of an inheritable disease when all of the following are met:

• The member displays clinical features, or is at direct risk of inheriting the mutation in question (pre-symptomatic); and
• The result of the test will directly impact the treatment being delivered to the member; and
• After history, physical examination, pedigree analysis, genetic counseling, and completion of conventional diagnostic studies, a definitive diagnosis remains uncertain, and one of the following diagnoses is suspected (this list is not all-inclusive):

* Medically necessary if results of the adrenocortical profile following cosyntropin stimulation test are equivocal or for purposes of genetic counseling.

** Electrophoresis is the appropriate initial laboratory test for individuals judged to be at-risk for a hemoglobin disorder.

In the absence of specific information regarding advances in the knowledge of mutation characteristics for a particular disorder, the current literature indicates that genetic tests for inherited disease need only be conducted once per lifetime of the member.

Note: Genetic testing of Aetna members is excluded from coverage under Aetna's benefit plans if the testing is performed primarily for the medical management of other family members who are not covered under an Aetna benefit plan.  In these circumstances, the insurance carrier for the family members who are not covered by Aetna should be contacted regarding coverage of genetic testing.  Occasionally, genetic testing of tissue samples from other family members who are not covered by Aetna may be required to provide the medical information necessary for the proper medical care of an Aetna member.  Aetna covers genetic testing for heritable disorders in non-Aetna members when all of the following conditions are met:

• The information is needed to adequately assess risk in the Aetna member; and
• The information will be used in the immediate care plan of the Aetna member; and
• The non-Aetna member's benefit plan, if any, will not cover the test (a copy of the denial letter*** from the non-Aetna member's benefit plan must be provided).

*** Aetna may also request a copy of the certificate of coverage from the non-member's health insurance plan if: (i) the denial letter from the non-member's insurance carrier fails to specify the basis for non-coverage; (ii) the denial is based on a specific plan exclusion; or (iii) the genetic test is denied by the non-member's insurance carrier as not medically necessary and the medical information provided to Aetna does not make clear why testing would not be of significant medical benefit to the non-member.

Medical Necessity Criteria for Specific Genetic Tests (I - XV):

1. Adenosis polyposis coli (APC):

   Aetna considers adenosis polyposis coli (APC) genetic testing medically necessary for either of the following indications:

   1. Members with greater than 20 colonic polyps; or
   2. Members with 1st-degree relatives (i.e., siblings, parents, and offspring) diagnosed with familial adenomatous polyposis (FAP) or with a documented APC mutation.  The specific APC mutation should be identified in the affected 1st-degree relative with FAP prior to testing the member, if feasible.  Full sequence APC genetic testing is considered medically necessary only when it is not possible to determine the family mutation first.

   Aetna considers APC genetic testing experimental and investigational for all other indications (e.g., desmoid tumor) because its effectiveness for indications other than the ones listed above has not been established.

2. CADASIL:
   
   Aetna considers DNA testing for CADASIL medically necessary for either of the following indications:

   1. Pre-symptomatic individuals where there is a family history consistent with an autosomal dominant pattern of inheritance and there is a known mutation in an affected member of the family; or
   2. Symptomatic individuals who have a family history consistent with an autosomal dominant pattern of inheritance of this condition (clinical signs and symptoms of CADASIL include stroke, cognitive defects and/or dementia, migraine, and psychiatric disturbances).

   Aetna considers CADASIL genetic testing experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established.

3. Catecholaminergic polymorphic ventricular tachycardia (CPVT):
   
   Aetna considers genetic testing for CPVT medically necessary for the following indications:

   1. Children or young adults (less than 40 years of age) with a 1st degree relative with a clinical diagnosis of CPVT, or a 1st or 2nd degree relative with a defined CPVT mutation; and
   2. Persons who display exercise- or emotion-induced PVT or ventricular fibrillation, occurring in a structurally normal heart.

4. Cystic fibrosis:

   Aetna considers genetic carrier testing for cystic fibrosis medically necessary for members in any of the following groups:

   1. Couples seeking prenatal care; or
   2. Couples who are planning a pregnancy; or
   3. Persons with a family history of cystic fibrosis; or
   4. Persons with a 1st degree relative identified as a cystic fibrosis carrier; or
   5. Reproductive partners of persons with cystic fibrosis.

   Aetna considers genetic carrier testing for cystic fibrosis experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established.

   Aetna considers a core panel of 25 mutations that are recommended by the American College of Medical Genetics (ACMG) medically necessary for cystic fibrosis genetic testing.  The standard CF transmembrane regulator (CFTR)mutation panel is as follows (Available at: http://www.acmg.net):

   ΔF508	ΔI507	G542X	G551D	W1282X	N1303K
   R553X	621+1G→ T	R117H	1717-1G→ A	A455E	R560T
   R1162X	G85E	R334W	R347P	711+1G→ T	1898+1G→ A
   2184delA	1078delT	3849+10kbC→ T	2789+5G→ A	3659delC	I148T
   3120+1G→ A

   
   
   Aetna considers experimental and investigational screening for cystic fibrosis mutations that extend beyond the standard mutation panel recommended by the ACMG.

5. Factor V Leiden:

   Aetna considers Factor V Leiden genetic testing medically necessary for members with any of the following indications:

   1. Age less than 50, any venous thrombosis; or
   2. Myocardial infarction in female smokers under age of 50 ; or
   3. Recurrent venous thrombosis; or
   4. Relatives of individuals with venous thrombosis under age of 50; or
   5. Venous thrombosis and a strong family history of thrombotic disease; or
   6. Venous thrombosis in pregnant women or women taking oral contraceptives; or
   7. Venous thrombosis in unusual sites (such as hepatic, mesenteric, and cerebral veins).

   Aetna considers Factor V Leiden genetic testing experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established .

   Aetna considers Factor V HR2 allele DNA mutation analysis experimental and investigational because its effectiveness has not been established.

6. Familial nephrotic syndrome (NPHS1, NPHS2):

   1. Aetna considers genetic testing for an NPHS1 mutation medically necessary for children with congenital nephrotic syndrome (nephrotic syndrome appearing within the first month of life) who are of Finnish descent or who have a family history of congenital nephrotic syndrome.  Genetic testing for NPHS1 mutations are considered experimental and investigational for screening other persons with nephrotic syndrome and for all other indications because its effectiveness for other indications other has not been established.
   2. Aetna considers genetic testing for an NPHS2 mutation medically necessary for children with steroid resistant nephrotic syndrome (SRNS) and for children who have a family history of SRNS.  Genetic testing for NPHS2 is considered experimental and investigational for persons with steroid-responsive nephrotic syndrome and for all other indications because its effectiveness for indications other than the ones listed above has not been established.

   Aetna considers genetic testing for familial nephrotic syndrome experimental and investigational for all other indications.

7. Fragile X:
   
   Aetna considers genetic testing for fragile X syndrome medically necessary for members in any of the following risk categories where the results of the test will affect a member's clinical management or reproductive decisions:

   1. Individuals with mental retardation, developmental delay, or autism; or
   2. Individuals planning a pregnancy who have either of the following:
      
      
      1. A family history of fragile X syndrome, or
      2. A family history of undiagnosed mental retardation; or
         

   3. Fetuses of known carrier mothers.  Prenatal testing of a fetus by amniocentesis or chorionic villus sampling is indicated following a positive Fragile X carrier test in the mother.

   Aetna considers Fragile X DNA testing medically necessary for members with a negative cytogenetic test for fragile X if they have any physical or behavioral characteristics of fragile X syndrome and have a family history of fragile X syndrome or undiagnosed mental retardation.

   Aetna considers Fragile X DNA testing medically necessary for members with a phenotype that is not typical for fragile X syndrome who have a cytogenetic test that is positive for fragile X.

   Aetna considers population-based fragile X syndrome screening of individuals who are not in any of the above-listed risk categories experimental and investigational because its effectiveness for indications other than the ones listed above has not been established.

8. Hereditary hemochromatosis:
   
   Aetna considers genetic testing for HFE gene mutations medically necessary for persons who meet all of the following criteria:

   1. Member who has symptoms consistent with iron overload; and
   2. Member who has 2 consecutive transferrin saturations of 45 % or more.

   Aetna considers genetic testing for HFE gene mutations medically necessary for 1st degree relatives of persons homozygous for HFE gene mutations.  Genetic testing for hereditary hemochromatosis is considered experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established.

9. Hereditary non-polyposis colorectal cancer (HNPCC):

   1. Aetna considers genetic testing for HNPCC (MLH1, MSH2, MSH6, PMS2 sequence analysis) medically necessary for members who meet either of the following criteria:

      1. Member meets Amsterdam II criteria or revised Bethesda guidelines (see appendix); or
      2. Member is diagnosed with endometrial cancer before age 50 years; or
      3. Member has a 1st- or 2nd-degree relative with a disease confirmed to be caused by a HNPCC mutation (genes MLH1, MSH2, MSH6, PMS2) upon testing of the 1st- or 2nd-degree relative.

   2. Microsatellite instability (MSI) testing or immunohistochemical (IHC) analysis of the tumor (colorectal and/or endometrial) is considered medically necessary as an initial test in persons with colorectal cancer who meet the revised Bethesda criteria (see appendix) in order to identify those persons who should proceed with HNPCC mutation analysis.

   See also CPB 0516 - Colorectal Cancer Screening.

10. Hereditary pancreatitis (PRSS1):

    Aetna considers genetic testing for hereditary pancreatitis (PRSS1 mutation) medically necessary in symptomatic persons with any of the following indications:

    1. A family history of pancreatitis in a 1st-degree (parent, sibling, child) or 2nd-degree (aunt, uncle, grandparent) relative; or
    2. An unexplained episode of documented pancreatitis occurring in a child that has required hospitalization, and where there is significant concern that hereditary pancreatitis should be excluded; or
    3. Recurrent (2 or more separate, documented episodes with hyper-amylasemia) attacks of acute pancreatitis for which there is no explanation (anatomical anomalies, ampullary or main pancreatic strictures, trauma, viral infection, gallstones, alcohol, drugs, hyperlipidemia, etc.); or
    4. Unexplained (idiopathic) chronic pancreatitis.

    This policy is based upon guidelines from the Consensus Committees of the European Registry of Hereditary Pancreatic Diseases, the Midwest Multi-Center Pancreatic Study Group and the International Association of Pancreatology (Ellis et al, 2001).

    Aetna considers genetic testing for hereditary pancreatitis experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established.

11. Long QT syndrome:

    Aetna considers genetic testing for long QT syndrome medically necessary for either of the following:

    1. Persons with a prolonged QT interval on resting electrocardiogram (a corrected QT interval (QTc) of 470 msec in males and 480 msec in females) without an identifiable external cause for QTc prolongation (such as heart failure, bradycardia, electrolyte imbalances, certain medications and other medical conditions); or
    2. Persons with 1st-degree relatives (siblings, parents, offspring) with a defined LQT mutation, or long QT syndrome in sudden death (1st or 2nd degree) close relatives.

    Aetna considers genetic testing for long QT syndrome experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established.

12. MYH-associated polyposis:

    Aetna considers testing for MYH mutations medically necessary for the following indications:

    1. Asymptomatic siblings of individuals with known MYH polyposis; or
    2. Individuals with personal history of adenomatous polyposis who have negative APC mutation testing and a negative family history for adenomatous polyposis; or
    3. Individuals with personal history of adenomatous polyposis whose family history is consistent with recessive inheritance (i.e., family history is positive only for sibling(s)).

    Aetna considers MYH mutations testing experimental and investigational for members of a polyposis family with clear autosomal dominant inheritance, or for any other indications because its effectiveness for indications other than the ones listed above has not been established.

13. Primary dystonia (DYT1):
    
    Aetna considers genetic testing for DYT1 medically necessary for the following indications:

    1. Parents of children with an established DYT1 mutation, for purposes of family planning; or
    2. Persons with onset of primary dystonia other than focal cranial-cervical dystonia after age 30 years who have a affected relative with early onset (before 30 years); or
    3. Persons with primary dystonia with onset before age 30 years.

    Aetna considers DYT-1 testing experimental and investigational for all other indications, including the following because its effectiveness for indications other than the ones listed above has not been established:

    1. Asymptomatic individuals (other than parents of affected children), including those with affected family members (genetic testing for dystonia (DYT-1) is not sufficient to make a diagnosis of dystonia unless clinical features show dystonia); or
    2. Persons with onset of symptoms after age 30 years who either have focal cranial-cervical dystonia; or 
    3. Persons with onset of symptoms after age 30 years who have no affected relative with early onset dystonia.

    This policy is adapted from guidelines from the European Federation of Neurological Societies.

14. SHOX-related short stature:

    Aetna considers genetic testing for SHOX-related short stature medically necessary for children and adolescents with any of the following features:

    1. Above-average body mass index (BMI); or
    2. Cubitus valgus (increased carrying angle); or
    3. Dislocation of the ulna at the elbow; or
    4. Increased sitting height/height ratio; or
    5. Madelung deformity of the forearm; or
    6. Muscular hypertrophy; or
    7. Reduced arm span/height ratio; or
    8. Short or bowed forearm.

    Aetna considers genetic testing for SHOX-related short stature experimental and investigational for all other indications because its effectiveness for indications other than the ones listed above has not been established. 

15. Hypertrophic cardiomyopathy (HCM):

    Aetna considers genetic testing for HCM medically necessary for individuals who are at-risk for development of HCM, defined as having a close (1st or 2nd degree) relative with established HCM, when there is a known pathogenic gene mutation present in an affected relative.  Aetna considers genetic testing for HCM experimental and investigational for all other indications because its effectiveness for indications other than the one listed above has not been established.

16. Familial hypocalciuric hypercalcemia:

    Aetna considers familial hypocalciuric hypercalcemia (FHH) medically necessary in any of the following:

    1. Atypical cases where no family members are available for testing; or
    2. Families with familial isolated hyperparathyroidism; or
    3. Infants or children under 10 years of age in whom neonatal hyperparathyroidism, neonatal severe hyperparathyroidism, and FHH are the commonest causes of parathyroid hormone-dependent hypercalcemia; or
    4. Individuals with overlap in the calcium/creatinine (Ca/Cr) clearance ratio, namely between 0.01 and 0.02; or
    5. Individuals with the phenotype of FHH whose parents are both normocalcemic (i.e., FHH possibly caused by a de novo CaSR mutation).

17. PTEN Gene Testing
    
    Based upon guidlines from the National Comprehensive Cancer Network, PTEN gene testing is considered medically necessary in individuals with a suspected or known clinical diagnosis of Cowden syndrome or Bannayan-Riley-Ruvalcaba syndrome (BRR), or a known family history of a PTEN mutation who meet any of the following criteria:

    1. A relative with a known deleterious PTEN gene mutation; or
    2. Personal history of any of the following: 
       
       
       1. Bannayan RIley-Ruvalcaba syndrome; or 
       2. Adult Lhermitte-Duclos disease (LDD); or
       3. Autism-spectrum disorder and macrocephaly; or 
       4. At least 2 biopsy-proven trichilemmomas; or 
       5. Macrocephaly plus one other major criteria*; or
       6. Three major criteria* without macrocephaly; or
       7. One major and at least three minor criteria*; or
       8. Four or more minor criteria*.
    3. Family history of both of the following: 
       
       
       1. At-risk relative (includes 1st-degree relative or more distand relatives if the 1st degree relative is unavailable or unwilling to be tested) with a clinical diagnosis of Cowden syndrome or BRR (no previous genetic testing); and 
       2. One major or two minor criteria* in the at-risk relative.

* Criteria for PTEN genetic testing purposes are:

Major:

• Breast cancer
• Mucocutaneous lesions
  
  
  • One biopsy-proven trichilemmoma
  • Multiple palmoplantar keratoses
  • Multi-focal or extensive oral mucosal papillomatosis
  • Multiple cutaneous facial papules (often verrucous)
  • Macular pigmentation of glans peni
• Macrocephaly (97th percentile or greater; 58 cm in adult women, 60 cm in adult men)
• Endometrial cancer
• Non-medullary thyroid cancer
• Multiple GI hamartomas or ganglioneuromas

Minor:

• Other thyroid lesions (e.g., adenoma, nodule(s), goiter)
• Mental retardation (IQ < 75)
• Autism spectrum disorder
• Single gastrointestinal hamartoma or ganglioneuroma
• Fibrocystic disease of the breast
• Lipomas
• Fibromas
• Renal cell carcinoma
• Uterine fibroids.

1. Li-Fraumeni syndrome (TP53 gene)
   
   TP53 gene testing is considered medically necessary for individuals with a suspected or known clinical diagnosis of Li-Fraumeni syndrome (LFS) or Li-Fraumeni-Like syndrome, or a known family history of a TP53 mutation.  Testing is considered medically necessary in individuals whose medical and/or family history is consistent with any of these:

   1. A relative with a known deleterious TP53 gene mutation; or
   2. A diagnosis of classic Li-Fraumeni syndrome, defined by all of the following:
      
      
      1. Diagnosis of sarcoma before the age of 45 years; and
      2. A parent, child, or full sibling diagnosed with cancer before the age of 45 years; and
      3. An additional 1st- or 2nd-degree relative in the same lineage with cancer diagnosed before age 45 years, or a sarcoma at any age; or
         
         
   3. Persons meeting Chompret criteria:
      
      
      1. Persons with a tumor from the LFS tumor spectrum (e.g., soft tissue sarcoma, osteosarcoma, brain tumor, breast cancer, adrenocortical carcinoma, leukemia, lung  bronchoalveolar cancer) before age 46 years AND at least one first- or second-degree relative with any of the aforementioned cancers (other than breast cancer if the proband has breast cancer) before the age of 56 years or with multiple primaries at any age; or
      2. Persons with multiple tumors (except multiple breast tumors), two of which belong to the LFS tumor spectrum with the initial cancer occurring before the age of 46 years; or
      3. Individuals with adrenocortical carcinoma or choroid plexus carcinoma at any age of onset, regardless of family history; or
         
         
   4. A diagnosis of breast cancer before age 30 years with a negative BRCA1/2 test especially if there is a family history of sarcoma, brain tumor, or adrenocortical carcinoma. 
      
      **** Cancers associated with Li-Fraumeni syndrome include but are not limited to premenopausal breast cancer, bone and soft tissue sarcomas, acute leukemia, brain tumor, adrenocortical carcinoma, choroid plexus carcinoma, colon cancer, and early onset of other adenocarcinomas or other childhood cancers.  Note that Ewing sarcoma is less likely to be related to Li-Fraumeni as compared to other sarcomas.
2. Peutz-Jeghers syndrome
   
   Based on NCCN guidelines, STK11 (LKB1) gene testing may be considered for individuals with a suspected or known clinical diagnosis of Peutz-Jeghers syndrome, or a known family history of a STK11 (LKB1) mutation.  Testing may be considered for individuals whose medical and/or family history is consistent with any of the following:
   
   
   1. A relative with a known deleterious STK11 (LKB1) gene mutation; or
   2. A clinical diagnosis of PJS based on at least 2 of the following features:
      
      
      1. At least 2 PJS-type hamartomatous polyps of the small intestine;
      2. Mucocutaneous hyperpigmentation of the mouth, lips, nose, eyes, genitalia, or fingers;
      3. A family history of PJS.

3. Ashkenazi Jewish Testing Panel
   
   Aetna considers medically necessary preconception or prenatal carrier screening for couples of Ashkenazi Jewish ancestry with a panel of genetic tests recommended by the American College of Medical Genetics (ACMG):

   1. Tay Sachs disease
   2. Canavan disease
   3. Cystic fibrosis
   4. Familial dysautonomia
   5. Bloom syndrome
   6. Fanconi anemia
   7. Niemann-Pick disease
   8. Gaucher disease
   9. Mucolipidosis IV
      
      If only one partner is of Ashkenazi Jewish ancestry, then testing of that partner is considered medically necessary. Testing of the other partner is considered medically necessary only if the result of testing of the Ashkenazi Jewish partner is positive.

4. Universal Genetic Test (Counsyl)

   Aetna considers as experimental and investigational components of the Counsyl Universal Genetic Test that are not recommended for routine preconceptional or prenatal screening by the American College of Medical Genetics and the American College of Obstetricians and Gynecologists. Components of the Counsyl Universal Genetic Test that are considered medically necessary for routine screening include the following:

   • Genetic testing for cystic fibrosis; and
   • Genetic testing for hemoglobinopathies (beta thalassemia and sickle cell disease) for persons of African, Southeast Asian, or Mediterranian descent; and
   • Ashkenazi Jewish genetic screening panel (Bloom syndrome, Canavan disease, Fanconi anemia, familial dysautonomia, Gaucher disease, mucolipidosis IV, Niemann-Pick disease types A and B, spinal muscular atrophy, and Tay-Sachs disease) for persons of Ashkenazi Jewish descent.

5. Aetna considers genetic testing experimental and investigational for any of the following:

   1. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C)
   2. Brugada syndrome
   3. Choroidal neovascularization (e.g., Retnagene)
   4. Coronary artery disease (e.g., the Corus CAD gene expression test)
   5. Dilated cardiomyopathy [CMD1A]
   6. Epidermolytic hyperkatosis
   7. Familial Alzheimer disease
   8. Familial amyotrophic lateral sclerosis (SOD1 mutation)
   9. Familial cold urticaria/familial cold autoinflammatory syndrome
   10. Familial partial lipodystrophy [FPLD2]) 
   11. Glioblastoma multiforme
   12. Hemiplegic migraine (HM)
   13. Hemophilia C (F11 (Factor XI))
   14. Klippel-Feil syndrome
   15. Lactose intolerance
   16. Malignant melanoma
   17. Myoclonus-dystonia (epsilon-sarcoglycan gene (SCGE) deletion analysis)
   18. Migrainous vertigo
   19. Osteogenesis imperfecta
   20. Parkinson disease
   21. Polycystic kidney disease
   22. Prostate cancer 
   23. Seizure (e.g., creatine transporter 1 sequencing for testing parents of individuals with seizures; GABRG2 mutations and SCN1A deletion test for infantile febrile seizures)
   24. Sleep-walkin
   25. Type 2 diabetes.

6. Aetna considers the following tests experimental and investigational.

   • Home genetic tests
   • OncoVue breast cancer risk test.

See also CPB 0189 - Genetic Counseling, CPB 0227 BRCA Testing, Prophylactic Mastectomy, and Prophylactic Oophorectomy, CPB 0349 Alzheimer's Disease: Diagnosis, and CPB 0715 - Pharmacogenetic and Pharmacodynamic Testing.

According to the American College of Medical Genetics (ACMG), an important issue in genetic testing is defining the scope of informed consent.  The obligation to counsel and obtain consent is inherent in the clinician-patient and investigator-subject relationships.  In the case of most genetic tests, the patient or subject should be informed that the test might yield information regarding a carrier or disease state that requires difficult choices regarding their current or future health, insurance coverage, career, marriage, or reproductive options.  The objective of informed consent is to preserve the individual's right to decide whether to have a genetic test.  This right includes the right of refusal should the individual decide the potential harm (stigmatization or undesired choices) outweighs the potential benefits.

DNA-based mutation analysis is not covered for routine carrier testing for the diagnosis of Tay-Sachs and Sandhoff disease.  Under accepted guidelines, diagnosis is primarily accomplished through biochemical assessment of serum, leukocyte, or platelet hexosaminidase A and B levels.  The literature states that mutation analysis is appropriate for individuals with persistently inconclusive enzyme-based results and to exclude pseudo-deficiency (non-disease related) mutations in carrier couples.

Testing of a member who is at substantial familial risk for being a heterozygote (carrier) for a particular detectable mutation that is recognized to be attributable to a specific genetic disorder is only covered for the purpose of prenatal counseling under plans with this benefit (see CPB 0189 - Genetic Counseling).

Confirmation by molecular analysis of inborn errors of metabolism by traditional screening methodologies (e.g., Guthrie microbiologic assays) is covered.  Rigorous clinical evaluation should precede diagnostic molecular testing.

In many instances, reliable mutation analysis requires accurate determination of specific allelic variations in a proband (affected individual in a family) before subsequent carrier testing in other at-risk family members can be accurately performed.  Coverage of testing for individuals who are not Aetna members is not provided, except under the limited circumstances outlined in the policy section above.

Hereditary non-polyposis colon cancer

Hereditary non-polyposis colon cancer ([HNPCC], Lynch syndrome) is one of the most common cancer predisposition syndromes affecting 1 in 200 individuals and accounting for 13 to 15 % of all colon cancer.  HNPCC is defined clinically by early-onset colon carcinoma and by the presence of other cancers such as endometrial, gastric, urinary tract and ovarian found in at least 3 first-degree relatives.  Two genes have been identified as being primary responsible for this syndrome: hMLH1 at chromosome band 3p21 accounts for 30 % of HNPCC2,3 and hMLH2 or FCC at chromosome band 2p22 which together with hMLH1 accounts for 90 % of HNPCC.

Unlike other genetic disorders that are easily diagnosed, the diagnosis of HNPCC relies on a very strongly positive family history of colon cancer.  Specifically, several organizations have defined criteria that must be met to make the diagnosis of HNPCC.

Although HNPCC lacks strict clinical distinctions that can be used to make the diagnosis, and therefore diagnosis is based on the strong family history, genetic testing is now available to study patient's DNA for mutations to one of the mismatch repair genes.  A mutation to one of these genes is a characteristic feature and confirms the diagnosis of HNPCC.  Identifying individuals with this disease and performing screening colonoscopies on affected persons may help reduce colon cancer mortality.

Microsatellite instability (MSI) is found in the colorectal cancer DNA (but not in the adjacent normal colorectal mucosa) of most individuals with germline mismatch repair gene mutations.  In combination with immunohistochemistry for MSH2 and MLH1, MSI testing using the Bethesda markers should be performed on the tumor tissue of individuals putatively affected with HNPCC.  A result of MSI-high in tumor DNA usually leads to consideration of germline testing for mutations in the MSH2 and MLH1 genes.  Individuals with MSI-low or microsatellite stable (MSS) results are unlikely to harbor mismatch repair gene mutations, and further genetic testing is usually not pursued.

HNPCC is caused by germline mutation of the DNA mismatch repair genes.  Over 95 % of HNPCC patients have mutations in either MLH1 or MSH2.  As a result, sequencing for mismatch repair gene mutations in suspected HNPCC families is usually limited to MLH1 and MSH2 and sometimes MSH6 and PMS2.  In general, MSH6 and PMS2 sequence analysis is performed in persons meeting aforementioned criteria for genetic testing for HNPCC, and who do not have mutations in either the MLH1 or MSH2 genes.  In addition, single site MSH6 or PMS2 testing may be appropriate for testing family members of persons with HNPCC with an identified MSH6 or PMS2 gene mutation.

HNPCC is a relatively rare disease, which makes screening the entire populace burdensome and ineffective.  The incidence of this disease, even among the families of patients with colon cancer, is too small to make screening effective. (See also CPB 0189 - Genetic Counseling and CPB 0227 - BRCA Testing, Prophylactic Mastectomy, and Prophylactic Oophorectomy).

Familial adenomatous polyposis (FAP)

Familial adenomatous polyposis (FAP) is caused by mutation of the adenomatous polyposis coli (APC) gene.  According to guidelines from the American Gastroenterological Association (AGA, 2001), adenomatous polyposis coli gene testing is indicated to confirm the diagnosis of familial adenomatous polyposis, provide pre-symptomatic testing for at-risk members (1st degree relatives 10 years or older of an affected patient), confirm the diagnosis of attenuated familial adenomatous polyposis in those with more than 20 adenomas, and test those 10 years or older at risk for attenuated FAP.

The AGA guidelines state that germline testing should first be performed on an affected member of the family to establish a detectable mutation in the pedigree.  If a mutation is found in an affected family member, then genetic testing of at-risk members will provide true positive or negative results.  The AGA guidelines state that, if a pedigree mutation is not identified, further testing of at-risk relatives should be suspended because the gene test will not be conclusive: a negative result could be a false negative because testing is not capable of detecting a mutation even if present.  When an affected family member is not available for evaluation, starting the test process with at-risk family members can provide only positive or inconclusive results.  In this circumstance, a true negative test result for an at-risk individual can only be obtained if another at-risk family member tests positive for a mutation.

MYH-associated polyposis

MYH is a DNA repair gene that corrects DNA base pair mismatch errors in the genetic code before replication.  Mutation of the MYH gene may result in colon cancer.  In this regard, the MYH gene has been found to be significantly involved in colon cancer, both in cases where there is a clear family history of the disease, as well as in cases without any sign of a hereditary cause.

The National Comprehensive Cancer Network (NCCN)'s practice guidelines on colorectal cancer screening (2006) recommended testing for MYH mutations for individuals with personal history of adenomatous polyposis (more than 10 adenomas, or more than 15 cumulative adenomas in 10 years) either consistent with recessive inheritance or with adenomatous polyposis with negative adenomatous polyposis coli (APC) mutation testing.  The guideline noted that when polyposis is present in a single person with negative family history, de novo APC mutation should be tested; if negative, testing for MYH should follow.  When family history is positive only for a sibling, recessive inheritance should be considered and MYH testing should be done first.  In a polyposis family with clear autosomal dominant inheritance, and absence of APC mutation, MYH testing is unlikely to be informative.  Members in such family are treated according to the polyposis phenotype, including classical or attenuated FAP.

Factor V Leiden mutation

Factor V Leiden mutation is the most common hereditary blood coagulation disorder in the United States.  It is present in 5 % of the Caucasian population and 1.2 % of the African-American population.  Factor V Leiden increases the risk of venous thrombosis 3 to 8 fold for heterozygous individuals and 30 to 140 fold for homozygous individuals.  Factor V Leiden mutation has been associated with the following complications:

• Cerebrovascular accident and myocardial infarction
• Deep venous thrombosis
• Gallbladder dysfunction
• Preeclampsia and/or eclampsia
• Pulmonary embolism
• Unexplained miscarriage
• Venous thrombosis
  

According to the American College of Medical Genetics, Factor V Leiden genetic testing is indicated in the following patients:

• Age less than 50, any venous thrombosis; or
• Myocardial infarction in female smokers under age 50; or
• Recurrent venous thrombosis; or
• Relatives of individuals with venous thrombosis under age 50; or
• Venous thrombosis and a strong family history of thrombotic disease; or
• Venous thrombosis in pregnant women or women taking oral contraceptives; or
• Venous thrombosis in unusual sites (such as hepatic, mesenteric, and cerebral veins).
  

The ACMG does not recommend random screening of the general population for factor V Leiden.  Routine testing is also not recommended for patients with a personal or family history of arterial thrombotic disorders (e.g., acute coronary syndromes or stroke) except for the special situation of myocardial infarction in young female smokers.  According to the ACMG, testing may be worthwhile for young patients (less than 50 years of age) who develop acute arterial thrombosis in the absence of other risk factors for atherosclerotic arterial occlusive disease.  The ACMG does not recommend prenatal testing or routine newborn screening for factor V Leiden mutation.

The ACMG does not recommend general screening for factor V Leiden mutation before administration of oral contraceptives.  The ACMG recommends targeted testing prior to oral contraceptive use in women with a personal or family history of venous thrombosis.

Factor V Leiden screening of asymptomatic individuals with other recognized environmental risk factors, such as surgery, trauma, paralysis, and malignancy is not necessary or recommended by the ACMG, since all such individuals should receive appropriate medical prophylaxis for thrombosis regardless of carrier status.  When Factor V Leiden testing is indicated, the ACMG recommends either direct DNA-based genotyping or factor V Leiden-specific functional assay (e.g., activated protein C (APC) resistance).  Patients who test positive by a functional assay should then be further studied with the DNA test for confirmation and to distinguish heterozygotes from homozygotes.  According to the ACMG, patients testing positive for factor V Leiden or APC resistance should be considered for molecular genetic testing for prothrombin 20210A, the most common thrombophilia with overlapping phenotype for which testing is easily and readily available.  The prothrombin 20210A mutation is the second most common inherited clotting abnormality, occurring in 2 % of the general population.  It is only a mild risk factor for thrombosis, but may potentiate other risk factors (such as Factor V Leiden, oral contraceptives, surgery, trauma, etc.).

A factor V gene haplotype (HR2) defined by the R2 polymorphism (A4070G) may confer mild APC resistance and interact with the factor V Leiden mutation to produce a more severe APC resistance phenotype (Bernardi et al, 1997; de Visser et al, 2000; Mingozzi et al, 2003).  In one study, co-inheritance of the HR2 haplotype increased the risk of venous thromboembolism associated with factor V Leiden by approximately 3-fold (Faioni et al, 1999).  However, double heterozygosity for factor V Leiden and the R2 polymorphism was not associated with a significantly higher risk of early or late pregnancy loss than a heterozygous factor V Leiden mutation alone (Zammiti et al, 2006).  Whether the HR2 haplotype alone is an independent thrombotic risk factor is still unclear.  Several studies have suggested that the HR2 haplotype is associated with a 2-fold increase in risk of venous thromboembolism (Alhenc-Gelas et al, 1999; Jadaon and Dashti, 2005).  In contrast, other studies (de Visser 2000; Luddington et al, 2000; Dindagur et al, 2006) found no significant increase in thrombotic risk (GeneTests, University of Washington, Seattle, 2007).

CADASIL

CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) is a rare, genetically inherited, congenital vascular disease of the brain that causes strokes, subcortical dementia, migraine-like headaches, and psychiatric disturbances.  CADASIL is very debilitating and symptoms usually surface around the age of 45.  Although CADASIL can be treated with surgery to repair the defective blood vessels, patients often die by the age of 65.  The exact incidence of CADASIL in the United States is unknown.

DNA testing for CADASIL is appropriate for symptomatic patients who have a family history consistent with an autosomal dominant pattern of inheritance of this condition.  Clinical signs and symptoms of CADASIL include stroke, cognitive defects and/or dementia, migraine, and psychiatric disturbances.  DNA testing is also indicated for pre-symptomatic patients where there is a family history consistent with an autosomal dominant pattern of inheritance and there is a known mutation in an affected member of the family.  This policy is consistent with guidelines on CADASIL genetic testing from the European Federation of Neurological Societies.

Cystic fibrosis

Cystic fibrosis is the most common potentially fatal autosomal recessive disease in the United States.  It is characterized by chronic progressive disease of the respiratory system, malabsorption due to pancreatic insufficiency, increased loss of sodium and chloride in sweat, and male infertility as a consequence of atresia of the vas deferens.  Pulmonary disease is the most common cause of mortality and morbidity in individuals with CF.  The incidence of this disease ranges from 1:500 in Amish (Ohio) to 1:90,000 in Hawaiian Orientals, and is estimated to be 1:2,500 newborns of European ancestry.  It occurs less frequently in people with other ethnic and racial backgrounds.  About 1:25 persons of European ancestry is a carrier (or heterozygote), possessing one normal and one abnormal CF gene.  Because of recent advances in clinical management of CF, babies born today are expected to live well into middle age.

Currently, the most frequently employed test for CF is the quantitative pilocarpine iontophoresis sweat test.  Sweat chloride is more reliable than sweat sodium for diagnostic purposes with a sensitivity of 98 % and a specificity of 83 %.  However, this test can not detect CF carriers because the electrolyte content of sweat is normal in heterozygotes (Wallach, 1991).  The gene for CF (cystic fibrosis trans-membrane conductance regulator, CFTR) was cloned, and the principal mutant gene in white people (DF508) was characterized in 1989.  This mutation is due to a 3-base-pair deletion that results in the loss of a phenylalanine at position 508 from the 1,480-amino acid coding region (Riordan et al, 1989).  This mutation is found in approximately 70 % of carriers of European ancestry, but the relative frequency varies from 30 % in Ashkenazi Jews to 88 % in Danes (Cutting et al, 1992).  Available evidence indicates that CFTR functions as a chloride channel, although it may also serve other functions.  Since then, more than 200 CF mutations have been described.  Five of the most common mutations (DF508, G542X, F551D, R553X, N1303K) constitute approximately 85 % of the alleles in the United States (Elias et al, 1991).  Thus, screening procedures that test for these 5 mutations will detect approximately 85 % of CF carriers.  The genetic screening test for CF is usually based on mouthwash samples collected by agitating sucrose or saline in the mouth.  The DNA of these cells are amplified, digested, and subjected to separation techniques that identify 3 to 5 common mutations.

A National Institutes of Health consensus panel (1997) recommended that genetic testing for CF should be offered to adults with a positive family history of CF, to partners of people with the disease, to couples currently planning a pregnancy, and to couples seeking prenatal testing.  However, the panel did not recommend genetic testing of CF to the general public or to newborn infants.

The American College of Obstetricians and Gynecologists (2001) has issued similar recommendations on genetic carrier testing for CF.  ACOG recommends that obstetricians should offer CF screening to:

• Couples in whom one or both members are white and who are planning a pregnancy or seeking prenatal care;
• Individuals with a family history of CF; and
• Reproductive partners of people who have CF.

ACOG also recommends that screening should be made available to couples in other racial and ethnic groups.  To date, over 900 mutations in the CF gene have been identified.  As it is impractical to test for every known mutation, the ACMG Accreditation of Genetic Services Committee has compiled a standard screening panel of 25 CF mutations, which represents the standard panel that ACMG recommends for screening in the U.S. population (Grody et al, 2001).  This 25-mutation panel incorporates all CF-causing mutations with an allele frequency of greater than or equal to 0.1 % in the general U.S. population, including mutation subsets shown to be sufficiently predominant in certain ethnic groups, such as Ashkenazi Jews and African Americans.  This standard panel of mutations is intended to provide the greatest pan-ethnic detectability that can practically be performed.

The ACOG's update on carrier screening for CF (2011) provided the following recommendations.

• If a patient has been screened previously, CF screening results should be documented but the test should not be repeated.
• Complete analysis of the CFTR gene by DNA sequencing is not appropriate for routine carrier screening.

Fragile X syndrome

Fragile X syndrome is the most common cause of inherited mental retardation, seen in approximately one in 1,200 males and one in 2,500 females.  Phenotypic abnormalities associated with Fragile X syndrome include mental retardation, autistic behaviors, characteristic narrow face with large jaw, and speech and language disorders.  Fragile X syndrome was originally thought to be transmitted in an X-linked recessive manner; however, the inheritance pattern of fragile X syndrome has been shown to be much more complex.

Standard chromosomal analysis does not consistently demonstrate the cytogenetic abnormality in patients with fragile X syndrome, and molecular diagnostic techniques (DNA testing) have become the diagnostic procedure of choice for fragile X syndrome.

Aetna's policy on coverage of fragile X genetic testing is based on guidelines fromm the ACMG (1994) and the ACOG (1995).

Lactose intolerance

Lactase-phlorizin hydrolase, which hydrolyzes lactose, the major carbohydrate in milk, plays a critical role in the nutrition of the mammalian neonate (Montgomery et al, 1991).  Lactose intolerance in adult humans is common, usually due to low levels of small intestinal lactase.  Low lactase levels result from either intestinal injury or (in the majority of the world's adult population) alterations in the genetic expression of lactase.  Although the mechanism of decreased lactase levels has been the subject of intensive investigation, no consensus has yet emerged.

The LactoTYPE Test (Prometheus Laboratories) is a blood test that is intended to identify patients with genetic-based lactose intolerance.  According to the manufacturer, this test provides a more definitive diagnosis and scientific explanation for patients with persistent symptoms.

There is insufficient evidence that the assessment of the genetic etiology of lactose intolerance would affect the management of patients such that clinical outcomes are improved.  Current guidelines on the management of lactose intolerance do not indicate that genetic testing is indicated (NHS, 2005; National Public Health Service for Wales, 2005).

Long QT syndrome

Voltage-gated sodium channels are transmembrane proteins that produce the ionic current responsible for the rising phase of the cardiac action potential and play an important role in the initiation, propagation, and maintenance of normal cardiac rhythm. Inherited mutations in the sodium channel alpha-subunit gene (SCN5A), the gene encoding the pore-forming subunit of the cardiac sodium channel, have been associated with distinct cardiac rhythm syndromes such as the congenital long QT3 syndrome (LQT3), Brugada syndrome, isolated conduction disease, sudden unexpected nocturnal death syndrome (SUNDS), and sudden infant death syndrome (SIDS).  Electrophysiological characterization of heterologously expressed mutant sodium channels have revealed gating defects that, in many cases, can explain the distinct phenotype associated with the rhythm disorder.

The long QT syndrome (LQTS) is a familial disease characterized by an abnormally prolonged QT interval and, usually, by stress-mediated life-threatening ventricular arrhythmias (Priori et al, 2001).  Characteristically, the first clinical manifestations of LQTS tend to appear during childhood or in teenagers.  Two variants of LQTS have been described: a rare recessive form with congenital deafness (Jervell and Lange-Nielsen syndrome, J-LN), and a more frequent autosomal dominant form (Romano-Ward syndrome, RW).  Five genes encoding subunits of cardiac ion channels have been associated to LQTS and genotype-phenotype correlation has been identified.  Of the 5 genetic variants of LQTS currently identified, LQT1 and LQT2 subtypes involve 2 genes, KCNQ1 and HERG, which encode major potassium currents.  LQT3 involves SCN5A, the gene encoding the cardiac sodium current.  LQT5 and LQT6 are rare subtypes also involving the major potassium currents.

The principal diagnostic and phenotypic hallmark of LQTS is abnormal prolongation of ventricular repolarization, measured as lengthening of the QT interval on the 12-lead ECG (Maron et al, 1998).  This is usually most easily identified in lead II or V1, V3, or V5, but all 12 leads should be examined and the longest QT interval used; care should also be taken to exclude the U wave from the QT measurement.

LQT3 appears to be the most malignant variant and may be the one less effectively managed by beta blockers. LQT1 and LQT2 have a higher frequency of syncopal events but their lethality is lower and the protection afforded by beta-blockers, particularly in LQT1, is much higher.  The Jervell and Lange-Nielsen recessive variant is associated with very early clinical manifestations and a poorer prognosis than the Romano-Ward autosomal dominant form.  The presence of syndactyly seems to represent a different genetic variant of LQTS also associated with a poor prognosis.

Guidelines on sudden cardiac death from the European College of Cardiology (Priori et al, 2001) state that identification of specific genetic variants of LQTS are useful in risk stratification.  The clinical variants presenting association of the cardiac phenotype with syndactyly or with deafness (Jervell and Lange-Nielsen syndrome) have a more severe prognosis.  Genetic defects on the cardiac sodium channel gene (SCN5A) are also associated with higher risk of sudden cardiac death.  In addition, identification of specific genetic variants may help in suggesting behavioral changes likely to reduce risk.  LQT1 patients are at very high risk during exercise, particularly swimming.  LQT2 patients are quite sensitive to loud noises, especially when they are asleep or resting.

Genetic testing for LQTS may be indicated in persons with close relatives that have a defined mutation.  Genetic testing may also be indicated in individuals with a prolonged QT interval on resting electrocardiogram (a corrected QT interval (QTc) of 470 msec in males and 480 msec in females) without an identifiable external cause for QTc prolongation.  Common external causes of QTc prolongation are listed in the table below.

Genetic testing for long QT syndrome has not been evaluated in patients who present with a borderline QT interval, suspicious symptoms (e.g., syncope), and no relevant family history (Roden, 2008).  In these patients, the incidence of false positive and false negative results and their implications for management remain unknown.

Genetic testing may also be necessary in person with long QT syndrome in sudden death close relatives.

Brugada syndrome

Brugada syndrome is an inherited condition comprising a specific EKG abnormality and an associated risk of ventricular fibrillation and sudden death in the setting of a structurally normal heart.  Brugada syndrome is characterized by ST-segment abnormalities on EKG and a high risk of ventricular arrhythmias and sudden death.  Brugada syndrome presents primarily during adulthood but age at diagnosis ranges from 2 days to 85 years.  Clinical presentations may also include sudden infant death syndrome and sudden unexpected nocturnal death syndrome, a typical presentation in individuals from Southeast Asia.

Brugada et al (2005) reported that Brugada syndrome and LQTS are both due to mutations in genes encoding ion channels and that the genetic abnormalities causing Brugada syndrome have been linked to mutations in the ion channel gene SCN5A.  Brugada stated that the syndrome has been identified only recently but an analysis of data from published studies indicates that the disease is responsible for 4 to 12 % of unexpected sudden deaths, and up to 50 % of all sudden death in patients with an apparently normal heart.  Brugada explained that Brugada syndrome is a clinical diagnosis based on syncopal or sudden death episodes in patients with a structurally normal heart and a characteristic ECG pattern.  The ECG shows ST segment elevation in the primordial leads V1-V3, with a morphology of the QRS complex resembling a right bundle branch block; this pattern may also be caused by J point elevation.  When ST elevation is the most prominent feature, the pattern is called "coved-type".  When the most prominent feature is J point elevation, without ST elevation the pattern is called "saddle-type".  Brugada pointed out that it is important to exclude other causes of ST segment elevation before making the diagnosis of Brugada syndrome.  Brugada syndrome is inherited in an autonomic dominant manner with variable penetrance.  Most individuals diagnosed with Brugada syndrome have an affected parent.  The proportion of cases caused by de novo mutations is estimated at 1 %.  Each child of an individual with Brugada syndrome has a 50 % chance of inheriting the mutation.  According to Brugada, antiarrhythmic drugs do not prevent sudden death in symptomatic or asymptomatic individuals with Brugada syndrome and that implantation of an automatic cardioverter-defibrillator is the only currently proven effective therapy.

To date the great majority of identified disease-causing mutations have been located in the SCN5A gene encoding the a subunit of the human cardiac voltage-gated sodium channel but such mutations can be identified in, at most, 30 % of affected people.  Moreover, a positive genetic test adds little or nothing to the clinical management of such a person (HRUK, 2007).  The identification of an SCN5A mutation does, of course, allow screening of family members but the usefulness of genetic screening may be less than for other familial syndromes, however, given that the routine 12-lead EKG (with or without provocative drug testing) appears to be a relatively effective method of screening for the condition.

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a disease of the myocardium in which a portion of the myocardium is hypertrophied without any obvious cause; it is among the most common genetically transmitted cardiovascular diseases.

The genetic abnormalities that cause HCM are heterogeneous.  Hypertrophic cardiomyopathy is most commonly due to a mutation in one of 9 genes that results in a mutated protein in the sarcomere.  Some of the genes responsible for HCM have not yet been identified, and among those genes that have been identified, the spectrum of possible disease-causing mutations is incomplete.  As a result, a thorough evaluation of known genes requires extensive DNA sequencing, which is onerous for routine clinical testing.  Less rigorous methods (such as selective sequencing) reduces the likelihood of identifying the responsible mutation.

Population studies have demonstrated that some patients are compound heterozygotes (inheriting 2 different mutations within a single HCM gene), double heterozygotes (inheriting mutations in 2 HCM genes), or homozygotes (inheriting the same mutation from both parents).  To be certain of detecting such genotypes, sequencing of candidate genes would need to continue in a given patient even after a single mutation was identified.

In many persons with HCM mutations, the disease can be mild and the symptoms absent or minimal.  In addition, phenotypic expression of HCM can be influenced by factors other than the basic genetic defect, and the clinical consequences of the genetic defect can vary.  There is sufficient heterogeneity in the clinical manifestations of a given gene mutation that, even when a patient's mutation is known, his or her clinical course can not be predicted with any degree of certainty.

In addition, the prognostic impact of a given mutation may relate to a particular family and not to the population at large.  Many families have their own "private" mutations and thus knowledge of the gene abnormalities can not be linked to experience from other families.

Family members with echocardiography evidence of HCM should be managed like other patients with HCM.  In general, genetically affected but phenotypically normal family members should not be subjected to the same activity restriction as patients with HCM.

Bos and colleagues (2009) stated that over the past 20 years, the pathogenic basis for HCM, the most common heritable cardiovascular disease, has been studied extensively.  Affecting about 1 in 500 persons, HCM is the most common cause of sudden cardiac death (SCD) among young athletes.  In recent years, genomic medicine has been moving from the bench to the bedside throughout all medical disciplines including cardiology.  Now, genomic medicine has entered clinical practice as it pertains to the evaluation and management of patients with HCM.  The continuous research and discoveries of new HCM susceptibility genes, the growing amount of data from genotype-phenotype correlation studies, and the introduction of commercially available genetic tests for HCM make it essential that cardiologists understand the diagnostic, prognostic, and therapeutic implications of HCM genetic testing.

Hudecova et al (2009) noted that the clinical symptoms of HCM are partly dependent on mutations in affected sarcomere genes.  Different mutations in the same gene can present as malign with a high-risk of SCD, while other mutations can be benign.  The clinical symptomatology can also be influenced by other factors such as the presence of polymorphisms in other genes.  Currently, the objective of intensive clinical research is to access the contribution of molecular genetic methods in HCM diagnostics as well as in risk stratification of SCD.  It is expected that genetic analyses will have an important consequence in the screening of the relatives of HCM patients and also in the prenatal diagnostics and genetic counseling.

Shephard and Semsarian (2009) stated that genetic heart disorders are an important cause of SCD in the young.  While pharmacotherapies have made some impact on the prevention of SCD, the introduction of implantable cardioverter-defibrillator (ICD) therapy has been the single major advance in the prevention of SCD in the young.  In addition, the awareness that most causes of SCD in the young are inherited, means family screening of relatives of young SCD victims allows identification of previously unrecognised at-risk individuals, thereby enabling prevention of SCD in relatives.  The role of genetic testing, both in living affected individuals as well as in the setting of a "molecular autopsy", is emerging as a key factor in early diagnosis of an underlying cardiovascular genetic disorder.

The Heart Failure Society of America's practice guideline on "Genetic evaluation of cardiomyopathy" (Hershberger et al, 2009) stated that genetic testing is primarily indicated for risk assessment in at-risk relatives who have little or no clinical evidence of cardiovascular disease.  Genetic testing for HCM should be considered for the one most clearly affected person in a family to facilitate family screening and management.  Specific genes available for testing for HCM include MYH7, MYBPC3, TNNT2, TNN13, TPM1, ACTC, MYL2, and MYL3. MYH7 and MYBPC each accounts for 30 % to 40 % of mutations; TNNT2 for 10 % to 20 %.  Genetic cause can be identified in 35 % to 45 % overall; up to 60 % to 65 % when the family history is positive.

The BlueCross BlueShield Association Technology Evaluation Center (TEC)'s assessement on genetic testing for predisposition to inherited HCM (2010) concluded that the use of genetic testing for inherited HCM meets the TEC criteria for individuals who are at-risk for development of HCM, defined as having a close relative with established HCM, when there is a known pathogenic gene mutation present in an affected relative.  In order to inform and direct genetic testing for at-risk individuals, genetic testing should be initially performed in at least 1 close relative with definite HCM (index case) if possible.  This testing is intended to document whether a known pathologic mutation is present in the family, and optimize the predictive value of predisposition testing for at-risk relatives.  Due to the complexity of genetic testing for HCM and the potential for misinterpretation of results, the decision to test and the interpretation of test results should be performed by, or in consultation with an expert in the area of medical genetics and/or HCM.

The TEC assessment also concluded that genetic testing for inherited HCM does not meet the TEC criteria for predisposition testing in individuals who are at-risk for development of HCM, defined as having a close relative with established HCM, when there is no known pathogenic gene mutation present in an affected relative.  This includes:

• Patients with a family history of HCM, with unknown genetic status of affected relatives; and
• Patients with a family history of HCM, when a pathogenic mutation has not been identified in affected relatives.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C)

Arrhythmogenic right ventricular dysplasia/cardiomyopathy is a condition characterized by progressive fibro-fatty replacement of the myocardium that predisposes individuals to ventricular tachycardia and sudden death.  The prevalence of ARVD/C is estimated to be 1 case per 10,000 population.  Familial occurrence with an autosomal dominant pattern of inheritance and variable penetrance has been demonstrated.  Recessive variants have been reported.  It is estimated that half of the individuals have a family history of ARVD/C and the remaining cases are new mutations. 

Genetic testing has not been demonstrated to be necessary to establish the diagnosis of ARVD/C or determine its prognosis.  Twelve-lead ECG and echocardiography can be used to identify affected relatives.

The genetic abnormalities that cause ARVD/C are heterogeneous.  The genes frequently associated with ARVD/C are PKP2 (plakophilin-2), DSG2 (desmoglein-2), and DSP (desmoplakin).  A significant proportion of ARVD/C cases have been reported with no linkage to known chromosomal loci; in one report, 50 % of families undergoing clinical and genetic screening did not show linkage with any known genetic loci (Corrado et al, 2000).

Most affected individuals live a normal lifestyle.  Management of individuals with ARVD/C is complicated by incomplete information on the natural history of the disease and the variability of disease expression even within families.  High-risk individuals with signs and symptoms of ARVD/C are treated with anti-arrhythmic medications and those at highest risk who have been resuscitated or who are unresponsive to or intolerant of anti-arrhythmic therapy may be considered for an ICD.

According to the Heart Failure Society of America's Practice Guideline on the genetic evaluation of cardiomyopathy (2009), the clinical utility for all genetic testing of cardiomyopathies remains to be defined.  The guideline stated, "[b]ecause the genetic knowledge base of cardiomyopathy is still emerging, practitioners caring for patients and families with genetic cardiomyopathy are encouraged to consider research participation."  The Multidisciplinary Study of Right Ventricular Dysplasia (North American registry) is a 5-year study funded by the National Institutes of Health to determine how the genes responsible for ARVD/C affect the onset, course, and severity of the disease.  Enrollment in the study was completed in May 2008 and the study is currently in the follow-up period.

Catecholaminergic polymorphic ventricular tachycardia (CPVT)

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly lethal form of inherited arrhythmogenic disease characterized by adrenergically mediated polymorphic ventricular tachycardia (Liu et al, 2007).  Mutations in the cardiac ryanodine receptor (RyR2) gene and the cardiac calsequestrin (CASQ2) gene are responsible for the autosomal dominant and recessive variants of CPVT, respectively.  The clinical presentation encompasses exercise- or emotion-induced syncopal events and a distinctive pattern of reproducible, stress-related, bi-directional ventricular tachycardia in the absence of both structural heart disease and a prolonged QT interval.

CPVT typically begins in childhood or adolescence.  The mortality rate in untreated individuals is 30 to 50 % by age 40 years.  Clinical evaluation by exercise stress testing and Holter monitoring and genetic screening can facilitate early diagnosis.  Beta-blockers are the most effective drugs for controlling arrhythmias in CPVT patients, yet about 30 % of patients with CPVT still experience cardiac arrhythmias on beta-blockers and eventually require an implantable cardioverter defibrillator.  Liu et al (2008) stated that molecular genetic screening of the genes encoding the cardiac RyR2 and CASQ2 is critical to confirm uncertain diagnosis of CPVT.

Katz et al (2009) noted that CPVT is a primary electrical myocardial disease characterized by exercise- and stress-related ventricular tachycardia manifested as syncope and sudden death.  The disease has a heterogeneous genetic basis, with mutations in the cardiac RyR2 gene accounting for an autosomal-dominant form (CPVT1) in approximately 50 % and mutations in the cardiac CASQ2 gene accounting for an autosomal-recessive form (CPVT2) in up to 2 % of CPVT cases.  Both RyR2 and calsequestrin are important participants in the cardiac cellular calcium homeostasis.  These researchers reviewed the physiology of the cardiac calcium homeostasis, including the cardiac excitation contraction coupling and myocyte calcium cycling.

Although the clinical presentation of CPVT is similar in many respects to the LQTS, there are important differences that are relevant to genetic testing.  CPVT appears to be a more malignant condition, as many people are asymptomatic before the index lethal event and the majority of cardiac events occur before 20 years of age.  Affected people are advised to avoid exercise-related triggers and start prophylactic beta-blockers with dose titration guided by treadmill testing.

Genetic testing has been recommended in individuals with clinical features considered typical of CPVT following expert clinical assessment (HRUK, 2008).  Clinically the condition is difficult to diagnose in asymptomatic family members as the ECG and echocardiogram are completely normal at rest.  Exercise stress testing has been advised in family members in order to identify exercise-induced ventricular arrhythmias, but the sensitivity of this clinical test is unknown.  Although the diagnostic yield from genetic testing is less than that for the LQTS (about 50 %) in patients with typical clinical features, a positive genetic test may be of value for the individual patient (given the prognostic implications) and for screening family members (given the difficulties in clinical screening methods) (HRUK, 2008).  The RyR2 gene is large and a ‘‘targeted’’ approach is usually undertaken, in which only exons that have been previously implicated are examined.

The 2006 guidelines from the American College of Cardiology on management of patients with ventricular arrhythmias and the prevention of sudden cardiac death (Zipes et al, 2006) included the following recommendations for patients with CPVT:

• There is evidence and/or general agreement supporting the use of beta blockers for patients clinically diagnosed on the basis of spontaneous of documented stress-induced ventricular arrhythmias.
• There is evidence and/or general agreement supporting the use of an implantable ICD in combination with beta blockers for survivors of cardiac arrest who have a reasonable expectation of survival with a good functional capacity for more than 1 year.
• The weight of evidence and/or opinion supports the use of beta blockers in patients without clinical manifestations who are diagnosed in childhood based upon genetic analysis.
• The weight of evidence and/or opinion supports the use of an ICD in combination with beta blockers for patients with a history of syncope and/or sustained ventricular tachycardia while receiving beta blockers who have a reasonable expectation of survival with a good functional capacity for more than 1 year.
• The usefulness and/or efficacy of beta blockers is less well established in patients without clinical evidence of arrhythmias who are diagnosed in adulthood based upon genetic analysis.

Hereditary hemochromatosis

Hemochromatosis, a condition involving excess accumulation of iron, can lead to iron overload, which in turn can result in complications such as cirrhosis, diabetes, cardiomyopathy, and arthritis (Burke 1992; Hanson et al, 2001). 

Hereditary hemochromatosis (HHC) is characterized by inappropriately increased iron absorption from the duodenum and upper intestine, with consequent deposition in various parenchymal organs, notably the liver, pancreas, joints, heart, pituitary gland and skin, with resultant end-organ damage (Limdi and Crampton, 2004).  Clinical features may be non-specific and include lethargy and malaise, or reflect target organ damage and present with abnormal liver tests, cirrhosis, diabetes mellitus, arthropathy, cardiomyopathy, skin pigmentation and gonadal failure.  Early recognition and treatment (phlebotomy) is essential to prevent irreversible complications such as cirrhosis and hepatocellular carcinoma.

HHC is an autosomal recessive condition associated with mutations of the HFE gene.  Two of the 37 allelic variants of the HFE gene, C282Y and H63D, are significantly correlated with HHC.  C282Y is the more severe mutation, and homozygosity for the C282Y genotype accounts for the majority of clinically penetrant cases.  Hanson et al (2001) reported that homozygosity for the C282Y mutation has been found in 52 to 100 % of previous studies on clinically diagnosed index cases.  Five percent of HHC probands were found by Hanson et al to be compound heterozygotes (C282Y/H63D), and 1.5 % were homozygous for the H63D mutation; 3.6 % were C282Y heterozygotes, and 5.2 % were H63D heterozygotes.  In 7 % of cases, C282Y and H63D mutations were not present.  In the general population, the frequency of the C282Y/C282Y genotype is 0.4 %.

HHC is a very common genetic defect in the Caucasian population.  C282Y heterozygosity ranges from 9.2 % in Europeans to nil in Asian, Indian subcontinent, African, Middle Eastern, Australian and Asian populations (Hanson et al, 2001).  The H63D carrier frequency is 22 % in European populations.

Accurate data on the penetrance of the different HFE genotypes are not available.  But current data suggest that clinical disease does not develop in a substantial proportion of people with this genotype.  Available data suggest that up to 38 % to 50 % of C282Y homozygotes may develop iron overload, with up to 10 % to 33 % eventually developing hemochromatosis-associated morbidity (Whitlock et al, 2006).  A pooled analysis found that patients with the HFE genotypes C282Y/H63D and H63D/H63D are also at increased risk for iron overload, yet overall, disease is likely to develop in fewer than 1 % of people with these genotypes (Burke, 1992).  Thus, DNA-based tests for hemochromatosis identify a genetic risk rather than the disease itself. 

Environmental factors such as diet and exposure to alcohol or other hepatotoxins may modify the clinical outcome in patients with hemochromatosis, and variations in other genes affecting iron metabolism may also be a factor.  As a result, the clinical condition of iron overload is most reliably diagnosed on the basis of biochemical evidence of excess body iron (Burke, 1992).

Whether it is beneficial to screen asymptomatic people for a genetic risk of iron overload is a matter of debate.  To date, population screening for HHC is not recommended because of uncertainties about optimal screening strategies, optimal care for susceptible persons, laboratory standardization, and the potential for stigmatization or discrimination (Hanson et al, 2001; Whitlock et al, 2006).  A systematic evidence review prepared for the U.S. Preventive Services Task Force concluded: "Research addressing genetic screening for hereditary hemochromatosis remains insufficient to confidently project the impact of, or estimate the benefit from, widespread or high-risk genetic screening for hereditary hemochromatosis" (Whitlock et al, 2006).

Familial nephrotic syndrome (NPHS1, NPHS2)

Nephrotic syndrome comes in 2 variants: (i) those sensitive to treatment with immunosuppressants (steroid-sensitive), and (ii) those resistant to immunosuppressants (steroid-resistant).  Familial forms of nephrotic syndrome are steroid resistant (Niaudet, 2007).  Mutations in two genes, NPHS1 and NPHS2, have been associated with a familial nephrotic syndrome.  Mutations in the gene for podocin, called NPHS2, also known as familial focal glomerulosclerosis, are observed in patients with both familial and sporadic steroid-resistant nephrotic syndrome (SRNS). 

Identifying children with nephrotic syndrome due to NPHS2 mutations can avoid unnecessary exposure to immunosuppressive therapy, because immunosuppressive therapy has not been shown to be effective in treating these children (Niaudet, 2007).  Thus, authorities have recommended testing for such mutations in those with a familial history of steroid resistant nephrotic syndrome and children with steroid-resistant disease .

Some have suggested that, to avoid unnecessary exposure to steroid therapy, all children with a first episode of the nephrotic syndrome should be screened for NPHS2 mutations (Niaudet, 2007).  However, given that over 85 % of children with idiopathic nephrotic syndrome are steroid-sensitive and only approximately 20 % of steroid-resistant patients have NPHS2 mutations, screening for abnormalities at this genetic locus would identify less than 5 % of all cases.  However, screening a child with a first episode of the nephrotic syndrome with a familial history of steroid-resistant nephrotic syndrome has been recommended because they are at increased risk for having a NPHS2 gene mutation.

Mutations in the gene for nephrin, called NPHS1, cause the congenital nephrotic syndrome of Finnish type (CNF) (Niaudet, 2007).  CNF is inherited as an autosomal recessive trait, with both sexes being involved equally.  There are no manifestations of the disease in heterozygous individuals.  Most infants with the CNF are born prematurely (35 to 38 weeks), with a low birth weight for gestational age.  Edema is present at birth or appears during the first week of life in 50 % of cases.  Severe nephrotic syndrome with marked ascites is always present by 3 months.  End-stage renal failure usually occurs between 3 and 8 years of age.  Prolonged survival is possible with aggressive supportive treatment, including dialysis and renal transplantation.

The nephrotic syndrome in CNF is always resistant to corticosteroids and immunosuppressive drugs, since this is not an immunologic disease (Niaudet, 2007).  Furthermore these drugs may be harmful due to affected individuals' already high susceptibility to infection.

The CNF becomes manifest during early fetal life, beginning at the gestation age of 15 to 16 weeks.  The initial symptom is fetal proteinuria, which leads to a more than 10-fold increase in the amniotic fluid alpha-fetoprotein (AFP) concentration (Niaudet, 2007).  A parallel, but less important increase in the maternal plasma AFP level is observed.  These changes are not specific, but they may permit the antenatal diagnosis of CNF in high risk families in which termination of the pregnancy might be considered.  However, false positive results do occur, often leading to abortion of healthy fetuses.

Genetic linkage and haplotype analyses may diminish the risk of false positive results in informative families (Niaudet, 2007).  The 4 major haplotypes, which cover 90 % of the CNF alleles in Finland, have been identified, resulting in a test with up to 95 % accuracy.

Authorities do not recommend screening for NPHS1 mutations for all children with the first episode of nephrotic syndrome, for the reasons noted above regarding NPHS2 mutation screening.  However, genetic testing may be indicated for infants with congenital nephrotic syndrome (i.e., appearing within the first months of life) who are of Finnish descent and/or who have a family history that suggests a familial cause of congenital nephrotic syndrome.  The primary purpose of this testing is for pregnancy planning.  Detection of an NPHS1 mutation also has therapeutic implications, as such nephrotic syndrome is steroid resistant.

Primary dystonia (DYT-1)

Dystonia consists of repetitive, patterned, twisting, and sustained movements that may be either slow or rapid.  Dystonic states are classified as primary, secondary, or psychogenic depending upon the cause (Jankovic, 2007).  By definition, primary dystonia is associated with no other neurologic impairment, such as intellectual, pyramidal, cerebellar, or sensory deficits.  Cerebral palsy is the most common cause of secondary dystonia.

Primary dystonia may be sporadic or inherited (Jankovic, 2007).  Cases with onset in childhood usually are inherited in an autosomal dominant pattern.  Many patients with hereditary dystonia have a mutation in the TOR1A (DYT1) gene that encodes the protein torsinA, an ATP-binding protein in the 9q34 locus.  The role of torsinA in the pathogenesis of primary dystonia is unknown.  DNA testing for the abnormal TOR1A gene can be performed on individuals with dystonia.  The purpose of such testing is to help rule out secondary or psychogenic causes of dystonia, and for family planning purposes.

Malignant melanoma

An estimated 8 to 12 % of persons with melanoma have a family history of the disease, but not all of these individuals have hereditary melanoma (Tsao and Haluska, 2007).  In some cases, the apparent familial inheritance pattern may be due to clustering of sporadic cases in families with common heavy sun exposure and susceptible skin type.

A melanoma susceptibility locus has been identified on chromosome 9p21; this has been designated CDKN2A (also known as MTS1 (multiple tumor suppressor 1)) (Tsao and Haluska, 2007).  There is a variable rate of CDKN2A mutations in patients with hereditary melanoma. The risk of CDKN2A mutation varies from approximately 10 % for families with at least 2 relatives having melanoma, to more than 40 % for families having multiple affected 1st degree relatives spanning several generations.

Persons at increased risk of melanoma are managed with close clinical surveillance and education in risk-reduction behavior (e.g., sun avoidance, sunscreen use). It is unclear how CDKN2A genetic test information would alter clinical recommendations (Tsao and Haluska, 2007).  The negative predictive value of a negative test for a CDKN2A mutation is also not established since many familial cases occur in the absence of CDKN2A mutations.  It is estimated that the prevalence of CDKN2A mutation carriers is less than 1 % in high incidence populations.  Thus, no mutations will be identifiable in the majority of families presenting to clinical geneticists.

The American Society of Clinical Oncology (ASCO) has issued a consensus report on the utility of genetic testing for cancer susceptibility (ASCO, 1996), and recommendations for the process of genetic testing were updated in 2003 (ASCO, 2003).  The report notes that the sensitivity and specificity of the commercially available test for CDKN2A mutations are not fully known.  Because of the difficulties with interpretation of the genetic tests, and because test results do not alter patient or family member management, ASCO recommends that CDKN2A testing be performed only in the context of a clinical trial.

The Scottish Intercollegiate Guidelines Network (SIGN, 2003) protocols on management of cutaneous melanoma reached similar conclusions, stating that "[g]enetic testing in familial or sporadic melanoma is not appropriate in a routine clinical setting and should only be undertaken in the context of appropriate research studies."

The Melanoma Genetics Consortium recommends that genetic testing for melanoma susceptibility should not be offered outside of a research setting (Kefford et al, 2002).  They state that “[u]ntil further data become available, however, clinical evaluation of risk remains the gold standard for preventing melanoma.  First-degree relatives of individuals at high risk should be engaged in the same programmes of melanoma prevention and surveillance irrespective of the results of any genetic testing.”

Charcot-Marie Tooth disease type 1A (PMP-22)

Charcot Marie Tooth disease, also known as peroneal muscular atrophy, progressive neural muscular atrophy, as well as hereditary motor and sensory neuropathy, is 1 of the 3 major types of hereditary neuropathy.  With an estimated prevalence of at least 1:2,500 (autosomal dominance), CMT is one of the most common genetic neuromuscular disorders affecting approximately 125,000 persons in the United States.  This hereditary peripheral neuropathy is genetically and clinically heterogeneous.  It is usually inherited in an autosomal dominant manner, and occasionally in an autosomal recessive manner.  Sporadic as well as X-linked cases have also been reported.  In the X-linked recessive patterns, only males develop the disease, although females who inherit the defective gene can pass the disease onto their sons.  In the X-linked dominant pattern, an affected mother can pass on the disorder to both sons and daughters, while an affected father can only pass it onto his daughters.  The clinical manifestations can vary greatly in severity and age of onset.  The clinical features may be so mild that they may be undetectable by patients, their families and physicians.

Charcot-Marie-Tooth disease is usually diagnosed by an extensive physical examination, assessing characteristic weakness in the foot, leg, and hand, as well as deformities and impaired function in walking and manual manipulation.  The clinical diagnosis is then confirmed by electromyogram and nerve conduction velocity tests, and sometimes by biopsy of muscle and of sural cutaneous nerve.  Since CMT is a hereditary disease, family history can also help to confirm the diagnosis.  Based on studies of motor nerve conduction velocity, CMT can be further classified into 2 types: (i) CMT Type I -- slow conduction velocity (less than 40 meters/second for the median nerve or less than 15 meters/second for the peroneal nerve) which accounts for 70 % of all CMT cases, and (ii) CMT Type II -- normal or near normal nerve conduction velocity with decreased amplitude which accounts for the remaining 30 % of CMT cases.  Charcot Marie Tooth Type I disease is a demyelinating neuropathy with hypertrophic changes in peripheral nerves, and has its onset usually during late childhood.  On the other hand, CMT Type II is a non-demyelinating neuronal disorder without hypertrophic changes, and has its onset generally during adolescence.

Both CMT Types I and II are characterized by a slow degeneration of peripheral nerves and roots, resulting in distal muscle atrophy commencing in the lower extremities, and affecting the upper extremities several years later.  Symptoms include foot drop or clubfoot, paresthesia in legs, sloping gait, later weakness and atrophy of hands, then arms, absence or reduction of deep tendon reflexes, and occasionally mild sensory loss.  Charcot Marie Tooth disease is not a fatal disorder.  It does not shorten the normal life expectancy of patients, and it does not affect them mentally.  As stated earlier, there is a wide range of variation in the clinical manifestations of CMT -- the degree of severity can vary considerably from patient to patient, even among affected family members within the same generation.  The condition can range from having no problems to having major difficulties in ambulation in early adult life, however, the latter is unusual.  Most patients are able to ambulate and have gainful employment until old age.  Currently, there is no specific treatment for this disease.  Management of the majority of patients with CMT disease consists of supportive care with emphasis on proper bracing, foot care, physical therapy and occupational counseling.  For example, the legs and shoes can be fitted with light braces and springs, respectively, to overcome foot drop.  If foot drop is severe and the disease has become stationary, the ankle can be stabilized by arthrodeses.

The underlying genetic basis for CMT Type I has been characterized.  A point mutation in the PMP22 gene which encodes a peripheral myelin protein with an apparent molecular weight of 22,000 or a DNA duplication of a specific region 5 megabases) including the PMP22 gene in the proximal short arm of chromosome 17 (band 17p11.2-p12) has been identified in 70 % of clinically diagnosed patients --- CMT Type IA.  Thus, patients with CMT Type IA represent approximately 50 % of all CMT cases.  Other CMT Type I patients (CMT Type IB) exhibit an abnormality (Duffy locus) in the proximal long arm of chromosome number 1 (band 1q21-22).  Presently, no test is available for the dominant CMTIB gene on chromosome 1.  On the other hand, a CMT Type IA DNA test is available commercially.  The test is accomplished through a blood sample analysis -- DNAs are extracted from leukocytes of patients and pulsed-field gel electrophoresis is employed to isolate large segments of DNA encompassing CMTIA duplication-specific junction fragments which are then detected by hybridization with aCMTIA duplication-specific probe (CMTIA-REP).  This probe identifies the homologous regions that flank the CMTIA duplication monomer unit.

A positive CMTIA DNA test means the presence of a 500 kilobases CMTIA duplication specific junction fragment, and is diagnostic for CMT Type IA.  A negative CMT Type IA means the absence of the CMTIA duplication specific junction fragment, and does not rule out a diagnosis of CMT disease.  This is because patients with CMT Type IA represent approximately 50 % of all CMT cases.  The value of this molecular test in family planning is questionable because of its relatively low detection rate and its inability to predict the severity of the disease.  Moreover, it is likely that there are undiscovered CMTI genes since there are dominant CMTI pedigrees who do not have abnormalities at the known chromosome 1 and 17 locations (CMT Type IC).  In addition, other investigators have reported X-linked forms of CMTI at the region of Xq13-21, and Xq26.

Since CMT is not life-threatening, rarely severely disabling, and has no specific treatment, it is unclear how the results of this CMT Type I DNA test, which can not predict the severity of the disease, would affect family planning.  Moreover, because of its low detection rate, the CMT Type I DNA test appears to be inferior to the conventional means of diagnosis through physical examination, family history, electromyography and nerve conduction velocity studies.  Thus, the sole value of genetic testing for CMTIA is to establish the diagnosis and to distinguish this from other causes of neuropathy.

Familial amyotrophic lateral sclerosis (SOD1 Mutation)

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease involving both the upper motor neurons (UMN) and lower motor neurons (LMN).  UMN signs include hyperreflexia, extensor plantar response, increased muscle tone, and weakness in a topographical representation.  LMN signs include weakness, muscle wasting, hyporeflexia, muscle cramps, and fasciculations.  In the early stage of the disease, the clinical aspects of ALS can vary.  Affected individuals typically present with asymmetric focal weakness of the extremities (stumbling or poor handgrip) or bulbar findings (dysarthria, dysphagia).  Other findings include muscle fasciculations, muscle cramps, and lability of affect but not necessarily mood.  Regardless of initial symptoms, atrophy and weakness eventually affect other muscles.  Approximately 5,000 people in the U.S. are diagnosed with AML each year.

Most people with ALS have a form of the condition that is described as sporadic or non-inherited.  The cause of sporadic ALS is largely unknown but probably involves a combination of genetic and environmental factors.  About 10 % of people with ALS have a familial form of the condition, which is caused by an inherited genetic mutation, usually as an autosomal dominant trait.  The mean age of onset of ALS in individuals with no known family history is 56 years and in familial ALS it is 46 years.

The diagnosis of ALS is based on clinical features, electrodiagnostic testing (EMG), and exclusion of other health conditions with related symptoms.  At present, genetic testing in ALS has no value in making the diagnosis.  The only genetic test currently available detects the SOD1 mutation.  Since only 20 % of familial ALS patients will test positively for an SOD1 mutation, this test has limited value in genetic counseling.

Migrainous vertigo

Migrainous vertigo is a term used to describe episodic vertigo in patients with a history of migraines or with other clinical features of migraine.  Approximately 20 to 33 % of migraine patients experience episodic vertigo.  The underlying cause of migrainous vertigo is not very well understood.  There are no confirmatory diagnostic tests or susceptible genes associated with migrainous vertigo.  Other conditions, specifically Meniere's disease and structural and vascular brainstem disease, must be excluded (Black, 2006).

Prostate cancer

At this time, there are no susceptibility genes that have been unequivocally associated with prostate cancer predisposition.  Genetic testing for prostate cancer is currently available only within the context of a research study.  A special report on prostate cancer genetics by the BlueCross BlueShield Association Technology Evaluation Center (BCBSA, 2008) stated that single-nucleotide polymorphisms (SNPs) do not predict certainty of disease, nor do they clearly predict aggressive versus indolent disease.  The report noted that, while the monitoring of high-risk men may improve outcomes, it is also possible that these could be offset by the harms of identifying and treating additional indolent disease.

Type 2 diabetes

Available evidence has shown that screening for a panel of gene variants associated with type 2 diabetes does not substantially improve prediction of risk for the disease than an assessment based on traditional risk factors.  Available evidence suggests that both genetic and environmental factors play a role in the development of type 2diabetes.  Recent genetic studies have identified 18 gene variants that appear to increase the risk for type 2 diabetes.

A study reported in the New England Journal of Medicine evaluated the potential utility of genetic screening in predicting future risk of type 2 diabetes (Meigs et al, 2008).  The investigators analyzed records from the Framingham Offspring Study, which follows a group of adult children of participants of the original Framingham Heart study, to evaluate risk factors for the development of cardiovascular disease, including diabetes.  Full genotype results for the 18 gene variants as well as clinical outcomes were available for 2,377 participants, 255 of whom developed type 2 diabetes during 28 years of follow-up.  Each participant was assigned a genotype score, based on the number of risk-associated gene copies inherited.  The investigators compared the predictive value of the genotype score to that of family history alone or of physiological risk factors.  Overall, the genetic score was 17.7 among those who developed diabetes and 17.1 among those who did not.  The investigators found that, while the genetic score did help predict who would develop diabetes, once other known risk factors were taken into consideration, it offered little additional predictive power.  The investigators concluded that: "[t]he genotype score resulted in the appropriate risk reclassification of, at most, 4 % of the subjects, compared with risk estimates based on age, sex, blood lipids, body mass index, family history, and other standard risk factors."  The investigators reported that "[o]ur findings underscore the view that identification of adverse phenotypic characteristics remains the cornerstone of approaches to predicting the risk of type 2 diabetes," the authors said.

A similar study among Swedish and Finnish patients, published in the same issue of the New England Journal of Medicine, also found only a small improvement in risk estimates when genetic factors were added to traditional risk factors (Lyssenko et al, 2008).

The OncoVue breast cancer risk test

The OncoVue breast cancer risk test (Intergenetics, Inc., Oklahoma City, OK) is a genetic-based breast cancer risk test that incorporates both individualized genetic-based single nucleotide polymorphisms (SNPs) and personal history measures to arrive at an estimate of a woman’s breast cancer risk at various stages in her life.

Cells that are collected from the inside of the cheek are analyzed using thousands of proprietary (Intergenetic, Inc.) combinations of multiple genes.  The genetic information and the data from the medical history are combined to assign a numeric value that tells a woman's lifetime risk of developing breast cancer.  Her OncoVue risk test will tell her if she is standard, moderate or high risk for developing breast cancer during each stage of her life.

OncoVue is based on an un-published case-controlled associative study that examined common genetic polymorphisms and medical history variables.  Currently, 117 common polymorphisms (mostly SNPs) located in over 87 genes believed to alter breast cancer risk are examined.  Most result in amino acid changes in the proteins encoded by the genes in which they occur.  The medical history variables include answers to questions concerning women’s reproductive histories, family histories of cancer and a few other questions related to general health.

There are no published controlled studies on the OncoVue breast cancer risk test in the peer-reviewed medical literature.

Gail (2009) evaluated the value of adding SNP genotypes to a breast cancer risk model.  Criteria that are based on 4 clinical or public health applications were used to compare the National Cancer Institute's Breast Cancer Risk Assessment Tool (BCRAT) with BCRATplus7, which includes 7 SNPs previously associated with breast cancer.  Criteria included number of expected life-threatening events for the decision to take tamoxifen, expected decision losses (in units of the loss from giving a mammogram to a woman without detectable breast cancer) for the decision to have a mammogram, rates of risk re-classification, and number of lives saved by risk-based allocation of screening mammography.  For all calculations, the following assumptions were made: Hardy-Weinberg equilibrium, linkage equilibrium across SNPs, additive effects of alleles at each locus, no interactions on the logistic scale among SNPs or with factors in BCRAT, and independence of SNPs from factors in BCRAT.  Improvements in expected numbers of life-threatening events were only 0.07 % and 0.81 % for deciding whether to take tamoxifen to prevent breast cancer for women aged 50 to 59 and 40 to 49 years, respectively.  For deciding whether to recommend screening mammograms to women aged 50 to 54 years, the reduction in expected losses was 0.86 % if the ideal breast cancer prevalence threshold for recommending mammography was that of women aged 50 to 54 years.  Cross-classification of risks indicated that some women classified by BCRAT would have different classifications with BCRATplus7, which might be useful if BCRATplus7 was well calibrated.  Improvements from BCRATplus7 were small for risk-based allocation of mammograms under costs constraints.  The author reported that the gains from BCRATplus7 were small in the applications examined and that models with SNPs, such as BCRATplus7, have not been validated for calibration in independent cohort data.  The author concluded that additional studies are needed to validate a model with SNPs and justify its use.

There is insufficient evidence on the effectiveness of the OncoVue breast cancer risk test in determining a woman’s breast cancer risk at various stages in her life.

The Universal genetic test (Counsyl Test)

According to the Food and Drug Administration (FDA), which regulates the manufacturers of genetic tests, and the Centers for Disease Control and Prevention (CDC), some genetic tests offered directly to consumers lack scientific validity, and others provide medical results that are meaningful only in the context of a full medical evaluation.

The Universal genetic test (Counsyl, Redwood City, CA), which is being marketed directly to consumers through the Internet as well as through medical centers in the U.S., uses targeted DNA mutation analysis to simultaneously test an individual or couple for over 100 genetic conditions.  Individuals may discover whether they are carriers, while couples may learn their probability of conceiving an affected child.  Approximately 35 to 40 % of persons who take the Counsyl test are carriers for at least 1 disease, and carrier-carrier couples are found about 0.6 to 0.8 % of the time.

Despite screening for over 100 mutations, the Universal genetic test lacks key components, such as carrier testing for Fragile X, the most common inherited cause of mental retardation.

The Universal genetic test for Tay Sachs Disease (TSD) is limited to 4 mutations, and does not include enzyme analysis, which is especially important in detecting Tay Sachs in non-Ashkenazi Jewish populations.

The Universal genetic test for CF includes the 5T/7T/9T (Poly(T)) variant; however, the ACMG and the ACOG recommend against inclusion of the Poly(T) variant in screening panels, as the intent of carrier screening is to identify couples at risk to have a child with classic CF (ACOG, 2005).  Instead, the guidelines recommend that the Poly(T) variant should be used as a reflex test for patients with the R117H mutation.  The Universal genetic test also includes I148T as a mutation in its CF analysis.  However, I148T has been shown to be common in the general public and is not disease causing unless it is paired with the 3199del6 mutation.  ACMG and ACOG have recommended that I148T be removed from screening panels and only performed as a reflex test (ACOG, 2005).

Counsyl provides carrier risk revisions even when there are insufficient data to calculate posterior risks (i.e., the risk that someone with no family history is a carrier despite a negative test result).  For example, in a Committee Opinion on Preconception and Prenatal Carrier Screening for Genetic Diseases in Individuals of Eastern European Jewish Descent, ACOG (2009) acknowledges the inability to calculate posterior risk in non-Ashkenazi Jewish populations because a priori carrier risk and detection rates are unknown: "The carrier frequency and the detection rate in non-Jewish individuals is unknown for all of these disorders, except for TSD and cystic fibrosis.  Therefore, it is difficult to accurately predict the couple’s risk of having a child with the disorder.”  The Committee Opinion further states “carrier screening of the non-Jewish partner is of limited value.”

Other defects detected by the Universal genetic test have limited prenatal consequences.  For example, Counsel tests for mutations associated with HFE-associated hereditary hemochromatosis, although affected females generally develop symptoms only after menopause.  Defects in blood clotting such as Factor V Leiden and MTHFR deficiency are common in the general population and can be managed medically and by modifying diet and by avoiding certain medications such as oral contraceptives.  Some carrier mutations identified by the Universal Genetic Test are associated with metabolic deficiencies but not overt birth defects.

Counsyl offers the Universal genetic test directly to consumers, a practice that is not supported by the ACMG.  An ACMG Statement on Direct-to-Consumer (DTC) Genetic Testing (2008) lists points on what they consider the “minimum requirement for any genetic testing protocol.”  With the Universal genetic test, there is an enhanced need for genetic consultation for persons to have full informed consent prior to testing as well as post-test genetic consultation for persons who are found to be carriers for each of the diseases tested.

The Universal genetic test has not been reviewed by the FDA and there is a lack of evidence in the peer-reviewed literature to support the clinical validity and/or test performance of the Universal genetic test.  Furthermore, no professional medical society recommends the Universal genetic test for pregnancy planning.  Many mutations, even in disease-causing genes, do not produce serious or even detectable illness so it is unclear how prenatal management would be altered by the Universal genetic test findings.

The phosphatase and tensin homolog (PTEN) gene test

Phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome is an autosomal dominant group of disorders with significant clinical overlap, most notably predisposition to hamartomatous polyposis of the gastro-intestinal tract.  Laurent-Puig et al (2009) stated that the occurrence of KRAS mutation is predictive of non-response and shorter survival in patients treated by anti-epidermal growth factor receptor (anti-EGFR) antibody for metastatic colorectal cancer (mCRC), leading the European Medicine Agency to limit its use to patients with wild-type KRAS tumors.  However, only 50 % of these patients will benefit from treatment, suggesting the need to identify additional biomarkers for cetuximab-based treatment efficacy.  These investigators retrospectively collected tumors from 173 patients with mCRC.  All but 1 patient received a cetuximab-based regimen as second-line or greater therapy.  KRAS and BRAF status were assessed by allelic discrimination.  EGFR amplification was assessed by chromogenic in situ hybridization and fluorescent in situ hybridization, and the expression of PTEN was assessed by immunochemistry.  In patients with KRAS wild-type tumors (n = 116), BRAF mutations (n = 5) were weakly associated with lack of response (p = 0.063) but were strongly associated with shorter progression-free survival (p < 0.001) and shorter overall survival (OS; p < 0.001).  A high EGFR polysomy or an EGFR amplification was found in 17.7 % of the patients and was associated with response (p = 0.015).  PTEN null expression was found in 19.9 % of the patients and was associated with shorter OS (p = 0.013).  In multi-variate analysis, BRAF mutation and PTEN expression status were associated with OS.  The authors concluded that BRAF status, EGFR amplification, and cytoplasmic expression of PTEN were associated with outcome measures in KRAS wild-type patients treated with a cetuximab-based regimen.  They stated that more studies in clinical trial cohorts are needed to confirm the clinical utility of these markers.

Siena et al (2009) noted that the monoclonal antibodies panitumumab and cetuximab that target the EGFR have expanded the range of treatment options for mCRC.  Initial evaluation of these agents as monotherapy in patients with EGFR-expressing chemotherapy-refractory tumors yielded response rates of approximately 10 %.  The realization that detection of positive EGFR expression by immunostaining does not reliably predict clinical outcome of EGFR-targeted treatment has led to an intense search for alternative predictive biomarkers.  Oncogenic activation of signaling pathways downstream of the EGFR, such as mutation of KRAS, BRAF, or PIK3CA oncogenes, or inactivation of the PTEN tumor suppressor gene is central to the progression of colorectal cancer.  Tumor KRAS mutations, which may be present in 35 % to 45 % of patients with colorectal cancer, have emerged as an important predictive marker of resistance to panitumumab or cetuximab treatment.  In addition, among colorectal tumors carrying wild-type KRAS, mutation of BRAF or PIK3CA or loss of PTEN expression may be associated with resistance to EGFR-targeted monoclonal antibody treatment, although these additional biomarkers require further validation before incorporation into clinical practice.  Additional knowledge of the molecular basis for sensitivity or resistance to EGFR-targeted monoclonal antibodies will allow the development of new treatment algorithms to identify patients who are most likely to respond to treatment and could also provide rationale for combining therapies to overcome primary resistance.  The use of KRAS mutations as a selection biomarker for anti-EGFR monoclonal antibody (e.g., panitumumab or cetuximab) treatment is the first major step toward individualized treatment for patients with mCRC.

Epsilon-sarcoglycan gene (SCGE) deletion analysis

Myoclonus-dystonia (M-D), an autosomal dominant inherited movement disorder, has been associated with mutations in the epsilon-sarcoglycan gene (SCGE) on 7q21.  Raymond et al (2008) noted that M-D due to SGCE mutations is characterized by early onset myoclonic jerks, often associated with dystonia.  Penetrance is influenced by parental sex, but other sex effects have not been established.  In 42 affected individuals from 11 families with identified mutations, these researchers found that sex was highly associated with age at onset regardless of mutation type; the median age onset for girls was 5 years versus 8 years for boys (p < 0.0097).  Moreover, the authors found no association between mutation type and phenotype.

Ritz et al (2009) stated that various mutations within the SGCE gene have been associated with M-D, but mutations are detected in only about 30 % of patients.  The lack of stringent clinical inclusion criteria and limitations of mutation screens by direct sequencing might explain this observation.  Eighty-six M-D index patients from the Dutch national referral center for M-D underwent neurological examination and were classified according to previously published criteria into definite, probable and possible M-D.  Sequence analysis of the SGCE gene and screening for copy number variations were performed.  In addition, screening was carried out for the 3 bp deletion in exon 5 of the DYT1 gene.  Based on clinical examination, 24 definite, 23 probable and 39 possible M-D patients were detected.  Thirteen of the 86 M-D index patients carried a SGCE mutation: 7 nonsense mutations, 2 splice site mutations, 3 missense mutations (2 within 1 patient) and 1 multi-exonic deletion.  In the definite M-D group, 50 % carried an SGCE mutation and 1 single patient in the probable group (4 %).  One possible M-D patient showed a 4 bp deletion in the DYT1 gene (c.934_937delAGAG).  The authors concluded that mutation carriers were mainly identified in the definite M-D group.  However, in 50 % of definite M-D cases, no mutation could be identified.

Gene expression profiling for coronary artery disease (CORUS CAD)

Evidence for the CORUS CAD gene expression profile has focused on the ability of the test to risk stratify nondiabetic persons for obstructive coronary artery disease. There is a lack of reliable evidence from prospective studies demonstrating that incorporation of the CORUS CAD alters management such that clinical outcomes are improved.

The Evaluation of Genomic Applications in Practice and Prevention (EGAPP, 2010) Working Group found insufficient evidence to recommend genomic profiling for assessing cardiovascular risk. The group reported that clinical evidence was inadequate to determine analytic validity, clinical validity or clinical utility. Clinical use of these tests is discouraged until further evidence supports improved clinical outcomes.

Home genetic tests

Walker (2010) stated that according to an undercover investigation by the Government Accountability Office (GAO), home genetic tests often provide incomplete or misleading information to consumers.  For the GAO investigation, investigators purchased 10 tests each from 4 different direct-to-consumer genetic tests companies: 23andMe, deCode Genetics, Navigenics, and Pathway Genomics.  Five saliva donors each sent 2 DNA samples to each company.  In one sample, the donor used his or her real personal and medical information, and for the second sample, they developed faux identifying and medical information.  The results, according to the GAO, were far from precise.  For example, a donor was told by a company that he had a "below average" risk of developing hypertension, but a second company rated his risk as "average", while a third company, using DNA from the same donor, said the sample revealed an "above average" risk for hypertension.  In some cases, the results conflicted with the donor's real medical condition.  None of the genetic tests currently offered to consumers has undergone FDA pre-market review.

Familial Cold Autoinflammatory Syndrome

Familial cold autoinflammatory syndrome (FCAS), also known as familial cold urticaria (FCU), is an autosomal dominant condition characterized by rash, conjunctivitis, fever/chills and arthralgias elicited by exposure to cold -- sometimes temperatures below 22° C (72° F).  It is rare and is estimated as having a prevalence of 1 per million people and mainly affects Americans and Europeans.  Familial cold autoinflammatory syndrome is one of the cryopyrin-associated periodic syndromes (CAPS) caused by mutations in the CIAS1/NALP3 (also known as NLRP3) gene at location 1q44.  Familial cold autoinflammatory syndrome shares symptoms, and should not be confused, with acquired cold urticaria, a more common condition mediated by different mechanisms that usually develop later in life and are rarely inherited.  There is insufficient evidence to support the use of genetic testing in the management of patients with FCAS/FCU.  UpToDate reviews on "Cold urticaria" (Maurer, 2011) and "Cryopyrin-associated periodic syndromes and related disorders" (Nigrovic, 2011) do not mention the use of genetic testing.

Santome Collazo et al (2010) noted that congenital adrenal hyperplasia (CAH) is not an infrequent genetic disorder for which mutation-based analysis for CYP21A2 gene is a useful tool.  An UpToDate review on "Diagnosis of classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency" (Merke, 2011) states that "[g]enetic testing also can be used to evaluate borderline cases.  Genetic testing detects approximately 95 percent of mutant alleles".  Furthermore, the Endocrine Society's clinical practice guideline on congenital adrenal hyperplasia (Speiser et al, 2010) suggested genotyping only when results of the adrenocortical profile following cosyntropin stimulation test are equivocal or for purposes of genetic counseling.  The Task Force recommends that genetic counseling be given to parents at birth of a CAH child, and to adolescents at the transition to adult care.

Malignant Hyperthermia 

Wappler (2010) stated that malignant hyperthermia (MH)-susceptible patients have an increased risk during anesthesia.  The aim of this review was to present current knowledge about pathophysiology and triggers of MH as well as concepts for safe anesthesiological management of these patients.  Trigger substances and mechanisms have been well-defined to date.  Anesthesia can be safely performed with i.v. anesthetics, nitrous oxide, non-depolarizing muscle relaxants, local anesthetics as well as xenon.  Attention must be directed to the preparation of the anesthetic machine because modern work-stations need longer cleansing times than their predecessors.  Alternatively, activated charcoal might be beneficial for elimination of volatile anesthetics.  Day case surgery can be performed in MH-susceptible patients, if all safety aspects are regarded.  Whether there is an association between MH susceptibility and other disorders is still a matter of debate.  The authors concluded that the incidence of MH is low, but the prevalence can be estimated as up to 1: 3,000.  Because MH is potentially lethal, it is relevant to establish management concepts for peri-operative care in susceptible patients.  This includes pre-operative genetic and in-vitro muscle contracture test (IVCT), preparation of the anesthetic work-station, use of non-triggering anesthetics, adequate monitoring, availability of sufficient quantities of dantrolene and appropriate post-operative care.  Taking these items into account, anesthesia can be safely performed in susceptible patients.

Moreover, an UpToDate review on "Susceptibility to malignant hyperthermia" (Litman, 2011) states that "the contracture test is performed at specific centers around the world (four in the United States).  Following testing, the referring physician receives a report indicating whether testing was positive, negative, or equivocal.  Positive or equivocal results should be followed-up with genetic testing.  Referral information can be found on the Malignant Hyperthermia Association of the United States (MHAUS) website".  Genetic testing for MH is indicated in the following groups:

• Patients with a positive or equivocal contracture test to determine the presence of a specific mutation.
• Individuals with a positive genetic test for MH in a family member.
• Patients with a clinical history suspicious for MH (acute MH episode, masseter muscle rigidity, post-operative myoglobinuria, heat or exercise induce rhabdomyolysis) who are unable or unwilling to undergo contracture testing.

Sleep-Walking

Licis et al (2011) stated that sleep-walking is a common and highly heritable sleep disorder.  However, inheritance patterns of sleep-walking are poorly understood and there have been no prior reports of genes or chromosomal localization of genes responsible for this disorder.  These researchers described the inheritance pattern of sleep-walking in a 4-generation family and identified the chromosomal location of a gene responsible for sleep-walking in this family.  A total of 9 affected and 13 unaffected family members of a single large family were interviewed and DNA samples collected.  Parametric linkage analysis was performed.  Sleep-walking was inherited as an autosomal dominant disorder with reduced penetrance in this family.  Genome-wide multi-point parametric linkage analysis for sleep-walking revealed a maximum logarithm of the odds score of 3.44 at chromosome 20q12-q13.12 between 55.6 and 61.4 cM.  The authors described the first genetic locus for sleep-walking at chromosome 20q12-q13.12; and concluded that sleep-walking may be transmitted as an autosomal dominant trait with reduced penetrance.

In an editorial that accompanied the afore-metnioned study, Dogu and Pressman (2011) noted that "[a]ccording to currently accepted evidence-based theories, the occurrence of sleepwalking requires genetic predisposition, priming factors such as severe sleep deprivation or stress, and, in addition, a proximal trigger factor such as noise or touch.  These factors form the background for a “perfect storm,” all of which must occur before a sleepwalking episode will occur.  Hereditary factors likely play an important role, with recessive and multifactorial inheritance patterns having been reported.  A recent genetic study has shown that the HLADQB1*05 Ser74 variant is a major susceptibility factor for sleepwalking in familial cases, but this finding has yet to be replicated.  Another study attempted to find a causal relationship between sleepwalking and sleep-disordered breathing in cosegregated families of both disorders.  However, this study was limited by the absence of molecular data .... The current diagnosis of sleepwalking is based almost entirely on clinical history.  There are no objective, independent means of confirming the diagnosis.  Additionally, treatment of sleepwalking is symptomatic, aimed at suppressing arousal or reducing deep sleep.  identification of causative genes may eventually permit development of an independent test and treatments aimed at the underlying causes of this disorder".

Choroidal Neovascularization

RetnaGene AMD (Sequenom Center for Molecular Medicine) is a laboratory developed genetic test to assess the risk of developing choroidal neovascularization (CNV), the wet form of age-related macular degeneration (AMD), a common eye disorder of the elderly that can lead to blindness. The test identifies at-risk Caucasians, age 60 and older. A report of the American Academy of Ophthalmology (Stone, et al., 2012) recommends avoidance of routine genetic testing for genetically complex disorders like age-related macular degeneration and late-onset primary open-angle glaucoma until specific treatment or surveillance strategies have been shown in one or more published clinical trials to be of benefit to individuals with specific disease-associated genotypes. The report recommends that, in the meantime, genotyping of such patients should be confined to research studies. The report stated that complex disorders (e.g., age-related macular degeneration and glaucoma) tend to be more common in the population than monogenic diseases, and the presence of any one of the disease-associated variants is not highly predictive of the development of disease. The report stated that, in many cases, standard clinical diagnostic methods like biomicroscopy, ophthalmoscopy, tonography, and perimetry will be more accurate for assessing a patient’s risk of vision loss from a complex disease than the assessment of a small number of genetic loci. The report said that genetic testing for complex diseases will become relevant to the routine practice of medicine as soon as clinical trials can demonstrate that patients with specific genotypes benefit from specific types of therapy or surveillance. The report concluded that, until such benefit can be demonstrated, the routine genetic testing of patients with complex eye diseases, or unaffected patients with a family history of such diseases, is not warranted.

Appendix

Amsterdam II criteria:

At least 3 relatives must have an HNPCC-related cancer*, and all of the following criteria must be present:

Revised Bethesda criteria:

Member must meet 1 or more of the following criteria:

• Colorectal cancer is diagnosed in a member with 1 or more 1st-degree relatives with an HNPCC-related cancer*, with one of the cancers diagnosed under age 50 years; or
• Colorectal cancer is diagnosed in a member with 2 or more 1st- or 2nd-degree relatives with an HNPCC-related cancer*, regardless of age; or
• Member has colorectal cancer diagnosed before age 50 years; or
• Member has colorectal cancer with microsatellite instability-high (MSI-H) histology, where cancer is diagnosed before age 60 years; or
• Member has synchronous or metachronous HNPCC-related cancers*, regardless of age.
  

* Hereditary nonpolyposis colorectal cancer (HNPCC)-related cancers include colorectal, endometrial, gastric, ovarian, pancreas, ureter and renal pelvis, brain (usually glioblastoma as seen in Turcot syndrome), and small intestinal cancers, as well as sebaceous gland adenomas and keratoacanthomas in Muir-Torre syndrome.