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DNA Analysis:
Huntington Disease
Huntington disease (HD) is an autosomal dominant neurodegenerative disorder characterized by involuntary movement and progressive dementia. Clinical presentation usually does not appear until adulthood. The HD phenotype is the result of an expansion of a CAG trinucleotide repeat in the huntingtin gene. Normal individuals have up to 26 CAG repeats. Repeat sizes from 27 to 35 are not typically associated with the HD phenotype in the tested individual but do represent a normal mutable allele which could expand upon transmission to the next generation. Repeat sizes from 36 to 39 are associated with an increasing probability of developing HD. However, the HD phenotype is not always penetrant for CAG repeat sizes in this range. Repeat sizes greater than or equal to 40 are associated with HD. The HD phenotype is fully penetrant. A correlation exists between the size of the CAG repeat and age of onset of this disorder.
CAG repeat ranges are based on recommendations from the American College of Medical Genetics/ American Society of Human Genetics Huntington Disease Genetic Testing Working Group.
- Confirmation of a HD diagnosis in symptomatic adults
- Confirmation of early onset HD in symptomatic individuals less than 18 years of age
- Predictive testing for asymptomatic adults with a 50% risk for HD
- Prenatal diagnosis for documented HD families
It is strongly recommended that asymptomatic individuals with a 50% risk for HD enroll in a predictive testing program. A testing center must follow the Huntington Disease Society of America national guidelines for HD testing. The HD Predictive Testing Program at UCSD consists of neurological and psychological evaluations, consultation with a medical geneticist, and DNA testing followed by genetic counseling and discussion of test results. Testing of symptomatic family members is also recommended. Strict patient confidentiality is maintained at all times. The HD Predictive Testing Program at UCSD can be reached at (858) 622-5800.
Direct mutation analysis: Our testing methodology incorporates polymerase chain reaction (PCR) technology with PAGE electrophoresis to analyze the CAG trinucleotide region of the huntingtin gene for determination of repeat size. A second PCR analysis is performed for those cases with identical repeat numbers in both huntingtin genes.
This assay has detected up to 72 CAG repeats. This level of detection identifies approximately 99% of individuals affected with Huntington disease. This assay will not detect the small number of remaining cases caused by other mechanisms such as deletion or point mutation.
Blood: 5 cc collected in a purple top (EDTA) or yellow top (acid citrate dextrose) vacutainer tube. Do not centrifuge or freeze. Sample may be refrigerated or stored at room temperature.
Please contact the laboratory at (858) 534-3093 for information on prenatal testing. Mutation status must be documented in both parents prior to prenatal studies. A blood sample from the mother is required for prenatal testing to rule out maternal cell contamination.
21 days
83890, 83894, 83898, 83912
For prenatal studies add 88235
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> Standard DNA Consent Form
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