Huntington Disease DNA Screen
General Information
Lab Name
Huntington Disease
Lab Code
HDTEST
Epic Name
HUNTINGTON DISEASE
Description
Huntington disease (HD) is an autosomal dominant genetic disorder. Expansion of a CAG trinucleotide repeat in the HTT gene occurs in 98-99% of Huntington disease cases, and is essentially absent in normal controls (Kremer et al. 1994). The number of CAG repeats does not reliably predict the age of onset, the rate of disease progression, or the severity of symptoms for an individual patient.
Indications for testing include:
- Confirmation of a clinical diagnosis of Huntington disease
- Presymptomatic testing for Huntington disease
Restrictions/exclusions from testing include:
- Presymptomatic testing of minors (< age 18) (including evaluations for adoptions)
- Anonymous testing
For additional information:
- Patient information is available on the UWMC's HDSA Center of Excellence Website (https://depts.washington.edu/hdcoe/).
- For current guidelines and protocols on genetic testing for Huntington disease, please refer to the American College of Medical Genetics or see Bean et al. 2014 edition.
Genetic Counseling can be useful to patients and families considering genetic testing. The laboratory can provide referrals to genetics clinics.
If confidentiality is an issue, please call Genetics Lab 206-598-6429. Anonymous testing is NOT performed. Testing on children requires prior approval by Genetics Lab.
References
- Bean L and Bayrak-Toydemir P. American College of Medical Genetics and Genomics Standards and Guidelines for Clinical Genetics Laboratories, 2014 edition: technical standards and guidelines for Huntington disease. Genet Med 2014, 16:e2. 25356969
- Kremer B, et al. A worldwide study of the Huntington's disease mutation. The sensitivity and specificity of measuring CAG repeats. N Engl J Med 1994, 330:1401-6. 8159192
- Mahbubul H, Hayden MR. Huntington Disease. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. Available at https://www.ncbi.nlm.nih.gov/books/NBK1305/
- Margolis RL and Ross CA. Diagnosis of Huntington disease. Clin Chem 2003, 49:1726-32. 14500613
Synonyms
Huntington's Chorea
Components
Code | Name |
---|---|
HDA1 | HD Allele 1 |
HDA2 | HD Allele 2 |
HDCI | HD Clinical Information |
HDIN | HD Interpretation |
HDMTH | HD Methods |
Interpretation
Method
Polymerase Chain Reaction (PCR)/Capillary Electrophoresis
The region of the HTT gene containing the CAG repeat is amplified and its size measured by capillary electrophoresis calibrated against HTT-specific cloned size standards. Precision (1 SD) is better than 0.5 CAG repeat units. This test was developed and its performance characteristics determined by the Department of Laboratory Medicine at the University of Washington.
Reference Range
See individual components
Ref. Range Notes
Expansion of a CAG repeat in the HTT gene is present in about 98% of Huntington disease cases and is essentially absent in normal controls. Alleles with 40 or more CAG repeats are abnormal, alleles with 36 to 39 repeats are abnormal with reduced penetrance, alleles with 27 to 35 repeats are normal but potentially mutable upon transmission to offspring, and alleles with 26 or fewer repeats are normal (Bean et al 2014).
Guidelines
Ordering & Collection
Specimen Type
Collection
Acceptable:
- Whole blood: 5 mL lavender top (EDTA) tube or yellow (ACD) top tube or 2 mL microtainer lavender top tube
- Extracted DNA from approved sample type (blood): 500 ng (concentration >10 ng/uL)
Unacceptable: Heparin green top tubes, buccal swab
Forms & Requisitions
Handling Instructions
- Whole blood samples in EDTA or ACD: Refrigerate upon receipt.
- Extracted DNA: Refrigerate upon receipt or keep frozen if the sample was received frozen.
Call Genetics lab for any questions at (206)598-7021.
Quantity
requested: Entire specimen
minimum: Blood: 1 mL. If volume is less than 1mL, do not cancel. Send to Genetics lab.
Processing
For clients outside of UW, please include any relevant clinical history. Testing on pediatric patients is only available if individuals are symptomatic. Presymptomatic testing on pediatric patients is not available.
If fetal tissue (cultured amniocytes or chorionic villi) was received for prenatal testing, consultation with the laboratory is required. Please notify the Genetics lab about prenatal studies via email at geneticshelp@uw.edu or call 206-598-7021.
Performance
LIS Dept Code
Genetics (GEN)
Performing Location(s)
UW-MT |
Genetics
Attention: Genetics Lab Tel: 206-598–6429 M–F (7:30 AM–4:00 PM) Tel (EXOME only): 206-543-0459 |
Faculty |
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Frequency
Performed weekly. Results within 2-3 weeks.
Available STAT?
No
Billing & Coding
CPT codes
81271
Billing Comments
For pricing information, contact Client Support Services 206-520-4600 or 800-713-5198.
LOINC
Interfaced Order Code
UOW850