Huntington Disease (HD) CAG Repeat Expansion
Also known as: HD PCR
Use
The Huntington Disease (HD) CAG Repeat Expansion test is a diagnostic tool used to confirm a diagnosis of Huntington disease in symptomatic individuals. It is also used for presymptomatic testing in adults with a family history of HD. Huntington disease is a neurodegenerative disorder that causes progressive cognitive, motor, and psychiatric disturbances, typically beginning between the ages of 35-44. The disease is caused by an expanded number of CAG repeats in the HTT gene. This test determines the number of CAG repeats to classify alleles into normal, mutable normal, reduced penetrance, and full penetrance categories for clinical interpretation.
Special Instructions
A completed HD-specific consent form signed by the patient or legal guardian and physician is required for all specimens. Testing for asymptomatic patients under the age of 18 years is not offered. Presymptomatic testing is strongly encouraged to be conducted through a counseling program approved by the Huntington Disease Society of America.
Limitations
This test will not detect other neurodegenerative disorders. Diagnostic errors can occur due to rare sequence variations, and the interpretation of test results may be impacted if the patient has had an allogeneic stem cell transplantation. The repeat sizing precision is +/- 2 for alleles less than or equal to 50 repeats, +/- 3 for alleles with 51 to 75 repeats, and +/- 4 for alleles greater than 75 repeats.
New York Approved
Methodology
PCR-based (PCR)
Biomarkers
LOINC Codes
- 31208-2
- 49637-2
- 49638-0
- 50621-2
Result Turnaround Time
7-10 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
2 mL
Minimum Volume
1 mL
Container
Lavender (EDTA), pink (K2EDTA)
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 1 week |
| Refrigerated | 1 month |
| Frozen | Unacceptable |
Other tests from different labs that may be relevant