Predictive testing for Huntington disease.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 5 mL whole blood. (Min: 3 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- A completed HD specific consent form, signed by the patient (or legal guardian) and physician, is required for all specimens. Testing for patients under the age of 18 years or fetal specimens is not offered. Presymptomatic patients are strongly encouraged to be tested through a counseling program approved by the Huntington Disease Society of America at (800) 345-4372. Call Genetics Processing with additional questions at 800-242-2787 ext 3301.
- Ambient: 72 hours; Refrigerated: 1 week; Frozen: 1 month
Characteristics: Neurodegenerative disorder causing progressive cognitive, motor, and psychiatric disturbances typically beginning at 35-44 years of age
(Although, 5 percent are affected as juveniles and 25 percent affected after age 50).
Incidence: 1 in 15,000.
Inheritance: Autosomal dominant.
Cause: Expanded number of CAG repeats in the HD gene (27-35 repeats-unaffected, intermediate; 36-39 repeats-reduced penetrance; 40+ repeats-affected, full penetrance).
Clinical Sensitivity and Specificity: 99 percent.
Methodology: Chimeric PCR followed by size analysis using capillary electrophoresis.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Other neurodegenerative disorders will not be detected. Rare, previously unreported variants may interfere with PCR amplification. Diagnostic errors can occur due to rare sequence variations.
Counseling and informed consent are required for Huntington Disease genetic testing. Consent forms are available online at www.aruplab.com.
|Phenotype||Number of CAG Repeats|
|Normal allele||Less than or equal to 26|
|Mutable normal allele||27-35|
|HD allele with reduced penetrance||36-39|
|HD allele||Greater than or equal to 40|
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|Component Test Code*||Component Chart Name||LOINC|
|0050604||Huntington Disease (HD) Allele 1||49637-2|
|0050606||Huntington Disease (HD) Allele 2||49638-0|
|0050607||Huntington Disease (HD) Interpretation||50621-2|
|2001353||Huntington Disease (HD) - Specimen||31208-2|
- HD genetic testing
- HTT genetic testing