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Huntington Disease (HD) Mutation by PCR (Extended TAT as of 11/20/20-no referral available)
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Ordering Recommendation
Diagnostic confirmation for Huntington disease (HD) in a symptomatic individual. Presymptomatic testing for adults with a family history of HD.
Mnemonic
Methodology
Polymerase Chain Reaction/Fragment Analysis
Performed
Varies
Reported
7-10 days after receipt of fully completed HD consent form
New York DOH Approval Status
Specimen Required
Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
Transport 3 mL whole blood. (Min: 1 mL)
Preferred transport temp: Refrigerated. Also acceptable: Room temperature.
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.
Room temperature: 1 week; Refrigerated: 1 month; Frozen: unacceptable
Reference Interval
Interpretive Data
Background Information for Huntington Disease (HD) Mutation by PCR:
Characteristics: Neurodegenerative disorder causing progressive cognitive, motor, and psychiatric disturbances typically beginning at 35-44 years of age. An estimated 5 percent of individuals with HD are symptomatic as juveniles and 25 percent of individuals after age 50.
Incidence: 1 in 15,000.
Inheritance: Autosomal dominant.
Cause: Expanded number of CAG repeats in the HTT gene. HD allele with reduced penetrance 36-39 CAG repeats; HD allele with full penetrance 40 or more CAG repeats.
Clinical Sensitivity and Specificity: 99 percent.
Methodology: Triplet repeat-primed polymerase chain reaction (PCR) followed by size analysis using capillary electrophoresis. 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.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Other neurodegenerative disorders will not be detected. Diagnostic errors can occur due to rare sequence variations. Interpretation of this test result may be impacted if this patient has had an allogeneic stem cell transplantation.
This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the U.S. Food and Drug Administration. This test was performed in a CLIA-certified laboratory and is intended for clinical purposes.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
| Allele type |
Number of CAG Repeats |
|---|---|
| Normal allele | Less than or equal to 26 |
| Mutable normal (intermediate) allele | 27-35 |
| HD allele with reduced penetrance | 36-39 |
| HD allele with full penetrance | Greater than or equal to 40 |
Laboratory Developed Test (LDT)
Note
Hotline History
CPT Codes
81271
Components
| 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 |
Aliases
- HD genetic testing
- HTT genetic testing
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