Ordering Recommendation

Diagnostic confirmation for Huntington disease (HD) in a symptomatic individual. Presymptomatic testing for adults with a family history of HD.

Mnemonic

HD

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

This test is New York DOH approved.

Specimen Required

Patient Preparation
Collect

Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).

Specimen Preparation

Transport 3 mL whole blood. (Min: 1 mL)

Storage/Transport Temperature

Preferred transport temp: Refrigerated. Also acceptable: Room temperature.

Unacceptable Conditions
Remarks

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.

Stability

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

Compliance Category

Laboratory Developed Test (LDT)

Note

Hotline History

N/A

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
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.

Aliases

  • HD genetic testing
  • HTT genetic testing
Huntington Disease (HD) Mutation by PCR (Extended TAT as of 11/20/20-no referral available)