ARUP's Laboratory Test Directory

Huntington Disease (HD) Mutation with Reflex to Southern Blot : 0040018
[ image for: Huntington Disease Consent Form]
Huntington Disease Consent Form
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Additional Technical Information


Mnemonic: HD

Ordering Recommendation: Diagnostic testing for Huntington disease.
Predictive testing for Huntington disease.
Methodology: Polymerase Chain Reaction/Fragment Analysis
Performed: Varies
Reported: 7-10 days after receipt of fully completed HD consent form
Specimen Required: Collect: Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).

Specimen Preparation: Transport 5 mL whole blood. (Min: 3 mL)

Storage/Transport Temperature: Refrigerated.

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 (collection to initiation of testing): Ambient: 72 hours; Refrigerated: 1 week; Frozen: 1 month
Reference Interval:
Negative: This individual has two normal alleles; and therefore, is neither a carrier nor will be affected with Huntington disease.
Interpretive Data: Huntington Disease Background Info:
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; alleles with greater than 80 CAG repeats may require Southern blot analysis to help estimate repeat size.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Other neurodegenerative disorders will not be detected. Sizing by Southern blot is not precise, varying up to +/-15 repeats. Rare, previously unreported variants may interfere with PCR amplification.



Counseling and informed consent are recommended for genetic testing. Consent forms are available online at www.aruplab.com.

See Compliance Statement C: www.aruplab.com/CS
 
Phenotype Number of CAG Repeats
Normal allele ≤26
Mutable normal allele 27-35
HD allele with reduced penetrance 36-39
HD allele ≥40

Note: If an expanded allele is detected by PCR and capillary electrophoresis, but cannot be sized (typically due to large expansions greater than 80 repeats), Southern blot will be added to determine the size of the expanded CAG repeat. Additional charges apply.
CPT Code(s): 81401
If reflexed, add 81479