Huntington Disease (HTT) Genetic Testing (Repeat Expansion)

Huntington Disease (HTT) Genetic Testing (Repeat Expansion)

Gene/Alternative Name

An expansion of the CAG repeats

Methodology

Repeat-Primed PCR (QP-PCR)

Test Description

This is a confirmatory testing for analysis of the HD gene at or after the time of the clinical diagnosis of HD. The presence of a CAG repeat expansion in a person with HD symptoms confirms the clinical impression and supports a diagnosis of HD. The absence of a CAG repeat expansion in a person felt clinically to have HD must prompt a re-evaluation of the person’s diagnosis and a reconsideration of the accuracy of the diagnosis in the family.

Clinical Significance

Huntington disease (HD) is a neurodegenerative disease of mid-life onset that produces choreic movements and cognitive decline, often accompanied by psychiatric changes. The disease is caused by an expansion of the CAG repeats in 3-5 out of 100,000 individuals. However, the prevalence of HD exceeds 15 per 100,000 in some populations, mostly of Western European origin. Juvenile-onset HD occurs in approximately 5% of affected patients, is rapidly progressive, and presents with rigidity, spasticity, and intellectual decline before the age of 20 years. The symptoms result from the selective loss of neurons, most notably in the caudate nucleus and putamen, and there is currently no effective treatment.

Limitations

Maximum reportable sizing: 150 repeats.

This test was developed and its performance characteristics determined by Celltechgen. It has not been cleared or approved by the Food and Drug Administration.

Specimen Requirements

Whole blood tube should be sent to the lab unopened. It is preferable not to perform additional testing on original tubes prior to PCR testing. A completed screening questionnaire must accompany specimens.

Specimen: Whole blood

Volume: 4 mL whole blood

Container: Lavender-top (EDTA) tube

Storage Instructions: Maintain specimen at room temperature.

Causes for Rejection: Frozen blood EDTA tube

Storage & Transportation

Ship at room temperature overnight, but stable up to 5 days post-collection at room temperature. Do not freeze.

CPT Code(s)*

81271

Turnaround Time

1-2 weeks