Huntington Disease (HTT) Genetic Testing (Repeat Expansion)

Whole blood

Whole blood; oral swab or extracted DNA (from blood or oral swab only)

4 mL

Whole blood: 4 mL; oral swab: 3 swabs; or extracted DNA: contact MNG Genetic Services 844-664-8378 (844-MNGTEST)

Lavender-top (EDTA) tube

Whole blood: lavender-top (EDTA) tube; oral swab: OCD-100 DNA Genotek; or extracted DNA: contact MNG Genetic Services 844-664-8378 (844-MNGTEST)

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.

Diagnostic testing

Maximum reportable sizing: 100 repeats

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

False positive or false negative results may occur for reasons that include insufficient information available about rare genetic variants, allele dropout, blood transfusions, bone marrow transplantation, somatic or tissue-specific mosaicism or mislabeled samples. Maximum reportable size of repeat expansion testing: ATN1: 110 repeats; ATXN1: 150 repeats (repeats greater than 40 in the ATXN1 gene cannot be assessed for CAT interruptions); ATXN2: 150 repeats; ATXN3: 120 repeats; ATXN7: 125 repeats; ATXN8/ATXN8OS: 150 repeats; ATXN10: 70 repeats; C9orf72: 65 repeats; CACNA1A: 145 repeats; CNBP: 373 base pairs (approximately 75 repeats); DMPK: 150 repeats; FXN: 1300 repeats; HTT: 100 repeats; JPH3: 100 repeats; NOP56: 65 repeats; PPP2R2B: 150 repeats; TBP: 120 repeats. Repeat sizes greater than the maximum reportable range are reported as greater than the largest reportable repeat size.

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

Repeat-Primed PCR (QP-PCR)

Repeat-primed PCR and fragment length analysis to identify number of nucleotide repeats