Diagnostic testing:
- Clinical suspicion of Huntington disease (provide a copy of the patient’s clinical notes with the requisition)
Diagnostic testing for this analysis (symptomatic patients) can only be requested by neurologists and medical geneticists.
Predictive testing:
- At least one affected relative
- At least one presymptomatic relative with a molecular test result of ≥36 CAG repeats
Predictive testing for this analysis (asymptomatic patients) can only be requested by medical geneticists.
Huntington disease is an autosomal dominant disorder caused by an expansion of 36 or more CAG trinucleotide repeats in HTT. Alleles with 26 or fewer repeats are not disease-causing and generally segregate as a stable repeat. Intermediate alleles of 27-35 repeats are not disease-causing but may expand to disease-causing lengths in offspring due to meiotic instability. Alleles with 36-39 repeats have reduced penetrance, with rare reports of elderly asymptomatic individuals with CAG repeats in this range. Alleles with 40 or more CAG repeats cause Huntington disease with full penetrance (PMID: 20301482).
This test consists of determining the number of CAG repeats in HTT by triplet-repeat primed PCR and capillary electrophoresis, as previously described (PMID: 23414820).
This test provides accurate sizing of alleles up to 100 CAG repeats and identifies expanded alleles >100 repeats. Analysis is dependent on accurate clinical diagnosis of affected individuals and on correct reporting of family relationships. DNA variants located in primer binding sites and rare genotyping errors can result in inaccurate diagnosis.
Turnaround time: 4-5 weeks
Specimen accepted:
- 2 x 4 mL blood in EDTA tubes (purple top tube)
- DNA: min 10 ug
- Amniotic fluid: min 10 ml
- Direct CVS: min 10 mg direct villi
- Cultured amniocytes or CVS: 2 x T25 flasks (confluent)
- For any other sample type, contact the laboratory for testing availability
Submit your test request using our molecular genetics requisition.