Primer site variations resulting in false-negative Huntingtons disease testing

Huntington’s disease (HD) genetic testing is routinely performed to confirm diagnosis or for predictive testing in asymptomatic individuals.1 Accurate testing results are critical for patients and families, impacting not only diagnosis but also prognosis, future care needs, treatment, genetic counselling and psychosocial factors (including persistent stigma attached to HD). Multiple Clinical Laboratory Improvement Amendments (CLIA)-certified laboratories now provide commercial-based genetic testing to size the HTT CAG repeat. They primarily use PCR-based assays, which involve amplification using flanking primers followed by capillary electrophoresis.2–4 In the majority of patients, test results confirm clinical observations but discrepancies in reporting CAG repeat lengths have been documented in 4% of patients.3 While most discrepancies are within a few CAG repeat sizes, that margin of error is especially critical in the partial penetrance, 36–39 repeat range.1 PCR methods are error-prone to genomic variants that…