Primer site variations resulting in false-negative Huntington’s disease testing

Guidelines for HTT triplet-repeat testing in Huntington’s disease (HD) have long been advanced. These include recommendations to use triplet-primed PCR (TP-PCR), given prior problems with primer annealing and the failure of single PCR-based methods to identify expanded alleles. Here, we document clinical history and exhaustive diagnostic testing for an affected proband with a history of progressive chorea. We demonstrate how genetic testing for HD through a commercial lab failed to identify an HTT (CAG)n expansion. Positive results were revealed through research testing and were confirmed in additional family members. When only homozygous wild-type alleles are identified in patients with a continued high clinical suspicion for manifest HD, commercial HTT testing laboratories should report the primers used, TP-PCR results or complementary methods. False-negative results in commercial genetic testing yield a much greater cost to patients, families and the healthcare system.