Single-Tube Screen for Rapid Detection of Repeat Expansions in Seven Common Spinocerebellar Ataxias

Abstract

Background: The autosomal dominantly inherited and genetically heterogeneous spinocerebellar ataxias (SCAs) exhibit highly similar clinical presentations. Many are caused by repeat expansions, of which at least 8 involve CAG repeats. Repeat expansion detection is the only method to confirm disease status in symptomatic individuals. We present a novel strategy to simultaneously screen for the presence of CAG repeat expansion in the genes responsible for SCAs 1, 2, 3, 6, 7, 12, and dentatorubral-pallidoluysian atrophy using a simplified single-tube assay. Methods: The method employs differentially labeled locus-specific primers and a common triplet-primed primer. Amplified products from each locus are distinguished by a combination of the product size and the fluorophore tag. The upper size limit of the normal allele range was used as the cutoff for distinguishing normal from potentially affected samples, with repeat expansion detected by presence of electrophoretic peaks extending beyond the cutoff. Results: Blinded evaluation of the assay on 60 genotype-known DNA samples correctly detected repeat expansion in the expected SCA repeat locus for all 31 DNA samples. Conclusions: In principle, this strategy can be applied to the simultaneous screening of any group of disease genes sharing the same repetitive units and/or their reverse complement.