Ataxia and progressive encephalopathy in a 4-year-old girl

The spinocerebellar ataxias (SCAs) are a rare group of neurodegenerative disorders with progressive cerebellar ataxia as the primary feature. These disorders are phenotypically and genetically variable, both between and within subtypes. Seven of the SCA subtypes are caused by CAG trinucleotide repeats within the respective genes, and clinically most of these diseases demonstrate anticipation. Testing for these disorders typically relies upon conventional polymerase chain reaction (PCR) and fragment analysis. However, conventional PCR may give false-negative results in cases in which the CAG expansion is unusually long. We report a case of spinocerebellar ataxia type 2 (SCA2) in a 4-year-old girl with false-negative conventional PCR results. Specifically, the SCA2 disorder is caused by a CAG repeat within the ATXN2 gene on chromosome 12. Subsequent confirmatory testing using modified PCR and primers specific for the CAG repeat were performed and revealed an expanded allele with 109 repeats in our patient.