Homozygous 31 trinucleotide repeats in the SCA2 allele are pathogenic for cerebellar ataxia

Abstract

Spinocerebellar ataxia type 2 (SCA2), an autosomal dominant cerebellar disorder belonging to the polyglutamine (polyQ) diseases, is characterized by progressive ataxia, slow saccadic eye movement, hyporeflexia, peripheral neuropathy, and pyramidal and extrapyramidal signs. 1 The cause of SCA2 is a CAG repeat expansion, sometimes interrupted by CAA within, in ATXN2 on chromosome 12q24. 2,3 Previous reports have shown that the presence of 33 or more heterozygous trinucleotide repeats is pathogenic, whereas 14 to 31 repeats is normal. 3,4 We report a case of late-onset SCA2 with homozygous alleles of 31 trinucleotide repeats in ATXN2.