No association of the SCA1 (CAG)₃₁ allele with Huntington's disease, myotonic dystrophy type 1 and spinocerebellar ataxia type 3

Trinucleotide repeat expansions are the underlying mutation in several neurodegenerative and neuromuscular disorders including at least eight spinocerebellar ataxias (SCA). The molecular mechanisms of repeat expansion are as yet insufficiently understood. Recently, an association of the SCA1 (CAG)₃₁ repeat allele with Huntington's disease and myotonic dystrophy type 1 was described. These findings implicate a possible role of the SCA1 (CAG)₃₁ allele in other triplet diseases. We analyzed the SCA1 CAG repeat length in a large sample of Huntington's disease (n = 182), myotonic dystrophy type 1 (n = 64) and SCA3 (n = 31) patients. In none of these groups was a significant association with the 31 repeat allele found. Our findings do not support the hypothesis that this allele is involved in the etiology of trinucleotide expansion.