Analysis of spinocerebellar ataxia type 1 (SCA1)-related CAG trinucleotide expansion in Japan

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disorder caused by expansion of a CAG trinucleotide repeat. We analyzed CAG repeat expansion in 25 families in the northeast of Japan with hereditary ataxia of Menzel type. Twenty of 38 patients in 12 families had expanded allele for SCA1. The number of CAG repeats correlated with the age at onset. Although the relationship between anticipation and the number of CAG repeats in successive generations was not ascertainable, there was a tendency to paternal bias for the accelerated age at onset. Study of the number of CAG repeats in various tissues showed no differences in the repeat length in lymphocytes, muscle, or brain; sperm, however, showed an obvious expansion. This may be a clue to a possible mechanism for the molecular basis of paternal anticipation of the disease. The SCA1 gene was transcribed from both wild and mutated alleles in muscles of affected individuals, but the repeat length was the same for both the muscle cDNA and the lymphocyte genomic DNA. These results suggest that, in the area of Japan where SCA1 is prevalent, 48% of families with spinocerebellar degeneration have SCA1 mutation.