A family with mild clinical manifestations of spinocerebellar ataxia type 1 (SCA1): correlation with smaller CAG repeats

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disorder caused by expansion of a CAG trinucleotide repeat. We analyzed CAG repeat expansion in one Japanese SCA1 family with mild clinical manifestations. Clinically, this SCA1 family showed less frequent nystagmus (p = 0.045, Fisher's exact-test) in comparison with duration-matched control patients with larger numbers of CAG repeats (48.4 ± 4.2, p < 0.01). Some patients showed no other signs than cerebellar ataxia in the earlier stage. All six patients had expanded alleles for SCA1 with relatively small CAG repeats (41.5 ± 1.0, mean ± SD), which may be related to the mild clinical symptoms of the disease. The present results also suggest that slow saccades and amyotrophy are constantly observed in 30-40% of SCA1 patients without regard to the size of CAG repeats, while the frequency of nystagmus decreases with reduction in size of the CAG expansion.