SCA6 mutation analysis in a large cohort of the Japanese patients with late-onset pure cerebellar ataxia

Spinocerebellar ataxia type 6 (SCA6) is caused by small CAG repeat expansion in the gene encoding the alpha(1A)-voltage-dependent-calcium channel subunit (CACNL1A4) on chromosome 19p13, and is a subgroup of the late-onset pure cerebellar ataxia (ADCA III). To investigate the prevalence of SCAB in the Japanese, we analyzed this mutation in 23 families and 12 probands with ADCA m. The specificity and stability of the CAG repeat were examined in additional individuals and families with other miscellaneous dominant SCAs. The CAG expansion of SCA6 gene was exclusively observed in 12 of 23 families (52%) and 12 proband cases with ADCA III, but not in others. The CAG repeat was 21-33 in the disease-associated alleles (n = 56), and 4-18 in normal alleles (n = 1148). Expanded alleles were stable during transmission, and a significant inverse correlation for CAG repeat number with age at onset was noted. Our results indicate that SCA6 shares approximately half of the ADCA III in the Japanese, and that gene mutations causing the remaining, have yet to be identified. (C) 1998 Elsevier Science B.V.