SCA6 is caused by CAG expansion in the alpha 1A voltage-dependent calcium c
hannel subunit gene. The authors studied an Italian family in which one pat
ient carried a fully expanded SCA6 allele with 26-CAG repeats, whereas the
other affected family member was homozygous for an intermediate-size allele
of 19-CAG repeats. Three family members, heterozygous for the intermediate
allele, were clinically unaffected. The findings demonstrate a dose-depend
ent pathogenic effect of an intermediate CAG expansion in the SCA6 gene.