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The mutation involved in spinocerebellar ataxia type 6(SCA6)is a small CAG expansion in the alpha1-A subunit of the voltage-dependent calcium channel gene.We looked for this mutation in 91 families with autosomal-dominant cerebellar ataxias and found that SCA6 is a minor locus in our series(2%) and is rare in France(1%).Furthermore,we did not detect the SCA6 mutation on 146 sporadic cases with isolated cerebellar ataxia or olivopontocerebellar atrophy.The normal and expanded alleles ranged from 4 to 15 and 22 to 28 CAG repeats,respectively,and age at onset was correlated to CAG repeat length(r=-0.87).In contrast with our SCA,the expanded allele was stable during transmission.Clinically,SCA6 patient(n= 12)presented with moderately to severe cerebellar ataxia with a lower frequency of associated signs compared with other SCA and a mean age at onset of 45+/-14 years,(range,24 to 67).MRI showed extensive cerebellar atrophy but not of the brainstem or cerebral cortex type. |
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