CAG repeat expansions in patients with sporadic cerebellar ataxia

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Abstract
CAG repeat expansions cause spinocerebellar ataxia type 1 (SCA1), SCA2, SCA3, SCA6 and dentatorubral‐pallidoluysian atrophy (DRPLA). So far these expansions have been examined mainly in ataxia patients with a family history. However, some sporadic cases with SCA have recently been reported. To elucidate the frequency and characteristics of sporadic SCAs, we screened 85 Japanese ataxia patients without a family history for the SCA1, SCA2, SCA3, SCA6 and DRPLA mutations. As a result, 19 patients (22%) were found to have expanded CAG repeats. Among sporadic SCAs, the SCA6 mutation was most frequently observed. The sporadic SCA6 patients had smaller CAG repeats and a later age of onset than SCA6 patients with an established family history. We also identified one father‐child pair in which intermediate sized CAG repeats expanded into the SCA2 disease range during transmission. These findings suggest that patients with ataxia even without a family history should be examined for a CAG repeat expansion.