CAG REPEAT EXPANSIONS IN PATIENTS WITH SPORADIC CEREBELLAR-ATAXIA

CAG repeat expansions cause spinocerebellar ataxia type 1 (SCA1), SCA2 . SCA3, SCA6 and dentatorubral-pallidoluysian atrophy (DRPLA). So Ear these expansions have been examined mainly in ataxia patients with a f amily history. However, some sporadic cases with SCA have recently bee n reported. To elucidate the frequency and characteristics of sporadic SCAs, we screened 85 Japanese ataxia patients without a family histor y 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 SC A6 patients had smaller CAG repeats and a later age of onset than SCA6 patients with an established family history. We also identified one f ather-child pair in which intermediate sized CAG repeats expanded into the SCA2 disease range during transmission. These findings suggest th at patients with ataxia even without a family history should be examin ed for a CAG repeat expansion.