OBJECTIVE: The aim of this study was to analyze the association between the variations of coenzyme Q2 4-hydroxybenzoate polyprenyltransferase gene (COQ2) and Japanese patients with multiple system atrophy (MSA). METHODS: We investigated the genetic variations in exons 1, 2, 6, and 7 of the COQ2 gene in 133 Japanese patients with MSA and 200 controls and analyzed the association between the variations and MSA. RESULTS: Six DNA variations (G21S, L25V, V66L, P157S, V393A, and X422K) were found in the 133 patients with MSA, and G21S and X422K were new variations that had never been reported. V66L was a common variation that was found in all 133 patients with MSA. G21S, P157S, V393A, and X422K did not show gene frequency differences between patients with MSA and controls. On the other hand, L25V was newly proven to be the only risk factor of sporadic MSA with predominant olivopontocerebellar ataxia. CONCLUSIONS: The present study suggests L25V variant of COQ2 gene as a genetic risk factor in Japanese patients with MSA with cerebellar ataxia.