identified two Japanese families with autosomal dominant cerebellar ataxia with a suggestion of a mild peripheral neuropathy including reduced vibration and absent reflexes with a 414‐kb deletion including the entire ITPR1 gene and exon 1 of the SUMF1 gene and a missense mutation Pro1059Leu in ITPR1 in the two families respectively. The gene discussed is ITPR1; the disease is autosomal dominant cerebellar ataxia.