SCA15 is characterized by very slowly progressive autosomal-dominant cerebellar ataxia and cerebellar atrophy.22, 23, 24, 25, 26, 27 Haploinsufficiency for ITPR1 accounted for 2% of dominant ataxia in a screen of a large series of well-characterized families with the age of onset in the affected individuals with ITPR1 deletions in this series being between 18 and 66 years.24 The gene discussed is ITPR1; the disease is autosomal dominant cerebellar ataxia.