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 Here, ITPR1 is linked to spinocerebellar ataxia type 15/16.