ITPR1 (inositol 1,4,5-trisphosphate receptor, type 1), an interacting partner of TRPC4, is causative for Gillespie syndrome characterized by bilateral iris hypoplasia, congenital hypotonia, non-progressive ataxia, progressive cerebellar atrophy, and intellectual disability as well as autism and schizophrenia (61, 62). This evidence concerns the gene ITPR1 and Progressive cerebellar ataxia.