ITPR1 and pontocerebellar hypoplasia: According to the amino acid substitutions reported for ITPR1 with an associated phenotype, (1) the IP3 binding domain, where amino acid substitutions usually cause infantile-onset SCA; (2) substitutions in the coupling domain mainly present as ataxic cerebral palsy, SCA15, and GLSP; and (3) the transmembrane domain, wherein a mutation in this domain typically will lead to GLSP and pontocerebellar hypoplasia (PCH) with ataxia.