encodes an intracellular receptor for inositol 1,4,5-trisphosphate. Upon stimulation by inositol 1,4,5-trisphosphate, this receptor mediates calcium release from the endoplasmic reticulum. Mutations in this gene cause spinocerebellar ataxia type 15, a disease associated with an heterogeneous group of cerebellar disorders. Multiple transcript variants have been identified for this gene. Inositol 1,4,5-triphosphate is an intracellular second messenger produced by phospholipase C through a G protein-dependent mechanism. It releases calcium from endoplasmic reticulum by binding to specific receptors that are coupled to calcium channels. These receptors are abundant in neuronal and nonneuronal tissues. The neuronal form of the receptor is abundant in the cerebellum, particularly the perikaryon of the Purkinje cells.