Phosphatase that specifically hydrolyzes the 5-phosphate of inositol 1,4,5-trisphosphate to inositol 1,4-bisphosphate, and inositol 1,3,4,5-tetrasphosphate to inositol 1,3,4-trisphosphate (PubMed:26051944). Plays a crucial role in the survival of cerebellar Purkinje cells (PubMed:26051944). 1D-myo-inositol 1,4,5-trisphosphate + H2O = 1D-myo-inositol 1,4-bisphosphate + phosphate 1D-myo-inositol 1,3,4,5-tetrakisphosphate + H2O = 1D-myo-inositol 1,3,4-trisphosphate + phosphate Interacts with TASOR. Expressed at high levels in cerebellar Purkinje cells (at protein level) (PubMed:26051944). Expressed in Sertoli cells of the testis (PubMed:31112734). Isoprenylation at Cys-409 is required for localization at the membrane. Genetic deletion causes a perinatal lethal phenotype in most mutant mice (PubMed:26051944). A small percentage of mutants thrive and have a phenotype characterized by an ataxic gait and progressive Purkinje cell degeneration (PubMed:26051944). Purkinje cell death is spatially patterned with surviving Purkinje cells appearing normal and maintaining molecular layer morphology (PubMed:26051944). Phosphatase activity toward phosphoinositol substrates is reduced in the mutant relative to wild-type littermates (PubMed:26051944). Belongs to the inositol 1,4,5-trisphosphate 5-phosphatase type I family.