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:8013665, PubMed:8769125, PubMed:8626616). Plays a crucial role in the survival of cerebellar Purkinje cells (By similarity). 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. Predominantly expressed in heart, brain, and skeletal muscle (PubMed:8006039). In brain; high level in Purkinje cells (PubMed:8013665). Isoprenylation at Cys-409 is required for localization at the membrane. Belongs to the inositol 1,4,5-trisphosphate 5-phosphatase type I family.