The function of INPP4A (inositol polyphosphate-4-phosphatase type I A, ENSG00000040933) is as follows. Catalyzes the hydrolysis of the 4-position phosphate of phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) (PubMed:15716355, PubMed:20463662). Also catalyzes inositol 1,3,4-trisphosphate and inositol 1,4-bisphosphate (By similarity). Antagonizes the PI3K-AKT/PKB signaling pathway by dephosphorylating phosphoinositides and thereby modulating cell cycle progression and cell survival (By similarity) (PubMed:30071275). May protect neurons from excitotoxic cell death by regulating the synaptic localization of cell surface N-methyl-D- aspartate-type glutamate receptors (NMDARs) and NMDAR-mediated excitatory postsynaptic current (By similarity). {ECO:0000250|UniProtKB:Q62784, ECO:0000250|UniProtKB:Q9EPW0, ECO:0000269|PubMed:15716355, ECO:0000269|PubMed:20463662, ECO:0000269|PubMed:30071275}. [Isoform 4]: Displays no 4-phosphatase activity for PtdIns(3,4)P2, Ins(3,4)P2, or Ins(1,3,4)P3. .