Fig4/Sac3 phosphatase, a 97-kDa protein, specifically removes the 5-phosphate from the inositol ring of PI(3,5)P2, a membrane-bound phospholipid, which acts as a molecular signal for trafficking and fusion of intracellular vesicles. It is broadly expressed in all eukaryotic cells and plays a vital role in intracellular membrane trafficking and signaling. 

Mutations in Fig4/Sac3 have been linked to pale tremor mice that exhibit neuropathy with severe central and peripheral neuronal degeneration, including the loss of neurons in the dorsal root ganglion and the sciatic nerve. Fig4/Sac3 knockout mice have been shown to be smaller in size and exhibit abnormal tremor and gait and neuronal autophagy.