The PtdIns3P and PtdIns(3,5)P2 3-phosphatase myotubularin gene is mutated in X-linked centronuclear myopathy, whereas its homologs MTMR2 and MTMR13 and the PtdIns(3,5)P2 5-phosphatase SAC3/FIG4 are implicated in Charcot–Marie–Tooth peripheral neuropathies. The gene discussed is FIG4; the disease is X-linked myotubular myopathy.