The Myotubularin family of Phosphatidyl-Inositol phosphatases is one of the largest phosphatase families in the human genome. Active members are able to hydrolyse PI lipids and have conserved specificity towards PtdIns 3P and PtdIns (3,5)P2 (left). The product of PtdIns (3,5)P2 hydrolysis, PtdIns 5P, is proposed to be an allosteric activator of MTM1 and MTMR3 (right, Schaletzky et al.)