The myotubularins (MTMs) constitute a large family of phosphoinositide lipid 
3-phosphatases with specificity for PtdIns3P and PtdIns (3,5)P2. Mutations in 
MTM proteins are associated with inherited conditions such as myotubular 
myopathy and Charcot-Marie-Tooth syndrome. The substrate lipids are known to be 
regulators of the endosomal pathway through recruitment of specific effector 
proteins. Hydrolysis of PtdIns (3,5)P2 provides a biosynthetic pathway to the 
production of PtdIns5P, which itself can allosterically activate MTMs. We review 
the properties of this intriguing family of proteins and discuss potential 
physiological functions that include regulation of the endocytic pathway.