The article presents a study which investigated the function of myotubularin 1 (MTM1), an endosomal phosphatidylinositol (3,4,5)-trisphosphate phosphatase that is mutated in patients with X-linked centronuclear myopathy. It mentions that the study confirmed that MTM1 loss of function causes an increase in endoplasmic reticulum (ER) tubules in XLCNM patient-derived myoblasts and that this is dependent on the accumulation of PI(3)P in endosome membranes.