Centronuclear myopathy (CNM), a severe congenital myopathy characterized by T-tubule defects and muscle weakness, is associated with mutations in three membrane trafficking-related genes: BIN1 (Bridging Integrator-1; also known as Amphiphysin 2, Amph2), DNM2 (Dynamin 2), and MTM1 (Myotubularin 1) (2). The gene discussed is MTM1; the disease is autosomal dominant centronuclear myopathy.