Myotubular myopathy is a slowly progressive, but rarely fatal, disease of voluntary muscle. Common symptoms of myotubular myopathy are drooping of the upper eyelids, facial weakness and foot drop, as well as some weakness of the limbs and trunk. People with the disease almost always lack reflexes in the affected muscles.
The name myotubular myopathy comes from the appearance of affected muscle fibres that resemble myotubes, a type of fibre normally found only during foetal development. The disease is also called centronuclear myopathy because the nuclei of affected muscle cells are found in the centre of each cell instead of at the periphery as is true with healthy muscle cells.