They get their name from the appearance of the muscle biopsies under the microscope. The nuclei are situated in the centre of the muscle fibres, rather than on the outer edges. Centrally-located nuclei are a common feature of immature muscle but not of healthy, mature muscle.
There are several different types of centronuclear myopathy (CNM), described according to the pattern of inheritance seen (see below). Each of these is very rare. There is currently no effective treatment or cure for these myopathies, so management of the conditions is very important. It can include physiotherapy, and where necessary, the use of ventilation and/or a feeding tube.