Muscular dystrophy. Light micrograph (LM) Muscular dystrophy (MD) is an inherited progressive condition. It often begins by affecting a particular group of muscles, before affecting the muscles more widely. Some types of MD eventually affect the heart or the muscles used for breathing, at which point the condition becomes life-threatening. There's no cure for MD, but treatment can help to manage many of the symptoms. This damage and weakness is due to the lack of a protein called dystrophin, which is necessary for normal muscle function. Loss of dystrophin leads to damage and degeneration of muscle cells. In response, skeletal muscle attempts to regenerate new fibres, giving rise to many small muscle cells. Eventually, muscle degeneration outpaces replacement and muscle tissue is partially replaced by connective tissue as seen here. Magnification: x 60 when printed at 10 cm high.