The term dystrophy means abnormal growth. However, muscular dystrophy is used to describe primary myopathies with a genetic basis and a progressive course characterized by progressive skeletal muscle weakness and wasting, defects in muscle proteins, and histological features of muscle fiber degeneration (necrosis) and regeneration. If possible, it is preferred to use other HPO terms to describe the precise phenotypic abnormalities.

Reduced strength of muscles.

The presence of disorganized areas called cores in the center of muscle fibers. There is a typical appearance of the biopsy on light microscopy, where the muscle cells have cores that are devoid of mitochondria and specific enzymes. Cores are typically well demarcated and centrally located, but may occasionally be multiple and of eccentric.