Myosin storage myopathy

Myosin storage myopathy is a condition that affects muscle (myopathy). This disorder causes muscle weakness that can worsen slowly over time. The signs and symptoms of myosin storage myopathy often begin in childhood, although they can begin later. The specific features of myosin storage myopathy and the severity of the condition can vary, even among members of the same family. 

Children with myosin storage myopathy may start walking later than usual and have a waddling gait. They can have trouble climbing stairs and difficulty lifting their arms above shoulder level. Weak shoulder muscles often make the shoulder blades (scapulae) "stick out" from the back, a sign known as scapular winging. Affected individuals may also have a spine that curves to the side (scoliosis). Some individuals can also develop weakness of the muscles that control breathing (respiratory insufficiency) or weakness of the heart (cardiac) muscle.

Myosin storage myopathy belongs to a group of disorders called congenital myopathies. The signs and symptoms of congenital myopathies are often present at birth (congenital) or soon after. Congenital myopathies may affect the muscles used for movement (skeletal muscle) and, less commonly, the cardiac muscle.