Paramyotonia Congenita

Paramyotonia congenita is an inherited condition that affects muscles used for movement (skeletal muscles), mainly in the face, neck, arms, and hands. Symptoms begin in infancy or early childhood and include episodes of sustained muscle tensing (myotonia) that prevent muscles from relaxing normally and lead to muscle weakness.  Symptoms in paramyotonia congenita worsen during exposure to cold temperatures, and unlike many other forms of myotonia, worsen with exercise and repeated movements. This condition is caused by mutations in the SCN4A gene and is inherited in an autosomal dominant pattern.