Definition of Myotonia congenita:

Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth.

Causes, incidence, and risk factors:

Myotonia congenita is caused by a change (mutation) to a gene. It is passed down from either one or both parents to the children (inherited).

Myotonia congenita is believed to be caused by a problem in the part of the muscle cells that are needed for muscles to relax. Abnormal repeated electrical discharges occur in the muscles, causing a stiffness called myotonia.