Myotonic dystrophy refers to a slowly progressing disease that onsets anytime from childhood through middle age.
Unlike many myopathies, it affects both the proximal and distal muscles (i.e., feet, hands, face, neck). One of the characteristic symptoms is muscular contraction that fails to relax in the usual fashion (myotonia). It is caused by a defect of an autosomal dominant gene. People with MD may have difficulties swallowing and may suffer from sleeping disorders. Some people with MD are also mentally disabled. Most patients suffer from abnormal heart rhythms. It is also known as Steinart's disease.