Myotonic Dystrophy - Description/Classification

Description/Classification

Two types of myotonic dystrophy exist. Type 1 (DM1), also known as Steinert disease, has a severe congenital form and a milder childhood-onset form. Type 2 (DM2), also known as proximal myotonic myopathy (PROMM), is rarer and generally manifests with milder signs and symptoms than DM1.

Other forms of myotonic dystrophy not associated with DM1 or DM2 genetic mutations have been described. One case which was proposed as a candidate for the "DM3" label, was later characterized as an unusual form of inclusion body myopathy associated with Paget's disease and frontotemporal dementia.

Myotonic dystrophy (DM) is an inherited disease, affecting males and females approximately equally. About 30,000 people in the United States are affected. Symptoms may appear at any time from infancy to adulthood. DM causes general weakness, usually beginning in the muscles of the hands, feet, neck, or face. It slowly progresses to involve other muscle groups, including the heart. DM affects a wide variety of other organ systems as well. A severe form of DM, congenital myotonic dystrophy or Thomsen's disease, may appear in newborns of mothers who have DM. Congenital means that the condition is present from birth. The incidence of congenital myotonic dystrophy is thought to be about 1:20,000. DM occurs in about 1 per 7,000–8,000 people and has been described in people from all over the world.