is an inherited condition that affects the muscles and other body systems. It is the most common form of muscular dystrophy that begins in adulthood, usually in a person's 20s or 30s. This condition is characterized by progressive muscle loss and weakness, particularly in the lower legs, hands, neck, and face. People with myotonic dystrophy often have prolonged muscle tensing (myotonia) and are not able to relax certain muscles after use. The severity of the condition varies widely among affected people, even among members of the same family.
There are two types of myotonic dystrophy: myotonic dystrophy type 1 and myotonic dystrophy type 2. The symptoms in people with myotonic dystrophy type 2 tend to be milder than in those with type 1. Although both types are inherited in an autosomal dominant pattern, they are caused by mutations in different genes. Myotonic dystrophy type 1 is caused by mutations in the DMPK gene, while type 2 is caused by mutations in the CNBP gene. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.