Myotonic dystrophy type 1,
one of the two types of myotonic dystrophy,
is an inherited type of muscular dystrophy that affects the muscles and other body systems (e.g., heart, eyes, pancreas). Myotonic dystrophy type 1 has been categorized into three somewhat overlapping subtypes: mild, classic, and congenital (present at birth). Symptoms of the mild form are the least severe with a normal life span. The classic form is characterized by muscle weakness and wasting, prolonged muscle tensing (myotonia), cataract, and often abnormal heart function; adults may become physically disabled and may have a shortened life span. The congenital form is characterized by severe generalized weakeness at birth (hypotonia), often causing complications with breathing and early death. The condition is inherited in an autosomal dominant pattern and is caused by mutations in the DMPK gene. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.