Myotonic dystrophy (DM) is a clinically and genetically heterogeneous disorder. There are two major forms:
●DM1, for a century known as Steinert's disease
●DM2, recognized in 1994 as a milder version of DM1.
The prevalence of DM is 1 in 8000 in the general population, but the proportions of myotonic dystrophy caused by DM1 and DM2 are unknown.
These autosomal dominant conditions are among the most common forms of adult-onset muscular dystrophy. However, DM is more than simply a muscular dystrophy per se, since affected individuals may show cataracts, cardiac conduction abnormalities, infertility, and insulin resistance. Furthermore, there is a severe congenital form of DM1 with marked developmental disability.