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.
One consequence of the multisystemic nature of this disorder is that individuals affected by DM1 or DM2 may first present to internists, cardiologists, ophthalmologists, endocrinologists, and pediatricians (in the case of DM1), before they see a neurologist.