Genetic epidemiology of myotonic dystrophy.

Prevalence rate of myotonic dystrophy (DM) was estimated in a large sample of the Italian population. Segregation analysis of the affected families suggests that subjects showing minor clinical signs, even in the absence of myotonic features, should be considered as bearers of the DM trait. An apparent excess of normal sibs among the offspring of DM subjects may be due to the late onset of the disease and possibly to a partial loss of affected individuals from the sample before diagnosis. Prevalence rate of DM in this study is estimated between 69 to 90 per million inhabitants; accordingly, DM might be the most frequent inherited neuromuscular disorder in human populations.