Prevalence of myotonic dystrophy type 1 in adults in western Sweden.

Myotonic dystrophy type 1 (DM1) is the most common inherited muscle disorder in adults. The prevalence differs widely between countries, but a figure of 13/100.000 is most frequently cited. It is a multi-organ disorder classified into four categories: congenital, childhood, adult/classical and late-onset/mild. The purpose of this study was to estimate the total and age adjusted prevalence of DM1 in adults in western Sweden (the Västra Götaland Region, VGR) as well as in the city of Gothenburg and also in the VGR except Gothenburg. Patients with the diagnosis of DM1 in the VGR were traced by outpatient registers at the Neuromuscular Center, contacted by regular mail and thereafter telephone interviewed about organ manifestations in order to ascertain the age at onset and thus the disease category. Medical records were examined to obtain detail accuracy. We detected 230 adult DM1 patients in the VGR which gives a prevalence of 17.8/100.000. The prevalence of DM1 in Gothenburg was 14.1/100.000, which was significantly lower than in the remaining region which was 19.7/100.000. There was no gender difference. The age adjusted prevalence rates showed that DM1 is most prevalent in the age group 35-44 years (23.9/100.000) and 45-54 years (25.8/100.000). DM1 prevalence in the western Sweden thus seems to be somewhat higher than elsewhere in Europe, and is especially high in the less densely populated areas of the region. The disease burden in the community is larger than what was known previously.