An Age-Standardized Prevalence Estimate and a Sex and Age Distribution of Myotonic Dystrophy Types 1 and 2 in the Rome Province, Italy.

Background: Prevalence estimates for the 2 forms of myotonic dystrophy types 1 and 2 (DM1 and DM2) are not exhaustive or non-available. Our aim was to estimate the minimum prevalence of DM1 and DM2 in Italy in the Rome province, applying standards of descriptive epidemiology.

Methods: All patients with a molecular diagnosis of DM1/DM2 and residents in the Rome province in 2013 have been enrolled, and the age-standardized prevalence has been calculated, assuming a Poisson distribution and adjusting for age.

Results: We identified 395 DM1 patients: the age-standardized prevalence for total, females and males was 9.65, 8.35 and 11.07/100,000, respectively. The mean age of subjects differed considerably according to CTG repeat length (p = 0.001). Forty DM2 patients were identified. The age-standardized prevalence for total, females and males was 0.99, 1.07 and 0.90/100,000, respectively. The mean age was 57.05.

Conclusions: We estimated for the first time the age-standardized prevalence and the sex and age distribution of DM1 and DM2 in a general population. A higher prevalence of males in DM1 and females in DM2 and a higher mean age of DM2 patients (+8 years) were ascertained. Prevalence of DM2 was 10% that of DM1. These prevalence values are probably lower than mutational rates due to the incomplete penetrance of DM1 mutations and to the clinical elusiveness of DM2. Our findings will be useful in designing cohort studies and for developing a disease registry.