Objective: To determine the incidence and prevalence of facioscapulohumeral muscular dystrophy (FSHD) in the Netherlands.Methods: Using 3-source capture-recapture methodology, we estimated the total yearly number of newly found symptomatic individuals with FSHD, including those not registered in any of the 3 sources. To this end, symptomatic individuals with FSHD were available from 3 large populationbased registries in the Netherlands if diagnosed within a 10-year period (January 1, 2001 to December 31, 2010). Multiplication of the incidence and disease duration delivered the prevalence estimate.Results: On average, 52 people are newly diagnosed with FSHD every year. This results in an incidence rate of 0.3/100,000 person-years in the Netherlands. The prevalence rate was 12/100,000, equivalent to 2,000 affected individuals.Conclusions: We present population-based incidence and prevalence estimates regarding symptomatic individuals with FSHD, including an estimation of the number of symptomatic individuals not present in any of the 3 used registries. This study shows that the total number of symptomatic persons with FSHD in the population may well be underestimated and a considerable number of affected individuals remain undiagnosed. This suggests that FSHD is one of the most prevalent neuromuscular disorders. Recently, a unifying genetic model of facioscapulohumeral muscular dystrophy (FSHD) was described, thereby facilitating identification of potential therapeutic targets.1 As clinical studies on FSHD interventions can be expected in the near future, accurate data on FSHD epidemiology are needed for trial readiness.Several studies reported on FSHD epidemiology (figure 1, table e-1 on the Neurology ® Web site at Neurology.org); 4 were performed after genetic testing became available but did not report on population-based incidence estimates.2 In the Netherlands, people newly diagnosed with a neuromuscular disorder are registered nationwide by 7 neuromuscular centers in CRAMP (Computer Registry of all Myopathies and Polyneuropathies).3 This registry provides an opportunity to study frequencies of FSHD among the Dutch population.FSHD frequencies are prone to underestimation because this disease is characterized by a high degree of clinical variability with a large proportion of individuals with mild symptoms. Moreover, relatives of persons diagnosed with FSHD may not seek medical attention. 4 We used capturerecapture methodology to estimate the total number of symptomatic individuals with FSHD by combining CRAMP data with 2 other large population-based registries. This includes those not *These authors contributed equally.

No abstract