Incidence and Prevalence of Congenital Myopathies ‐ A Population‐Based Study From Western Sweden

OBJECTIVE: Congenital myopathies are a group of rare genetic muscle disorders. Previous studies have estimated point prevalences which only include surviving individuals. Our aim was to perform an epidemiological study with strict inclusion criteria, using modern diagnostic technology to present both incidences and prevalences, and to describe the genetic and muscle pathological characteristics of these disorders. METHODS: A retrospective, population-based epidemiological study was conducted in western Sweden between 1985 and 2022. All patients diagnosed with congenital myopathies during this period were included. RESULTS: In total, 104 patients were identified whereas 25 died during the follow-up. The total birth prevalence (estimated lifetime risk) was 14.9 per 100,000 live births, whereas the total cumulative incidence by age 35 years was 12.3 per 100,000 inhabitants, and the total point prevalence was 3.9 per 100,000 inhabitants. The most common histopathological type was congenital myopathy with nonspecific changes (birth prevalence 4.1 per 100,000 live births), followed by core myopathy and centronuclear myopathy (2.1 per 100,000). The most common causative genes were MYH2 (3.9 per 100,000) and RYR1 (2.0 per 100,000). Despite using next-generation sequencing, 1 in 5 cases lacked a genetic diagnosis. Among those without a genetic cause, 4 of 5 had nonspecific histopathological changes. INTERPRETATION: By including all patients identified, both alive and deceased, our estimated incidence figures are considerably higher than estimates of point prevalence, which only includes living patients. As the mortality in these diseases is significant, incidence figures better reflect the occurrence in the population and are important for evidence-based health care planning and resource allocation. ANN NEUROL 2026;99:382-392.