Presentation (CTI)

OBJECTIVES: Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD) are rare, X-linked disorders caused by complete or partial absence of functional dystrophin, respectively. DMD is usually diagnosed before 10 years of age, while BMD often manifests during adolescence and generally follows a milder clinical course. Genetic testing can reliably tell apart DMD and BMD but historically its use was limited, resulting in potential diagnostic misclassifications. Both conditions are associated with progressive muscle damage, substantial morbidity and premature death, underscoring the importance of developing therapies to halt, slow down or reverse disease progression. This study aimed to characterize the DMD and BMD patient populations across Sweden, Denmark, and Finland, providing updated epidemiological insights.
METHODS: Patients were identified via DMD- and BMD-specific ICD-10 codes in nationwide health registers (Finland’s Care Register for Specialized Healthcare, and the National Patient Registers in Sweden and Denmark). Only male patients were included as females are often asymptomatic carriers. Incident cases were analyzed from 2008 onwards in Sweden and Finland and from 2003 onwards in Denmark, applying lookback periods to ensure accurate classification as incident cases. Prevalence was assessed for the period 2018-2022.
RESULTS: This study identified 413 incident DMD patients and 311 incident BMD patients across Sweden, Denmark, and Finland. Most DMD cases (55-65%) were diagnosed between 0-5 years and 27-33% between 6-17 years, while BMD diagnoses occurred most frequently in adulthood (35-68%). During 2018-2022, the average yearly prevalence rates were 3.0/100,000 (DMD) and 1.4/100,000 (BMD) in Sweden, 2.7/100,000 (DMD) and 1.8/100,000 (BMD) in Denmark, and 2.3/100,000 (DMD) and 3.1/100,000 (BMD) in Finland.
CONCLUSIONS: This study provides contemporary epidemiological data for DMD and BMD in Scandinavia. The observed inter-country differences in disease and age distribution likely reflect differences in both genetic predisposition and diagnostic practices.