Natural history of Becker muscular dystrophy: a multicenter study of 225 patients

Objective Becker muscular dystrophy (BMD) is a milder variant of Duchenne muscular dystrophy (DMD), a lethal X‐linked muscular disorder. Here, we aim to investigat the clinical involvement of skeletal, respiratory, cardiac, and central nervous systems in patients with BMD, as well as genotype–phenotype relationships. Methods This nationwide cohort study investigated the clinical manifestations and genotype–phenotype relationships in 225 patients with BMD having in‐frame deletion from 22 medical centers. The primary outcome was to elucidate the association of genotype with skeletal muscle, respiratory, cardiac, and central nervous system disorders. Descriptive statistics were used to analyze the data. Results The average age of the subjects was 31.5 (range, 1–81) years. Initial symptoms of BMD were muscular (60%), followed by asymptomatic hypercreatine kinasemia (32.4%) and central nervous system disorders (5.3%). Gait disturbance was observed in 53.8% of patients and the average age at wheelchair introduction was 36.5 years. The ventilator introduction rate was 6.7% at an average age of 36.6 years. More than 30% of patients had an abnormal electrocardiogram and approximately 15% had heart failure symptoms. Cardiac function on echocardiography varied significantly among the patients. The frequencies of seizures and intellectual/developmental disability were 8.0% and 16.9%, respectively. Exon 45–47deletion (del) was the most common (22.6%), followed by exon 45–48del (13.1%). Patients with exon 45–49del patients demonstrated severe skeletal muscle damage. Patients with exon 45–47del and exon 45–55del patients did not require ventilator use. Interpretation The study provides important prognostic information for patients and clinicians to establish therapy plans and to implement preventative medicine.