The prevalence of hereditary neuromuscular disorders in Northern Norway

AIM: To investigate the point prevalence of hereditary neuromuscular disorders on January 1, 2020 in Northern Norway. METHODS: From January 1, 1999, until January 1, 2020, we screened medical and genetic hospital records in Northern Norway for hereditary neuromuscular disorders. RESULTS: We identified 542 patients with a hereditary neuromuscular disorder living in Northern Norway, giving a point prevalence of 111.9/100,000 on January 1, 2020. The prevalence of children (<18 years old) and adults (≥18 years old) were 57.8/100,000 and 125.1/100,000, respectively. Inherited neuropathies had a prevalence of 38.8/100,000. Charcot–Marie–Tooth and hereditary neuropathy with liability to pressure palsies had a prevalence of 29.9/100,000 and 8.3/100,000, respectively. We calculated a prevalence of 3.7/100,000 for spinal muscular atrophies and 2.4/100,000 for Kennedy disease. Inherited myopathies were found in 67.7/100,000. Among these, we registered 13.4/100,000 myotonic dystrophy type 1, 6.8/100,000 myotonic dystrophy type 2, 7.3/100,000 Duchenne muscular dystrophy, 1.6/100,000 Becker muscular dystrophy, 3.7/100,000 facioscapulohumeral muscular dystrophy, 12.8/100,000 limb‐girdle muscular dystrophy, 2.5/100,000 hypokalemic periodic paralysis and 11.4/100,000 myotonia congenita. CONCLUSION: Our total prevalence was higher than previously hypothesized in European population‐based studies. The prevalence was especially high for myotonia congenita and limb‐girdle muscular dystrophy. The prevalence of Charcot–Marie–Tooth polyneuropathy was higher than in most European studies, but lower than previously reported in epidemiological studies in other regions of Norway.