Congenital Myasthenic Syndromes in Belgium: Genetic and Clinical Characterization of Pediatric and Adult Patients

Background: Congenital myasthenic syndromes (CMS) are a group of genetic disorders characterized by impaired neuromuscular transmission. CMS typically present at a young age with fatigable muscle weakness, often with an abnormal response after repetitive nerve stimulation (RNS). Pharmacologic treatment can improve symptoms, depending on the underlying defect. Prevalence is likely underestimated. This study reports on patients with CMS followed in Belgium in 2022. Methods: Data were gathered retrospectively from the medical charts. Only likely pathogenic and pathogenic variants were included in the analysis. Results: We identi fied 37 patients, resulting in an estimated prevalence of 3.19 per 1,000,000. The patients harbored pathogenic variants in CHRNE , RAPSN , DOK7 , PREPL , CHRNB1 , CHRNG , COLQ , MUSK , CHRND , GFPT1, and GMPPB. CHRNE was the most commonly affected gene. Most patients showed disease onset at birth, during infancy, or during childhood. Symptom onset was at adult age in seven patients, caused by variants in CHRNE , DOK7 , MUSK , CHRND, and GMPPB . Severity and distribution of weakness varied, as did the presence of respiratory involvement, feeding problems, and extraneuromuscular manifestations. RNS was performed in 23 patients of whom 18 demonstrated a pathologic decrement. Most treatment responses were predictable based on the genotype. Conclusions: This is the first pooled characterization of patients with CMS in Belgium. We broaden the phenotypical spectrum of pathogenic variants in CHRNE with adult-onset CMS. Systematically documenting larger cohorts of patients with CMS can aid in better clinical characterization and earlier recognition of this rare disease. We emphasize the importance of establishing a molecular genetic diagnosis to tailor treatment choices. (c) 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.