A retrospective study based on data from 235 adults collected by a total of 23 French expert centres, during a follow-up period averaging 34 years, shows all the diagnostic difficulties of congenital myasthenic syndromes, with :
- onset in adulthood in 12.3% of cases,
- an average delay before clinical diagnosis of 17.2 years and before genetic diagnosis of 22 years,
- an initial misdiagnosis in 58.7% of patients (congenital myopathy, seronegative autoimmune myasthenia, muscular dystrophy, etc.).
The results of this major study also highlight the importance of having a genetic diagnosis, as this has an influence on the phenotype and course, as well as on the risks of exacerbation, respiratory assistance and loss of walking ability. However, the majority of patients in the French cohort had a favourable long-term prognosis and were neither ventilated nor using a wheelchair at the time of their last consultation.
