Familial occurrence of multiple CMs was first described in 1949;1 however, it was only in 2002 that molecular characterization of a subset of these patients led to the identification of heterozygous mutations in RASA1. 2 To date, > 100 mutations in this gene have been reported, and no genotype–phenotype correlation is seen.1, 3 Approximately 30% of RASA1 mutation carriers have a de novo mutation, and the penetrance is high (96.5%).4 The gene discussed is RASA1; the disease is congenital myasthenic syndrome.