Congenital myasthenic syndromes (CMS) have some phenotypic overlap with seronegative myasthenia gravis (SNMG). The aim of this single center study was to assess the minimum occurrence of CMS misdiagno Show more
Congenital myasthenic syndromes (CMS) have some phenotypic overlap with seronegative myasthenia gravis (SNMG). The aim of this single center study was to assess the minimum occurrence of CMS misdiagnosed as double SNMG in a Brazilian cohort. The genetic analysis of the most common mutations in CHRNE, RAPSN, and DOK7 genes was used as the main screening tool. We performed genetic analysis in 22 patients with a previous diagnosis of 'double' SNMG. In this study, one CMS patient was confirmed due to the presence of compound heterozygous variants in the CHRNE gene (c.130insG/p.Cys210Phe). This study confirmed that CMS due to CHNRE mutations can be mistaken for SNMG. In addition, our study estimated the prevalence of misdiagnosed CMS to be 4.5% in 'double' SNMG patients of our center. Based on our findings, genetic screening could be helpful in the diagnostic workup of patients with 'double' SNMG in whom differential diagnosis is recommended. Show less