Study of the prevalence of familial autoimmune myasthenia gravis in a Spanish cohort

Abstract Background Myasthenia gravis (MG) is an autoimmune disease caused by a failure of neuromuscular transmission. Familial clustering has been reported despite MG usually manifesting as a sporadic condition presumed not to be inherited. Our study investigated the prevalence of FAMG in a Spanish cohort, characterizing their phenotype, antibody titres and thymus findings. Material/methods We investigated the presence of familial cases in 462 MG patients, characterizing by age and MGFA class at debut, quantitative MG score, antibody titres, MGFA post-intervention status and thymus pathology. Results Sixteen cases from 8 unrelated pedigrees were identified. The prevalence of FAMG cases was 3.46%. Mean age at onset was 57.8 ± 17.4 years (range = 23–82). Distribution at debut was: 6 ocular, 4 IIa, 4IIb, 1 IIIa and 1 IIIb. Thymoma was identified in two of the 7 thymectomized individuals. Conclusions The prevalence of FAMG in Spain is similar to other populations. Post-intervention status did not differ from sporadic autoimmune MG. As in other neuromuscular disorders, phenotype and inheritance heterogeneity are present in FAMG. In addition to the interfamilial heterogeneity observed, members of the same family affected with FAMG may even present different ages of onset, severity and thymus involvement. Further studies are necessary to clarify the role of genetic risk factors in this form of autoimmune MG.