Review of 40 genes causing congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders characterized by compromised neuromuscular signal transmission due to pathogenic germline variants in genes expressed at the neuromuscular junction (NMJ). A total of 40 genes have been reported in CMS (AGRN, ALG14, ALG2, CHAT, CHD8, CHRNA1, CHRNB1, CHRND, CHRNE, CHRNG, COL13A1, COLQ, DES, DOK7, DPAGT1, GFPT1, GMPPB, LAMA5, LAMB2, LRP4, MACF1, MUSK, MYO9A, PLEC, PREPL, PTPN11, PURA, RAPSN, RPH3A, SCN4A, SLC18A3, SLC25A1, SLC5A7, SNAP25, SYT2, TEFM, TOR1AIP1, UNC13A, UNC50 and VAMP1). The 40 genes are putatively classified into 13 subtypes by pathomechanical, clinical, and therapeutic features. A unique feature shared by recently identified genes is that CMS is concomitantly recognized in other mostly severer diseases. For example, four recently identified genes exhibit the following phenotypes: PURA-CMS, developmental delay; TEFM-CMS, mitochondrial disease; PTPN11-CMS, Noonan syndrome/Leopard syndrome; and DES-CMS, desmin myopathy. Conversely, these diseases are not always associated with CMS, although genetic and/or environmental factors that determine the involvement of the NMJ remain to be identified. In this review, particular emphasis will be placed on five recently identified genes (MACF1, TEFM, PTPN11, DES and UNC50).