CHRNB1 and congenital myasthenic syndrome: About 75% of the CMS cases are due to mutations in genes that encode different subunits of the acetylcholine receptor (CHRNA1, CHRNB1, CHRND, CHRNE) or proteins important to maintain the structure or function of the NMJ, such as MUSK, RAPSN or DOK7 [16, 17].