This post-synaptic defect is thought to be due to impaired glycosylation of the acetylcholine receptor (AChR) subunits and can be observed not only in patients with GMPPB mutations but also in association with mutations in genes encoding other proteins with a crucial role in glycosylation (i.e., ALG2, ALG14, DPAGT1, and GFPT1), also leading to congenital myasthenic syndrome [10]. This evidence concerns the gene GMPPB and congenital myasthenic syndrome.