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. 2018 Jun 5;19(6):1677. doi: 10.3390/ijms19061677

Figure 1.

Figure 1

Schematic of the neuromuscular junction (NMJ) and the main molecules involved in congenital myasthenic syndromes. CMS result from presynaptic (ChAT, ChT, MUNC13-1, MYO9, PREPL, SYT2, VAChT, and VAMP1), synaptic basal lamina (COLQ and COL13A1), and postsynaptic defects (AChR subunits: α, β, δ and ε, AGRN, DOK7, MUSK, LRP4, and rapsyn). An increasing number of presynaptic CMS is being reported due to abnormalities in the synthesis, recycling or release of acetylcholine (normal arrows). The Agrin-LRP4-MuSK signaling pathway (bold arrows) is crucial for the clustering of the AChRs at the postsynaptic muscle membrane. Novel genes encoding for ubiquitous molecules (GFPT1, DPAGT1, ALG2, ALG14, and GMPPB) are represented in the endoplasmic reticulum (ER) in a simplified view of the N-glycosylation pathway. Post-translational modifications of the saccharide structure of the AChR and other NMJ proteins take place at the ER and Golgi apparatus (dashed arrows), before reaching the muscle cell surface as mature proteins. ACh, acetylcholine; AChE, acetylcholinesterase; AcCoA, acetyl coenzyme A; Ch, choline; VGNa + C, voltage-gated sodium channel.