Mutations in the C ‐Terminal Domain of C ol Q in Endplate Acetylcholinesterase Deficiency Compromise C ol Q – M u SK Interaction

Acetylcholinesterase ( AC h E ) at the neuromuscular junction ( NMJ ) is mostly composed of an asymmetric form in which three tetramers of catalytic AC h E subunits are linked to a triple helical collagen Q ( C ol Q ). Mutations in COLQ cause endplate AC h E deficiency. We report three patients with endplate AC h E deficiency with five recessive COLQ mutations. Sedimentation profiles showed that p. V al322 A sp and p. A rg227 X , but not p. C ys444 T yr, p. A sp447 H is, or p. A rg452 C ys, inhibit formation of triple helical C ol Q . In vitro overlay of mutant C ol Q ‐tailed AC h E on muscle sections of Colq −/− mice revealed that p.Cys444Tyr, p.Asp447His, and p.Arg452Cys in the C‐terminal domain ( CTD ) abrogate anchoring C ol Q ‐tailed AC h E to the NMJ . In vitro plate‐binding assay similarly demonstrated that the three mutants inhibit binding of ColQ‐tailed AC h E to M u SK . We also confirmed the pathogenicity of p.Asp447His by treating Colq −/− mice with adeno‐associated virus serotype 8 carrying mutant COLQ ‐p.Asp447His. The treated mice showed no improvement in motor functions and no anchoring of C ol Q ‐tailed AC h E at the NMJ . Electroporation of mutant COLQ harboring p. C ys444 T yr, p. A sp447 H is, and p. A rg452 C ys into anterior tibial muscles of Colq −/− mice similarly failed to anchor C ol Q ‐tailed AC h E at the NMJ . We proved that the missense mutations in C ol Q – CTD cause endplate AC h E deficiency by compromising C ol Q – M u SK interaction at the NMJ .