Distinct ALS and MG populations are seropositive for LRP4 autoantibodies (Tsivgoulis et al., 2014; Tzartos et al., 2014) and double seronegative for Agrin or MuSK, suggesting that seropositivity is not a byproduct of generalized NMJ breakdown. Here, MUSK is linked to amyotrophic lateral sclerosis.