MUSK and myasthenia gravis: Auto-antibodies against MuSK and LRP4 cause Myasthenia gravis (Verschuuren et al., 2013; Plomp et al., 2015), whereas mutations affecting the function of each of these proteins are involved in Myasthenic Congenital Syndromes (Engel et al., 2015), thus demonstrating the requirement of these postsynaptic proteins for mature NMJ maintenance.