Immunologically, MuSK antibodies are mainly IgG4 subclass (Koneczny, 2018) and known to cause MG by inhibiting binding between MuSK and Lrp4 independently of complement activation (Huijbers et al., 2013), but IgG1-3 MuSK antibodies can disperse preformed agrin-independent AChR clusters (Koneczny et al., 2013). Here, MUSK is linked to myasthenia gravis.