MUSK and myasthenia gravis: While anti-AChR antibodies, the most common autoantibodies in MG patients, are predominantly IgG1 and IgG3, anti-MuSK antibodies are predominantly IgG4 (Rivner et al. 2018), which seems to be associated with poor response to IVIg both in MG and CIDP (Wright et al. 2015).