Lee et al. found that the frequency of new emigrant/transitional B cells and mature B cells that express polyreactive and autoreactive B cell receptors (BCRs) is higher in both AChR-MG and MuSK-MG, which would support the concept that patients with MG have defects in both central and peripheral B cell tolerance (Figure 3) [100]. The gene discussed is MUSK; the disease is myasthenia gravis.