IgG4-RD is characterized by a number of abnormalities in the differentiation of cells of the B-cell lineage, including increased serum levels of IgG, IgG4, and often IgE; infiltration of affected tissues by IgG4-secreting plasma; and the presence of increased frequencies of circulating plasma cells/plasmablasts [13–15]. The gene discussed is IGHE; the disease is immunoglobulin G4-related sclerosing disease.