Low concentrations of IgD are secreted under physiological conditions (Rowe et al., 1973; Walsh and Kay, 1986), whereas increased IgD can occur in atypical situations such as IgD myeloma, skin allergy, hyper IgE and hyper IgD syndromes, and autoimmune disorders such as RA and SLE (Rostenberg and Penaloza, 1978; Drenth et al., 1996; Sechet et al., 2003). This evidence concerns the gene IGHE and rheumatoid arthritis.