More recently, Darrah et al. investigated the prevalence and clinical significance of different anti-PAD4 isotypes and IgG subclasses, and found that anti-PAD4 IgG1, IgG3, and IgE antibodies identify discrete disease subsets in RA [24]; however, no associations with clinically relevant outcomes were identified in that study. The gene discussed is PADI4; the disease is rheumatoid arthritis.