C3 secretion from isolated human islets is augmented by IL-1β exposure, and C3 expression in freshly isolated islets correlated with expression of pro-inflammatory cytokines, as well as with donor body mass index, and HbA1c, linking islet C3 expression with islet inflammation, obesity and diabetes. The gene discussed is C3; the disease is obesity due to melanocortin 4 receptor deficiency.