Recently, several studies have highlighted the expression of OPN in adipose tissue of both humans and mice and its involvement in obesity and obesity-associated T2D promoting inflammation and the accumulation of macrophages in adipose tissue (Gómez-Ambrosi et al., 2007; Nomiyama et al., 2007). The gene discussed is SPP1; the disease is obesity due to melanocortin 4 receptor deficiency.