When the adipocyte size enlarges to reach the diffusional limit of oxygen from the vasculature, the low oxygen tension in adipose tissue induces the activation of hypoxia-inducible factor 1α (HIF-1α), which plays an important role in triggering inflammation and obesity-related metabolic disorders [38]. The gene discussed is HIF1A; the disease is obesity due to melanocortin 4 receptor deficiency.