The proliferation of macrophages leads to macrophage accumulation in the course of obesity development and is followed by greater migration and aggravated accumulation of macrophages in adipose tissue (mediated by the CCL2/IL-1β/C-X-C motif chemokine ligand 12 (CXCL12) signalling pathway) [110,111]. The gene discussed is CXCL12; the disease is obesity due to melanocortin 4 receptor deficiency.