Secondly, obesity that is often characterized by reduced levels of physical activity (PA), promotes osteoclast activity and bone resorption triggering the expression of receptor activator of nuclear factor κ B (RANK), favoring binding to its ligand RANKL, and conversely inhibiting OPG pathway (11). The gene discussed is TNFRSF11A; the disease is obesity due to melanocortin 4 receptor deficiency.