the interaction between bones (osteoblastic and osteoclastic activities) kidneys, gut and important hormones including PTH and IGF-I.25–31 The latter process entails an important adaptation mechanism that efficiently defend the body against the deleterious effects of hypocalcaemia (PTH increases 1 alpha hydroxylation of vitamin D in the kidney that increases intestinal calcium absorption and increases osteoclastic activity to maintain serum calcium). The gene discussed is PTH; the disease is Hypocalcemia.