VDR and rickets: As already outlined above, calcium malabsorption in Vdr null mice causes hypocalcemia after weaning and leads to the induction of hyperparathyroidism and hypophosphatemia.(13, 14, 15) The deficit in calcium supply hampers bone mineralization and ultimately gives rise to the development of hyperosteoidosis and osteomalacia.(13, 14, 15) Moreover, rickets will develop, characterized by an enlargement and disorganization of the zone of hypertrophic chondrocytes, which leads to a progressive widening of the epiphyseal growth plates.