Intravenous administration of potent bisphosphonates usually leads to hypocalcaemia and secondary hyperparathyroidism (which are mild and transient in many cases, but may persist for a long time in others), with serum PTH level increase depending on the status of vitamin D (Rosen and Brown, 2003; Breen and Shane, 2004; Caspar et al, 2004; Tanvetyanon and Stiff, 2006). The gene discussed is PTH; the disease is secondary hyperparathyroidism.