The importance of CaSR in calcium homeostasis is emphasized by the pathological conditions of calcium homeostasis caused by inactivating and activating CaSR mutations such as Familial Hypocalciuric Hypercalcaemia (FHH), Neonatal Severe Hyperparathyroidism (NSHPT) [7], [8]; and Autosomal Dominant Hypocalcaemia (ADH) [9]. The gene discussed is CASR; the disease is neonatal severe primary hyperparathyroidism.