These mutations may cause a loss of CaSR function and give rise to hypercalcaemic disorders such as FHH type 1 (FHH1), neonatal severe hyperparathyroidism (NSHPT) and adult-onset primary hyperparathyroidism (PHPT); or lead to a gain of function that is associated with hypocalcaemic disorders such as ADH type 1 (ADH1) and Bartter syndrome type V (Table 1) (Hannan & Thakker 2013). The gene discussed is CASR; the disease is neonatal severe primary hyperparathyroidism.