CASR and neonatal severe primary hyperparathyroidism: Alteration in the activity or function of the extracellular Ca2+ (Ca2+ext)-sensing receptor (CaR; also named CaSR or CaS) is linked to several genetic disorders of calcium homeostasis1, such as familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT)2, both caused by loss-of-function mutations of the CaR gene, and those that occur as a consequence of gain-of function mutations of the CaR, e.g., autosomal dominant hypocalcemia (ADH) and Bartter syndrome (BS) type V3–5.