PTH and primary hyperparathyroidism: The CaSR plays a major role in the maintenance of the concentration of ionized calcium in the serum through the regulation of PTH circulating levels.[49] Polymorphisms in the CaSR gene are considered for association with primary hyperparathyroidism,[28–31] familial hypocalciuric hypercalcemia (FHH) and severe neonatal hyperparathyroidism (NSHPT),[50,51] ESRD,[52,53] and colorectal cancer.[54–56] The most commonly studied polymorphisms of the CaSR are rs1801725 (A986S), rs1042636 (R990G), and rs1801726 (Q1011E).