CASR and hyperparathyroidism: Studies in calciotropic tissues such as parathyroid gland, kidney, or bone have shown the CaSR to be critical for sensing [Ca2+]o (Brennan et al., 1833; Riccardi and Kemp, 2012; Goltzman and Hendy, 2015) and is targeted with activators (calcimimetics) toward treating hyperparathyroidism, and inhibiting it using negative allosteric modulators (calcilytics) for genetic forms of hypocalcemia (Hannan et al., 2017; Nemeth et al., 2018).