CASR and hypoparathyroidism, familial isolated 1: Deletion of this region or point mutations present in this region in the human disease autosomal dominant hypoparathyroidism (ADH) increase the sensitivity of the CaSR to Ca2+.(28,29) It has been postulated, therefore, that loop 2 may play a key role in maintaining the CaSR in an inactive state in part through the two disulfide linkages involving cysteine residues C129 and C131.