CASR is a calcium-sensing receptor and plays an important role in regulating PTH secretion. It is expressed in many different tissues, such as parathyroid cells, pituitary cells, kidney, fibroblasts, keratinocytes and human colon epithelial cells. CASR is a potential therapeutic target for the treatment of many diseases, including hyperparathyroidism and osteoporosis. Mutations in the CASR gene can result in gain or loss of receptor function. Familial Hypocalciuric Hypercalcemia (FHH) and Neonatal Severe Primary Hyperparathyroidism (NSHPT) have been associated with loss of CASR function, while Autosomal Dominant Hypocalcemia (ADH) and Bartter syndrome type V have been associated with gain of CASR function.