The CALC1 gene produces a prepropeptide from which calcitonin (CT) is a cleavage product (Nelkin BD et al, 1984). CT is a polypeptide hormone that is produced in the thyroid gland. It acts to reduce blood calcium, opposing the effects of parathyroid hormone. The CT receptor (Gorn AH et al, 1992) binds CT and mediates its actions. The ligand:receptor complex couples to the G protein alpha s subunit, which stimulates adenylyl cyclase and increases intracellular cAMP levels (Gorn AH et al, 1992).