Parathyroid hormone / parathyroid hormone-related peptide receptor, also known as PTH / PTHrP type I receptor, PTH/PTHr receptor, Parathyroid hormone 1 receptor, PTH1 receptor, PTH1R and PTHR, is a multi-pass membrane protein which belongs to theG-protein coupled receptor 2 family. PTH1R is expressed in most tissues. It is most abundant in kidney, bone and liver. PTH1R is expressed in high levels in bone and kidney and regulates calcium ion homeostasis through activation of adenylate cyclase and phospholipase C. In bone, PTH1R is expressed on the surface of osteoblasts. When the receptor is activated, these cells in turn stimulate osteoclasts to ultimately increase the resorption rate. PTH1R is a receptor for parathyroid hormone and for parathyroid hormone-related peptide. The activity of PTH1R is mediated by G proteins which activate adenylyl cyclase and also a phosphatidylinositol-calcium second messenger system. Defects in PTH1R are the cause of Jansen metaphyseal chondrodysplasia (JMC), chondrodysplasia Blomstrand type (BOCD), enchondromatosis multiple (ENCHOM), Eiken skeletal dysplasia (EISD) and primary failure of tooth eruption (PFE).