[PTH/PTHrP receptor and pseudohypoparathyroidism].

The PTH/PTHrP receptor, a G protein coupled receptor, mediates the actions of PTH and PTHrP. Homozygous inactivating mutations in this receptor cause a rare disorder called Blomstrand chondrodystrophy. Since this disease is lethal in utero or perinatal period, the existence of PTH resistance has not been verified. Inactivating mutations in PTH/PTHrP receptor have not been found in the patients with pseudohypoparathyroidism (PsH), a group of disorders characterized by biochemical hypoparathyroidism and unresponsiveness to PTH. In patients with PsH type Ia, numerous heterozygous inactivating mutations have been identified in the gene (GNAS1) encoding the alpha-subunit of Gs protein (Gs alpha) which couples multiple receptors to the stimulation of adenylate cyclase. It is suggested that some abnormality in GNAS1 outside the coding exons may lead to PsH type Ib. To explain the heredity and phenotypic variation of PsH, tissue- or cell-specific imprinting of Gs alpha has been implicated.