[Pseudohypoparathyroidism; where is the hitch?].

Pseudohypoparathyroidism is a condition in which for some reason the normal effect of PTH in the target organ fails to occur. In the Ia type here described the signal transmission is impaired due to abnormal genetic development of the stimulating G protein (Gs) in the cell membrane resulting in insufficient cAMP production after binding of PTH on the membrane receptor. The failure to occur of the normal PTH effect impairs the calcium homeostasis. In many cases this type of pseudohypoparathyroidism is associated with phenotypical characteristics such as short stature, round face, obesity, brachydactyly, subcutaneous and intracerebral calcifications and sometimes bradyphrenia. Since the Gs protein aspecifically also brings about production of cAMP after binding of other polypeptide hormones to this hormone-specific receptor, several hormone resistances may be present concurrently.