Characterization of Albright hereditary osteodystrophy and related disorders.

Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder with characteristic skeletal and developmental defects and reduced expression or activity of the alpha chain of the G protein that stimulates adenylyl cyclase (Gs alpha). Most patients with AHO exhibit target tissue resistance to multiple hormones whose actions are mediated by cyclic AMP (cAMP) as a second messenger, such as the parathyroid hormone (PTH). This form of the disorder is known as pseudohypoparathyroidism (PHP) type Ia. Patients with PHP type Ia usually have relatives with AHO who do not exhibit hormone resistance despite having the same defect in Gs alpha. This variant, yet unexplained, is known as pseudopseudohypoparathyroidism (PPHP). PHP type Ib is manifested by a limited hormone resistance to PTH and is believed to be caused by defects in the PTH receptor. Patients with PHP type Ic have normal Gs alpha activity and show morphologic defects similar to those in AHO as well as resistance to multiple hormones. PHP type II, a much rarer disease, is probably caused by vitamin D deficiency.