Albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) is an autosomal dominant inherited disorder with characteristic skeletal and developmental defects and in some patients target tissue resistance to multiple hormones. Patients with AHO typically have short stature, a round face, obesity, brachydactyly, and subcutaneous ossifications. Most subjects with AHO also show resistance to parathyroid hormone and other hormones that all act via stimulation of adenylyl cyclase and production of the second messenger cAMP. This form of AHO has been termed pseudohypoparathyroidism (PHP) type Ia. The molecular basis of AHO is deficiency of G,α, the α subunit of the guanine nucleotide-binding protein that couples cell surface receptors for many hormones and neurotransmitters to the stimulation of adenylyl cyclase. Remarkably, individuals with PHP type la often have relatives with AHO who do not develop hormone resistance despite G,α deficiency. This variant of AHO has been termed pseudo-pseu-dohypoparathyroidism. A variety of unique point mutations and small deletions in the G,α gene have been identified in affected members of AHO kindreds. A thorough clinical, biochemical, and genetic evaluation is required to distinguish AHO from other forms of PHP. Patients with PHP type Ic have somatic defects that are similar to those in AHO and manifest resistance to multiple hormones, yet they have apparently normal G,α activity. These subjects may have a defect in the adenylyl cyclase catalytic unit. In patients with PHP type Ib, hormone resistance is limited to parathyroid hormone (PTH) target tissues. These subjects lack somatic abnormalities and have normal levels of G,α. A defect in the PTH receptor may account for PTH resistance. Finally, subjects with PHP type II may have an acquired disorder resulting from vitamin D deficiency.