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Characterization of Albright hereditary osteodystrophy and related disorders
B B Koo1, W F Schwindinger, M A Levine
1Division of Endocrinology and Metabolism, School of Medicine, Johns Hopkins University, Baltimore, MD, USA.
Abstract:
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.
Insights
Albright hereditary osteodystrophy (AHO) involves skeletal defects and hormone resistance due to Gs alpha defects. Pseudohypoparathyroidism (PHP) is a common form, while pseudopseudohypoparathyroidism (PPHP) presents without hormone resistance.
Area of Science:
- Endocrinology
- Genetics
- Molecular Biology
Background:
- Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterized by skeletal and developmental abnormalities.
- It is associated with reduced expression or activity of the alpha chain of the G protein that stimulates adenylyl cyclase (Gs alpha).
- Many AHO patients exhibit hormone resistance, particularly to parathyroid hormone (PTH), leading to pseudohypoparathyroidism (PHP) type Ia.
Purpose of the Study:
- To outline the different clinical classifications of Albright hereditary osteodystrophy (AHO) and pseudohypoparathyroidism (PHP).
- To differentiate between PHP type Ia, pseudopseudohypoparathyroidism (PPHP), PHP type Ib, PHP type Ic, and PHP type II.
- To highlight the underlying molecular defects and clinical manifestations of each subtype.
Main Methods:
- Clinical description of Albright hereditary osteodystrophy (AHO) and its variants.
- Discussion of hormone resistance mechanisms mediated by cyclic AMP (cAMP).
- Categorization based on Gs alpha activity, PTH receptor defects, and potential vitamin D deficiency.
Main Results:
- AHO presents with skeletal defects and Gs alpha dysfunction.
- PHP type Ia involves hormone resistance due to Gs alpha defects.
- PPHP shares AHO features but lacks hormone resistance; PHP Ib involves PTH resistance possibly due to receptor defects; PHP Ic has normal Gs alpha but hormone resistance; PHP II is linked to vitamin D deficiency.
Conclusions:
- AHO encompasses a spectrum of disorders with varying degrees of skeletal defects and hormone resistance.
- Genetic defects in Gs alpha and PTH receptor, as well as vitamin D status, contribute to the diverse clinical presentations.
- Accurate classification is crucial for understanding the pathophysiology and managing patients with these related conditions.