McCune-Albright syndrome
McCune-Albright syndrome is a complex disorder affecting the bones, skin, and endocrine system, caused by random genetic mutations that occur early in development.
Overview
This syndrome is characterized by polyostotic fibrous dysplasia, where bone is replaced by fibrous scar-like tissue, often on one side of the body. This can lead to fractures, deformities, and asymmetric growth of the skull, jaw, or limbs. Affected individuals also typically present with light brown skin patches known as café-au-lait spots, which often feature irregular borders compared to those seen in other conditions.
Endocrine Involvement
The syndrome frequently causes hormone-related issues, including:
- Precocious puberty: Early onset of menstruation, sometimes as early as age 2, due to excess estrogen.
- Thyroid issues: Enlargement of the thyroid (goiter) or nodules, often leading to hyperthyroidism.
- Growth hormone excess: Can lead to acromegaly, characterized by large hands and feet, arthritis, and facial changes.
- Cushing syndrome: Rarely, an excess of cortisol occurs, typically before age 2.
Causes & Inheritance
McCune-Albright syndrome is caused by a mutation in the GNAS gene, which leads to the constant activation of the adenylate cyclase enzyme. This condition is not inherited; it results from a random mutation occurring early in development, leading to mosaicism, where only some of the body's cells carry the mutation. Because the mutation is not present in every cell, it is not passed to the next generation.