Which are the causes of McCune Albright?

TL;DR: McCune-Albright syndrome is caused by a post-zygotic, somatic activating mutation in the GNAS gene, which occurs randomly after fertilization rather than being inherited from parents. This genetic change leads to the overactivity of signaling pathways in various tissues, resulting in the characteristic features of McCune-Albright syndrome, such as fibrous dysplasia of bone, café-au-lait skin spots, and endocrine hyperfunction.

What is the underlying cause of McCune-Albright syndrome?

The primary cause of McCune-Albright syndrome is a specific genetic "typo" known as a somatic mutation in the GNAS gene. Unlike many genetic conditions where a mutation is present in every cell of the body from conception, this mutation occurs randomly in a single cell during early embryonic development. As that cell divides to create new cells, only the descendants of that specific mutated cell carry the genetic alteration. This phenomenon is known as "mosaicism," which explains why McCune-Albright syndrome presents with such a wide variety of symptoms; the severity and location of the disease depend entirely on where in the body these mutated cells migrated during growth.

Is McCune-Albright syndrome a hereditary condition?

No, McCune-Albright syndrome is not hereditary. Because the mutation is somatic—meaning it happens after fertilization in the developing embryo—it is not found in the sperm or egg cells of the parents. Consequently, there is no increased risk of a parent passing McCune-Albright syndrome to their children. There are no known environmental, dietary, or lifestyle triggers that cause this mutation; it is widely considered a sporadic, random biological event.

How does the GNAS mutation affect the body?

The GNAS gene provides instructions for making a protein called Gs-alpha, which acts like an "on" switch for cellular signaling. In McCune-Albright syndrome, the mutation forces this switch to stay permanently in the "on" position. Think of it like a light switch that is stuck; the cell receives constant, uncontrolled signals to grow or produce hormones. This results in several clinical manifestations:

• Endocrine Hyperfunction: Glands like the thyroid, pituitary, or ovaries produce excessive hormones, leading to conditions like precocious puberty or hyperthyroidism.


• Fibrous Dysplasia: Bone tissue is replaced by abnormal, fibrous, scar-like tissue, which can lead to pain, fractures, and skeletal deformities.


• Café-au-lait spots: These are flat, light-brown skin lesions caused by the overproduction of pigment in skin cells carrying the mutation.

Is the etiology of McCune-Albright syndrome fully understood?

While we understand that the GNAS mutation is the root cause, researchers are still investigating exactly why the mutation causes different clinical presentations in different patients. At DiseaseMaps.org, we have seen 62 community members share their unique journeys, highlighting how the mosaic nature of McCune-Albright syndrome creates a spectrum of severity. Current research is focused on understanding the molecular pathways downstream of the GNAS mutation to develop targeted therapies that can "turn off" the overactive signaling without damaging healthy cells.

Next steps

• Consult with an endocrinologist and an orthopedist experienced in managing rare bone and hormonal disorders.


• Connect with the 62 members of the McCune-Albright syndrome community on DiseaseMaps.org to share experiences and coping strategies.


• Monitor for endocrine dysfunction through regular blood work as recommended by your clinical care team.


• Check ClinicalTrials.gov periodically for updates on research regarding GNAS-related signaling inhibitors.

Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician with any questions regarding a medical condition.

References

• National Institutes of Health (NIH) Genetic and Rare Diseases (GARD) Information Center: McCune-Albright syndrome.


• Orphanet: McCune-Albright syndrome (ORPHA:560).


• OMIM (Online Mendelian Inheritance in Man): McCune-Albright Syndrome; MAS (#174800).


• National Organization for Rare Disorders (NORD): McCune-Albright Syndrome.