What Is McCune-Albright Syndrome?

McCune-Albright Syndrome (MAS) is a rare genetic condition that affects multiple systems in the body. It is caused by a post-zygotic mutation in the GNAS gene, which leads to the overactivation of a signaling pathway involved in bone, skin, and hormone-producing tissues. Because this mutation occurs after fertilization, McCune-Albright Syndrome is not inherited and varies greatly from person to person.

The condition is part of a group of disorders known as mosaic genetic syndromes, meaning not all cells in the body carry the mutation. This can lead to a wide range of clinical features, depending on which tissues are affected.

Understanding the Genetic Cause: The GNAS Gene

At the heart of McCune-Albright syndrome is a mutation in the GNAS gene. This gene plays a key role in regulating hormones and cellular activity. When mutated, it causes certain cells in the body to function abnormally.

This GNAS mutation is somatic, meaning it arises during early development and is not passed down through families. Because of its mosaic nature, individuals with MAS may experience symptoms that range from mild to more complex, depending on how many and which cells are affected.

Recognizing Features and Diagnosis

The diagnosis of McCune-Albright syndrome is typically based on a combination of physical findings and clinical history. Common features that may suggest MAS include:

• Fibrous dysplasia of bone – where normal bone is replaced with fibrous tissue, leading to fractures or deformities
• Jagged-edged birthmarks –  birthmarks with increased skin pigment, often called café-au-lait macules. The borders tend to be jagged and irregular. The macules are usually present at birth and do not change significantly over a patient’s lifetime.
• Endocrine abnormalities – such as early puberty, thyroid dysfunction, or issues with other hormone-producing glands

A diagnosis is often made through clinical evaluation, imaging studies, and in some cases, genetic testing that identifies the GNAS mutation. Because symptoms can differ widely, MAS is considered a diagnosis based on a combination of findings rather than a single test.

Guidelines and Care Considerations

There are no universally agreed-upon treatments for McCune-Albright syndrome due to its complexity and variability. However, clinical care often involves a multidisciplinary approach. Medical professionals may refer to published MAS management guidelines or recommendations in academic literature to help guide care.

Management usually focuses on monitoring and addressing specific symptoms. This may involve imaging to track bone lesions, endocrinology consultations to manage hormone-related issues, and other specialties as needed. While there is no cure, many of the condition’s effects can be managed with appropriate support.

FDMAS Alliance, in collaboration with clinical researchers from around the world,  maintains the most up-to-date clinical guidelines for FD/MAS, with a forthcoming update currently in development and expected to be published soon.

Why Awareness Matters

Because McCune-Albright syndrome is rare, increasing public understanding is an important step toward advancing research and improving long-term care strategies. Broader awareness supports earlier identification, fosters collaboration in the medical community, and helps drive momentum for the development of new insights.

Individuals and communities can also contribute to this progress in many ways. Whether by spreading awareness, supporting advocacy, or participating in events, getting involved can help move the conversation forward. Learn more about how to take part at our Get Involved page.

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