McCune-Albright Syndrome

What is McCune-Albright syndrome?

McCune-Albright syndrome (also known as fibrous dysplasia/McCune-Albright) is a genetic condition that affects your bones, skin and endocrine system (hormone-producing tissues). McCune-Albright syndrome causes scars on bone tissue (fibrous dysplasia), skin pigmentation and increased function of growth-regulating glands. The condition can be fairly mild in some, and quite severe to life-threatening in others.

Who does McCune-Albright syndrome affect?

McCune-Albright syndrome can affect any child because it’s the result of a new genetic mutation. These types of mutations are unpredictable. This genetic mutation occurs shortly after conception/fertilization due to an error when cells divide and replicate.

How common is McCune-Albright syndrome?

McCune-Albright syndrome is a rare condition that occurs an estimated once out of every 100,000 to 1,000,000 births worldwide.

How does McCune-Albright syndrome affect my child’s body?

McCune-Albright syndrome might affect your child’s height and weight due to bone growth and endocrine system symptoms of the condition. Your child may have a specific type of birthmark on their body called café-au-lait spots. Your child may also experience early puberty as a symptom. If you notice symptoms affecting your child’s ability to thrive, contact your healthcare provider for a unique treatment plan that’s focused on alleviating your child’s symptoms.

What are the symptoms of McCune-Albright syndrome?

Symptoms of McCune-Albright syndrome affect your bones, skin and endocrine system. Symptoms range in severity and affect each person diagnosed with the condition differently.

Bone symptoms

The most common symptom that affects bones is fibrous dysplasia. Fibrous dysplasia is a condition where scar tissue grows in the place of normal bone. As your body grows and develops, the areas of fibrous tissue also grow and weaken your bone, causing bone fractures or bones to grow irregularly (deformed). People diagnosed with McCune-Albright syndrome might experience mild to severe cases of fibrous dysplasia based on how many bones have affected tissue.

A less common symptom of McCune-Albright syndrome is cancerous bone lesions (tumors) as a result of fibrous dysplasia, which occurs in less than 1% of people with the condition.

Other symptoms of McCune-Albright syndrome that affect the bones include:

• Asymmetrical bone growth of the face.
• Bone pain and discomfort.
• Loss of mobility.
• Rickets or osteomalacia.
• Scoliosis.
• Short stature.
• Uneven bone growth of the legs (causing a limp).

Skin symptoms

Babies born with McCune-Albright syndrome may have patches of skin that are a different color than the rest of the skin on their body (skin pigmentation). These patches normally take on a light brown to dark brown color and appear with uneven, jagged borders (café-au-lait spots). These spots may only show up on one side of their body. Café-au-lait spots may become more prevalent on their skin as your child becomes older.

Endocrine system symptoms

McCune-Albright syndrome may affect a child’s endocrine system, which is a series of glands that produce hormones. This condition can cause early puberty in children, especially in children assigned female at birth, who may begin menstruating by two years of age. Early menstruation occurs because excess female sex hormones (estrogen) excrete from cysts that form in their ovaries. Children assigned male at birth might experience early puberty as well.

Nearly 50% of people diagnosed with McCune-Albright syndrome have an enlarged thyroid gland. When the thyroid gland enlarges, it produces too much of the thyroid hormone (hyperthyroidism) that causes a fast heart rate, excessive sweating, high blood pressure and weight loss.

Other endocrine system symptoms of McCune-Albright syndrome include:

• The pituitary gland produces too many growth hormones, resulting in large hands and feet, rounded facial features and/or arthritis (acromegaly).
• The adrenal glands produce too much cortisol (stress hormone), which causes obesity and delayed growth (Cushing’s syndrome).

What causes McCune-Albright syndrome?

A mutation of the GNAS1 gene causes McCune-Albright syndrome. The GNAS1 gene makes proteins that regulate hormone activity. The mutation causes an enzyme (adenylate cyclase), which is a type of protein, to overproduce hormones and cause symptoms of McCune-Albright syndrome.

The genetic mutation is the result of a change in DNA that happens after conception (somatic mutation) and isn’t a condition that’s passed from parents to the child. The genetic mutation is not the result of something that the parents did or did not do during pregnancy. There have been no proven cases of people with McCune-Albright syndrome having a child with the same condition. The cause of somatic mutations is unknown and research suggests they occur randomly or sporadically.

How is McCune-Albright syndrome diagnosed?

McCune-Albright syndrome is typically diagnosed during early childhood. Your healthcare provider will examine your child for physical symptoms of the condition, like endocrine irregularities, café-au-lait spots on their skin and fibrous dysplasia. Diagnosis usually triggers after signs of early puberty or irregular bone growth.

What tests diagnose McCune-Albright syndrome?

Tests that diagnose McCune-Albright syndrome include:

• Blood tests to check endocrine function.
• Genetic testing to identify the gene mutation responsible for symptoms, which usually involves taking a biopsy of their skin or other tissues.
• Imaging tests like an X-ray to examine bone growth.

How is McCune-Albright syndrome treated?

Treatment is unique for each person diagnosed with McCune-Albright syndrome. There isn’t a cure for the condition and treatment aims to reduce symptoms. Treatment could include:

• Medicine to treat bone growth symptoms like bisphosphonates, which reduce the risk of bone fractures.
• Medicine to treat early puberty like aromatase inhibitors.
• Medicine to treat hyperthyroidism like antithyroids.
• Physical therapy and occupational therapy to target mobility challenges.
• Surgery to treat bone growth symptoms like fibrous dysplasia.

How can I reduce my risk of having a child with McCune-Albright syndrome?

McCune-Albright syndrome occurs because of a new genetic mutation. You can’t prevent it from happening.

Talk with your healthcare provider about genetic testing if you plan on becoming pregnant to see if you’re at risk of having a child with a genetic condition.

What can I expect if I have a child with McCune-Albright syndrome?

Prognosis is dependent on the severity of the diagnosis in your child. Most people diagnosed with McCune-Albright syndrome have a normal life expectancy. Your healthcare provider will work closely to provide the best treatment that’ll reduce your child’s symptoms and alleviate any discomfort.

Your child might be shorter than their peers because their growth plates closed too soon during early puberty, but early intervention and treatment can improve their chances of postponing puberty changes that occur too soon.

Stay up to date with your child’s developmental milestones to make sure your child is growing on track.

There is a very small risk that cancer can develop as a result of your child’s diagnosis, so it’s important to schedule regular visits with your child’s healthcare provider.

Women with McCune-Albright may have a higher chance for breast cancer that occurs at an earlier age than usual, so it’s important to discuss this with your healthcare provider and receive recommended screenings.

When should I see my healthcare provider?

You should visit your healthcare provider if your child experiences symptoms of McCune-Albright syndrome, including:

• Anxiety, hyperactivity, mood swings or difficulty sleeping (signs of hyperthyroidism).
• Bone growth causing irregularities in the shape of their bones.
• Difficulty walking.
• Early menstruation.
• Severe pain in their bones.

If you believe your child has a bone fracture or broken bone, with symptoms of pain, swelling, difficulty moving or bearing weight on that part of their body and bruising, visit the emergency room.

What questions should I ask my doctor?

• Does my child need medication to alleviate symptoms of McCune-Albright syndrome?
• Will my child need surgery to address fibrous dysplasia?
• Are there any side effects to the medicine that my child needs to take to alleviate their symptoms?

A note from Cleveland Clinic

Hearing your child has a rare genetic diagnosis can be intimidating for a new parent, but early intervention and treatment are available to combat your child’s symptoms of McCune-Albright syndrome. Your healthcare provider might suggest visiting a genetic counselor who’s an expert in genetics, as well as providing emotional support to help you better understand the diagnosis and walk you through the steps you can take to support your child so they can live a healthy and fulfilling life.