Specialties & Conditions McCune-Albright Syndrome and Fibrous Dysplasia (MAS/FD)
McCune-Albright Syndrome and Fibrous Dysplasia (MAS/FD)
Specialty
Program
What Is MAS/FD?
MAS/FD is a rare condition that can affect many parts of the body. Symptoms and severity are different for each person. Some people may only have one body system affected, while others may have multiple.
Systems Affected by MAS/FD
FD occurs when a change in the GNAS gene causes bone to form as fibrous tissue (like scar tissue) instead of healthy bone. These weak, abnormal areas can cause pain, fractures, deformities, or functional problems, depending on which bones are involved.
- Types:
- Monostotic — one bone affected
- Polyostotic — multiple bones affected
- Complications: scoliosis (spine), vision or hearing loss (skull)
- Diagnosis: seen on x-ray or bone scan; CT scan is best for the skull
- Timing: most lesions develop by age 5; functional issues usually appear by age 10. Lesions may stay active into early adulthood, then typically slow down.
In MAS, puberty may start too early—before age 8 in girls and before age 9 in boys.
- Girls: Ovarian cysts may form and disappear throughout childhood, producing estrogen that causes breast development, vaginal bleeding, and growth spurts. These cysts usually resolve on their own and do not affect future fertility.
- Boys: Less common. Signs include penis growth, pubic/underarm hair, and growth spurts from testosterone.
The thyroid is a butterfly-shaped gland in the neck that regulates temperature, appetite, and growth. In MAS/FD, it may become overactive (hyperthyroidism), causing symptoms like feeling hot, increased appetite, weight loss, rapid heartbeat, trouble sleeping, and fast growth. Some may also have hyperactivity, shaking, or tremors. People with MAS/FD can also develop thyroid nodules or cysts.
Some people make too much growth hormone (GH) which causes rapid growth and makes fibrous dysplasia lesions expand and grow. This can increase risk of vision loss in FD involving the skull.
A rare complication of MAS/FD where the adrenal glands make too much cortisol, usually in early childhood. It can cause poor height growth, rapid weight gain, and high blood pressure.
In FD, affected bones may release extra FGF23, a hormone that makes the kidneys lose too much phosphorus. This leads to low blood phosphorus, which can cause bone pain, muscle weakness, rickets, and fractures.
What Causes MAS/FD?
MAS/FD happens because of a change (variant) in the GNAS gene, which makes the gene “always on” in certain cells. This change occurs randomly in some of a person’s cells and is not passed from parent to child. While there is no cure, there are treatments that can help manage symptoms. Our team also partners with other hospitals that are studying new medications for MAS/FD.
What Are the Signs & Symptoms of MAS/FD?
MAS/FD can affect different parts of the body:
- Skin: Café-au-lait macules (coffee-colored birthmarks) that stay stable over time; may be harder to see in darker skin.
- Bones: Fibrous dysplasia (abnormal bone) and low phosphorus levels that can cause rickets.
- Endocrine system: Overproduction of certain hormones, leading to early puberty, excess growth hormone, or adrenal problems.
How Is MAS/FD Diagnosed?
Providers may use several tests to check for MAS/FD and related conditions, such as:
- Blood and urine tests
- X-rays and bone scans
- Thyroid, testicular, or ovarian ultrasounds
- CT scans for skull involvement
- Vision, hearing, and dental exams if the skull is affected
A biopsy of an affected area can confirm a GNAS gene variant.
How Is MAS/FD Treated?
There is no single treatment for MAS/FD—care depends on the symptoms.
- Fibrous Dysplasia: No cure, but research on medications is ongoing. Surgery may be needed for affected bones.
- Pain management:
- Supplements (phosphorus + vitamin D) may help
- Pain relievers: acetaminophen, ibuprofen, naproxen
- Severe pain may require bisphosphonates
- Pain management:
- Precocious Puberty: Medications can block extra estrogen or testosterone. Additional medications may be added if puberty progresses or cysts recur.
- Thyroid: Treated with medication and/or surgery.
- Growth Hormone (GH) Excess: Treated with medication
- Cushing Syndrome: Treated with medications or surgery depending on age and severity
- Hypophosphatemia: Treated with phosphate supplements and active vitamin D. Research is exploring new medications targeting high FGF23.
What to Expect with Our Care Team
If MAS/FD is already suspected or diagnosed, our team may ask you to do blood work, urine studies, and/or imaging studies, before your first visit with us. We will review all of the results at the visit and develop a personalized treatment plan based on the results and any symptoms experienced.
Research
Research is ongoing to improve our understanding of MAS/FD and develop more effective treatments for patients. Partnership between patients, advocates, physicians, and scientists is important to help develop better treatments for patients with MAS/FD.
Additional Resources
Make an Appointment
Call our KIDS DOC team to request a Bone Health appointment. We’ll review your request to determine whether your child should see an endocrinology or orthopedic specialist, then contact you to schedule.