McCune-Albright syndrome

Definition

McCune-Albright syndrome is a genetic disease that affects the bones and color (pigmentation) of the skin.

Alternative Names

Polyostotic fibrous dysplasia

Causes

McCune-Albright syndrome is caused by mutations in the GNAS1 gene. A small number, but not all, of the patient's cells contain this faulty gene (mosaicism).

This disease is not inherited.

Symptoms

The hallmark symptom of McCune-Albright syndrome is early puberty in girls. Menstrual periods may begin in early childhood, long before the breasts or pubic hair develop (which normally occur first). Puberty and menstrual bleeding may begin as early as 4 - 6 months in girls.

Early sexual development may also occur in boys, but not as often as in girls.

Other symptoms include:

• Bone fractures
• Deformities of the bones in the face
• Gigantism
• Irregular, large patchy café-au-lait spots, especially on the back

Exams and Tests

A physical examination may show signs of:

• Abnormal bone growth in the skull
• Abnormal heart rhythms (arrhythmias)
• Acromegaly
• Adrenal abnormalities
• Gigantism
• Hyperparathyroidism
• Hyperthyroidism
• Hypophosphatemia
• Large café-au-lait spots on the skin
• Liver disease, jaundice, fatty liver
• Ovarian cysts
• Pituitary or thyroid tumors
• Scar-like tissue in the bone (fibrous dysplasia)

Tests may show too much:

• Adrenal hormones
• Blood prolactin
• Growth hormone

Other tests that may be done include:

• MRI of the head
• X-rays of the bones

Genetic testing is available for the GNAS1 gene.

Treatment

There is no specific treatment for McCune-Albright syndrome. Drugs that block estrogen production, such as testolactone, have been tried with some success.

Adrenal abnormalities (such as Cushing syndrome) may be treated with surgery to remove the adrenal glands. Gigantism and pituitary adenoma will need treatment with hormone inhibitors or surgery.

Outlook (Prognosis)

Lifespan is relatively normal.

Possible Complications

• Blindness
• Cosmetic problems from bone abnormalities
• Deafness
• Osteitis fibrosa cystica
• Premature puberty
• Repeated broken bones
• Tumors of the bone (rare)

When to Contact a Medical Professional

Call your health care provider if your child starts puberty early, or has other symptoms of McCune-Albright syndrome. Genetic counseling, and possibly genetic testing, may be recommended if the disease is diagnosed.

References

Garibaldi L, Chemaitilly W. Disorders of pubertal development. In: Kliegman RM, Stanton BF, St. Geme J, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 556.

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