McCune-Albright syndrome

Definition

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

Causes, incidence, and risk factors

McCune-Albright syndrome is caused by mutations in the GNAS1 gene. The abnormal gene is present in a fraction, but not all, of the patient's cells (mosaicism).

This disease is not inherited. It is caused by a new change (mutation) to the DNA that occurs in the womb while the baby is developing. This mutation is not passed on to any of the person's children.

Symptoms

The hallmark symptom of McCune-Albright syndrome is premature 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 it is not as common as it is 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

Signs 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's syndrome) may be treated with surgery to remove the adrenal glands. Gigantism and pituitary adenoma will need treatment with hormone inhibitors or surgery.

Expectations (prognosis)

Lifespan is relatively normal.

Complications

• Blindness
• Cosmetic problems from bone abnormalities
• Deafness
• Osteitis fibrosa cystica
• Premature puberty
• Repeated broken bones
• Tumors

Calling your health care provider

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. Disorders of Pubertal Development. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 563.