Polyostotic fibrous dysplasia

Alternative names
McCune-Albright syndrome

Definition
McCune-Albright syndrome is a genetic disease affecting the bones and pigmentation of the skin, which also causes hormonal problems and premature sexual development.

Causes, incidence, and risk factors

The hallmark of McCune-Albright syndrome is premature puberty in girls. Menstrual Periods may begin in early childhood, long before the appearance of breast or pubic hair development, which normally occur first. Early sexual development may also occur in boys, but this is not as common as it is in girls.

These children have abnormal fibrous dysplasia (abnormal fibrous development) in the bone that can lead to fractures, deformities, and abnormal X-rays. Abnormal bone growth in the skull can lead to Blindness or deafness due to “pinched” nerves.

Deformities may appear in the facial bones and cause cosmetic problems. In addition, the children have cafe-au-lait spots on their skin, which may be present from birth.

McCune-Albright syndrome is caused by mutations in the GNAS1 gene. It is associated with mosaicism, meaning that the abnormal gene is present in a fraction, but not all, of the patient’s cells.

This disease is not inherited, it is sporadic. This means that a new mutation of the DNA occurs in the womb during development of the patient. This mutation is not passed on to any children the patient later has.

Symptoms

     
  • Irregular, patchy cafe-au-lait spots, especially on the back  
  • Vaginal bleeding (first menstruation) at a very early age  
  • Premature puberty       o early breast development       o early pubic and armpit hair development  
  • Some patients get more broken bones  
  • Rarely, a form of gigantism (overgrowth of the body caused by excess hormones)

Signs and tests
A physical examination may show signs of:

     
  • Hyperthyroidism (occasionally)  
  • Adrenal abnormalities (occasionally)  
  • Acromegaly (occasionally)  
  • Cafe-au-lait spots of the skin

Tests may show signs of Hyperthyroidism, hyperparathyroidism, excess adrenal hormones, or excess blood prolactin or growth hormone.

X-rays show fibrous dysplasia that affects multiple bones. An MRI of the head may show a type of tumor called an adenoma in the pituitary gland. Genetic testing may be available for the GNAS1 gene.

Treatment

There is not a specific treatment for McCune-Albright syndrome. Drugs that inhibit estrogen production, such as testolactone, have been tried with some success.

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

Expectations (prognosis)
Life span is relatively normal.

Complications

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

Calling your health care provider
Call your health care provider if your child develops evidence of premature puberty (before the expected age) or has other symptoms suggestive of McCune-Albright syndrome. Genetic counseling, and possibly genetic testing, may be recommended if the disease is diagnosed.

Johns Hopkins patient information

Last revised: December 8, 2012
by Armen E. Martirosyan, M.D.

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