Definition of McCune-Albright syndrome:

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

Children with McCune-Albright syndrome have abnormal fibrous dysplasia (scar-like tissue) 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.