McCune-Albright syndrome

Alternative names

Polyostotic fibrous dysplasia

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