Definition of Rett syndrome:

Rett syndrome is a disorder of the nervous system that leads to developmental reversals, especially in the areas of expressive language and hand use.

Causes, incidence, and risk factors:

Rett syndrome occurs almost exclusively in girls and may be misdiagnosed as autism or cerebral palsy.

Studies have linked many Rett syndrome cases to a defect in the methl-CpG-binding protein 2 (MeCP2) gene. This gene is on the X chromosome. Females have two X chromosomes, so even when one has this significant defect, the other X chromosome is normal enough for the child to survive.

Males born with this defective gene do not have a second X chromosome to make up for the problem. Therefore, the defect usually results in miscarriage, stillbirth, or very early death.

The condition affects about 1 out of 10,000 children. Groups of the disease have appeared within families and certain geographic regions, including Norway, Sweden, and northern Italy.