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 75% of Rett syndrome cases to a defect in the methl-CpG-binding protein 2 (MeCP2) gene. The gene associated with Rett syndrome is on the X chromosome. Females have two X chromosomes, so even when one has this significant defect, the other X chromosome provides enough normal protein for the child to survive.

Males born with this defect do not have a second X chromosome to compensate for the problem. Therefore, the defect is usually lethal, leading to miscarriage, stillbirth, or very early death.

Most cases of the defect occur without causes. However, there seem to be groups of the disease within families and certain geographic regions, for example Norway, Sweden, and northern Italy.