Rett syndrome is a problem with the development of the nervous system. It is most common in girls. Boys with Rett syndrome are usually stillborn or die shortly after birth.

Many people with Rett syndrome live into adulthood. Most have severe disabilities, including an inability to talk or walk.

Rett syndrome is most often caused by nonhereditary mutations on a specific gene on one X chromosome.

Females have two X chromosomes. Males have one X and one Y chromosome. Males usually die from Rett syndrome because they lack a second normal X chromosome. The second normal X chromosome in girls may provide some protection.

In Rett syndrome, the mutated gene affects methyl cytosine binding protein 2 (MECP2). When it is mutated, there is a deficiency of this important protein. Not everyone with the MECP2 mutation will have Rett syndrome. Some females may be normal or have only mild symptoms.

It is not clear what causes the Rett gene to mutate. Rett syndrome is usually nonhereditary. This means it does not run in families.