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

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.

An infant with Rett syndrome usually has normal development for the first 6 - 18 months. Symptoms range from mild to severe.

Symptoms may include:

• Hypotonia (floppy arms and legs) -- frequently the first sign
• Slowing head growth beginning at approximately 5 - 6 months of age
• Change in development
• Severe language development problems
• Loss of purposeful hand movements; for example, the grasp used to pick up small objects is replaced by repetitive hand motions like hand wringing or constant placement of hands in mouth
• Apraxia
• Shaky, unsteady, or stiff gait; or toe walking
• Loss of social engagement
• Seizures
• Breathing problems -- problems tend to get worse with stress; breathing is usually normal during sleep and abnormal while awake
• Scoliosis
• Loss of normal sleep patterns
• Poor circulation that can lead to cold and bluish arms and legs
• Intellectual disabilities and learning difficulties (assessing cognitive skills in those with Rett syndrome, however, is difficult because of the speech and hand motion abnormalities)
• Gastrointestinal problems including ongoing, severe constipation and gastroesophageal reflux (GERD)
• Excessive saliva and drooling

Genetic tests may be used to search for the gene mutations that cause Rett syndrome. However, since this gene defect is not identified in everyone with the disease, the diagnosis of Rett syndrome is still based on the symptoms.

There are several different types of Rett syndrome:

• Classical (meets the diagnostic criteria)
• Provisional (some evidence between ages 1 and 3)
• Atypical

Rett syndrome is classified as atypical if:

• It begins early (soon after birth) or late (beyond 18 months of age, sometimes as late as 3 or 4 years old).
• Speech and hand skill problems are mild.
• It is found in a boy (very rare).