Rhett's Syndrome is a rare neruo-developmental disorder that is caused by sporadic mutations in a gene located on the X chromosome. It almost exclusively affects girls. 1 in 10,000-15,000 females are affected. It is the only one of the Autism Spectrum Disorders (ASD) with a biological test to determine diagnosis.

Characteristics include:

*Normal development until 6 - 18 months of age, when language and motor milestones regress, purposeful hand use is lost, and deceleration of head growth is seen.

*Development of sterotyped hand movements may occur. An example is constant hand wringing.

*Breathing irregularities such as hyperventilation, breath-holding, or sighing may be seen.

*Appearance of pooly coordinated gait or trunk movement is observed.