Alpha-thalassemia-X-linked intellectual disability syndrome (ATR-X syndrome) is a rare genetic disorder that affects the development of the brain and other organs. It is caused by a mutation in the ATRX gene, which is located on the X chromosome. People with ATR-X syndrome typically have intellectual disability, delayed development, and physical abnormalities such as low muscle tone, small head size, and distinctive facial features. They may also have problems with speech, language, and behavior. Treatment typically includes physical, occupational, and speech therapy, as well as medications to help manage symptoms.