The official TSA policy is:
Autism, Autism Spectrum & Intellectual Disabilities
Inform the TSA Officer
Passengers with intellectual disabilities or developmental disabilities, such as Down syndrome or autism, can be screened without being separated from their traveling companions if traveling with one. You or your traveling companion may consult the TSA officer about the best way to relieve any concerns during the screening process. You may also provide the officer with the TSA notification card or other medical documentation to describe your condition.