Dr. Levy says, while about 80% of autism is idiopathic (of unknown cause), there are at present many known causes of autism including FAS, rubella, Fragile X Syndrome, and more. In addition, according to a a report published in Pediatrics in 2009 entitled "Prevalence of parent-reported diagnosis of autism spectrum disorder among children in the US, 2007," as many as 40% of children who received an autism spectrum disorder at some point in their lives are no longer diagnosable on the autism spectrum.
Tero Toivanen on 10 Feb 10New research provides insight into why fragile X syndrome, the most common known cause of autism and mental retardation, is associated with an extreme hypersensitivity to sounds, touch, smells, and visual stimuli that causes sensory overload and results in social withdrawal, hyperarousal, and anxiety.