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.