Autism likely causes

What is clear is that, like many psychiatric diagnoses, ASD and severe autism are not disease entities. Rather, they are manmade labels used to denote or categorize a particular constellation of symptoms. Not all of these symptoms occur together many of them can involve various causes and some or all of the symptoms can be caused by qualitatively different effects on the brain. As a result, the labeling of autism forms is something... 

Not quite. Autism in identical twins can be caused by a shared fetal environmental impact rather than by direct genetic transmission. The reality is that like mental retardation, autism is a behaviorally defined syndrome with a possibly wide variety of both genetic and nongenetic causes. The often-quoted concordance rate of 90 percent among identical twins is accurate for broad autism but not for severe (narrow) autism, for which twin concordance is only about 60 percent. Also in contrast to the ABC News report, the concordance among fraternal twins can be as high as 23 percent for broad autism.55... 

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