At this point, the cause of autism or the spectrum of ASD remain unknown. Scientific evidence supports the conclusion that ASD is a behavioural syndrom that results from various brain abnormalities. The genetic of autism is complex and up till now no genetic markers or biological markers of the disorder has been reliably identified. Current postulation is that the disorder is an expression of a heterogenic pool of genes instead of a single or a couple of gene interactions.

Although in the last decade, there was an increase in interest in the relationship between environmental toxins, diets and the disorder of autism, up till now, there is no scientific evidence which demonstrate a causal relationship between ASD and these toxins or diets.