The cause of Autism Spectrum Disorder (ASD) is unknown, although unproven theories abound. Autism is a complicated disorder, and most likely a set of disorders for which easy answers to the cause are not likely to be found. It is now clearly understood that it is not an emotional disorder as some of the early clinicians believed (e.g. Kanner, Bettelheim). The one theory that does have strong scientific evidence is that genetics can contribute to the occurrence of ASD. Studies show the concordance rate for identical twins is much higher than for fraternal twins and ongoing research is beginning to identify genes that may put an individual at risk.
In the last decade, there has been increased theorising about the role of environmental toxins and vaccinations, but there is no convincing evidence that ASD is caused by either of these. With or without the use of the preservative Thimerosal, there are numerous scientific studies showing no association between vaccines and ASD. Moreover, there is not one scientific study that has shown a causal link. Adherence to these speculative beliefs is tragic because many more children are harmed by not receiving life-saving vaccines. Not surprisingly, we are seeing increases in these illnesses that can be prevented through childhood vaccination.
Finding the answer will require long-term, painstaking, rigorous, and sophisticated scientific investigation. Professional responsibility and ethics demand that care be taken not to over-speculate, misrepresent nor present mere hypotheses as facts about the causes of autism.