Honestly, it is not known with any certainty, what the cause/causes are for autism. The least that can be done is to stick with reputable scientific sources for information..
Now the National Autism Association believes (believe being the important word) that:
"Vaccinations can trigger or exacerbate autism in some, if not many, children, especially those who are genetically predisposed to immune, autoimmune or inflammatory conditions.
Other environmental exposures may trigger, or exacerbate, autism in certain children, especially those who are genetically predisposed to immune, autoimmune or inflammatory conditions."
Here is a new study:
http://guardianlv.com/2014/08/autism-cause-identification-gives-rise-to-potential-cure-video/
Scientists have possibly uncovered the cause of autism, and in doing so have given rise to a potential cure. Researchers have discovered that children and teenagers with autism have a synapse surplus in the brain, rendering their brain structure different from that of others. The study was published in the most recent edition of the journal Neuron.
Read more at http://guardianlv.com/2014/08/autism-cause-identification-gives-rise-to-potential-cure-video/#3eABqi...
They have not determined the how or why either. Until science can, stay away from disreputable sources, but don't close any chapters yet.They are not finished.