Depends on when the vaccine is taken. There are chemicals that do cause Down's Syndrome, if they're consumed by the mother when the child is growing up inside her. It's also possible there are similar triggers for autism. Statistically, older fathers are more likely to produce autistic daughters. (Why exactly this happens is still in the air.) There are currently no known chemicals that would cause autism, specifically, in adults, but there are dozens of other known chemicals that do injure the brain and change how it works. Causing or curing in-born mental disorders is hence not outside the realm of possibility.