"Vaccines" (not sure which ones and in what combination) are causing autoimmune disease, which results in autism. The reason is complicated, but boils down to the fact that the vaccines we take cause us to respond to molecules which are already present and harmless in the body, as well as disease-causing ones.

If we were born with the antibodies naturally, we would still be autistic, but it would happen over a long enough span of time to weed out the kinks, by way of diet (which is the single most effective way of managing the symptoms of autism). As the buddhists say, patience/balance is key.