Autism symptoms reduced nearly 50 percent two years after fecal transplant. In a new study, researchers demonstrate long-term beneficial effects for children diagnosed with ASD through a revolutionary fecal transplant technique known as microbiota transfer therapy (MTT). Source 8u.
I think it might be the cause for certain behavioral patterns in some situations for ASD, but in my opinion it really comes down to the individual. Each person with ASD can have it differently, as well as operating differently compared to other people with or without the condition.