Just started reading Dr. David Perlmutter's book Brain Maker: The Power of Gut Microbes to Heal and Protect Your Brain–for Life (2015), and in the introduction:

And then there's Autism, which has surged seven - to eight - fold just in the past 15 yerars, making this study truly a modern - day epidemic.

...

then

Now for the good news: New, leading-edge science coming from the most well-respected institutions around the world is discovering that to an extraordinary degree, brain health and, on the flip side, brain diseases, are dictated by what goes on in the gut. That's right: what's taking place in your intestines today is determining your risk for any number of neurological conditions.

And, chapter 5 is titled

Autism and the Gut
On the Frontiers of Brain Medicine