On the topic of metabolic disturbances in Autism, huge fan of the work Dr. Randy Blakely is doing on the links between Serotonin metabolism and Autism. One of the most surprising, and strongest (25-30% of patients), biomarkers for Autism is actually Platelet Hyperserotonemia (high levels of bound Serotonin in the blood).

For decades it's been without explanation but recently Dr Blakely has described a bunch of cases where it was narrowed down to SERT transporter polymorphisms and inflammation.

Worth a watch for those interested in the weeds of this stuff: https://www.youtube.com/watch?v=cpDtuKV5CJs

I've got a pet hypothesis that differences in Serotonin metabolism (and receptor hypersensitivity) might play a role in why SSRIs aren't generally considered a first line treatment for ASD symptoms, https://www.pnas.org/doi/abs/10.1073/pnas.1112345109