https://cosmosmagazine.com/health/body-and-mind/autism-gut-m...
https://cosmosmagazine.com/health/body-and-mind/autism-gut-m...
"Whether those microbial deficits actually help cause the disorders is unclear, [...]"
For the time being it appears to be careful in only suggesting correlation, not causation.
> "researchers recently reported in Frontiers in Psychiatry that fecal transplants improved symptoms in two depressed patients"
It's very reasonable to think that a lot of these systems are bidirectional, and for any individual, you may not know which part of the body was dysfunctional first.
I would suggest that rather than look at childhood experiences exclusively, we can look at current circumstances. It's much, much easier to be depressed when you're poor and have no hope for a better life, for example.