Stephen Skolnick is a gut microbiome expert blogging at Eat Shit And Prosper. His most recent post argues that contra the psychiatric consensus, schizophrenia isn't genetic at all - it's caused by a gut microbe. He argues:

1. Scientists think schizophrenia is genetic because it obviously runs in families
2. But the twin concordance rates are pretty low - if your identical twin has schizophrenia, there's only about a 30%-40% chance that you get it too. Is that really what we would expect from a genetic disease?
3. Also, scientists have looked for schizophrenia genes, and can only find about 1-2% as many as they were expecting.
4. So maybe we should ask how a disease can run in families without being genetic. Gut microbiota provide an answer: most people "catch" their gut microbiome from their parents.
5. Studies find that schizophrenics have very high levels of a gut bacterium called Ruminococcus gnavus.
6. This bacterium secretes psychoactive chemicals. Constant exposure to these chemicals might be the cause of schizophrenia.

I disagree with all of this. Going in order:

https://www.astralcodexten.com/p/contra-skolnick-on-schizophrenia