Title is a bit misleading. It’s not a fecal transplant. It’s tablets and powder (for the pitt-hopkins cases) of microbes from fecal donors. Consumes orally.
I had a similar question to.
From my understanding of the study, which was double blind placebo study, it does not treat autism but its shown to greatly improve symptoms of autism.
They basically wiped the gut clean with antibiotics then started treating and saw improvements.
Could be that GI issues increase irritability which makes the measured autism symptoms more aggressive but it looks very promising for families.