Many autistic children have extremely limited diets. For example, a geneticist friend of mine saw a case where an autistic child had been referred for genetic testing because of horrific, chronic, spontaneous wounds on gums and skin. Turned out to be scurvy, because he had exclusively eaten Wheat Thins for the last 3-4 years, which aren’t fortified with vitamin C.

I would fully expect that a monotonous diet leads to a heavy skew in the gut microbiome as specific bacterial species that thrive on that diet are selected for, others against. It makes some sense that a fecal transplant could repair the damage. If the diet has shifted or expanded, the transplant could lead to long term benefits by restoring newly-viable bacterial species, perhaps by facilitating digestion of the new types of food.

I’d be curious to see a factoring out of the diet composition, gut microbiome, genetics, and severity of autism symptoms.