Biological plausibility of the gut-brain axis in autism.

Organic abnormalities with neuroinflammatory and psychiatric consequences involving abnormal kynurenine and purine metabolism, neurotransmitter and cytokine imbalances, and altered levels of nutrients and metabolites are noted in autism, and many of these abnormalities-specifically including increased intestinal permeability, microbial metabolites, and heightened serum levels of endotoxin-originate from the gut.