SNCA and Parkinson disease: The PD-associated gut dysbiosis, such as increased Akkermansia and decreased SCFAs-producing bacteria, can increase the intestinal permeability and intestinal inflammation, which subsequently facilitates exposure of the intestinal neural plexus to toxins such as lipopolysaccharide (LPS) and pesticides; this can lead to abnormal aggregation of α-synuclein fibrils and generation of Lewy bodies (22).