SNCA and Parkinson disease: Cluster 1 (red nodes) was the larger cluster with 29 co-occurrence terms: gastrointestinal microbiome, Parkinson’s disease, chain fatty acids, multiple sclerosis, short-chain fatty acids, alpha-synuclein, metabolism, ischemic stroke, mechanisms, enteric nervous system, nervous system, brain axis, metabolites, fecal microbiota transplantation, metabolomics, vagus nerve, etc. The topic of Cluster 1 is the mechanism of the gastrointestinal microbiome in Parkinson’s disease, multiple sclerosis, and ischemic stroke.