FFAR2 and rheumatoid arthritis: Intersection analysis using a Venn diagram of RA-related, gut microbiota-related, and ferroptosis-related genes identified, for the first time, 16 genes potentially mediating RA pathology and involved in gut microbiota metabolism and ferroptosis (EGFR, MAPK8, NQO1, APOE, TGFB1, LCN2, HMOX1, NR1H4, PLIN2, PTGS2, CDKN1A, IL6, FFAR2, GPX3, JUN, and MYC).