RIPK2 and Oral ulcer: Among 23 genes with more than 3 instrumental variables, 11 genes (RIPK2, CXCL6, ARFIP1, TDGF1, TIRAP, TNFSF8, TLR1, GLCE, MICA, and CTSS) have a association with mouth ulcers using the MR egger method.