ST8SIA1 and rheumatoid arthritis: To illustrate the action of hub genes in RA one step further, we conducted a GSEA analysis, and the results showed that the primary immunodeficiency was significantly enriched in the high-expression subgroup of all 4 hub genes, and the intestinal immune network for IgA was enriched in CYFIP2 high-expression and ST8SIA1 high-expression subgroups, while hematopoietic cell lineage, Th1 and Th2 cell differentiation were enriched in ST8SIA1 high-expression and TYMS high-expression subgroups at the same time.