Confirmed by gene association studies and genome-wide association studies (GWAS), genetic polymorphisms related to both RA and endometriosis include the interleukin-6 (IL-6) gene, interleukin-10 (IL-10) gene, vascular endothelial growth factor gene, protein tyrosine phosphatase non-receptor type 22 gene, and signal transducer and activator of transcription 4 gene (18). Here, IL6 is linked to rheumatoid arthritis.