The OCTN1 gene is located at chromosome 5 (5q31.1) in the inflammatory bowel disease 5 (IBD5) locus, known for its implication of susceptibility to Crohn’s disease (CD), ulcerative colitis (UC), and rheumatoid arthritis (RA) [14,25,26,27,28]. The gene discussed is SLC22A4; the disease is rheumatoid arthritis.