HLA-DRB1 and rheumatoid arthritis: In RA, the HLA-DRB1 gene is significantly linked to disease susceptibility, particularly through alleles containing the “shared epitope” sequence.[26,27] Although iridocyclitis is not as strongly associated with HLA-DRB1 as RA, evidence suggests that other immune-related genes involved in cytokine signaling pathways may overlap between the 2 conditions.