HLA-DRB1 and polyarticular arthritis: In the subtype-specific association analysis (Supplementary Table 4), an increased risk associated with HLA-DRB1*08:01 was largely attributable to the subtypes oligoarthritis (OR = 4.98, 95% CI: 3.22–7.70) and RF-negative polyarthritis (OR = 4.5, 95% CI: 2.62–7.72).