WDFY4 and rheumatoid arthritis: In stratification analyses, a significantly increased risk for RA associated with the WDFY4 rs7097397 AG genotype was evident among female patients, younger patients, C-reactive protein (CRP) negative patients and both anti-cyclic citrullinated peptide antibody (ACPA) positive patients and negative patients compared with the WDFY4 rs7097397 AA genotype.