"this is the first genome-wide association study of Rheumatoid Factor positivity in Rheumatoid Arthritis. Variation at the IRX1 locus on chromosome 5p15.3 is associated with the presence of Rheumatoid Factor. Our findings indicate that IRX1 and HLA-DRB1 are the strongest genetic factors for Rheumatoid Factor production in Rheumatoid Arthritis."xsd:string