HLA-DRB1 and rheumatoid arthritis: Detailed studies on interactions between genetic and environmental risk factors for RA so far mainly been reported from Europe and the USA, and have demonstrated that the major genetic risk factor for RA, i.e. presence of certain HLA-DRB1 (MIM ID*142857) alleles exert their effects only in the subset of RA that is defined by the presence of ACPA [3], [4].