HLA-DRB1 and rheumatoid arthritis: The DRB1*04 allele of the human leukocyte antigen (HLA) system is a known risk factor for the development of rheumatoid arthritis (RA) [1] and is associated with increased serum levels of antibodies against cyclic citrullinated antibodies (anti-CCP) together with HLA-DRB1 *01 and HLA-DRB1*10 alleles.