CDK6 and rheumatoid arthritis: While concordance of HLA-DRB1*04 and PTPN22 SNP in anti-CEP-1 positive RA was demonstrated previously in a single cohort [17,19], the involvement of genetic variants of PADI4 and CDK6 in risk of development of RA subgroups only in the absence of HLA-DRB1*04 is a new finding.