HLA-DRB1 and rheumatoid arthritis: Indeed, since the genetic contribution to RA and periodontitis is substantial and may account for 60% and 50% of the RA and CP risk profile, respectively [55,56], some genetic variations, particularly the HLA-DRB1 alleles associated with shared epitope coding, may enhance susceptibility to RA development in CP patients, as both diseases share genetic risk factors like MHC class II HLA-DRB1 alleles and cytokine single nucleotide polymorphisms, including the KCNQ1 gene [57].