Genetic factors contribute significantly to RA. In particular, the human leukocyte antigen (HLA) locus accounts for about 50% of genetic predisposition to RA, with a strong involvement of HLA-DRB1, a major histocompatibility complex (MHC) class II molecule, with several HLA-DRB1 alleles implicated across different ethnic populations.6 Other non-HLA susceptibility genes, such as protein-arginine deiminase type 4 (PADI4) and IL-2 receptor subunit α, are also implicated in RA.
SLE is a complex genetic disease with the involvement of multiple genes. HLA class II DRB is also implicated in SLE.3,8
HLA-B27, an MHC class I molecule, has a strong association with AS. HLA-B27 testing is routinely used to screen for AS.4