HLA-DRB1 and rheumatoid arthritis: However, a specific MHC class II DRB1 gene variant, namely the HLA-DRB1*04, has been associated with both an increased risk of rheumatoid arthritis and a reduced risk of developing schizophrenia [17,18,30], suggesting that a common immunogenetic background may promote the autoimmune disorder and protects from the mental one.