HLA-DRB1 and rheumatoid arthritis: Nonmodifiable risk factors for arthritis are aging, female sex, family history of rheumatoid arthritis, multiple genetic factors such as HLA-DRB1 alleles and peptidyl arginine deaminase-4, low education level, high birth weight, and environmental risks such as air pollution, silica dust, solvents, ultraviolet light and, in rheumatoid arthritis, hormones related to women [30–34].