Epidemiology and etiology of rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) is a chronic inflammatory disease that primarily affects the joints. The prevalence and incidence of RA vary among different populations. In the majority of epidemiologic studies carried out in North America, the prevalence of RA is estimated to be 0.5-1.1%, and the incidence, 20 to 50 cases per 100,000 population. The prevalence of RA in Korea has been reported to be 1.1-2.1%. Some studies have shown a decline in both the prevalence and incidence of RA after the 1960s, but more recent trends in RA incidence are not as well-known. RA is considered to be a multifactorial disease that results from interactions among genetic and environmental factors. The genetic contribution to RA pathogenesis has been estimated to be approximately 60%, and the HLA region has consistently shown the strongest genetic association with RA. Moreover, recent genetic studies of RA have identified a number of novel RA susceptibility genes, such as PAD14, PTPN22, STAT4, and TRAF1-C5. Though several genes, including HLA-DRB1 and STAT4, have been confirmed to be shared susceptibility genes among Asians and Caucasians, some of the susceptibility genes, such as PAD14 and PTPN22, are restricted to specific ethnic populations, revealing the presence of genetic heterogeneity in RA. Among environmental factors, smoking has by far the strongest association with RA in both the development of the disease and worse outcomes. A major gene-environment interaction between the HLA shared epitope and smoking is one of the most important findings from recent etiologic studies of RA. Further studies of RA susceptible genes and environmental risk factors will bring us closer to understanding the pathogenesis of RA.