Mechanisms of disease: genetics of rheumatoid arthritis--ethnic differences in disease-associated genes.

Large studies on the genetics of common rheumatic diseases, such as rheumatoid arthritis and systemic lupus erythematosus, have identified multiple polymorphisms related to disease susceptibility, including peptidylarginine deiminase 4 (PADI4) and protein tyrosine phosphatase N22 (PTPN22). Some of the identified genes are associated with multiple autoimmune disorders, and some seem to have unique associations with particular disease entities. Although the molecules encoded by these genes have a primary role in the molecular pathways of autoimmunity, genetic variations and contribution to disease susceptibility seem to vary between ethnic groups. In this Review, we report the findings on genes associated with rheumatoid arthritis and focus on the differences in the frequency of polymorphisms between various ethnic groups.