Further, epidemiological studies confirm that the functional C1858T PTPN22 SNP is associated with susceptibility to several autoimmune diseases both organ-specific (T1D) and systemic [RA and systemic lupus erythematosus (SLE)] in different populations and that its prevalence is ethnicity-dependent (13, 26, 30). Here, PTPN22 is linked to rheumatoid arthritis.