PTPN22 and rheumatoid arthritis: Among individuals with the high-risk HLA genotype for T1D, the PTPN22 1858T allele is independently associated with the development of persistent islet autoimmunity.67 Compared to healthy controls, individuals with T1D are more likely to have either one or two copies of 1858T allele.66 In a recent meta-analysis of PTPN22, the 1858T allele was significantly associated with T1D across different ethnic groups (odds ratio 1.9, 95% CI 1.859–2.041).68PTPN22 is also associated with rheumatoid arthritis, systemic lupus erythematosus, Graves’ disease, and Crohn disease.66