A missense variant in exon 14 of PTPN22 (resulting in an arginine to tryptophan change at position 620 of the encoded protein) represents a strong genetic risk factor for some IMDs (e.g., RA, T1D, or systemic lupus erythematosus) and a protective variant for others (e.g., CD) [68]. Here, PTPN22 is linked to type 1 diabetes mellitus.