Our data on the co-inheritance of PTPN22 variant genotype (TT) and HLA-DQ alleles show that T1DM patients who had the homozygous variant PTPN22 genotype (TT), always carried one or more of the high risk DQ alleles (DQ 2–2, 2–3, 2–5, 2–8 and 8–8, Fig 4). Here, PTPN22 is linked to type 1 diabetes mellitus.