PTPN22 and type 1 diabetes mellitus: In type 1 diabetes (T1D), for example, HLA, INS and several genes in the IL‐2 pathway (including PTPN22 and IL2RA) have variants with alleles with relatively large effects on risk (Odds Ratios (ORs) > 1.2), and it is these loci that have yielded most biological insights so far (Dendrou et al. 2009; Downes et al. 2010; Ferreira et al. 2019; Garg et al. 2012; Smyth et al. 2008; Todd et al. 2016; Vafiadis et al. 1997), subsequently taken forward to translation and clinical trials (Marcovecchio et al. 2020).