In our analyses of the causal effect of hypothyroidism on T1DM, there are 78 SNPs involving 56 genes listed below: PDE8B, TNFRSF11B, MIR1208, SPATA13, ILDR1, TPO, AGO2, EDARADD, C12orf42, CPT1C, LOC107986195, PNPT1, NOD2, MIR3681HG, IQCN, LINC00824, VAV3, LOC105373724, C1QTNF6, HORMAD2, VDAC1, NCR3, LOC105372548, MACIR, LOC101927745, LOC107986913, SH2B3, TLR3, PLEKHA1, TNFRSF18, CLNK, LINC02265, ELMO1, ACAP1, EFCAB13, LOC105376819, BACH2, PHTF1, IL21-AS1, LOC105378414, RAB5B, ARID5B, LINC02357, STAT4, AHI1-DT, FLT3, RTKN2, RAD51B, RASGRP1, MAF, TG, PLGRKT, PTCSC2, SH2D2A, SASH1 and LPP. This evidence concerns the gene IL21 and type 1 diabetes mellitus.