Five type 1 diabetes risk loci were nominally associated (p < 0.05) with lower stimulated C-peptide at DCCT eligibility: rs1264813 tagging HLA-A*24 (β [SE] = −0.34 [0.08], p = 2.80 × 10−5), rs151234 (IL27) (β [SE] = −0.32 [0.08], p = 3.15 × 10−5), rs12971201 (PTPN2) (β [SE] = −0.13 [0.05], p = 9.38 × 10−3), rs689 (INS) (β [SE] = −0.18 [0.07], p = 0.011), and rs193778 (DEXI) (β [SE] = −0.11 [0.06], p = 0.044). Here, IL27 is linked to type 1 diabetes mellitus.