Shared genetic risk contributes to type 1 and type 2 diabetes etiology.

The extent to which shared genetic risk contributes to T1D and T2D etiology is unknown. In this study, we generated T1D association data of 15k samples imputed into the HRC panel which we compared to published T2D association data imputed into 1000 Genomes. The effects of genetic variants on T1D and T2D risk at known loci and genome-wide were positively correlated. Increased risk of T1D and T2D was correlated with higher fasting insulin and glucose level and decreased birth weight, among other correlations. Variants with T1D and T2D association were further enriched in pancreatic, adipose, B cell, and endoderm regulatory elements. We fine-mapped causal variants at known loci and found evidence for co-localization at five signals, four of which had same direction of effect. Shared risk variants were associated with quantitative measures of islet function and early growth, and were expression QTLs in relevant tissues. We further identified a shared variant at GLIS3 in islet accessible chromatin with allelic effects on enhancer activity. Our findings identify a shared genetic risk involving effects on islet function as well as insulin resistance, growth and development in the etiology of T1D and T2D, supporting a role for T2D-relevant processes in addition to autoimmunity in T1D risk.