Monogenic causes in the Type 1 Diabetes Genetics Consortium cohort; low genetic risk for autoimmunity in case selection

Hypothesis About 1% of patients clinically diagnosed as type 1 diabetes have non-autoimmune monogenic diabetes. The distinction has important therapeutic implications but, given the low prevalence and high cost of testing, selecting patients to test is important. We tested the hypothesis that low genetic risk for type 1 diabetes can substantially contribute to this selection. Methods As proof of principle, we examined by exome sequencing families with two or more children, recruited by the Type 1 Diabetes Genetics Consortium and selected for negativity for two autoantibodies and absence of risk HLA haplotypes. Results We examined 46 families that met the criteria. Of the 17 with an affected parent, seven (41.2%) had actionable monogenic variants. Of 29 families with no affected parent, 14 (48.3%) had such variants, including five with recessive pathogenic variants of WFS1 but no report of other features of Wolfram syndrome. Our approach diagnosed 55.8% of the estimated number of monogenic families in the entire T1DGC cohort, by sequencing only 11.1% of the autoantibody-negative ones. Conclusions Our findings justify proceeding to large-scale prospective screening studies using markers of autoimmunity, even in the absence of an affected parent. We also confirm that non-syndromic WFS1 variants are common among cases of monogenic diabetes misdiagnosed as type 1 diabetes.