Monogenic Diabetes Misdiagnosed as Type 1

Proportion of monogenic diabetes among patients diagnosed as type 1 diabetes.

The exomes of all patients negative for four T1D autoantibodies will be sequenced and pathogenic variants in genes known to cause monogenic diabetes will be called and annotated. The frequency of genes carrying such variants among these patients will be compared to control exomes from public databases.

Proportion of patients carrying mutations in previously unstudied genes that meet statistical criteria of pathogenicity for monogenic diabetes.

Exomes not found to carry a mutation (per outcome 1) will be analyzed to discover pathogenic variants in novel genes. Genes mutated in more than one unrelated probands will be statistically evaluated to see if variants in these gene occur more frequently than in control exomes. The number of probands that is needed to fulfill this criterion will depend on the gene's tolerance to protein-altering mutations.

Risk-prediction score for monogenic diabetes mutation in antibody negative T1D patients

Composit score with a statistically significant ROC curve for predicting monogenic diabetes in individuals previously diagnosed as T1D. It will be based on age of onset, T1D polygenic risk score. The risk score will aim to predict monogenic diabetes in cases with clinical T1D diagnosis and known to be antibody negative. The scale will be calculated as follows: From the exome sequencing, the investigators will be able to determine genotype at the three most important loci determining risk for autoimmune T1D (HLA, INS and PTPN22).The composite risk score, along with family history, age of onset, HbA1c+4\*insulin dose/kg (as proxy for residual beta cell function) will be subjected to logistic regression for an overall risk. The ROC curve will be used to select a point likely to capture most cases unlikely to have autoimmune T1D, sacrificing specificity to maximize sensitivity. Data will be validated with jackknife cross-validation.