DecodeDiabetes · Expanding the genetic etiological and diagnostic spectrum of monogenic diabetes mellitus

Whole genome sequencing is quickly becoming a routine clinical instrument. However, our ability to decipher DNA variants is still largely limited to protein-coding exons, which comprise 1% of the genome. Most known Mendelian mutations are in exons, yet genetic testing still fails to show causal coding mutations in more than 50% of well-characterized Mendelian disorders. This defines a pressing need to interpret noncoding genome sequences, and to establish the role of noncoding mutations in Mendelian disease.A recent case study harnessed whole genome sequencing, epigenomics, and functional genomics to show that mutations in an enhancer cause most cases of neonatal diabetes due to pancreas agenesis. This example raises major questions: (i) what is the overall impact of penetrant regulatory mutations in human diabetes? (ii) do regulatory mutations cause distinct forms of diabetes? (iii) more generally, can we develop a strategy to systematically tackle regulatory variation in Mendelian disease?The current project will address these questions with unique resources. First, we have created epigenomic and functional perturbation resources to interpret the regulatory genome in embryonic pancreas and adult pancreatic islets. Second, we have collected an unprecedented international cohort of patients with a phenotype consistent with monogenic diabetes, yet lacking mutations in known gene culprits after genetic testing, and therefore with increased likelihood of harboring noncoding mutations. Third, we have developed a prototype platform to sequence regulatory mutations in a large number of patients.These resources will be combined with innovative strategies to uncover causal enhancer mutations underlying Mendelian diabetes. If successful, this project will expand the diagnostic spectrum of diabetes, it will discover new genetic regulators of diabetes-relevant networks, and will provide a framework to understand regulatory variation in Mendelian disease.