Type 2 diabetes, T2D, is a complex disorder with heterogeneous backgrounds. Several disease forms could belong to a context named today as T2D, with a wide spectrum ranging from mono-and/or oligogenic forms, often with an early onset disease, to polygenic ones, due to environment and predisposing genetic background. Our aim is to verify, by a Next Generation Sequencing (NGS) approach, whether Italian patients with early-onset T2D are enriched for mutations in monogenic diabetes genes (MODY and Neonatal Diabetes, ND) than patients with late-onset disease. We will study 4730 T2D patients from 6 Italian T2D study-cohorts. Among these, 300 individuals with age at diagnosis 65 years (late-onset T2D, used as "super controls") will be screened. DNA will be subjected to NGS targeted of 27 MODY- and ND- genes by a custom panel (TSCA Illumina) on MiSeq-Illumina platform. All identified variants will be classified by a filtering/prioritization strategy, based on quality, allele frequency, predicted functional impact and absence in our in-house database. Statistical analyses by burden tests will be carried out to evaluate statistically significant differences in the distribution of MODY-/ND-genes mutations in two study-groups. While tailored, pharmacological treatment is a reality for monogenic diabetes, this is not the case in patients with T2D. Thus, defining the role of MODY and ND-gene mutations in patients with early-onset T2D will help: a) to guide most appropriate clinical and pharmacological treatment for their specific genetic subtype; b) to anticipate long-term clinical evolution and risk of complications; c) to perform genetic counseling in their families. This will be of importance both in children with incidental hyperglycemia and in undiagnosed patients; it could lead also to reclassifying diabetes in patients previously misdiagnosed as having "classical" T2D, with benefits on therapeutic options.
Among individuals with T2D, there is substantial variability in disease pathogenesis and progression, including the risk of developing chronic complications. Also the ability to respond to the several anti-hyperglycemia treatment options may vary a lot. It is, therefore, not surprising, though unfortunate, that currently there is no way to predict precisely the risk neither of developing T2D nor, once it is diagnosed, of its progression and treatment responses. In contrast, personalized medicine is already feasible for some monogenic forms of diabetes. For example, patients affected by GCK-related diabetes are unlikely to develop chronic complications even after decades of disease, so to be not obliged to pharmacological treatments of their generally mild hyperglycemia. In addition, patients with ND due to mutations in KCNJ11 can stop insulin injections and switch to high-dose sulphonilureas, a treatment that will properly manage hyperglycemia as well as neurological symptoms, when present. Similar data have been obtained in some patients with ND due to mutations in ABCC8. Finally, low-dose sulphonilureas is the treatment of choice for patients affected by HNF4A- and HNF1A-related diabetes.
It is conceivable that thanks to NGS approaches, times from precision medicine will come soon also for some patients with T2D. Such an ambitious goal can be pursued only through a collaborative effort between clinical investigators, geneticists, molecular biologists and diabetic family members. Accordingly, addressing the role of monogenic diabetes gene mutations on early-onset T2D in Italy, the primary goal of this project, will certainly help: a) to guide the most appropriate clinical management and pharmacological treatment according to their specific genetic subtype, when identified; b) to anticipate long-term clinical evolution and the risk of complications; c) to perform genetic counseling in their families which may trigger molecular testing also in additional family members. This will be of importance both in children with incidental hyperglycemia and undiagnosed patients; it will eventually lead also to reclassifying diabetes in patients previously misdiagnosed as having "classical" T2D, with likely beneficial effects on therapeutic options.
We have already successfully experienced the above-described NGS approach to pursue the goal of better addressing the molecular causes of multigenerational diabetes mellitus in adult patients (i.e. we defined "familial diabetes of the adulthood", FDA) as ascertained from a large cohort of adult patients diagnosed as having T2D.
We carried out targeted resequencing of the 27 genes so far reported to cause MODY and/or ND on the probands from our large family collection. This was based on the hypothesis that relatively low-severity mutations in genes causing classical early onset monogenic forms of diabetes play a role on the fine-tuning of glucose homeostasis, thus becoming pathogenic for less sever forms of the disease, which develop in the adulthood. In fact, these data (Prudente S., manuscript in preparation) indicate that approximately one third of FDA patients do carry mutations in MODY and ND-genes (these data will be presented as oral communication to the next 78th ADA Scientific Meeting at San Diego, CA).