Why Do Finland and Sardinia Have So Much Type 1 Diabetes? Genetics Offers a New Clue

For more than four decades, researchers have noticed something striking: Finland and Sardinia have Type 1 diabetes rates in children that far exceed those of neighboring European countries. Yet despite intensive study, no one has fully explained why. The obvious culprit—genetics—has not provided a clear answer, leaving scientists searching for a deeper understanding of what makes these two populations different.

Scientists have identified roughly 80 genetic regions, plus specific variants in the HLA and INS genes, that increase Type 1 diabetes risk. But here's the puzzle: when researchers compare how common these variants are across European populations, the frequencies are remarkably similar. Finland and Sardinia should not stand out nearly as much as they do based on these known risk factors alone.

In fact, when researchers looked at HLA class II genes specifically, the math suggested Sardinia should have lower Type 1 diabetes rates than Finland—but the opposite is true, with Sardinia's rates roughly 40 percent higher. This mismatch between prediction and reality has frustrated researchers for years.

Recent advances in genetics have shifted how scientists think about complex diseases. Instead of focusing only on common genetic variants, researchers now recognize that thousands—even tens of thousands—of rare genetic variations can influence disease risk. Most of these rare variants are located in regulatory regions of DNA that control how genes work, and each one has an extremely small effect on its own.

This newer model, called the 'omnigenic model,' is now being applied to Type 1 diabetes. The idea is that while individual rare variants are invisible to large genetic studies, their combined effects across many biological pathways involved in Type 1 diabetes could be substantial. Importantly, because populations have different histories, they may have accumulated different collections of these rare variants.

Finland and Sardinia are both geographically isolated at the margins of Europe with distinctive histories. Over many generations, this isolation may have shaped which rare genetic variants became common in each population, potentially contributing to their higher Type 1 diabetes rates in ways that standard genetic studies have yet to fully capture.

This new perspective suggests that solving the Type 1 diabetes puzzle in Finland and Sardinia may require looking beyond the genetic variants scientists already know about. Instead, researchers may need to study the thousands of rare variants specific to each population, and how they interact across the multiple biological systems involved in Type 1 diabetes development. Understanding these populations better could ultimately provide insights into Type 1 diabetes risk more broadly.

Source: Genes. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.