For many molecular studies, blood data are the most convenient source. But type 2 diabetes arises from a network of organs and cell types—for example, in adipose tissue, the liver, skeletal muscle, or the insulin-producing cells of the pancreas.

“Our analysis shows how incomplete it is to try to explain mechanisms using data from blood alone,” says Dr. Ozvan Bocher from Université de Bretagne Occidentale (France) and the Institute of Translational Genomics at Helmholtz Munich, first author of the publication. “Across seven diabetes-relevant tissues, we identified causal evidence for 676 genes—and at the same time found that a large proportion of these effects do not appear in blood.”