In this latter test, we could reveal a significant increase of blood glucose level in tcf7l2exI/+ heterozygous animals compared with tcf7l2+/+ controls (Fig. 1A) indicating that in zebrafish, under specific nutritional contexts, partial loss of tcf7l2 activity can lead to an increase of blood glucose, a condition that somehow mimics T2D. Here, TCF7L2 is linked to type 2 diabetes mellitus.