HNF1A and maturity-onset diabetes of the young type 3: Here, we leveraged upon MODY3 patient-derived hiPSCs to reveal the impact of a patient-specific heterozygous HNF1A+/H126D mutation on essential glucose transporter GLUT2 expression and glucose uptake function in pancreatic β cells, thereby affecting the insulin secretory function of pancreatic β cells in humans.