For db/db mice, which develop increased hyperinsulinemia compared to DIO mice42 (Figs. 4c and 5b), GLP-1-dependent insulinotropic action (Fig. 5a, b) and glucose tolerance (Fig. 5c) were also restored, but required a higher dose of implanted C-STARDB6 cells (Fig. 5a–c). This evidence concerns the gene GCG and hyperinsulinism.