Interestingly, the deletion of Mafb in diet-induced obese Mafa-deficient mice shows impaired islet formation, a decreased number of β-cells and diabetes, which is more advanced than those in diet-induced obese Mafa-deficient mice, suggesting that MAFB may have a role in the maintenance of adult β-cells with a reduced expression of MAFA [74], although another study demonstrated that MAFB alone was unable to rescue the β-cell defects in mice lacking Mafa [75]. This evidence concerns the gene MAFA and diabetes mellitus.