In non-obese diabetic (NOD) mice (a model of spontaneous type 1 diabetes), Treg cell numbers and Foxp3 expression decrease with the age of the animals [17], Treg function also declines with aging of the NOD mice [18], although there were also studies where decrease of Treg frequencies was not discovered [19, 20]. This evidence concerns the gene FOXP3 and type 1 diabetes mellitus.