These data suggest that a higher thymic output of CD4+Foxp3− T cells likely contributes, at least in part, to the low percentages of peripheral CD4+Foxp3+ Tregs (i.e., decreased Treg : Teff ratio) found in NOD mice in our colony, thus leading to an imbalance between Tregs and Teffs that may contribute to the development of the high incidence of full-blown diabetes. The gene discussed is FOXP3; the disease is diabetes mellitus.