UBD and type 1 diabetes mellitus: These results provide unique insight into the pathogenesis of T1D because, in the rat, two obligate susceptibility genes (Vβ13 and RT1B/Du), one strong resistance gene (Ubash3a), and one penetrance-enhancing gene (Ubd) have been identified and incorporated into a plausible, granular disease model, something not yet achieved in studies of human T1D.