A P53-independent role of murine P19Arf was demonstrated in a P19Arf−/− mouse that was crossed into a double Tp53−/−; Mdm2−/− background, which also increased tumor susceptibility, and subsequent reintroduction of P19Arf into these triple knockout mice resulted G1 cell cycle arrest [299,300]. The gene discussed is TP53; the disease is neoplasm.