Cdk4 knockout mice display significantly reduced body size, impaired fertility, and insulin-deficient diabetes due to abnormal postnatal islet cell development (Rane et al. 1999; Tsutsui et al. 1999; Moons et al. 2002; Martin et al. 2003; Mettus and Rane 2003). The gene discussed is CDK4; the disease is diabetes mellitus.