For example, previous studies have demonstrated the simultaneous deleterious effects of intercrossing xeroderma pigmentosum (XP) (Xpa−/− or Xpc−/−) mice with CS (Csa−/−, Csb−/−, XpdXPCS) mice, which results in double mutants with very short life spans and dramatic progeroid features (Murai et al., 2001; Andressoo et al., 2006; van der Pluijm et al., 2007). The gene discussed is XPA; the disease is xeroderma pigmentosum.