Yet, in human or mouse cells, Polη conducts error-free TLS through CPDs (Yoon et al., 2009; Yoon et al., 2019b), and mutational inactivation of Polη results in the skin cancer-prone syndrome xeroderma pigmentosum variant (XPV; Johnson et al., 1999a; Masutani et al., 1999). The gene discussed is POLH; the disease is Xeroderma pigmentosum variant.