ERCC4 and xeroderma pigmentosum: In this study we investigated LCL cells from two NER knockout patients suffering from Xeroderma pigmentosum (XPA -/- (homozygous: XPA: NM_000380.4:c.368del, NP_000371.1: p.Leu123fs) and (XPF -/- (ERCC4: NM_0052236.3:c1811+1G>A)/NM_005236.3: c.2395C>T, NP_005227.1: p.Arg799Trp)) as positive controls for establishing maximum UV sensitivity.