ERCC1 and xeroderma pigmentosum: Second, it was shown that reducing the factors participating in the prevention of R-loop formation or their resolution leads to the active transformation of these structures into DNA DSBs by the NER endonucleases XPF (ERCC1) and XPG (ERCC5), which are named after the rare autosomal recessive congenital syndrome xeroderma pigmentosum (XP) [91].