If the adducts occurred at the active transcription site, the lesions would be recognised by RNA polymerase II followed by stalling of transcription elongation and recruitment of several proteins, including the Cockayne syndrome proteins CSA and CSB, the TFIIH complex with XPB and XPD helicases that will unwind the DNA double helix around the lesion. This evidence concerns the gene ERCC3 and Down syndrome.