Trichothiodystrophy (TTD) is a more heterogeneous disorder caused by defects involving the basal process of gene expression and, when caused by defects in the dual functional transcription-repair complex TFIIH, both GG- and TC-NER are affected as well (6), adding XP and CS symptoms to the TTD spectrum. This evidence concerns the gene GTF2H4 and trichothiodystrophy.