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. The gene discussed is GTF2H5; the disease is Cowden syndrome 1.