First, the importance of the C-terminus to XPD function is underscored by the fact that a deletion mutation resulting in the loss of the final 17 C-terminal amino acids, including residue 751, is known to cause the clinical phenotype of trichothiodystrophy, which is characterized by deficiencies in NER[9]; curiously, trichothiodystrophy is not generally associated with an increased risk of cancer, although this may be at least partially attributable to the fact that patients tend to die young of other causes. This evidence concerns the gene ERCC2 and cancer.