Trichothiodystrophy: recent advances.
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A wide spectrum of clinical signs and symptoms has been reported in association with trichothiodystrophy (TTD). At the one end of the spectrum, patients show only the hair defect. At the other, there is a complex association of hair defect, nail dystrophy, mental retardation, growth retardation and ichthyosis. Two types of ichthyosis have been identified: congenital lamellar ichthyosis (Tay's syndrome) and acquired ichthyosis vulgaris. This form of ichthyosis has been reported in association with severe photosensitivity. In recent years, two aspects of TTD have been investigated in greater detail: the biochemical composition of the hair shaft and the biological aspects of the photosensitivity. Amino acid composition and distribution patterns of proteins in two-dimensional gel electrophoresis may vary from case to case indicating quantitative and qualitative variations amongst high-sulfur proteins (HSP) in TTD hairs. Quantitative changes of qualitatively normal HSP have been reported in TTD-variants. There is no simple correlation between abnormal hair composition and involvement of scalp hairs, or impairment of other systems. A cellular defect similar to xeroderma pigmentosum (XP) group D has been identified in patients with documented photosensitivity. Contrary to authentic XP-D, the latter do not show increased frequency or early development of skin cancer. Furthermore, similar or different cellular responses to UV challenge in vitro have been reported in a limited number of TTD patients without abnormal light sensitivity. Hence, even though defective DNA repair in cultured cells appears to be similar in TTD and XP-D phenotype, differences in the clinical phenotype suggest that genes are affected differently in the two cases. The basic gene defect(s) responsible for TTD, photosensitivity, and other biochemical deficiencies in this complex association of disturbed neuroectoderma-derived tissues remains to be elucidated.