A heterogeneous group disorders characterized by short, brittle hair with low-sulfur content (due to an abnormal synthesis of the sulfur containing keratins). The abnormalities are usually obvious at birth, with variable clinical expression. Trichothiodystrophy is an autosomal recessive disorder. In the photosensitive group 95% have mutations within the XPD (ERCC2) gene (localized to 19q13.2-q13.3). The remaining cases are caused by mutations within the XPB gene. So far, no gene has been isolated for the nonphotosensitive group. The variants of Trichothiodystrophy depending on their different associations are: BIDS syndrome, IBIDS syndrome, PIBIDS syndrome, Sabinas syndrome, SIBIDS syndrome, Itin syndrome and Pollitt syndrome.