Trichothiodystrophy describes a group of diseases characterized by short, brittle, low-sulfur hair. The reason is a disturbed synthesis of sulfur-containing keratins. The syndromes of the various TTD syndromes range from retarded growth, reduced ability to congenital ichthyosis and nail anomalies.

About half of those affected suffer from photosensitivity caused by defects in the excision repair of UV-damaged DNA. In patients with photosensitivity, mutations in the XPD / ERCC2 gene are the most common cause of the disease. Mutations in the XPB gene trigger the remaining cases.

The different associations lead to the distinction in six different disease variants (BIDS, IBIDS, PIBIDS, SIBIDS, ONMR, and Pollit syndrome).