Tricothiodystrophy, Non Photosensitive 1 (TTDN1)

TTDN1 protein shares 92% identity with the mouse homolog. Northern blot analysis of several human tissues detected a 1.3-kb transcript expressed at highest levels in liver and kidney. Intermediate expression was detected in skeletal muscle, pancreas, heart, and placenta, and low expression was detected in brain and lung. TTDN1 is not essential for cell proliferation and viability. The severity of the clinical features did not correlate with the type of mutation, indicating that other factors besides TTDN1 mutations influence the severity of the disorder. Since only a small proportion of the analyzed cases were mutated in TTDN1, the nonphotosensitive form of TTD is genetically heterogeneous. Mutations in TTDN1 do not affect the response to ultraviolet (UV) light or the steady state level of the repair/transcription factor IIH (TFIIH).