Abnormal XPD-induced nuclear receptor transactivation in DNA repair disorders: trichothiodystrophy and xeroderma...

Area of Science:

• Molecular biology
• Genetics
• Biochemistry

Background:

• XPD (ERCC2) is a DNA helicase crucial for DNA repair and transcription.
• XPD mutations lead to distinct clinical syndromes like trichothiodystrophy (TTD) and xeroderma pigmentosum (XP).
• These syndromes present with varied phenotypes, including developmental issues, skin cancer predisposition, and hair abnormalities.

Purpose of the Study:

• To investigate the clinical variability and molecular mechanisms in compound heterozygous XPD mutation patients.
• To assess the impact of XPD mutations on transcription factor IIH (TFIIH)-dependent nuclear receptor function.
• To correlate specific XPD mutations with distinct clinical phenotypes and functional assays.

Main Methods:

• Clinical evaluation of nine compound heterozygous XPD patients with TTD, XP, or XP/TTD phenotypes.
• Analysis of XPD mutations and their association with clinical presentations.
• Functional studies of TFIIH-dependent transactivation by vitamin D receptor (VDR) and thyroid receptor in patient-derived cells.

Main Results:

• Nine patients with compound heterozygous XPD mutations presented with diverse phenotypes: four TTD, three XP, and two XP/TTD.
• Vitamin D receptor (VDR) transactivation, measured by CYP24 and osteopontin stimulation, was abnormal in most patients but not strictly correlated with specific clinical phenotypes.
• Thyroid receptor transactivation showed no significant differences from normal controls.

Conclusions:

• XPD mutations in compound heterozygotes can result in a spectrum of TTD, XP, and XP/TTD phenotypes.
• Abnormal VDR stimulation is a common finding in patients with XPD mutations, irrespective of their specific clinical presentation.
• These findings highlight the complex genotype-phenotype correlations and functional consequences of XPD mutations.