Preprint: Loss of XPD helicase activity traps DNA repair complex TFIIH in a futile cycle, causing severe Cockayne syndrome features
A bioRxiv preprint shows that specific XPD mutations associated with Cockayne syndrome — rather than the milder xeroderma pigmentosum — prevent proper damage removal by locking the nucleotide excision repair machinery in persistent, misdirected DNA incision.
A preprint deposited to bioRxiv on 11 September 2026 addresses a longstanding puzzle in DNA repair biology: why certain mutations in XPD, a helicase subunit of the ten-component TFIIH complex, cause severe Cockayne syndrome (CS) features — including progressive neurodegeneration — whilst most XPD mutations cause the comparatively milder condition xeroderma pigmentosum.
Nucleotide excision repair (NER) removes helix-distorting DNA lesions. TFIIH's XPB and XPD subunits unwind DNA to allow damage verification and subsequent endonucleolytic incision. The authors report that when XPD helicase activity is abolished by CS-associated mutations, TFIIH becomes trapped in a futile repair cycle: DNA is incised at incorrect positions, generating persistent DNA strand breaks without actually removing the damage. This toxic intermediate, rather than failed repair per se, is proposed to underlie the severe neurological phenotype.
The mechanistic model has potential implications for understanding other NER-related disorders and may inform thinking about therapeutic strategies for Cockayne syndrome, though the preprint does not propose clinical interventions. The work has not yet been peer-reviewed. It is primarily relevant to researchers in DNA repair, rare disease, and neurogenetics.
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Primary sourcePreprint bioRxiv (Cold Spring Harbor Laboratory) · 2026-09-11Helicase-deficient TFIIH causes severe disease features via persistent DNA excision without damage removal