XRCC1 is a molecular scaffold protein that assembles multi-protein complexes involved in DNA single-strand break repair1,2. Here we show that biallelic mutations in the human XRCC1 gene are associated with ocular motor apraxia, axonal neuropathy, and progressive cerebellar ataxia. Cells from a patient with mutations in XRCC1 exhibited not only reduced rates of single-strand break repair but also elevated levels of protein ADP-ribosylation. This latter phenotype is recapitulated in a related syndrome caused by mutations in the XRCC1 partner protein PNKP3,4,5 and implicates hyperactivation of poly(ADP-ribose) polymerase/s as a cause of cerebellar ataxia. Indeed, remarkably, genetic deletion of Parp1 rescued normal cerebellar ADP-ribose levels and reduced the loss of cerebellar neurons and ataxia in Xrcc1-defective mice, identifying a molecular mechanism by which endogenous single-strand breaks trigger neuropathology. Collectively, these data establish the importance of XRCC1 protein complexes for normal neurological function and identify PARP1 as a therapeutic target in DNA strand break repair-defective disease.

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This work was funded by MRC Programme Grants (MR/J006750/1 and MR/P010121/1) to K.W.C., a ‘Science without Borders’ postdoctoral fellowship (CAPES Foundation, Ministry of Education, Brazil, BEX9769-13-7) to N.H., and funding to G.Y. from Genome Canada, the Canadian Institutes of Health Research, the Ontario Genomics Institute, Ontario Research Fund, Genome Quebec, the Children’s Hospital of Eastern Ontario Foundation, and the Hospital for Sick Children. K.S. was funded by the BBSRC grant BB/K019015/1 and P.J.M. acknowledges the National Institutes of Health (NS-37956, CA-21765), the CCSG (P30 CA21765), and the American Lebanese and Syrian Associated Charities of St. Jude Children’s Research Hospital for support. We thank the patient and her family for their contribution to this study. This work was selected for study by the Care4Rare Canada (Enhanced Care for Rare Genetic Diseases in Canada) Consortium Gene Discovery Steering Committee (for committee members, see below). We thank D. Dyment for his advice and discussion. We thank S. van der Velde-Visser and J. Schuurs-Hoeijmakers for Epstein-Barr virus transformation of the patient’s and sibling’s LCLs. We also thank S. El-Khamisy and A. Ridley for preliminary analyses and assistance with the mouse work.

Author information

Author notes

    • Nicolas C. Hoch
    •  & Hana Hanzlikova

    These authors contributed equally to this work.


  1. Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9RH, UK

    • Nicolas C. Hoch
    • , Hana Hanzlikova
    • , Stuart L. Rulten
    • , Emilia Komulainen
    • , Limei Ju
    • , Peter Hornyak
    • , Zhihong Zeng
    • , William Gittens
    •  & Keith W. Caldecott
  2. CAPES Foundation, Ministry of Education of Brazil, Brasilia/DF 70040-020, Brazil

    • Nicolas C. Hoch
  3. Department of Human Genetics, McGill University and Genome Québec Innovation Centre, Montréal, Québec, H3A 0G4, Canada

    • Martine Tétreault
  4. Neuroscience, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK

    • Stephanie A. Rey
    •  & Kevin Staras
  5. Department of Clinical Genetics, Erasmus MC, PO Box 2040, 3000 CA, Rotterdam, the Netherlands

    • Grazia M. S. Mancini
  6. St. Jude Children’s Research Hospital, Memphis, Tennessee 38105, USA

    • Peter J. McKinnon
  7. Leibniz Institute for Age Research, Fritz Lipmann Institute, 1107745 Jena, Germany

    • Zhao-Qi Wang
  8. The Children’s Hospital of Eastern Ontario Research Institute, Ottawa, K1L 8H1, Canada

    • Justin D. Wagner
  9. Division of Clinical and Metabolic Genetics, and Division of Neurology, The Hospital for Sick Children, University of Toronto, Toronto, M5G 1X8, Canada

    • Grace Yoon
  10. The Children’s Hospital of Eastern Ontario Research Institute, Ottawa, Ontario K1L 8H1, Canada

    • Kym Boycott
    • , Alex MacKenzie
    • , Dennis Bulman
    •  & David Dyment
  11. Department of Human Genetics, McGill University and Genome Québec Innovation Centre, Montréal, Québec H3A 0G4, Canada

    • Jacek Majewski
  12. Program in Genetics and Genome Biology and the Centre for Computational Medicine, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada

    • Michael Brudno


  1. Care4Rare Canada Consortium


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H.H. generated gene-edited RPE-1 cell lines and designed and conducted the immunofluorescence, high-content imaging (Olympus ScanR), protein complementation, and double-strand break repair experiments. N.H. analysed XRCC1-patient cells by western blotting and RT-qPCR and designed and conducted sister chromatid exchange and comet assays. S.L.R., E.K., and L.J. designed and conducted mouse behaviour and histopathology experiments. S.R. and K.S. designed and conducted electrophysiology experiments. P.H. prepared recombinant XRCC1. Z.Z. generated CRISPR guide constructs. W.G. conducted preliminary CPT/ADP-ribose experiments. G.M.S.M. provided PNKP-patient fibroblasts. P.J.M. and Z.-Q.W. provided mouse models. G.Y. identified and oversaw genetic analysis of the patient, and J.W. and M.T. conducted exome analysis. K.W.C. conceived and managed the project, and wrote the manuscript with H.H. and N.H. All authors edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Grace Yoon or Keith W. Caldecott.

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