Hypomorphic PCNA mutation underlies a novel human DNA repair disorder. E. L. Baple1, H. Chambers2, H. E. Cross3, H. Fawcett4, Y. Nakazawa5,6, B. A. Chioza1, G. V. Harlalka1, S. Mansour7, A. Sreekantan-Nair1, M. A. Patton1, M. Muggenthaler1, P. Rich8, K. Wagner9, R. Coblentz9, C. K. Stein10, .J. I. Last11, A. M. R. Taylor11, A. P. Jackson12, T. Ogi5,6, A. R. Lehmann4, C. M. Green2,13, A. H. Crosby1 1) Medical Research, RILD Wellcome Wolfson Centre, University of Exeter, Exeter, Exeter, United Kingdom; 2) University of Cambridge, Cambridge, United Kingdom; 3) Department of Ophthalmology, University of Arizona College of Medicine, Tucson, Arizona, USA; 4) Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom; 5) Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; 6) Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan; 7) SW Thames Regional Genetics Service, St. Georges Healthcare NHS Trust, London, United Kingdom; 8) Department of Neuroradiology, St. Georges Hospital, London, United Kingdom; 9) Windows of Hope Genetic Study, Walnut Creek, Ohio, USA; 10) SUNY Upstate Medical University, Syracuse, New York, USA; 11) School of Cancer Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom; 12) MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom; 13) Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.

   A number of human disorders, including Cockayne syndrome, UV-sensitive syndrome, xeroderma pigmentosum and trichothiodystrophy, result from the mutation of genes encoding molecules important for nucleotide excision repair. We describe a novel DNA repair disorder identified amongst the Ohio Amish community. The cardinal clinical features of this disorder include postnatal growth retardation, hearing loss, premature aging, telangiectasia, neurodegeneration, photophobia, photosensitivity and predisposition to sun induced malignancy. Assuming autosomal recessive inheritance and that a founder mutation was responsible for the condition, we used a combination of autozygosity mapping and linkage analysis to identify the underlying molecular cause. Our genetic investigation identified a homozygous missense (p.Ser228Ile) sequence alteration of the proliferating cell nuclear antigen (PCNA) associated with the disease phenotype. PCNA is a highly conserved sliding clamp protein essential for DNA replication and repair. Due to this fundamental role, mutations in PCNA that profoundly impair protein function would be incompatible with life. Interestingly, while the p.Ser228Ile alteration appears to have no effect on protein levels or DNA replication, patient cells exhibit significant abnormalities in response to UV irradiation displaying substantial reductions in both UV survival and RNA synthesis recovery. Importantly the defective transcriptional responses to UV light are completely rescued by wild type PCNA molecule, demonstrating that the mutation is causative. Furthermore we show that the p.Ser228Ile change profoundly alters the capacity of PCNA to interact with a specific subset of partner proteins. These proteins include XPG and the DNA metabolism enzymes Flap endonuclease 1 and DNA Ligase 1, molecules fundamental to genomic integrity, thus providing an explanation for the separation of function effect. Taken together our findings detail the first mutation of PCNA in humans, associated with a unique neurodegenerative disease displaying clinical and molecular features common to other DNA repair disorders, which we show to be attributable to a hypomorphic amino acid alteration. Further investigation of the altered biological processes underlying this syndrome should provide valuable insight into the neurodegenerative disease mechanisms involved in DNA damage tolerance and repair disorders.

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