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J Med Genet doi:10.1136/jmg.2009.068866
  • Original article

A novel splice variant of the DNA-PKcs gene is associated with clinical and cellular radiosensitvity in a xeroderma pigmentosum patient.

Open Access
  1. Fatemeh Abbaszadeh1,
  2. Peter H Clingen2,
  3. Colin F Arlett3,
  4. Piers N Plowman4,
  5. Emma C Bourton5,
  6. Matthew Themis5,
  7. Evgeny M Makarov5,
  8. Robert F Newbold5,
  9. Michael H Green6,
  10. Christopher N Parris5,*
  1. 1 Institute of Cancer Researh, Royal Marsden Hospital, Surrey, United Kingdom;
  2. 2 University College London Cancer Institute, United Kingdom;
  3. 3 University of Sussex, United Kingdom;
  4. 4 Bart's and the London Hospital, United Kingdom;
  5. 5 Brunel University, United Kingdom;
  6. 6 Brighton University, United Kingdom
  1. Correspondence to: Christopher Noel Parris, Biosciences, Brunel University, Brunel University,, School of Health Sciences and Social Care, Division of Biosciences, Uxbridge, UB8 3PH, United Kingdom; christopher.parris{at}brunel.ac.uk
  • Received 22 May 2009
  • Accepted 10 September 2009
  • Published Online First 24 September 2009

Abstract

Background: Radiotherapy-induced DNA double strand breaks (DSB) are critical cytotoxic lesions. Inherited defects in DSB DNA repair pathways lead to hypersensitivity to ionising radiation, immunodeficiency and increased cancer incidence. A patient with xeroderma pigmentosum complementation group C, with a scalp angiosarcoma exhibited dramatic clinical radiosensitivity following radiotherapy, resulting in death. A fibroblast cell line from non-affected skin (XP14BRneo17) was hypersensitive to ionising radiation and defective in DNA double strand break repair.

Aim: To determine the genetic defect causing cellular radiation hypersensitivity in XP14BRneo17 cells.

Methods: Functional genetic complementation whereby copies of human chromosomes containing genes involved in DNA DSB repair (chromosomes 2, 5, 8 10, 13 and 22) were individually transferred to XP14BRneo17 cells in an attempt to correct the radiation hypersensitivity. Clonogenic survival assays and γ-H2AX immunofluorescence were conducted to measure radiation sensitivity and repair of DNA DSBs. DNA sequencing of defective DNA repair genes was performed.

Results: Transfer of chromosome 8 (location of DNA-PKcs gene), and transfection of a mammalian expression construct containing the DNA-PKcs cDNA restored normal ionising radiation sensitivity and repair of DNA DSBs in XP14BRneo17 cells. DNA sequencing of the DNA-PKcs coding region revealed a 249 bp deletion (between base pairs 3656-3904) encompassing exon 31 of the gene.

Conclusion: We provide evidence of a novel splice variant of the DNA-PKcs gene associated with radiosensitivity in a xeroderma pigmentosum patient and report the first double mutant in distinct DNA repair pathways being consistent with viability.

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