title: XRCC4 deficiency in human subjects causes a marked neurological phenotype but no overt immunodeficiency.
abstract: BACKGROUND
  Nonhomologous end-joining (NHEJ) is the major DNA double-strand break (DSB) repair mechanism in human cells. The final rejoining step requires DNA ligase IV (LIG4) together with the partner proteins X-ray repair cross-complementing protein 4 (XRCC4) and XRCC4-like factor. Patients with mutations in genes encoding LIG4, XRCC4-like factor, or the other NHEJ proteins DNA-dependent protein kinase catalytic subunit and Artemis are DSB repair defective and immunodeficient because of the requirement for NHEJ during V(D)J recombination.
  
  
  OBJECTIVE
  We found a patient displaying microcephaly and progressive ataxia but a normal immune response. We sought to determine pathogenic mutations and to describe the molecular pathogenesis of the patient.
  
  
  METHODS
  We performed next-generation exome sequencing. We evaluated the DSB repair activities and V(D)J recombination capacity of the patient's cells, as well as performing a standard blood immunologic characterization.
  
  
  RESULTS
  We identified causal mutations in the XRCC4 gene. The patient's cells are radiosensitive and display the most severe DSB repair defect we have encountered using patient-derived cell lines. In marked contrast, a V(D)J recombination plasmid assay revealed that the patient's cells did not display the junction abnormalities that are characteristic of other NHEJ-defective cell lines. The mutant protein can interact efficiently with LIG4 and functions normally in in vitro assays and when transiently expressed in vivo. However, the mutation makes the protein unstable, and it undergoes proteasome-mediated degradation.
  
  
  CONCLUSIONS
  Our findings reveal a novel separation of impact phenotype: there is a pronounced DSB repair defect and marked clinical neurological manifestation but no clinical immunodeficiency.
authors.affiliation: Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan; Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Chaowan
authors.initials: C
authors.lastname: Guo
authors.affiliation: Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan; Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Nakazawa
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: Lisa
authors.initials: L
authors.lastname: Woodbine
authors.affiliation: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Andrea
authors.initials: A
authors.lastname: Björkman
authors.affiliation: Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Mayuko
authors.initials: M
authors.lastname: Shimada
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: Heather
authors.initials: H
authors.lastname: Fawcett
authors.affiliation: Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan; Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Nan
authors.initials: N
authors.lastname: Jia
authors.affiliation: Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Course of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Kaname
authors.initials: K
authors.lastname: Ohyama
authors.affiliation: Department of Stem Cell Biology, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Tao-Sheng
authors.initials: TS
authors.lastname: Li
authors.affiliation: Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nagayama
authors.affiliation: Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Radiation Medical Sciences, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
authors.forename: Norisato
authors.initials: N
authors.lastname: Mitsutake
authors.affiliation: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Pan-Hammarström
authors.affiliation: Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Gennery
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Lehmann
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom. Electronic address: p.a.jeggo@sussex.ac.uk.
authors.forename: Penny A
authors.initials: PA
authors.lastname: Jeggo
authors.affiliation: Department of Genetics, Research Institute of Environmental Medicine (RIeM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan; Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan; Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, Japan. Electronic address: togi@riem.nagoya-u.ac.jp.
authors.forename: Tomoo
authors.initials: T
authors.lastname: Ogi
mesh_terms: D001259:Ataxia / Q000235:genetics* / Q000276:immunology; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000235:genetics* / Q000276:immunology; D008831:Microcephaly / Q000235:genetics* / Q000276:immunology; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D055550:Protein Stability; D011836:Radiation Tolerance / Q000235:genetics; D060152:V(D)J Recombination / Q000235:genetics; D055815:Young Adult
chemical_list: D004268:DNA-Binding Proteins; C000607893:LIG4 protein, human; C101467:XRCC4 protein, human; D011088:DNA Ligases; D000072481:DNA Ligase ATP
keywords: DNA double-strand break repair; XRCC4/LIG4; double-strand break repair deficiency; immunodeficiency; microcephaly; nonhomologous end-joining