Chaowan Guo1, Yuka Nakazawa1, Lisa Woodbine2, Andrea Björkman3, Mayuko Shimada4, Heather Fawcett2, Nan Jia1, Kaname Ohyama5, Tao-Sheng Li6, Yuji Nagayama7, Norisato Mitsutake8, Qiang Pan-Hammarström3, Andrew R Gennery9, Alan R Lehmann2, Penny A Jeggo10, Tomoo Ogi11. 1. 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. 2. Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom. 3. Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden. 4. Nagasaki University Research Centre for Genomic Instability and Carcinogenesis (NRGIC), Nagasaki, Japan; Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan. 5. 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. 6. Department of Stem Cell Biology, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan. 7. Department of Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan. 8. 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. 9. Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom. 10. Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, United Kingdom. Electronic address: p.a.jeggo@sussex.ac.uk. 11. 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.
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. CONCLUSION: 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.
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. CONCLUSION: 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: Jerome Irianto; Yuntao Xia; Charlotte R Pfeifer; Avathamsa Athirasala; Jiazheng Ji; Cory Alvey; Manu Tewari; Rachel R Bennett; Shane M Harding; Andrea J Liu; Roger A Greenberg; Dennis E Discher Journal: Curr Biol Date: 2016-12-15 Impact factor: 10.834
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