Mutations in the NHEJ component XRCC4 cause primordial dwarfism

Am J Hum Genet. 2015 Mar 5;96(3):412-24. doi: 10.1016/j.ajhg.2015.01.013.

Jennie E Murray ¹, Mirjam van der Burg ², Hanna IJspeert ², Paula Carroll ¹, Qian Wu ³, Takashi Ochi ³, Andrea Leitch ¹, Edward S Miller ⁴, Boris Kysela ⁵, Alireza Jawad ², Armand Bottani ⁶, Francesco Brancati ⁷, Marco Cappa ⁸, Valerie Cormier-Daire ⁹, Charu Deshpande ¹⁰, Eissa A Faqeih ¹¹, Gail E Graham ¹², Emmanuelle Ranza ⁶, Tom L Blundell ³, Andrew P Jackson ¹³, Grant S Stewart ¹⁴, Louise S Bicknell ¹

Affiliations

1 MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK.
2 Department of Immunology, Erasmus MC, University Medical Center Rotterdam, 3015 Rotterdam, the Netherlands.
3 Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK.
4 School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, UK.
5 School of Clinical and Experimental Medicine, University of Birmingham, Birmingham B15 2TT, UK.
6 Department of Genetic Medicine, University Hospitals of Geneva, 1205 Geneva, Switzerland.
7 Department of Medical, Oral and Biotechnological Sciences, Gabriele D'Annunzio University of Chieti-Pescara, 66100 Chieti, Italy.
8 Endocrinology and Diabetes Unit, IRCCS Bambino Gesù Children's Hospital, 00165 Rome, Italy.
9 Department of Genetics, INSERM UMR 1163, Université Paris Descartes-Sorbonne Paris Cité, Institut Imagine, Hôpital Necker Enfants Malades, Assistance Publique-Hôpitaux de Paris, Paris 75015, France.
10 Department of Genetics, Guy's Hospital, Guy's and St Thomas' NHS Foundation Trust, London SE1 9RT, UK.
11 Children's Specialist Hospital, King Fahad Medical City, Riyadh 11525, Saudi Arabia.
12 Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, ON K1H 8L1, Canada.
13 MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK. Electronic address: andrew.jackson@igmm.ed.ac.uk.
14 School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, UK. Electronic address: g.s.stewart@bham.ac.uk.

PMID: 25728776 DOI: 10.1016/j.ajhg.2015.01.013

Abstract

Non-homologous end joining (NHEJ) is a key cellular process ensuring genome integrity. Mutations in several components of the NHEJ pathway have been identified, often associated with severe combined immunodeficiency (SCID), consistent with the requirement for NHEJ during V(D)J recombination to ensure diversity of the adaptive immune system. In contrast, we have recently found that biallelic mutations in LIG4 are a common cause of microcephalic primordial dwarfism (MPD), a phenotype characterized by prenatal-onset extreme global growth failure. Here we provide definitive molecular genetic evidence supported by biochemical, cellular, and immunological data for mutations in XRCC4, encoding the obligate binding partner of LIG4, causing MPD. We report the identification of biallelic mutations in XRCC4 in five families. Biochemical and cellular studies demonstrate that these alterations substantially decrease XRCC4 protein levels leading to reduced cellular Ligase IV activity. Consequently, NHEJ-dependent repair of ionizing-radiation-induced DNA double-strand breaks is compromised in XRCC4 cells. Similarly, immunoglobulin junctional diversification is impaired in cells. However, immunoglobulin levels are normal, and individuals lack overt signs of immunodeficiency. Additionally, in contrast to individuals with LIG4 mutations, pancytopenia leading to bone marrow failure has not been observed. Hence, alterations that alter different NHEJ proteins give rise to a phenotypic spectrum, from SCID to extreme growth failure, with deficiencies in certain key components of this repair pathway predominantly exhibiting growth deficits, reflecting differential developmental requirements for NHEJ proteins to support growth and immune maturation.

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