Michel Renouil, Cecile Dalloz, Renier Vélez-Cruz, Vincent Laugel, Alain Sarasin, Alain Fourmaintraux, Hélène Dollfus, Isabelle Desguerre, Valérie Cormier-Daire, Anne Stary, Jean-Marc Egly, Etude des relations instabilité génétique et cancer ( ERIGC ), Centre National de la Recherche Scientifique ( CNRS ), Handicaps génétiques de l'enfant ( Inserm U393 ), Université Paris Descartes - Paris 5 ( UPD5 ) -Institut National de la Santé et de la Recherche Médicale ( INSERM ), Institut de génétique et biologie moléculaire et cellulaire ( IGBMC ), Université Louis Pasteur - Strasbourg I-Institut National de la Santé et de la Recherche Médicale ( INSERM ) -Centre National de la Recherche Scientifique ( CNRS ), Génomes et cancer ( GC (FRE2939) ), Université Paris-Sud - Paris 11 ( UP11 ) -Institut Gustave Roussy ( IGR ) -Centre National de la Recherche Scientifique ( CNRS ), Service de génétique médicale, CHU Strasbourg-Hôpital de Hautepierre [Strasbourg], Etude des relations instabilité génétique et cancer (ERIGC), Centre National de la Recherche Scientifique (CNRS), Handicaps génétiques de l'enfant (Inserm U393), Institut National de la Santé et de la Recherche Médicale (INSERM)-Université Paris Descartes - Paris 5 (UPD5), Institut de génétique et biologie moléculaire et cellulaire (IGBMC), Université Louis Pasteur - Strasbourg I-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Génomes et cancer (GC (FRE2939)), Université Paris-Sud - Paris 11 (UP11)-Institut Gustave Roussy (IGR)-Centre National de la Recherche Scientifique (CNRS), and Université Paris Descartes - Paris 5 (UPD5)-Institut National de la Santé et de la Recherche Médicale (INSERM)
Cockayne syndrome is an autosomal recessive neurodegenerative disorder characterized by a specific defect in the repair of UV-induced DNA lesions. Most cases of Cockayne syndrome are caused by mutations in the CSB gene but the pathophysiological mechanisms are poorly understood. We report the clinical and molecular data of two severely affected Cockayne patients with undetectable CSB protein and mRNA. Both patients showed severe growth failure, microcephaly, mental retardation, congenital cataracts, retinal pigmentary degeneration, photosensitivity and died at the ages of 6 and 8 years. UV irradiation assays demonstrated that both patients had the classical DNA repair defect. Genomic DNA sequencing of the CSB gene showed a homozygous deletion involving non-coding exon 1 and upstream regulatory sequences, but none of the coding exons. Functional complementation using a wild-type CSB expression plasmid fully corrected the DNA repair defect in transfected fibroblasts. Horibata et al recently proposed that all type of CSB mutations result in a defect in UV damage repair that is responsible for the photosensitivity observed in the syndrome, but that only truncated CSB polypeptides generated by nonsense mutations have some additional inhibitory functions in transcription or in oxidative damage repair, which are necessary to lead to the other features of the phenotype. Our patients do not fit the proposed paradigm and new hypotheses are required to account for the pathophysiology of Cockayne syndrome, at the crossroads between DNA repair and transcription.