Symptoms Of Cockayne Syndrome Research Articles

Whole exome sequencing identifies a novel variant causing cockayne syndrome type I in a consanguineous Pakistani family

Background Cockayne syndrome (CS) is a rare neurodegenerative disorder characterized by impaired neurological functions, cachectic dwarfism, microcephaly and photosensitivity. Complementation assays identify two groups of this disorder, CS type I (CSA) and CS type II (CSB), caused by mutations in ERCC8 and ERCC6, respectively. Objectives This study aimed to investigate the genetic basis of a consanguineous Pakistani family with three affected individuals presenting with typical clinical symptoms of CS. Methods We employed whole exome sequencing of the proband and then Sanger sequenced all the family members to confirm its segregation in the family. Different bioinformatics tools were used to predict pathogenicity of this variant. Results Variants were filtered according to the pedigree structure. We identified a novel homozygous variant (c.202A>T; p.Ile68Phe) in ERCC8 gene in the proband. The variant was found to segregate in the family. Conclusions These findings add to the genetic heterogeneity of ERCC8 and expands the mutation spectrum. Also, identification of this variant can facilitate prenatal diagnosis/genetic counselling set ups in Pakistan where this disease largely remains undiagnosed.

Neurovascular dysfunction and neuroinflammation in a Cockayne syndrome mouse model.

Cockayne syndrome (CS) is a rare, autosomal genetic disorder characterized by premature aging-like features, such as cachectic dwarfism, retinal atrophy, and progressive neurodegeneration. The molecular defect in CS lies in genes associated with the transcription-coupled branch of the nucleotide excision DNA repair (NER) pathway, though it is not yet clear how DNA repair deficiency leads to the multiorgan dysfunction symptoms of CS. In this work, we used a mouse model of severe CS with complete loss of NER (Csa−/−/Xpa−/−), which recapitulates several CS-related phenotypes, resulting in premature death of these mice at approximately 20 weeks of age. Although this CS model exhibits a severe progeroid phenotype, we found no evidence of in vitro endothelial cell dysfunction, as assessed by measuring population doubling time, migration capacity, and ICAM-1 expression. Furthermore, aortas from CX mice did not exhibit early senescence nor reduced angiogenesis capacity. Despite these observations, CX mice presented blood brain barrier disruption and increased senescence of brain endothelial cells. This was accompanied by an upregulation of inflammatory markers in the brains of CX mice, such as ICAM-1, TNFα, p-p65, and glial cell activation. Inhibition of neovascularization did not exacerbate neither astro- nor microgliosis, suggesting that the pro-inflammatory phenotype is independent of the neurovascular dysfunction present in CX mice. These findings have implications for the etiology of this disease and could contribute to the study of novel therapeutic targets for treating Cockayne syndrome patients.

Cockayne syndrome pathogenesis: Lessons from mouse models

Cockayne syndrome (CS) is a rare multisystem disorder characterized by cachectic dwarfism, nervous system abnormalities and features of premature aging. CS symptoms are associated with mutations in 5 genes, CSA, CSB, XPB, XPD and XPG encoding for proteins involved in the transcription-coupled subpathway of nucleotide excision DNA repair (NER). Mutant mice have been generated for all CS-associated genes and provide tools to examine how the cellular defects translate into CS symptoms. Mice deficient for Csa or Csb genetically mimic CS in man, and develop mild CS symptoms including reduced fat tissue, photoreceptor cell loss, and mild, but characteristic, nervous system pathology. These mild CS models are converted into severe CS models with short life span, progressive nervous system degeneration and cachectic dwarfism after simultaneous complete inactivation of global genome NER. A spectrum of mild-to-severe CS-like symptoms occurs in Xpb, Xpd, and Xpg mice that genetically mimic patients with a disorder that combines CS symptoms with another NER syndrome, xeroderma pigmentosum. In conclusion, CS mouse models mice develop a range of CS phenotypes and open promising perspectives for testing interventional approaches.

Mitochondrial CSA and CSB: Protein interactions and protection from ageing associated DNA mutations

Cockayne syndrome (CS) is a rare autosomal recessive disease with progeroid symptoms, which is caused mainly by mutations in the CS genes CSA and CSB. Although the relevance of mitochondria in the aging process is known for several decades, research focused primarily on the role of the CS proteins in the nucleus. Recently, however, mitochondrial contribution to aging-associated symptoms of CS has been described. Inside mitochondria, CS proteins have roles, which partially differ from their nuclear functions. Up to now it is known that mitochondrial CS proteins are associated with base excision repair (BER) and transcription of mitochondrial DNA. However, it has been hypothesized that these are not the only functions of mitochondrial CS proteins as the occurrence of mutations like the common deletion are in need of separate explanations.

QS148. Associated Malignancies With Cockayne Syndrome. A Case Report of One Family and Review of The Literature

Introduction: Cockayne syndrome is a rare autosomal recessive genetic disorder. Patients with this disorder exhibit premature aging, cachetic dwarfism, lack of subcutaneous fat, neurological alterations, light insensitivity, and failure to thrive. The syndrome results from proteins that are defective in DNA repair and transcription. As the DNA damage accumulates, it can lead to malfunctioning cells or cell death, and the signs and symptoms of Cockayne syndrome. The aim of this review is to present a mother, brother and sister with the Cockayne Syndrome, to investigate the genetic disorder’s association with neoplasms, and discuss the implications of this association. Patients: Patient number one is a 34 year-old, 32 pound female with Cockayne syndrome. At the age of 25, she was admitted to the hospital with bloody stools and a palpable abdominal mass. Colonoscopy demonstrated a large polypoid, splenic flexure mass; a biopsy showed adenocarcinoma. She underwent definitive treatment for a Stage III, moderately to poorly differentiated adenocarcinoma. About one year later a routine screening CT scan of the abdomen and pelvis identified a 6 cm right hepatic mass; a biopsy established that it was a metastasis of colonic origin and a subsequent right hepatic lobectomy was performed. There has been no evidence of recurrence to date. Patient number two is 62 years old, has Cockayne syndrome, and is the mother of patient number one. She presented with a non-tender abdominal mass. CT scan of the abdomen and pelvis demonstrated a 15 cm abdomino-pelvic mass arising from the left ovary. A left salpingo-oophorectomy and small bowel resection was performed. Final pathology showed a Stage A adenocarcinoma of the left ovary. She has had no further diagnosed malignancies since. Patient number three, the 36 year-old brother of patient number one, also has Cockayne syndrome. He presented with a 4 cm fungating mass on his left ankle that was excised. The final pathology report showed a benign vascular neoplasm. No other neoplasms have been diagnosed in this patient. Conclusion: Cockayne syndrome is characterized by growth failure and multisystem progressive degeneration. Although the syndrome arises from a deficiency in DNA repair, neoplasms, are not often reported in association with this syndrome. Interestingly, all three individuals in a family afflicted with Cockayne syndrome we were following at our community hospital were diagnosed with a neoplasm. We report and describe Cockayne syndrome in this Italian immigrant family, along with their associated neoplasms as a unique cluster that has never before been described.

Restoring DNA repair capacity of cells from three distinct diseases by XPD gene-recombinant adenovirus

The nucleotide excision repair (NER) is one of the major human DNA repair pathways. Defects in one of the proteins that act in this system result in three distinct autosomal recessive syndromes: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). TFIIH is a nine-protein complex essential for NER activity, initiation of RNA polymerase II transcription and with a possible role in cell cycle regulation. XPD is part of the TFIIH complex and has a helicase function, unwinding the DNA in the 5' --> 3' direction. Mutations in the XPD gene are found in XP, TTD and XP/CS patients, the latter exhibiting both XP and CS symptoms. Correction of DNA repair defects of these cells by transducing the complementing wild-type gene is one potential strategy for helping these patients. Over the last years, adenovirus vectors have been largely used in gene delivering because of their efficient transduction, high titer, and stability. In this work, we present the construction of a recombinant adenovirus carrying the XPD gene, which is coexpressed with the EGFP reporter gene by an IRES sequence, making it easier to follow cell infection. Infection by this recombinant adenovirus grants full correction of SV40-transformed and primary skin fibroblasts obtained from XP-D, TTD and XP/CS patients.

Severe growth retardation and short life span of double-mutant mice lacking Xpa and exon 15 of Xpg

In addition to xeroderma pigmentosum (XP), mutations in the human XPG gene cause an early onset of Cockayne syndrome (CS) in some patients (XP-G/CS) with characteristics, such as growth retardation and a short life span. In the previous studies, we generated four Xpg mutant mice with two different C-terminal truncations, null, or a base substitution mutation to identify the protein region that causes the onset of CS, and found that the CS-causing mutations, null or a deletion of the last 360 amino acids, completely inhibited the NER activity of mouse XPG (Xpg), but the non-CS-causing mutations, XpgD811A (base substitution that eliminates the nuclease activity of Xpg) or XpgΔex15 (deletion of the exon 15 corresponding to the last 183 amino acids), resulted in the retention of residual NER activity. To understand why mutations that completely eliminate the NER activity of Xpg cause CS but those that abolish the nuclease activity without totally eliminating the NER activity of Xpg do not result in CS, we made a series of Xpg mutant mice with Xpa-null mutant allele and found that mice with the non-CS-causing deletion mutation ( XpgΔex15) exhibited the CS phenotype when XPA was also absent but the base substitution mutation ( XpgD811A) that eliminated the Xpg nuclease activity did not. These results indicate that Xpg has a second function, beside NER, and that the disruption of this second function (deletion of the last 183 amino acids) when combined with an NER defect causes CS. When we compared amino acid sequences corresponding to the exon 15 of Xpg, a significant homology was conserved among vertebrates, but not in Drosophila and Saccharomyces cerevisiae. These observations suggest that the second function of XPG may be conserved only in vertebrates and CS symptoms may occur in its absence.

Cerebro-Oculo-Facio-Skeletal Syndrome with a Nucleotide Excision–Repair Defect and a Mutated XPD Gene, with Prenatal Diagnosis in a Triplet Pregnancy

Cerebro-oculo-facio-skeletal (COFS) syndrome is a recessively inherited rapidly progressive neurologic disorder leading to brain atrophy, with calcifications, cataracts, microcornea, optic atrophy, progressive joint contractures, and growth failure. Cockayne syndrome (CS) is a recessively inherited neurodegenerative disorder characterized by low to normal birth weight, growth failure, brain dysmyelination with calcium deposits, cutaneous photosensitivity, pigmentary retinopathy and/or cataracts, and sensorineural hearing loss. Cultured CS cells are hypersensitive to UV radiation, because of impaired nucleotide-excision repair (NER) of UV-induced damage in actively transcribed DNA, whereas global genome NER is unaffected. The abnormalities in CS are caused by mutated CSA or CSB genes. Another class of patients with CS symptoms have mutations in the XPB, XPD, or XPG genes, which result in UV hypersensitivity as well as defective global NER; such patients may concurrently have clinical features of another NER syndrome, xeroderma pigmentosum (XP). Clinically observed similarities between COFS syndrome and CS have been followed by discoveries of cases of COFS syndrome that are associated with mutations in the XPG and CSB genes. Here we report the first involvement of the XPD gene in a new case of UV-sensitive COFS syndrome, with heterozygous substitutions-a R616W null mutation (previously seen in patients in XP complementation group D) and a unique D681N mutation-demonstrating that a third gene can be involved in COFS syndrome. We propose that COFS syndrome be included within the already known spectrum of NER disorders: XP, CS, and trichothiodystrophy. We predict that future patients with COFS syndrome will be found to have mutations in the CSA or XPB genes, and we document successful use of DNA repair for prenatal diagnosis in triplet and singleton pregnancies at risk for COFS syndrome. This result strongly underlines the need for screening of patients with COFS syndrome, for either UV sensitivity or DNA-repair abnormalities.

Molecular mechanism of nucleotide excision repair.

From its very beginning, life has faced the fundamental problem that the form in which genetic information is stored is not chemically inert. DNA integrity is challenged by the damaging effect of numerous chemical and physical agents, compromizing its function. To protect this Achilles heel, an intricate network of DNA repair systems has evolved early in evolution. One of these is nucleotide excision repair (NER), a highly versatile and sophisticated DNA damage removal pathway that counteracts the deleterious effects of a multitude of DNA lesions, including major types of damage induced by environmental sources. The most relevant lesions subject to NER are cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts (6-4PPs), two major kinds of injury produced by the shortwave UV component of sunlight. In addition, numerous bulky chemical adducts are eliminated by this process. Within the divergent spectrum of NER lesions, significant distortion of the DNA helix appears to be a common denominator. Defects in NER underlie the extreme photosensitivity and predisposition to skin cancer observed with the prototype repair syndrome xeroderma pigmentosum (XP). Seven XP complementation groups have been identified, representing distinct repair genes XPA–G (discussed in detail below). In the last decade, all key NER factors have been cloned and the core of the ‘cut-and-paste’ reaction has been reconstituted in vitro from purified components. Recently, XPC (complexed to hHR23B) has been identified as a DNA-damage sensor and repair-recruitment factor. The general transcription factor complex TFIIH, containing the XPB and XPD helicases, mediates strand separation at the site of the lesion. XPA verifies the damage in an open DNA conformation and is crucial in the assembly of the remainder of the repair machinery. Replication protein A (RPA) stabilizes the opened DNA complex and is involved in positioning the XPG and ERCC1–XPF endonucleases responsible for the DNA incisions around the lesion. After removal of the damagecontaining oligonucleotide, typically 24–32 nucleotides in length, general replication factors fill in the remaining gap and close it. Two modes of NER can be distinguished: repair of lesions over the entire genome, referred to as global genome NER (GG–NER), and repair of transcription-blocking lesions present in transcribed DNA strands, hence called transcription-coupled NER (TC–NER). Most XP groups harbor defects in a common component of both NER subpathways. GG–NER is dependent on the activity of all factors mentioned above, including the GG– NER-specific complex XPC–hHR23B. The rate of repair for GG–NER strongly depends on the type of lesion. For instance, 6-4PPs are removed much faster from the genome than CPDs, probably because of differences in affinity of the damage sensor XPC–hHR23B. In addition, the location (accessibility) of a lesion influences the removal rate in vivo. In TC–NER, damage is detected by the elongating RNA polymerase II complex when it encounters a lesion. Interestingly, a distinct disorder, Cockayne syndrome (CS), is associated with a specific defect in transcription-coupled repair. The identification of two complementation groups (CS-A and CS-B) shows that at least two gene products are specifically needed for fast and efficient repair of transcribed strands. Phenotypically, CS is a very pleiotropic condition characterized by photosensitivity as well as severe neurological, developmental, and premature aging features. Most of these symptoms are not seen even with totally NERdeficient XP patients. The additional symptoms of CS suggest that transcription-coupled repair and/or the CS proteins have functions beyond NER. Also, non-NERspecific lesions (such as oxidative damage) that stall transcription elongation appear to be removed in a transcription-coupled fashion, linking a blocked polymerase to multiple repair pathways. Intriguingly, some XP-B, XP-D, and XP-G patients display CS features combined with XP manifestations. Yet other XP-B and XP-D individuals suffer from the CS-like brittle-hair syndrome trichothiodystrophy (TTD). This clinical conundrum points to additional roles of these NER factors as well. A recent mouse model for TTD has linked mutations in the XPD subunit of the dual functional TFIIH complex with deficiencies in basal transcription underlying at least some of the TTD manifestations. Thus, NER defects are associated with a surprisingly wide clinical heterogeneity due to additional functions of the NER factors involved. 1Corresponding author. E-MAIL Hoeijmakers@gen.fgg.eur.nl; FAX 31 10 408 9468.

DNA Repair and Ultraviolet Mutagenesis in Cells From a New Patient With Xeroderma Pigmentosum Group G and Cockayne Syndrome Resemble Xeroderma Pigmentosum Cells

Xeroderma pigmentosum (XP)/Cockayne syndrome (CS) complex is a combination of clinical features of two rare genetic disorders in one individual. A sun-sensitive boy (XP20BE) who had severe symptoms of CS, with dwarfism, microcephaly, retinal degeneration, and mental impairment, had XP-type pigmentation and died at 6 y with marked cachexia (weight 14.5 lb) without skin cancers. We evaluated his cultured cells for characteristic CS or XP DNA-repair abnormalities. The level of ultraviolet (UV)-induced unscheduled DNA synthesis was less than 5% of normal, characteristic of the excision-repair defect of XP. Cell fusion studies indicated that his cells were in XP complementation group G. His cells were hypersensitive to killing by UV, and their post-UV recovery of RNA synthesis was abnormally low, features of both CS and XP. Post-UV survival of plasmid pSP189 in his cells was markedly reduced, and post-UV plasmid mutation frequency was higher than with normal cells, as in both CS and XP. Sequence analysis of the mutated plasmid marker gene showed normal frequency of plasmids with multiple base substitutions, as in CS, and an abnormally increased frequency of G:C-->A:T mutations, a feature of XP. Transfection of UV-treated pRSVcat with or without photoreactivation revealed that his cells, like XP cells, could not repair either cyclobutane pyrimidine dimers or non-dimer photoproducts. These results indicate that the DNA-repair features of the XP20BE (XP-G/CS) cells are phenotypically more like XP cells than CS cells, whereas clinically the CS phenotype is more prominent than XP.

A 3′→ 5′ XPB Helicase Defect in Repair/Transcription Factor TFIIH of Xeroderma Pigmentosum Group B Affects Both DNA Repair and Transcription

XPB is a subunit of the basal transcription factor TFIIH, which is also involved in nucleotide excision repair (NER) and potentially in cell cycle regulation. A frameshift mutation in the 3'-end of the XPB gene is responsible for a concurrence of two disorders: xeroderma pigmentosum (XP) and Cockayne's syndrome (CS). We have isolated TFIIH from cells derived from a patient (XP11BE) who carries this frameshift mutation (TFIIHmut) and from the mother of this patient (TFIIHwt) to determine the biochemical consequences of the mutation. Although identical in composition and stoichiometry to TFIIHwt, TFIIHmut shows a reduced 3' --> 5' XPB helicase activity. A decrease in helicase and DNA-dependent ATPase activities was also observed with the mutated recombinant XPB protein. The XPB mutation causes a severe NER defect. In addition, we provide evidence for a decrease in basal transcription activity in vitro. The latter defect may provide an explanation for many of the XP and CS symptoms that are difficult to rationalize based solely on an NER defect. Thus, this work presents the first detailed analysis of a naturally occurring mutation in a basal transcription factor and supports the concept that the combined XP/CS clinical entity is actually the result of a combined transcription/repair deficiency.

42 Deficiencies in DNA repair and its clinical impacts

All organisms have an evolved an intricate network of DNA repair systems, that permits elimination of virtually any type of DNA injury. Genetic defects in DNA repair pathways or in damage-induced cell cycle arrest result in genetic instability and a strong predisposition to cancer. Examples of this class of human syndromes are xeroderma pigmentosum (XP), Bloom's syndrome, Fanconi's anaemia, and ataxia telangiectasia. One of the major damage repair pathways is nucleotide excision repair (NER). This system. removes a broad spectrum of DNA lesions among which the mam UV-induced injury and bulky chemical adducts. Three NER-deficient human syndromes characterized by marked photosensitivity are known: XP, Cockayne syndrome (CS) and trichothiodystrophy (TTD). XP patients show pigmentation abnormalities and an over 1000 × increased risk of skin cancer caused by defects in one of at least 7 genes (XPA to XPG). CS displays sun sensitivity and overall developmental impairment. Two responsible genes are known: CSA and CSB. TTD is characterized by brittle hair, ichthyosis and many CS symptoms. The NER defect in TTD is due to mutations in TTDA, XPB or XPD. There are no indications for an increased risk of cancer in CS and TTD. Some patients show a combined XP + CS picture. They have been assigned to XPB, XPD or XPG. Several of the protein (complex)es involved in NER participate in other DNA transactions as well. The XPF/ERCC1 complex probably has a dual involvement in a mitotic recombination pathway. All three NER genes associated with TTD are also implicated in basal transcription. This notion has important clinical implications. It is likely that the TTD symptoms not explained by a NER defect are caused by subtle insufficiencies in basal transcription. Thus TTD may represent a combined ‘repair/transcription syndrome’. To analyze the complex geno-phenotype relationship between mutations in NER genes and the clinical symptoms we have utilized gene targeting in mouse embryonal stem cells, to generate mouse mutants carrying defined genetic changes in various repair genes. The mouse models provide valuable tools for studying relationship between molecular defect and clinical symptoms, including cancer predisposition. All organisms have an evolved an intricate network of DNA repair systems, that permits elimination of virtually any type of DNA injury. Genetic defects in DNA repair pathways or in damage-induced cell cycle arrest result in genetic instability and a strong predisposition to cancer. Examples of this class of human syndromes are xeroderma pigmentosum (XP), Bloom's syndrome, Fanconi's anaemia, and ataxia telangiectasia. One of the major damage repair pathways is nucleotide excision repair (NER). This system. removes a broad spectrum of DNA lesions among which the mam UV-induced injury and bulky chemical adducts. Three NER-deficient human syndromes characterized by marked photosensitivity are known: XP, Cockayne syndrome (CS) and trichothiodystrophy (TTD). XP patients show pigmentation abnormalities and an over 1000 × increased risk of skin cancer caused by defects in one of at least 7 genes (XPA to XPG). CS displays sun sensitivity and overall developmental impairment. Two responsible genes are known: CSA and CSB. TTD is characterized by brittle hair, ichthyosis and many CS symptoms. The NER defect in TTD is due to mutations in TTDA, XPB or XPD. There are no indications for an increased risk of cancer in CS and TTD. Some patients show a combined XP + CS picture. They have been assigned to XPB, XPD or XPG. Several of the protein (complex)es involved in NER participate in other DNA transactions as well. The XPF/ERCC1 complex probably has a dual involvement in a mitotic recombination pathway. All three NER genes associated with TTD are also implicated in basal transcription. This notion has important clinical implications. It is likely that the TTD symptoms not explained by a NER defect are caused by subtle insufficiencies in basal transcription. Thus TTD may represent a combined ‘repair/transcription syndrome’. To analyze the complex geno-phenotype relationship between mutations in NER genes and the clinical symptoms we have utilized gene targeting in mouse embryonal stem cells, to generate mouse mutants carrying defined genetic changes in various repair genes. The mouse models provide valuable tools for studying relationship between molecular defect and clinical symptoms, including cancer predisposition.