Mutation update for the CSB/ERCC6 and CSA/ERCC8 genes involved in Cockayne syndrome

Genome Instability in Development and Aging: Insights from Nucleotide Excision Repair in Humans, Mice, and Worms

DNA damage causally contributes to aging and cancer. Congenital defects in nucleotide excision repair (NER) lead to distinct cancer-prone and premature aging syndromes. The genetics of NER mutations have provided important insights into the distinct consequences of genome instability. Recent work in mice and C. elegans has shed new light on the mechanisms through which developing and aging animals respond to persistent DNA damage. The various NER mouse mutants have served as important disease models for Xeroderma pigmentosum (XP), Cockayne syndrome (CS), and trichothiodystrophy (TTD), while the traceable genetics of C. elegans have allowed the mechanistic delineation of the distinct outcomes of genome instability in metazoan development and aging. Intriguingly, highly conserved longevity assurance mechanisms respond to transcription-blocking DNA lesions in mammals as well as in worms and counteract the detrimental consequences of persistent DNA damage. The insulin-like growth factor signaling (IIS) effector transcription factor DAF-16 could indeed overcome DNA damage-driven developmental growth delay and functional deterioration even when DNA damage persists. Longevity assurance mechanisms might thus delay DNA damage-driven aging by raising the threshold when accumulating DNA damage becomes detrimental for physiological tissue functioning.

CSB-PGBD3 Mutations Cause Premature Ovarian Failure

Premature ovarian failure (POF) is a rare, heterogeneous disorder characterized by cessation of menstruation occurring before the age of 40 years. Genetic etiology is responsible for perhaps 25% of cases, but most cases are sporadic and unexplained. In this study, through whole exome sequencing in a non-consanguineous family having four affected members with POF and Sanger sequencing in 432 sporadic cases, we identified three novel mutations in the fusion gene CSB-PGBD3. Subsequently functional studies suggest that mutated CSB-PGBD3 fusion protein was impaired in response to DNA damage, as indicated by delayed or absent recruitment to damaged sites. Our data provide the first evidence that mutations in the CSB-PGBD3 fusion protein can cause human disease, even in the presence of functional CSB, thus potentially explaining conservation of the fusion protein for 43 My since marmoset. The localization of the CSB-PGBD3 fusion protein to UVA-induced nuclear DNA repair foci further suggests that the CSB-PGBD3 fusion protein, like many other proteins that can cause POF, modulates or participates in DNA repair.

The Cockayne Syndrome Natural History (CoSyNH) study: clinical findings in 102 individuals and recommendations for care

Purpose:

Cockayne syndrome (CS) is a rare, autosomal-recessive disorder characterized by microcephaly, impaired postnatal growth, and premature pathological aging. It has historically been considered a DNA repair disorder; fibroblasts from classic patients often exhibit impaired transcription-coupled nucleotide excision repair. Previous studies have largely been restricted to case reports and small series, and no guidelines for care have been established.

Genet Med18 5, 483–493.

Methods:

One hundred two study participants were identified through a network of collaborating clinicians and the Amy and Friends CS support groups. Families with a diagnosis of CS could also self-recruit. Comprehensive clinical information for analysis was obtained directly from families and their clinicians.

Genet Med18 5, 483–493.

Results and Conclusion:

We present the most complete evaluation of Cockayne syndrome to date, including detailed information on the prevalence and onset of clinical features, achievement of neurodevelopmental milestones, and patient management. We confirm that the most valuable prognostic factor in CS is the presence of early cataracts. Using this evidence, we have created simple guidelines for the care of individuals with CS. We aim to assist clinicians in the recognition, diagnosis, and management of this condition and to enable families to understand what problems they may encounter as CS progresses.

Genet Med18 5, 483–493.

Effect of ERCC8 tagSNPs and their association with H. pylori infection, smoking, and alcohol consumption on gastric cancer and atrophic gastritis risk

Excision repair cross-complementing group 8 (ERCC8) plays a critical role in DNA repair. Genetic polymorphisms in ERCC8 may contribute to the risk of cancer development. We selected tag single nucleotide polymorphisms (tagSNPs) in Chinese patients from the HapMap database to investigate associations with gastric cancer and its precursors. Genomic DNA was extracted from 394 controls, 394 atrophic gastritis, and 394 gastric cancer cases in northern Chinese patients, and genotypes were identified using the Sequenom MassARRAY system. We found that the ERCC8 rs158572 GG+GA genotype showed a 1.651-fold (95 % confidence interval (CI) = 1.109-2.457, P = 0.013) increased risk of gastric cancer compared with the AA genotype, especially in diffuse type. Stratified analysis comparing the common genotype revealed significantly increased gastric cancer risk in males and individuals older than 50 years with rs158572 GA/GG/GG+GA genotypes, while individuals older than 50 years with rs158916 CT/CC+CT genotypes were less susceptible to atrophic gastritis. Haplotype analysis showed that the G-T haplotype was associated with increased risk of gastric cancer. Statistically significant interactions between the two ERCC8 tagSNPs and Helicobacter pylori infection were observed for gastric cancer and atrophic gastritis risk (P < 0.05). Smokers and drinkers with ERCC8 rs158572 GG+GA genotype were more susceptible to gastric cancer compared with non-smokers and non-drinkers homozygous for AA. Our findings suggested that ERCC8 rs158572 and rs158916, alone or together with environmental factors, might be associated with gastric cancer and atrophic gastritis susceptibility. Further validation of our results in larger populations along with additional studies evaluating the underlying molecular function is required.

Reversal of mitochondrial defects with CSB-dependent serine protease inhibitors in patient cells of the progeroid Cockayne syndrome

UV-sensitive syndrome (UV(S)S) and Cockayne syndrome (CS) are human disorders caused by CSA or CSB gene mutations; both conditions cause defective transcription-coupled repair and photosensitivity. Patients with CS also display neurological and developmental abnormalities and dramatic premature aging, and their cells are hypersensitive to oxidative stress. We report CSA/CSB-dependent depletion of the mitochondrial DNA polymerase-γ catalytic subunit (POLG1), due to HTRA3 serine protease accumulation in CS, but not in UV(s)S or control fibroblasts. Inhibition of serine proteases restored physiological POLG1 levels in either CS fibroblasts and in CSB-silenced cells. Moreover, patient-derived CS cells displayed greater nitroso-redox imbalance than UV(S)S cells. Scavengers of reactive oxygen species and peroxynitrite normalized HTRA3 and POLG1 levels in CS cells, and notably, increased mitochondrial oxidative phosphorylation, which was altered in CS cells. These data reveal critical deregulation of proteases potentially linked to progeroid phenotypes in CS, and our results suggest rescue strategies as a therapeutic option.

Novel ABHD12 Mutations in PHARC Patients

Objective:

This study examines ABHD12 mutation analysis in 2 PHARC patients, originally thought to be Usher syndrome.

Methods:

The ABHD12 gene of 2 patients, who suffered from deaf-blindness and dysfunctional central and peripheral nervous systems, were sequenced.

Results:

We identified that both cases carried the same novel splice site mutation in the ABHD12 gene. However, 1 had epilepsy and the other had peripheral neuropathy. Based on haplotype analysis, the mutation is likely not a hot spot, but rather could be attributable to a common ancestor.

Conclusion:

This study shows that PHARC has phenotypic variability, even within a family, which is consistent with previous reports. Differential diagnosis of “deaf-blindness” diseases is crucial. Confirming the presence of associated symptoms is necessary for differentiating some deaf-blindness syndromes. In addition, mutation analysis is a useful tool for confirming the diagnosis.

The Multifunctions of WD40 Proteins in Genome Integrity and Cell Cycle Progression

Eukaryotic genome encodes numerous WD40 repeat proteins, which generally function as platforms of protein-protein interactions and are involved in numerous biological process, such as signal transduction, gene transcriptional regulation, protein modifications, cytoskeleton assembly, vesicular trafficking, DNA damage and repair, cell death and cell cycle progression. Among these diverse functions, genome integrity maintenance and cell cycle progression are extremely important as deregulation of them is clinically linked to uncontrolled proliferative diseases such as cancer. Thus, we mainly summarize and discuss the recent understanding of WD40 proteins and their molecular mechanisms linked to genome stability and cell cycle progression in this review, thereby demonstrating their pervasiveness and importance in cellular networks.

Identification of two missense mutations of ERCC6 in three Chinese sisters with Cockayne syndrome by whole exome sequencing

Cockayne syndrome (CS) is a rare autosomal recessive disorder, the primary manifestations of which are poor growth and neurologic abnormality. Mutations of the ERCC6 and ERCC8 genes are the predominant cause of Cockayne syndrome, and the ERCC6 gene mutation is present in approximately 65% of cases. The present report describes a case of Cockayne syndrome in a Chinese family, with the patients carrying two missense mutations (c.1595A>G, p.Asp532Gly and c.1607T>G, p.Leu536Trp) in the ERCC6 gene in an apparently compound heterozygote status, especially, p.Asp532Gly has never been reported. The compound heterozygote mutation was found in three patients in the family using whole exome sequencing. The patients' father and mother carried a heterozygous allele at different locations of the ERCC6 gene, which was confirmed by Sanger DNA sequencing. The two mutations are both located in the highly conserved motif I of ATP-binding helicase and are considered "Damaging," "Probably Damaging," "Disease Causing," and "Conserved", indicating the role of DNA damage in the pathogenetic process of the disease. The results not only enrich the ERCC6 mutations database, but also indicate that whole exome sequencing will be a powerful tool for discovering the disease causing mutations in clinical diagnosis.

A C. elegans homolog of the Cockayne syndrome complementation group A gene

Cockayne syndrome (CS) is a debilitating and complex disorder that results from inherited mutations in the CS complementation genes A and B, CSA and CSB. The links between the molecular functions of the CS genes and the complex pathophysiology of CS are as of yet poorly understood and are the subject of intense debate. While mouse models reflect the complexity of CS, studies on simpler genetic models might shed new light on the consequences of CS mutations. Here we describe a functional homolog of the human CSA gene in Caenorhabditis elegans. Similar to its human counterpart, mutations in the nematode csa-1 gene lead to developmental growth defects as a consequence of DNA lesions.

Progressive demyelinating neuropathy correlates with clinical severity in Cockayne syndrome

OBJECTIVE

Cockayne syndrome (CS) is characterized by postnatal growth failure and progressive multi-organ dysfunctions. CSA and CSB gene mutations account for the majority of cases and three degrees of severity are delineated. A peripheral neuropathy is known to be associated with CS but the type, severity and correlation of the nerve involvement with CS subtypes remain unknown in genetically identified patients.

METHODS

Clinical and nerve conduction studies (NCS) in 25 CS patients with CSA (n=13) CSB (n=12) mutations.

RESULTS

NCS show a widespread decrease in motor and sensory conduction velocities (CV) in all severe and classical form of CS. In one patient, CV were normal at age 8months but severe slowing was detected at 2years. Conduction block and/or temporal dispersion were observed in 68% of patients.

CONCLUSIONS

CS is associated with a progressive sensory and motor neuropathy. Signs of segmental demyelination, including conduction blocks, may not be obvious before the age of 2years. CV slowing is correlated with the CS clinical severity.

SIGNIFICANCE

NCS should be performed in patients with suspected CS as an additional tool to guide the diagnosis before molecular studies. Further studies focused on NCS course are required in order to assess its relevance as a biomarker in research therapy projects.

Cell-autonomous progeroid changes in conditional mouse models for repair endonuclease XPG deficiency

As part of the Nucleotide Excision Repair (NER) process, the endonuclease XPG is involved in repair of helix-distorting DNA lesions, but the protein has also been implicated in several other DNA repair systems, complicating genotype-phenotype relationship in XPG patients. Defects in XPG can cause either the cancer-prone condition xeroderma pigmentosum (XP) alone, or XP combined with the severe neurodevelopmental disorder Cockayne Syndrome (CS), or the infantile lethal cerebro-oculo-facio-skeletal (COFS) syndrome, characterized by dramatic growth failure, progressive neurodevelopmental abnormalities and greatly reduced life expectancy. Here, we present a novel (conditional) Xpg^−/− mouse model which -in a C57BL6/FVB F1 hybrid genetic background- displays many progeroid features, including cessation of growth, loss of subcutaneous fat, kyphosis, osteoporosis, retinal photoreceptor loss, liver aging, extensive neurodegeneration, and a short lifespan of 4–5 months. We show that deletion of XPG specifically in the liver reproduces the progeroid features in the liver, yet abolishes the effect on growth or lifespan. In addition, specific XPG deletion in neurons and glia of the forebrain creates a progressive neurodegenerative phenotype that shows many characteristics of human XPG deficiency. Our findings therefore exclude that both the liver as well as the neurological phenotype are a secondary consequence of derailment in other cell types, organs or tissues (e.g. vascular abnormalities) and support a cell-autonomous origin caused by the DNA repair defect itself. In addition they allow the dissection of the complex aging process in tissue- and cell-type-specific components. Moreover, our data highlight the critical importance of genetic background in mouse aging studies, establish the Xpg^−/− mouse as a valid model for the severe form of human XPG patients and segmental accelerated aging, and strengthen the link between DNA damage and aging.

Accumulation of DNA damage has been implicated in aging. Many premature aging syndromes are due to defective DNA repair systems. The endonuclease XPG is involved in repair of helix-distorting DNA lesions, and XPG defects cause the cancer-prone condition xeroderma pigmentosum (XP) alone or combined with the severe neurodevelopmental progeroid disorder Cockayne syndrome (CS). Here, we present a novel (conditional) Xpg^−/− mouse model which -in a C57BL6/FVB F1 hybrid background- displays many progressive progeroid features, including early cessation of growth, cachexia, kyphosis, osteoporosis, neurodegeneration, liver aging, retinal degeneration, and reduced lifespan. In a constitutive mutant with a complex phenotype it is difficult to dissect cause and consequence. We have therefore generated liver- and forebrain-specific Xpg mutants and demonstrate that they exhibit progressive anisokaryosis and neurodegeneration, respectively, indicating that a cell-intrinsic repair defect in neurons can account for neuronal degeneration. These findings strengthen the link between DNA damage and the complex process of aging.

ERCC6 dysfunction presenting as progressive neurological decline with brain hypomyelination

Mutations in ERCC6 are associated with growth failure, intellectual disability, neurological dysfunction and deterioration, premature aging, and photosensitivity. We describe siblings with biallelic ERCC6 mutations (NM_000124.2:c. [543+4delA];[2008C>T]) and brain hypomyelination, microcephaly, cognitive decline, and skill regression but without photosensitivity or progeria. DNA repair assays on cultured skin fibroblasts confirmed a defect of transcription-coupled nucleotide excision repair and increased ultraviolet light sensitivity. This report expands the disease spectrum associated with ERCC6 mutations.

The cockayne syndrome B protein is essential for neuronal differentiation and neuritogenesis

Cockayne syndrome (CS) is a progressive developmental and neurodegenerative disorder resulting in premature death at childhood and cells derived from CS patients display DNA repair and transcriptional defects. CS is caused by mutations in csa and csb genes, and patients with csb mutation are more prevalent. A hallmark feature of CSB patients is neurodegeneration but the precise molecular cause for this defect remains enigmatic. Further, it is not clear whether the neurodegenerative condition is due to loss of CSB-mediated functions in adult neurogenesis. In this study, we examined the role of CSB in neurogenesis by using the human neural progenitor cells that have self-renewal and differentiation capabilities. In this model system, stable CSB knockdown dramatically reduced the differentiation potential of human neural progenitor cells revealing a key role for CSB in neurogenesis. Neurite outgrowth, a characteristic feature of differentiated neurons, was also greatly abolished in CSB-suppressed cells. In corroboration with this, expression of MAP2 (microtubule-associated protein 2), a crucial player in neuritogenesis, was also impaired in CSB-suppressed cells. Consistent with reduced MAP2 expression in CSB-depleted neural cells, tandem affinity purification and chromatin immunoprecipitation studies revealed a potential role for CSB in the assembly of transcription complex on MAP2 promoter. Altogether, our data led us to conclude that CSB has a crucial role in coordinated regulation of transcription and chromatin remodeling activities that are required during neurogenesis.

Genetic disorders associated with postnatal microcephaly

Several genetic disorders are characterized by normal head size at birth, followed by deceleration in head growth resulting in postnatal microcephaly. Among these are classic disorders such as Angelman syndrome and MECP2-related disorder (formerly Rett syndrome), as well as more recently described clinical entities associated with mutations in CASK, CDKL5, CREBBP, and EP300 (Rubinstein-Taybi syndrome), FOXG1, SLC9A6 (Christianson syndrome), and TCF4 (Pitt-Hopkins syndrome). These disorders can be identified clinically by phenotyping across multiple neurodevelopmental and neurobehavioral realms, and enough data are available to recognize these postnatal microcephaly disorders as separate diagnostic entities in their own right. A second diagnostic grouping, comprised of Warburg MICRO syndrome, Cockayne syndrome, and Cerebral-oculo-facial skeletal syndrome, share similar features of somatic growth failure, ophthalmologic, and dysmorphologic features. Many postnatal microcephaly syndromes are caused by mutations in genes important in the regulation of gene expression in the developing forebrain and hindbrain, although important synaptic structural genes also play a role. This is an emerging group of disorders with a fascinating combination of brain malformations, specific epilepsies, movement disorders, and other complex neurobehavioral abnormalities.

Cockayne syndrome protein A is a transcription factor of RNA polymerase I and stimulates ribosomal biogenesis and growth

Mutations in the Cockayne syndrome A (CSA) protein account for 20% of Cockayne syndrome (CS) cases, a childhood disorder of premature aging and early death. Hitherto, CSA has exclusively been described as DNA repair factor of the transcription-coupled branch of nucleotide excision repair. Here we show a novel function of CSA as transcription factor of RNA polymerase I in the nucleolus. Knockdown of CSA reduces pre-rRNA synthesis by RNA polymerase I. CSA associates with RNA polymerase I and the active fraction of the rDNA and stimulates re-initiation of rDNA transcription by recruiting the Cockayne syndrome proteins TFIIH and CSB. Moreover, compared with CSA deficient parental CS cells, CSA transfected CS cells reveal significantly more rRNA with induced growth and enhanced global translation. A previously unknown global dysregulation of ribosomal biogenesis most likely contributes to the reduced growth and premature aging of CS patients.

Molecular basis of transcriptional fidelity and DNA lesion-induced transcriptional mutagenesis

Maintaining high transcriptional fidelity is essential for life. Some DNA lesions lead to significant changes in transcriptional fidelity. In this review, we will summarize recent progress towards understanding the molecular basis of RNA polymerase II (Pol II) transcriptional fidelity and DNA lesion-induced transcriptional mutagenesis. In particular, we will focus on the three key checkpoint steps of controlling Pol II transcriptional fidelity: insertion (specific nucleotide selection and incorporation), extension (differentiation of RNA transcript extension of a matched over mismatched 3'-RNA terminus), and proofreading (preferential removal of misincorporated nucleotides from the 3'-RNA end). We will also discuss some novel insights into the molecular basis and chemical perspectives of controlling Pol II transcriptional fidelity through structural, computational, and chemical biology approaches.

Cockayne syndrome: varied requirement of transcription-coupled nucleotide excision repair for the removal of three structurally different adducts from transcribed DNA

Hereditary defects in the transcription-coupled nucleotide excision repair (TC-NER) pathway of damaged DNA cause severe neurodegenerative disease Cockayne syndrome (CS), however the origin and chemical nature of the underlying DNA damage had remained unknown. To find out, to which degree the structural properties of DNA lesions determine the extent of transcription arrest in human CS cells, we performed quantitative host cell reactivation analyses of expression vectors containing various synthetic adducts. We found that a single 3-(deoxyguanosin-N²-yl)-2-acetylaminofluorene adduct (dG(N²)-AAF) constitutes an unsurmountable obstacle to transcription in both CS-A and CS-B cells and is removed exclusively by the CSA- and CSB-dependent pathway. In contrast, contribution of the CS proteins to the removal of two other transcription-blocking DNA lesions – N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG(C8)-AAF) and cyclobutane thymine-thymine (TT) dimer – is only minor (TT dimer) or none (dG(C8)-AAF). The unique properties of dG(N²)-AAF identify this adduct as a prototype for a new class of DNA lesions that escape the alternative global genome repair and could be critical for the CS pathogenesis.

WITHDRAWN: Two Novel Heterozygous Mutations of CSA Cause Cockayne Syndrome in a Chinese Family

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A new mutation in the CSB gene in a Chinese patient with mild Cockayne syndrome

Key Clinical Message

Cockayne syndrome (CS) is a rare autosomal recessive genetic disease characterized by growth failure and progressive neurological degeneration. Here we report a mild form of CS patient who was homozygous for the C526T transition resulting in a new nonsense mutation, which converts Arg176 to a stop codon.

ERCC6L2 mutations link a distinct bone-marrow-failure syndrome to DNA repair and mitochondrial function

Exome sequencing was performed in three index cases with bone marrow failure and neurological dysfunction and whose parents are first-degree cousins. Homozygous truncating mutations were identified in ERCC6L2 in two of the individuals. Both of these mutations affect the subcellular localization and stability of ERCC6L2. We show here that knockdown of ERCC6L2 in human A549 cells significantly reduced their viability upon exposure to the DNA-damaging agents mitomycin C and Irofulven, but not etoposide and camptothecin, suggesting a role in nucleotide excision repair. ERCC6L2-knockdown cells also displayed H2AX phosphorylation, which significantly increased upon genotoxic stress, suggesting an early DNA-damage response. Intriguingly, ERCC6L2 was seen to translocate to the mitochondria and the nucleus in response to DNA damage, and ERCC6L2 knockdown induced intracellular reactive oxygen species (ROS). Treatment with the ROS scavenger N-acetyl cysteine attenuated the Irofulven-induced cytotoxicity in ERCC6L2-knockdown cells and abolished ERCCGL2 traffic to the mitochondria and nucleus in response to this DNA-damaging agent. Collectively, these observations identify a distinct bone-marrow-failure syndrome due to mutations in ERCC6L2, a gene implicated in DNA repair and mitochondrial function.

Systemic DNA damage responses: organismal adaptations to genome instability

DNA damage checkpoints are important tumor-suppressor mechanisms that halt cell cycle progression to allow time for DNA repair, or induce senescence and apoptosis to remove damaged cells permanently. Non-cell-autonomous DNA damage responses activate the innate immune system in multiple metazoan species. These responses not only enable clearance of damaged cells and contribute to tissue remodeling and regeneration but can also result in chronic inflammation and tissue damage. Germline DNA damage-induced systemic stress resistance (GDISR) is mediated by an ancestral innate immune response and results in organismal adjustments to the presence of damaged cells. We discuss GDISR as an organismal DNA damage checkpoint mechanism through which elevated somatic endurance can extend reproductive lifespan when germ cells require extended time for restoring genome stability.

Search and insights into novel genetic alterations leading to classical and atypical Werner syndrome

Segmental progeroid syndromes are a group of disorders with multiple features resembling accelerated aging. Adult-onset Werner syndrome (WS) and childhood-onset Hutchinson-Gilford progeria syndrome are the best known examples. The discovery of genes responsible for such syndromes has facilitated our understanding of the basic mechanisms of aging as well as the pathogenesis of other common, age-related diseases. Our International Registry of Werner Syndrome accesses progeroid pedigrees from all over the world, including those for whom we have ruled out a mutation at the WRN locus. Cases without WRN mutations are operationally categorized as 'atypical WS' (AWS). In 2003, we identified LMNA mutations among a subset of AWS cases using a candidate gene approach. As of 2013, the Registry has 142 WS patients with WRN mutations, 11 AWS patients with LMNA mutations, and 49 AWS patients that have neither WRN nor LMNA mutations. Efforts are underway to identify the responsible genes for AWS with unknown genetic causes. While WS and AWS are rare disorders, the causative genes have been shown to have much wider implications for cancer, cardiovascular disease and the biology of aging. Remarkably, centenarian studies revealed WRN and LMNA polymorphic variants among those who have escaped various geriatric disorders.

A novel ERCC6 splicing variant associated with a mild Cockayne syndrome phenotype

BACKGROUND

Cockayne syndrome is an autosomal recessive, heterogeneous syndrome with classical features, including short stature, microcephaly, developmental delay, neuropathy, and photosensitivity. New genomic approaches offer improved molecular diagnostic potential.

METHODS

Whole-exome sequencing was employed to study a consanguineous extended family with severe short stature and variable presentations of peripheral neuropathy, lipoatrophy, photosensitivity, webbed neck, and hirsutism.

RESULTS

We identified a novel homozygous ERCC6 variant at the donor splice site of intron 9 (c.1992 + 3A>G), which was predicted to only slightly perturb splicing efficiencies. Assessment of primary fibroblast-derived mRNAs, however, revealed a dominant splicing species that utilized an unsuspected putative donor splice site within exon 9, resulting in predicted early protein termination (p.Arg637Serfs*34).

CONCLUSIONS

We describe a new splicing ERCC6 defect causal of Cockayne syndrome. The application of exome sequence analysis was integral to diagnosis, given the complexity of phenotypic presentation in the affected family members. The novel splicing defect, furthermore, illustrates how a seemingly minor change in the relative strength of a splice site can have significant biological consequences.

Tracking the Cognitive, Social, and Neuroanatomical Profile in Early Neurodegeneration: Type III Cockayne Syndrome

Cockayne syndrome (CS) is an autosomal recessive disease associated with premature aging, progressive multiorgan degeneration, and nervous system abnormalities including cerebral and cerebellar atrophy, brain calcifications, and white matter abnormalities. Although several clinical descriptions of CS patients have reported developmental delay and cognitive impairment with relative preservation of social skills, no previous studies have carried out a comprehensive neuropsychological and social cognition assessment. Furthermore, no previous research in individuals with CS has examined the relationship between brain atrophy and performance on neuropsychological and social cognition tests. This study describes the case of an atypical late-onset type III CS patient who exceeds the mean life expectancy of individuals with this pathology. The patient and a group of healthy controls underwent a comprehensive assessment that included multiple neuropsychological and social cognition (emotion recognition, theory of mind, and empathy) tasks. In addition, we compared the pattern of atrophy in the patient to controls and to its concordance with ERCC8 gene expression in a healthy brain. The results showed memory, language, and executive deficits that contrast with the relative preservation of social cognition skills. The cognitive profile of the patient was consistent with his pattern of global cerebral and cerebellar loss of gray matter volume (frontal structures, bilateral cerebellum, basal ganglia, temporal lobe, and occipito-temporal/occipito-parietal regions), which in turn was anatomically consistent with the ERCC8 gene expression level in a healthy donor’s brain. The study of exceptional cases, such as the one described here, is fundamental to elucidating the processes that affect the brain in premature aging diseases, and such studies provide an important source of information for understanding the problems associated with normal and pathological aging.

Mammalian transcription-coupled excision repair

Transcriptional arrest caused by DNA damage is detrimental for cells and organisms as it impinges on gene expression and thereby on cell growth and survival. To alleviate transcriptional arrest, cells trigger a transcription-dependent genome surveillance pathway, termed transcription-coupled nucleotide excision repair (TC-NER) that ensures rapid removal of such transcription-impeding DNA lesions and prevents persistent stalling of transcription. Defective TC-NER is causatively linked to Cockayne syndrome, a rare severe genetic disorder with multisystem abnormalities that results in patients' death in early adulthood. Here we review recent data on how damage-arrested transcription is actively coupled to TC-NER in mammals and discuss new emerging models concerning the role of TC-NER-specific factors in this process.

UVSSA and USP7, a new couple in transcription-coupled DNA repair

Transcription-coupled nucleotide excision repair (TC-NER) specifically removes transcription-blocking lesions from our genome. Defects in this pathway are associated with two human disorders: Cockayne syndrome (CS) and UV-sensitive syndrome (UV^SS). Despite a similar cellular defect in the UV DNA damage response, patients with these syndromes exhibit strikingly distinct symptoms; CS patients display severe developmental, neurological, and premature aging features, whereas the phenotype of UV^SS patients is mostly restricted to UV hypersensitivity. The exact molecular mechanism behind these clinical differences is still unknown; however, they might be explained by additional functions of CS proteins beyond TC-NER. A short overview of the current hypotheses addressing possible molecular mechanisms and the proteins involved are presented in this review. In addition, we will focus on two new players involved in TC-NER which were recently identified: UV-stimulated scaffold protein A (UVSSA) and ubiquitin-specific protease 7 (USP7). UVSSA has been found to be the causative gene for UV^SS and, together with USP7, is implicated in regulating TC-NER activity. We will discuss the function of UVSSA and USP7 and how the discovery of these proteins contributes to a better understanding of the molecular mechanisms underlying the clinical differences between UV^SS and the more severe CS.

Regulatory interplay of Cockayne syndrome B ATPase and stress-response gene ATF3 following genotoxic stress

Cockayne syndrome type B ATPase (CSB) belongs to the SwItch/Sucrose nonfermentable family. Its mutations are linked to Cockayne syndrome phenotypes and classically are thought to be caused by defects in transcription-coupled repair, a subtype of DNA repair. Here we show that after UV-C irradiation, immediate early genes such as activating transcription factor 3 (ATF3) are overexpressed. Although the ATF3 target genes, including dihydrofolate reductase (DHFR), were unable to recover RNA synthesis in CSB-deficient cells, transcription was restored rapidly in normal cells. There the synthesis of DHFR mRNA restarts on the arrival of RNA polymerase II and CSB and the subsequent release of ATF3 from its cAMP response element/ATF target site. In CSB-deficient cells ATF3 remains bound to the promoter, thereby preventing the arrival of polymerase II and the restart of transcription. Silencing of ATF3, as well as stable introduction of wild-type CSB, restores RNA synthesis in UV-irradiated CSB cells, suggesting that, in addition to its role in DNA repair, CSB activity likely is involved in the reversal of inhibitory properties on a gene-promoter region. We present strong experimental data supporting our view that the transcriptional defects observed in UV-irradiated CSB cells are largely the result of a permanent transcriptional repression of a certain set of genes in addition to some defect in DNA repair.

Malfunction of nuclease ERCC1-XPF results in diverse clinical manifestations and causes Cockayne syndrome, xeroderma pigmentosum, and Fanconi anemia

Cockayne syndrome (CS) is a genetic disorder characterized by developmental abnormalities and photodermatosis resulting from the lack of transcription-coupled nucleotide excision repair, which is responsible for the removal of photodamage from actively transcribed genes. To date, all identified causative mutations for CS have been in the two known CS-associated genes, ERCC8 (CSA) and ERCC6 (CSB). For the rare combined xeroderma pigmentosum (XP) and CS phenotype, all identified mutations are in three of the XP-associated genes, ERCC3 (XPB), ERCC2 (XPD), and ERCC5 (XPG). In a previous report, we identified several CS cases who did not have mutations in any of these genes. In this paper, we describe three CS individuals deficient in ERCC1 or ERCC4 (XPF). Remarkably, one of these individuals with XP complementation group F (XP-F) had clinical features of three different DNA-repair disorders--CS, XP, and Fanconi anemia (FA). Our results, together with those from Bogliolo et al., who describe XPF alterations resulting in FA alone, indicate a multifunctional role for XPF.

Multiple interaction partners for Cockayne syndrome proteins: implications for genome and transcriptome maintenance

Cockayne syndrome (CS) is characterized by progressive multisystem degeneration and is classified as a segmental premature aging syndrome. The majority of CS cases are caused by defects in the CS complementation group B (CSB) protein and the rest are mainly caused by defects in the CS complementation group A (CSA) protein. Cells from CS patients are sensitive to UV light and a number of other DNA damaging agents including various types of oxidative stress. The cells also display transcription deficiencies, abnormal apoptotic response to DNA damage, and DNA repair deficiencies. Herein we have critically reviewed the current knowledge about known protein interactions of the CS proteins. The review focuses on the participation of the CSB and CSA proteins in many different protein interactions and complexes, and how these interactions inform us about pathways that are defective in the disease.

From laboratory tests to functional characterisation of Cockayne syndrome

The significant progress made over the last few years on the pathogenesis of Cockayne syndrome (CS) greatly improved our knowledge on several aspects crucial for development and ageing, demonstrating that this disorder, even if rare, represents a valuable tool to clarify key aspects of human health. Primary cells from patients have been instrumental to elucidate the multiple roles of CS proteins and to approach the dissection of the complex interplay between repair and transcription that is central to the CS clinical phenotype. Here we discuss the results of the cellular assays applied for confirmation of the clinical diagnosis as well as the results of genetic and molecular studies in DNA repair defective patients. Furthermore, we provide a general overview of recent in vivo and in vitro studies indicating that both CSA and CSB proteins are involved in distinct aspects of the cellular responses to UV and oxidative stress, transcription and regulation of gene expression, chromatin remodelling, redox balance and cellular bioenergetics. In light of the literature data, we will finally discuss how inactivation of specific functional roles of CS proteins may differentially affect the phenotype, thus explaining the wide range in type and severity of symptoms reported in CS patients.

Arresting transcription and sentencing the cell: the consequences of blocked transcription

Bulky DNA adducts induced by agents like ultraviolet light, cisplatin and oxidative metabolism pose a block to elongation by RNA polymerase II (RNAPII). The arrested RNAPII can initiate the repair of transcription-blocking DNA lesions by transcription-coupled nucleotide excision repair (TC-NER) to permit efficient recovery of mRNA synthesis while widespread sustained transcription blocks lead to apoptosis. Therefore, RNAPII serves as a processive DNA damage sensor that identifies transcription-blocking DNA lesions. Cockayne syndrome (CS) is an autosomal recessive disorder characterized by a complex phenotype that includes clinical photosensitivity, progressive neurological degeneration and premature-aging. CS is associated with defects in TC-NER and the recovery of mRNA synthesis, making CS cells exquisitely sensitive to a variety of DNA damaging agents. These defects in the coupling of repair and transcription appear to underlie some of the complex clinical features of CS. Recent insight into the consequences of blocked transcription and their relationship to CS will be discussed.

Genome maintenance and transcription integrity in aging and disease

DNA damage contributes to cancer development and aging. Congenital syndromes that affect DNA repair processes are characterized by cancer susceptibility, developmental defects, and accelerated aging (Schumacher et al., 2008). DNA damage interferes with DNA metabolism by blocking replication and transcription. DNA polymerase blockage leads to replication arrest and can gives rise to genome instability. Transcription, on the other hand, is an essential process for utilizing the information encoded in the genome. DNA damage that interferes with transcription can lead to apoptosis and cellular senescence. Both processes are powerful tumor suppressors (Bartek and Lukas, 2007). Cellular response mechanisms to stalled RNA polymerase II complexes have only recently started to be uncovered. Transcription-coupled DNA damage responses might thus play important roles for the adjustments to DNA damage accumulation in the aging organism (Garinis et al., 2009). Here we review human disorders that are caused by defects in genome stability to explore the role of DNA damage in aging and disease. We discuss how the nucleotide excision repair system functions at the interface of transcription and repair and conclude with concepts how therapeutic targeting of transcription might be utilized in the treatment of cancer.

Conceptual developments in the causes of Cockayne syndrome

Cockayne syndrome is an autosomal recessive disease that covers a wide range of symptoms, from mild photosensitivity to severe neonatal lethal disorder. The pathology of Cockayne syndrome may be caused by several mechanisms such as a DNA repair deficiency, transcription dysregulation, altered redox balance and mitochondrial dysfunction. Conceivably each of these mechanisms participates during a different stage in life of a Cockayne syndrome patient. Endogenous reactive oxygen is considered as an ultimate cause of DNA damage that contributes to Cockayne syndrome pathology. Here we demonstrate that mitochondrial reactive oxygen does not cause detectable nuclear DNA damage. This observation implies that a significant component of Cockayne syndrome pathology may be due to abnormal mitochondrial function independent of nuclear DNA damage. The source of nuclear DNA damage to central nervous system tissue most likely occurs from extrinsic neurotransmitter signaling.

Cockayne syndrome: the expanding clinical and mutational spectrum

Cockayne syndrome is a progressive multisystem disorder characterized by a specific cellular defect in transcription-coupled repair. Typical features include developmental delay, failure to thrive, microcephaly, cutaneous photosensitivity, dental anomalies, progressive hearing loss, pigmentary retinopathy, cataracts and enophthalmia. Various levels of severity have been described including the "classical" or moderate type I CS, the early-onset or severe type II and the mild or late-onset type III. Adult-onset cases with prolonged survival and normal initial development have also been identified. At the opposite end of the scale, the most severely affected patients, showing a prenatal onset of the symptoms, are overlapping with the cerebro-oculo-facio-skeletal (COFS) syndrome. These overlapping subtypes build a continuous spectrum without clear thresholds. Revised diagnostic criteria are proposed to improve the recognition of the disease. Two thirds of the patients are linked to mutations in the CSB (ERCC6) gene, one third to mutations in the CSA (ERCC8) gene. At least 78 different mutations are known in the CSB gene and 30 in the CSA gene to date, in more than 120 genetically confirmed patients. Large clinical and molecular databases are needed to unravel genotype-phenotype correlations and to gain more insight into the underlying molecular mechanisms.

Structure, function and regulation of CSB: a multi-talented gymnast

The Cockayne syndrome complementation group B protein, CSB, plays pivotal roles in transcription regulation and DNA repair. CSB belongs to the SNF2/SWI2 ATP-dependent chromatin remodeling protein family, and studies from many laboratories have revealed that CSB has multiple activities and modes of regulation. To understand the underlying mechanisms of Cockayne syndrome, it is necessary to understand how the biochemical activities of CSB are used to carry out its biological functions. In this review, we summarize our current knowledge of the structure, function and regulation of CSB, and discuss how these properties can impact the biological functions of this chromatin remodeler.

Genetic syndromes caused by mutations in epigenetic genes

The orchestrated organization of epigenetic factors that control chromatin dynamism, including DNA methylation, histone marks, non-coding RNAs (ncRNAs) and chromatin-remodeling proteins, is essential for the proper function of tissue homeostasis, cell identity and development. Indeed, deregulation of epigenetic profiles has been described in several human pathologies, including complex diseases (such as cancer, cardiovascular and neurological diseases), metabolic pathologies (type 2 diabetes and obesity) and imprinting disorders. Over the last decade it has become increasingly clear that mutations of genes involved in epigenetic mechanism, such as DNA methyltransferases, methyl-binding domain proteins, histone deacetylases, histone methylases and members of the SWI/SNF family of chromatin remodelers are linked to human disorders, including Immunodeficiency Centromeric instability Facial syndrome 1, Rett syndrome, Rubinstein-Taybi syndrome, Sotos syndrome or alpha-thalassemia/mental retardation X-linked syndrome, among others. As new members of the epigenetic machinery are described, the number of human syndromes associated with epigenetic alterations increases. As recent examples, mutations of histone demethylases and members of the non-coding RNA machinery have recently been associated with Kabuki syndrome, Claes-Jensen X-linked mental retardation syndrome and Goiter syndrome. In this review, we describe the variety of germline mutations of epigenetic modifiers that are known to be associated with human disorders, and discuss the therapeutic potential of epigenetic drugs as palliative care strategies in the treatment of such disorders.

What role (if any) does the highly conserved CSB-PGBD3 fusion protein play in Cockayne syndrome?

The PGBD3 piggyBac transposon inserted into CSB intron 5 early in the primate lineage. As a result of alternative splicing, the human CSB gene now encodes three proteins: CSB, a CSB-PGBD3 fusion protein that joins the N-terminal CSB domain to the C-terminal PGBD3 transposase domain, and PGBD3 transposase. The fusion protein is as highly conserved as CSB, suggesting that it is advantageous in health; however, expression of the fusion protein in CSB-null cells induces a constitutive interferon (IFN) response. The fusion protein binds in vivo to PGBD3-related MER85 elements, but is also tethered to c-Jun, TEAD1, and CTCF motifs by interactions with the cognate transcription factors. The fusion protein regulates nearby genes from the c-Jun (and to a lesser extent TEAD1 and CTCF) motifs, but not from MER85 elements. We speculate that the fusion protein interferes with CSB-dependent chromatin remodeling, generating double-stranded RNA (dsRNA) that induces an IFN response through endosomal TLR or cytoplasmic RIG-I and/or MDA5 RNA sensors. We suggest that the fusion protein was fixed in primates because an elevated IFN response may help to fight viral infection. We also speculate that an inappropriate IFN response may contribute to the clinical presentation of CS.

A possible cranio-oro-facial phenotype in Cockayne syndrome

Background

Cockayne Syndrome CS (Type A – CSA; or CS Type I OMIM #216400) (Type B – CSB; or CS Type II OMIM #133540) is a rare autosomal recessive neurological disease caused by defects in DNA repair characterized by progressive cachectic dwarfism, progressive intellectual disability with cerebral leukodystrophy, microcephaly, progressive pigmentary retinopathy, sensorineural deafness photosensitivity and possibly orofacial and dental anomalies.

Methods

We studied the cranio-oro-facial status of a group of 17 CS patients from 15 families participating in the National Hospital Program for Clinical Research (PHRC) 2005 « Clinical and molecular study of Cockayne syndrome ». All patients were examined by two investigators using the Diagnosing Dental Defects Database (D[4]/phenodent) record form.

Results

Various oro-facial and dental anomalies were found: retrognathia; micrognathia; high- arched narrow palate; tooth crowding; hypodontia (missing permanent lateral incisor, second premolars or molars), screwdriver shaped incisors, microdontia, radiculomegaly, and enamel hypoplasia. Eruption was usually normal. Dental caries was associated with enamel defects, a high sugar/carbohydrate soft food diet, poor oral hygiene and dry mouth. Cephalometric analysis revealed mid-face hypoplasia, a small retroposed mandible and hypo-development of the skull.

Conclusion

CS patients may have associated oro-dental features, some of which may be more frequent in CS children – some of them being described for the first time in this paper (agenesis of second permanent molars and radiculomegaly). The high susceptibility to rampant caries is related to a combination of factors as well as enamel developmental defects. Specific attention to these anomalies may contribute to diagnosis and help plan management.

Identification of Two Novel ERCC6 Mutations in Old Order Amish with Cockayne Syndrome

Cockayne syndrome (CS) is a rare autosomal recessive disorder characterized by progressive multisystem degeneration and segmental premature aging. Mutations in the DNA repair gene ERCC6 are responsible for the majority of CS cases reported. In this study, we identified 4 patients presenting with CS from 2 Old Order Amish families. Sequence analysis of the ERCC6 gene revealed 2 novel mutations associated with the disorder in these patients. The patients from family 1 were homozygous for a splice-site mutation, c.2709 + 1G>T, in intron 14 of ERCC6, whereas the patients from family 2 were compound heterozygous for c.2709 + 1G>T and a short deletion in exon 5 (c.1293_1320del). Our findings provide evidence of allelic heterogeneity in Old Order Amish, which is extremely uncommon for a rare condition in an isolated founder population.

DNA-Reparatur und Alterung

Die letzten Jahre haben erhebliche Fortschritte im Verständnis der Biologie des Alterns erbracht. Die Bedeutung genomischer Instabilität als kausaler Faktor der funktionellen Degeneration in der Alterung wurde besonders durch Untersuchungen an progeroiden Syndromen deutlich. Humane Progerien stellen seltene Erbkrankheiten dar, welche von ausgesprochener Diversität und Komplexität gekennzeichnet sind. Die Manifestationen progeroider Syndrome reflektieren sowohl die Funktion der involvierten DNA-Reparatur- und Schadensantwortmechanismen als auch die komplexen physiologischen Reaktionen auf DNA-Läsionen. Untersuchungen an biologischen Modellsystemen progeroider Erkrankungen haben Verbindungen zwischen der DNA-Schadensantwort und genetischen Regulationsmechanismen der Alterung aufgezeigt. Durch diese Erkenntnisse hat sich einerseits das Verständnis der Ursachen von Progerie und Alterung verbessert, andererseits werden neue Strategien erkenntlich, welche zur Entwicklung präventiver Interventionen zur Behandlung progeroider Symptome und altersbedingter Erkrankungen führen könnten.

Cockayne syndrome b maintains neural precursor function

Neurodevelopmental defects are observed in the hereditary disorder Cockayne syndrome (CS). The gene most frequently mutated in CS, Cockayne Syndrome B (CSB), is required for the repair of bulky DNA adducts in transcribed genes during transcription-coupled nucleotide excision repair. CSB also plays a role in chromatin remodeling and mitochondrial function. The role of CSB in neural development is poorly understood. Here we report that the abundance of neural progenitors is normal in Csb(-/-) mice and the frequency of apoptotic cells in the neurogenic niche of the adult subependymal zone is similar in Csb(-/-) and wild type mice. Both embryonic and adult Csb(-/-) neural precursors exhibited defective self-renewal in the neurosphere assay. In Csb(-/-) neural precursors, self-renewal progressively decreased in serially passaged neurospheres. The data also indicate that Csb and the nucleotide excision repair protein Xpa preserve embryonic neural stem cell self-renewal after UV DNA damage. Although Csb(-/-) neural precursors do not exhibit altered neuronal lineage commitment after low-dose UV (1J/m(2)) in vitro, neurons differentiated in vitro from Csb(-/-) neural precursors that had been irradiated with 1J/m(2) UV exhibited defective neurite outgrowth. These findings identify a function for Csb in neural precursors.

Dysregulation of RNA polymerase I transcription during disease

Transcription of the ribosomal RNA genes by the dedicated RNA polymerase I enzyme and subsequent processing of the ribosomal RNA are fundamental control steps in the synthesis of functional ribosomes. Dysregulation of Pol I transcription and ribosome biogenesis is linked to the etiology of a broad range of human diseases. Diseases caused by loss of function mutations in the molecular constituents of the ribosome, or factors intimately associated with RNA polymerase I transcription and processing are collectively termed ribosomopathies. Ribosomopathies are generally rare and treatment options are extremely limited tending to be more palliative than curative. Other more common diseases are associated with profound changes in cellular growth such as cardiac hypertrophy, atrophy or cancer. In contrast to ribosomopathies, altered RNA polymerase I transcriptional activity in these diseases largely results from dysregulated upstream oncogenic pathways or by direct modulation by oncogenes or tumor suppressors at the level of the RNA polymerase I transcription apparatus itself. Ribosomopathies associated with mutations in ribosomal proteins and ribosomal RNA processing or assembly factors have been covered by recent excellent reviews. In contrast, here we review our current knowledge of human diseases specifically associated with dysregulation of RNA polymerase I transcription and its associated regulatory apparatus, including some cases where this dysregulation is directly causative in disease. We will also provide insight into and discussion of possible therapeutic approaches to treat patients with dysregulated RNA polymerase I transcription. This article is part of a Special Issue entitled: Transcription by Odd Pols.

Tethering of the conserved piggyBac transposase fusion protein CSB-PGBD3 to chromosomal AP-1 proteins regulates expression of nearby genes in humans

The CSB-PGBD3 fusion protein arose more than 43 million years ago when a 2.5-kb piggyBac 3 (PGBD3) transposon inserted into intron 5 of the Cockayne syndrome Group B (CSB) gene in the common ancestor of all higher primates. As a result, full-length CSB is now coexpressed with an abundant CSB-PGBD3 fusion protein by alternative splicing of CSB exons 1-5 to the PGBD3 transposase. An internal deletion of the piggyBac transposase ORF also gave rise to 889 dispersed, 140-bp MER85 elements that were mobilized in trans by PGBD3 transposase. The CSB-PGBD3 fusion protein binds MER85s in vitro and induces a strong interferon-like innate antiviral immune response when expressed in CSB-null UVSS1KO cells. To explore the connection between DNA binding and gene expression changes induced by CSB-PGBD3, we investigated the genome-wide DNA binding profile of the fusion protein. CSB-PGBD3 binds to 363 MER85 elements in vivo, but these sites do not correlate with gene expression changes induced by the fusion protein. Instead, CSB-PGBD3 is enriched at AP-1, TEAD1, and CTCF motifs, presumably through protein-protein interactions with the cognate transcription factors; moreover, recruitment of CSB-PGBD3 to AP-1 and TEAD1 motifs correlates with nearby genes regulated by CSB-PGBD3 expression in UVSS1KO cells and downregulated by CSB rescue of mutant CS1AN cells. Consistent with these data, the N-terminal CSB domain of the CSB-PGBD3 fusion protein interacts with the AP-1 transcription factor c-Jun and with RNA polymerase II, and a chimeric CSB-LacI construct containing only the N-terminus of CSB upregulates many of the genes induced by CSB-PGBD3. We conclude that the CSB-PGBD3 fusion protein substantially reshapes the transcriptome in CS patient CS1AN and that continued expression of the CSB-PGBD3 fusion protein in the absence of functional CSB may affect the clinical presentation of CS patients by directly altering the transcriptional program.

A population-based study of DNA repair gene variants in relation to non-melanoma skin cancer as a marker of a cancer-prone phenotype

For unknown reasons, non-melanoma skin cancer (NMSC) is associated with increased risk of other malignancies. Focusing solely on DNA repair or DNA repair-related genes, this study tested the hypothesis that DNA repair gene variants contribute to the increased cancer risk associated with a personal history of NMSC. From the parent CLUE II cohort study, established in 1989 in Washington County, MD, the study consisted of a cancer-free control group (n 5 2296) compared with three mutually exclusive groups of cancer cases ascertained through 2007: (i) Other (non-NMSC) cancer only (n 5 2349); (ii) NMSC only (n 5 694) and (iii) NMSC plus other cancer (n 5 577). The frequency of minor alleles in 759 DNA repair gene single nucleotide polymorphisms (SNPs) was compared in these four groups. Comparing those with both NMSC and other cancer versus those with no cancer, 10 SNPs had allelic trend P-values <0.01. The two top-ranked SNPs were both within the thymine DNA glycosylase gene (TDG). One was a non-synonymous coding SNP (rs2888805) [per allele odds ratio (OR) 1.40, 95% confidence interval (CI) 1.16-1.70; P-value 5 0.0006] and the other was an intronic SNP in high linkage disequilibrium with rs2888805 (rs4135150). None of the associations had a P-value <6.6310(-5), the threshold for statistical significance after correcting for multiple comparisons. The results pinpoint DNA repair genes most likely to contribute to the NMSC cancer-prone phenotype. A promising lead is genetic variants in TDG, important not only in base excision repair but also in regulating the epigenome and gene expression, which may contribute to the NMSC-associated increase in overall cancer risk.