Reduced XPC DNA repair gene mRNA levels in clinically normal parents of xeroderma pigmentosum patients

DNA repair-related heritable photosensitivity syndromes: Mutation landscape in a multiethnic cohort of 17 multigenerational families with high degree of consanguinity

Inherited photosensitivity syndromes are a heterogeneous group of genetic skin disorders with tremendous phenotypic variability, characterized by photosensitivity and defective DNA repair, especially nucleotide excision repair. A cohort of 17 Iranian families with heritable photosensitivity syndromes was evaluated to identify their genetic defect. The patients' DNA was analyzed with either whole-exome sequencing or RNA sequencing (RNA-Seq). The interpretations of the genomic results were guided by genome-wide homozygosity mapping. Haplotype analysis was performed for cases with recurrent mutations. RNA-Seq, in addition to mutation detection, was also utilized to confirm the pathogenicity. Thirteen sequence variants, including six previously unreported pathogenic variants, were disclosed in 17 Iranian families, with XPC as the most common mutated gene in 10 families (59%). In one patient, RNA-Seq, as a first-tier diagnostic approach, revealed a non-canonical homozygous germline variant: XPC:c.413-9 T > A. The Sashimi plot showed skipping of exon 4 with dramatic XPC down-expression. Haplotype analysis of XPC:c.2251-1 G>C and XPC:1243 C>T in four families showed common haplotypes of 1.7 Mb and 2.6 Mb, respectively, denoting a founder effect. Lastly, two extremely rare cases were presented in this report: a homozygous UVSSA:c .1990 C>T was disclosed, and ERCC2-related cerebro-oculo-facio-skeletal (COFS) syndrome with an early childhood death. A direct comparison of our data with the results of previously reported cohorts demonstrates the international mutation landscape of DNA repair-related photosensitivity disorders, although population-specific differences were observed.

The French Cohort of DNA Repair-Deficient Xeroderma Pigmentosum Patients: Risk of Hematological Malignancies

BACKGROUND

Xeroderma pigmentosum (XP) is a rare genetic disorder characterized by a high incidence of skin cancers. These patients are deficient in nucleotide excision repair caused by mutations in one of the 7 XP genes.

METHODS

We diagnosed 181 XP patients using UV-induced DNA repair measurements and/or DNA sequencing from 1982 to 2022 in France.

RESULTS

As all XP patients, the French ones are very sensitive to UV exposure but since they are usually very well protected, they develop relatively few skin cancers. A majority of French XP patients originate from North Africa and bear a founder mutation on the XPC gene. The striking discovery is that these patients are at a very high risk to develop aggressive and lethal internal tumors such as hematological malignancies (more than a 100-fold risk compared to the general population for myelodysplasia/leukemia) with a median age of death of 25 years, and brain, gynecological, and thyroid tumors with even lower median ages of death. The high mutation rates found in XP-C internal tumors allow us to think that these XP patients could be successfully treated by immunotherapies. A full analysis of the molecular origins of these DNA repair-deficient tumors is discussed. Several explanations for this high predisposition risk are proposed.

CONCLUSIONS

As the age of the XP population is increasing due to better photo-protection, the risk of lethal internal tumors is a new Damocles sword that hangs over XP-C patients. This review of the French cohort is of particular importance for alerting physicians and families to the prevention and early detection of aggressive internal tumors in XP patients.

Increased risk of internal tumors in DNA repair-deficient xeroderma pigmentosum patients: analysis of four international cohorts

Background

Xeroderma pigmentosum (XP) is a rare, autosomal, recessive DNA repair-deficiency disorder with a frequency of 1–3 per million livebirths in Europe and USA but with higher frequencies in isolated islands or in countries with a high level of consanguinity. XP is characterized by high incidence of skin cancers on sun-exposed sites. Recent improvement in life expectancy of XP patients suggests an increased risk of frequently aggressive and lethal internal tumors. Our purpose was to quantify relative risks of internal tumor development for XP patients by tumor type, XP-subtype, patients’ ages and ethnicity through comparison with the US general population.

Methods

We analyzed four independent international well-characterized XP cohorts (from USA, UK, France and Brazil) with a total of 434 patients, where 11.3% developed internal tumors and compared them to the American general population. We also compiled, through PubMed/Medline, a dataset of 89 internal tumors in XP patients published between 1958 and 2020.

Results

In the combined 4-XP cohort, relative risk of internal tumors was 34 (95% confidence interval (CI) 25–47) times higher than in the general population (p-value = 1.0E−47) and tumor arose 50 years earlier. The XP-C group was at the highest risk for the 0–20 years old-patients (OR = 665; 95% CI 368–1200; p-value = 4.3E−30). The highest risks were observed for tumors of central nervous system (OR = 331; 95% CI 171–641; p-value = 2.4E−20), hematological malignancies (OR = 120; 95% CI 77–186; p-value = 3.7E−36), thyroid (OR = 74; 95% CI 31–179; p-value = 1.2E−8) and gynecological tumors (OR = 91; 95% CI 42–193; p-value = 3.5E−12). The type of mutation on the XPC gene is associated with different classes of internal tumors. The majority of French XP-C patients (80%) are originated from North Africa and carried the XPC delTG founder mutation specific from the South Mediterranean area. The OR is extremely high for young (0–20 years) patients with more than 1300-fold increase for the French XPs carrying the founder mutation.

Conclusion

Because the age of XP population is increasing due to better sun-protection and knowledge of the disease, these results are of particular importance for the physicians to help in early prevention and detection of internal tumors in their XP patients. Few preventive blood analyses or simple medical imaging may help to better detect early cancer appearance in this population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02203-1.

Mutagenicity Profile Induced by UVB Light in Human Xeroderma Pigmentosum Group C Cells†

Nucleotide excision repair (NER) is one of the main pathways for genome protection against structural DNA damage caused by sunlight, which in turn is extensively related to skin cancer development. The mutation spectra induced by UVB were investigated by whole-exome sequencing of randomly selected clones of NER-proficient and XP-C-deficient human skin fibroblasts. As a model, a cell line unable to recognize and remove lesions (XP-C) was used and compared to the complemented isogenic control (COMP). As expected, a significant increase of mutagenesis was observed in irradiated XP-C cells, mainly C>T transitions, but also CC>TT and C>A base substitutions. Remarkably, the C>T mutations occur mainly at the second base of dipyrimidine sites in pyrimidine-rich sequence contexts, with 5'TC sequence the most mutated. Although T>N mutations were also significantly increased, they were not directly related to pyrimidine dimers. Moreover, the large-scale study of a single UVB irradiation on XP-C cells allowed recovering the typical mutation spectrum found in human skin cancer tumors. Eventually, the data may be used for comparison with the mutational profiles of skin tumors obtained from XP-C patients and may help to understand the mutational process in nonaffected individuals.

Clinical and Mutational Spectrum of Xeroderma Pigmentosum in Egypt: Identification of Six Novel Mutations and Implications for Ancestral Origins

Xeroderma pigmentosum is a rare autosomal recessive skin disorder characterized by freckle-like dry pigmented skin, photosensitivity, and photophobia. Skin and ocular symptoms are confined to sun exposed areas of the body. Patients have markedly increased risk for UV-induced skin, ocular, and oral cancers. Some patients develop neurodegenerative symptoms, including diminished tendon reflexes and microcephaly. In this study, we describe clinical and genetic findings of 36 XP patients from Egypt, a highly consanguineous population from North Africa. Thorough clinical evaluation followed by Sanger sequencing of XPA and XPC genes were done. Six novel and seven previously reported mutations were identified. Phenotype-genotype correlation was investigated. We report clinical and molecular findings consistent with previous reports of countries sharing common population structure, and geographical and historical backgrounds with implications on common ancestral origins and historical migration flows. Clinical and genetic profiling improves diagnosis, management, counselling, and implementation of future targeted therapies.

FANCA Gene Mutations in North African Fanconi Anemia Patients

Populations in North Africa (NA) are characterized by a high rate of consanguinity. Consequently, the proportion of founder mutations might be higher than expected and could be a major cause for the high prevalence of recessive genetic disorders like Fanconi anemia (FA). We report clinical, cytogenetic, and molecular characterization of FANCA in 29 North African FA patients from Tunisia, Libya, and Algeria. Cytogenetic tests revealed high rates of spontaneous chromosome breakages for all patients except two of them. FANCA molecular analysis was performed using three different molecular approaches which allowed us to identify causal mutations as homozygous or compound heterozygous forms. It included a nonsense mutation (c.2749C > T; p.Arg917Ter), one reported missense mutation (c.1304G > A; p.Arg435His), a novel missense variant (c.1258G > A; p.Asp409Glu), and the FANCA most common reported mutation (c.3788_3790delTCT; p.Phe1263del). Furthermore, three founder mutations were identified in 86.7% of the 22 Tunisian patients: (1) a deletion of exon 15, in 36.4% patients (8/22); (2), a deletion of exons 4 and 5 in 23% (5/22) and (3) an intronic mutation c.2222 + 166G > A, in 27.3% (6/22). Despite the relatively small number of patients studied, our results depict the mutational landscape of FA among NA populations and it should be taken into consideration for appropriate genetic counseling.

Xeroderma Pigmentosum C (XPC) Mutations in Primary Fibroblasts Impair Base Excision Repair Pathway and Increase Oxidative DNA Damage

Xeroderma Pigmentosum C (XPC) is a multi-functional protein that is involved not only in the repair of bulky lesions, post-irradiation, via nucleotide excision repair (NER) per se but also in oxidative DNA damage mending. Since base excision repair (BER) is the primary regulator of oxidative DNA damage, we characterized, post-Ultraviolet B-rays (UVB)-irradiation, the detailed effect of three different XPC mutations in primary fibroblasts derived from XP-C patients on mRNA, protein expression and activity of different BER factors. We found that XP-C fibroblasts are characterized by downregulated expression of different BER factors including OGG1, MYH, APE1, LIG3, XRCC1, and Polβ. Such a downregulation was also observed at OGG1, MYH, and APE1 protein levels. This was accompanied with an increase in DNA oxidative lesions, as evidenced by 8-oxoguanine levels, immediately post-UVB-irradiation. Unlike in normal control cells, these oxidative lesions persisted over time in XP-C cells having lower excision repair capacities. Taken together, our results indicated that an impaired BER pathway in XP-C fibroblasts leads to longer persistence and delayed repair of oxidative DNA damage. This might explain the diverse clinical phenotypes in XP-C patients suffering from cancer in both photo-protected and photo-exposed areas. Therapeutic strategies based on reinforcement of BER pathway might therefore represent an innovative path for limiting the drawbacks of NER-based diseases, as in XP-C case.

Comprehensive germline mutation analysis and clinical profile in a large cohort of Brazilian xeroderma pigmentosum patients

BACKGROUND

Xeroderma pigmentosum (XP) patients present a high risk of developing skin cancer and other complications at an early age. This disease is characterized by mutations in the genes related to the DNA repair system.

OBJECTIVES

To describe the clinical and molecular findings in a cohort of 32 Brazilian individuals who received a clinical diagnosis of XP.

METHODS

Twenty-seven families were screened for germline variants in eight XP-related genes.

RESULTS

All patients (N = 32) were diagnosed with bi-allelic germline pathogenic or potentially pathogenic variants, including nine variants previously undescribed. The c.2251-1G>C XPC pathogenic variant, reported as the founder mutation in Comorian and Pakistani patients, was observed in 15 cases in homozygous or compound heterozygous. Seven homozygous patients for POLH/XPV variants developed their symptoms by an average age of 7.7 years. ERCC2/XPD, DDB2/XPE and ERCC5/XPG variants were found in a few patients. Aside from melanoma and non-melanoma skin tumours, a set of patients developed skin sebaceous carcinoma, leiomyosarcoma, angiosarcoma, mucoepidermoid carcinoma, gastric adenocarcinoma and serous ovarian carcinoma.

CONCLUSIONS

We reported a high frequency of XPC variants in 32 XP Brazilian patients. Nine new variants in XP-related genes, unexpected non-skin cancer lesions and an anticipation of the clinical manifestation in POLH/XPV cases were also described.

Reproductive Health in Xeroderma Pigmentosum: Features of Premature Aging

OBJECTIVE

To assess the age at menarche and menopause of women with xeroderma pigmentosum, a DNA repair disease with premature aging, in a longitudinal natural history study.

METHODS

We conducted a natural history study that reviewed medical records for gynecologic and reproductive health of all female patients with xeroderma pigmentosum aged older than 9 years examined at the National Institutes of Health (NIH). We performed gynecologic and laboratory examinations on a subset of the patients. Women in a second subset, who could not be examined, were interviewed using a questionnaire. Women who were deceased or lost to follow-up formed a third subset.

RESULTS

Sixty females with xeroderma pigmentosum aged older than 9 years (median 29 years, range 10-61 years) were evaluated at the NIH from 1971 to 2018. Of these 60, 31 had history, questionnaire, record review, and gynecologic evaluation; 14 had record review and questionnaire interview by telephone; and 15 had only NIH record review. Menarche in females with xeroderma pigmentosum occurred at a median age of 12.0 years (range 9-17 years), which was comparable with the U.S. general population. Among the 18 patients with menopause, the median age at menopause of 29.5 years (range 18-49.5 years) was more than 20 years younger than in the U.S. general population (52.9 years). Premature menopause (before age 40 years) occurred in 14 of the 45 (31%) women aged 18 years or older, and primary ovarian insufficiency was documented in nine of them. There were 32 live births among 21 of the women, five of whom subsequently developed premature menopause.

CONCLUSION

Females with xeroderma pigmentosum in our study had a normal age at menarche and were fertile but had increased incidence of premature menopause. Premature menopause, a symptom of premature aging, should be considered for gynecologic and reproductive health as well as implicating DNA repair in maintaining normal ovarian function.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT00001813.

Identification of a novel protein truncating mutation p.Asp98* in XPC associated with xeroderma pigmentosum in a consanguineous Pakistani family

BACKGROUND

Xeroderma pigmentosum (XP) is a rare genetic disorder, which is characterized by hyper-sensitivity to solar ultraviolet (UV) radiation. Clinical consequences of sun exposure are skin lesions and an increased risk of developing skin cancer. Genetic studies have identified eight genes associated with xeroderma pigmentosum. The proteins encoded by these genes are mainly involved in DNA repair mechanisms.

METHODS

Molecular genetic characterization of patients with xeroderma pigmentosum involved positional cloning methods such as homozygosity mapping and subsequent candidate gene analysis. Mutation screening was performed through Sanger DNA sequencing.

RESULTS AND DISCUSSION

In this case study, we report a novel protein truncating mutation in XPC associated with autosomal recessive xeroderma pigmentosum in a consanguineous Pakistani family. Genetic mapping revealed a novel single base insertion of a thymine nucleotide NM_004628.4: c.291dupT (c.291_292insT) in the second exon of XPC. The identified mutation leads to a premature stop codon (TGA) at amino acid position 98 (p.Asp98*) and thus presumably results in a truncated protein. The Xeroderma pigmentosum, complementation group C (XPC) is located on 3p25.1 and encodes a protein involved in nucleotide excision repair. The identified mutation presumably truncates all functional domains of the XPC protein, which likely results in the loss of protein function.

CONCLUSION

The study expands the knowledge of the mutational spectrum of XPC and is valuable for genetic counseling of affected individuals and their families.

Familial predisposition to TP53/complex karyotype MDS and leukemia in DNA repair-deficient xeroderma pigmentosum

There is a Blood Commentary on this article in this issue.

XPC gene mutations in families with xeroderma pigmentosum from Pakistan; prevalent founder effect

Xeroderma pigmentosum (XP) is a rare autosomal recessive skin disorder characterized by hyperpigmentation, premature skin aging, ocular and cutaneous photosensitivity, and increased risk of skin carcinoma. We investigated seven consanguineous XP families with nine patients from Pakistan. All the Patients exhibited typical clinical symptoms of XP since first year of life. Whole genome SNP genotyping identified a 14 Mb autozygous region segregating with the disease phenotype on chromosome 3p25.1. DNA sequencing of XPC gene revealed a founder homozygous splice site mutation (c.2251-1G>C) in patients from six families (A-F) and a homozygous nonsense mutation (c.1399C>T; p.Gln467*) in patients of family G. This is the first report of XPC mutations, underlying XP phenotype, in Pakistani population.

Splice variants of the endonucleases XPF and XPG contain residual DNA repair capabilities and could be a valuable tool for personalized medicine

The two endonucleases XPF and XPG are essentially involved in nucleotide excision repair (NER) and interstrand crosslink (ICL) repair. Defects in these two proteins result in severe diseases like xeroderma pigmentosum (XP). We applied our newly CRISPR/Cas9 generated human XPF knockout cell line with complete loss of XPF and primary fibroblasts from an XP-G patient (XP20BE) to analyze until now uncharacterized spontaneous mRNA splice variants of these two endonucleases. Functional analyses of these variants were performed using luciferase-based reporter gene assays. Two XPF and XPG splice variants with residual repair capabilities in NER, as well as ICL repair could be identified. Almost all variants are severely C-terminally truncated and lack important protein-protein interaction domains. Interestingly, XPF-202, differing to XPF-003 in the first 12 amino acids only, had no repair capability at all, suggesting an important role of this region during DNA repair, potentially concerning protein-protein interaction. We also identified splice variants of XPF and XPG exerting inhibitory effects on NER. Moreover, we showed that the XPF and XPG splice variants presented with different inter-individual expression patterns in healthy donors, as well as in various tissues. With regard to their residual repair capability and dominant-negative effects, functionally relevant spontaneous XPF and XPG splice variants present promising prognostic marker candidates for individual cancer risk, disease outcome, or therapeutic success. This merits further investigations, large association studies, and translational research within clinical trials in the future.

Xeroderma Pigmentosum with Severe Neurological Manifestations/De Sanctis-Cacchione Syndrome and a Novel XPC Mutation

Several genetic disorders caused by defective nucleotide excision repair that affect the skin and the nervous system have been described, including Xeroderma Pigmentosum (XP), De Sanctis–Cacchione syndrome (DSC), Cockayne syndrome, and Trichothiodystrophy. Cutaneous photosensitivity with an increased risk of skin malignancy is a common feature of these disorders, but clinical manifestations commonly overlap these syndromes. Several genes have been found to be altered in these pathologies, but we lack more genotype-phenotype correlations in order to make an accurate diagnosis. Very few cases of DSC syndrome have been reported in the literature. We present a case of a 12-year-old Colombian male, with multiple skin lesions in sun-exposed areas from the age of 3 months and a history of 15 skin cancers. He also displayed severe neurologic abnormalities (intellectual disability, ataxia, altered speech, and hyperreflexia), short stature, and microcephaly, which are features associated with DSC. Genetic testing revealed a novel germline mutation in the XP-C gene (c.547A>T). This is the first case of an XP-C mutation causing De Sanctis–Cacchione syndrome. Multigene panel testing is becoming more widely available and accessible in the clinical setting and will help rapidly unveil the molecular etiology of these rare genetic disorders.

Diagnosis of Xeroderma Pigmentosum Groups A and C by Detection of Two Prevalent Mutations in West Algerian Population: A Rapid Genotyping Tool for the Frequent XPC Mutation c.1643_1644delTG

Xeroderma pigmentosum (XP) is a rare autosomal recessive disorder. Considering that XP patients have a defect of the nucleotide excision repair (NER) pathway which enables them to repair DNA damage caused by UV light, they have an increased risk of developing skin and eyes cancers. In the present study, we investigated the involvement of the prevalent XPA and XPC genes mutations—nonsense mutation (c.682C>T, p.Arg228X) and a two-base-pair (2 bp) deletion (c.1643_1644delTG or p.Val548Ala fsX25), respectively—in 19 index cases from 19 unrelated families in the West of Algeria. For the genetic diagnosis of XPA gene, we proceeded to PCR-RFLP. For the XPC gene, we validated a routine analysis which includes a specific amplification of a short region surrounding the 2 bp deletion using a fluorescent primer and fragment sizing (GeneScan size) on a sequencing gel. Among the 19 index cases, there were 17 homozygous patients for the 2 bp deletion in the XPC gene and 2 homozygous patients carrying the nonsense XPA mutation. Finally, XPC appears to be the major disease-causing gene concerning xeroderma pigmentosum in North Africa. The use of fragment sizing is the simplest method to analyze this 2 bp deletion for the DNA samples coming from countries where the mutation c.1643_1644delTG of XPC gene is prevalent.

Xeroderma pigmentosum: diagnostic procedures, interdisciplinary patient care, and novel therapeutic approaches

Xeroderma pigmentosum (XP) is an autosomal recessive disease, caused by a gene defect in the nucleotide-excision-repair (NER) pathway or in translesional DNA synthesis. At the age of eight, patients already develop their first skin cancers due to this DNA repair defect. In contrast, in the Caucasian population the first tumor formation in UV exposed skin regions occurs at a mean age of 60. The clinical picture among patients suffering from XP is highly diverse and includes signs of accelerated skin aging, and UV-induced skin cancers, as well as ophthalmologic and neurological symptoms. Patients should therefore receive interdisciplinary care. This includes dermatologists, ophthalmologists, ENT specialists, neurologists, and human geneticists. Patients with XP are clinically diagnosed, but this may be supported by molecular-genetic and functional analyses. These analyses allow pinpointing the exact disease-causing gene defect (complementation group assignment, detection of the type and location of the mutation within the gene). The resulting information is already relevant to predict the course of disease and symptoms and probably will be utilized for individualized therapeutic approaches in the future. Recently, enhanced repair of UV photolesions in xeroderma pigmentosum group C cells induced by translational readthrough of premature termination codons by certain antibiotics could be demonstrated.

Consanguinity and genetic diseases in North Africa and immigrants to Europe

Endemic diseases are caused by environmental and genetic factors. While in this special issue several chapters deal with environmental factors, including infections, the present focus is on genetic causes of disease clustering due to inbreeding and recessive disease mechanisms. Consanguinity is implying sharing of genetic heritage because of marriage between close relatives originating from a common ancestor. With limited natural selection, recessive genes may become more frequent in an inbred compared with an outbred population. Consanguinity is common in North Africa (NA), and the estimates range from 40 to 49% of all marriages in Tunisia and 29-33% in Morocco. As a consequence, recessive disorders are common in the NA region, and we give some examples. Thalassaemia and sickle cell disease/anaemia constitute the most common inherited recessive disorders globally and they are common in NA, but with immigration they have spread to Europe and to other parts of the world. Another example is familial Mediterranean fever, which is common in the Eastern Mediterranean area. With immigrantion from that area to Sweden, it has become the most common hereditary autoinflammatory disease in that country, and there is no evidence that any native Swede would have been diagnosed with this disease. The examples discussed in this chapter show that the historic movement of populations and current immigration are influencing the concept of 'endemic' disease.

Transcription-coupled RNA surveillance in human genetic diseases caused by splice site mutations

Current estimates indicate that approximately one-third of all disease-causing mutations are expected to disrupt splicing. Abnormal splicing often leads to disruption of the reading frame with introduction of a premature termination codon (PTC) that targets the mRNA for degradation in the cytoplasm by nonsense mediated decay (NMD). In addition to NMD there are RNA surveillance mechanisms that act in the nucleus while transcripts are still associated with the chromatin template. However, the significance of nuclear RNA quality control in the context of human genetic diseases is unknown. Here we used patient-derived lymphoblastoid cell lines as disease models to address how biogenesis of mRNAs is affected by splice site mutations. We observed that most of the mutations analyzed introduce PTCs and trigger mRNA degradation in the cytoplasm. However, for some mutant transcripts, RNA levels associated with chromatin were found down-regulated. Quantification of nascent transcripts further revealed that a subset of genes containing splicing mutations (SM) have reduced transcriptional activity. Following treatment with the translation inhibitor cycloheximide the cytoplasmic levels of mutant RNAs increased, while the levels of chromatin-associated transcripts remained unaltered. These results suggest that transcription-coupled surveillance mechanisms operate independently from NMD to reduce cellular levels of abnormal RNAs caused by SM.

DNA damage and gene therapy of xeroderma pigmentosum, a human DNA repair-deficient disease

Xeroderma pigmentosum (XP) is a genetic disease characterized by hypersensitivity to ultra-violet and a very high risk of skin cancer induction on exposed body sites. This syndrome is caused by germinal mutations on nucleotide excision repair genes. No cure is available for these patients except a complete protection from all types of UV radiations. We reviewed the various techniques to complement or to correct the genetic defect in XP cells. We, particularly, developed the correction of XP-C skin cells using the fidelity of the homologous recombination pathway during repair of double-strand break (DSB) in the presence of XPC wild type sequences. We used engineered nucleases (meganuclease or TALE nuclease) to induce a DSB located at 90 bp of the mutation to be corrected. Expression of specific TALE nuclease in the presence of a repair matrix containing a long stretch of homologous wild type XPC sequences allowed us a successful gene correction of the original TG deletion found in numerous North African XP patients. Some engineered nucleases are sensitive to epigenetic modifications, such as cytosine methylation. In case of methylated sequences to be corrected, modified nucleases or demethylation of the whole genome should be envisaged. Overall, we showed that specifically-designed TALE-nuclease allowed us to correct a 2 bp deletion in the XPC gene leading to patient's cells proficient for DNA repair and showing normal UV-sensitivity. The corrected gene is still in the same position in the human genome and under the regulation of its physiological promoter. This result is a first step toward gene therapy in XP patients.

Targeted gene therapy of xeroderma pigmentosum cells using meganuclease and TALEN™

Xeroderma pigmentosum group C (XP-C) is a rare human syndrome characterized by hypersensitivity to UV light and a dramatic predisposition to skin neoplasms. XP-C cells are deficient in the nucleotide excision repair (NER) pathway, a complex process involved in the recognition and removal of DNA lesions. Several XPC mutations have been described, including a founder mutation in North African patients involving the deletion of a TG dinucleotide (ΔTG) located in the middle of exon 9. This deletion leads to the expression of an inactive truncated XPC protein, normally involved in the first step of NER. New approaches used for gene correction are based on the ability of engineered nucleases such as Meganucleases, Zinc-Finger nucleases or TALE nucleases to accurately generate a double strand break at a specific locus and promote correction by homologous recombination through the insertion of an exogenous DNA repair matrix. Here, we describe the targeted correction of the ΔTG mutation in XP-C cells using engineered meganuclease and TALEN™. The methylated status of the XPC locus, known to inhibit both of these nuclease activities, led us to adapt our experimental design to optimize their in vivo efficacies. We show that demethylating treatment as well as the use of TALEN™ insensitive to CpG methylation enable successful correction of the ΔTG mutation. Such genetic correction leads to re-expression of the full-length XPC protein and to the recovery of NER capacity, attested by UV-C resistance of the corrected cells. Overall, we demonstrate that nuclease-based targeted approaches offer reliable and efficient strategies for gene correction.

Repair of UV photolesions in xeroderma pigmentosum group C cells induced by translational readthrough of premature termination codons

About 12% of human genetic disorders involve premature termination codons (PTCs). Aminoglycoside antibiotics have been proposed for restoring full-length proteins by readthrough of PTC. To assess the efficiency of readthrough, we selected homozygous and compound heterozygous skin fibroblasts from xeroderma pigmentosum (XP) patients with different PTCs in the XPC DNA repair gene. XP patients have a nucleotide excision repair defect and a 10,000-fold increased risk of UV-induced skin cancer. In six of eight PTC-containing XP-C cells, treatment with Geneticin and gentamicin resulted in (i) stabilized XPC-mRNA, which would have been degraded by nonsense-mediated decay; (ii) increased expression of XPC protein that localized to UV-damaged sites; (iii) recruitment of XPB and XPD proteins to UV DNA damage sites; and (iv) increased repair of 6-4 photoproducts and cyclobutane pyrimidine dimers. Expression of PTC in a transfected vector revealed that readthrough depends on the PTC sequence and its location within the gene. This sensitive DNA repair assay system demonstrates the complexity of response to PTC readthrough inducers. The efficiency of aminoglycoside-mediated readthrough depends on the type and copy number of PTC, the downstream 4+ nucleotide, and the location within the exon. Treatment with small-molecule nonaminoglycoside compounds (PTC124, BZ16, or RTC14) resulted in similarly increased XPC mRNA expression and photoproduct removal with less toxicity than with the aminoglycosides. Characterizing PTC structure and parameters governing effective PTC readthrough may provide a unique prophylactic therapy for skin cancer prevention in XP-C patients.

Two novel mutations in ABHD12: expansion of the mutation spectrum in PHARC and assessment of their functional effects

PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts) is a recently described autosomal-recessive neurodegenerative disease caused by mutations in the α-β-hydrolase domain-containing 12 gene (ABHD12). Only five homozygous ABHD12 mutations have been reported and the pathogenesis of PHARC remains unclear. We evaluated a woman who manifested short stature as well as the typical features of PHARC. Sequence analysis of ABHD12 revealed a novel heterozygous c.1129A>T (p.Lys377*) mutation. Targeted comparative genomic hybridization detected a 59-kb deletion that encompasses exon 1 of ABHD12 and exons 1-4 of an adjacent gene, GINS1, and includes the promoters of both genes. The heterozygous deletion was also carried by the patient's asymptomatic mother. Quantitative reverse transcription-PCR demonstrated ∼50% decreased expression of ABHD12 RNA in lymphoblastoid cell lines from both individuals. Activity-based protein profiling of serine hydrolases revealed absence of ABHD12 hydrolase activity in the patient and 50% reduction in her mother. This is the first report of compound heterozygosity in PHARC and the first study to describe how a mutation might affect ABHD12 expression and function. The possible involvement of haploinsufficiency for GINS1, a DNA replication complex protein, in the short stature of the patient and her mother requires further studies.

DNA repair activity in fish and interest in ecotoxicology: a review

The knowledge of DNA repair in a target species is of first importance as it is the primary line of defense against genotoxicants, and a better knowledge of DNA repair capacity in fish could help to interpret genotoxicity data and/or assist in the choice of target species, developmental stage and tissues to focus on, both for environmental biomonitoring studies and DNA repair testing. This review focuses in a first part on what is presently known on a mechanistic basis, about the various DNA repair systems in fish, in vivo and in established cell lines. Data on base excision repair (BER), direct reversal with O⁶-alkylguanine transferase and double strand breaks repair, although rather scarce, are being reviewed, as well as nucleotide excision repair (NER) and photoreactivation repair (PER), which are by far the most studied repair mechanisms in fish. Most of these repair mechanisms seem to be strongly species and tissue dependent; they also depend on the developmental stage of the organisms. BER is efficient in vivo, although no data has been found on in vitro models. NER activity is quite low or even inexistent depending on the studies; however this lack is partly compensated by a strong PER activity, especially in early developmental stage. In a second part, a survey of the ecotoxicological studies integrating DNA repair as a parameter responding to single or mixture of contaminant is realized. Three main approaches are being used: the measurement of DNA repair gene expression after exposure, although it has not yet been clearly established whether gene expression is indicative of repair capacity; the monitoring of DNA damage removal by following DNA repair kinetics; and the modulation of DNA repair activity following exposure in situ, in order to assess the impact of exposure history on DNA repair capacity. Since all DNA repair processes are possible targets for environmental pollutants, we can also wonder at which extent such a modulation of repair capacities in fish could be the base for the development of new biomarkers of genotoxicity. Knowing the importance of the germ cell DNA integrity in the reproductive success of aquatic organisms, the DNA repair capacity of such cells deserve to be more studied, as well as DNA repair capacities of established fish cell lines. The limited amount of available data, which shows low/slow DNA repair capacities of fish cell lines compared with mammalian cell lines, concerned mainly the NER system; thus this point merits to be explored more deeply. Additionally, since some of the DNA repair systems appear more efficient in embryo larval stages, it would be of interest to consider embryonic cell lineages more closely.

The influence of DNA repair on neurological degeneration, cachexia, skin cancer and internal neoplasms: autopsy report of four xeroderma pigmentosum patients (XP-A, XP-C and XP-D)

Background

To investigate the association of DNA nucleotide excision repair (NER) defects with neurological degeneration, cachexia and cancer, we performed autopsies on 4 adult xeroderma pigmentosum (XP) patients with different clinical features and defects in NER complementation groups XP-A, XP-C or XP-D.

Results

The XP-A (XP12BE) and XP-D (XP18BE) patients exhibited progressive neurological deterioration with sensorineural hearing loss. The clinical spectrum encompassed severe cachexia in the XP-A (XP12BE) patient, numerous skin cancers in the XP-A and two XP-C (XP24BE and XP1BE) patients and only few skin cancers in the XP-D patient. Two XP-C patients developed internal neoplasms including glioblastoma in XP24BE and uterine adenocarcinoma in XP1BE. At autopsy, the brains of the 44 yr XP-A and the 45 yr XP-D patients were profoundly atrophic and characterized microscopically by diffuse neuronal loss, myelin pallor and gliosis. Unlike the XP-A patient, the XP-D patient had a thickened calvarium, and the brain showed vacuolization of the neuropil in the cerebrum, cerebellum and brainstem, and patchy Purkinje cell loss. Axonal neuropathy and chronic denervation atrophy of the skeletal muscles were observed in the XP-A patient, but not in the XP-D patient.

Conclusions

These clinical manifestations and autopsy findings indicate advanced involvement of the central and peripheral nervous system. Despite similar defects in DNA repair, different clinicopathological phenotypes are seen in the four cases, and therefore distinct patterns of neurodegeneration characterize XP-D, XP-A and XP-C patients.

c.1643_1644delTG XPC mutation is more frequent in Moroccan patients with xeroderma pigmentosum

Xeroderma pigmentosum is a rare autosomal recessive disease characterized by hypersensitivity to UV light which is due to alterations of the nucleotide excision repair pathway. Eight genes (XPA to XPG and XPV) are responsible for the disease. Among them, the XPC gene is known to be the most mutated in Mediterranean patients. The aim of this study was to determine the frequency of the most common XPC mutation and describe the clinical features of Moroccan patients with xeroderma pigmentosum. Twenty four patients belonging to 21 unrelated Moroccan families and 58 healthy subjects were investigated. After clinical examination, the screening for the c.1643_1644delTG (p.Val548AlafsX25) mutation in the XPC gene was performed by PCR and automated sequencing of exon 9 in all patients and controls. The molecular analysis showed that among the 24 patients, 17 were homozygous for the c.1643_1644delTG mutation and all their tested parents were heterozygous, whereas the others (7 patients) did not carry the mutation. The frequency of this mutation was estimated to be 76.19 % (16/21 families). None of the 58 healthy individuals carried this mutation. In addition, clinical investigation showed that the majority of the patients bearing this mutation have the same clinical features. Our results revealed that the p.Val548AlafsX25 mutation is the major cause (76.19 %) of xeroderma pigmentosum in Moroccan families. This would have an important impact on improving management of patients and their relatives.

Founder mutations in Tunisia: implications for diagnosis in North Africa and Middle East

Background

Tunisia is a North African country of 10 million inhabitants. The native background population is Berber. However, throughout its history, Tunisia has been the site of invasions and migratory waves of allogenic populations and ethnic groups such as Phoenicians, Romans, Vandals, Arabs, Ottomans and French. Like neighbouring and Middle Eastern countries, the Tunisian population shows a relatively high rate of consanguinity and endogamy that favor expression of recessive genetic disorders at relatively high rates. Many factors could contribute to the recurrence of monogenic morbid trait expression. Among them, founder mutations that arise in one ancestral individual and diffuse through generations in isolated communities.

Method

We report here on founder mutations in the Tunisian population by a systematic review of all available data from PubMed, other sources of the scientific literature as well as unpublished data from our research laboratory.

Results

We identified two different classes of founder mutations. The first includes founder mutations so far reported only among Tunisians that are responsible for 30 genetic diseases. The second group represents founder haplotypes described in 51 inherited conditions that occur among Tunisians and are also shared with other North African and Middle Eastern countries. Several heavily disabilitating diseases are caused by recessive founder mutations. They include, among others, neuromuscular diseases such as congenital muscular dystrophy and spastic paraglegia and also severe genodermatoses such as dystrophic epidermolysis bullosa and xeroderma pigmentosa.

Conclusion

This report provides informations on founder mutations for 73 genetic diseases either specific to Tunisians or shared by other populations. Taking into account the relatively high number and frequency of genetic diseases in the region and the limited resources, screening for these founder mutations should provide a rapid and cost effective tool for molecular diagnosis. Indeed, our report should help designing appropriate measures for carrier screening, better evaluation of diseases burden and setting up of preventive measures at the regional level.

Genomic instability in breast and ovarian cancers: translation into clinical predictive biomarkers

Breast and ovarian cancer are among the most common malignancies diagnosed in women worldwide. Together, they account for the majority of cancer-related deaths in women. These cancer types share a number of features, including their association with hereditary cancer syndromes caused by heterozygous germline mutations in BRCA1 or BRCA2. BRCA-associated breast and ovarian cancers are hallmarked by genomic instability and high sensitivity to DNA double-strand break (DSB) inducing agents due to loss of error-free DSB repair via homologous recombination (HR). Recently, poly(ADP-ribose) polymerase inhibitors, a new class of drugs that selectively target HR-deficient tumor cells, have been shown to be highly active in BRCA-associated breast and ovarian cancers. This finding has renewed interest in hallmarks of HR deficiency and the use of other DSB-inducing agents, such as platinum salts or bifunctional alkylators, in breast and ovarian cancer patients. In this review we discuss the similarities between breast and ovarian cancer, the hallmarks of genomic instability in BRCA-mutated and BRCA-like breast and ovarian cancers, and the efforts to search for predictive markers of HR deficiency in order to individualize therapy in breast and ovarian cancer.

Carrier frequency of the recurrent mutation c.1643_1644delTG in the XPC gene and birth prevalence of the xeroderma pigmentosum in Morocco

Xeroderma pigmentosum (XP) is an autosomal recessive inherited disease which is genetically heterogeneous. The prevalence of this genodermatosis is estimated to be 1/1 000 000 in the USA; it is more common in Japan and probably in other populations with high levels of consanguinity. The molecular diagnosis and identification of mutation in patients requires the knowledge of the causative gene by the determination of XP complementation groups. Soufir et al. have reported that XPC is the major disease-causing gene with a recurrent mutation in the Mediterranean region. The mutation c.1643_1644delTG (p.Val548AlafsX25) represents alone 74% of all the XP probands tested and 87% in XP type C in North African patients with founder effect. We used molecular epidemiological methods in the present study to calculate the frequency of heterozygote for this mutation in Moroccan newborns and estimate the prevalence of XP in the Moroccan population. DNA extracted from umbilical cord blood samples of 250 newborns were tested for the recurrent XPC mutation c.1643_1644delTG using real-time polymerase chain reaction. Heterozygotes profiles were confirmed by direct sequencing. Among 250 newborns tested, one subject was heterozygous for the mutation c.1643_1644delTG. The carrier frequency was estimated to be 1/250 which would imply that the prevalence of XP would be approximately 1/80 504 considering the effect of consanguinity. This is the first report of the prevalence of XP in an Arab country and it shows that the prevalence of xeroderma pigmentosum is higher than that found in Europe and the USA.

Preclinical corrective gene transfer in xeroderma pigmentosum human skin stem cells

Xeroderma pigmentosum (XP) is a devastating disease associated with dramatic skin cancer proneness. XP cells are deficient in nucleotide excision repair (NER) of bulky DNA adducts including ultraviolet (UV)-induced mutagenic lesions. Approaches of corrective gene transfer in NER-deficient keratinocyte stem cells hold great hope for the long-term treatment of XP patients. To face this challenge, we developed a retrovirus-based strategy to safely transduce the wild-type XPC gene into clonogenic human primary XP-C keratinocytes. De novo expression of XPC was maintained in both mass population and derived independent candidate stem cells (holoclones) after more than 130 population doublings (PD) in culture upon serial propagation (>10(40) cells). Analyses of retrovirus integration sequences in isolated keratinocyte stem cells suggested the absence of adverse effects such as oncogenic activation or clonal expansion. Furthermore, corrected XP-C keratinocytes exhibited full NER capacity as well as normal features of epidermal differentiation in both organotypic skin cultures and in a preclinical murine model of human skin regeneration in vivo. The achievement of a long-term genetic correction of XP-C epidermal stem cells constitutes the first preclinical model of ex vivo gene therapy for XP-C patients.

Xeroderma pigmentosum variant: complementary molecular approaches to detect a 13 base pair deletion in the DNA polymerase eta gene

Deficiencies of DNA polymerase eta-an enzyme mediating replication past UV-induced DNA damage-predispose individuals to xeroderma pigmentosum variant (XPV) and result in a high incidence of skin cancers. We designed, developed and assessed several complementary molecular approaches to detect a genetically inherited deletion within DNA polymerase eta. RNA was reverse transcribed from XPV fibroblasts and from normal human cells, and standard polymerase chain reaction (PCR) was conducted on the cDNA targeting a region with a 13 base pair deletion within the polymerase eta gene. PCR products were subjected to restriction fragment length polymorphism (RFLP) analysis and cycle DNA sequencing. The deletion was found to eliminate a BsrGI restriction site and affected the number of resultant fragments visualized after gel electrophoresis. Cycle sequencing of polymerase eta-specific amplicons from XPV and normal cells provided a second approach for detecting the mutation. Additionally, the use of a fluorescent nucleic acid dye-EvaGreen-in real-time PCR and melt curve analysis distinguished normal and XPV patient-derived amplicons as well as heteroduplexes that represent heterozygotic carriers without the need for high resolution melt analysis-compatible software. Our approaches are easily adaptable by diagnostic laboratories that screen for or verify genetically inherited disorders and identify carriers of a defective gene.

In vitro functional effects of XPC gene rare variants from bladder cancer patients

The XPC gene is involved in repair of bulky DNA adducts formed by carcinogenic metabolites and oxidative DNA damage, both known bladder cancer risk factors. Single nucleotide polymorphisms (SNPs) in XPC have been associated with increased bladder cancer risk. Recently, rarer genetic variants have been identified but it is difficult to ascertain which are of functional importance. During a mutation screen of XPC in DNA from 33 bladder tumour samples and matched blood samples, we identified five novel variants in the patients' germ line DNA. In a case-control study of 771 bladder cancer cases and 800 controls, c.905T>C (Phe302Ser), c.1177C>T (Arg393Trp), c.*156G>A [3' untranslated region (UTR)] and c.2251-37C>A (in an intronic C>G SNP site) were found to be rare variants, with a combined odds ratio of 3.1 (95% confidence interval 1.0-9.8, P=0.048) for carriage of one variant. The fifth variant was a 2% minor allele frequency SNP not associated with bladder cancer. The two non-synonymous coding variants were predicted to have functional effects using analytical algorithms; a reduced recruitment of GFP-tagged XPC plasmids containing either c.905T>C or c.1177C>T to sites of 408 nm wavelength laser-induced oxidative DNA damage was found in vitro. c.*156G>A appeared to be associated with reduced messenger RNA stability in an in vitro plasmid-based assay. Although the laser microbeam assay is relevant to a range of DNA repair genes, our 3' UTR assay based on Green fluorescent protein(GFP) has widespread applicability and could be used to assess any gene. These assays may be useful in determining which rare variants are functional, prior to large genotyping efforts.

Cancer and neurologic degeneration in xeroderma pigmentosum: long term follow-up characterises the role of DNA repair

BACKGROUND

The frequency of cancer, neurologic degeneration and mortality in xeroderma pigmentosum (XP) patients with defective DNA repair was determined in a four decade natural history study.

METHODS

All 106 XP patients admitted to the National Institutes of Health from 1971 to 2009 were evaluated from clinical records and follow-up.

RESULTS

In the 65 per cent (n=69) of patients with skin cancer, non-melanoma skin cancer (NMSC) was increased 10,000-fold and melanoma was increased 2000-fold in patients under age 20. The 9 year median age at diagnosis of first non-melanoma skin cancer (NMSC) (n=64) was significantly younger than the 22 year median age at diagnosis of first melanoma (n=38)-a relative age reversal from the general population suggesting different mechanisms of carcinogenesis between NMSC and melanoma. XP patients with pronounced burning on minimal sun exposure (n=65) were less likely to develop skin cancer than those who did not. This may be related to the extreme sun protection they receive from an earlier age, decreasing their total ultraviolet exposure. Progressive neurologic degeneration was present in 24% (n=25) with 16/25 in complementation group XP-D. The most common causes of death were skin cancer (34%, n=10), neurologic degeneration (31%, n=9), and internal cancer (17%, n=5). The median age at death (29 years) in XP patients with neurodegeneration was significantly younger than those XP patients without neurodegeneration (37 years) (p=0.02).

CONCLUSION

This 39 year follow-up study of XP patients indicates a major role of DNA repair genes in the aetiology of skin cancer and neurologic degeneration.

Ala499Val (C>T) and Lys939Gln (A>C) polymorphisms of the XPC gene: their correlation with the risk of primary gallbladder adenocarcinoma--a case-control study in China

Genetic variations in the gene XPC may be associated with increased risk for gallbladder cancer (GBC). In this study, we detected two non-synonymous polymorphisms in XPC (Ala499Val and Lys939Gln) in 334 cases of GBC and 329 subjects of hospital-based age- and sex frequency-matched controls in China using a polymerase chain reaction-restriction fragment length polymorphism assay. Allelic association analysis for the two single-nucleotide polymorphisms (SNPs) showed that the risk allele T of Ala499Val was significantly associated with GBC [odds ratio (OR)=1.40, 95% confidence interval (CI): 1.11-1.76, P=0.005), with a population attributive risk of 5.3%. Logistic regression analysis revealed that Ala499Val CT heterozygote (OR=1.56, 95% CI: 1.13-2.14, P=0.002) and TT homozygote (OR=1.93, 95% CI: 1.04-3.55, P=0.048) had a significantly increased risk compared with CC homozygotes. Genetic analysis suggested that either the SNPs directly exert an effect or the linked functional gene impact of the disease trait likely follows an additive or dominant model. Gene interaction analysis demonstrated that the effects of XPC diplotypes (defined as the number of risk genotypes at the two SNP loci) were highly dependent on gallstone. The data from this case-control study indicated that XPC exonic variants contributed to the risk of GBC in this Chinese population.

Diagnosing xeroderma pigmentosum group C by immunohistochemistry

Xeroderma pigmentosum (XP) is a group of rare inherited human neurocutaneous diseases, and the group C (XPC) is the major group of patients with XP in Europe, North America, and South America. Current molecular diagnostic methods for XP require specialized, expensive, and time-consuming UV sensitivity and DNA repair assays followed by gene sequencing. To determine whether immunohistochemistry (IHC) would be a robust alternative method to diagnose patients with XPC, we stained sections of paraffin-embedded skin biopsies for XPC by IHC, using 69 archived blocks from confirmed or clinically suspect patients with XPA, XPC, XPD, XPE, and without XP. We found that XPC expression was strong in all skin biopsies from patients without (14 of 14) and other patients with XP (4 of 4), whereas XPC expression was lost in all biopsies from confirmed XPC patients (29 of 29). Patches of strong XPC signal could be detected in sun-damaged skin, squamous and basal cell carcinomas from patients with XPC that colocalized with strong expression of p53 and Ki-67. Patients with XPC can therefore be diagnosed by IHC from paraffin-embedded skin biopsies from regions of skin that are without sun damage or sun-induced tumors. IHC is therefore a robust alternative method to diagnose patients with XPC. This fast and inexpensive method should increase the options for the diagnosis of patients with XPC from paraffin-embedded skin biopsies and could be developed for other complementation groups.

Founder mutations in xeroderma pigmentosum

In this issue, Soufir et al. report a founder mutation in the XPC DNA repair gene in 74% of families with xeroderma pigmentosum (XP) in the Maghreb region (Algeria, Morocco, and Tunisia) of northern Africa. These patients have a high frequency of skin cancer. The presence of this founder mutation provides an opportunity for genetic counseling and early diagnosis of XP.

XPC branch-point sequence mutations disrupt U2 snRNP binding, resulting in abnormal pre-mRNA splicing in xeroderma pigmentosum patients

Mutations in two branch-point sequences (BPS) in intron 3 of the XPC DNA repair gene affect pre-mRNA splicing in association with xeroderma pigmentosum (XP) with many skin cancers (XP101TMA) or no skin cancer (XP72TMA), respectively. To investigate the mechanism of these abnormalities we now report that transfection of minigenes with these mutations revealed abnormal XPC pre-mRNA splicing that mimicked pre-mRNA splicing in the patients' cells. DNA oligonucleotide-directed RNase H digestion demonstrated that mutations in these BPS disrupt U2 snRNP-BPS interaction. XP101TMA cells had no detectable XPC protein but XP72TMA had 29% of normal levels. A small amount of XPC protein was detected at sites of localized ultraviolet (UV)-damaged DNA in XP72TMA cells which then recruited other nucleotide excision repair (NER) proteins. In contrast, XP101TMA cells had no detectable recruitment of XPC or other NER proteins. Post-UV survival and photoproduct assays revealed greater reduction in DNA repair in XP101TMA cells than in XP72TMA. Thus mutations in XPC BPS resulted in disruption of U2 snRNP-BPS interaction leading to abnormal pre-mRNA splicing and reduced XPC protein. At the cellular level these changes were associated with features of reduced DNA repair including diminished NER protein recruitment, reduced post-UV survival and impaired photoproduct removal.

Disorders of nucleotide excision repair: the genetic and molecular basis of heterogeneity

Mutations in genes on the nucleotide excision repair pathway are associated with diseases, such as xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy, that involve skin cancer and developmental and neurological symptoms. These mutations cause the defective repair of damaged DNA and increased transcription arrest but, except for skin cancer, the links between repair and disease have not been obvious. Widely different clinical syndromes seem to result from mutations in the same gene, even when the mutations result in complete loss of function. The mapping of mutations in recently solved protein structures has begun to clarify the links between the molecular defects and phenotypes, but the identification of additional sources of clinical variability is still necessary.

Wastewater treatment effluent alters nucleotide excision repair in zebrafish (Danio rerio)

Wastewater treatment effluent is a complex mixture of anthropogenic pollutants including estrogenic substances and chemicals, such as polyaromatic hydrocarbons, that cause bulky DNA adducts. Significant research focuses on reproductive effects of aquatic estrogens from wastewater treatment plants. However, other studies suggest genotoxic and immunological effects occur at lower concentrations of wastewater treatment effluent than reproductive endpoints. Recently, effects of estrogen on DNA repair processes in zebrafish have been suggested as a possible mechanism by which estrogen can modulate incidence of DNA mutations. Because wastewater treatment facilities are a significant source of estrogenic compounds, we hypothesized that exposure to whole effluents would also affect DNA repair in zebrafish (Danio rerio). Exposure to effluent from multiple treatment facilities in northern Maine decreased repair of DNA adducts in zebrafish liver cells. Expression of two nucleotide excision repair genes, XPC and XPA, were quantified and showed varied response after exposure in adult male zebrafish. Evidence of estrogen and aryl hydrocarbon receptor activation after exposure varied between treatment plants and temporally within treatment plants when evaluated using a traditional biomarker, vitellogenin-1 (VTG) and, cytochrome p450 1A1 (CYP1A1) mRNA abundance. This research highlights the continuing importance of examining non-reproductive effects of wastewater treatment effluent.

High frequency of the V548A fs X572 XPC mutation in Tunisia: implication for molecular diagnosis

Xeroderma pigmentosum (XP, OMIM 278700-278780) is a group of autosomal recessive diseases characterized by hypersensitivity to UV rays. There are seven complementation groups of XP (XPA to XPG) and XPV. Among them, the XP group C (XP-C) is the most prevalent type in Western Europe and in the United States. We report here on the clinical and genetic investigation of XP-C patients in 14 Tunisian families. As the XPC V548A fs X572 mutation has been identified in Algerian and Moroccan populations, Tunisian patients were first screened for this mutation by a direct sequencing of exon 9 of the XPC gene. All patients with a severe clinical form had this mutation, thus showing the homogeneity of the mutational spectrum of XPC in Tunisia. A potential founder effect was searched and confirmed by haplotype analysis. Taking into account the similarity of the genetic background, we propose a direct screening of this mutation as a rapid and cost-effective tool for the diagnosis of XP-C in North Africa.