[Xeroderma Pigmentosum].

Xeroderma pigmentosum is a DNA repair disorder characterized by the occurrence of pigmented freckles and skin cancers on sun-exposed areas. Additionally, more than 50% of patients present with progressive degenerative neurological symptoms. Eight clinical subtypes of this condition are known, and neurological symptoms can be seen in XP-A, B, D, F, G complementation groups.

Eixo XPC-P53-H202 e disfunção mitocondrial: qual é o fator central? / XPC-p53-H2O2 axis and mitochondrial disfunction: Which is the key player

A ausência de XPC, uma proteína canonicamente envolvida em reparo de DNA por excisão de nucleotídeos, está associada a vários fenótipos característicos de disfunção mitocondrial como o desequilíbrio entre os complexos da cadeia transportadora de elétrons (CTE), redução no consumo de oxigênio, maior produção de peróxido de hidrogênio, e maior sensibilidade a agentes que causam estresse mitocondrial. Contudo, uma descrição mecanística da relação entre deficiência de XPC e disfunção mitocondrial ainda não está bem estabelecida. Aqui mostramos que a deficiência de XPC está associada ao aumento na expressão do supressor de tumor p53. Essa alteração é acompanhada pelo aumento da expressão de diversas proteínas que participam em importantes funções mitocondriais. A inibição de p53 reverte a superexpressão de algumas dessas proteínas. O tratamento com o inibidor do Complexo III da CTE antimicina A induz aumento da expressão de p53 de forma mais acentuada na linhagem Xpc-/-, enquanto o tratamento com o antioxidante N-acetilcisteína diminue a produção basal de H2O2, expressão de p53 e sensibilidade aumentada ao tratamento com antimicina A. Em conjunto, nossos resultados suportam a hipótese de que o aumento da produção de H2O2 em células Xpc-/- tem um papel causal na regulação da expressão de p53 e na disfunção mitocondrial

Although XPC has been initially implicated in the nucleotide excision DNA repair pathway, its deficiency is associated with mitochondrial dysfunction, including unbalanced electron transport chain (ETC) activity, lower oxygen consumption, increased hydrogen peroxide production, and greater sensitivity to mitochondrial stress. However, a mechanistic understanding of the role of XPC in regulating mitochondrial function is still not well established. Here we show that XPC deficiency is associated with increased expression of the tumor suppressor p53, which is accompanied by increased expression of several proteins that participate in important mitochondrial functions. Inhibition of p53 reverses the overexpression of some of these proteins. In addition, treatment with the ETC inhibitor antimycin A induces p53 expression more robustly in the Xpc-/- cells, while treatment with the antioxidant N-acetylcysteine decreases basal H2O2 production, p53 expression and sensitivity to antimycin A treatment. Together, our results support a model in which increased H2O2 production in Xpc-/- causes upregulation of p53 expression and mitochondrial dysfunction

The present status of xeroderma pigmentosum in Japan and a tentative severity classification scale.

Xeroderma pigmentosum (XP) is a rare autosomal recessive hereditary disease. Patients with XP have severe hypersensitivity to sunlight, resulting in skin cancers, and some patients have neurological symptoms. In Japan, XP complementation group A (XP-A) is the most common form, and it is associated with severe neurological symptoms. We performed a nationwide survey on XP to determine the present status of XP in Japan. The distribution of complementation groups in Japan was considerably different from that in other countries, but there was a higher frequency in group A and the variant type, which is similar to previous reports in Japan. Basal cell carcinoma was the most frequent skin cancer that patients with XP developed, followed by squamous cell carcinoma and malignant melanoma. The frequency of these skin cancers in patients with XP-A has decreased, and these skin cancers have been occurring in much older people than those previously observed. Diagnosing XP in patients at younger ages seems to encourage patients and their parents to use sun protection, which helps prevent skin cancer. We also created a tentative scale for classifying the severity of XP, and we evaluated the neurological symptoms of XP-A using this severity scale. Our classification correlated well with patients' age, suggesting that it may be useful and feasible in clinical practice to assess the progression of symptoms of each patient with XP and evaluate the effects of treatment in the future.

Xeroderma pigmentosum complementation group G patient with a novel homozygous missense mutation and no neurological abnormalities.

We describe an unusual xeroderma pigmentosum (XP) patient with a mutation in XP complementation group G, representing only the third reported Japanese XP-G patient. A 40-year-old men (XP3HM), born from consanguineous parents experienced sun sensitivity and pigmentary changes of sun-exposed skin since childhood. He developed a squamous cell carcinoma on his lower lip at the age of 40. He has neither neurological abnormalities nor Cockayne syndrome. The primary fibroblasts of the patient were hypersensitive to killing by UV (D(0) = 0.6 J/m(2)) and the post-UV unscheduled DNA synthesis was 8% of normal. Host cell reactivation complementation analysis implicated XP complementation group G. We identified a novel homozygous mutation (c.194T>C) in a conserved portion of the XPG(ERCC5) gene, resulting in a predicted amino acid change; p.L65P. We confirmed that this genetic change reduced DNA repair thus linking this mutation to increased skin cancer.

Lesions of cortical GABAergic interneurons and acetylcholine neurons in xeroderma pigmentosum group A.

Xeroderma pigmentosum (XP) is a rare genetic disorder caused by inherited disturbances in the nucleotide excision repair system; patients with XP groups A (XP-A), B, D, and G were shown to have progressive neurological disturbances. Particularly, XP-A patients, which account for approximately half of Japanese XP patients, show severe neurological disorders, including mental retardation and epilepsy. Herein, we performed an immunohistochemical analysis of the number of GABAergic interneurons (GABAis), including calbindin-D28K, parvalbumin, and calretinin, in the cerebral cortex and acetylcholinergic neurons (AchNs) in the nucleus basalis of Meynert (NM) and in the pedunculopontine tegmental nucleus (PPN) in six autopsy cases of XP-A in order to investigate the relationships between mental dysfunction and GABAis and AchNs. The density and percentages of neurons that were immunoreactive for calbindin-D28K and parvalbumin were significantly reduced in the frontal and temporal cortices in XP-A cases, although the density of neurons that were immunoreactive for MAP2 did not differ from that in controls. Additionally, XP-A cases showed reduced AchNs in both the NM and the PPN. The observed reductions of cortical GABAis and AchNs may be involved in the mental disturbances, the higher occurrence of epilepsy, and/or the abnormalities in rapid eye movement sleep in patients with XP-A.

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.

[Ocular malignancies of xeroderma pigmentosum: clinical and therapeutic features]. / Tumeurs oculopalpébrales malignes dans le xeroderma pigmentosum: aspects cliniques et thérapeutiques.

BACKGROUND: Our aim was to determine the epidemiological, clinical and histopathological features as well as the most suitable therapeutic management of malignant ocular tumours in xeroderma pigmentosum based on a retrospective study of 32 patients. PATIENTS AND METHODS: Our study was conducted in the ophthalmology unit of the Charles-Nicolle hospital between January 2001 and January 2004. A complete bilateral ophthalmologic investigation was performed for all patients and the severity of photophobia was scored on a four-point scale. RESULTS: Thirty-two xeroderma pigmentosum patients were examined during this period. Photophobia was found in 66% of cases and 19 of 32 patients (59%) were presenting ocular and periocular malignancies. The mean age of patients was 19 years (four to 40 years). Thirty-three tumours were diagnosed in these 19 patients. Blindness was noted in 3/26 (12%) eyes in patients without malignant tumour and in 10/38 (26%) eyes in patients with malignant tumour. CONCLUSION: Various types of malignant ocular-cutaneous tumours relating to sunlight developed in xeroderma pigmentosum patients. These disorders are more prevalent in severe and moderate forms of xeroderma pigmentosum. Lesions occur almost exclusively in the eyelids, conjunctiva, limbus and/or cornea. The rapid regression of these tumours, particularly in the cornea and limbus, may cause blindness, emphasising the importance of early management and regular monitoring of patients in order to allow early diagnosis of this condition, thereby ensuring the least mutilant treatment possible.

Blood-derived gene-expression profiling in unravelling susceptibility to recessive disease.

Identification of new disease predisposition genes with chip-based technologies typically requires extensive financial and sample resources. We have recently shown that combining peripheral blood genome and transcriptome (BGT) information in highly selected materials can be a successful low-cost approach to unravelling dominant tumour susceptibility. In this study, we extended our investigations to recessively inherited tumour predisposition, and identified a homozygous germline mutation in the damage-specific DNA binding protein 2 (DDB2) gene in a patient with several facial tumours, for which doctors had been unable to provide a diagnosis. Our results provide proof of principle that BGT is a powerful approach for both dominant and recessive genes. In addition to tumour susceptibility, the method may be useful in characterising genetic defects underlying other disease phenotypes.

Xeroderma pigmentosum group E and DDB2, a smaller subunit of damage-specific DNA binding protein: proposed classification of xeroderma pigmentosum, Cockayne syndrome, and ultraviolet-sensitive syndrome.

Xeroderma pigmentosum is a rare photosensitive syndrome that comprises eight different genetic diseases (A to G; variant (V)). Although genotype-phenotype correlations have been evaluated in most XP groups, the relationship between the E subgroup of xeroderma pigmentosum (XP-E) and damage-specific DNA binding protein (DDB) still remained a mystery. Recent studies have provided new insight for XP-E and the role(s) of DDB2, a smaller subunit of DDB. Reclassification studies have confirmed that mutations in DDB2 give rise to XP-E. The mouse model of XP-E demonstrated that DDB2 was well conserved between mouse and human and was critical in controlling proper cell-survival through regulating the tumor suppressor p53-mediated responses after ultraviolet (UV)-irradiation: i.e. defective DDB2 causes the resistance to cell-killing by UV-irradiation due to decreased p53-mediated apoptosis. These phenotypes are unique to XP-E because other XP groups show normal (XP-V) or hypersensitivity (XP-A, B, C, D, F, and G) to UV-irradiation. Thus XP-E is defined as a skin cancer prone disease with unique resistance to UV-irradiation.

Life-threatening vocal cord paralysis in a patient with group A xeroderma pigmentosum.

We report a 19-year-old male with group A xeroderma pigmentosum who presented life-threatening vocal cord paralysis. At 3 months of age, he became sensitive to sunlight, and at the age of 4 years he was diagnosed with group A xeroderma pigmentosum. The neurologic symptoms progressed slowly thereafter. From the age of 18 years, he reported the development of occasional episodic inspiratory stridor and dyspnea, but the cause remained unknown. At the age of 19, he had a common cold and became severely dyspneic and cyanotic. Immediate examination of the glottis upon arrival by an otorhinolaryngologist using a fibroscope indicated complete paralysis of both vocal cords, and tracheal intubation resulted in marked improvement of respiration. Tracheostomy was performed thereafter. Inspiratory stridor and dyspnea are the common symptoms in this disease, and some patients with group A xeroderma pigmentosum undergo a tracheostomy, but the pathogenesis remains unknown. To our knowledge, vocal cord paralysis has never been reported in patients with group A xeroderma pigmentosum. This case is presented to illustrate the importance of fibroscopy in the examination of vocal cords in patients with group A xeroderma pigmentosum before the development of life-threatening events.

Complementation of the DNA repair deficiency in human xeroderma pigmentosum group a and C cells by recombinant adenovirus-mediated gene transfer.

Nucleotide excision repair (NER) is one of the most versatile DNA repair mechanisms, ensuring the proper functioning and trustworthy transmission of genetic information in all living cells. The phenotypic consequences caused by NER defects in humans are autosomal recessive diseases such as xeroderma pigmentosum (XP). This syndrome is the most sun-sensitive disorder leading to a high frequency of skin cancer. The majority of patients with XP carry mutations in the XPA or XPC genes that encode proteins involved in recognition of DNA damage induced by UV light at the beginning of the NER process. Cells cultured from XPA and XPC patients are hypersensitive to UV light, as a result of malfunctioning DNA repair. So far there is no effective long-term treatment for these patients. Skin cancer prevention can only be achieved by strict avoidance of sunlight exposure or by the use of sunscreen agents. We have constructed recombinant adenoviruses carrying the XPA and XPC genes that were used to infect XP-A and XP-C immortalized and primary fibroblast cell lines. UV survival curves and unscheduled DNA synthesis confirmed complete phenotypic reversion in XP DNA repair deficient cells with no trace of cytotoxicity. Moreover, transgene expression is stable for at least 60 days after infection. This efficient adenovirus gene delivery approach may be an important tool to better understand XP deficiency and the causes of DNA damage induced skin cancer.

The founding members of xeroderma pigmentosum group G produce XPG protein with severely impaired endonuclease activity.

Of the eight human genes implicated in xeroderma pigmentosum, defects in XPG produce some of the most clinically diverse symptoms. These range from mild freckling to severe skeletal and neurologic abnormalities characteristic of Cockayne syndrome. Mildly affected xeroderma pigmentosum group G patients have diminished XPG endonuclease activity in nucleotide excision repair, whereas severely affected xeroderma pigmentosum group G/Cockayne syndrome patients produce truncated XPG proteins that are unable to function in either nucleotide excision repair or the transcription-coupled repair of oxidative lesions. The first two xeroderma pigmentosum group G patients, XP2BI and XP3BR, were reported before the relationship between xeroderma pigmentosum group G and Cockayne syndrome was appreciated. Here we provide evidence that both patients produce truncated proteins from one XPG allele. From the second allele, XP2BI generates full-length XPG of 1186 amino acids containing a single L858P substitution that has reduced stability and greatly impaired endonuclease activity. In XP3BR, a single base deletion and alternative splicing at a rare noncanonical AT-AC intron produces a 1185 amino acid protein containing 44 internal non-XPG residues. This protein is stably expressed but it also has greatly impaired endonuclease activity. These four XPG products can thus account for the severe ultraviolet sensitivity of XP2BI and XP3BR fibroblasts. These cells, unlike those from xeroderma pigmentosum group G/Cockayne syndrome patients, are capable of limited transcription-coupled repair of oxidative lesions. Our results suggest that the L858P protein in XP2BI and the almost full-length XPG protein in XP3BR are responsible for this activity and for the absence of severe early onset Cockayne syndrome symptoms in these patients.

Abnormal regulation of DDB2 gene expression in xeroderma pigmentosum group E strains.

A damage-specific DNA binding protein (DDB) activity is absent from a subset (DDB(-)) of cells from individuals initially classified as group E of xeroderma pigmentosum (XP), a hereditary, photosensitive disease with a high incidence of skin malignancies. In these cases, mutations have been identified in the DDB2 gene (DDB2(-)) that codes for the small subunit, p48, of the DDB heterodimer. In four DDB2(- )strains, neither p48 nor DDB activity were observed before or after UV-irradiation, despite an unusually strong up-regulation of DDB2 mRNA levels after UV-irradiation. In a fifth strain, XP82TO, p48 was detectable and both DDB2 mRNA and p48 levels were more up-regulated after UV-irradiation than in normal primary cells. Moreover, DDB activity also became apparent after irradiation. XP82TO showed very mild clinical manifestations compared with the other DDB(-) patients. These results, coupled with our findings that most, if not all DDB(+) cells classified as XP-E were misclassified, suggests a direct correlation between DDB2 levels and the XP-E phenotype.

Association between DNA repair-deficiency and high level of p53 mutations in melanoma of Xeroderma pigmentosum.

Xeroderma pigmentosum (XP) is an inheritable disease characterized by sun-sensitivity and a high frequency of skin cancers including melanoma. We have analyzed two different groups of XP: the XP complementation group C (XP-C), deficient in global nucleotide excision repair but proficient in transcription-coupled repair and associated with a very early onset of skin cancers; and the XP variant (XPV), deficient in the bypass of DNA photoproducts. To get new insights into the biology of melanoma in XP patients, we studied 20 melanomas from four XP-C and two XPV patients in terms of pathology, immunohistochemistry of p53, mutations in exons 4-9 of the p53 gene, and polymorphisms of the p53 gene at codon 72. All statistical tests were two-sided. The majority of the XP melanomas were of the lentigo maligna melanoma (LMM) type, as found in the elderly. p53 point mutations were found in 60% of XP-C melanomas and in only 10% of XPV melanomas, this latter frequency being similar to what has been reported in the general population. Mutations show the specific UV-signature because the majority were CC to tandem and C to T transitions located at the bipyrimidine sites known to be hotspots of UV-induced DNA lesions. All DNA lesions giving rise to mutations in XP-C melanomas were located on the nontranscribed strand of the p53 gene, demonstrating that these patients' cells were able to carry out preferential repair in vivo. The LMMs found in XP-C are associated with an accumulation of unrepaired DNA lesions and may represent a good model for the LMM induction in the elderly.

The cytotoxicity of DNA carboxymethylation and methylation by the model carboxymethylating agent azaserine in human cells.

Carboxymethylating agents are potential sources of endogenous DNA damage that have been proposed as possible contributors to gastrointestinal carcinogenesis. The cytotoxicity of the model DNA carboxymethylating agent azaserine was investigated in human cells. Expression of the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) did not affect sensitivity to the drug in two related Raji Burkitt's lymphoma cell lines. DNA mismatch repair-defective variants of Raji cells which display increased tolerance to DNA methylation damage were not selectively resistant to azaserine. Complementary results were obtained with a second carboxymethylating agent, potassium diazoacetate. In contrast, lymphoblastoid cell lines representative of each of the xeroderma pigmentosum complementation groups, including the variant, were all significantly more sensitive to azaserine than nucleotide excision repair-proficient cells. The hypersensitivity of XP cells was not due to systematic differences in the concentrations of intracellular thiol compounds or related thiol metabolizing enzymes. The data indicate that of the two types of potentially lethal DNA damage which azaserine introduces, carboxymethylated bases and O(6)-methylguanine, the former are repaired by nucleotide excision repair and are a more significant contributor to azaserine lethality in human cells.