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.

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.

A lack of radiation-induced ornithine decarboxylase activity prevents enhanced reactivation of herpes simplex virus and is linked to non-cancer proneness in xeroderma pigmentosum patients

Patients with xeroderma pigmentosum (XP), a DNA repair disorder, run a large risk of developing skin cancer in sun-exposed areas. Cancer proneness in these patients correlates with a mammalian SOS-like response, "enhanced reactivation (ER) of viruses." Here, we report that radiation-induced activation of the ornithine decarboxylase (ODC) gene, a putative proto-oncogene, is required for this response. Various diploid fibroblast strains derived from a non-cancer-prone subclass of XP patients, which lack the ER response, were irradiated with 2 J/m2 and assessed for gene induction. In these fibroblasts, an absence of induction of ODC by UV-C was observed at the levels of mRNA, protein, and enzyme activity. This lack of induction is quite specific because the genes for fos and collagenase were induced as they were in normal XP cells. The apparent linkage between non-cancer proneness and a lack of ER and ODC induction was confirmed in a fibroblast strain derived from a patient with another DNA repair disorder, trichothiodystrophy, which does not lead to cancer proneness: in these cells, no induction of the ER response nor of ODC occurs after UV-C irradiation. Repair deficiency, however, is not essential because the simultaneous lack of ODC and ER induction after 10 J/m2 UV-C was found in at least one repair-proficient fibroblast. Next, a specific inhibitor of ODC, difluoromethylornithine, at a dose of 10 mM, completely blocked the ER response in cultured normal skin fibroblasts, suggesting that the ODC enzyme is in fact essential for the ER response. Difluoromethylornithine, although it did not affect other processes such as DNA repair, leads to a block in the cell division cycle at the G1-S transition. Interestingly, other blockers of this transition, wortmannin (500 nM) and mimosine (100 mM), also decreased the ER response. Finally, the ER and ODC responses also seem to be linked after treatment with X-irradiation (3 Gy), suggesting that both are part of a general response to DNA damage, at least in human skin fibroblasts. Apart from the abnormal ER and ODC responses, fibroblasts from non-tumor-prone XP patients react in the same way to radiation as do fibroblasts from tumor-prone XP patients with respect to other parameters. Thus, the lack of ODC induction after radiation may help to protect XP patients against skin carcinogenesis.

Truncated XPA protein detected in atypical group A xeroderma pigmentosum

XPA protein from a patient with typical group A xeroderma pigmentosum (XP) and three atypical group-A XP patients were analysed. Immunoblot analysis of XPA proteins revealed that a typical group-A XP patient showed no XPA protein band, while a smaller, truncated XPA protein, which appears to be responsible for mid skin lesions and minimal neurological abnormalities, was detected in cells from three atypical group-A XP patients. Furthermore, the difference in the amount of truncated XPA protein correlated with the mildness of neurological manifestations in these three atypical group-A XP patients. The results suggest a correlation between clinical manifestations and qualitative and quantitative abnormalities of XPA protein products.

Sister chromatid exchanges in cells defective in mismatch, post-replication and excision repair

Three processes associated with DNA damage and genomic instability have been defined experimentally as operating during or soon after DNA replication: mismatch repair, post-replication repair and sister chromatid exchange. All these processes appear to operate on damage and/or errors in newly replicated DNA. Both mismatch repair and post-replication repair involve resynthesis of up to 1 kb of newly synthesized DNA: mismatch repair operates on single-base or slippage errors; post-replication repair operates on persistent gaps in newly synthesized DNA caused by damage on parental strands. Using colon cancer cells with different mismatch repair capacity, together with normal cells and excision-repair-defective and post-replication-repair-defective xeroderma pigmentosum (XP) cells, we analysed possible interactions between these processes. No evidence for overlap of mismatch repair with excision or post-replication repair was found. However, post-replication-repair-defective XP variant cells that were SV40 transformed showed higher UV-induced sister chromatid exchange frequencies than did untransformed cells. This suggests that sister chromatid exchanges in the XP variant are closely involved with UV-induced replication errors that are enhanced by transformation.

Processing of directly and indirectly ultraviolet-induced DNA damage in human cells

Mutations caused by ultraviolet (UV)-induced DNA damage represent the initial genetic changes in the tumorigenesis of UV-induced skin cancer. Different wavelengths of UV radiation cause different kinds of DNA damage and mutations. UVB (290-320 nm) generates pyrimidine dimers by direct excitation of the DNA molecule. UVA (320-400 nm) can damage the DNA only indirectly through a photosensitized reaction. This indirect action is mediated mainly by singlet oxygen, which generates purine base modifications, and has been implicated in the carcinogenic effects of UVA. In order to study the processing of directly and indirectly UV-induced DNA damage in human cells, we first treated the replicating plasmid pRSVcat with up to 10 kJ/m2 UVB or with the photosensitizer methylene blue plus visible light (which generates singlet oxygen) in vitro. Then, the damaged plasmid was transfected into normal or repair deficient xeroderma pigmentosum complementation group A (XP-A) cells. DNA repair was assessed by measuring activity of reactivated chloramphenicol acetyltransferase (CAT) enzyme, encoded by the plasmid's cat gene, in cell extracts after 3 days. While XP-A cells exhibited a significantly reduced repair of UVB-induced DNA damage, they showed a normal repair of singlet oxygen-induced DNA damage. This indicates a differential DNA repair pathway for directly and indirectly UV-induced DNA damage in human cells. Irradiation of the plasmid with UVA alone did not result in a genotoxic effect. Only in conjunction with a cell extract, which provides all candidate cellular photosensitizers, did we find a reduced CAT activity after transfection. This indicates that the genotoxicity of UVA is mediated by a cellular photosensitizer.

Molecular and cellular analysis of the DNA repair defect in a patient in xeroderma pigmentosum complementation group D who has the clinical features of xeroderma pigmentosum and Cockayne syndrome

Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are quite distinct genetic disorders that are associated with defects in excision repair of UV-induced DNA damage. A few patients have been described previously with the clinical features of both disorders. In this paper we describe an individual in this category who has unusual cellular responses to UV light. We show that his cultured fibroblasts and lymphocytes are extremely sensitive to irradiation with UV-C, despite a level of nucleotide excision repair that is 30%-40% that of normal cells. The deficiency is assigned to the XP-D complementation group, and we have identified two causative mutations in the XPD gene: a gly-->arg change at amino acid 675 in the allele inherited from the patient's mother and a -1 frameshift at amino acid 669 in the allele inherited from his father. These mutations are in the C-terminal 20% of the 760-amino-acid XPD protein, in a region where we have recently identified several mutations in patients with trichothiodystrophy.

Assignment of six patients with xeroderma pigmentosum in Hokkaido area to a variant form

Six Japanese patients in Hokkaido area were diagnosed as xeroderma pigmentosum (XP) at two University Hospital; one patient, a 29 years old female (XP2AS) at Asahikawa Medical College, and five patients, namely, a 53 years old male (XP1SA), a 45 years old female (XP2SA), a 46 years old female (XP3SA), a 47 years old male (XP4SA) and a 34 years old male (XP5SA) at Hokkaido University School of Medicine. All these XP patients showed mild skin symptoms and had no apparent neurological abnormalities. To identify genetic complementation groups of these patients, DNA repair capacities in skin fibroblasts derived from the patients were analyzed by ultraviolet light (UV)-induced unscheduled DNA synthesis (UDS), and also by colony-forming abilities of UV-irradiated cells incubated with or without caffeine added in post-UV culture medium. The levels of UDS measured by autoradiography in these XP cells irradiated with 20 J/m2 of UV were 67 to 84% of those of normal human fibroblasts. Although one XP cell strain (XP2AS) showed about 2-fold greater sensitivity to killing by UV than normal cells, UV sensitivities of the rest of 5 XP strains were similar or only slightly higher than those of normal cells. However, UV sensitivities of all the 6 XP cell strains markedly increased by addition of 1 mM caffeine in the post-UV incubation medium, a phenomenon characteristic of XP variant cells. We also analyzed post-replication repair in XP1SA cells by sedimentation of newly-synthesized DNA in alkaline sucrose gradient, and found that this strain is defective in this repair system. From these results, we concluded that all the 6 XP strains studied here belong to XP variants.

[A variant of xeroderma pigmentosum: two cases of pigmented xerodermoid]

Two patients (sister and brother) of pigmented xerodermoid are presented: the character of clinical signs (phothosensitivity, poikilodermia, keratoses and keratomas, furthermore in the brother the squamous cell epithelioma of left thigh), according to them the case history (appearance of precancerous conditions and carcinoma in early adult life) made the disease suspicious to a variant of xeroderma pigmentosum. A DNA reparation test was also carried out, which confirmed the above clinical diagnosis in both patients.

Molecular analysis of CXPD mutations in the repair-deficient hamster mutants UV5 and UVL-13

The cDNA sequence of the Chinese hamster xeroderma pigmentosum group D (CXPD) nucleotide excision repair gene was analyzed from three Chinese hamster ovary (CHO) cell lines: repair proficient strain AA8 and repair deficient, UV complementation group 2 strains UV5 and UVL-13. CXPD encodes a presumed ATP-dependent DNA helicase and is single copy in CHO lines due to the hemizygosity of chromosome 9. Comparison of the deduced wild-type AA8 CXPD protein sequence with that of the Chinese hamster V79 lung-derived cell line revealed two amino acid polymorphisms. Position 285 is glutamine in AA8 and arginine in V79, and position 298 is alanine in AA8 and threonine in V79. Comparison with the human XPD, Saccharomyces cerevisiae RAD3, and Schizosaccharomyces pombe rad15 homologs shows variability at these positions. Analysis of the CXPD sequence in the repair deficient CHO lines UV5 and UVL-13 revealed, in each case, a single base substitution resulting in an amino acid substitution. Position 116 is tyrosine in UV5 and cysteine in AA8, and the corresponding positions of XPD, RAD3, and rad15 are cysteine. Position 615 is glutamic acid in UVL-13 and glycine in AA8, and the corresponding positions of XPD, RAD3, and rad15 are glycine. In both UV5 and UVL-13, positions 285 and 298 are glutamine and alanine, respectively, as seen in AA8. These results suggest that cysteine 116 and glycine 615 are critical to the repair function of CXPD.

Isolation of active recombinant XPG protein, a human DNA repair endonuclease

Complementation group G of xeroderma pigmentosum (XP-G) is one of the most rare and phenotypically heterogeneous forms of this inherited disorder. XP-G patients vary from having a very mild defect in DNA repair to being severely affected, and a few cases are also associated with the neurological complications of Cockayne's syndrome. The XPG gene encodes an acidic protein with a predicted molecular mass of 133 kDa that confers normal UV resistance when expressed in XP-G cells. Here we report the isolation of full-length XPG as a soluble protein expressed from a recombinant baculovirus. The purified polypeptide corrects the DNA nucleotide excision repair defect of XP-G cell extracts in vitro, and it acts as a magnesium-dependent single-stranded DNA endonuclease. This is the first direct evidence for a human protein with properties that implicate it in the incision step of nucleotide excision repair.

Assignment of xeroderma pigmentosum group C (XPC) gene to chromosome 3p25

The human gene XPC (formerly designated XPCC), which corrects the repair deficiency of xeroderma pigmentosum (XP) group C cells, was mapped to 3p25. A cDNA probe for Southern blot hybridization and diagnostic PCR analyses of hybrid clone panels informative for human chromosomes in general and portions of chromosome 3 in particular produced the initial results. Fluorescence in situ hybridization utilizing both a yeast artificial chromosome DNA containing the gene and XPC cDNA as probes provided verification and specific regional assignment. A conflicting assignment of XPC to chromosome 5 is discussed in light of inadequacies in the exclusive use of microcell-mediated chromosome transfer for gene mapping.

Absence of DNA repair deficiency in the confirmed heterozygotes of xeroderma pigmentosum group A

This study was performed to elucidate whether xeroderma pigmentosum complementation group A (XPA) carrier has DNA repair abnormality against sun-exposure and ultraviolet (UV)-mimetic chemical carcinogen 4-nitroquinoline 1-oxide (4NQO). Here we report three sporadic cases of XP that were defined as group A by genetic complementation test as well as polymerase chain reaction (PCR) analysis to detect the point mutation in the responsible gene for XPA. DNA repair analyses in the skin fibroblasts revealed that the cells from the patients were much more sensitive to UV and 4NQO and had extremely low UV-induced unscheduled DNA synthesis (UDS) than control cells, whereas the cells from the carriers (heterozygotes of XP) had sensitivity to UV and 4NQO and levels of UV-induced UDS similar to normal cells. These results indicate that the obligate heterozygotes, despite having a mutated allele in XPA complementing gene demonstrated by PCR, have no DNA repair abnormality after UV irradiation and UV-mimetic 4NQO treatment. Our observations imply that XPA heterozygotes do not have higher risk of skin cancers than normal subjects based on their DNA repair abnormality.

A case of xeroderma pigmentosum complementation group F with neurological abnormalities

We report a 48-year-old Japanese man suffering from xeroderma pigmentosum associated with mental retardation, cerebral atrophy and cerebellar ataxia. Cultured fibroblasts from an unexposed area of skin had reduced DNA repair capacity after UV irradiation, with higher sensitivity to UV than normal cells in colony-forming ability and host cell reactivation using herpes simplex virus. Genetic complementation tests by cell fusion with polyethylene glycol revealed that the patient belonged to group F. He died of bile duct cancer at the age of 50. This is the first report of an XP-F patient with neurological abnormalities.

Characterization of a complex chromosomal rearrangement maps the locus for in vitro complementation of xeroderma pigmentosum group D to human chromosome band 19q13

Microcell-mediated chromosome transfer (MMCT) is a powerful genetic technique that permits the transfer of a single chromosome from one mammalian cell to another. The utility of MMCT for gene mapping strategies is critically dependent on the careful characterization of the chromosomes being transferred. We have recently reported the identification of a single rearranged human chromosome, designated Tneo, which corrects the UV sensitivity and excision repair defect of cells of xeroderma pigmentosum genetic complementation group D (XP-D) in culture (Flejter WL et al., Proc Natl Acad Sci USA 89:261-265, 1992). Additionally, those studies demonstrated a role for the excision repair cross-complementing 2 (ERCC2) gene in the observed phenotypic correction. We now report the results of detailed conventional and molecular cytogenetic characterization of the complementing Tneo chromosome. This analysis revealed a complex rearrangement involving material from human chromosomes 16, 17, and 19. Characterization of deletions of Tneo which retained or lost XP-D complementing ability mapped the gene responsible for phenotypic correction to a small region of the terminal q-arm of this chromosome. This region includes the previously described human DNA repair gene cluster located in the region 19q13.2-q13.3, a result consistent with the notion that the in vitro correction of XP-D cells by the Tneo chromosome is rendered by the ERCC2 locus. The data illustrate the potential value of detailed cytogenetic characterization of a human chromosome present in a somatic cell hybrid, even when that material involves complex rearrangements.

Expression cloning of a human DNA repair gene involved in xeroderma pigmentosum group C

Xeroderma pigmentosum (XP) is a rare human autosomal recessive disease characterized by solar sensitivity, high predisposition for developing cancers on areas exposed to sunlight, and, in some cases, neurological abnormalities. XP cells are defective in DNA repair, and complementation of this defect has been used to identify eight genetic groups (A-G and variant). We have developed a simple, highly efficient complementary DNA expression system for use in human cells. Here we use this system to isolate a cDNA clone that restores the ultraviolet sensitivity and unscheduled DNA synthesis of XP-C cells to normal levels. The XP-C complementing clone XPCC encodes a highly hydrophilic protein which is composed of a predicted 823 amino acids and shares limited homology with the product of the yeast DNA repair gene RAD4. The XPCC transcript is undetectable by northern blotting in most XP-C cell lines examined.

Xeroderma pigmentosum variant with multisystem involvement

BACKGROUND

Xeroderma pigmentosum (XP) is a hereditary disorder characterized by recessive inheritance and elevated rates of skin carcinogenesis. There are seven complementation groups (A through G) for which the genetic defect results in a failure to repair DNA damage from UV light and sunlight; one group, the variant, fails to replicate UV-damaged DNA correctly. Patients in XP groups A, B, D, and G have associated neurologic problems, the most severe being known as the DeSanctis-Cacchione syndrome.

OBSERVATIONS

We describe a patient with XP from consanguineous parents who has severe multisystem involvement similar to that of the DeSanctis-Cacchione syndrome. Extensive laboratory investigation showed that cells from this patient exhibit DNA replication after irradiation with UV light that is characteristic of the XP variant. The cells also show normal sensitivity to UV light and normal excision repair, consistent with XP variant classification. The presence of the neurologic symptoms is quite unusual in an XP variant.

CONCLUSION

Our patient clearly fits into the XP variant category based on normal survival, caffeine toxic reaction, photoproduct excision and repair, and the deficient replication of UV-damaged DNA. This patient seems to be rare, however, among XP variants in displaying severe neurologic symptoms. Because of the consanguineous parents, the possibility that some of this patient's findings are from non-XP-related abnormalities must also be entertained. However, other consanguineous patients with XP variant, eg, XPIOCA, have been described who do not show neurologic abnormalities. In view of the difficulty of defining an XP group from clinical symptoms alone, we urge the term xeroderma pigmentosum variant be used only in the context of the laboratory studies of patients with XP that contain normal repair but deficient semiconservative replication of UV-damaged DNA.

DNA excision repair in mammalian cell extracts

The many genetic complementation groups of DNA excision-repair defective mammalian cells indicate the considerable complexity of the excision repair process. The cloning of several repair genes is taking the field a step closer to mechanistic studies of the actions and interactions of repair proteins. Early biochemical studies of mammalian DNA repair in vitro are now at hand. Repair synthesis in damaged DNA can be monitored by following the incorporation of radiolabelled nucleotides. Synthesis is carried out by mammalian cell extracts and is defective in extracts from cell lines derived from individuals with the excision-repair disorder xeroderma pigmentosum. Biochemical complementation of the defective extracts can be used to purify repair proteins. Repair of damage caused by agents including ultraviolet irradiation, psoralens, and platinating compounds has been observed. Neutralising antibodies against the human single-stranded DNA binding protein (HSSB) have demonstrated a requirement for this protein in DNA excision repair as well as in DNA replication.

Malignant schwannoma associated with xeroderma pigmentosum in a patient belonging to complementation group D

A 43-year-old man with xeroderma pigmentosum, XP97TO, was allocated to complementation group D. He had had moderate photosensitivity at age 1 year and freckles by age 6 but no neurologic abnormalities. Nevertheless, his fibroblasts in culture had the XP-D phenotype. They showed a sevenfold hypersensitivity to killing by 254 nm ultraviolet radiation and a diminished level (29%) of unscheduled DNA synthesis. Phototesting revealed delayed maximum erythema at 72 hours after UVB exposure and a lowered minimal erythema dose. Lentigo maligna developed on the patient's face, and a rapidly growing malignant schwannoma was found on the left trigeminal nerve. This may be the first case of a peripheral nervous tissue neoplasm in xeroderma pigmentosum.

Clonal chromosome rearrangements in a fibroblast strain from a patient affected by xeroderma pigmentosum (complementation group C)

We report the results of DNA repair studies and cytogenetic investigations in a patient presenting acute phothosensitivity and cancerous skin lesions. In lymphocytes and fibroblasts a reduced level of unscheduled DNA synthesis after UV irradiation was found and the presence of xeroderma pigmentosum, complementation group C, mutation was demonstrated by complementation analysis. In lymphocyte and fibroblast cultures the frequency of spontaneous chromosome gaps and breaks was normal, whereas the frequency of chromosome rearrangements was higher than expected. In fibroblasts from the 4th to the 18th passage of the culture, 4 reciprocal translocations with a clonal distribution were identified. The rearranged chromosomes were Nos. 2, 13, 14 and 15, Nos. 2 and 13 being both involved in 3 different translocations with breakpoints at 2q21, 2q31, 2p23 and 13q31, 13q12 or 3. The biological significance of this finding is discussed in view of a possible correlation with the DNA repair defect and a possible relevance in tumor development of specific chromosome rearrangements.

No apparent neurologic defect in a patient with xeroderma pigmentosum complementation group D

A 31-year-old female patient with xeroderma pigmentosum (XP) XP43KO was assigned to complementation group D by the cell-fusion complementation methods. Cultured XP43KO cells from our patient had the defective DNA repair phenotype showing a residual level of ultraviolet (UV)-induced unscheduled DNA synthesis (45% of normal) and an eightfold higher sensitivity to 254-nm UV killing, compared with normal cells. The phototest on the patient revealed the delayed maximum reaction to UV-B-induced erythema and lower minimal erythema doses at 290- and 300-nm monochromatic wavelengths. However, the XP43KO patient showed no apparent neurologic abnormalities and rather mild or moderate skin lesions at the age of 31 years, although DNA repair deficiency in XP43KO cells from our patient fell into the range of group D cells.

A further definition of characteristics of DNA-excision repair in xeroderma pigmentosum complementation group A strains

The location in the genome of excision repair following exposure to UV (254 nm) of two XP complementation group A strains, XP12BE and XP8LO, that differ considerably in their excision-repair rates, have been determined. Capacity for repair in XP8LO has also been determined. Sites repaired in DNA in a 24-h post-UV period were located relative to the remaining pyrimidine dimers using the M. luteus UV-endonuclease to nick partially repaired DNA and sedimentation in alkaline sucrose to size the resulting DNA. Repair in group A occurs randomly throughout the genome in a manner similar to that observed for normal cells but in contrast to domain-limited repair in group C strains. This observation defines a further similarity of the excision repair detected in group A compared to normal cells that is in addition to the previously reported related characteristics of the respective excision rate curves. A reduced repair capacity in XP8LO relative to normal cells was detected. This strain, which repairs DNA at an initial rate identical to that of normal strains when irradiated with doses of 5 J/m2 or less, repairs DNA at a slower than normal but constant rate at higher doses. This leads to the suggestion that XP8LO is defective in the number of repair enzyme complexes compared to normal cells.

Interspecies complementation analysis of xeroderma pigmentosum and UV-sensitive Chinese hamster cells

Complementation analysis was performed 24 h after fusion of UV-sensitive CHO cells (CHO 12 RO) with XP cells of complementation groups A, B, C, D, F and G. The parental cells are characterized by low levels of unscheduled DNA synthesis (UDS). In all combinations, the UDS levels observed in heterokaryons were higher than those in parental mutant cells, clearly indicating cooperation of human and Chinese hamster repair functions. In heterokaryons of CHO 12 RO with XP-A and XP-C cells, the UDS values reached about the normal human level, whereas in heterokaryons with XP-B, XP-D and XP-F, UDS was restored at a level approaching that in wild-type CHO cells. The results obtained after fusion of CHO cells with two representative cell strains from the XP-G group, XP 2 BI and XP 3 BR, were inconsistent. Fusion with XP 3 BR cells yielded UDS levels ranging from wild-type Chinese hamster to normal human, whereas fusion with XP 2 BI cells resulted in a slight increase in UDS which even after 48 h remained below the level found in wild-type CHO cells. The occurrence of complementation in these interspecies heterokaryons indicates that the genetic defect in the CHO 12 RO cells is different from the defects in the XP complementation groups tested.

A seventh complementation group in excision-deficient xeroderma pigmentosum

Cells from a xeroderma pigmentosum patient XP2BI who has reached 17 years of age with no keratoses or skin tumours constitute a new, 7th complementation group G. These cells exhibit a low residual level of excision repair, 2% of normal after a UV dose of 5 J/m2 and an impairment of post-replication repair characteristic of excision-defective XPs. They are also sensitive to the lethal effects of UV and defective in host-cell reactivation of UV-irradiated SV40 DNA.

[Photosensitization and DNA repair. Possible nosologic relationship between Xeroderma pigmentosum and Cockayne's syndrome]

UV-sensitivity is a common feature of several diseases including Xeroderma pigmentosum (XP), Cockayne syndrome (CS) and Bloom syndrome (BS). In 12 children with such diseases, cell viability and DNA repair following UV-irradiation as well as PHA transformation of lymphocytes were studied. In 5 of 6 XP cases, in 1 child with CS and in 1 of 2 children with BS, DNA repair and PHA transformation of lymphocytes showed extremely depressed values. A similar study was performed in 2 children with a rare association of XP and CS. Results suggest a relationship between these 2 diseases

Five complementation groups in xeroderma pigmentosum

A collaborative study was undertaken to determine the relationship between the three DNA repair complementation groups in xeroderma pigmentosum found at Erasmus University, Rotterdam, and the four groups found at the National Institutes of Health, Bethesda. The results of this study reveal that there are five currently known complementation groups in xeroderma pigmentosum.

Xeroderma pigmentosum and pigmented xerodermoid

Xeroderma pigmentosum (XP) is a rare hereditary disease in which the skin is extremely sensitive to sunlight. After a slight exposure to sunlight the skin develops widespread poikiloderma including multiple hyperplasia and malignancies of epidermal and dermal origin. We could confirm Cleaver's results in finding dark repair replication very much reduced, not only in cultured fibroblasts, but also in epidermal cells and lymphocytes. Our investigation is based on three solitary cases of autosomal recessive inheritance. Working in this field, we found a condition similar to XP induced by excessive sun exposure of the skin over decades with manifestations after 30 years of age. We therefore term it "pigmented xerodermoid". Repair replication in epidermal cells seems to be normal. In our two cases we found a strong and almost total depression of DNA synthesis after application of low doses of UV light, while in normal skin the premitotic DNA synthesis is only reduced to a degree which is a function of irradiated energy.

Studies in the childhood psychoses. I. Diagnostic criteria and classification

Until the last decade there was considerable confusion about the nosology of childhood psychoses. As Kanner (1958) has pointed out, certain psychodynamically orientated writers (Szurek, 1956; Beres, 1956) have eschewed the important operation of differential diagnosis. This has led to the notion of ‘equality of schizophrenias' (Darr and Worden, 1951) and thus to the idea of a single psychosis of childhood. The controversy over this approach has now waned in the face of empirical evidence from aetiological, phenomenological and follow-up studies, and many authors have stressed the importance of age of onset in their typologies or in their attempts at a more comprehensive classification (Kanner and Lesser, 1958; Mahler et al., 1949, 1952; Bender, 1947, 1959; Anthony, 1958, 1962, and Eisenberg, 1967). As this is also central to the present study it merits examination in greater detail.