Xeroderma pigmentosum patients from Germany: clinical symptoms and DNA repair characteristics

XPG: a multitasking genome caretaker

The XPG/ERCC5 endonuclease was originally identified as the causative gene for Xeroderma Pigmentosum complementation group G. Ever since its discovery, in depth biochemical, structural and cell biological studies have provided detailed mechanistic insight into its function in excising DNA damage in nucleotide excision repair, together with the ERCC1–XPF endonuclease. In recent years, it has become evident that XPG has additional important roles in genome maintenance that are independent of its function in NER, as XPG has been implicated in protecting replication forks by promoting homologous recombination as well as in resolving R-loops. Here, we provide an overview of the multitasking of XPG in genome maintenance, by describing in detail how its activity in NER is regulated and the evidence that points to important functions outside of NER. Furthermore, we present the various disease phenotypes associated with inherited XPG deficiency and discuss current ideas on how XPG deficiency leads to these different types of disease.

Rare exon 10 deletion in POLH gene in a family with xeroderma pigmentosum variant correlating with protein expression by immunohistochemistry

Xeroderma pigmentosum (XP) is a rare autosomal recessive disease characterized by severe cutaneous and ocular sensitivity to sunlight, leading to skin cancer. Most XP patients belong to the XP complementation groups (XP-A to XP-G), due to mutations in genes involved in nucleotide excision repair (NER). On the other hand, the XP Variant type (XP-V, OMIM#278750), which accounts for about 20% of all XP patients, is associated with normal NER function. The disease gene is POLH, which encodes polymerase η (pol η) allowing translesion synthesis in regions of DNA damage. We observed an Italian family presenting with photosensitivity, freckling since childhood and multiple skin cancers. Complete sequence analysis of XPA, XPC, XPD/ERCC2 genes and exons 1-9 and 11 of POLH gene did not reveal pathological mutations. No PCR product was observed for exon 10 in POLH gene. By RT-PCR analysis followed by POLH exon 10 sequencing, all affected members were found to harbor a homozygous 170-nucleotide deletion. The same deletion was previously described in 3 XP-V families, one of southern Italian descent and two from Algeria, suggesting a possible founder mutation. The deletion determines a severe protein truncation and defective pol η activity. Immunohistochemical study showed markedly reduced pol η expression in skin lesions of the affected siblings compared to the normal control skin.

Phenotype-specific adverse effects of XPD mutations on human prenatal development implicate impairment of TFIIH-mediated functions in placenta

Mutations in XPD (ERCC2), XPB (ERCC3), and TTD-A (GTF2H5), genes involved in nucleotide excision repair and transcription, can cause several disorders including trichothiodystrophy (TTD) and xeroderma pigmentosum (XP). In this study, we tested the hypothesis that mutations in the XPD gene affect placental development in a phenotype-specific manner. To test our hypothesis and decipher potential biologic mechanisms, we compared all XPD-associated TTD (n=43) and XP (n=37) cases reported in the literature with respect to frequencies of gestational complications. Our genetic epidemiologic investigations of TTD and XP revealed that the exact genetic abnormality was relevant to the mechanism leading to gestational complications such as preeclampsia. Through structural mapping, we localized the preeclampsia-associated mutations to a C-terminal motif and the helicase surfaces of XPD, most likely affecting XPD's binding to cdk-activating kinase (CAK) and p44 subunits of transcription factor (TF) IIH. Our results suggested a link between TTD- but not XP-associated XPD mutations, placental maldevelopment and risk of pregnancy complications, possibly due to impairment of TFIIH-mediated functions in placenta. Our findings highlight the importance of the fetal genotype in development of gestational complications, such as preeclampsia. Therefore, future studies of genetic associations of preeclampsia and other placental vascular complications may benefit from focusing on genetic variants within the fetal DNA.

Incidence of xeroderma pigmentosum in Larkana, Pakistan: a 7-year study

Xeroderma pigmentosum (XP) is a rare autosomal recessive inherited disorder caused by a defect in the normal repair of DNA of various cutaneous cell types damaged by exposure to ultraviolet radiation. We present our 7-year experience with 36 XP patients who either visited the Department of Dermatology or were seen in the medical camps arranged in remote areas for patients' welfare, from 1995 to 2001. For ease of discussion we classified all cases into the following subgroups on clinical grounds only: mild, those with light brown freckles on the face alone; moderate, those with dark brown freckles with burning on the face, neck, ears, chest, hands and photophobia but without other associated obvious cutaneous and ocular changes; severe, those with extensive dark brown freckles with burning on the exposed parts as well as on the unexposed parts of the body, i.e. the chest, back, abdomen and arms including other associated cutaneous and ocular changes such as ulcers and malignancy. Of 36 patients, three (8.3%) were classified as mild, nine (25%) moderate and 24 (66.7%) severe; there were 18 males and 18 females, age range 2-30 years (mean 8.9 years). Seventeen patients had cutaneous changes: actinic keratosis, keratoacanthoma, fissures and ulcerative nodules on the exposed parts of the body. Four patients had wide ulcers, along with mass formation and severe pigmentation on the face, neck and head. Twenty-nine patients developed ocular symptoms: photophobia, conjunctivitis, corneal keratitis and lid ulcer. One patient had complete loss of vision. Histopathological findings revealed that six patients had squamous cell carcinoma (SCC) on the face, head, ear or lip. More than one sibling (two to four) was affected in four families. The majority of cases (20/36, 55.6%) were from the Brohi tribe (skin type III), while the remaining cases (16/36, 44.4%) were from the Sindhi population (skin type IV). The large number of XP patients seen in those with skin type III (Brohi tribe) compared with skin type IV (Sindhi population) indicates that the skin type and the race has a considerable value in the pathogenesis of XP. Furthermore, 24 of 36 patients were in the severe group and six of these had SCC. Moreover, no neurological abnormalities were observed in our patients. All patients were treated according to disease severity by prescribing oral antibiotics, local steroids, sunscreens and/or chemotherapy followed by irradiation in malignant cases. Two patients died because of extensive SCC.

Xeroderma pigmentosum and trichothiodystrophy are associated with different mutations in the XPD (ERCC2) repair/transcription gene

The xeroderma pigmentosum group D (XPD) protein has a dual function, both in nucleotide excision repair of DNA damage and in basal transcription. Mutations in the XPD gene can result in three distinct clinical phenotypes, XP, trichothiodystrophy (TTD), and XP with Cockayne syndrome. To determine if the clinical phenotypes of XP and TTD can be attributed to the sites of the mutations, we have identified the mutations in a large group of TTD and XP-D patients. Most sites of mutations differed between XP and TTD, but there are three sites at which the same mutation is found in XP and TTD patients. Since the corresponding patients were all compound heterozygotes with different mutations in the two alleles, the alleles were tested separately in a yeast complementation assay. The mutations which are found in both XP and TTD patients behaved as null alleles, suggesting that the disease phenotype was determined by the other allele. If we eliminate the null mutations, the remaining mutagenic pattern is consistent with the site of the mutation determining the phenotype.

Neurocutaneous syndromes associated with pigmentary skin lesions

Tremendous strides have been made in our understanding of genetic disorders, including those that involve both the skin and the nervous system. The list of well-established neurocutaneous syndromes has increased during a few decades from a few classical phakomatoses to more than 30 entities. The dermatologist has the opportunity to facilitate precise diagnosis and optimal care for these patients by recognition of the cutaneous markers for these diseases. We have attempted to provide an overview of some recent advances in those syndromes manifested by pigmentary skin changes, emphasizing the clinical spectrum of each disorder and providing guidelines for an approach to management.

A contribution to the understanding of the heredity of skin tumors

At least 21 multiple tumors of the skin are inherited autosomal-dominantly. Eighteen are benign and three are malignant. One-third of these tumors have no associated lesions, another third is associated with benign visceral lesions, and a final third belongs to the group of cancer associated genodermatoses. The solitary variants of these tumors, however, are sporadic, not inherited.

Expression of mitochondrial genes and DNA-repair-related nuclear genes is altered in xeroderma pigmentosum fibroblasts

Differential hybridization was used to detect repair defects in xeroderma pigmentosum (XP) that are not amenable to current analyses. cDNA libraries were constructed from cytoplasmic RNA of normal and XP fibroblast strains (complementation groups A and D) and analyzed for differential gene expression. More than 40,000 lambda gt10 cDNA clones were differentially screened with in vitro transcripts made from cDNA in the pBluescript vector. Six differential clones were detected in the libraries of the XP group A and D strains which caused stronger or weaker signals when probed with transcripts from XP strains than with those from the normal strains. Two clones coded for mitochondrial genes: mitochondrial 16 S rRNA and ATPase 6L. Overexpression of mitochondrial genes in XP may indicate that functions of the ATP-generating system are impaired since such functions are intensified whenever they become insufficient, for example as a consequence of DNA damage. It is tempting to assume that abnormal mitochondria are one of the causes for the neurological malfunctions in XP. Furthermore, densitometric analysis of Northern blots revealed that mRNA of lactate dehydrogenase, chain M, was less abundant in four XP group A strains (extent of reduction: 70%) and in two XP group D strains (extent of reduction: 58%). Enzyme activity was also diminished. In addition, mRNA of the gene for glyceraldehyde-3-phosphate dehydrogenase was less expressed in the same XP group A and D fibroblast strains investigated (reduction in both complementation groups: 50%). Both glycolytic enzymes have nuclear functions apart from their role in sugar metabolism. Lactate dehydrogenase, chain M, is identical to a helix-destabilizing protein; it is closely associated with chromatin and unfolded DNA, suggesting a role in DNA synthesis and transcription. The 37-kDa subunit of glyceraldehyde-3-phosphate dehydrogenase is involved in transcription and was shown to be identical to uracil-DNA glycosylase, a base-excision repair enzyme. We presume that the nuclear functions of these glycolytic enzymes may be thwarted in the XP strains investigated and may account for malfunctions in XP, particularly for neurological disturbances.

Oculocutaneous manifestations in xeroderma pigmentosa

Xeroderma pigmentosum (XP) is a rare genetic disease characterised by defective DNA repair leading to clinical and cellular hypersensitivity to ultraviolet radiation. The oculocutaneous features of 10 patients with XP were studied retrospectively. General features included parental consanguinity (40%), familiarity (60%), onset of symptoms in first 2 years (50%), malignant skin neoplasms (60%), and carcinoma of the tongue (20%). Among the ocular features, 50% of patients presented with photophobia. Lid freckles or atrophic skin lesions were seen in all patients. Lower lid tumours were seen in 30%, chronic conjunctival congestion in 40%, corneal opacification in 40%, squamous cell carcinoma of limbus in 20%, bilateral pterygium in 40%, and visual impairment in 50%. The clinical features (ocular and cutaneous) of the cases are discussed.

Enhanced expression of mitochondrial genes in xeroderma pigmentosum fibroblast strains from various complementation groups

cDNA libraries constructed from cytoplasmic RNA of normal and xeroderma pigmentosum (XP) fibroblast strains were screened for differential gene expression. XP fibroblast strains included one representative of the complementation groups A, C, D, and one XP variant strain. The XP lambda gt10 cDNA libraries were differentially screened with in vitro transcripts made from cDNA in the pBluescript vector using both the same XP strain and the normal fibroblast strain. Eight differential clones were detected in the libraries of the XP group A, D, and C strains, which caused stronger signals when probed with transcripts from XP strains than with those from the normal strain. The cDNA clones were sequenced. Seven of the eight clones detected coded for three mitochondrial genes: subunit I of cytochrome c oxidase (complex IV of the respiratory chain), apocytochrome b (subunit of complex III), and 16-S rRNA. Two clones representing essentially (a) subunit I of cytochrome c oxidase and (b) 16-S rRNA diverged from the sequence of the human mitochondrial genome present in the data-base libraries. Clone a exhibited a transition mutation, clone b reflected a transcript of a mitochondrial genome rearranged in the 16-S rRNA gene, including four nucleotides of the adjacent tRNA(Leu) gene. The apparently enhanced expression of mitochondrial genes in XP cells, together with the changes in DNA sequence, seem to indicate that functions of the ATP-generating system were impaired. This defect may have originated from mutations due to lack of DNA repair. The data can be interpreted in the light of mitochondrial changes that cause human neuromyopathies to occur. In analogy to these diseases the neurological symptoms in XP might be explained by abnormal mitochondria.

Xeroderma pigmentosum-Cockayne syndrome complex in two patients: absence of skin tumors despite severe deficiency of DNA excision repair

Two brothers had a complex combination of two DNA repair disorders: Cockayne syndrome and xeroderma pigmentosum. This rare combination has previously been observed in only two other patients. The clinical signs shared by these two brothers and the two other previously described patients include severe sun sensitivity, freckling, diminished stature, hearing and movement impairment, and neurologic degeneration. Although defective UV-induced unscheduled DNA synthesis has been demonstrated (5% of normal), no skin cancers have appeared in these 38- and 41-year-old brothers, whereas skin cancers developed at a relatively early age in the two previously described patients who also had defective UV-induced unscheduled DNA synthesis.

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.

Fibroblasts derived from patients with dysplastic nevus syndrome are not more sensitive towards 254-nm and 312-nm ultraviolet light than fibroblasts from normal donors

DNA repair capacity of 18 fibroblast strains from patients with dysplastic nevus syndrome, 5 of them with malignant melanoma, was investigated and their colony-forming ability (D0) after UV exposure was determined as a measurement of this. Seventeen fibroblast strains from normal donors served as controls. The dose/response experiments included up to 11 dose levels and two UV wavelength ranges: UV-C (using a low-pressure mercury lamp emitting predominantly 254-nm light) and UV-B (artificial "sunlamp" radiation centering around 312-nm light). The exponential segments of the dose/response curves were analysed by linear regression and the negative reciprocals of the regression coefficients, D0, were calculated for each cell strain and each wavelength range. When comparing D0 values of individual cell strains from patients with and without melanomas with the mean value for all normal donors, only 4 out of 18 showed increased sensitivity towards UV-B. This difference, however, was not statistically significant. On the contrary, weighted-mean D0 values for fibroblast strains from patients with and without melanoma were found to be slightly but significantly higher than those for normal donors (significance level: 5%), indicating that cell strains from these patients were less sensitive to UV light (UV-C and UV-B) of both wavelength. This result, which on the basis of current literature data is somewhat unexpected, holds true within the limits of experimental accuracy of +/- 12%.

A case of xeroderma pigmentosum group D determined by photobiological study

A case of xeroderma pigmentosum group D in 36-year-old woman (XP85TO) is reported. The patient had severe photosensitivity from age 4, and developed multiple basal cell epitheliomas and solar keratoses but exhibited no apparent neurological defects. A skin phototest by monochromatic ultraviolet light revealed a delayed peak of erythema 48 h after irradiation and lowered minimal erythemal doses. Unscheduled DNA synthesis induced in XP85TO cells was 36.0% in dermal fibroblasts and 32.6% in epidermal keratinocytes compared with normal cells. The XP85TO cells were sensitive to ultraviolet killing (n = 1.0, D0 = 0.80 J/m2). In complementation analysis, XP85TO cells did not complement with xeroderma pigmentosum group D cells. These results indicate that patient XP85TO had xeroderma pigmentosum group D. The Japanese group D patients including XP85TO case showed delayed onset of skin malignant tumors and neurological abnormalities, compared with the group D patients in Europe and the United States. These findings suggest a possible ethnic variation of the clinical phenotype, despite the similar repair defect and ultraviolet hyperssensitivity.

The effects of inhibitors of topoisomerase II and quinacrine on ultraviolet-light-induced DNA incision in normal and xeroderma pigmentosum fibroblasts

The aim of our work was to investigate whether DNA topoisomerase II participates in the repair-specific incision of UV-irradiated genomic DNA. Therefore, the influence upon DNA incision of the topoisomerase II inhibitors (nalidixic and oxolinic acid, novobiocin and coumermycin A1) as well as the intercalating agent quinacrine has been measured in normal human fibroblasts using the alkaline elution technique. In addition, inhibition by novobiocin has been determined in fibroblast strains from 11 normal donors and from 16 xeroderma pigmentosum (XP) patients belonging to the complementation groups A, C, D, E, and XP variant. Nalidixic and oxolonic acid did not inhibit endonucleolytic cleavage, whereas novobiocin was a potent inhibitor of DNA incision. It was observed that in normal and in all XP strains 50% inhibition by novobiocin occurred on average in the dose range 315-590 microM. Since inhibition by novobiocin was not paralleled by that with the other topoisomerase II inhibitors nalidixic and oxolinic acid, it must be concluded that reduction of enzyme-catalysed breaks was not due to the participation of topoisomerase II in the incision step, but to the displacement of ATP at the binding site of the DNA-incising enzyme. This enzyme absolutely requires ATP as a cofactor for endonucleolytic cleavage. Quinacrine, however, inhibited DNA incision in normal fibroblasts at a mean Ki of 318 microM. Inhibition by this intercalating agent seems to be caused by structural perturbations in DNA, which render it a poor substrate for endonucleolytic cleavage.

Comparison of DNA-incising capacities in fibroblast strains from the Mannheim XP collection after treatment with N-acetoxy-2-acetylaminofluorene and UV light

The DNA-incising capacity was determined in 8 normal and 23 XP fibroblast strains of the Mannheim XP collection using the alkaline elution technique after treatment with both UV light and the "UV-like" carcinogen (Ac)2ONFln. Experimental conditions were chosen to allow for selective monitoring of repair-specific enzyme-catalyzed breaks. In order to compare DNA-incising capacities of the various cell strains after UV irradiation with those after treatment with (Ac)2ONFln, dose-response experiments including up to 8 dose levels were performed. The elution curves were analyzed by linear regression analysis. Elution velocities (in terms of DNA single-strand breaks per 10(6) nucleotides) were plotted against the square root of the doses. The slope of the resulting regression line yielded a characteristic term, designated EO, for the DNA-incising capacity of each cell strain. In contrast to normal fibroblasts, EO was found to be reduced in all XP cell strains belonging to the complementation groups A, C, D, E, F (or G) and I investigated, after treatment with both UV light or (Ac)2ONFln. Surprisingly, XP variant strains also exhibited lower EO values. A comparison of post-UV with post-(Ac)2ONFln DNA-incising capacities revealed that reduction in the EO values was very similar in all XP cell strains tested. These data suggest that the sensitivity of XP cells towards UV light or (Ac)2ONFln is due to the same enzymatic defect, namely impaired incision of DNA containing pyrimidine dimers or (Ac)2ONFln-DNA adducts.

Xeroderma pigmentosum complementation group F in a non-Japanese patient

Genetic complementation studies allowed assignment of a 22-year-old-white woman to the rare complementation group of classic, excision-defective xeroderma pigmentosum (group F cell strain), previously reported only in patients from Japan. She manifested mild cutaneous changes, with no tumors and normal sensitivity to monochromatic ultraviolet irradiation. Unscheduled deoxyribonucleic acid synthesis in cultured fibroblasts (XP126LO) after irradiation with germicidal ultraviolet light was reduced to 13% of control values during the first 2 hours and rose to 45% of normal by 7 to 8 hours.

DNA repair synthesis in fibroblast strains from patients with actinic keratosis, squamous cell carcinoma, basal cell carcinoma, or malignant melanoma after treatment with ultraviolet light, N-acetoxy-2-acetyl-aminofluorene, methyl methanesulfonate, and N-methyl-N-nitrosourea

Fibroblast strains derived from skin biopsies of patients with actinic keratosis (6), malignant melanoma (18), squamous cell carcinoma (11), and basal cell carcinoma (12) were investigated for DNA repair synthesis, with 16 fibroblast strains for normal donors as controls. Cells were exposed to UV light, the "UV-like" carcinogen (Ac)2ONFln, and the methylating carcinogens MeSO2OMe and MeNOUr. Dose-response experiments, which included 10 dose levels, were performed, the data analyzed by linear regression, and the slope of the regression line (term: G0) used as a measure of DNA repair synthesis. The mean experimental variability of G0 of individual fibroblast strains was 9.5%-15.4%, depending upon exposure. For comparison of all cell strains belonging to the same skin malignancy group with those of the control group, G0 values of the individual strains were combined to yield group-specific weighted mean G0 values. In addition, the capacity to incise UV-damaged DNA was measured in 24 cell strains from patients with skin tumors using the alkaline elution technique. For quantitating DNA-incising capacity, the initial velocities of the elution curves were plotted versus the UV dose, and the slope of the resulting regression line was used to obtain the characteristic value E0. The mean experimental variability of E0 of individual strains was +/- 22%. These E0 values were combined to yield weighted mean values of groups. The fibroblast strains in the groups of patients with actinic keratosis and malignant melanoma were found to have normal mean G0 values when DNA repair synthesis was challenged with UV light or one of the three carcinogens. However, the squamous cell carcinoma group exhibited significantly lower mean G0 values after treatment with UV light (82% that of normal donors), (Ac)2ONFln (70%), MeSO2OMe (70%), and MeNOUr (69%). The basal cell carcinoma group showed significantly diminished repair synthesis upon treatment with UV light (81% that of normal donors) and MeSO2OMe (67%). In contrast to these findings, in no skin malignancy group was post UV DNA-incising capacity (E0) significantly diminished, although it should be noted that group sizes were only half as large as for G0 determinations. These data may be interpreted as indicating that DNA excision repair is impaired in fibroblast strains from patients with squamous cell carcinoma and-to a lesser extent-basal cell carcinoma.(ABSTRACT TRUNCATED AT 400 WORDS)

Xeroderma pigmentosum and keratoconus

Two XP patients are presented. A corneal perforation in the left eye of the first patient necessitated an at-random transplantation à chaud. The graft was remarkably well tolerated, which is possibly explained by UV-light-induced suppression of the cellular immune response in the patient. The right eye of this patient and both eyes of the second patient had a keratoconus. Keratoconus in XP may be the result of disturbances in the cell differentiation and the function of epithelial cells and keratocytes, due to UV-light-induced deficient DNA repair synthesis.

Xeroderma pigmentosum patients from Germany: repair capacity of 45 XP fibroblast strains of the Mannheim XP Collection as measured by colony-forming ability and unscheduled DNA synthesis following treatment with methyl methanesulfonate and N-methyl-N-nitrosourea

A total of 45 XP fibroblast strains from the Mannheim XP Collection (representatives of XP complementation groups A, C, D, E, F or G, I, and XP variants) were investigated for colony-forming ability (term: D0) after treatment with up to ten doses of the methylating carcinogen MeSO2OMe. As controls 16 fibroblast strains from normal donors were used. Except for 4 XP strains (1 from group C and 3 from group D) which, however, were borderline cases, none of the remaining 41 XP strains was found to be more sensitive than normal controls. This held true within the limits of an experimental accuracy (experimental variability of D0 values) of +/- 7%. When weighted means were calculated for XP complementation groups and compared with that of normal donors at a significance level of 5%, no significant difference was detected. In contrast, after exposure of 6 XP group D strains to MeNOUr, a weighted mean D0 value was obtained which was significantly decreased by 27%. Unscheduled DNA synthesis (term: G0 which serves as a measure of excision repair) after exposure to MeNOUr was quantitatively the same (experimental variability: +/- 8%) both in the group of normal strains and in most of the XP complementation groups. Exceptions were group E and group F (or G) which had higher, and group I which had lower repair. Analogous G0 values measured after exposure to MeSO2OMe (experimental variability: +/- 13%), however, differed from that of the control strains: they were lower in XP complementation groups A, D, E, F (or G), and I. However, groups A, E, F (or G), and I including only 3 individual strains or less may be considered to be possibly ill-represented. Yet, group D including 11 XP strains did show reduction of the mean G0 value by 35%. From this it is concluded that there are repair defects in XP group D strains with regard to MeSO2OMe-induced adducts. These defects seem to be small.

Xeroderma pigmentosum patients from the Federal Republic of Germany: decrease in post-UV colony-forming ability in 30 xeroderma pigmentosum fibroblast strains is quantitatively correlated with a decrease in DNA-incising capacity

A total of 16 normal and 46 XP fibroblast strains from the Mannheim Collection were investigated for colony-forming ability following exposure to both UV light and the "UV-like" carcinogen (Ac)2ONFln. The dose-response experiments included up to 13 dose levels. The exponential segments of the curves were analysed by linear regression and the negative reciprocal of the regression coefficient (D0) was calculated for each cell strain. For quantitating the DNA-incising capacity, DNA elution curves were determined at several UV dose levels. Plotting the initial velocities of the elution curves versus the UV dose yielded a regression line, the slope of which was used to obtain the characteristic value E0. Comparing D0 with E0 values showed that cell strains in which colony-forming ability was reduced suffered a reduction of DNA-incising capacity of the same magnitude. There were only 3 exceptional strains in which reduction of DNA-incising capacity was less pronounced than reduction of colony-forming ability. We have previously shown (Fischer et al. 1982) that D0 values from 27 XP strains of the Mannheim Collection were correlated with clinical symptoms. This correlation is now being extended by relating colony-forming ability to the magnitude of the DNA incision defect. From our data we conclude that the best quantitative biochemical denominator to explain the sun sensitivity of XP is that of a defective incision of UV-damaged DNA. A considerable similarity in sensitivity towards both UV light and (Ac)2ONFln was found in 16 normal and 46 XP strains. This seems to indicate that UV- and (Ac)2ONFln-induced DNA damage are removed to a large extent by the same pathways in human fibroblasts.

A ninth complementation group in xeroderma pigmentosum, XP I

A new complementation group of excision-deficient xeroderma pigmentosum (XP) is described in 2 patients living in the F.R.G. Dermatological, ophthalmological and neurological symptoms of XP are presented together with DNA repair characteristics such as unscheduled DNA synthesis, colony-forming ability and alkaline elution studied in cultured fibroblasts. The results are compared to normal controls.

Clinical and biological studies of 26 cases of xeroderma pigmentosum in northeast district of Japan

Twenty-six patients with xeroderma pigmentosum (XP), who live in the Northeast (Tohoku) District of Japan, were examined for the clinical characteristics of UV-induced DNA synthesis (unscheduled DNA synthesis, UDS) and UV sensitivity of skin fibroblasts or lymphoblastoid cells, or both. A history of consanguineous marriage within two generations was found in 19 of 26 cases (73%). Two pairs of siblings showed similar manifestations and almost the same levels of UDS and of UV sensitivity. Squamous cell carcinoma, basal cell carcinoma, or both were observed on the exposed skin in 14 patients, but no malignant melanoma was found. Cancer had developed in approximately 71% (10/14) of the cancer-bearing patients by the age of 20, and 8 of them belonged to the UDS-deficient group. Neurological manifestations were associated with nine patients, including 3 with typical de Sanctis-Cacchione syndrome (DSC), and most of the cells derived from these patients had a UDS level less than 10% of that of the normal cells. A clear correlation between the levels of UDS and UV sensitivity, on the one hand, and the severity of clinical manifestations on the other could not be detected, but it seems that the UDS-deficient group is generally much more sensitive to UV in terms of cell killing and the induction of sister chromatid exchange (SCE) than the UDS-proficient group. After a photosensitivity test, one patient with mild skin manifestations showed distinct skin tanning without preceding erythema.

SV40-induced transformation and T-antigen production is enhanced in normal and repair-deficient human fibroblasts after pretreatment of cells with UV light

Human fibroblasts irradiated with UV light were infected with simian virus 40 and tested either for transformation or T-antigen production. At UV doses that allowed approximately 5-10% of the irradiated cells to survive, the number of surviving transformed colonies increased. This result was confirmed by testing for T-antigen 96 h post infection by means of indirect immunofluorescence. Since these results were obtained for a normal cell line as well as for two UV excision repair-deficient ones (XP groups A and D), it was concluded that excision repair functions cannot play a decisive role in the events leading to increased transformation and T-antigen production. It is proposed that the relative increase of transformation and T-antigen production is the expression of host functions which are induced by DNA damage threatening cell survival.

Spontaneous in vitro malignant transformation in a xeroderma pigmentosum fibroblast line

This paper deals with a spontaneous malignant transformation in one of our XP fibroblast lines. This cell line, designated XP29MA, was derived from a 14-year-old boy who did not show skin tumors or precancerous alterations either at the time of clinical examination or when the biopsy was taken. We have compared the following features in both the malignant and the benign cell line from which the malignant line developed: tumor formation in nude mice, repair capacity, cytogenetic status, light and electron microscopic characteristics. The benign cell line XP29MA had a doubling time of 4.3 d, did not form tumors in nude mice, showed a very low repair capacity (as determined by colony-forming ability, unscheduled DNA synthesis and alkaline elution) but exhibited a normal cytogenetic and ultrastructural status. In contrast, the transformed cell line XP29MAmal grew three times faster, formed colonies in methyl cellulose, gave rise to fibrosarcomas in nude mice, showed a drastically higher repair capacity, and was characterized by an extreme genetic imbalance, resulting from numerical and structural chromosome alterations of Nos. 1, 3, 4, 8, 12, 16, 17, 18, 20 and 21. Ultrastructural examination revealed fusiform and polygonal cells, the latter exhibiting large indented nuclei, vesicular dilatations of the endoplasmatic reticulum and numerous lysosomes. The higher repair capacity in XP29MAmal cells is tentatively explained in terms of reversion, enhancement of post-replication repair and/or expression of SOS-type functions.