The Iberian legacy into a young genetic xeroderma pigmentosum cluster in central Brazil.

In central Brazil, in the municipality of Faina (state of Goiás), the small and isolated village of Araras comprises a genetic cluster of xeroderma pigmentosum (XP) patients. The high level of consanguinity and the geographical isolation gave rise to a high frequency of XP patients. Recently, two founder events were identified affecting that community, with two independent mutations at the POLH gene, c.764 + 1 G > A (intron 6) and c.907 C > T; p.Arg303* (exon 8). These deleterious mutations lead to the xeroderma pigmentosum variant syndrome (XP-V). Previous reports identified both mutations in other countries: the intron 6 mutation in six patients (four families) from Northern Spain (Basque Country and Cantabria) and the exon 8 mutation in two patients from different families in Europe, one of them from Kosovo. In order to investigate the ancestry of the XP patients and the age for these mutations at Araras, we generated genotyping information for 22 XP-V patients from Brazil (16), Spain (6) and Kosovo (1). The local genomic ancestry and the shared haplotype segments among the patients showed that the intron 6 mutation at Araras is associated with an Iberian genetic legacy. All patients from Goiás, homozygotes for intron 6 mutation, share with the Spanish patients identical-by-descent (IBD) genomic segments comprising the mutation. The entrance date for the Iberian haplotype at the village was calculated to be approximately 200 years old. This result is in agreement with the historical arrival of Iberian individuals at the Goiás state (BR). Patients from Goiás and the three families from Spain share 1.8 cM (family 14), 1.7 cM (family 15), and a more significant segment of 4.7 cM within family 13. On the other hand, the patients carrying the exon 8 mutation do not share any specific genetic segment, indicating an old genetic distance between them or even no common ancestry.

A genetic cluster of patients with variant xeroderma pigmentosum with two different founder mutations.

BACKGROUND: Xeroderma pigmentosum (XP) is a rare human syndrome associated with hypersensitivity to sunlight and a high frequency of skin tumours at an early age. We identified a community in the state of Goias (central Brazil), a sunny and tropical region, with a high incidence of XP (17 patients among approximately 1000 inhabitants). OBJECTIVES: To identify gene mutations in the affected community and map the distribution of the affected alleles, correlating the mutations with clinical phenotypes. METHODS: Functional analyses of DNA repair capacity and cell-cycle responses after ultraviolet exposure were investigated in cells from local patients with XP, allowing the identification of the mutated gene, which was then sequenced to locate the mutations. A specific assay was designed for mapping the distribution of these mutations in the community. RESULTS: Skin primary fibroblasts showed normal DNA damage removal but abnormal DNA synthesis after ultraviolet irradiation and deficient expression of the Polη protein, which is encoded by POLH. We detected two different POLH mutations: one at the splice donor site of intron 6 (c.764 +1 G>A), and the other in exon 8 (c.907 C>T, p.Arg303X). The mutation at intron 6 is novel, whereas the mutation at exon 8 has been previously described in Europe. Thus, these mutations were likely brought to the community long ago, suggesting two founder effects for this rare disease. CONCLUSIONS: This work describes a genetic cluster involving POLH, and, particularly unexpected, with two independent founder mutations, including one that likely originated in Europe.

Unexpected extradermatological findings in 31 patients with xeroderma pigmentosum type C.

BACKGROUND: Xeroderma pigmentosum type C (XP-C) is a rare, autosomal, recessive condition characterized by the association of various clinical manifestations mostly involving the skin and eyes. OBJECTIVES: To evaluate the clinical manifestations in a homogeneous, genetically characterized cohort of patients with XP-C. METHODS: All patients with XP-C, which was confirmed genetically or by unscheduled DNA synthesis, from the registry of our department and from the French association of patients 'Les Enfants de la Lune' were contacted. During a planned consultation, clinical information was collected using a standardized case-record form. RESULTS: In total, 31 patients were seen. The mean age at diagnosis was 2.95 years; skin symptoms started at a mean age of 1.49 years. Among the patients, 52% had relatively short stature, with a height-for-weight z-score below -1 SD; 62% showed pyramidal syndrome and 45% had photophobia and/or conjunctivitis. Four patients had several pyogenic granulomas. Twenty-four patients (77%) had skin cancer. The mean age of onset of the first skin cancer was 4.76 years (range 2-14.5 years). Basal-cell carcinoma was the most frequent cancer. Melanomas were rare and mostly desmoplastic. Multinodular thyroid was the most frequent internal tumour. CONCLUSIONS: Our data highlight several new aspects of XP-C. Patients with XP-C are at risk of developing pyogenic granulomas, desmoplastic melanomas and multinodular thyroid. Involvement of the central nervous system is frequent, but its mechanism remains unclear. The relatively short stature of the patients needs further investigation in order to be explained. XP-C is not only a cancer-prone disorder but is also a polysystemic disorder.

Transmembrane diffusion of gemcitabine by a nanoparticulate squalenoyl prodrug: an original drug delivery pathway.

We have designed an amphiphilic prodrug of gemcitabine (dFdC) by its covalent coupling to a derivative of squalene, a natural lipid. The resulting bioconjugate self-assembled spontaneously in water as nanoparticles that displayed a promising in vivo anticancer activity. The aim of the present study was to provide further insight into the in vitro subcellular localization and on the metabolization pathway of the prodrug. Cells treated with radiolabelled squalenoyl gemcitabine (SQdFdC) were studied by differential detergent permeation, and microautography coupled to fluorescent immunolabeling and confocal microscopy. This revealed that the bioconjugate accumulated within cellular membranes, especially in those of the endoplasmic reticulum. Radio-chromatography analysis proved that SQdFdC delivered dFdC directly in the cell cytoplasm. Mass spectrometry studies confirmed that gemcitabine was then either converted into its biologically active triphosphate metabolite or exported from the cells through membrane transporters. To our knowledge, this is the first description of such an intracellular drug delivery pathway. In vitro cytotoxicity assays revealed that SQdFdC was more active than dFdC on a transporter-deficient human resistant leukemia model, which was explained by the subcellular distribution of the drugs and their metabolites. The squalenoylation drug delivery strategy might, therefore, dramatically improve the efficacy of gemcitabine on transporter-deficient resistant cancer in the clinical context.

DNA repair pathways and human metastatic malignant melanoma.

Melanoma causes a considerable public health burden because of its dramatic rise in incidence worldwide since the mid-1960s and because the metastatic disease remains incurable, has a short median survival and is characterized by resistance to almost all classes of cytotoxic agents. DNA repair pathways are multiple and are able to repair, usually in an error-free manner, all kinds of DNA damage induced by exogenous and endogenous genotoxic agents. This review describes the role of DNA repair process in protecting us from cancer and particularly nucleotide excision deficiencies that are associated with melanoma development. Resistance of tumoral cells to antitumoral regimen can be caused by overexpression of DNA repair processes. We showed that melanoma metastasis was associated with higher expression of some DNA repair pathways leading to a better surveillance of replication fork fidelity. We showed a partially coordinated regulation of these repair genes. P53 and several transcription factors may regulate numerous of these repair genes. The repair pathways that are overexpressed in metastatic melanoma are those particularly efficient in repairing the major DNA damage produced by cytotoxic treatments. This implies that better analysis of DNA repair regulation is necessary to identify novel therapeutic targets and to allow clinicians to propose tailored therapies.

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

Cockayne syndrome is an autosomal recessive multisystem disorder characterized principally by neurological and sensory impairment, cachectic dwarfism, and photosensitivity. This rare disease is linked to mutations in the CSB/ERCC6 and CSA/ERCC8 genes encoding proteins involved in the transcription-coupled DNA repair pathway. The clinical spectrum of Cockayne syndrome encompasses a wide range of severity from severe prenatal forms to mild and late-onset presentations. We have reviewed the 45 published mutations in CSA and CSB to date and we report 43 new mutations in these genes together with the corresponding clinical data. Among the 84 reported kindreds, 52 (62%) have mutations in the CSB gene. Many types of mutations are scattered along the whole coding sequence of both genes, but clusters of missense mutations can be recognized and highlight the role of particular motifs in the proteins. Genotype-phenotype correlation hypotheses are considered with regard to these new molecular and clinical data. Additional cases of molecular prenatal diagnosis are reported and the strategy for prenatal testing is discussed. Two web-based locus-specific databases have been created to list all identified variants and to allow the inclusion of future reports (www.umd.be/CSA/ and www.umd.be/CSB/).

A microarray to measure repair of damaged plasmids by cell lysates.

DNA repair mechanisms constitute major defences against agents that cause cancer, degenerative disease and aging. Different repair systems cooperate to maintain the integrity of genetic information. Investigations of DNA repair involvement in human pathology require an efficient tool that takes into account the variety and complexity of repair systems. We have developed a highly sensitive damaged plasmid microarray to quantify cell lysate excision/synthesis (ES) capacities using small amounts of proteins. This microsystem is based on efficient immobilization and conservation on hydrogel coated glass slides of plasmid DNA damaged with a panel of genotoxic agents. Fluorescent signals are generated from incorporation of labelled dNTPs by DNA excision-repair synthesis mechanisms at plasmid sites. Highly precise DNA repair phenotypes i.e. simultaneous quantitative measures of ES capacities toward seven lesions repaired by distinct repair pathways, are obtained. Applied to the characterization of xeroderma pigmentosum (XP) cells at basal level and in response to a low dose of UVB irradiation, the assay showed the multifunctional role of different XP proteins in cell protection against all types of damage. On the other hand, measurement of the ES of peripheral blood mononuclear cells from six donors revealed significant diversity between individuals. Our results illustrate the power of such a parallelized approach with high potential for several applications including the discovery of new cancer biomarkers and the screening of chemical agents modulating DNA repair systems.

Xeroderma pigmentosum group C in a French Caucasian patient with multiple melanoma and unusual long-term survival.

We report the case of an 83-year-old French woman with multiple melanomas showing a severe DNA repair deficiency, corrected after transfection by XPC cDNA. Two biallelic mutations in the XPC gene are reported: an inactivating frameshift mutation in exon 15 (c.2544delG, p.W848X) and a missense mutation in exon 11 (c.2108 C>T, P703L). We demonstrate that these new mutations are involved in the DNA repair deficiency and confirm the diagnosis of xeroderma pigmentosum from complementation group C (XP-C). We speculate that the coexistence of a MC1R variant may be involved in the phenotype of multiple melanomas and that the unusual long-term survival may be related to a lower ultraviolet radiation exposure and to a regular clinical follow-up. This patient appears to be the first French Caucasian XP-C case and one of the oldest living patients with XP reported worldwide.

Cerebro-oculo-facio-skeletal syndrome: three additional cases with CSB mutations, new diagnostic criteria and an approach to investigation.

BACKGROUND: The cerebro-oculo-facio-skeletal syndrome (COFS syndrome) is an autosomal recessive disorder which was initially described in a specific aboriginal population from Manitoba. In recent years, COFS syndrome has been linked in this original population to a defective DNA repair pathway and to a homozygous mutation in the major gene underlying Cockayne syndrome (CSB). However, most reports of suspected COFS syndrome outside this population have not been confirmed at the molecular level, leading to considerable heterogeneity within the syndrome and confusing overlaps between COFS syndrome and other eye and brain disorders. OBJECTIVE: To refine the delineation of the syndrome on genetically proven COFS cases. METHODS: We report the exhaustive clinical, cellular and molecular data of three unrelated COFS patients with mutations in the CSB gene. RESULTS: All three patients present the cardinal features of COFS syndrome including extreme microcephaly, congenital cataracts, facial dysmorphism and arthrogryposis. They also exhibit a predominantly postnatal growth failure, a severe psychomotor retardation, with axial hypotonia and peripheral hypertonia and neonatal feeding difficulties. Fibroblasts from the patients show the same DNA repair defect which can be complemented by transfection of the CSB wild-type cDNA. Five new mutations in the CSB gene have been identified in these patients. CONCLUSIONS: Our data indicate that COFS syndrome represents the most severe end of the Cockayne spectrum. New diagnostic criteria for COFS syndrome are proposed, based on our findings and on the few genetically proven COFS cases from the literature.

Overexpression of matrix metalloproteinase 1 in dermal fibroblasts from DNA repair-deficient/cancer-prone xeroderma pigmentosum group C patients.

Xeroderma pigmentosum (XP) is a rare, recessively inherited genetic disease characterized by skin cancer proneness and premature aging in photoexposed area. The disease results from defective nucleotide excision repair of ultraviolet (UV)-induced DNA lesions. Reconstruction of group C (XP-C) skin in vitro previously suggested that patients' dermal fibroblasts might be involved in promoting skin cancer development, as they elicited microinvasions of both control and XP-C keratinocytes within dermal equivalents. Here we show that in the absence of UV exposure XP-C fibroblasts exhibit aged-like features such as an elongated and dendritic shape. We analysed the repertoire of expression of matrix metalloproteinases (MMPs) involved in skin aging and cancer. All XP-C fibroblasts tested in this study overexpressed specifically and significantly MMP1. MMP1 expression was also found increased in the dermis of XP-C skin sections suggesting the active contribution of XP-C mesenchymal cells to skin aging and exacerbated carcinogenesis. Increased MMP1 expression in cultured XP-C fibroblasts resulted from MMP1 mRNA accumulation and enhanced transcriptional activity of the MMP1 gene promoter. Deletion analysis revealed the essential role of AP-1 activation in constitutive MMP1 overexpression in XP-C primary fibroblasts. In parallel, levels of reactive oxygen species and FOSB DNA-binding activity were found increased in XP-C fibroblasts. Altogether, these observations suggest that beyond its role in nucleotide excision repair the XPC protein may be important in cell metabolism and fate in the absence of UV.

High expression of DNA repair pathways is associated with metastasis in melanoma patients.

We have identified a gene-profile signature for human primary malignant melanoma associated with metastasis to distant sites and poor prognosis. We analyse the differential gene expression by looking at whole biological pathways rather than individual genes. Among the most significant pathways associated with progression to metastasis, we found the DNA replication (P=10(-14)) and the DNA repair pathways (P=10(-16)). We concentrated our analysis on DNA repair and found that 48 genes of this category, among a list of 234 genes, are associated with metastatic progression. These genes belong essentially to the pathways allowing recovery of stalled replication forks due to spontaneous blockage or induced DNA lesions. Because almost all these differentially expressed repair genes were overexpressed in primary tumors with bad prognosis, we speculate that primary melanoma cells that will metastasize try to replicate in a fast and error-free mode. In contrast to the progression from melanocytes to primary melanoma, genetic stability appears to be necessary for a melanoma cell to give rise to distant metastasis. This overexpression of repair genes explains nicely the extraordinary resistance of metastatic melanoma to chemo- and radio-therapy. Our results may open a new avenue for the discovery of drugs active on human metastatic melanoma.

Frequent alteration of DNA damage signalling and repair pathways in human colorectal cancers with microsatellite instability.

Accumulation of frameshift mutations at genes containing coding mononucleotide repeats is thought to be the major molecular mechanism by which mismatch repair-deficient cells accumulate functional alterations. These mutations resulting from microsatellite instability (MSI) can affect genes involved in pathways with a putative oncogenic role, but may also arise in genes without any expected role in MSI carcinogenesis because of the high mutation background of these tumours. We here screened 39 MSI colorectal tumours for the presence of mutations in 25 genes involved in DNA damage signalling and repair pathways. Using a maximum likelihood statistical method, these genes were divided into two different groups that differed significantly in their mutation frequencies, and likely represent mutations that do or do not provide selective pressure during MSI tumour progression. Interestingly, the so-called real-target mutational events were found to be distributed among genes involved in different functional pathways of the DNA metabolism, for example, DNA damage signalling (DNA-PKcs, ATR), double-strand break (DSB) repair (DNA-PKcs, RAD50), mismatch repair (MSH3, MSH6, MBD4) and replication (POLD3). In particular, mutations in MRE11 and/or RAD50 were observed in the vast majority of the tumours and resulted in the concomitant loss of immunohistochemical expression of both proteins. These data might explain why MSI colorectal cancers (CRC) behave differently in response to a wide variety of chemotherapeutic agents, notably those targeting DNA. More generally, they give further insights into how MSI leads to functional changes with synergistic effects in oncogenic pathways.

Wide clinical variability among 13 new Cockayne syndrome cases confirmed by biochemical assays.

Cockayne syndrome is a multi-systemic, autosomal recessive disease characterised by postnatal growth failure and progressive multi-organ dysfunction. The main clinical features are severe dwarfism (<-2 SD), microcephaly (<-3 SD), psychomotor delay, sensorial loss (cataracts, pigmentary retinopathy, and deafness), and cutaneous photosensitivity. Here, 13 new cases of Cockayne syndrome are reported, which have been clinically diagnosed and confirmed using a biochemical transcription assay. The wide clinical variability, ranging from prenatal features to normal psychomotor development, is emphasised. When cardinal features are lacking, the diagnosis of Cockayne syndrome should be considered when presented with growth retardation, microcephaly, and one of the suggesting features such as enophthalmia, limb ataxia, abnormal auditory evoked responses, or increased ventricular size on cerebral imaging.

INK4a-ARF mutations in skin carcinomas from UV irradiated hairless mice.

To characterize further the role of the INK4a-ARF locus in the multistep process of skin carcinogenesis, we performed a mutational analysis of this locus in skin lesions from hairless mice either irradiated with UVB alone or with a solar simulator delivering UVA + B. INK4a-ARF mutations were present in five of 57 squamous cell carcinomas (9%), but no mutation was detected in precancerous lesions. All mutations were C:G > T:A transitions located at dipyrimidic sites, the hallmark of UVB mutagenesis. Three mutations affected only the p19(ARF) reading frame, whereas two mutations affected only the p16(INK4a) transcript. This study demonstrates for the first time UV-induced mutations of INK4a-ARF that occur in a small percentage in late stages skin tumors.

[A whole family affected by xeroderma pigmentosum: clinical and genetic particularities]. / Xeroderma pigmentosum: particularités cliniques et génétiques d'une famille dont tous les membres sont atteints.

INTRODUCTION: Xeroderma pigmentosum is a relatively frequent genodermatosis in North Africa. It is characterized by abnormal sensitivity to ultraviolet light, responsible for the early occurrence of multiple cutaneous neoplasms. We present the results of the clinical and biological investigations in a family in which all its members exhibited xeroderma pigmentosum. PATIENTS AND METHODS: Since 1962, the father, mother, the 5 children and the maternal uncle were all followed-up in the dermatology department in Tunis for a variant of xeroderma pigmentosum. Clinical (dermatological, neurological and ophthalmologic), biological, photobiological and molecular biology investigations were carried out. RESULTS: Diagnosis of a variant of xeroderma pigmentosum was established on the delayed appearance (after the age of 4) of poikiloderma and the early onset of multiple carcinomas, without neurological disorders. Fifty-eight squamous cell and 3 basal cell carcinomas were diagnosed and treated by surgical exeresis or radiotherapy. The third child, treated with etretinate for 6 years, had developed 38 carcinomas. Contrary to the parents, whose first carcinomas had appeared at the age of 34 and 40 years, the cutaneous cancers in the children appeared early, between the ages of 17 and 24. The minimal erythematous dose was normal in all these patients. Conversely, the phototest revealed persistent erythema and the delayed appearance of multiple dyskeratosis cells. Molecular biology confirmed the diagnosis of xeroderma pigmentosum with the presence of a low level DNA repair. The third child, the father and the uncle respectively exhibited DNA repair rates of 32, 57 and 72%, compared with normal controls. The results of the complementarity tests conducted in the third child suggested that this family belonged to the genetic F group. Discussion The clinical and molecular data confirmed the diagnosis of xeroderma pigmentosum in this family and their genetic F group profile. However, this family exhibited clinical (the cutaneous involvement was more severe in the children) and molecular heterogeneity and the level of DNA repair was high in comparison with the levels (between 12 and 15%) reported by Japanese authors in group F xeroderma pigmentosum. The third child exhibited 10-fold more carcinomas that his siblings. This high rate of carcinoma may be explained by excessive exposure to sun and/or the retinoid treatment, particularly since his DNA repair rate (32%) was relatively high compared with that of severe (0-5%) and moderate (5-15%) forms of the disease.

Germline and somatic mutations of the INK4a-ARF gene in a xeroderma pigmentosum group C patient.

Xeroderma pigmentosum is an inheritable autosomal recessive DNA repair deficient syndrome characterized by a high predisposition to skin cancers. An elevated proportion of tumors from xeroderma pigmentosum patients harbor ultraviolet-induced mutations (CC:GG > TT:AA tandem transitions) of the p53 and/or the INK4a-ARF genes. Here, we report the clinical and molecular features of a 12 y old xeroderma pigmentosum patient who, in addition to severe cutaneous clinical symptoms, also had three unusual tumors, a mediastinal lymphoblastic lymphoma, an atypical fibroxanthoma, and an epithelioid hemangioma. Single strand conformation polymorphism and sequencing analysis of the p53 and INK4a-ARF genes were carried out in DNA from normal skin and different tumors (four actinic keratosis, two microinvasive squamous cell carcinomas, one basal cell carcinoma, and one atypical fibroxanthoma) from the patient. After characterization of the xeroderma pigmentosum C complementation group, we found unexpectedly that this patient also carried a germline mutation of the INK4a-ARF locus affecting the p16INK4A reading frame. Three different somatic mutations that all harbor the signature of ultraviolet light (two of p16INK4A and one of p53) were also detected in the basal cell carcinoma. We hypothesize that the germline mutation of p16INK4A, in association with the nucleotide excision repair defect, could explain the patient's unusual phenotype. Furthermore, this study confirms that concomitant somatic mutations of INK4a-ARF and p53 occur in some xeroderma pigmentosum associated tumors, and seem to accumulate during tumor progression rather than the initiation step.

Association of RET codon 691 polymorphism in radiation-induced human thyroid tumours with C-cell hyperplasia in peritumoural tissue.

The RET proto-oncogene encodes a protein structurally related to transmembrane receptors with an intracellular tyrosine kinase domain. In human thyroid gland, the RET proto-oncogene is normally expressed in parafollicular C-cells. Thyroid C-cell hyperplasia is associated with inherited medullary thyroid carcinomas and is considered as a pre-neoplastic stage of C-cells disease. It has also been observed in thyroid tissues adjacent to follicular and papillary carcinomas. In order to study the relationship between a misfunctioning of the RET proto-oncogene and the presence of C-cell hyperplasia, we compared a series of thyroid glands presenting sporadic or radiation-associated tumours, as well as samples of unrelated normal thyroid tissues, for alteration in exons 10 and 11 of the gene and for the presence or absence of C-cell hyperplasia. Here we report a significantly higher frequency of C-cell hyperplasia present in peritumoural thyroid tissues of radiation-induced epithelial thyroid tumours, than in peritumoural of sporadic thyroid tumours or in control normal thyroid tissues (P=0.001). A G691S RET polymorphism was present with a higher frequency in radiation-induced epithelial thyroid tumours (55%) than in sporadic tumours (20%) and in control normal thyroid tissues (15%). Interestingly, this polymorphism was associated in the majority (88%) of radiation-induced tumours with a C-cell hyperplasia in the peritumoural tissues. Several explanations for this association are discussed.

Effects of XPD mutations on ultraviolet-induced apoptosis in relation to skin cancer-proneness in repair-deficient syndromes.

To understand the relationship between DNA repair, apoptosis, transcription, and cancer-proneness, we have studied the apoptotic response and the recovery of RNA synthesis following ultraviolet C and ultraviolet B irradiation in nucleotide excision repair deficient diploid fibroblasts from the cancer-prone xeroderma pigmentosum (XP) syndrome patients and the non-cancer-prone trichothiodystrophy (TTD) patients. Analysis of four XPD and four TTD/XPD fibroblast strains presenting different mutations on the XPD gene has shown that XPD cells are more sensitive to ultraviolet-induced apoptosis than TTD/XPD cells, and this response seems to be modulated by the type and the location of the mutation on the XPD gene. Moreover, the other xeroderma pigmentosum fibroblast strains analyzed (groups A and C) are more sensitive to undergo apoptosis after ultraviolet irradiation than normal human fibroblasts, showing that the cancer-proneness of xeroderma pigmentosum patients is not due to a deficiency in the ultraviolet-induced apoptotic response. We have also found that cells from transcription-coupled repair deficient XPA, XPD, TTD/XPD, and Cockayne's syndrome patients undergo apoptosis at lower ultraviolet doses than transcription-coupled repair proficient cells (normal human fibroblasts and XPC), indicating that blockage of RNA polymerase II at unrepaired lesions on the transcribed strand is the trigger. Moreover, XPD and XPA cells are more sensitive to ultraviolet-induced apoptosis than trichothiodystrophy and Cockayne's syndrome fibroblasts, suggesting that both cyclobutane pyrimidine dimers and pyrimidine 6-4 pyrimidone on the transcribed strand trigger apoptosis. Finally, we show that apoptosis is directly proportional to the level of inhibition of transcription, which depends on the density of ultraviolet-induced lesions occurring on transcribed sequences.

Two individuals with features of both xeroderma pigmentosum and trichothiodystrophy highlight the complexity of the clinical outcomes of mutations in the XPD gene.

The xeroderma pigmentosum group D (XPD) protein is a subunit of transcription factor TFIIH with DNA helicase activity. TFIIH has two functions, in basal transcription and nucleotide excision repair. Mutations in XPD that affect DNA repair but not transcription result in the skin cancer-prone disorder, xeroderma pigmentosum (XP). If transcription is also affected, the result is the multi-system disorder trichothiodystrophy (TTD), in which there is no skin cancer predisposition, or in rare cases, XP combined with Cockayne syndrome. Up till now there have been no reports of combined clinical features of XP and TTD. We have now identified two patients with some features of both these disorders. One of these, XP189MA, a 3-year-old girl with sun sensitivity, mental and physical developmental delay, has XPD mutations not previously reported, and barely detectable levels of nucleotide excision repair. The other, XP38BR, a 28-year-old woman with sun sensitivity, pigmentation changes and skin cancers typical of XP, has a mutation that has been identified previously, but only in TTD patients with no features of XP. The level of repair of UV damage in XP38BR is substantially higher than that in other patients with the same mutation. With both patients, polarized light microscopy revealed a 'tiger-tail' appearance of the hair, and amino acid analysis of the hair shafts show levels of sulfur-containing proteins intermediate between those of normal and TTD individuals. Our findings highlight the complexities of genotype-phenotype relationships in the XPD gene.