Cockayne syndrome (CS) is a genetic disorder characterized by developmental abnormalities and photodermatosis resulting from the lack of transcription-coupled nucleotide excision repair, which is responsible for the removal of photodamage from actively transcribed genes. To date, all identified causative mutations for CS have been in the two known CS-associated genes, ERCC8 (CSA) and ERCC6 (CSB). For the rare combined xeroderma pigmentosum (XP) and CS phenotype, all identified mutations are in three of the XP-associated genes, ERCC3 (XPB), ERCC2 (XPD), and ERCC5 (XPG). In a previous report, we identified several CS cases who did not have mutations in any of these genes. In this paper, we describe three CS individuals deficient in ERCC1 or ERCC4 (XPF). Remarkably, one of these individuals with XP complementation group F (XP-F) had clinical features of three different DNA-repair disorders--CS, XP, and Fanconi anemia (FA). Our results, together with those from Bogliolo et al., who describe XPF alterations resulting in FA alone, indicate a multifunctional role for XPF.

Xeroderma pigmentosum (XP) is a rare DNA repair disorder characterized by increased susceptibility to UV radiation (UVR)-induced skin pigmentation, skin cancers, ocular surface disease, and, in some patients, sunburn and neurological degeneration. Genetically, it is assigned to eight complementation groups (XP-A to -G and variant). For the last 5 y, the UK national multidisciplinary XP service has provided follow-up for 89 XP patients, representing most of the XP patients in the United Kingdom. Causative mutations, DNA repair levels, and more than 60 clinical variables relating to dermatology, ophthalmology, and neurology have been measured, using scoring systems to categorize disease severity. This deep phenotyping has revealed unanticipated heterogeneity of clinical features, between and within complementation groups. Skin cancer is most common in XP-C, XP-E, and XP-V patients, previously considered to be the milder groups based on cellular analyses. These patients have normal sunburn reactions and are therefore diagnosed later and are less likely to adhere to UVR protection. XP-C patients are specifically hypersensitive to ocular damage, and XP-F and XP-G patients appear to be much less susceptible to skin cancer than other XP groups. Within XP groups, different mutations confer susceptibility or resistance to neurological damage. Our findings on this large cohort of XP patients under long-term follow-up reveal that XP is more heterogeneous than has previously been appreciated. Our data now enable provision of personalized prognostic information and management advice for each XP patient, as well as providing new insights into the functions of the XP proteins.UV radiation | nucleotide excision repair | skin cancer | ocular disease | neurodegeneration

No abstract

We initially performed exome-sequencing 11 of the two UV S S-A patients, Kps3 and XP24KO (details described in Methods, Supplementary Note, Table 2c). The patients were homozygous for c.367A>T mutation in UVSSA, which led to a premature termination, p.Lys123* (Fig. 1a, b). We identified the same homozygous mutation in Kps2 (sib. of Kps3), and a homozygous c.87delG, causing a frameshift p.Ile31Phefs*9, in an Israeli patient UV S S24TA (Fig. 1b, c, Supplementary Note, Supplementary Fig. 1). The identified mutations are summarized in Fig. 1d. We did not detect the 80kDa UVSSA protein in any of the UV S S-A patients (Fig. 1e). We additionally examined several mild xeroderma pigmentosum (XP) cases; in one such case, XP70TO 12 (Supplementary Table 1), we identified a homozygous p.Cys32Arg, in the UVSSA (Fig. 1c, d), implying that XP70TO is also in the UV S S-A group. The mutant protein was stably expressed in XP70TO cells (Fig. 1f, Supplementary Fig. 2a-d). 4Allele frequencies of the identified mutations in a control population were examined (Supplementary Note, Supplementary Fig. 3a). Haploinsufficiency for UVSSA is negligible as the parents of Kps2/Kps3 showed no symptoms 4 . In parallel with exome-sequencing, we performed whole-genome SNP-genotyping to identify runs-of-homozygosity (ROH) shared among the patients. We identified three overlapping-ROHs (> 1Mbps) on autosomes, one of which encompasses the UVSSA locus (Fig. 1g, Supplementary Table 3a, b, Supplementary Fig. 3b, c). No chromosome copy number variation was detected (Supplementary Fig. 3d).The above findings strongly suggest that the mutations in UVSSA in the UV S S-A patients are causal for the disease; we therefore, next examined the NER-activities in the UV S S-A cells (Fig. 2). Unscheduled-DNA-synthesis (UDS 13 , defective in XP) was nearly normal; however, RNA-synthesis-recovery (RRS 14 , defective in UV S S and in CS) was reduced in all cell-strains mutated in UVSSA ( Fig. 2a, b; UDS and RRS were measured using a recently-developed rapid non-radioactive system 15,16 ). Similarly, siRNA-based depletion of the UVSSA gene (Fig. 2c) caused a drastic reduction of RRS (Fig. 2d, Supplementary Fig. 4), whereas UDS was unaffected (Fig. 2e). Ectopic-expression of the wild-type UVSSA cDNA in UV S S-A cells restored normal RRS ( Fig. 2f; V5-tagged-UVSSA immunofluorescent-staining shown in Fig. 2g), while it did not affect RRS-level in normal, CS-A, or CS-B cells; neither ERCC8 nor ERCC6 cDNA expression in UV S S-A cells restored the RRS-level.We conclude that KIAA1530/UVSSA is the causal gene for UV S S-A.ERCC8 and ERCC6 genes are responsible for both CS and UV S S 7,8 . To evaluate whether UVSSA mutations may also result in CS-phenotypes, we sequenced 5 the UVSSA gene of 61 CS-patients whose genetic defects had not yet been determined (Supplementary Table 4). We found no obvious mutations except for four novel heterozygous changes. These changes as well as the SNPs, also found in control and UV S S-A individuals, do not affect the RRS-activity (Suppleme...

How subunits of the transcription/repair factor TFIIH cooperate to allow for the removal of DNA lesions or for the transcription of genes is crucial to understand the functioning of this complex. Here, we reveal that p8/TTD-A, the tenth subunit of TFIIH, has a critical role in DNA repair where it triggers DNA opening by stimulating XPB ATPase activity together with the damage recognition factor XPC-hHR23B. Fluorescent antibody labeling shows that such opening is needed for the recruitment of XPA to the site of the damage. By contrast, p8 is dispensable for RNA synthesis and doesn't interfere with the transcriptional function of CAK, although both interact with the XPD subunit. Interestingly, p8 overexpression in TTD-XPD cells counteracts the detrimental effect of XPD mutations by restoring the cellular TFIIH concentration. These findings resolve the primary functions of p8 and unveil how TFIIH components specifically direct the complex toward repair or transcription.

Trichothiodystrophy (TTD) is a rare hereditary multisystem disorder associated with defects in nucleotide excision repair (NER) as a consequence of mutations in XPD, XPB or TTDA, three genes that are all related to TFIIH, the multiprotein complex involved in NER and transcription. Here we show that all the mutations found in TTD cases, irrespective of whether they are homozygotes, hemizygotes or compound heterozygotes, cause a substantial and specific reduction (by up to 70%) in the cellular concentration of TFIIH. Intriguingly, the degree of reduction in the level of TFIIH does not correlate with the severity of the pathological phenotype, suggesting that the severity of the clinical features in TTD cannot be related solely to the effects of mutations on the stability of TFIIH. We have also measured TFIIH levels in cells in which different mutations in the XPD gene are associated with clinical symptoms not of TTD but of the highly cancer-prone disorder xeroderma pigmentosum (XP). We have found mild reductions (up to 40%) in TFIIH content in some but not all of these cell strains. We conclude that the severity of the clinical features in TTD patients and the clinical outcome of differentially mutated XPD proteins is likely to depend both on the effects that each mutation has on the stability of TFIIH and on the transcriptional activity of the residual TFIIH complexes.

No abstract

UV-sensitive syndrome (UV S S) is a recently-identified autosomal recessive disorder characterized by mild cutaneous symptoms and defective transcription-coupled repair (TC-NER), the subpathway of nucleotide excision repair (NER) that rapidly removes damage that can block progression of the transcription machinery in actively-transcribed regions of DNA. Cockayne syndrome (CS) is another genetic disorder with sun sensitivity and defective TC-NER, caused by mutations in the CSA or CSB genes. The clinical hallmarks of CS include neurological/developmental abnormalities and premature aging. UV S S is genetically heterogeneous, in that it appears in individuals with mutations in CSB or in a still-unidentified gene. We report the identification of a UV S S patient (UV S S1VI) with a novel mutation in the CSA gene (p.trp361cys) that confers hypersensitivity to UV light, but not to inducers of oxidative damage that are notably cytotoxic in cells from CS patients. The defect in UV S S1VI cells is corrected by expression of the WT CSA gene. Expression of the p.trp361cys-mutated CSA cDNA increases the resistance of cells from a CS-A patient to oxidative stress, but does not correct their UV hypersensitivity. These findings imply that some mutations in the CSA gene may interfere with the TC-NERdependent removal of UV-induced damage without affecting its role in the oxidative stress response. The differential sensitivity toward oxidative stress might explain the difference between the range and severity of symptoms in CS and the mild manifestations in UV s S patients that are limited to skin photosensitivity without precocious aging or neurodegeneration.