Correlation of the clinical manifestations and gene mutations of Japanese xeroderma pigmentosum group A patients

XPA deficiency affects the ubiquitin-proteasome system function

Xeroderma pigmentosum complementation group A (XPA), is defective in xeroderma pigmentosum patients, causing pre-disposition to skin cancer and neurological abnormalities, which is not well understood. Here, we analyzed the XPA-deficient cells transcriptional profile under oxidative stress. The imbalance in of ubiquitin-proteasome system (UPS) gene expression was observed in XPA-deficient cells and the involvement of nuclear factor erythroid 2-related factor-2 (NFE2L2) was indicated. Co-immunoprecipitation assays showed the interaction between XPA, apurinic-apyrimidinic endonuclease 1 (APE1) and NFE2L2 proteins. Decreased NFE2L2 protein expression and proteasome activity was also observed in XPA-deficient cells. The data suggest the involvement of the growth arrest and DNA-damage-inducible beta (GADD45β) in NFE2L2 functions. Similar results were obtained in xpa-1 (RNAi) Caenorhabditis elegans suggesting the conservation of XPA and NFE2L2 interactions. In conclusion, stress response activation occurs in XPA-deficient cells under oxidative stress; however, these cells fail to activate the UPS cytoprotective response, which may contribute to XPA patient's phenotypes.

Predominant neurological phenotype in a Hungarian family with two novel mutations in the XPA gene-case series

OBJECTIVE

The prevalence of xeroderma pigmentosum (XP) is quite low in Europe, which may result in a delay in determining the appropriate diagnosis. Furthermore, some subtypes of XP, including XPA, may manifest themselves with quite severe neurological symptoms in addition to the characteristic dermatological lesions. Accordingly, the aim of the current study is to highlight the predominant neurological aspects of XPA, as well as mild-to-moderate dermatological signs in a Hungarian family with 5 affected siblings.

CASE REPORTS

The symptoms of the Caucasian male proband started to develop at 13-14 years of age with predominantly cerebellar, hippocampal, and brainstem alterations. His elder sister and three younger brothers all presented similar, but less expressed neurological signs. The diagnostic work-up, including clinical exome sequencing, revealed 2 novel compound heterozygous mutations (p.Gln146_Tyr148delinsHis, p.Arg258TyrfsTer5) in the XPA gene. Surprisingly, only mild-to-moderate dermatological alterations were observed, and less severe characteristic ophthalmological and auditory signs were detected.

CONCLUSIONS

In summary, we present the first family with genetically confirmed XPA in the Central-Eastern region of Europe, clearly supporting the notion that disturbed function of the C-terminal region of the XPA protein contributes to the development of age-dependent neurologically predominant signs. This case series may help clinicians recognize this rare disorder.

A summary of mutations in the UV-sensitive disorders: xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy

The human diseases xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy are caused by mutations in a set of interacting gene products, which carry out the process of nucleotide excision repair. The majority of the genes have now been cloned and many mutations in the genes identified. The relationships between the distribution of mutations in the genes and the clinical presentations can be used for diagnosis and for understanding the functions and the modes of interaction among the gene products. The summary presented here represents currently known mutations that can be used as the basis for future studies of the structure, function, and biochemical properties of the proteins involved in this set of complex disorders, and may allow determination of the critical sites for mutations leading to different clinical manifestations. The summary indicates where more data are needed for some complementation groups that have few reported mutations, and for the groups for which the gene(s) are not yet cloned. These include the Xeroderma pigmentosum (XP) variant, the trichothiodystrophy group A (TTDA), and ultraviolet sensitive syndrome (UVs) groups. We also recommend that the XP-group E should be defined explicitly through molecular terms, because assignment by complementation in culture has been difficult. XP-E by this definition contains only those cell lines and patients that have mutations in the small subunit, DDB2, of a damage-specific DNA binding protein.

Higher susceptibility to apoptosis following ultraviolet B irradiation of xeroderma pigmentosum fibroblasts is accompanied by upregulation of p53 and downregulation of bcl-2

Apoptosis plays an important part as a defence mechanism in eliminating damaged cells. Among the complex factors which regulate apoptosis, the p53 tumour suppressor protein which is induced by DNA damage has been suggested to play a crucial part. Cells from xeroderma pigmentosum (XP) patients, which are defective in nucleotide excision repair, express higher levels of p53 and are highly susceptible to cell death after ultraviolet (UV) irradiation. To examine the relationships between DNA damage, p53 and apoptosis, normal and XP group A fibroblasts were exposed to UVB, and expressions of molecules involved in apoptosis were examined. Apoptosis of XP and normal cells was clearly detected at 48 h after irradiation with UVB at doses of 5 and 40 mJ/cm2, respectively. Cells were positive by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) staining under these exposure conditions. At 6 h after irradiation, p53 protein expression was induced in normal and XP cells at minimal doses of 10 and 2.5 mJ/cm2, respectively. Bcl-2 protein, an inhibitor of apoptosis, was downregulated prior to cell death following UVB exposure at doses that induced apoptosis in both cell types. These results suggest that DNA damage due to UVB induces apoptosis by upregulating proapoptotic molecules such as p53, and by downregulating anti-apoptotic molecules such as Bcl-2.

Molecular studies of Japanese patients with group A xeroderma pigmentosum using polymerase chain reaction and restriction fragment length polymorphism and nonradioactive single strand conformation polymorphism analyses

Xeroderma pigmentosum is an autosomal recessive disease characterized by extreme sensitivity of the skin to ultraviolet light, which results in a high incidence of early skin cancer. We report here the molecular analysis of the xeroderma pigmentosum group A complementing genes of five Japanese patients with group A xeroderma pigmentosum and their families, by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis, and by PCR and non-radioactive single strand conformation polymorphism (SSCP) analysis using the Pharmacia PhastSystem. Four of the five patients were found to be homozygous for a known splicing mutation of intron 3. One patient was found to be heterozygous for the splicing mutation of intron 3 and a known nonsense mutation of exon 6. This nonradioactive PCR-SSCP technique was as useful for the molecular diagnosis of patients with group A xeroderma pigmentosum as was PCR-RFLP analysis.

The DNA damage-recognition problem in human and other eukaryotic cells: the XPA damage binding protein

The capacity of human and other eukaryotic cells to recognize a disparate variety of damaged sites in DNA, and selectively excise and repair them, resides in a deceptively small simple protein, a 38-42 kDa zinc-finger binding protein, XPA (xeroderma pigmentosum group A), that has no inherent catalytic properties. One key to its damage-recognition ability resides in a DNA-binding domain which combines a zinc finger and a single-strand binding region which may infiltrate small single-stranded regions caused by helix-destabilizing lesions. Another is the augmentation of its binding capacity by interactions with other single-stranded binding proteins and helicases which co-operate in the binding and are unloaded at the binding site to facilitate further unwinding of the DNA and subsequent catalysis. The properties of these reactions suggest there must be considerable conformational changes in XPA and associated proteins to provide a flexible fit to a wide variety of damaged structures in the DNA.

PCR-RFLP analysis as an aid to genetic counseling of families of Japanese patients with group A xeroderma pigmentosum

Because Japanese patients with complementation group A xeroderma pigmentosum (XP-A) show early skin cancer and severe neurologic dysfunction, their family members are greatly concerned about the risk of inherited disease. In contrast to western XP-A patients, almost all Japanese XP-A patients have two of the three mutations (nonsense mutation in exon 3, splicing mutation in intron 3, and non-sense mutation in exon 6), which are easily detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. This work was aimed to see whether PCR-RFLP analysis is useful for genetic counseling of XP patients' siblings who are potential carriers of an XP-A gene mutation. In two of the three case studies presented, the probands were homozygous for the splicing mutation in intron 3 of the gene. In their siblings receiving genetic counseling, no mutation was found in the mutation site in one case, and one splicing mutation was found in the second case. In the third case, the proband was a compound heterozygote for the splicing mutation and for an unidentified mutation; in her sibling, no mutation was found in either of these mutation sites. No mutation was found in the siblings' spouses. On the basis of these findings, we reassured the prospective parents that there was little probability of having XP children, but in the second and third cases, we told them that their apparently unaffected children might be carriers. Each couple subsequently had one unaffected child. Thus, PCR-RFLP analysis is useful for genetic counseling of family members of XP-A patients.