Here we report on two causative mutations of the XPD gene in XP61OS, a Japanese XP group D patient who has only mild skin symptoms of XP without CS, TTD, or other neurological complications.
These results establish the essential function of the XPD protein in mammals and in cellular viability and are consistent with the notion that only subtle XPD mutations are found in XP, XP/Cockayne syndrome, and trichothiodystrophy patients.
To characterize nucleotide excision repair properties of cells from trichothiodystrophy (TTD) patients genetically-related to the xeroderma pigmentosum (XP) group D, TTD skin fibroblasts from two unrelated patients (TTD1VI and TTD2VI) belonging to the TTD/XPD group were transformed with a plasmid containing SV40 large T antigen-coding sequences and some DNA repair properties, such as unscheduled DNA synthesis (UDS), UV-survival, in vitro repair synthesis of cell extracts and reactivation of UV-irradiated reporter plasmid were studied.
No major modifications of the ERCC-2 gene were detected with two cDNA probes in either XP-D or TTD patients indicating that the association between TTD and XP-D is not likely to result from a large deletion or rearrangement involving this gene.
Two individuals with features of both xeroderma pigmentosum and trichothiodystrophy highlight the complexity of the clinical outcomes of mutations in the XPD gene.
These cellular phenotypes are amenable to experimental strategies employing complementation, an approach previously used to demonstrate the correction of XP-D phenotypes following the introduction of the XPD (ERCC2) gene.
Functional and molecular genetic analyses of nine newly identified XPD-deficient patients reveal a novel mutation resulting in TTD as well as in XP/CS complex phenotypes.
The Xeroderma pigmentosum group D (XPD, also referred to as excision repair cross complementing gene 2, ERCC2) is one of key genes involved in nucleotide excision repair and two potentially functional polymorphisms of XPD (Asp312Asn and Lys751Gln) have been widely investigated in various cancers including prostate cancer.
Genome sequence analysis indicated that the patient harbored a compound heterozygous mutation of c.1621A>C and c.591_594del, resulting in p.S541R and p.Y197* in ERCC2: then, patient was diagnosed with XP-D. Y197* has not been described before.
Nucleotide sequence analysis of the ERCC2 cDNA from five XP group D cell strains [XP6BE(SV40), XP17PV, XP102LO, A31-27 (a HeLa/XP102LO hybrid), and XP-CS-2] revealed mutations predominantly affecting previously identified functional domains.
Thus, we are developing a model for gene therapy in XP, particularly for patients belonging to group D. We report here the construction of a retroviral vector (LXPDSN) containing the XPD (ERCC2) cDNA, which fully complements the DNA repair deficiency of primary skin fibroblasts.
In most cases, xeroderma pigmentosum group D (XP-D) and trichothiodystrophy (TTD) patients carry mutations in the carboxy-terminal domain of the evolutionarily conserved helicase XPD, which is one of the subunits of the transcription/repair factor TFIIH (refs 1,2).
To study the relationships between mutagenesis and carcinogenesis, we compared the mutations and their frequency induced by ultraviolet irradiation at 254 nm (UV-C) in XP-D (GM-08207B/XP6BE), TTD/XP-D (TTD1VI-LAS-KMT11) and wild-type (MRC-5V1) human cells.
When the genotype frequencies of XPD (Llys751Gln) and XRCC1 (Arg399Gln) genes were examined in the patient and control groups, no significant difference was detected, while a significant association was found in XRCC4 (VNTR in intron 3 and G-1394T) polymorphisms.
We investigated the genetic basis for these findings by analysing the Asp312Asn and Lys751Gln polymorphisms of the XPD (ERCC2) DNA repair gene in the same subjects.