MOLECULAR ANALYSIS OF THE XP-D GENE IN ITALIAN FAMILIES WITH PATIENTSAFFECTED BY TRICHOTHIODYSTROPHY AND XERODERMA-PIGMENTOSUM GROUP-D

In several patients with the rare hereditary disorder trichothiodystro phy (TTD), a DNA repair defect has been shown to be in the same gene a s in xeroderma pigmentosum complementation group D (XP-D). The ERCC-2 gene (excision repair cross-complementing rodent repair deficiency of group 2) has recently been identified as a strong candidate gene for X P-D, since it restores normal UV sensitivity to XP-D cells after trans fection. Using Southern blotting, we have analysed the ERCC-2 gene in DNA samples from 28 members of nine Italian families with individuals affected by XP-D (three patients) or by TTD with photosensitivity due to the XP-D defect (eight patients). No major modifications of the ERC C-2 gene were detected with two cDNA probes in either XP-D or TTD pati ents indicating that the association between TTD and XP-D is not likel y to result from a large deletion or rearrangement involving this gene . We found two RFLPs after digestion of the DNA samples with TaqI or M spI, but neither of them could be related to the molecular alteration determining the pathological phenotype. We also analysed a human homol ogue detected with the hamster sequence isolated by Arrand et al. (198 9), which specifically, but partially, complements the DNA repair defi ciency in XP-D cells. Our analysis demonstrated that this gene is not the primary gene defective in XP-D. In fact two RFLPs detected with a genomic probe do not co-segregate with the disease in an XP-D family.