Localized induction of micronuclei in the oral mucosa of xeroderma pigmentosum patients

Xeroderma pigmentosum (XP) patients are predisposed not only to skin cancers but also to tumors on the tip of the tongue. Although this enhanced risk has been attributed to a defect in the repair of DNA damage induced by ultraviolet rays from sunlight there is a lack of data showing that DNA damage is occurring in vivo at these sites. In order to determine whether a relationship exists between exposure to ultraviolet light and the level of chromosomal breakage occurring in epithelial tissue in XP patients, the exfoliated cell micronucleus test was applied to different sites in the oral cavities of four XP patients: the right and left buccal mucosa, the dorsal tip of the tongue and the palate. Six Egyptian controls were sampled concurrently. Micronucleus (MN) frequencies were higher in XP patients than in controls for all sites except the palate, where technical difficulties were encountered. In addition, an unequal distribution of the frequency of micronucleated cells was found in the different sample sites of the oral cavity in the XP patients, with the greatest elevation in frequencies among cells collected from the dorsal tip of the tongue. In contrast, the frequency of micronucleated cells did not vary significantly in samples from different sites obtained from the controls. These data suggest that the complex interplay of host and environmental factors can affect MN frequencies when this endpoint is used to quantify in vivo genotoxic damage in a tissue.