Cytogenetic challenge assays for assessment of DNA repair capacities.

Different challenge assays have been used to investigate cellular responses following exposure to DNA damaging agents. Our protocol uses X- or gamma-rays or ultraviolet light to challenge cells to repair the induced damage, and chromosome aberrations as a biomarker to indicate DNA repair proficiency. The assay was used successfully to demonstrate base- and nucleotide-excision repair deficiency in certain polymorphic DNA repair genes, namely XRCC1 751Gln and XPD 312Asn, respectively. In addition, populations with elevated exposure to certain environmental mutagenic agents-cigarette smokers, pesticide sprayers, and residents who lived near uranium mining and milling sites-showed DNA repair deficiency. Because expression of chromosome aberrations is associated with a significantly increased incidence of both cancer morbidity and mortality, the challenge assay may be useful in predicting cancer risk. The protocol for the assay is straightforward and the data have practical applications.