Light scatter and DNA accessibility to propidium iodide of ataxia telangiectasia and Fanconi anemia cells

Cells from individuals with genetic diseases ataxia telangiectasia (AT) and Fanconi anemia (FA) exhibit hypersensitivity to ionizing radiation (AT) or DNA cross-linking agents (FA) which may be caused by multiple factors incl uding defects in chromatin structure and DNA repair. In this study, a combi nation of cytometric techniques was employed to study the chromatin conform ation of AT and FA cells. Nuclei of peripheral blood mononuclear cells (PBM Cs) and of skin fibroblasts established from AT and FA patients were analyz ed by light scattering and fluorimetric titration with the DNA-intercalatin g dye propidium iodide. The light scatter measurements revealed the presenc e of small-sized nuclei with reduced granularity in PBMCs and fibroblasts f rom both AT and FA patients. The fluorometric titration data could be inter preted by assuming two classes of propidium iodide binding sites with diffe rent affinities. The number of high-affinity sites in AT and FA fibroblasts was significantly larger (by 20%) than in control cells. Our findings show the applicability of cytometric techniques for the rapid assessment of chr omatin conformation and also suggest the possibility to identify AT and FA carriers. (C) 2001 Academic Press.