A twin study of sister chromatid exchanges in human lymphocytes following carcinogen exposure and DNA repair incubation.

Sister chromatid exchanges (SCEs) were analyzed in peripheral lymphocytes obtained from nine healthy monozygotic (MZ) and nine healthy dizygotic (DZ) pairs of male twins. In addition, increases in SCE rates following in vitro treatment of whole blood with 100 microM N-acetoxy-2-acethylaminofluorene (NA-AAF), and after an 18-h DNA repair incubation period, were analyzed in the same twins. There was no significant intrapair difference in the variance of SCE frequencies among MZ and DZ twins at the baseline level, after NA-AAF treatment, or after a DNA repair incubation period. It was concluded that genetic factors probably do not contribute significantly to the individual variation that has been observed in baseline or NA-AAF-induced SCE rates. Thus, any observed alterations in SCE frequencies are probably caused by environmental influences.