Evaluation of sister chromatid exchanges in Bloom's syndrome

The pattern of sister chromatid labelling and incidence of sister chromatid exchanges (SCE), including the effects of caffeine on SCE, were examined with several techniques in normal human cells and in those of a patient with Bloom's syndrome following 1--3 mitotic cycles. The results indicate, in confirmation of those obtained by others with different cells, that SCE in the cells studied is not due to a post-replication repair process, but more likely involves exchanges between the double strands of chromatids.