BUdR-giemsa labeling and satellite association in human leukocytes.

Satellite associations were analysed in differentially stained human leukocyte chromosomes, obtained from four patients with Down's syndrome and four normal probands. A particular type of close association between two acrocentrics, showing a non-random arrangement of sister chromatids in a concordant dark-to-dark and light-to-light alignment, was found to be more common in patients with Down's syndrome compared with the normal controls. Apart from this particular type of association, sister chromatids are randomly arranged in satellite associations between two acrocentrics in both groups of probands. Considerable differences in the mean frequencies of satellite associations between first and second metaphases of the same individual were found in some probands of both groups of individuals. Since a high degree of inter-individual variability in the proliferative response of human leukocytes in culture is well established, the use of BUdR-Giemsa labeling for comparative analysis of satellite association frequencies is suggested.