Sister-chromatid exchanges in lymphocytes from infants with Down's syndrome

Abstract

Sister-chromatid exchange (SCE) frequencies were studied in blood lymphocytes from 12 patients (3 females and 9 males) with Down's syndrome (DS). The mean frequency of SCE per metaphase for the patients (both sexes) was 9.2 ± 0.8 which was significantly higher ( P < 0.01) than the mean SCE value (5.1 ± 0.2) scored for 16 healthy infants (8 females and 8 males). A significant increase in the mean frequency of SCE in 12 parents of infants with DS (8.7 ± 0.9 SCE/cell) was noticeable when compared with 20 parents of normal infants (6.3 ± 0.1 SCE/cell). Increases in cellular division with reduction in their replication were also observed in patients with DS. Treatment with mitomycin C (0.05 μg/ml), hycanthone (0.1 μg/ml)_and γ-radiation (0.1 Gy) revealed a significant ( P < 0.01) increase in frequencies of SCE in DS lymphocytes and in those of their parents as compared to controls. These data may reveal a familial hypersensitivity reaction to these agents. The results indicate a genomic instability and deranged DNA-repair mechanisms which are accentuated by exposure to mutagenic agents, the underlying causal factor for which might be genetic.