Determination of the breakpoints of 1;7 translocations in myelodysplastic syndrome by in situ hybridization using chromosome-specific alpha satellite DNA from human chromosomes 1 and 7.

A whole-arm translocation involving the short arm of chromosome 7 and the long arm of chromosome 1 occurs nonrandomly in myelodysplastic syndrome and acute nonlymphocytic leukemia. In situ hybridization, using alpha satellite DNA specific for the centromeric regions of chromosomes 1 (probe pSD1-1) and 7 (probe p21-4), was performed to determine the exact breakpoints of the translocation. Both probes hybridized to the centromeric region of the translocation chromosome in metaphases from two patients with myelodysplastic syndrome. Both probes hybridized with approximately equal strength to either chromosome 1 or 7 and to the 1;7 translocation chromosome, suggesting that the t(1;7) had retained the chromosome-specific alpha satellite DNA from both chromosomes. These studies permit us to propose a new description, t(1;7)(cen;cen), for this translocation.