In situ hybridization to interphase nuclei in acute leukemia.

Numerical chromosome abnormalities were studied in 17 acute lymphoblastic leukemias and one hyperdiploid acute myeloblastic leukemia by fluorescence in situ hybridization (FISH) using YAC clones specific to chromosomes 21 and 6. The results agreed well with cytogenetic findings. Hyperdiploid leukemias with more than 50 chromosomes usually had 4 copies of chromosome 21 and three of chromosome 6, while diploid and pseudodiploid cases were confirmed to have two copies of the two chromosomes. Interesting discrepancies were also observed. In one patient, trisomy 6 was detected by FISH but not by cytogenetics because of the probable inclusion of a chromosome 6 segment within a marker chromosome. The percentages of nuclei with 3 or 4 spots (chromosome 21) and three spots (chromosome 6) in hyperdiploid cells were significantly different in some patients, whereas they might be identical from cytogenetic data.