Chromosome abnormalities involving heterochromatic regions in monocytic leukemia.

We report two cases of monocytic leukemia associated with cytogenetic changes involving the juxtacentromeric heterochromatin of different chromosomes. In a patient with chronic myelomonocytic leukemia (CMMoL) we describe a translocation t(1;9)(q12;q13) in which the duplicated derivative chromosome 9q + showed a huge centromeric C-band, derived by fusion of the heterochromatic regions of chromosomes 1 and 9. The constitutional karyotype showed two heterochromatin polymorphisms, 1qh + and inv(9qh). In the second case, an acute monoblastic leukemia was associated with an abnormally elongated juxtacentromeric heterochromatic region of chromosome 4 that was not constitutionally present.