DNA measurements of chromosomes 9 and 22 of six patients with t(9;22) and chronic myeloid leukemia.

More than 90% of the cases of chronic myeloid leukemia are characterized by the presence of a so-called Philadelphia chromosome. This Philadelphia chromosome has been shown to be a product of a translocation between chromosomes 9 an 22 in the majority of cases. It is present in the bone marrow and unstimulated blood cultures. Visual examination of this chromosome gave the impression that small differences in length might exist between patients. Therefore, DNA measurements were undertaken on six patients with t(9;22) and chronic myeloid leukemia. Metaphases obtained from unstimulated peripheral blood cultures were Q-banded for photography and identification of chromosomes 9 and 22. Feulgen staining was performed, and the preidentified cells were photographed again. Cytophotometry of the photographic negatives was done using a Hidacsys-Arrayscan computer program. Relative DNA contents were calculated for the normal chromosomes 9 and 22 and both chromosomes involved in the translocation. Between 7 and 17 cells were measured per patient. The results indicated that no differences existed between the patients regarding the amount of material translocated from chromosome 22 to 9. In all patients from the sum of the DNA contents of the normal chromosomes 9 and 22 was less than that of the translocation chromosomes. Possible explanations for this observation are discussed.