Genetic rearrangements in leukaemia and lymphoma / J.M. Goldman, D.G. Harnden.

Date:
1986
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genetic rearrangements in leukaemia and lymphoma / J.M. Goldman, D.G. Harnden. Source: Wellcome Collection.

    103/200 (page 87)
    THE PHILADELPHIA CHROMOSOME TRANSLOCATION 87 simple translocations were located ui terminal bands. The reverse distribution was observed in the complex translocations, in which only three of the 33 break sites were located in terminal bands. As can be seen from Figure 4.2, only six of the 67 breaks in the simple translocations failed to be located in a terminal band. In 121 patients with complex translocations, 16 breakpoints excluding those on no. 9, involved terminal bands - however, 11 of these occurred in patients who had four or more chromosomes involved in very complex rearrangements. Thus, these data confirm the original observation of Mitelman and Levan. We now understand why this strange distribution of breakpoints was observed. A detailed explanation will be presented later in this chapter; for the moment, it is sufficient to say that we now know that there are no simple translocations that do not involve no. 9. Thus the break of no. 9 at 9q34 was overlooked because most of the preparations had short, contracted chromosomes and a translocation involving the movement of a terminal band (12pl3 for example) to 9q34 with the translocation of no. 9 to the Ph' chromosome could not be detected. A partial karyotype from one patient can illustrate this point (Fig. 4.3). The upper part of Figure 4.3 shows a partial karyotype of the typical t(9;22) and the lower part contains pairs 9,14, and 22 from a patient whom we initially considered to have a t(14;22)(q32;ql 1). Reassessment of the photographs of banded cells after the publication of the findings of Hagemeijer et al. revealed that band 9q34 of the two no. 9s stained differently, with one somewhat darker - presumably representing a translocation from 14q32 that we had overlooked. This change is so subtle that one would not have had much confidence several years ago in classifying this as a three-way translocation. Fig. 4.3 Partial karyotype from a patient initially considered to have t(14;22)(q32;qll), as depicted in the upper part. Reassessment of banded cells showed that the two no. 9s stained differently, with the right hand one somewhat darker - presumably representing a translocation from 14q32 (see text).