Q Chromosomes

B-cells must rearrange their immunoglobulin heavy chain genes at chromosome 14 at band q32 to create their idiotype specificity. This predisposition of normal B-cells may be the cause of the common finding in all B-cell malignancies that chromosome translocations involving 14q32 are common. Since 14q32 is at the telomeric end of the long arm, most balanced trans-

Fig. 5. Chromosome 13. Left, schematic view. Middle, deletions: each line indicates the part of chromosome 13 that has been deleted in one patient. Right, structural abnormalities: each dot indicates a clonal breakpoint in one patient. Note that there are two rows of dots for 13q14. Data from the International Working Party on Chromosomes in CLL (6).

Fig. 6. Impact of the complexity of the karyotype on overall survival for CLL patients. Normal karyotype (n = 293), 1, one abnormality (n = 176), 2, two clonal abnormalities (n = 64), 3, complex karyotypes with three or more abnormalities (n = 71). Data from the International Working Party on Chromosomes in CLL (6).

Fig. 6. Impact of the complexity of the karyotype on overall survival for CLL patients. Normal karyotype (n = 293), 1, one abnormality (n = 176), 2, two clonal abnormalities (n = 64), 3, complex karyotypes with three or more abnormalities (n = 71). Data from the International Working Party on Chromosomes in CLL (6).

locations give rise to an elongation of the chromosome, called 14q+ chromosomes. However, the translocation partner may be very different in various diseases: the BCL-2 gene at 18q21 in follicular lymphoma, the BCL-1/cyclin D1 gene on 11q13 in mantle cell lymphoma, and the MYC gene on 8q24 in Burkitt's lymphoma, as well as many other less common translocation partners are seen. In CLL, these translocations are rarely found as the only abnormality (Fig. 1) and might be regarded as an additional finding with no specific role in the pathogenesis. However, the presence of additional abnormalities has an adverse prognostic impact in CLL (Fig. 6).

In follicular lymphoma, BCL-2 is almost always translocated to the immunoglobulin heavy chain gene on 14q32. However, when BCL-2 translocations occur in CLL, it more commonly translocates to the light chain genes on 2p13 and 22q11 instead (Fig. 2) (21). The biological significance of this finding is unclear.

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Fig. 7. Impact of specific karyotypic abnormality on overall survival of CLL patients; only single aberrations. Data from the International Working Party on Chromosomes in CLL (6).

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