Chromosome 22 breakpoints in variant Philadelphia translocations and Philadelphia-negative chronic myeloid leukemia

The standard t(9;22)(q34;q11) found in Philadelphia (Ph) chromosome positive chronic myeloid leukemia (CML) involves a highly restricted (5.8 kb) chromosome 22 breakpoint cluster region (bcr), which results in the formation of a chimeric gene comprising exons from the 5' end of bcr and protooncogene c-abl coding sequences from chromosome 9. In a survey of 21 patients with hematologic and clinical features of CML we detected rearrangement of the chromosome 22 bcr by gene probe analysis in all cases, including 16 with a standard t(9;22), two with variant Ph translocations [t(10;22)(q26;q11);t(11;22)(p15;q11)], one with a complex Ph translocation [t(9;11;22)(q34;q13;q11)], one with a complex translocation and a masked Ph[t(9;14;22) (q34;q24;q11)], and one Ph-negative case with a t(1;9)(p32;q34). These observations further substantiate the suggestion that, despite karyotypic heterogeneity, a common underlying molecular lesion, the bcr-abl gene chimera, is involved in the disease pathogenesis of CML.     

Four cases with complex Philadelphia translocations, including one with appearance de novo of a "masked" Ph

Four cases of chronic myelogenous leukemia (CML) with complex Philadelphia (Ph) translocations are described. The first case was that of a 50-year-old woman in the chronic phase of CML. Her leukemic cells showed a complex Ph translocation involving chromosomes #9, #11, and #22 [i.e., t(9;9;22;11)(11qter----11q11::9q11----9q34:: 9p11----9pter;22qter----22q11::9q34?;11 pter----11q11::22q11----22qter)]. In addition to the complex Ph translocation, the leukemic cells contained del(10)(p13). The second case was that of a 21-year-old man whose leukemic cells contained a translocation involving chromosomes #5, #9, and #22 [i.e., t(5;22;9)(q31;q11;q34)], resulting in a "masked" Ph chromosome. The third case was that of a 37-year-old man whose leukemic cells had a complex Ph translocation involving chromosomes #8, #9, and #22 [i.e., t(8;9;22)(q13;q34;q11)]. The fourth patient was a 41-year-old woman diagnosed as having CML in myeloid blastic phase, at which time the first specimen was examined by us. This blood sample showed a karyotype of 45,XX, -9, -17, -22, +mar1, +mar2,9q+. No Ph chromosome was present. A standard Ph translocation was detected in the cells obtained from the spleen, when the patient underwent splenectomy for treatment of the blastic crisis. Subsequent specimens obtained from the blood and bone marrow showed that the leukemic cells contained three clones: 45,XX, -9, -17, -22, +mar1, +mar2,9q+/46,XX, -17, +mar1,t(9;22)(q34;q11)/46,XX,t(9;22)(q34;q11). Cells with the "masked" Ph chromosome were thought to have been derived from the clone with the standard Ph translocation. We postulate that some variant Ph translocations, including those with a "masked" Ph chromosome, may be generated by a stepwise process following the genesis of a standard Ph translocation.     

The Philadelphia (Ph) chromosome in leukemia. II. Variant Ph translocations in acute lymphoblastic leukemia

Nearly 20 patients with a masked Philadelphia (Ph) translocation have been described in chronic myelocytic leukemia. We report two instances of acute lymphoblastic leukemia (ALL) with variant Ph translocations. One case, involving a 26-year-old male, was associated with a variant t(14;22)(q32;q11) translocation. The second case involved a 36-year-old male with a more complex translocation, t(9;15;22)(q12;q26;q11). In each case, cells with a masked Ph translocation were observed. These appear to be the first ALL cases reported with a masked Ph chromosome. The findings are discussed in relation to recent knowledge regarding the genesis of the Ph chromosome.     

Chromosomal in situ hybridization and Southern blot analyses using c-abl, c-sis, or bcr probe in chronic myelogenous leukemia cells with variant Philadelphia translocations

The Philadelphia (Ph) chromosome is a cytogenetic hallmark of chronic myelogenous leukemia (CML). Whereas the majority of Ph-positive CML patients show the standard Ph translocation involving chromosomes 9 and 22, t(9;22)(q34;q11), the minority of cases exhibit a variant type of Ph translocation involving these two and other chromosomes (complex type) or those involving #22 and chromosomes other than #9 (simple type). To get an insight into the nature of variant Ph translocations and the process of their formation, we examined the localization of the c-abl and c-sis oncogenes and the breakpoint cluster region (bcr) gene by chromosomal in situ hybridization in ten variant Ph translocations of CML including five simple and five complex ones as initially interpreted. In situ hybridization showed that c-abl localized to band 9q34 and c-sis localized to band 22q12-q13 were translocated on the Ph and on one of the rearranged chromosomes other than #9, respectively, in all the variant translocations examined. On the other hand, bcr localized to band 22q11 was translocated on various chromosomes but mostly on chromosome 9. Parallel Southern blot analyses on DNA from leukemic cells of five patients including two with simple translocations and three with complex ones revealed rearrangements of bcr with breakpoints occurring mostly in a 5' portion of 5.8-kb BamHI/BglII sequences, which are quite similar to those detected so far in CML cases with the standard Ph translocation. The present findings strongly suggest that variant Ph translocations of CML are all complex, and some of them are formed stepwisely from the standard translocation.     

A cytogenetic and molecular analysis of five variant Philadelphia translocations in chronic myeloid leukemia

Three patients had complex translocations involving 9q34, 22q11, and a third chromosome (Xq11, 7q11.2, or 15q11.2). Two patients had apparently simple variant Philadelphia (Ph) translocations, t(19;22) and t(11;22), with no obvious involvement of chromosome 9, and the Ph was masked in the t(11;22). In situ hybridization studies showed transposition of the abl gene from chromosome 9q34 to the breakpoint cluster region (bcr) of chromosome 22 in all five patients; this was confirmed by rearrangements of the bcr gene in leukemic DNA. In situ hybridization also showed that the bcr-3' and c-sis probes consistently translocated to recipient chromosomes X, 1, 7, 11, and 15, whereas IgC lambda remained on chromosome 22q. These results confirm that association of abl and bcr is a consistent feature of chronic myeloid leukemia irrespective of the cytogenetic presentation and support the conclusion of Hagemeijer that all simple variant Ph translocations are, in fact, complex and involve at least three chromosomes.     

A unique, complex variant philadelphia chromosome translocation in a patient with typical chronic myelogenous leukemia

The Philadelphia (Ph) chromosome [der(22) t(9;22)(q34;q11)] is the characteristic chromosomal abnormality found in chronic myelogenous leukemia (CML). This chromosome has been reported in patients with other chromosomal abnormalities. In this study, we describe a patient with hematologically typical chronic-phase CML with an unusual and complex translocation involving chromosomes 9, 11, and 22. These complex translocations were identified by G-banded conventional cytogenetics and confirmed by fluorescence in situ hybridization (FISH) using whole chromosome painting probes (wcp). To the best of our knowledge, these are unique translocations involving the short and the long arms of chromosome 9 in 4 different translocations with the short arm of chromosome 11 and the long arm of chromosome 22.     

Cytogenetic and molecular studies in patients with chronic myeloid leukemia and variant Philadelphia translocations

Out of 105 Philadelphia (Ph) positive chronic myeloid leukemia patients analyzed, six (5.7%) carried a variant Ph translocation, namely t(6;9;9;10;22)(q24;p13;q34;p15;q11); t(9;13;22)(q34;q21;q11);der(2)(2pter----2q31::9q21---- 9q34::22q11----22qter) and der(9)t(2;9) (9pter----9q21::2q31----2qter);t(7;9;22)(q11;q34 ;q11), 14q + ;t(7;9;22)(q35;q34;q11), and t(9;11;22) (q34;q13;q11), respectively. Five of these patients were analyzed with Southern blotting. Three of them showed an atypical molecular pattern; namely, the patient with t(9;13;22) showed no rearrangement in the breakpoint cluster region (bcr), the patient with t(7;9;22)(q35;q34;q11) showed a 3' deletion, and the patient with t(7;9;22), 14q + showed a bcr rearrangement 3' to the exon 4 of the M-BCR. Chromosome in situ hybridization studies demonstrated that in patient one, a two-step translocation occurred: the first step moved the 3' bcr from chromosome 22 to chromosome 9, and the second moved the terminal part of 22q, carrying the c-sis protooncogene, to 10p. Variant Ph translocations appear to be associated with atypical molecular breakpoints.     

Molecular differentiation of two different translocations producing two apparent Ph chromosomes in a patient with CML

A case of chronic myelogenous leukemia (CML) is described whose leukemic cells appeared to contain two Philadelphia (Ph) chromosomes originating from different translocations involving the two chromosomes 22. The karyotype of the affected cells, established on two different occasions, was: 46,XY,t(9;22)(q34;q11),t(15;22)(p11;q11) with no normal chromosomes 22 and only one 9q+ in each of 115 marrow cells examined. The same findings were present in 50 peripheral blood cells cultured without phytohemagglutinin (PHA) stimulation. When stimulated with PHA, a normal male karyotype was present in the 11 cells examined. There were no additional chromosomal abnormalities and no indication of a blastic crisis after nearly 1 year following the original study. Analysis of the breakpoint cluster region (bcr) on chromosome 22 in the DNA of the affected cells (marrow) revealed evidence for one rearranged chromosome 22 and one normal chromosome 22, indicating that the t(15;22) was not due to the usual Ph translocation seen in CML. The results point to the crucial usefulness of molecular analysis in confirming cytogenetic results related to Ph translocations in CML.     

Variant Ph translocations in chronic myeloid leukemia

Variant translocations were found in eight of 142 consecutive patients with Ph-positive, chronic myeloid leukemia encountered in our laboratory during the last decade. Two patients had simple, two-way variant translocations: t(17;22)(p13;q11) and t(16;22)(q24;q11). Both of these patients had an additional translocation involving chromosomes #9: t(7;9)(q22;q34) and t(9;17)(q34;q21), respectively. Complex variant translocations were found in four cases: t(2;9;22)(p23q12;q34;q11), t(3;9;22)(p21;q34;q11), t(9;12;22)(q34;q13;q11q13), and t(13;17;22)(p11;p11q21;q11). In two cases, the only discernable cytogenetic aberration was del(22)(q11). A review of the chromosomal breakpoints involved in this series and in 185 cases of variant Ph translocations previously reported in the literature reveals that a disproportionately large number of breakpoints are located in light-staining regions of G-banded chromosomes. Furthermore, the breakpoints in simple variant translocations are more often located in terminal chromosomal regions, whereas, the breakpoints in complex translocations typically affect nonterminal bands. No obvious correlation was detected between variant Ph translocation breakpoints and either fragile sites, oncogene locations, or consistent chromosome breakpoints in other malignancies.     

Chromosome abnormalities in leukemia and lymphoma

Nonrandom chromosome changes have been identified in a number of malignant human tumors. The leukemias are among the best studied malignant cells and they provide the largest body of relevant cytogenetic data. In chronic myeloid leukemia, a reasonably consistent translocation [t(9;22) (q34;q11)] is observed in 93 percent of all Ph1 positive patients. In the other patients, translocations are either two-way, involving No. 22 with some other chromosome or complex translocations involving Nos. 9 and 22 and another chromosome. In acute nonlymphocytic leukemia, two translocations are each specifically associated with leukemic cells arrested at two different stages of maturation. One of these, t(8;21)(q22;q22), is found mainly in patients with acute myeloblastic leukemia with maturation (AML-M2). The other, t(15;17)(q22?;q21?), is seen only in patients with acute promyelocytic leukemia (APL-M3). Various translocations have been observed in B-cell acute lymphoblastic leukemia or in Burkitt lymphoma. The most common is t(8;14)(q24;q32), but variants of this, namely t(2;8)(p13?;q24) and t(8;22)(q24;q11), have also been observed; in all of these, the consistent change involves 8q24. The various immunoglobulin loci are located on chromosomes 2, 14, and 22 in the same chromosome band affected by the translocations in B-cell leukemia. These translocations may occur randomly. If a specific translocation provides a particular cell type with a growth advantage, then selection could act to cause the proliferation of this aneuploid cell line vis-a-vis cells with a normal karyotype. In this view, the chromosome change could be the fundamental event leading to the leukemic transformation of an otherwise normal cell. The challenge for the future is to define the genes located at the sites of consistent translocations in myeloid leukemias and to determine the alterations in gene function that are associated with the translocation.     

The incidence, type, and subsequent evolution of 14 variant Ph1 translocations in 180 South African patients with Ph1-positive chronic myeloid leukemia

A Philadelphia (Ph1) chromosome translocation was found in 180 of 198 cases of chronic myeloid leukemia (CML). A standard t(9;22) was present in 166 patients, 83 of whom were black, 79 white, and 4 of "mixed" ancestry; whereas a variant Ph1 translocation was detected in 14 patients (7.8%), 11 of whom were black and only 3 white. There was a higher frequency of a variant Ph1 among black patients compared with whites. The significantly higher frequency of a variant among our patients compared with surveys from elsewhere could be due to differing environmental agents. Simple variants were detected in four patients. Complex variants were found in eight cases; in one of these patients, only chromosomes #9 and #22 were involved, but a complex rearrangement of chromosome #9 had occurred. A "masked" Ph1 translocation was detected in two cases, both of which showed monosomy #22 because the Ph1 chromosome was incorporated or interchanged with chromosome #9. Karyotypic evolution of the Ph1-positive cell line was observed more frequently in the variant group (71.4%) than the standard group (29.5%). This difference was significant (p less than 0.005). There was no difference in the type of clonal changes seen in standard and variant groups. The majority of clonal changes were observed during the acute stage in both groups. In the variant group, there was no obvious correlation between the type of variant, type of clonal change, blast morphology, or survival. Their initial survival pattern resembled that of Ph1-negative cases, but those patients who survived longer than 1 year showed a survival trend similar to standard Ph1-positive cases. Possible explanations for the specificity of chromosome #22 involvement and the constancy of the 22q11 breakpoint in all these variant translocations are discussed.     

"Masked" Ph1 chromosome in a complex three-way translocation

A patient with myelofibrosis was found to have a 46,XX,del(1)(q24),del(11)(p11),-22,+mar karyotype in unstimulated peripheral blood (PB) and spleen cells. On detailed cytogenetic examination it was determined that this patient had an apparently "masked" Ph1 chromosome contained in a complex three-way translocation. Since phytohemagglutinin (PHA)-stimulated PB and spleen cells were essentially normal, the masked Ph1 chromosome was assumed to be an acquired cytogenetic abnormality. The portion missing from the masked Ph1 chromosome was apparently translocated onto del(1). Thus, the detailed karyotype was 46,XX,t(1;11;22)(q24;p11;q11 or q12),t(1;22)(q24;q11 or q12). This complex rearrangement was present primarily in cells belonging to the granulocyte-macrophage cell lineage, whereas E-rosetting cells, and presumably T lymphocytes, had normal karyotypes.     

The cytogenetics of chronic granulocytic leukaemia.

The chromosome abnormalities associated with the classical type of chronic granulocytic leukaemia (CGL) involve a deletion of chromosome number 22 (Ph1) and translocation of the deleted material to another autosome, usually a number 9, t(9;22) (q34;q11). There is no clinically detectable difference between patients showing usual or unusual sites of translocation of 22q. In the chronic phase the typical translocation without additional abnormalities accounts for about two-thirds of the cases. Additional abnormalities include -Y and +8; difference of prognosis in association with aneuploidy has not yet been demonstrated. The presence of Ph1-negative cells in the chronic phase may be related to the time of ascertainment. The isochromosome for the long arm of number 17 is pathognomonic of impending metamorphosis. Additional chromosomal abnormalities are found in the majority of cases in the acute phase. Recent advances in immunological techniques for distinguishing different cytological types of blast cells, in patients who present with acute leukaemia with the Ph1 chromosome, have provided insight into the relationship of the Ph1 chromosome to the pathogenesis of the disease.     

Breakpoint cluster region rearrangements in chronic myelogenous leukemia with a masked Philadelphia chromosome

Cytogenetic and molecular analyses were performed in a case of chronic myelogenous leukemia. The cytogenetic study revealed that the leukemic cells of this patient contained a three-way translocation involving chromosomes #5, #9, and #22, resulting in a masked Philadelphia chromosome; the karyotype of the leukemic cells was 46,XY,t(5;22;9)(q31;q11;q34). Southern blot analysis of leukemic cell DNA was performed using a 1.1 kb HindIII-EcoRI breakpoint cluster region (bcr) probe. The results showed that BglII digested DNA showed two abnormal bcr fragments (i.e., 5.2 kb and 2.7 kb) in contrast to the results with DNA from two patients with a standard Ph chromosome [t(9;22)(q34;q11)] who showed one normal 5.0-kb bcr fragment in addition to altered fragments of about 4.3 kb or 4.0 kb. Bam HI digests of DNA from the leukemic cells of the patient with the masked Ph chromosome showed two bands (3.3 kb and 6.5 kb), whereas, DNA from the two patients with standard Ph translocations showed only a 3.3-kb bcr fragment. The results indicate that the molecular events in a masked Ph affect the bcr locus in a manner similar to that seen in standard Ph chromosomes.     

The Philadelphia (Ph) chromosome in leukemia. I. A new mechanism due to interstitial deletion and insertion in chronic myelocytic leukemia

The Philadelphia (Ph) chromosome in leukemia is invariably derived from chromosome #22. A break occurs in the long (q) arm of chromosome #22 and, in every case observed until now, all of the material from that breakpoint through the telomere of chromosome #22 has been reciprocally translocated to another chromosome, most often chromosome #9. With the t(9;22) translocation, the oncogene c-sis moves from chromosome #22 onto 9q and the oncogene c-abl moves reciprocally from chromosome #9 onto 22q. We report a new mechanism for the genesis of the Ph chromosome in chronic myelocytic leukemia (CML) involving interstitial deletion of chromosome #22 with insertion of the deleted material into another chromosome: 46,XX,dir ins(11;22)(q13;q11q13). The distal portion of chromosome #22, including the telomere, appeared to have been retained in the Ph chromosome. There was no visible involvement of chromosome #9. This insertional deletion is of potential importance in evaluating the roles of oncogenes such as c-abl and c-sis in the Ph rearrangement in the origin of leukemia.     

A fluorescence in situ hybridization study of complex t(9;22) in two chronic myelocytic leukemia cases with a masked Philadelphia chromosome

The t(9;22)(q34;q11) is evident in more than 90% of patients with chronic myelocytic leukemia (CML) and gives rise to the Philadelphia chromosome (Ph). Approximately 5%-10% of CML patients show variant translocations involving other chromosomes in addition to chromosomes 9 and 22. In some variant translocations, additional material is transferred on der(22), resulting in a masked Ph chromosome. In this paper, we report two apparently Ph-negative (Ph-) CML cases showing a t(7;9;22)(q22;q34;q11) and a t(8;9;22)(q12;q34;q11), respectively. A detailed molecular cytogenetic characterization was performed by fluorescence in situ hybridization (FISH), which disclosed the presence of the 5'BCR/3'ABL fusion gene on the der(7) and der(8) chromosomes, respectively. Derivative (22) appeared as a masked Ph chromosome in both cases. FISH analysis with appropriate BAC/PAC clones allowed us to precisely characterize the complex chromosomal rearrangements that were not detected by conventional cytogenetic analysis.     

Complex translocation involving chromosomes #1, #9, and #22 in a patient with chronic myelogenous leukemia

A case of Philadelphia chromosome positive chronic myelogenous leukemia with a complex translocation involving chromosomes #1, #9, and #22 is described. All cells in the bone marrow showed this rearrangement, and Q-banding analysis showed the predominant karyotype to be 46,XY, t(1;9;22)(p22;q34;q11).     

Inversion of chromosome 3 in a case of chronic myelogenous leukemia with abnormal thrombopoiesis

A patient with chronic myelogenous leukemia (CML) associated with a remarkable increase of micromegakaryocytes in bone marrow was revealed to have an abnormality of a long arm of chromosome #3, i.e., inv(3)(q21q26), in addition to a complex Ph translocation: t(9;22;15)(q34;q11;q22). Although several cases of acute leukemia with inv(3)(q21q26) and abnormal megakaryocytes have been reported, this is the first case in which the association of inv(3)(q21q26) with a megakaryocytic abnormality was observed in a patient with CML. Our findings suggest that this structural rearrangement may be more specifically associated with abnormal thrombopoiesis than are other structural anomalies of 3q.