1. ¹Genzyme Genetics, Santa Fe, NM, USA
2. ²Department of Pediatrics, University of New Mexico, Albuquerque, NM, USA
3. ³Department of Pathology, University of New Mexico, Albuquerque, NM, USA
4. ⁴Department of Pediatrics, the University of Arizona, Tucson, AZ, USA

Correspondence: Dr KD Montgomery, Genzyme Genetics, 2000 Vivigen Way, Santa Fe, NM 87505, USA. Fax: +1 505 438 2220; E-mail: Karen.Montgomery@genzyme.com

Received 30 January 2004; Accepted 26 May 2004; Published online 29 July 2004.

TO THE EDITOR

Jumping translocations have been observed in many types of neoplasia, including hematopoietic cancers, where they are associated with poor prognosis.¹ The most common chromosome region found in jumping translocations is the long arm of chromosome 1 (1q).¹ The presence of the Philadelphia translocation (Ph+) in children with acute lymphoblastic leukemia (ALL) may also confer a poor prognosis in the presence of other high-risk features.² This report is the first description of a child with a jumping translocation of 1q and Ph+ ALL. The tumor cells of this child also showed myeloid antigen expression, which occurs with high frequency in Ph+ ALL.³

An 8-year-old female presented with a 1-week history of fever, vomiting and leg pain. Physical examination was remarkable for pallor, cervical adenopathy and hepatosplenomegaly. Laboratory examination showed 524 10⁹ leukocytes/l (88% blasts, 3% neutrophils, 4% lymphocytes, 5% monocytes), 74 g hemoglobin/l, and 117 10⁹ platelets/l. Her cerebral spinal fluid showed the rare presence of leukemic cells (POG CNS 2). Bone marrow examination revealed >95% blasts, with a subset containing distinct cytoplasmic granules that were Sudan Black B positive. Blasts were characterized by weak CD45, HLA-DR, CD19, CD10, TdT positivity and partial expression of CD13, CD33, and CD20. Based on this three-color flow cytometric immunophentoyping, a diagnosis of myeloid antigen positive ALL (My+ ALL) was made.

The patient achieved remission with an anthracycline-based induction sequence, but soon relapsed while on Pediatric Oncology Group ALL Study 9406. In her second remission, she underwent allogeneic bone marrow transplantation from a male HLA-identical sibling. She relapsed a second time 16 months after transplant with a WBC of 89.2 10⁹/l composed of 81% blasts and bone marrow morphology consistent with My+ ALL. The patient was transplanted a second time, in relapse, using a different HLA-matched male sibling donor. Hematopoietic engraftment was achieved by day 40 post-transplantation. At 30 months after the second bone marrow transplant, the child died of complications while in hematologic remission.

The diagnostic chromosome analysis of unstimulated bone marrow cells showed three related, divergent clones, including a stemline in which the t(9;22)(q34;11.2) was the sole anomaly detected. Putative evidence for cytogenetic progression was observed with the presence of two sideline clones, that had, in addition to the Philadephia translocation, either an add(19)(p13.3) or an add(2)(p13) with an add(7)(q11.2) (Figure 1a and b). When the patient relapsed 16 months after BMT from a male sibling donor, chromosome analysis showed a donor/recipient mosaic karyotype with three distinct clonal populations. The predominant cell line was 46,XY (donor); also prominent was a cell line that occurred at presentation, the 46,XX,t(9;22)(q34;11.2),add(19)(p13.3). Critically, cells from this clone were found with a jumping translocation of 1q (Figure 1c). The 1q breakpoint appeared to be consistently at 1q11, but there were multiple clonal recipient chromosomes (chromosomes 4, 6 and 21; Figure 1d). Since this cell line appeared to be targeted for tumor progression and the acquisition of jumping translocations, characterization of the aberrant chromosome 19 was essential. Spectral karyotyping (SKY) analysis (Figure 2a) showed that this chromosome contained segments of chromosomes 6 and 19. However, there was indication that some chromosome 10 material could also be present in this rearrangement. FISH analysis with whole chromosome paints for chromosomes 6 and 10 (Figure 2b) confirmed that only chromosome 6 material was translocated to 19p. Combining G-banding, FISH, and SKY analyses, we determined that the basic karyotype of this cell line was: 46,XX,t(9;22)(q34;q11.2),der(19)t(6;19)(p21.121.3;p13.3).

Figure 1.

(a) G-banded karyotype of one cell line at diagnosis showing the t(9;22)(q34;q11.2) and the add(19)(p13.3) (arrow). (b) G-banded karyotype of a second cell line at diagnosis: in addition to the t(9;22)(q34;q11.2), there are undefined aberrations of 2p and 7q (arrows). (c) G-banded karyotype from the specimen at relapse following the first bone marrow transplant, with the jumping translocation 1;4 (arrow), t(9;22)(q34;q11.2) and add(19)(p13.3). (d) G-banded partial karyotypes showing jumping translocations of 1q with acceptor chromosomes 4, 6 and 21, each occurring in individual metaphases in a background of t(9;22)(q34;q11.2) and add(19)(p13.3).

Full figure and legend (47K)

Figure 2.

(a) Spectral karyotype at relapse after first BMT. The reverse DAPI image is on the left and the SKY classified image on the right for each chromosome pair. The translocation (9;22)(q34;q11.2) is apparent on the derivative 9 and the additional material on 19p is shown to originate from chromosome 6. In this metaphase, the jumping translocation of 1q is found at 4qter. (b) FISH to a metaphase cell at relapse (same specimen as in Figure 2a) hybridized with whole chromosome painting probes for chromosome 6 (Spectrum Green™) and chromosome 10 (rhodamine), plus a centromere-specific probe for the X chromosome (SG). The arrow indicates the extra material on 19p that is derived from chromosome 6 sequences. (c) FISH with the SOC-1 probe for 1qh (directly labeled with Cy3) hybridized to the same specimen as in Figure 2a. Three signals are seen in metaphase and interphase (inset) cells, two from the intact #1 chromosomes (white arrows) and one from the jumping translocation 1;4 (yellow arrow). The probe, a deoxyoligomer isolated from a human repetitive DNA library, is from a divergent region of human satellite II–III sequences. This probe is now commercially available.

Full figure and legend (192K)

Standard chromosome analysis 3 weeks later, postreinduction, showed predominantly donor male cells; the cell line containing the derivative 19 was present in four of 20 cells analyzed, but no jumping translocations were found. However, interphase FISH analysis with a probe for the heterochromatic region of 1q (Figure 2c and Table 1) revealed that 7% of the cells analyzed had three signals, indicative of persistence an extra copy of 1q. Chromosome analysis of a follow-up specimen, 2 weeks later when morphologic remission was attained, found no jumping translocations in 21 metaphase cells examined; interphase FISH analysis indicated that three signals for 1qh were present in 2% of nuclei scored. Clinical reportable ranges for this probe have not been determined; the significance of this low level of signal is unclear. No cytogenetic analysis was performed on the autopsy specimen.

Table 1 - Interphase FISH analyses for 1qh probe. In total, 200 cells were scored for each specimen.

Full table

This case exemplifies the merit of using a combination of molecular cytogenetic techniques in the analysis and monitoring of chromosomal rearrangements. The use of interphase FISH for the X and Y centromeres in combination with the 1qh probe, for instance, allowed us to identify cells from the patient, rather than the donor, that contained an extra copy of 1q. The use of painting probes subsequent to SKY analysis confirmed ambiguities in the spectral karyotype, and allowed us to define the t(6;19). This type of multistep analysis is useful in adequately identifying the progression of chromosomal rearrangements in specimens from patients with high-risk genotypes.

The biological effect of the apparently unbalanced translocation between the short arms of chromosomes 6 and 19 is unclear. The involved regions contain genes implicated in leukomogenesis, including E2A at 19p13.3. The E2A locus appears to have variant molecular breakpoints and is rearranged in cells with jumping translocations and with multiple disease associations.⁴

The pathogenicity of jumping translocations of 1q, thought to be an early event in cytogenetic evolution,⁵ may be a direct effect of partial trisomy of 1q, of changes in specific gene activity resulting from translocation, and/or of a global instability related in the transposition of 1q heterochromatin. One gene that may be specifically related to the 'pathogenetic' effects of jumping translocations is EAT/mcl-1. This Bcl-2 related gene maps to 1q21 and was overexpressed in the tumor cells of a patient with AML and jumping translocations of 1q. The EAT/mcl-1 gene confers resistance to apoptosis and is not normally upregulated in AML.⁶

The nature of heterochromatin, found concentrated in proximal 1q, may result in an instability that encourages the formation of jumping translocations and then influences their effects at the site of translocation. Chromatin in this region is subject to hypomethylation leading to decondensation and resulting chromosomal instability.⁷ Heterochromatin is thought to effect genes within its control by silencing,⁸ possibly with that direct effect at the multiple recipient sites of a jumping translocation.

The aggressive course of the disease in this child is consistent with the cytogenetic composition of her tumor cells and her clinical profile. Her tumor progression adds to a growing body of evidence that the presence of jumping translocations heralds a poor outcome in an intrinsically therapy resistant Ph+ tumor. The observation of similarly affected patients in future clinical trials may provide insight into the pathogenesis and successful treatment of children whose tumors develop jumping translocations.