Interphase cytogenetic study of childhood acute lymphoblastic leukemia

High hyperdiploid childhood acute lymphoblastic leukemia

High hyperdiploidy (51-67 chromosomes) is the most common cytogenetic abnormality pattern in childhood B-cell precursor acute lymphoblastic leukemia (ALL), occurring in 25-30% of such cases. High hyperdiploid ALL is characterized cytogenetically by a nonrandom gain of chromosomes X, 4, 6, 10, 14, 17, 18, and 21 and clinically by a favorable prognosis. Despite the high frequency of this karyotypic subgroup, many questions remain regarding the epidemiology, etiology, presence of other genetic changes, the time and cell of origin, and the formation and pathogenetic consequences of high hyperdiploidy. However, during the last few years, several studies have addressed some of these important issues, and these, as well as previous reports on high hyperdiploid childhood ALL, are reviewed herein.

A strategy to detect chromosomal abnormalities in children with acute lymphoblastic leukemia

Conventional cytogenetics (CC) can be used to identify chromosomal abnormalities that are predictors of treatment outcome in acute lymphoblastic leukemia (ALL). The detection of abnormalities in ALL is difficult because low mitotic index and poor-quality metaphases are obtained. Flow cytometry (FC) and fluorescence in situ hybridization (FISH) can be used to detect aneuploidy in any phase of the cell cycle, increasing the number of analyzable cells. The aim of this study was to develop a strategy combining these methods to improve the frequency of chromosome abnormality detection. One hundred children with newly diagnosed ALL were included. CC and DNA content analysis by FC were performed in all patients. The numerical abnormalities identified by both methods were compared and patients were classified as concordant or discordant. FISH was used to support aneuploidy results in discrepant cases using centromeric probes for the chromosomes most frequently involved in aneuploidy. CC and FC showed high concordance (86%). Fourteen cases were discrepant: nine showed hypodiploidy and low hyperdiploidy by cytogenetics and five showed high hyperdiploidy by FC. FISH confirmed aneuploidy in 12 cases in which it could be performed. High hyperdiploidy was the most common abnormality; the 31 cases showing this aneuploidy were identified by FC. The search for abnormalities must begin by measuring DNA content to detect this aneuploidy, which is useful to evaluate the patient's risk. However, it is important to screen for structural abnormalities by CC or molecular techniques. This strategy may detect chromosomal abnormalities, optimizing resources in laboratories where not all the screening methods are available.

Preponderant mitotic activity of nonleukemic cells plays an important role in failures to detect abnormal clone in childhood acute lymphoblastic leukemia

At diagnosis, clonal chromosomal abnormalities are found in the bone marrow blasts in more than two thirds of children with acute lymphoblastic leukemia (ALL). Practically, however, failure to detect these abnormalities is frequent and usually attributed to poor marrow sampling, inadequate metaphases, and/or a preponderant mitotic activity among nonleukemic cells. The authors applied fluorescence in situ hybridization (FISH) techniques to re-examine 30 cases of karyotypically "normal" childhood ALL to explore the role of preponderant mitotic activities of nonleukemic cells in failures to detect clonal abnormalities. The FISH test were performed using TEL/AML1 fusion gene probe and the centromere probes for chromosome 8 and 10 to detect the t(12;21) translocation and/or hyperdiploidy. Half of the karyotypically "normal" ALL cases examined have been found to have abnormal clones with t(12;21) rearrangement and/or hyperdiploidy by this specially designed FISH assay. Contrary to expectation, the authors found a higher incidence (52%) of clonal abnormalities in cases where over 20 metaphases had been examined than in cases (44%) where fewer than 20 metaphases had been analyzed. These findings suggest that a preponderant mitotic activity of nonleukemic cells plays an important role in failures to detect an abnormal clone by conventional cytogenetic studies. Therefore, karyotypically "normal" childhood ALL patients should undergo FISH studies to rule out the presence of t(12;21) and/or hyperdiploid clone.

The investigation of karyotypic instability in the high-hyperdiploidy subgroup of acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) of childhood has been cytogenetically well characterized, and approximately 25% of cases will have a high-hyperdiploid (51-68) chromosome complement. In a 5 year period a consecutive series of 152 presentation ALL's were karyotyped. In all cases a result was obtained and 138 (91%) had a detectable abnormal clone of which 44 (29%) were high-hyperdiploid. Within the high-hyperdiploidy group karyotypic cell to cell variation was observed in many cases. To provide further evidence of this phenomenon a dual-color fluorescence in-situ hybridization (FISH) experiment was performed on stored fixed suspension from 14 ALL's with such a karyotype. In each case 4-6 probes were investigated, employing probes to centromeres of chromosomes X, 4, 6, 8, and 10 and a locus specific probe to chromosome 21q22. It was found that the FISH produced results that were generally in good agreement with the G-banding findings and supported the notion of karyotypic cell to cell variation. FISH further showed that most of cases would have two extra copies of chromosome 21 in the majority of leukemic cells and a single extra copy in the minority. A further finding was that fewer cells contained extra copies of chromosomes 6, 8 and 10 than was expected based on the comparison of the signal number of the other probes investigated. In contrast chromosomes X, 4, and 21 seldom displayed this feature. We have demonstrated that karyotypic instability as defined by karyotypic cell to cell variation is a feature of the high-hyperdiploid subgroup in childhood ALL. It is questioned whether the underlying defect resulting in the observed karyotypic instability of this subgroup is one of the primary causative events in the formation of the leukemia.

Comparative genomic hybridization in pediatric acute lymphoblastic leukemia

Comparative genomic hybridization (CGH) was used to clarify the chromosomal status of 15 patients diagnosed with childhood acute lymphoblastic leukemia (ALL). Bone marrow samples from 10 of the 15 patients were selected because no metaphases were obtained for cytogenetic analysis. Three patients with normal trypsin and giemsa banding (GTG) karyotypes were also studied by CGH to determine whether significant abnormalities might have been missed by banding analysis, and samples from an additional 2 patients with hyperdiploidy were also included. Seven of the 10 patients with failed GTG banding analysis were found to be chromosomally abnormal by CGH; 2 out of 3 patients with normal GTG band karyotypes were abnormal, indicating that the metaphases available for karyotyping were not malignant cells, and that CGH analysis of hyperdiploid samples provided more accurate resolution than karyotyping alone. The prognostic value of chromosomal aberrations detected by CGII and the efficiency of the technique suggest a central role for CGH in routine clinical cytogenetics.

The value of interphase fluorescence in situ hybridization in the study of patients with lymphoproliferative disorders: further evidence for a higher sensitivity of detecting chromosomes 7 and 8 aneuploidy

Dual-color interphase fluorescence in situ hybridization (I-FISH) for chromosomes 7 and 8 was studied retrospectively on 32 patients with suspected lymphoid disorders, and the results were compared with standard cytogenetics. One of 29 (3.4%) patients with lymphoid malignancy showed cytogenetically detectable aneuploidy for chromosomes 7 and 8. In an additional 5 patients (17.2%), I-FISH unmasked chromosomal loss and gain that were not detected by standard metaphase analysis. This represents 19% of the 21 studied patients with acute lymphoblastic leukemia (ALL). These findings indicate that aneuploidies for chromosomes 7 and 8 are underreported in ALL and further demonstrate higher sensitivity of I-FISH for detecting numerical chromosomal rearrangements in leukemic cells.

Detection of chromosome over- and underrepresentations in hyperdiploid acute lymphoblastic leukemia by comparative genomic hybridization

Chromosomal analysis of acute lymphoblastic leukemia (ALL) is often difficult because of the suboptimal in vitro growth of the immature lymphoid cell and the poor morphology obtained. In this study, we describe the application of comparative genomic hybridization (CGH) to investigate the genomic abnormalities in 14 patients with ALL, all of whom had cytogenetically identified numerical aberrations or gross chromosomal structural alteration. With the use of CGH, regional or whole chromosome overrepresentation or both were found to be more frequent than underrepresentation (52 gains vs. 6 losses), the most common gains being chromosomes 21 and X. The results of the comparison between CGH and conventional R-banding analysis could be classified into three categories: (1) in three cases, including two with trisomy, CGH and banding analysis gave identical results; (2) in six cases with hyperdiploidy and two cases presenting chromosome structural abnormalities, the results were consistent but with minor discrepancies; (3) in three cases, including two with triploidy and tetraploidy and one with chimeric karyotype together with +22, the data from CGH and cytogenetical analysis were discrepant. CGH could not find the triploidy and tetraploidy. Our results suggest that CGH has certain value in the detection of gains or losses of chromosome materials in hyperdiploid ALL. Nevertheless, the combination of CGH and conventional karyotyping provides more precise information on the genomic imbalance in ALL.

A case of acute lymphoblastic leukemia, near-triploidy, and poor outcome: characterization by fluorescence in situ hybridization using chromosome-specific libraries from all human chromosomes

We have applied fluorescence in situ hybridization (FISH) using chromosome-specific libraries from all 24 chromosomes on metaphase spreads from bone marrow cells, in order to resolve the chromosomal changes in leukemic cells from a 10-year-old boy with acute lymphoblastic leukemia (ALL), near-triploidy, and a subsequent poor outcome. The FISH analysis revealed a pattern of chromosome gains and losses that differed from all cases previously described. Most of the affected chromosomes were present in three copies (trisomy for chromosomes 1, 2, 5, 6, 7, 11, 12, 13, 14, 16, 17, 18, 19, 20, and 22), but the patient had four copies of chromosomes 8 and 21, two copies of chromosomes 3, 4, 9, 10, 15, and X, and one Y chromosome. No structural abnormalities could be detected. Thus, the karyotype of the malignant clone was 66,XXY-3,-4,+8,-9,-10,-15,+21.

Diagnostic and prognostic significance of chromosome abnormalities in childhood acute lymphoblastic leukemia

Current intensive chemotherapies cure about 70% of the children with ALL. On the other hand a significant number of the children are not cured despite intensive treatment. At the same time some highly curable patients are treated too intensively and suffer from unnecessary side effects of the chemo- and radiotherapy applied. In order to further improve the therapeutic results in this disease, we have to distinguish between the cases with a better and a worse prognosis. The initial karyotype (both numerical and structural chromosome abnormalities) proved to be one of the most reliable prognostic parameters, leading to the suggestion of developing genotype-specific therapies. Although the prognosis in patients with pseudodiploid karyotype is usually unfavorable, a significantly better prognosis can be observed in those with more than 50 chromosomes. Because the latter patients can achieve remission on a metabolite-based therapy, the toxic effects of more aggressive chemotherapy with anthracyclines and genotoxic agents can be avoided; thus, the reliable and accurate identification of patients with > 50 chromosomes is of particular importance. For this purpose three methods: chromosome analysis, DNA flow cytometry, and fluorescence in situ hybridization can be used. In 1993 it was decided to develop a comprehensive nationwide project in order to perform the initial genetic analysis of all ALL children diagnosed in the hematological/oncological centers of Hungary. Here the data obtained on 187 ALL patients diagnosed in the period from 1993 to 1995 are presented. In about 75% of patients (in 140 of 187) chromosome analysis was performed, in 78 cases (55.7%) successfully. The proportion of patients with abnormal karyotype was 36 of 78 (46.1%), and hyperdiploidy with more than 50 chromosomes was detected in 13 of 78 (16.6%) children. The lower ratio of hyperdiploid cases in our patients as compared to the data in the literature may be due to technical difficulties and the small number of patients studied, but it may reflect real geographic characteristics. Using flow cytometry, seven of 31 patients investigated (22.5%) proved to be hyperdiploid with a DNA index above 1.16. A higher ratio of hyperdiploid patients in this study calls attention to the significance of simultaneous application of the two methods. Taken together, 16 of 80 (20.0%) successfully studied patients proved to be hyperdiploid (> 50 chromosomes and/or DNA index above 1.16). The pattern of chromosome involvement in our study determined by chromosome analysis and/or FISH technique proved also to be different from the data of large international series. In addition to trisomies of chromosomes 4, 6, 10, 14, 17, 18, 21, and X, which are known to be the most frequently involved chromosomes, trisomies of chromosomes 3, 8, 11, and 13 were also observed with a high frequency. Comparison of survival curves of various cytogenetic subgroups showed a significant difference between diploid-pseudodiploid and diploid-hyperdiploid A (with 47-50 chromosomes) subgroups. No favorable prognosis of hyperdiploid patients (> 50 chromosomes) could be proved. Because of the small number of patients studied, prognostic differences of cytogenetic subgroups need further confirmation. The clinical and genetic differences observed, however, call attention to the necessity for further genetic studies of ALL patients in Hungary, because these differences may reflect real geographic characteristics and may be related to different environmental mutagen/carcinogen effects of the given geographic area. It is essential to determine whether or not these differences really exist and if they do to reveal the causes leading to these differences. In our view this is one of the routes by which the therapeutic results in childhood ALL can be further improved simultaneously with the avoidance of early and late toxicity of chemotherapy.

Detection of trisomy 12 in chronic lymphocytic leukaemia: comparison of a polymerase chain reaction based technique with fluorescence in situ hybridization

Trisomy 12 is the most frequent chromosomal aberration in chronic lymphocytic leukaemia (CLL) and seems to indicate a poor prognosis. To detect this abnormality we tested the applicability of the polymerase chain reaction (PCR) and compared it to the current standard fluorescence in situ hybridization (FISH). Two DNA regions containing variable numbers of tandem repeats (VNTR) located on (a) the long and (b) the short arm of chromosome 12 were chosen for PCR analysis. 8/72 patients (11%) were trisomy 12 positive compared to 16% by FISH. Chromosomal imbalances were only detected by PCR if at least 20% of the cells carried the numerical aberration.