11q23异常恶性血液病的临床和细胞遗传学研究

目的 评估１１ｑ２３异常与恶性血液病的临床,血液学和预后的相互联系。方法 采用骨髓直接法和（或）培养法制备色体标本,用Ｒ显带技术,对６０００例恶性血液病进行核型分析。结果 ６０００例恶性血液病中发现２８例有１１ｑ２３异常,发生率为０．４７％。异常类型有７种：ｔ（４;１１）（ｑ２１;ｑ２３）１０例;ｔ（１１;１９）（ｑ２３;ｐ１３）５例;ｔ（９;１１）（ｐ１２;ｑ２３）２例;ｔ（１０;１１）（ｐ１５     

应用荧光原位杂交技术检测84例慢性淋巴细胞白血病遗传学异常及预后分析

 摘要 目的：探讨荧光原位杂交 (fluorescence in situ hybridization,FISH) 技术检测慢性淋巴细胞白血病(chronic lymphocytic leukemia,CLL)患者的遗传学异常,并分析与其他预后指标的相关性及预后价值。方法：回顾性分析采用FISH技术进行着丝粒探针CSP12(12p11.1～12q11.1)和序列特异性探针D13s25(13q14.3)、ATM (11q22.3)、RB1(13q14)、p53(17p13.1)检测过的84例CLL患者的临床以及实验室资料。分析FISH技术检测CLL患者中遗传学异常的发生率,并分析遗传学异常与CLL患者年龄、性别、Binet分期、血清乳酸脱氢酶(lactate dehydrogenase,LDH)、CD38表达、生存期之间的相关性。结果：(1)84例CLL患者中,62例有至少有一种遗传学异常。遗传学异常的检出率为73.8%。(2)共发现5种遗传学异常,依次为13q14缺失（56%）、P53缺失（28.6%）、-12（16.7%）、ATM缺失（13.1%）、+12（13.1%）。其中-12为CLL病人中新发现遗传学异常。(3)分析上述5种遗传学异常与年龄、性别、Binet分期、LDH水平、CD38表达的关系,在>60岁年龄病人里,+12阳性率显著高于<60岁病人(24%VS3%, P=0.042),与性别、Bient分期、LDH水平、CD38表达无关。(4)在LDH增高组中,CD38高表达的病例比例增高（67%VS20%, P=0.015）。(5) 伴有del(17p13)或del(11q22)或复杂异常中位生存时间为75个月,单纯具有del(13q14)异常组的中位生存时间为150个月,其他中位生存时间为120月,但两两比较没有达到统计学差异。结论：(1)FISH技术是一种在分析CLL患者遗传学异常方面较为快速、准确和敏感的方法; (2)CLL病人中除了常见13q14缺失、P53缺失、ATM缺失、+12之外,还可以出现-12异常。     

Trisomy 13 in a patient with common acute lymphoblastic leukemia: description of a case and review of the literature

Trisomy 13 occurring as a single cytogenetic abnormality has been associated with undifferentiated or biphenotypic acute leukemias and with an adverse prognostic outcome. We describe for the first time a case of B-cell common acute lymphoblastic leukemia (ALL) with trisomy 13 at diagnosis in an 18-year-old boy. The leukemic cells did not express myelocytic or T-cell associated antigens and no molecular abnormalities were detected. Following treatment, according to the GIMEMA ALL 0496 protocol, the patient achieved a brief (2 months) complete remission. At relapse, cytogenetic analysis showed karyotypic evolution that included two novel subclones carrying a del(6q), a del(7q), and an add(17q) in association with trisomy 13. In addition, immunophenotypic analysis revealed the coexpression of the CD33 and CD7 antigens on common ALL blasts, in accordance with other reported cases that displayed a predominant biphenotypic leukemia profile. The patient failed to obtain a second remission and died soon after due to infective complications. This report indicates that trisomy 13 can be found also in B-lineage ALL and underlines that this cytogenetic abnormality may identify a subgroup of male patients with clonal evolution potential and an adverse clinical outcome.     

Pediatric acute myeloid leukemia with t(7;21)(p22;q22)

The t(7;21)(p22;q22) resulting in RUNX1‐USP42 fusion, is a rare but recurrent cytogenetic abnormality associated with acute myeloid leukemia (AML) and myelodysplastic syndromes. The prognostic significance of this translocation has not been well established due to the limited number of patients. Herein, we report three pediatric AML patients with t(7;21)(p22;q22). All three patients presented with pancytopenia or leukopenia at diagnosis, accompanied by abnormal immunophenotypic expression of CD7 and CD56 on leukemic blasts. One patient had t(7;21)(p22;q22) as the sole abnormality, whereas the other two patients had additional numerical and structural aberrations including loss of 5q material. Fluorescence in situ hybridization analysis on interphase cells or sequential examination of metaphases showed the RUNX1 rearrangement and confirmed translocation 7;21. Genomic SNP microarray analysis, performed on DNA extracted from the bone marrow from the patient with isolated t(7;21)(p22;q22), showed a 32.2 Mb copy neutral loss of heterozygosity (cnLOH) within the short arm of chromosome 11. After 2‐4 cycles of chemotherapy, all three patients underwent allogeneic hematopoietic stem cell transplantation (HSCT). One patient died due to complications related to viral reactivation and graft‐versus‐host disease. The other two patients achieved complete remission after HSCT. Our data displayed the accompanying cytogenetic abnormalities including del(5q) and cnLOH of 11p, the frequent pathological features shared with other reported cases, and clinical outcome in pediatric AML patients with t(7;21)(p22;q22). The heterogeneity in AML harboring similar cytogenetic alterations may be attributed to additional uncovered genetic lesions.     

The predictive value of initial cytogenetic studies in 148 adults with acute nonlymphocytic leukemia: a 12-year study (1970-1982)

When leukemic blood or marrow specimens from 148 adults with newly diagnosed acute nonlymphocytic leukemia (ANLL) were studied with chromosome banding techniques, 79 were found to have clonal abnormalities. Among 130 treated patients, the 53 with initially normal karyotypes had a significantly longer survival rate than the 16 in whom no normal metaphases were observed (p = 0.02). The 55 patients with both normal and abnormal metaphase cells had an intermediate survival. Once a complete remission had been attained, however, there was no significant difference in median survival between those patients with entirely normal karyotypes and those with abnormal karyotypes. Among the various FAB morphologic subsets of ANLL, the differences in complete remission rate and overall survival between the various cytogenetic subsets were greatest in acute myelogenous leukemia (AML, M1 + M2). The presence of an abnormal clone was a more important predictor of clinical outcome (p = 0.02) than the presence of normal stem cell clones. Aneuploidy alone (hyperdiploidy or hypodiploidy) was not of predictive value, indicating that the use of banding techniques to identify structural rearrangements in pseudodiploid cells was essential. Clonal chromosomal abnormalities were nonrandom and acquired, and specific abnormalities were closely associated with specific clinical-pathologic subsets of ANLL. All 13 patients with acute promyelocytic leukemia and adequate cytogenetic specimens had t(15;17); this translocation was not found in any other subset of ANLL. Six patients with AML (M2) had t(8;21) or a variant of this rearrangement. Seven patients had inv(16)(p13q22) associated with acute myelomonocytic leukemia (AMMoL, M4) and abnormal marrow eosinophils. Two patients had ins(3;3) and thrombocytosis. Four patients had a translocation involving 11q, but none of these had acute monocytic leukemia (AMoL, M5); no patient had del(11q).     

Clinical significance of cytogenetic findings at diagnosis and in remission in childhood and adult acute lymphoblastic leukemia: experience from India

We report cytogenetic findings in 114 patients of acute lymphoblastic leukemia (ALL), which includes 78 children (< or = 15 years) and 36 adults (16-60 years). Chromosome aberrations were detected in 109 (95%) cases. A lower frequency of hyperdiploidy (15%) in children and a higher frequency of hypodiploidy both in children (38.4%) and adults (44.4%) were found, in contrast to literature. Translocations were detected in one third of adult and pediatric cases. The incidence of t(9;22) was comparatively low in adults (7.7%). Frequency of t(1:19) was also low in overall ALL cases. Various other recurrent abnormalities such as del(6q), abn(11q23), i(9p), abn(12q13), del(7q), and i(17q) were seen in our cases; a striking difference in the incidence of del(6q) (41%) and abn(11q23) (30%) was found in our series versus reported literature. Ploidy distribution indicated association of pseudo- and hypodiploidy with B-lineage, and hypodiploidy with T-lineage in children. The occurrence of del(6q) was more frequent in pediatric ALL with highly aberrant pattern and also with lymphadenopathy. Abn(11q23) was found to be early-B and pre-B specific. Kaplan-Meier analysis of overall survival revealed prognostic value of sex, FAB, immunophenotype, and cytogenetic findings. Females and T-ALL patients had a better prognosis, whereas males and B-ALL patients had poor outcome in overall and pediatric age groups. Prognostic evaluation of cytogenetics indicated translocations as an independent high-risk predictor in childhood (P < 0.008) and adult ALL (P < 0.01). Childhood ALL with t(8;14) and t(4;11) and adults with t(9;22) had poor survival. Cytogenetics of remission marrows demonstrated disappearance of abnormal clones in 31.4%, and expansion in normal clones in 50% of patients. Persistence of original clones and development of new clones were observed in 20% and 33% of patients, respectively; whereas karyotype evolution was identified in 10% of patients. The prognostic significance of cytogenetic findings at diagnosis, and differential cytogenetic response in so-called clinical remission in our study indicated the utmost need for more intensive therapy for eradication of resistant clones, and necessity of sequential cytogenetic follow-up in these patients for identification of minimal residual disease.     

A unique clone involving multiple structural chromosome rearrangements in a myelodysplastic syndrome case

In a young female patient presenting with a myelodysplastic syndrome (MDS), a unique clone involving six structural chromosome rearrangements was identified using G-banding and molecular cytogenetic techniques. Fifty GTG-banded metaphases from bone marrow were initially analyzed and all metaphases contained all of the six structural chromosome rearrangements. To further define the GTG-banded karyotype, a series of fluorescence in situ hybridization and primed in situ labeling experiments were performed and the karyotype was then characterized as: 46,XX,r(5)(p13q13),der(20)t(5;20),dup(11)(p11.2p15), r(11)(p15q25),del(13)(q14),idic(22)(p11). The patient quickly progressed to acute nonlymphocytic leukemia three months after the diagnosis and died of a hemorrhage in the brain parenchyma two months later. In this case, the multiple structural chromosome rearrangements conferred an obvious cellular proliferative advantage and indicated a very poor prognosis. Considering that multiple chromosome abnormalities associated with MDS transformation are often polyclonal, this unique clone involving six structural chromosome rearrangements make our case highly unusual.     

Cytogenetic study of acute lymphoblastic leukemia and its correlation with immunophenotype and genotype.

Among 72 Chinese patients with acute lymphoblastic leukemia (ALL), 50 had clonal chromosomal abnormalities. Structural abnormalities were detected in 42 patients: these included t(9;22) in 9, t(1;19) in 6, t(4;11) in 5, del(11)(q23) in 4, and del(6q) in 4. Adults had a higher incidence of t(9;22) and t(1;19) but a lower incidence of t(4;11) and hyperdiploid greater than 50 karyotype than children. A significant difference was also noted in white blood cell (WBC) count among various karyotypic groups. Patients with chromosomal abnormalities t(9;22), t(1;19), t(4;11) and del(11) (q23) had a shorter complete remission duration as compared with patients free of these abnormalities. Immunophenotyping was performed on 69 patients. All patients with t(9;22), t(1;19), and t(4;11) had B-lineage ALL restricted to certain stages of maturation: groups III and IV, groups IV and V, and group II, respectively (according to the classification of Foon and Tood). Among patients with t(9;22), t(4;11), and del(11)(q23), which have been considered to be associated with acute mixed-lineage leukemia, one each, respectively, showed myeloid antigen expression on the leukemic blasts (My+ ALL). No cross-lineage rearrangements of immunoglobulin (Ig) or T-cell receptor (TCR) genes were detected in these karyotypic subgroups of patients who underwent gene analysis.     

A myelodysplastic syndrome with marrow eosinophilia terminating in acute nonlymphocytic leukemia, associated with an abnormal chromosome 16

A patient presented with a myelodysplastic syndrome and bone marrow eosinophilia that evolved six months later into an acute nonlymphocytic leukemia (ANLL). Cytogenetic analyses of the bone marrow revealed 86% of the metaphases with 45,X-Y,inv(16)(p13;q22),t(11;17) (q11;q25),del(21)(q13) and 14% of the metaphases with the same abnormalities but with a Y chromosome. The association of ANLL, bone marrow eosinophilia, and abnormal chromosome 16 has previously been reported and has been suggested to have a favorable prognosis. Our patient is unique in that ANLL was preceded by a preleukemic phase associated with bone marrow eosinophilia. When complete remission was achieved, the bone marrow cytogenetics returned to normal, and the eosinophilia disappeared.     

Translocation (2;8)(p12;q24) associated with a cryptic t(12;21)(p13;q22) TEL/AML1 gene rearrangement in a child with acute lymphoblastic leukemia

We report a case of childhood acute lymphoblastic leukemia with the simultaneous occurrence of a t(2;8)(p12;q24) typically associated with mature B cell or Burkitt leukemia, and a t(12;21)(p13;q22) exclusively associated with pre-B cell ALL. The lymphoblasts were characterized as L2 morphology by the French-American-British classification. However, there were atypical morphologic findings for L2 ALL, including vacuolization in some cells. The lymphoblasts were periodic acid-Schiff positive and myeloperoxidase negative. Immunophenotypic analysis revealed that the majority of lymphoblasts were TdT+, CD10+, CD19+, CD20-, and cytoplasmic mu+. These features were consistent with an immature pre-B cell leukemia phenotype with some characteristics of a mature B-cell leukemia. A t(2;8)(p12;q24)(p12;q24), characteristic of mature B-cell leukemia or Burkitt type leukemia, was detected by conventional cytogenetics with no other cytogenetic abnormalities. However, diagnostic peripheral blood and bone marrow specimens demonstrated simultaneous occurrence of a cryptic t(12;21)(p13;q22) by both FISH and RT-PCR. The simultaneous occurrence of these translocations in a pediatric patient have implications for the pathogenesis of leukemias with t(2;8)(p12;q24) as well as t(12;21)(p12;q22). Analysis of additional cases of leukemia with translocations involving the MYC locus on 8q24 will be required to determine the frequency of association with the cryptic t(12;21)(p13;22), and the prognostic significance of the simultaneous occurrence of the translocations.     

Different distribution of NOTCH1 mutations in chronic lymphocytic leukemia with isolated trisomy 12 or associated with other chromosomal alterations

Chronic lymphocytic leukemia (CLL) is the most common leukemia among adults in Western countries. Chromosomal abnormalities commonly found using conventional cytogenetics and FISH are del(11)(q22-23), trisomy 12, del(13)(q14), and del(17)(p13). Trisomy 12 is the most frequent numerical abnormality in CLL. It can appear isolated or associated with other chromosomal aberrations, including t(14;18)(q32;q21) and trisomy 18. The aim of this study was to determine whether CLL patients with isolated trisomy 12 or associated with other chromosomal alterations have different clinico-pathological features, including a different distribution NOTCH1 mutation. Patients were classified into four groups: Group 1, isolated trisomy 12 (n=14); Group 2, trisomy 12 plus trisomy 18 (n=4); Group 3, trisomy 12 plus t(14;18) (n=8); and Group 4: patients with trisomy 12 plus other abnormalities not involving BCL2 (n=28). The Binet stage and expression of ZAP70 were significantly different among cytogenetic groups. NOTCH1 mutations were detected in 6/12 (50%) patients from Group 1, 4/25 (16%) patients from Group 4, and in no patient from groups 2 and 3 (P=0.020). Patients in Group 2 had a more rapid disease progression (median Treatment-free Survival 2 months) as against patients from Groups 1 (50 months), 3 (69 months), or 4 (68 months; P=0.001). These findings indicate that the distribution of NOTCH1 mutations in CLL with trisomy 12 is heterogeneous and that the presence of additional chromosomal abnormalities such as trisomy 18 could change the prognosis of these patients.     

Cytogenetic aberrations in adult acute lymphocytic leukemia: optimal technique may influence the results.

The aim of the present study was to analyse the distribution of cytogenetic aberrations in adult ALL in a population based material and compare the results with literature data. Forty-one patients were diagnosed during a 12-year period. The age varied between 14 and 82 (mean 37, median 32). Thirty-two patients were cytogenetically investigated and in all cases analysable metaphases were obtained (range 10-29, mean 24, median 25, success rate: 100%). Nine (28%) patients had a T-phenotype and 23 (72%) had a pre-B phenotype. High hyperdiploidy was found in four patients (13%). Hypodiploidy was found in 5 patients (16%), 10 (31%) had a pseudodiploid chromosome mode and four (13%) showed low hyperdiploidy (chromosome mode 47-51). Chromosomes 10 and 18 were most frequently involved in numerical aberrations. Structural aberrations most frequently involved chromosomes 6, 9 and 22. t(9;22) was seen in six cases (19%), del(6q) in five cases (16%) and der(9p) in five cases (16%). High hyperdiploid clones, which are associated with a favorable prognosis, were found with the same frequency as in other studies. The frequency of t(9;22) was 19% in our study, others have found frequencies between 11% and 30%. Compared to previously published studies our patients with t(9;22) were younger. Furthermore, those with del(6q) were older, showing a median age equivalent to the patient group as a whole. The differences between our data and previously published studies may be explained by population-based derived data and especially by an optimal technique in obtaining metaphases.     

A diminutive chromosome 21 centromere in acute lymphoblastic leukemia

A chance observation of a tiny constitutional variant for the centromere of chromosome 21 in two patients with acute lymphoblastic leukemia (ALL), suggested a possible correlation with the cytogenetic findings in their leukemic cells. Interphase FISH revealed three 13/21 centromeric signals and a single MLL signal in the blast cells of each patient. Metaphase FISH with dual-color application of whole-chromosome paint (wcp) and centromeric probes for chromosome 21 showed two copies of chromosome 21, one with a tiny centromeric signal which corresponded to the invisible centromere in the interphase cells. Patient 2700 had a normal karyotype in his bone marrow at diagnosis. All metaphases from his stimulated peripheral blood also had the tiny chromosome 21 centromere, proving it to be a constitutional variant. Patient 3314 showed the abnormal karyotype 46,XY,inv(1)(p?q?),del(11)(q?),del(12)(p?),inc in his bone marrow. Interphase FISH revealed only one copy each of the ABL and ETV6 genes, in addition to the loss of the MLL signal. The question arises, is there an association between the diminutive centromeric signals for chromosome 21 and the chromosomal instability demonstrated by the deletions of key genes from the leukemic blasts of these two patients?     

Isodicentric 20q- in two cases of B-cell acute lymphocytic leukemia with the respective t(9;20)(p11;q11.2) and t(9;22)(q34;q11.2)

The cytogenetic anomaly der(20)del(20)(q11.2q13.3)idic(20)(p11), or idic(20q-) in short form, has been reported in 13 cases of myelodysplastic syndrome, one case of chronic myelomonocytic leukemia, and one case of acute myeloid leukemia since 2004. To our knowledge, it has not previously been described in lymphoid diseases. Here we report the cases of two patients with B-cell acute lymphocytic leukemia (ALL) having a novel idic(20q-). One was a 34-year-old man with B-cell ALL whose leukemic cells at presentation had a karyotype of 45,XY,dic(9;20)(p11;q11.2); at relapse, a small marker chromosome was found coexisting with the dic(9;20). The other was a 39-year-old woman with Ph-positive B-cell-ALL whose leukemic cells contained both t(9;22)(q34;q11.2) and a small marker chromosome. A series of FISH analyses using the appropriate probes revealed the small marker chromosome in both patients to be an idic(20q-), confirming the dic(9;20)(p11;q11.2) in one case and revealing a BCR/ABL fusion gene in the other. One patient achieved complete remission but relapsed; the other did not achieve complete remission. Both patients died with a short survival time, despite receiving intensive chemotherapy. These two cases show that idic(20q-) can appear not only in myeloid diseases but also in lymphoid diseases.     

Cytogenetics of agnogenic myeloid metaplasia: a study of 61 patients

Agnogenic myeloid metaplasia (AMM) or idiopathic myelofibrosis is a chronic myeloproliferative disorder characterized by fibrotic bone marrow, extramedullar haematopoiesis, and a leukoerythroblastic picture in circulating blood. The cytogenetic data on AMM are scanty and no recurring chromosome abnormality has been associated with the natural course of this disease. Trisomy 1q, del(13q), del(20q), and trisomy 8, appear in about two thirds of patients with demonstrable chromosome aberrations. We report on the cytogenetic analyses of 61 consecutive patients with AMM studied at diagnosis. The metaphases could not be found in 10/61 (16.4%) patients, and chromosome studies were successful in 51 patients. Twenty-one patients (41%) had an abnormal clone, whereas 30 (59%) patients had a normal karyotype. Most frequent pathological findings included trisomy 8 (either alone or within a complex karyotype) in five patients, aberrations of chromosome 12 (translocation in two, monosomy in two, and trisomy in one patient), and aberrations of chromosome 20 (interstitial deletion in two, monosomy in two, and trisomy in one patient). We also detected aberrations of chromosome 13 (translocation in two and an interstitial deletion and trisomy in one patient each) and chromosome 18 (derivative 18 in two patients and a monosomy and deletion in one patient each). Three patients exhibited complex aberrations involving several chromosomes, sometimes with a mosaicisam. A near-tetraploid karyotype was observed in a single patient. Balanced translocations [t(2;16)(q31;q24), t(5;13)(q13;q32), t(12;13)(p12;q13), and t(12;16)(q24;q24)] were present in four patients. While the series of patients studied displayed chromosomal aberrations that are frequently observed in AMM, we found some new abnormalities (balanced translocations and polyploidy) that are rarely observed in AMM.     

t(2;14)(p13;q32): a recurring abnormality in lymphocytic leukemia. A Pediatric Oncology Group study.

Chromosome banding studies of 1,411 children with newly diagnosed acute lymphocytic leukemia (ALL) identified two patients with the t(2;14)(p13;q32) chromosome abnormality and a third patient with a complex three-way translocation involving the same breakpoints on chromosomes 2 and 14 but also involving chromosome 12 at band q11. The three cases demonstrated variability of immunophenotypes: one was a T-cell ALL, and two were early pre-B ALLs. All three patients achieved complete remissions and have remained in remission for 14-19 months.     

Reciprocal translocation (11;19)(q23;p13) in congenital acute lymphoblastic leukemia

The cytogenetic, clinical, and immunologic findings ina 4-month-old girl with acute lymphoblastic leukemia (ALL) are reported. The malignant lymphoblasts were characterized cytogenetically by the reciprocal translocation t(11;19)(q23;p13); immunologically by an immature pre-B-ALL phenotype. In spite of the high-risk nature of the leukemia, the patient attained complete remission relatively quickly and is still free of disease 3 years after diagnosis. Because the only two previously reported ALL patients with t(11;19) also seem to have responded well to therapy, this cytogenetic abnormality might turn out to be an indicator of favorable prognosis in ALL.     

11q23 abnormalities in children with acute nonlymphocytic leukemia (M4-M5). Association with previous chemotherapy

Cytogenetic studies of 12 patients aged less than 14 years with acute nonlymphoblastic leukemia (ANLL) (M4-M5) showed structural abnormalities on chromosome 11 at band q23-q24 in five cases (41.8%). Four of these 12 patients had ANLL (M4-M5) after treatment with cytostatics for non-Hodgkin lymphoma in one case and for an acute lymphoblastic leukemia (ALL) in the other three. Three of these four cases had 11q23 abnormalities [one [one 46,XY,t(11;17)(q23;25); another 47,XY,+8,-15,del(11)(q23),+der(15)t(15;?)(p11;?); the third 47,XX,+8,t(3;17) (p11;q25),t(4;11)(q21;q23)] and one had a normal karyotype on being diagnosed ANLL (M4-M5). The notable increase of ANLL (M4-M5) in our patients who had received cytostatics as treatment for a previous neoplasia makes evaluation of our results timely in comparison with those of other groups who use these therapeutic protocols.     

Isolated del(14)(q21) in a case of precursor B-cell acute lymphoblastic leukemia

We present a case of del(14)(q21) as a sole abnormality in a 4-year-old boy diagnosed with precursor B-cell acute lymphoblastic leukemia (pre-B ALL). To our knowledge, this is the first case of isolated del(14)(q21) in pre-B ALL. Two pretreatment bone marrow samples obtained 5 days apart were analyzed by cytogenetics. The G-banded karyotypes of the two samples were similar, differing only in the ratio of normal/abnormal metaphases detected. Both samples showed a del(14)(q21) as the only abnormality. Fluorescence in situ hybridization performed using the probes TEL/AML1 and immunoglobulin heavy chain (IGH) showed no fusion involving the TEL and AML1 genes and only a single IGH signal in 20% of the interphase cells analyzed.