Partial chromosome 21 amplification in a child with acute lymphoblastic leukemia

Constitutional abnormalities of chromosome 21 predispose to iAMP21-acute lymphoblastic leukaemia

In addition to Down syndrome, individuals with other constitutional abnormalities of chromosome 21 have an increased risk of developing childhood acute lymphoblastic leukaemia (ALL). Specifically, carriers of the Robertsonian translocation between chromosomes 15 and 21, rob(15;21) (q10; q10)c, have ∼2,700 increased risk of developing ALL with iAMP21 (intrachromosomal amplification of chromosome 21). In these patients, chromosome 15 as well as chromosome 21 is involved in the formation of iAMP21, referred to here as der(21)(15;21). Individuals with constitutional ring chromosomes involving chromosome 21, r(21)c, are also predisposed to iAMP21-ALL, involving the same series of mutational processes as seen in sporadic- and der(21)(15;21)-iAMP21 ALL. Evidence is accumulating that the dicentric nature of the Robertsonian and ring chromosome is the initiating factor in the formation of the complex iAMP21 structure. Unravelling these intriguing predispositions to iAMP21-ALL may provide insight into how other complex rearrangements arise in cancer.

An international study of intrachromosomal amplification of chromosome 21 (iAMP21): cytogenetic characterization and outcome

Intrachromosomal amplification of chromosome 21 (iAMP21) defines a distinct cytogenetic subgroup of childhood B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). To date, fluorescence in situ hybridisation (FISH), with probes specific for the RUNX1 gene, provides the only reliable detection method (five or more RUNX1 signals per cell). Patients with iAMP21 are older (median age 9 years) with a low white cell count. Previously, we demonstrated a high relapse risk when these patients were treated as standard risk. Recent studies have shown improved outcome on intensive therapy. In view of these treatment implications, accurate identification is essential. Here we have studied the cytogenetics and outcome of 530 iAMP21 patients that highlighted the association of specific secondary chromosomal and genetic changes with iAMP21 to assist in diagnosis, including the gain of chromosome X, loss or deletion of chromosome 7, ETV6 and RB1 deletions. These iAMP21 patients when treated as high risk showed the same improved outcome as those in trial-based studies regardless of the backbone chemotherapy regimen given. This study reinforces the importance of intensified treatment to reduce the risk of relapse in iAMP21 patients. This now well-defined patient subgroup should be recognised by World Health Organisation (WHO) as a distinct entity of BCP-ALL.

Pediatric B-lymphoblastic leukemia with RUNX1 amplification: clinicopathologic study of eight cases

B-lymphoblastic leukemia (a.k.a. precursor B-cell acute lymphoblastic leukemia) is a heterogeneous disease at the clinical, morphologic, immunophenotypic and genetic levels. Recurrent genetic abnormalities in B-lymphoblastic leukemia with prognostic significance are well known and specifically delineated in the WHO 2008 classification (eg hyperdiploidy, t(9;22)(q34;q11.2); BCR-ABL1, t(12;21)(p13;q22); ETV6-RUNX1). In recent years, a subgroup of B-lymphoblastic leukemia with the recurring genetic alteration of RUNX1 amplification has emerged. This subgroup has a low incidence (2%) and an increased risk of relapse and overall worse outcome. Given these apparently distinctive clinicopathologic features, we evaluated eight cases of pediatric B-lymphoblastic leukemia with RUNX1 amplification treated on Children's Oncology Group protocols from 2000-2009. Compared with 25 consecutive B-lymphoblastic leukemia cases without RUNX1 amplification, we identified a trend toward male predominance (P-value=0.082) and low white blood cell count at presentation (P-value=0.081) in B-lymphoblastic leukemia with RUNX1 amplification. Older age at presentation was significant (median age 9.5 years, P-value=0.006). There was no significant difference in the presence of central nervous system disease, CD20 or myeloid antigen positivity on the blasts or percent circulating blasts in B-lymphoblastic leukemia with RUNX1 amplification versus other B-lymphoblastic leukemia types. Seven of eight patients (88%) are alive and free of disease at the time of last checkup (mean 50 months, range 14-116 months). Although we see a relatively good outcome in our small cohort of patients, recent findings from the Children's Oncology Group on a large set of patients suggests otherwise that these patients may have an inferior outcome compared with patients with B-lymphoblastic leukemia without RUNX1 amplification. Long-term follow-up in larger cohorts including minimal residual disease correlation is required.

Intrachromosomal amplification of chromosome 21 (iAMP21) may arise from a breakage-fusion-bridge cycle

Intrachromosomal amplification of chromosome 21 (iAMP21), involving amplification of the RUNX1 gene and duplication of chromosome 21, dup(21q), defines a new cytogenetic subgroup in B-lineage acute lymphoblastic leukemia (ALL) with a poor prognosis. Characterization of this abnormality has become vital to ensure that the most accurate detection method is used. We have previously defined common regions of amplification and deletion of chromosome 21 in these patients, although the level and extent of amplification within the amplicon was highly variable. This study, using interphase fluorescence in situ hybridization (FISH) with chromosome 21 locus specific probes, substantiated these findings in a large series of patients and confirmed that the amplicon always included RUNX1. Thus, FISH with probes directed to the RUNX1 gene remains the most reliable detection method. Metaphase FISH, supported by G- and multiple color chromosomal banding (mBAND) revealed the patient specific morphology and genetic profile of the dup(21q) chromosomes, as well as the complexity of the intrachromosomal changes giving rise to them. These findings suggested that iAMP21 had arisen from a breakage-fusion-bridge cycle: a mechanism previously described in tumors, which we report for the first time in ALL.

A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera

Myeloproliferative disorders are clonal haematopoietic stem cell malignancies characterized by independency or hypersensitivity of haematopoietic progenitors to numerous cytokines. The molecular basis of most myeloproliferative disorders is unknown. On the basis of the model of chronic myeloid leukaemia, it is expected that a constitutive tyrosine kinase activity could be at the origin of these diseases. Polycythaemia vera is an acquired myeloproliferative disorder, characterized by the presence of polycythaemia diversely associated with thrombocytosis, leukocytosis and splenomegaly. Polycythaemia vera progenitors are hypersensitive to erythropoietin and other cytokines. Here, we describe a clonal and recurrent mutation in the JH2 pseudo-kinase domain of the Janus kinase 2 (JAK2) gene in most (> 80%) polycythaemia vera patients. The mutation, a valine-to-phenylalanine substitution at amino acid position 617, leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity and induces erythrocytosis in a mouse model. As this mutation is also found in other myeloproliferative disorders, this unique mutation will permit a new molecular classification of these disorders and novel therapeutical approaches.

Establishment and characterization of a new human erythroleukemic cell line, ERY-1

The growth factor-independent erythroleukemic cell line ERY-1 was established from the peripheral blood of a 87-year-old woman with chronic myeloid leukemia (CML) in the acute phase. Immunophenotyping showed that fresh leukemic cells were positive for CD13, CD33, CD36 and CD235a (glycophorin A), a phenotype compatible with that of erythroblastic cells. Cytogenetic and fluorescence in situ hybridization (FISH) analysis demonstrated classical t(9;22)(q34;q11) chromosomic translocation associated with a duplication of the BCR-ABL fusion gene. Other cytogenetic abnormalities were detected in all analyzed mitosis, the most frequent being a trisomy of chromosome 8. The established ERY-1 cell line retains these immunophenotypic and cytogenetic features, and light and electron microscopy confirmed the relatively mature erythroblastic phenotype of the cells. In addition, ERY-1 cell line expressed beta-globin mRNA and a non-phosphorylable form of the erythropoietin receptor, even in presence of erythropoietin. Of note, the proliferation of ERY-1 cells was inhibited by TGFbeta1 or STI-571 (Gleevec), without significant induction of further differentiation. In conclusion, ERY-1 is a new growth factor-independent human erythroleukemic cell line with a relatively mature phenotype that may be useful to study the molecular events involved in erythroblastic differentiation.

Cryptic translocations involving chromosome 20 in polycythemia vera

A systematic cytogenetic study was performed in 49 patients with polycythemia vera (PV) in order to investigate the occurrence of subtelomeric rearrangements of chromosome 20, the most frequently rearranged chromosome in this myeloproliferative disorder. Partial deletion of the long arm of chromosome 20 was observed in two patients and two cryptic translocations, t(1;20)(p36;q13) and t(18;20)(p11;q13) in two others, all previously treated. The localization of the breakpoints of the translocated 20 chromosomes was different in the two translocations, as shown by fluorescence in situ hybridization (FISH) to metaphase chromosomes using BAC clones. Although infrequent (2/49), cryptic translocations of chromosome 20 deserve to be detected as preliminary to identification of molecular defects in PV.

ABL oncogene amplification with p16(INK4a) gene deletion in precursor T-cell acute lymphoblastic leukemia/lymphoma: report of the first case

Gene amplification is a relatively rare event in hematologic malignancies. The ABL gene on chromosome band 9q34 is a proto-oncogene and is the well-known translocation partner of the BCR gene on 22q11 giving rise to t(9;22)(q34;q11), which is the hallmark of chronic myeloid leukemia and is the most common chromosomal abnormality in adult acute lymphoblastic leukemia (ALL). Amplification of ABL is an exceedingly rare event, with only less than 5 cases reported in the literature. The p16(INK4a) (or CDKN2A) gene on 9p21 is a tumor suppressor gene, and deletion thereof is recently recognized as one of the most common genetic abnormalities in ALL. The authors herein describe an 8-year-old male patient with precursor T-cell ALL harboring both ABL gene amplification and p16(INK4a) gene deletion. Fluorescence in situ hybridization (FISH) analysis using BCR/ABL probes revealed five or more ABL signals, indicating amplification in 51.5% of interphase nuclei. FISH using p16(INK4a) gene probes showed heterozygous p16(INK4a) deletion in 71.0%. On conventional cytogenetic analysis, however, only 10 metaphases were available, which showed the normal karyotype, 46,XY[10], serving no evidence for the findings on FISH. This is the first report of an ALL case with ABL amplification, and the authors speculate that both ABL proto-oncogene amplification and the p16(INK4a) tumor suppressor gene deletion have been implicated in leukemogenesis in the present case, although whether the ABL amplification truly contributes to the leukemogenesis or merely an epiphenomenon representing underlying genomic instability remains to be determined.

[Cytogenetic abnormalities in acute lymphoblastic leukemia]

Acute lymphoblastic leukemias (ALL) represent malignant clonal proliferations of stem cells committed in lymphoid differentiation, B or T-cell ALL. Clonal chromosomal abnormalities are found in 80% children and 70% adult cases. They are associated with an independent prognostic value which modifies the therapeutic approach and therefore karyotyping at diagnosis is mandatory. Molecular techniques such as FISH and RT-PCR are very helpful too as cryptic chromosomal abnormalities have been described. In this review, numerical and structural abnormalities are described: frequency, diagnosis and prognosis value as well as genes involved in structural abnormalities.

Amplification of AML1 on a duplicated chromosome 21 in acute lymphoblastic leukemia: a study of 20 cases

This study identifies multiple copies of the AML1 gene on a duplicated chromosome 21, dup(21), as a recurrent abnormality in acute lymphoblastic leukemia (ALL). Clusters of AML1 signals were visible at interphase by fluorescence in situ hybridization (FISH). In metaphase, they appeared tandemly duplicated on marker chromosomes of five distinct morphological types: large or small acrocentrics, metacentrics, submetacentrics or rings. The markers comprised only chromosome 21 material. Karyotypes were near-diploid and, besides dup(21), no other established chromosomal changes were observed. A total of 20 patients, 1.5 and <0.5% among consecutive series of childhood and adult ALL respectively, showed this phenomenon. Their median age was 9 years, white cell counts were low and all had a pre-B/common immunophenotype. Although this series is not the first report of this abnormality, it is the largest, permitting a detailed description of the variety of morphological forms that duplicated chromosome 21 can assume.

Identical abnormality of the short arm of chromosome 18 in two Philadelphia-positive chronic myelocytic leukemia patients with erythroblastic transformation, resulting in duplication of BCR-ABL1 fusion

Two patients with Ph-positive chronic myelocytic leukemia in erythroblastic transformation and rearrangement of the short arm of chromosome 18 are reported. Fluorescence in situ hybridization studies showed that the 18p rearrangement resulted from translocation of the main part of chromosome 22 long arm to 18p, including BCR-ABL1 fusion. The 18p abnormality resulted, thus, in loss of 18p and duplication of BCR-ABL1 in both patients. The possible relation to the erythroblastic type of blastic phase is briefly discussed. In addition an apparently intact germline ABL1 gene was duplicated and inserted into chromosome 6 at band p21 in one of these patients.

ETV6/AML1 fusion by FISH in adult acute lymphoblastic leukemia

Dual-color interphase fluorescence in situ hybridization (FISH) with ETV6 and AML1 probes was used for the first time on a series of 159 adult patients with acute lymphoblastic leukemia (ALL), for detection of the t(12;21)(p13;q22) translocation. Seven patients (4.4%) were found, with 50-100% of positive cells, of whom one of two tested, proved negative for the fusion product by RT-PCR. Two of them, aged 43 and 50 years, are the oldest patients so far confirmed to have the translocation. Three who relapsed at 10, 11 and 24 months, suggest that adults may not enjoy the good short-term prognosis reported for t(12;21)-positive children. Thirty-one-negative cases had signal numbers differing from the two expected for each gene. In 15 cases these results were consistent with the karyotype. In nine cases with uninformative cytogenetics, the numbers were consistent with those for centromeres and indicated a hidden aneuploidy. Loss of ETV6 genes in two cases and AML1 amplification in three others were not suspected from the cytogenetics. In conclusion, FISH proved to be reliable in defining ETV6/AML1 positivity in this group of patients as well as providing valuable insights into negative cases.

Pentasomy 21 with two isochromosomes 21 in a case of acute myeloid leukemia without maturation

Here, we report a 72-year-old male patient with acute myeloid leukemia (AML) without maturation. Cytogenetic study of a bone marrow culture revealed the following karyotype: 47,XX,+21,+i(21)(q10)x2. Fluorescence in situ hybridization study with a locus specific probe for 21q22 verified a pentasomy of 21q as a sole clonal cytogenetic abnormality. To our knowledge, this is the first report of pentasomy 21q in AML without Down syndrome.

Chromosome 21 abnormalities with AML1 amplification in acute lymphoblastic leukemia

Fluorescence in situ hybridization (FISH) studies were performed in three cases of acute lymphoblastic leukemia (ALL) with marker chromosomes to analyze the contribution of chromosome 21 in these markers. FISH with a chromosome 21 painting probe confirmed that chromosome 21 was involved in all three cases. FISH with YAC probes showed that the number of extra copies varied according to their location on chromosome 21. Attention was focused on the AML1 gene, which was present as five copies in most of the cells exhibiting the marker chromosomes. As controls, 11 cases of childhood ALL were studied with PAC probes covering AML1. The results agreed with the banded karyotypes in 10 patients. FISH uncovered a clone with four copies of AML1 which were only observed by FISH analysis of interphase nuclei in one patient. No point mutation was detected in exons 3-5, encoding the runt domain of AML1, in the three cases, suggesting an oncogenic role of wild-type AML1 amplification.

B-cell acute lymphoblastic leukemia with tandem t(14;14)(q11;q32)

Translocation (14;14)(q11;q32) was associated with acute lymphoblastic leukemia in a child. The B-cell lineage of the leukemic cells led us to perform FISH studies, which showed that the chromosomal breakpoints were telomeric to TCRA/D and IGH loci. These findings show that FISH analyses are necessary when unusual features are associated with a recurrent translocation.

Amplification of AML1 in childhood acute lymphoblastic leukemias

Amplification of AML1 has been confirmed by fluorescence in situ hybridization analysis in two cases of childhood acute lymphoblastic leukemia. It remains to be elucidated whether this amplification results in up-regulation of the normal AML1 gene product or a potentially mutant AML1 transcript.

Complex chromosome abnormality mimicking t(8;21)in an acute myeloblastic leukemia

A patient with acute myeloblastic leukemia (AML) and karyotypic abnormality mimicking t(8;21) is reported. Because of the uncommon morphology of blasts for AML with t(8;21), and absence of AML1-ETO fusion in the RT-PCR analysis, fluorescence in situ hybridization (FISH) was applied to precise the abnormality. FISH revealed a complex rearrangement involving chromosomes 7, 21 and 8, and involvement of the AML1 gene without evidence of AML1-ETO fusion. This case of unusual AML illustrates the necessity of collecting all hematologic, cytogenetic, and eventual FISH and RT-PCR data to analyse genetic rearrangements in leukemic patients.

A novel dicentric deleted chromosome 21 arising from tandem translocation

We present a 26-year-old patient with myelodysplastic syndrome (MDS). Initial bone marrow cytogenetics with G-banding showed a rearranged chromosome 21, which was dicentric and bisatellited on CBG- and NOR-banding. Fluorescence in situ hybridization helped to characterize the structure, using a whole chromosome 21 paint and the locus specific AML1 gene probe. The rearranged 21 consisted solely of chromosome 21 material, contained only one copy of AML1, and was not a trisomy, but a deleted tandem translocation. The MDS transformed to acute myeloid leukemia (AML), and the patient died almost 12 months post-diagnosis. Cytogenetics was performed three times during the course of the disease, and the dicentric chromosome 21 was present throughout. Although there are a number of published rearrangements of chromosome 21 in MDS and AML, most are isodicentrics. We could not find another case of an abnormal chromosome 21 with the same structure as reported here.

Microdissection and FISH investigations in acute myeloid leukemia: a step forward to full identification of complex karyotypic changes

Complex chromosomal rearrangements in malignant hemopathies frequently remain unclarified because of paucity of material for further fluorescence in situ hybridization analyses and/or lack of suitable probes. Chromosome microdissection (MD) can be an adequate approach to elucidate chromosome aberrations unrecognizable by conventional karyotyping. We applied MD in two patients with acute myeloid leukemia (AML) and unidentified chromosome changes at karyotype. Microdissection of a ring chromosome in an AML-M5 case revealed 21q polysomy. In an AML-M4 case, MD of an add(15p) disclosed a t(8;15) with over-representation of both 8q22 and 8q24 bands. YAC probes were helpful in showing duplication of the ETO gene at 8q22, and amplification of C-MYC, at 8q24.

Acute megakaryocytic leukaemia with acquired polysomy 21 and translocation t(1;21)

Cytogenetic study of a young child with acute megakaryocytic leukaemia (AML-M7) has shown a karyotype with 49-50 chromosomes with one and two acquired extra chromosomes 21. Fluorescence in situ hybridization detected a minor clone with translocation t(1;21) and loss of a part of chromosome band 1p36. Trisomy and polysomy 21 are not uncommon in AML-M7. A more systematic search for chromosome 21 rearrangements in AML-M7 using FISH techniques is proposed.

Isodicentric chromosome 21: a novel aberration in acute myeloid leukemia

We present here a 78-year-old female patient with acute myeloid leukemia (AML), French-American-British classification M2, exhibiting isodicentric chromosome 21, idic(21)(q22), at the time of diagnosis. The patient had three idic(21)(q22), besides the del(5)(q13q32), add(21)(q22), dic(21;22) (q22;q13), and +22. Fluorescence in situ hybridization studies with whole-chromosome painting and centromere-specific probes for chromosome 21 verified the diagnosis of idic(21)(q22). There were no distinct clinicohematological characteristics of AML with isodicentric 21. The patient was treated with remission-induction therapy followed by consolidation therapy. Two years later, the patient showed the disappearance of isodicentric 21 but retained del(5)(q13q32) and gained other chromosomal abnormalities, +add(17)(p11) and -16. To our knowledge, this is the first report of AML with acquired idic(21)(q22).

Acute lymphoblastic leukemia and chromosome 21

A short review of chromosome 21 abnormalities in acute lymphoblastic leukemia (ALL) is presented. Trisomy and polysomy 21 are nonrandom anomalies that are frequently observed in ALL. Their occurrence, although not specific, as well as the high incidence of acute leukemia in subjects with constitutional trisomy 21, suggests that chromosome 21 plays a particular role in leukemogenesis. More specific to ALL, t(12;21)(p13;q22), resulting in a fusion TEL-AML1, gene has recently been shown to be the most frequent translocation in childhood B-cell lineage ALL (20-30% of cases). In addition, the importance of analysis of marker chromosomes with fluorescence in situ hybridization (FISH) techniques is underscored as partial amplifications or rearrangements of chromosome 21 may be implicated.