Chromosome 7 abnormalities in children with Down syndrome and preleukemia

Transient abnormal myelopoiesis in a Down syndrome newborn followed by acute myeloid leukemia: identification of the same chromosomal abnormality in both stages

A transient abnormal myelopoiesis was observed in a newborn with Down syndrome. Cytogenetic study revealed multiple oligoclonal abnormalities: 47,XY,inv(6)(p23q21),+21c[3]/47,XY,der(7)t(1;7)(q25;p15),+21c[1]/47,XY,del(13)(q?),+21c[1]/47,XY,+21c[15]. Ten months after the patient achieved remission, the transient abnormal myelopoiesis evolved to an acute megakaryoblastic leukemia. Cytogenetic study revealed only a single clonal abnormality, 47,XY,der(7)t(1;7)(q25;p15),+21c, identical to one of the structural changes seen at birth. Sequence analysis of the GATA1 gene revealed a deletion-insertion mutation within the exon 2 introducing a stop codon after Arg 64. It may be that the der(7)t(1;7)(q25;p15) abnormality played some selective role in the development of acute megakaryoblastic leukemia in this patient. To our knowledge, the present case is unique in demonstrating a subclone with der(7)t(1;7)(q25;p15) evolving to acute leukemia.

Chromosome 7 abnormalities in acute megakaryoblastic leukemia associated with Down syndrome

A 2-year-old girl with Down syndrome (DS) developed acute megakaryoblastic leukemia (AMKL) following a transient myeloproliferative disorder (TMD). The blast cells showed an altered karyotype of 47,XX,r(7),+21c. Serial cytogenetic studies during the course of the illness showed rapid stepwise clonal chromosome changes, including a ring chromosome 7, associated with treatment refractoriness. We reviewed 10 published cases of Down syndrome-related AMKL (DS-AMKL) showing chromosome 7 abnormalities and found that these changes do not carry the same prognostic weight as for non-DS children. For DS-AMKL, therefore, other prognostic factors besides clonal cytogenetic changes need to be identified for planning optimal therapy.

A case of myelodysplastic syndrome with acquired monosomy 7 in a child with a constitutional t(1;19) and a mosaicism for trisomy 21

A 3-year-old patient presented with anemia, thrombocytopenia, and blasts in the peripheral blood. A bone marrow aspirate revealed a myelodysplastic syndrome (MDS). A mosaic abnormal female karyotype 46,XX, t(1;19)(q42; p13.1)c[12]/ 47,idem,+21c[3]/ 47,idem,-7,+21c,+mar[7] was obtained on G-banded metaphases from unstimulated bone marrow aspirate cell culture. To rule out constitutional abnormalities, we performed a cytogenetic analysis on the patient's phytohemagglutinin-stimulated peripheral blood and cultured skin fibroblasts. A karyotype of 46,XX,t(1;19) (q42;p13.1)c was found in all 20 peripheral lymphocytes analyzed, confirming the constitutional origin of the translocation. In addition, 5 out of 50 cells from two separate cultures of the skin fibroblasts contained an extra chromosome 21. The presence of two cell lines in multiple cultures indicates that the patient is a true low-level mosaic for trisomy 21. Because of the finding of monosomy 7 and a marker chromosome only in the trisomy 21 clone, we conclude that the leukemic clone arose from a hematopoietic precursor with constitutional trisomy 21. It is also possible that the t(1;19) played some role in the development of the MDS. Because acute myelogenous leukemia (AML) and MDS with Down syndrome (DS) have distinct biologic and clinical features, the identification of DS patients with a mild or normal phenotype in the AML/MDS population is of fundamental importance for clinical diagnosis and management.

Distinctive multidrug sensitivity and outcome of acute erythroblastic and megakaryoblastic leukemia in children with Down syndrome

We assessed the in vitro chemosensitivity of acute erythroblastic and megakaryoblastic leukemia cells from children with Down syndrome (DS) compared to non-DS children. We conducted in vitro tests using the MTT assay of bone marrow samples from 12 children with DS and 16 children without DS. Patients were newly diagnosed based on the morphology and expression of platelet-specific antigens. Induction failure occurred more frequently in the non-DS group (n = 4) than in the DS group (n = 0, P = .053). Children with DS had a superior event-free survival (EFS) probability of 0.750 at 4 years, compared to an EFS probability of 0.375 for non-DS children (P = .049). Blast cells from DS patients were significantly more sensitive to daunorubicin, melphalan, mitoxantrone, 4-hydroperoxy-cyclophosphamide, vincristine, etoposide, bleomycin, and pirarubicin than those from non-DS patients. Four of the 16 non-DS patients were found to have acquired an extra chromosome 21 in their leukemia cells: blasts from these patients also tended to have greater chemosensitivity than those from patients without an extra chromosome 21. Blast cells from DS patients are markedly sensitive to various drugs. These results suggest that the fragility of blast cells derived from DS patients may be related to an increased susceptibility to apoptosis.

Childhood myeloid leukaemias

Childhood myeloid leukaemias are a diverse collection of conditions. Although many are also seen in adults, some are peculiar to childhood. In childhood AML, as in adults, cytogenetic abnormalities are associated with specific clinical features and define prognostic groups. In infants under 1 year with AML, the incidence of 11q23 abnormalities is particularly high. The finding of identical 11q23 breakpoints in infant leukaemia as in therapy-related leukaemias suggests a role for in utero exposure to topoisomerase II inhibitors. There are a number of constitutional disorders that predispose children to develop AML, usually with a preceding myelodysplastic phase. Monosomy (or deletion of the long arm) of chromosome 7 is the most frequent chromosome abnormality in the bone marrow of such patients. Abnormalities of chromosome 7 are also common cytogenetic findings in all morphological subgroups of childhood myelodysplasia, either as a primary abnormality or associated with disease progression.

Childhood myeloproliferative disorders

Disorders classified as paediatric myeloproliferative disorders (MPD), such as juvenile chronic myeloid leukaemia (JCML), and as paediatric myelodysplastic syndrome (MDS), are essentially diseases characterized by abnormal myeloproliferation and they share similar genetic events on chromosome 7. As such, the abnormalities of increased myeloproliferation in childhood (AIMC) should be considered under the same heading. Constitutional and other genetic factors play an essential role in children and include the NF1 gene, whereas toxic exposure is of greater importance in adults. The most common cytogenetic alteration is that of monosomy or deletion of the long arm of chromosome 7. Critical regions have been identified and mapped by fluorescence in situ hybridization (FISH). It appears that the similar critical regions on chromosome 7 are involved, and suggests that these regions may contain genes important in the pathogenesis of AIMC.

Myelodysplastic syndrome after regression of transient abnormal myelopoiesis in a Down syndrome infant: different clonal origin?

A boy with Down syndrome who developed myelodysplastic syndrome after regression of transient abnormal myelopoiesis (TAM) is described. His blast cells in TAM had other chromosome abnormalities in addition to trisomy 21;50,XY,+21c,+12,+14,+21. Serial chromosome analysis in follow-up showed abnormal clones involving monosomy 7. Myelodysplastic syndrome was diagnosed. Because two clones had different karyotypes, they might have derived from different clones.

Monosomy 7 and 7q--associated with myeloid malignancy

An association between the complete or partial loss of chromosome 7 and preleukaemic myelodysplasia or acute myeloid leukaemia has been recognized from the early days of tumour cytogenetic analysis. Detection of such abnormalities usually heralds a poor prognosis. The loss of DNA on chromosome 7 has led to speculation that tumour-suppressor genes may play a significant role in this form of leukaemogenesis, although it may be part of a multistep process. A further association with leukaemia secondary to carcinogen exposure including previous chemotherapy or a number of congenital anaemias has increased the interest in discovering the gene or genes on chromosome 7. Banded chromosome analysis has suggested that there are two broad critical regions on the long arm of chromosome 7 at bands 7q22 and 7q34-q36 that may contain the relevant genes. Initial molecular analysis has confirmed these two regions to be of significance. The advent of fluorescence in-situ hybridization techniques has facilitated some definition of the 7q22 region, with identification of candidate genes for further functional analysis. It is becoming clear that there will be more than one gene on chromosome 7 involved in the leukaemic process and with the definition of these genes it may be possible to look for associations with different phenotypes and prognosis. As for the reason for chromosome 7 showing a particular predisposition to total or partial loss we may speculate that the DNA sequence and structure may confer a 'fragility' on the chromosome. A greater understanding of the DNA structure of the long arm may provide real insight into the mechanisms of leukaemia. We would like to speculate in the long term that this could lead to the ability to screen for leukaemia susceptibility and avoidance of 'inducers' in those at risk.

Chromosome 7 and Haematological Malignancies

Abnormalities of chromosome 7 are the most common clonal chromosomal changes observed in myelodysplasia (MDS) and the second most frequent in acute myeloid leukaemia (AML) [1-5]. These changes may consist of long arm deletion (7q-) or total loss of the whole chromosome (monosomy 7) from bone marrow cells [1, 4, 6-24] and was first reported in association with myeloid disease in 1964 with the report of 3 cases of refractory anaemia, granulocytic hyperplasia [25]. The association between chromosome 7 alterations, MDS and AML in children and adults is clear, however, a rare association with lymphoid malignancies has also been recently reported. The abnormalities may occur in de novo MDS/AML, secondary cases following exposure to drugs, radiotherapy and toxins and in addition in a range of constitutional disorders including Fanconi's anaemia, congenital neutropenia and neurofibromatosis type 1 (NF1). The broad spread of conditions in which this consistent genetic change can occur leads one to speculate that there is an underlying instability in chromosome 7 and that genes on this chromosome play a role in the development of malignancy. The loss of DNA associated with malignant progression suggests the presence of a tumour suppressor gene (or genes) [26, 27]. Patients with monosomy 7 usually present as classical MDS with abnormal erythroid, megakaryocyte and myeloid differentiation [7, 28]. From a mechanistic perspective, increased cell proliferation and apoptosis is a common feature possibly induced by the failure of normal haematopoietic maturation. In all groups the presence of chromosome 7 abnormalities defines a poor prognostic group [29]. The majority of patients with MDS transform to a form of acute leukaemia resistant to therapy, including bone marrow transplantation (BMT). Although fluorescence in situ hybridization (FISH) has accelerated the study of these disorders at the cytogenetic and molecular levels, [4, 30, 31, 32, 33] no gene has been clearly implicated. A few candidate genes are under investigation. While the loss of chromsome 7 material is crutial in the malignant process it is almost certainly not the primary molecular abnormality. An initiating event genetic event predisposing to chromosome breakage and loss probably occurs in haematopoietic cells permitting chromosome 7 loss and progression to clonal malignancy as a secondary event.

Involvement of 11p15 and 3q21q26 in therapy-related myeloid leukemia (t-ML) in children. Case reports and review of the literature

The cytogenetic findings of therapy-related myeloid leukemia (t-ML) in three children are presented. These included one male patient with acute lymphoblastic leukemia (ALL) who underwent bone marrow transplantation and developed therapy-related myeloproliferative disease (t-MPD) in the female-donor hematopoietic cells 2.5 years after receiving radiation and epipodophyllotoxin therapy for ALL testicular relapse. Bone marrow leukemic cell karyotype revealed 46,XX,add (11)(p15) and a normal female karyotype in the peripheral blood lymphocytes. The other two children, one with ALL and one with ganglioneuroblastoma, developed fatal t-MPD and therapy-related acute myeloblastic leukemia (t-AML) preceded by myelodysplastic syndrome (t-MDS), respectively, 5 years after diagnosis, following administration of alkylating agents and irradiation. Monosomy 7 was present in both, and was combined with inv(3)(q21q26) in the second patient. Our review of the cytogenetic findings in 91 previously reported pediatric patients with t-ML suggested that the involvement of 11p15 and 3q21-->23, 3q24-q26 with or without a combination of translocation 11q23 and -7/7q-, respectively, are nonrandom aberrations of t-ML in children. Comparison of the chromosomal changes in t-ML between the pediatric and an adult series revealed some differences which may result from differences in treatment modalities and which, in addition, may indicate a possible role of genetic and/or age-dependent factors in the pathogenesis of therapy-related leukemogenesis in children.

Review of the cytogenetic changes in acute megakaryoblastic leukemia: one disease or several?

The karyotypes of 116 cases of acute megakaryoblastic leukemia (AMKL) were reviewed, including 43 pediatric patients with Down syndrome (DS) and 73 non-DS patients. DS patients with AMKL often had a history of transient leukemia or myelodysplasia with an early age of onset of AMKL (median 23 months). In these patients, the frequency of additional cytogenetic change (numerical or structural) was low, with 10 of the 43 DS patients showing no additional cytogenetic change. A second group of patients had t(1;22)(p13;q13) or other cytogenetic abnormality involving 22q13. These patients had no history of transient leukemia but showed very early onset of AMKL. In this group of patients, marked organomegaly was noted; these patients also showed few specific additional cytogenetic changes. The remaining AMKL patients had a median age of 30 years with much more frequent cytogenetic changes, including rearrangement of 3q21 and 3q26-27, trisomy 21, and other specific changes. Based on the karyotype and clinical data, we hypothesize that AMKL may represent at least three separate disease entities with different genetic alterations giving rise to similar, but not identical, disorders. Subclassification of AMKL on the basis of the cytogenetic changes in the leukemic cells appears to be justified.

Karyotypic analysis in primary myelodysplastic syndromes

Cytogenetics has provided new insights into the biology and pathogenesis of myelodysplastic syndromes. In patients with refractory anemia, it has provided proof of clonality and has helped differentiate chronic myelomonocytic leukemia from chronic myeloid leukemia. As a prognostic tool, cytogenetics has been predictive of duration of survival and leukemic transformation. However, its role as an independent prognostic factor compared with recent prognostic scoring systems remains to be determined. New techniques such as fluorescent in situ hybridization using chromosome-specific DNA probes may expand the usefulness of cytogenetics. The prognostic impact of cytogenetics may not be fully realized until more effective treatments become available.