Leukemia in a trisomy 21 mosaic: specific involvement of the trisomic cells

Syndromic thrombocytopenia and predisposition to acute myelogenous leukemia caused by constitutional microdeletions on chromosome 21q

Several lines of evidence support the presence of dosage-sensitive genes on chromosome 21 that regulate leukemogenesis and hematopoiesis. We report a detailed clinical and molecular characterization of 3 patients with chronic thrombocytopenia caused by distinct constitutional microdeletions involving chromosomal region 21q22.12. The patients exhibited growth restriction, dysmorphic features, and developmental delays. One patient developed acute myelogenous leukemia (AML) at 6 years of age. All 3 deletions included the RUNX1, CLIC6, DSCR, and KCNE1 genes. Our data provide additional support for the role of RUNX1 haploinsufficiency in megakaryopoiesis and predisposition to AML. The leukemic clone had trisomy 21 resulting from duplication of chromosome 21 containing the RUNX1 deletion. This shows that genes other than RUNX1 must also play a role in AML associated with trisomy 21. We recommend that children with syndromic thrombocytopenia have clinical array-comparative genomic hybridization analysis and appropriate cytogenetic studies to facilitate our ability to provide a definitive diagnosis.

Trisomy 21 in neoplastic cells

Trisomy 21 as an acquired clonal chromosome change has been described in 642 of the 10,625 human neoplasms with chromosome aberrations known from the cytogenetic literature. A total of 590 of the 642 cases (92%) are hematologic disorders and malignant lymphomas. The incidence of trisomy 21 is similar (4.1%-6.7%) in acute myeloid leukemia (AML), chronic myeloid leukemia, myeloproliferative disorders, myelodysplastic syndromes, chronic lymphoproliferative disorders, and malignant lymphomas; it is substantially higher (14.8%) in acute lymphocytic leukemia (ALL). In most cases, the extra chromosome 21 is present together with other numerical and/or structural changes. Acquired trisomy 21 is the only karyotypic abnormality in only 0.4%. Trisomy 21 has never been reported as the sole anomaly in a solid tumor. The cytogenetic literature contains information on 62 patients with constitutional trisomy 21 and a malignant disorder in which the tumor cells have been analyzed by banding techniques. Thirty-four of the 62 patients had AML, 16 had ALL, and 2 had acute undifferentiated leukemia. The 52 leukemic Down syndrome (DS) cases account for 1.4% of the total acute leukemias, an overrepresentation that parallels the generally increased risk of leukemia development in DS. Sixty-three percent of the ALL patients and 79% of those with AML had additional changes superimposed on constitutional trisomy 21. These included several of the characteristic primary leukemia-associated aberrations: 5q-, 7q-, +8, and t(8;21) in AML, and t(1;19), t(4;11), 6q-, and 14q + in ALL. Thus, it seems that the pattern of acquired karyotypic changes is similar in patients with DS and in individuals with a normal constitutional karyotype.

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.

Duplication of 1q in a child with down syndrome and myelodysplastic syndrome

Cytogenetic analysis of bone marrow cells was performed on a 2-year-old African-American male with Down syndrome (DS) and myelodysplastic syndrome (MDS), specifically refractory anemia with excess blasts in transformation (RAEB-T). Chromosome analysis showed, in addition to the constitutional trisomy 21, a trisomy of chromosome 11 and a dup(1)(q23q31). This duplication of 1q is apparently a new chromosomal abnormality in a child with MDS. Partial trisomy of the long arm of chromosome 1 has been reported by several authors and appears to represent a nonrandom chromosomal anomaly in patients with MDS/acute myelogenous leukemia and DS.

Risks of leukaemia and solid tumours in individuals with Down's syndrome

BACKGROUND

Individuals with Down's syndrome have a greater risk of leukaemia than the general population, but reliable estimates of the age-specific risk are lacking and little is known about the risk of solid tumours.

METHODS

We identified 2814 individuals with Down's syndrome from the Danish Cytogenetic Register, and linked the data to the Danish Cancer Registry. The number of person-years at risk was 48453. Standardised incidence ratio (SIR) and 95% CI were calculated of the basis of cancer rates specific for age and sex in the general population.

FINDINGS

60 cases of cancer were found, with 49.8 expected (SIR 1.20 [95% CI 0.92-1.55]). Leukaemia constituted 60% of cases of malignant disease overall and 97% of cases in children. The SIR for leukaemia varied with age, being 56 (38-81) at age 0-4 years and 10 (4-20) at 5-29 years. No cases of leukaemia were seen after the age of 29 years. The SIR for acute myeloid leukaemia was 3.8 (1.7-8.4) times higher than that for acute lymphoblastic leukaemia in children aged 0-4 years. The cumulative risk for leukaemia by the age of 5 years was 2.1% and that by 30 years was 2.7%. Only 24 solid tumours were seen, with 47.8 expected (0.50 [0.32-0.75]). No cases of breast cancer were found, with 7.3 expected (p=0.0007). Higher than expected numbers of testicular cancers, ovarian cancers, and retinoblastomas were seen but were not significant. INTREPRETATION: The occurrence of cancer in Down's syndrome is unique with a high risk of leukaemia in children and a decreased risk of solid tumours in all age-groups. The distinctive pattern of malignant diseases may provide clues in the search for leukaemogenic genes and tumour-suppressor genes on chromosome 21.

Duplication and loss of chromosome 21 in two children with Down syndrome and acute leukemia

Acute leukemia in Down syndrome (DS) is often associated with additional changes in the number or structure of chromosome 21. We present two DS patients whose leukemic karyotypes were associated with changes in chromosome 21 ploidy. Patient 1 developed acute lymphocytic leukemia (type L1); disomy for chromosome 21 was evident in all blast cells examined. Loss of the paternal chromosome in the leukemic clone produced maternal uniparental disomy with isodisomy over a 25-cM interval. The second patient had acute monoblastic leukemia (type M5) with tetrasomy 21 in all leukemic cells. DNA polymorphism analysis showed duplicate paternal chromosomes in the constitutional genotype. The maternal chromosome was subsequently duplicated in the leukemic clone. The distinct inheritance patterns of chromosome 21 in the blast cells of these patients would appear to indicate that leukemogenesis occurred by different genetic mechanisms in each individual.

Myelodysplastic syndrome in a child with constitutional trisomy 8 mosaicism and normal phenotype

Trisomy 8 is a frequently acquired cytogenetic abnormality in myeloid malignancies, but may also represent a constitutional chromosome abnormality with a wide phenotypic variation. We report a case of myelodysplastic syndrome (MDS) that developed in a child with trisomy 8 mosaicism and normal phenotype. Bone marrow (BM) cells all showed trisomy 8 with additional clonal abnormalities in most cells. Based on the present case and a review of previously published cases of myeloid malignancies in patients with trisomy 8 mosaicism, it appears likely that the malignant cells developed from the trisomic cell population, suggesting that constitutional trisomy 8 may be a predisposing condition to myeloid malignancies. Trisomy 8 in malignant cells is usually considered an acquired abnormality, but this implies a risk of ignoring a constitutional trisomy 8 mosaicism. Examination for constitutional trisomy 8, despite a normal phenotype, may therefore be warranted in hematologic malignancies with trisomy 8 of BM cells to evaluate further the possible association and to preclude erroneous use of trisomy 8 as a tumor marker.

Karyotype evolution in a patient with Down syndrome and acute leukemia following a congenital leukemoid reaction

We report the serial cytogenetic study of a patient with Down syndrome who experienced a congenital leukemoid reaction, underwent a spontaneous remission within four months, and subsequently developed acute myeloid leukemia at 16 months. A blood chromosome study to rule out Down syndrome performed at age 24 days, during the leukemoid reaction, revealed a 47,XX,+21 karyotype. The diagnosis of acute leukemia was made at 16 months, at which time a chromosome study, on bone marrow, was performed. This analysis revealed a clonal karyotype of 47,XX,+21,-22,+der(22)t(1;22)(q21;q13) in all but one cell studied. The single apparently nonclonal cell showed a karyotype of 49,XX,+12,-13,-19,+der(19)t(19;?)(q11;?)x2,+21,+22. A third chromosome study at 19 months indicated the original leukemic clone with t(1;22) (q21;q13) had been replaced by the clone represented by the single cell with 49 chromosomes seen in the previous chromosome study. This case of an infant with Down syndrome and acute leukemia illustrated rapid evolution and a transitory nature to clonal chromosome aberrations while retaining AML morphology and course.

Hypothesis: meiotic origin of trisomic neoplasms

The gain of single additional chromosomes is a very common finding among the nonrandom abnormalities with human neoplasms. According to the current opinion, such trisomies result from a disease-related mitotic nondisjunction. In contrast, we suggest that some of these trisomies may in fact represent tissue-confined residual cell populations of meiotic origin. Our hypothesis is based on recent findings of uniparental disomies in humans (i.e., two homologous chromosomes are derived from the same parent) and on the notion that many of these disomies probably are the result of the successful correction of an initially trisomic conceptus. Thus, the trisomic neoplasm may represent the original trisomic karyotype, whereas the apparently normal disomic constitutional karyotype may be the acquired, corrected one. We propose molecular genetic strategies to test our hypothesis and suggest that constitutional uniparental disomies may be associated with an increased probability of developing neoplastic diseases characterized by trisomies for the respective chromosomes.

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.

Acute lymphoblastic leukemia with trisomy 21 constitutional mosaicism

Acute lymphoblastic leukemia was diagnosed in an 11-year-old girl with mild signs of Down's syndrome. She was known since birth to have a constitutional mosaicism (46,XX/47,XX,+21c). At initial diagnosis of acute leukemia, additional chromosome changes were found in bone marrow blasts: hyperdiploidy > 50, with a structural abnormality. She was treated with a standard chemotherapeutic protocol, and has remained in complete remission for more than 3 years. The constitutional mosaicism evolved toward normalization year after year in the blood and under the effect of chemotherapy in the bone marrow.

Transient abnormal myelopoiesis in Down's syndrome

Recent data have elucidated the pathogenesis of transient abnormal myelopoiesis (TAM) to a great extent. TAM is a monoclonal disorder which resolves spontaneously and the target cell in this disorder is a multipotent stem cell which is capable of differentiating into megakaryocytes. The pathogeneses of TAM/AMKL (acute megakaryoblastic leukemia) appears to be closely associated with abnormal quality and quantity of a gene located on chromosome 21. AMKL developing after the regression of TAM appears to come from the same clone as the TAM, which apparently experiences some kind of genetic alterations. It seems that the gene responsible for TAM will soon be cloned in the near future. However, the mechanism of spontaneous regression of TAM has as yet not been clarified. The expanding clone in the transient physiological immunodeficient state, during the perinatal period, might be eliminated with the maturation of more mature immunosurveillance. Alternatively, the TAM clone might be destined to undergo spontaneous death, which is called "programmed cell death" (apoptosis). The mechanism of this phenomenon awaits further elucidation.

Down's syndrome and mixed acute leukemia in infants

The routine use of panels of monoclonal antibodies has been complementary to the French-American-British (FAB) leukemia classification, and has unmasked the occurrence of mixed acute leukemia (myeloid-lymphoid). It is widely accepted that children with Down's syndrome (DS) have a high incidence of acute leukemia. There is an extensive body of literature emphasizing the cytogenetic findings in these children. However, information as to the immunophenotype is often limited to the lymphoid surface determinants. The authors report two children with DS whose leukemic blasts were studied with a panel of 17 monoclonal antibodies (myeloid, lymphoid, and megakaryocytic) by flow cytometric examination and were classified as biphenotypic acute leukemia. The blast population coexpressed myeloid and T-cell surface markers. The lymphoid origin was ruled out on the basis of negative terminal deoxynucleotidyl transferase and molecular analysis demonstrating germline configuration for the JH and beta TCR genes.

Isolation of a yeast artificial chromosome spanning the 8;21 translocation breakpoint t(8;21)(q22;q22.3) in acute myelogenous leukemia

The 8;21 translocation is one of the most common specific rearrangements in acute myelogenous leukemia. We have identified markers (D21S65 and a Not I boundary clone, Not-42, referred to as probe B) flanking the chromosome 21 translocation breakpoint (21q22.3) that demonstrate physical linkage in normal genomic DNA, by using at least three restriction endonucleases (Not I, Sac II, and BssHII), and that are located not more than 250-280 kilobases apart. Pulsed-field gel analysis of DNA from somatic cell hybrids containing the 8;21 translocation chromosomes demonstrates rearrangement of these markers. A 470-kilobase yeast artificial chromosome, YAC-Not-42, has been isolated that contains both probes. Mapping of lambda subclones constructed from YAC-Not-42 suggests that greater than 95% (25/26 probes tested) of the yeast artificial chromosome DNA is located on the proximal (D21S65) side of the breakpoint. In situ hybridization studies using metaphase chromosomes from five acute myelogenous leukemia patients with the 8;21 translocation confirmed these results and demonstrated the translocation of probe B to the derivative chromosome 8. A chromosome walk of approximately 39 kilobases from probe B has allowed identification of the breakpoint in DNA from a somatic cell hybrid containing the derivative chromosome 8. Since probe B contains conserved DNA sequences and is in close proximity to the translocation breakpoint, it may represent a portion of the involved gene on chromosome 21.

Clinical characteristics and treatment outcome of children with acute lymphocytic leukemia and Down's syndrome. A Pediatric Oncology Group study

Of 2947 children with acute lymphocytic leukemia (ALL), treated during three consecutive studies of the Pediatric Oncology Group (1974-1986), 52 (1.8%) had Down's Syndrome (DS). Comparison of clinical and laboratory characteristics showed no significant differences in leukocyte count, racial distribution, sex ratio, platelet count, incidence of mediastinal mass, lymphadenopathy or hepatosplenomegaly, or percentage of blood or bone marrow blasts for children with ALL with or without Down's Syndrome (DS-ALL or NDS-ALL, respectively). However, children with DS-ALL were slightly older at the time of presentation and had higher hemoglobin values. The relative frequency of each major immunophenotype (early pre-B, pre-B, T, or B) was also comparable for patients with or without DS. For this report, treatment regimens were categorized as either conventional (no consolidation therapy) or intensive. Cox regression analysis revealed that the presence of DS, a higher leukocyte count, black race, or age older than 10 years was independently associated with a poorer event-free survival (EFS) for children treated with conventional chemotherapy. However, for the cohort of children who received intensive chemotherapy, DS was no longer an independent risk factor. In fact, event-free survival (EFS) was markedly improved to a level comparable with that observed in the children diagnosed as having NDS-ALL. On the other hand, serious toxicity, requiring interruption of treatment, was significantly more frequent in the intensively treated children with DS compared with similarly treated patients with NDS-ALL, although deaths resulting from toxicity occurred infrequently.

Acute nonlymphocytic leukemia in a patient with a constitutional inv(4)

We describe a case of acute nonlymphocytic leukemia (ANLL) in a patient with a constitutional chromosome anomaly, inv(4)(p16q26). The patient had extensive occupational exposure to toxic chemicals. Reports of constitutional or acquired chromosome inversions in human malignancies are quite uncommon. The constitutional changes associated with hematologic malignancies include trisomy 21, balanced translocations, deletions, and sex chromosome anomalies. The breakpoints on chromosome 4 in our case are 4p16, to which the murine leukemia viral (v-raf) oncogene, pseudogene 1, has been mapped, and 4q26, which is the locus of the IL-2 gene. Activation of these genes could have played a role in the pathogenesis of the patient's leukemia.

Dicentric chromosome in the bone marrow of a child with megakaryoblastic leukaemia and Down's syndrome

A two year old girl with Down's syndrome (constitutional karyotype: 47 + 21), presenting with pancytopenia, developed acute megakaryoblastic leukaemia (AMKL). Her bone marrow contained an abnormal clone with a novel dicentric chromosome derived from chromosomes 5 and 7 (karyotype 46, XX, -5, -7, +dic (5;7) (p 13; p 11.2), +21. This case provides further evidence for a connection between chromosome 21 and this unusual form of childhood leukaemia, and raises questions about the loss of short arm material from chromosomes 5 and 7 compared with the more usual monosomy or long arm loss.

Down's syndrome and leukemia: epidemiology, genetics, cytogenetics and mechanisms of leukemogenesis

The association of Down's syndrome and leukemia has been documented for over 50 years. Multiple studies have established the incidence of leukemia in Down's syndrome patients to be 10- to 20-fold higher than that in the general population. The age of onset for leukemia in these children is bimodal, peaking first in the newborn period and again at 3-6 years. This increased risk extends into adulthood. All cytogenetic types of Down's syndrome apparently predispose to leukemia. The proportion of acute lymphoblastic leukemia and acute nonlymphoblastic leukemia in patients with Down's syndrome is similar to non-Down's syndrome leukemia patients matched for age. There are case reports in which leukemia, Down's syndrome, and other chromosomal aberrations cluster within a family. In these kindreds, there may be a familial tendency toward nondisjunction. Congenital leukemia also occurs with increased frequency in Down's syndrome patients, and is characterized by a preponderance of acute nonlymphoblastic leukemia (similar to non-Down's syndrome patients). Transient leukemoid reactions have been observed in Down's syndrome patients, as well as in phenotypically normal children with constitutional trisomy 21 mosaicism. The transient leukemoid reactions are characterized by a high spontaneous remission rate. However, in some Downs syndrome patients with apparent transient leukemoid reaction, leukemia relapse following periods of spontaneous remission have been reported. Cytogenetic studies of leukemic cells in Down's syndrome patients show a tendency toward hyperdiploidy. Besides trisomy 21, there is no other specific cytogenetic abnormality that is characteristic of the leukemia cells in Down's syndrome patients. The possible mechanisms for leukemogenesis in Down's syndrome patients may involve factors at the levels of the organism, the organ/system, the cell, the chromosomes or the DNA.

Megakaryoblastic leukemia and Down's syndrome: a review

Megakaryoblastic leukemia and transient leukemia in Down's syndrome have been reviewed using case reports from the literature and our own experience at the Hospital for Sick Children. The following conclusions have been reached: (1) approximately 20% of leukemia (excluding transient leukemia) in Down's syndrome is acute megakaryoblastic leukemia; (2) approximately 20% of all leukemia in Down's syndrome is transient leukemia; (3) transient leukemia in Down's syndrome is acute megakaryoblastic leukemia; (4) recurrence of acute megakaryoblastic leukemia occurs in 20% of the cases of transient leukemia; and (5) the incidence of acute megakaryoblastic leukemia in Down's syndrome is estimated to be 400 times that in normal children. These observations suggest that a specific form of leukemia, namely acute megakaryoblastic leukemia, has a remarkable association with Down's syndrome.