Gene mutations in myelodysplasia

Consilience across evolving dysplasias affecting myeloid, cervical, esophageal, gastric and liver cells: common themes and emerging patterns

In the present paper, an attempt is made to identify common biologic themes across dysplastic states affecting the marrow, gastro intestinal tissue, the cervix and liver as well as unifying patterns during disease evolution. The following algorithm appears generally applicable, although individual variations must necessarily be anticipated. It appears that there is an initial transforming event which in all dysplasias except that affecting the marrow has been found to be infectious. Increased cellular proliferation-increased apoptosis, telomere shortening, appearance of telomerase expression and clonal expansion follow the initial insult. Abnormalities in the cytokine environment are universally described and it is likely that the quintessential monoclonality aspect of dysplasia predisposes to accumulation of genetic mutations, and microsatellite instability leading to the appearance of evolved sub-clones. The conversion of a dysplastic phenotype to a malignant one reflects the success of one such sub-clone in developing a survival advantage over a large population of prematurely apoptotic neighbors. This state is usually acquired by silencing tumor suppressor genes through hypermethylation or actual loss or dysfunction. Thus, excessive apoptosis of cells resulting from a persistent infectious process predisposes the organ towards developing a cancerous phenotype. Evidence for the shared pathology is presented at length with the hope that these parallels between dysplastic states will be helpful in both biologic and therapeutic research.

Molecular analysis of the cyclin-dependent kinase inhibitor genes, p15, p16, p18 and p19 in the myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a heterogeneous group of clonal blood disorders characterized by dyshematopoiesis with a frequent evolution to acute leukemia. Chromosomal deletions rather than translocations are the predominant karyotypic abnormalities in MDS, suggesting a recessive mechanism in the pathogenesis of MDS, such as inactivation of tumor suppressor genes. A group of cyclin-dependent kinase inhibitors, p15 (INK4B), p16 (INK4A), p18 (INK4C) and p19 (INK4D), are candidate tumor suppressor genes. To determine whether genetic alterations of these genes play an important role in the development and/or progression of MDS, we examined 46 samples from MDS patients by Southern blotting, single-strand-conformation polymorphism (SSCP) using polymerase chain reaction (PCR) and sequencing of DNA. These samples included 13 refractory anemias (RA), four refractory anemias with ringed sideroblasts (RARS), 16 refractory anemias with an excess of blasts (RAEB), eight refractory anemias with an excess of blasts in transformation (RAEB-T) and five chronic myelomonocytic leukemia (CMMoL) samples. Except for allelic polymorphisms or silent point mutations, no alterations of coding regions of these four CDKI genes were identified. In summary, genetic abnormalities of the p15, p16, p18 and p19 genes are rare events in the development and/or progression of MDS.

The myelodysplastic syndromes in 1996: complex stem cell disorders confounded by dual actions of cytokines

Based upon recent studies of apoptosis, proliferation, cytokines and genic abnormalities, a new hypothesis regarding the pathology of myelodysplastic syndromes is being proposed. The transforming abnormality which affects an early progenitor hemopoietic stem cell is poorly defined so far but confers a growth advantage on this cell eventually leading to monoclonal hemopoiesis at least affecting the non-lymphoid bone marrow cells. Several cytokines confound the picture by exerting dual effects of stimulating the proliferation of immature cells while inducing the apoptosis in their maturing progeny thereby producing the clinical syndrome of cytopenias despite cellular marrows. Since a number of these offending cytokines share the same common lipid intracellular signalling pathway, interfering with the generation of specific phospholipid second messengers should hypothetically result in a dual effect as well. Alleviation of cytopenias (due to attenuation of apoptosis) should be accompanied by a decrease in the progeny of the transformed stem cell (due to suppression of proliferation) eventually allowing for resumption of polyclonal hemopoiesis.

Detection of major and minor bcr/abl fusion gene transcripts in a patient with acute undifferentiated leukemia secondary to treatment with an alkylating agent

In this paper we describe a patient with bcr/abl positive acute undifferentiated leukemia (AUL) derived from acquired sideroblastic anemia secondary to ifosphamide treatment given for the preceding non-Hodgkin lymphoma of the lung. Cytogenetically, Philadelphia chromosome was not detected through the whole course in this patient, and multiple chromosomal abnormalities including 5q- and monosomy 7 were found at the stage of sideroblastic anemia. The reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed no bcr/abl fusion transcript at the diagnosis of malignant lymphoma. The mRNA encoding the major bcr/abl fusion protein then appeared in the stage of sideroblastic anemia. Finally, the mRNA encoding both major and minor bcr/abl was detected in the stage of AUL transformation. MLL gene rearrangement was not found by RT-PCR analysis at any stage of the disorder. These results may be direct evidence for the induction of the bcr/abl fusion gene by treatment with an alkylating agent (ifosphamide).

t(8;21) myelodysplasia, an early presentation of M2 AML

The reciprocal translocation of genetic material between chromosomes 8 and 21, t(8;21), is usually restricted to cases of acute myeloid leukaemia (AML). Cases of AML with t(8;21) exhibit characteristic dysplastic features in myeloid and erythroid lineages with reduction in megakaryocytes. We report details of three patients presenting with myelodysplastic features; two had a typical t(8;21), and the third had a variant t(8;21) translocation. We discuss the significance of t(8;21) in the aetiology of myelodysplastic syndrome (MDS) and implications for the management of such patients.

Epidemiological and etiological aspects of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are increasingly recognized as a cause of bone marrow failure, and are at least as frequent as acute myeloid leukemias. While the overall incidence is about 2-4/100,000/year, incidence figures rise steeply with age. Incidence rates of 20-30/100,000/year in persons over 70 demonstrate that MDS are among the most common hematological neoplasias in this age group. However, due to difficulties of diagnosis and classification, patient registration in population-based registers is far from complete. As a prerequisite for truly representative statistics, future revisions of disease classification systems must incorporate MDS as a separate group of disorders. The difficulties in conducting epidemiological studies also impede the identification of risk factors for the development of MDS. Current knowledge of occupational risk factors is also reviewed here. More rapid progress in our understanding of MDS may come from recent advances in methodology that have begun to shed some light on the cytogenetic and molecular aspects of leukemogenesis in general, and MDS in particular. Non-random chromosomal changes can be found in about 50% of cases at diagnosis, but they are probably late events in the evolution of MDS, reflecting the progressive genomic instability of the premalignant clone. Proto-oncogene mutations have also been suggested to be relevant to the pathogenesis of MDS, but longitudinal studies of point mutations of the N-ras proto-oncogene revealed that such events, although often associated with rapid deterioration and transformation to AML, also appear to be late events during the course of disease. Therefore, it remains a major challenge to identify those lesions that initiate the multistep development of preleukemia. As the incidence of MDS correlates strongly with age, it is reasonable to presume that age-dependent changes of the hematopoietic system may play a role in the initiation of MDS. Aging is probably associated with a compromised marrow reserve through reduction in the size of the stem cell pool. Through increased proliferative activity, the remaining stem cells may be particularly vulnerable to mutagenic insults. Immunological attack on stem cells, mitochondrial DNA mutations, and the regulatory influence of the hematopoietic microenvironment must also be considered as possibly contributing to the early stages of MDS.

Quantitative determination of the ratio of mutated to normal ras genes in the blood of leukemia patients by allele-specific PCR

By combining allele-specific PCR amplification and a PCR-based quantitation approach, a method has been developed to estimate the mutated K-ras gene content in the blood of AML patients as a percentage of total K-ras. One PCR primer set was designed not to discriminate between mutant K-ras and wild-type K-ras and thus amplified the total K-ras gene. The other PCR primer set was designed to be allele-specific for K-ras gene containing a G to C mutation at codon 12. This primer set could discriminate the mutant and wild-type genes when the proportion of the mutated sequence was 0.2% of the total K-ras gene. To test the method on biological specimens, genomic DNA samples were analyzed from the peripheral blood of a patient who had secondary AML with the same codon 12 K-ras mutation. Two samples taken from this patient 2 months apart during follow-up had myeloblast cell contents of 67 and 80%. However, the percentage of mutated K-ras was 50% in both samples, suggesting that this patient may be inherently heterozygotic in this particular mutation. This ratio of mutated to normal K-ras in the patient's cells was confirmed by RNA-SSCP analysis and RNA sequencing. This quantitation method can provide a sensitive and specific estimation of the content of mutated K-ras alleles in patient samples.

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.

Late-appearing Philadelphia chromosome in a patient with acute nonlymphocytic leukaemia derived from myelodysplastic syndrome: detection of P210- and P190-type bcr/abl fusion gene transcripts at the leukaemic stage

We describe a patient with acute nonlymphocytic leukaemia (ANLL) derived from myelodysplastic syndrome in whom the Philadelphia chromosome (Ph1) first emerged at the late stage of ANLL transformation. Cytogenetically, the Ph1 chromosome was not detected until the late stage of ANLL transformation, 14 months after the transformation following a 3-month history of refractory anaemia with excess of blasts. The cells with and without the Ph1 chromosome had a common abnormal chromosome, t(3;3) (q21;q26). The reverse transcription-polymerase chain reaction analysis showed no bcr/abl message at diagnosis. However, the mRNA encoding P210bcr/abl was detected in the early stage of ANLL transformation. Furthermore, the mRNAs encoding both P210bcr/abl and P190bcr/abl were detected in the late stage of ANLL transformation when the Ph1 chromosome was detected by cytogenetic analysis. These evidences support a multistep pathogenesis of leukaemias, and the products of bcr/abl fusion gene may influence the course of disease.

Clonality in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) comprises a group of acquired hematological disorders which is characterized by a progressive peripheral blood pancytopenia of one or more cell lineages. A high percentage of blast cells in either bone marrow or peripheral blood predisposes for the transformation to acute myeloid leukemia. The clinical presentation with pancytopenia suggest that all cell lineages are affected by MDS. The first experiments with X-linked restriction fragment length polymorphism (RFLP) indicated that MDS is a stem cell disorder since the clonal deletions could be detected in all cell lineages. During the 1st decade several new molecular biological techniques such as polymerase chain reaction, and fluorescent in situ hybridization (FISH) were applied to study molecular aberrations in subpopulations of cells. Molecular aberrations in all subpopulations would indicate that MDS is a stem cell disorder. The clonal studies in MDS are equivocal. Studies involving the expression of chromosomal abnormalities (standard karyotyping and FISH) in different cell lineages suggest that the pluripotent stem cell is not affected in MDS since the lymphoid cells usually do not express the abnormal karyotype. Results obtained by RFLP vary widely. Some studies indicate that the lymphoid lineage is not involved, while other studies find a polyclonal expression of the polymorphic genes in lymphoid cells. One study using PCR demonstrated mutations in the ras-oncogenes in T-cells as well as myeloid cells, suggesting that a common ancestor of myeloid and lymphoid cells is affected by MDS. This review discusses the different experimental approaches carried out to solve the discussion whether MDS is a stem cell disorder.

The role of integrins in granulocyte dysfunction in myelodysplastic syndrome

The aim of the present study was to evaluate the function of granulocytes in 20 patients affected by myelodysplastic syndrome (MDS) and correlate this with the expression of surface membrane integrins. The granulocytes showed a deficit in chemotaxis (34 +/- 12 vs 84 +/- 10, p < 0.01) in superoxide release (12 +/- 7 vs 30 +/- 10, p < 0.01) and in aggregation 12 +/- 6 vs 36 +/- 9, p < 0.01 using fMLP as stimulus. We also demonstrated with cytofluorimetric and alkaline phosphatase immunoenzymatic analysis (APAAP), decreased expression of CD11b/CD18 receptor detected by OKM1 (p < 0.001) and CD18 detected by MoAb IOT-18 (p < 0.001). PMNs CD11b/CD18 up-regulation and APAAP image analysis studies showed a lower level of expression of CD11b/CD18 in granulocytes from MDS patients compared to controls (p < 0.001). We concluded that granulocyte dysfunction in MDS may be correlated with modification of leukocyte integrins.

The CD11/CD18 granulocyte adhesion molecules in myelodysplastic syndromes

We have evaluated the function of granulocytes in 14 patients suffering from myelodysplastic syndrome (MDS). We also evaluated the functional and immunochemical activities of five monoclonal antibodies (MoAbs) reactive with the CD11/CD18 leucocyte adhesion molecules of granulocytes. Granulocytes showed a decrease in chemotaxis (P < 0.001) and in aggregation (P < 0.01) using various agents as a stimulus. Cytofluorimetric and immunoenzymatic assays with alkaline phosphatase (APAAP) analysis showed decreased expression of the CD11b/CD18 receptor detected by OKM1 (P < 0.001). Despite LFA-1 and-CD11a/CD18 was expressed in normal amounts. The studies of upregulation of granulocytes CD11b/CD18 and image analysis of immunochemical preparation (APAAP) demonstrated decreased expression of CD11b/CD18 in granulocytes from MDS compared to controls (P < 0.001). We conclude that granulocyte dysfunction in MDS may be correlated with decreased expression of surface CD11b/CD18 leucocyte adhesion molecules or their structural modification.