Molecular analysis of the bcr rearrangement in a case of Ph'-negative blastic crisis of Ph'-positive chronic myelogenous leukemia

The SKM-1 leukemic cell line established from a patient with progression to myelomonocytic leukemia in myelodysplastic syndrome (MDS)-contribution to better understanding of MDS

Although molecular and cytogenetic studies strongly point to the role of oncogenes, the mechanisms underlying the development of MDS and their progressive evolution to AML are still largely unknown. It has been postulated that AML has a preleukemic stage and a multi step pathogenesis, with the preleukemic stem cell able to undergo clonal evolution, with the acquisition of karyotypic abnormalities, leading to the development of acute leukemic subclones. The activations of the ras oncogenes or inactivation of the p53 anti-oncogene by point mutations have been described recently in several cases of MDS as well as AML, suggesting a critical role for these alterations in the development of these myelogenous leukemias. We reported previously establishment of a leukemic cell line, SKM-1, from the patient who initially possessed multiple point mutations of ras genes but lost these mutations during disease progression to myelomonocytic leukemia with acquisition of chromosomal abnormalities involving the p53 anti-oncogene. This process is characterized by genetic instabilities probably due to the failure of their DNA repairment leading to abnormal control of cell proliferation and differentiation. Studying this cell line, SKM-1, is a promising approach to understand the mechanisms of the initiation, disease progression, alterations of DNA repairment, and genetic instability in MDS and myelogenous malignancies.

Trisomy 13 in acute leukemia

Trisomy 13 occurring as a sole cytogenetic abnormality has recently been demonstrated to have adverse prognostic significance in acute leukemia. Trisomy 13 is seen primarily in an older male population, and has been reported in treatment-associated acute leukemia and acute leukemia evolved from myelodysplastic syndromes, as well as in de novo leukemia. The 36 cases of acute leukemia with trisomy 13 reported to date include 26 AML, 6 AUL, 2 ALL and 2 mixed lineage patients. Immunophenotyping studies have demonstrated an undifferentiated phenotype or biphenotypic markers in most cases. Trisomy 13 is associated with a low complete remission rate and with brief remission duration. The role of the additional copy of chromosome 13 in the pathogenesis of these cases of acute leukemia and the gene(s) of importance on chromosome 13 are yet to be determined.

Trisomy 13: a preferentially male chromosome aberration interfering specifically with myeloid proliferation and differentiation? Report of a case and review of the literature

A case of trisomy 13 is presented: a 73-year-old man with acute nonlymphocytic leukemia (ANLL), FAB borderline M1/M2, and peripheral leukocyte and platelet counts that were difficult to control with chemotherapy. A literature review shows that 35 cases of trisomy 13 are known at present. They are characterized by male predominance (76%), preferentially myeloid disorders (ANLL, myelodysplastic syndromes, chronic myeloid leukemia), leucocytosis, and relatively high platelet counts and hemoglobins. It is suggested that trisomy 13 is a specific nosologic entity with male predominance and characterized by interference with proliferation and differentiation in the myeloid differentiation series.

Ras activation in myelodysplastic syndromes: clinical and molecular study of the chronic phase of the disease

We studied N-ras and Ki-ras point mutations respectively at codons 12-13 and 12 in 15 patients with myelodysplastic syndromes (MDS) using the polymerase chain reaction (PCR) method for DNA amplification, and slot blot hybridization to allele specific oligonucleotide (ASO) probes. We analysed peripheral blood and bone marrow samples collected at diagnosis and repeatedly during the chronic phase of the disease to define when the activation occurred and in which haemopoietic cell populations, in order to establish possible relationships between clinical and molecular features. In three cases the N-ras oncogene was mutated at codon 12 in every cell population, both at diagnosis and throughout the chronic phase. Point mutations were not seen at the 12 codon of the Ki-ras oncogene. In patients lacking activated ras oncogene at diagnosis, mutations were not discovered during the entire period of observation. Therefore in our cases disease progression and leukaemic transformation did not correlate with the presence of the activated N-ras. Our data suggest that ras activation occurs early in the pathogenesis of MDS and involves a haemopoietic progenitor with multiple differentiative capacity, without however conferring an apparent proliferative advantage on its progeny.

Clonal B lymphocytes lack bcr rearrangement in Ph-positive chronic myelogenous leukaemia

Philadelphia (Ph) chromosome-positive chronic myelogenous leukaemia (CML) was studied in a subject heterozygous for the X chromosome-linked alloenzyme system of glucose-6-phosphate dehydrogenase (G6PD). Determination of G6PD mosaicism showed homogeneous expression in granulocytes, erythrocytes and platelets. Cytogenetic studies showed the typical Ph translocation in all metaphases from bone marrow and peripheral blood myeloid cells, bcr rearrangement was detected in bone marrow and in granulocytes. B cells were stimulated with Epstein-Barr virus (EBV) in order to evaluate involvement of lymphocytes, EBV-transformed lymphoblastoid cells expressed a single G6PD phenotype and therefore probably derived from the leukaemic stem cell. However they had a normal karyotype and a constitutional bcr restriction pattern. Molecular analysis in this case of CML clarifies the differentiative potential of cells belonging to the leukaemic clone, by demonstrating that clonal Ph-negative B cells maintain normal differentiative capacity and have a bcr gene sequence which is not rearranged.