MLL/ENL fusion in congenital acute lymphoblastic leukemia with a unique t(11;18;19)

A new chromosomal three-way rearrangement involving MLL masked by a t(9;19)(p11;p13) in an infant with acute myeloid leukemia

Infants diagnosed with acute myelogenous leukemia (AML) are likely to have subtypes M4 or M5 characterized by 11q23 abnormalities like a t(9;11)(p22;q23). Detection of all possible types of chromosomal abnormalities, including mixed lineage leukemia (MLL) gene rearrangements at 11q23, is of importance for the identification of biological subgroups, which might differ in drug resistance and/or clinical outcome. Here, we report the clinical, conventional banding and molecular cytogenetics data of a 6-month-old boy with an AML-M5 presenting with a unique cryptic rearrangement involving the MLL gene: a three-way t(9;19;11)(p11.2;p13.1;q23).

Cancer genetics of epigenetic genes

The cancer epigenome is characterised by specific DNA methylation and chromatin modification patterns. The proteins that mediate these changes are encoded by the epigenetics genes here defined as: DNA methyltransferases (DNMT), methyl-CpG-binding domain (MBD) proteins, histone acetyltransferases (HAT), histone deacetylases (HDAC), histone methyltransferases (HMT) and histone demethylases. We review the evidence that these genes can be targeted by mutations and expression changes in human cancers.

Chromatin modifier enzymes, the histone code and cancer

In all organisms, cell proliferation is orchestrated by coordinated patterns of gene expression. Transcription results from the activity of the RNA polymerase machinery and depends on the ability of transcription activators and repressors to access chromatin at specific promoters. During the last decades, increasing evidence supports aberrant transcription regulation as contributing to the development of human cancers. In fact, transcription regulatory proteins are often identified in oncogenic chromosomal rearrangements and are overexpressed in a variety of malignancies. Most transcription regulators are large proteins, containing multiple structural and functional domains some with enzymatic activity. These activities modify the structure of the chromatin, occluding certain DNA regions and exposing others for interaction with the transcription machinery. Thus, chromatin modifiers represent an additional level of transcription regulation. In this review we focus on several families of transcription activators and repressors that catalyse histone post-translational modifications (acetylation, methylation, phosphorylation, ubiquitination and SUMOylation); and how these enzymatic activities might alter the correct cell proliferation program, leading to cancer.

Molecular Pathogenesis of MLL-Associated Leukemias

Chromosome translocations disrupting the MLL gene are associated with various hematologic malignancies but are particularly common in infant and secondary therapy-related acute leukemias. The normal MLL-encoded protein is an essential component of a supercomplex with chromatin-modulating activity conferred by histone acetylase and methyltransferase activities, and the protein plays a key role in the developmental regulation of gene expression, including Hox gene expression. In leukemia, this function is subverted by breakage, recombination, and the formation of chimeric fusion with one of many alternative partners. Such MLL translocations result in the replacement of the C-terminal functional domains of MLL with those of a fusion partner, yielding a newly formed MLL chimeric protein with an altered function that endows hematopoietic progenitors with self-renewing and leukemogenic activity. This potent impact of the MLL chimera can be attributed to one of 2 kinds of activity of the fusion partner: direct transcriptional transactivation or dimerization/oligomerization. Key unresolved issues currently being addressed include the set of target genes for MLL fusions, the stem cell of origin for the leukemias, the role of additional secondary mutations, and the origins or etiology of the MLL gene fusions themselves. Further elaboration of the biology of MLL gene-associated leukemia should lead to novel and specific therapeutic strategies.

A der(19)t(12;19)(q12;p13.3) in a case of pediatric acute leukemia with unusual immunophenotype

We describe a case of acute leukemia in a child with an unusual immunophenotype and a novel cytogenetic abnormality. The leukemia blasts expressed myeloid, natural killer and B-lineage associated antigens. Cytogenetics showed the presence of a novel unbalanced chromosomal translocation, der(19)t(12;19)(q12;p13.3). The patient achieved and maintained remission with myeloid-directed chemotherapy. The differential diagnosis of the immunophenotype and the potential fusion genes are discussed.

Acute leukemia

This article provides a review of the acute leukemias with updated basic and practical information. The main emphasis is on techniques used to arrive at the correct diagnosis. Although morphology and cytochemistry were the mainstays of diagnosis in the past, new developments in immunophenotyping, cytogenetics, molecular biology, and in vitro assays have improved the understanding of this disease dramatically and enable the identification of new entities with distinct clinicobiologic features.

Acute leukemia cytogenetics: an evaluation of combining G-band karyotyping with multi-color spectral karyotyping

We have, during a 12-month period, evaluated the adjuvant effect of combining G-band karyotyping and multi-color spectral karyotyping (SKY) in acute leukemia patients. Forty-four cases were evaluated; fewer cases than those routinely analyzed by G-band cytogenetics had mitoses left for SKY analysis. Of the 44 patients, 35 were acute myeloid leukemia (AML) and 9 acute lymphatic leukemia (ALL) cases. Twenty-seven of 35 AML and 7 of 9 ALL patients had an abnormal G-band karyotype. Thirteen of these 34 abnormal cases had a simple clonal chromosome aberration, and the remaining 21 cases had a complex karyotype. The SKY confirmed the simple karyotype in 11 and in 7 with a complex karyotype. In 13 of the cases with a complex karyotype, ambiguous structural aberrations were classified, in 6 of these, SKY disclosed cryptic translocations. Thus, SKY either extended or confirmed G-band karyotypes in 31 of 34 analyzed abnormal cases. Cases where SKY did not reveal the abnormal clone showed only few abnormal mitoses by G-banding (2/23, 2/25, and 4/27). Additional or confirmatory information was therefore obtained in 91% of analyzed cases, and SKY proved to be a valuable additional tool for hematologic cytogenetics.

Translocation (3;5)(p26;q13) in a patient with chronic T-cell lymphoproliferative disorder

A 67-year-old patient with large granular lymphocyte (LGL) leukemia is described. At fluorescence-activated cell sorting (FACS) analysis of the peripheral blood, the lymphocytes were positive for CD3, CD4, CD5, CD29, CD45RA, CD57, and TCR alpha/beta and negative for CD7, CD8, CD16, CD56, CD19, CD22, and TCR gamma/delta. Bone marrow histology and immunohistochemistry did not reveal any lymphocyte infiltration. Cytogenetic examination of peripheral blood cultures showed a clone with the karyotype 46,XY,t(3;5)(p26;q13). Molecular analysis revealed rearrangement of the gamma-T-cell-receptor chain. The region 3p25-3p26 which harbors the von Hippel-Lindau tumor suppressor gene and the RAF1 oncogene has been rearranged in a few cases of T-cell leukemia. The translocation in this case has not yet been described and may reflect an alternative mechanism in the pathogenesis of these disorders.