Prenatal chromosomal diversification of leukemia in monozygotic twins

Previous studies on concordant acute lymphoblastic leukemia (ALL) in identical twins have identified the leukemia as monoclonal with MLL or ETV6-RUNX1 gene fusion as early or initiating events in utero. In the latter case, postnatal latency is associated with secondary genetic events such as ETV6 deletion. We describe here a pair of infant twins with concordant acute monoblastic leukemia (AML). They are a unique pair in that their leukemia blasts display extensive intraclonal chromosomal diversity. Comparison of the leukemic cells between the two twins by karyotype and fluorescence in situ hybridization identifies a common or shared stem line and extensive subclonal diversity for which the twins\u27 leukemic populations are divergent. This case of leukemia illustrates in utero initiation with early imposition of chromosomal instability, the progressively divergent evolution of which can be mapped in the twins into pre- and postnatal periods

Unregulated actin polymerization by WASp causes defects of mitosis and cytokinesis in X-linked neutropenia

Specific mutations in the human gene encoding the Wiskott-Aldrich syndrome protein (WASp) that compromise normal auto-inhibition of WASp result in unregulated activation of the actin-related protein 2/3 complex and increased actin polymerizing activity. These activating mutations are associated with an X-linked form of neutropenia with an intrinsic failure of myelopoiesis and an increase in the incidence of cytogenetic abnormalities. To study the underlying mechanisms, active mutant WASpI294T was expressed by gene transfer. This caused enhanced and delocalized actin polymerization throughout the cell, decreased proliferation, and increased apoptosis. Cells became binucleated, suggesting a failure of cytokinesis, and micronuclei were formed, indicative of genomic instability. Live cell imaging demonstrated a delay in mitosis from prometaphase to anaphase and confirmed that multinucleation was a result of aborted cytokinesis. During mitosis, filamentous actin was abnormally localized around the spindle and chromosomes throughout their alignment and separation, and it accumulated within the cleavage furrow around the spindle midzone. These findings reveal a novel mechanism for inhibition of myelopoiesis through defective mitosis and cytokinesis due to hyperactivation and mislocalization of actin polymerization

Distinctive genotypes in infants with T-cell acute lymphoblastic leukaemia

Infant T-cell acute lymphoblastic leukaemia (iT-ALL) is a very rare and poorly defined entity with a poor prognosis. We assembled a unique series of 13 infants with T-ALL, which allowed us to identify genotypic abnormalities and to investigate prenatal origins. Matched samples (diagnosis/remission) were analysed by single nucleotide polymorphism-array to identify genomic losses and gains. In three cases, we identified a recurrent somatic deletion on chromosome 3. These losses result in the complete deletion of MLF1 and have not previously been described in T-ALL. We observed two cases with an 11p13 deletion (LMO2-related), one of which also harboured a deletion of RB1. Another case presented a large 11q14·1-11q23·2 deletion that included ATM and only five patients (38%) showed deletions of CDKN2A/B. Four cases showed NOTCH1 mutations; in one case FBXW7 was the sole mutation and three cases showed alterations in PTEN. KMT2A rearrangements (KMT2A-r) were detected in three out of 13 cases. For three patients, mutations and copy number alterations (including deletion of PTEN) could be backtracked to birth using neonatal blood spot DNA, demonstrating an in utero origin. Overall, our data indicates that iT-ALL has a diverse but distinctive profile of genotypic abnormalities when compared to T-ALL in older children and adults

A molecular cytogenetic study of chromosome regions 11q23 and 21q22 in childhood leukaemia

Non random chromosomal abnormalities are associated with specific subgroups of leukaemia. These abnormalities include structural rearrangements which frequently involve specific loci containing genes which have been implicated in leukaemogenesis. The object of this study, was to explore two specific chromosomal regions, 11q23 and 21q22, frequently associated with leukaemias seen in early childhood. Abnormalities of chromosome 11 at band q23 (which usually involve the MLL gene) are commonly found in infant leukaemias. Using fluorescence in situ hybridisation (FISH) with locus-specific probes spanning the region between D11S622 and THY1, which includes MLL, subtle inter- and intra-chromosomal changes were detected in the leukaemic cells from a series of infant patients showing complex or ambiguous rearrangements involving 11q23. These include duplication, insertion, rearrangement and loss of heterozygosity for MLL, and the involvement of loci immediately proximal and distal to the gene. Structural and numerical changes of chromosome 21 are common in childhood leukaemia and include several well characterised translocations involving the AML1 gene at 21q22. Using FISH with a panel of locus-specific probes for chromosome 21, acquired structural abnormalities have been characterised in patients with Down syndrome (DS) (trisomy 21) and leukaemia, and neonates with transient abnormal myelopoiesis (TAM) (both DS and non-DS). Subtle structural changes were detected in each group of patients, providing evidence for the instability of chromosome 21 in the form of cryptic intra-clonal changes such as deletions and translocations undetectable by conventional cytogenetics. This work, on chromosome 21, has resulted in two regions, one at 21q11.l, involving regions within and adjacent to locus D21S215, and one at 21q22.3, between the loci containing 7 and D21S55, now being actively investigated for the presence of novel genes involved in leukaemogenesis as part of a subsequent PhD study and as an ongoing 5-year post-doctoral project

Molecular cytogenetics in childhood leukemia

In the last decade molecular cytogenetics, or fluorescence in situ hybridization (FISH), has become an important complementary procedure to routine chromosomal analysis. The most significant consequence from cytogenetic studies in childhood leukemia has been the association of specific chromosomal abnormalities with different patient subgroups, particularly in relation to prognosis. In childhood acute myeloid leukemia (AML), the rearrangements t(8;21)(q22;q22), t(15;17)(q22;q12), and inv(16)(p13q22) are associated with a good outcome. Conversely, deletions of the long arm of chromosome 5, monosomy 5 or 7, in association with a complex karyotype, are related to a poor prognosis. Karyotypes with a favorable outcome in childhood acute lymphoblastic leukemia (ALL) include high hyperdiploidy (51-65 chromosomes) and the translocation, t(12;21)(p13;q22). The Philadelphia translocation, t(9;22)(q34;q11), rearrangements involving the MLL gene and near haploidy (23-29 chromosomes) are associated with a short overall survival (2). Metaphase and interphase FISH are increasingly being used to screen routinely for such chromosomal abnormalities in childhood leukemia. Metaphase FISH also plays a role in the identification of new nonrandom chromosomal changes of prognostic significance.<br/

Clonal origins of relapse in ETV6-RUNX1 acute lymphoblastic leukemia

B-cell precursor childhood acute lymphoblastic leukemia with ETV6-RUNX1 (TELAML1) fusion has an overall good prognosis, but relapses occur, usually after cessation of treatment and occasionally many years later. We have investigated the clonal origins of relapse by comparing the profiles of genomewide copy number alterations at presentation in 21 patients with those in matched relapse (12-119 months). We identified, in total, 159 copy number alterations at presentation and 231 at relapse (excluding Ig/TCR). Deletions of CDKN2A/B or CCNC (6q16.2-3) or both increased from 38% at presentation to 76% in relapse, suggesting that cell-cycle deregulation contributed to emergence of relapse. A novel observation was recurrent gain of chromosome 16 (2 patients at presentation, 4 at relapse) and deletion of plasmocytoma variant translocation 1 in 3 patients. The data indicate that, irrespective of time to relapse, the relapse clone was derived from either a major or minor clone at presentation. Backtracking analysis by FISH identified a minor subclone at diagnosis whose genotype matched that observed in relapse similar to 10 years later. These data indicate subclonal diversity at diagnosis, providing a variable basis for intraclonal origins of relapse and extended periods (years) of dormancy, possibly by quiescence, for stem cells in ETV6-RUNX1(+) acute lymphoblastic leukemia. (Blood. 2011; 117(23): 6247-6254