| 1. |
- Nordlund, Jessica, et al.
(author)
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Genome-wide signatures of differential DNA methylation in pediatric acute lymphoblastic leukemia
- 2013
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In: Genome Biology. - : Springer Science and Business Media LLC. - 1465-6906 .- 1474-760X. ; 14:9, s. r105-
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Journal article (peer-reviewed)abstract
- BACKGROUND:Although aberrant DNA methylation has been observed previously in acute lymphoblastic leukemia (ALL), the patterns of differential methylation have not been comprehensively determined in all subtypes of ALL on a genome-wide scale. The relationship between DNA methylation, cytogenetic background, drug resistance and relapse in ALL is poorly understood.RESULTS:We surveyed the DNA methylation levels of 435,941 CpG sites in samples from 764 children at diagnosis of ALL and from 27 children at relapse. This survey uncovered four characteristic methylation signatures. First, compared with control blood cells, the methylomes of ALL cells shared 9,406 predominantly hypermethylated CpG sites, independent of cytogenetic background. Second, each cytogenetic subtype of ALL displayed a unique set of hyper- and hypomethylated CpG sites. The CpG sites that constituted these two signatures differed in their functional genomic enrichment to regions with marks of active or repressed chromatin. Third, we identified subtype-specific differential methylation in promoter and enhancer regions that were strongly correlated with gene expression. Fourth, a set of 6,612 CpG sites was predominantly hypermethylated in ALL cells at relapse, compared with matched samples at diagnosis. Analysis of relapse-free survival identified CpG sites with subtype-specific differential methylation that divided the patients into different risk groups, depending on their methylation status.CONCLUSIONS:Our results suggest an important biological role for DNA methylation in the differences between ALL subtypes and in their clinical outcome after treatment.
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| 2. |
- Milani, Lili, et al.
(author)
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DNA methylation for subtype classification and prediction of treatment outcome in patients with childhood acute lymphoblastic leukemia.
- 2010
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In: Blood. - : American Society of Hematology. - 0006-4971 .- 1528-0020. ; 115:6, s. 1214-25
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Journal article (peer-reviewed)abstract
- Despite improvements in the prognosis of childhood acute lymphoblastic leukemia (ALL), subgroups of patients would benefit from alternative treatment approaches. Our aim was to identify genes with DNA methylation profiles that could identify such groups. We determined the methylation levels of 1320 CpG sites in regulatory regions of 416 genes in cells from 401 children diagnosed with ALL. Hierarchical clustering of 300 CpG sites distinguished between T-lineage ALL and B-cell precursor (BCP) ALL and between the main cytogenetic subtypes of BCP ALL. It also stratified patients with high hyperdiploidy and t(12;21) ALL into 2 subgroups with different probability of relapse. By using supervised learning, we constructed multivariate classifiers by external cross-validation procedures. We identified 40 genes that consistently contributed to accurate discrimination between the main subtypes of BCP ALL and gene sets that discriminated between subtypes of ALL and between ALL and controls in pairwise classification analyses. We also identified 20 individual genes with DNA methylation levels that predicted relapse of leukemia. Thus, methylation analysis should be explored as a method to improve stratification of ALL patients. The genes highlighted in our study are not enriched to specific pathways, but the gene expression levels are inversely correlated to the methylation levels.
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| 3. |
- Nordlund, Jessica, et al.
(author)
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Digital gene expression profiling of primary acute lymphoblastic leukemia cells
- 2012
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In: Leukemia. - : Nature Publishing Group. - 0887-6924 .- 1476-5551. ; 26:6, s. 1218-1227
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Journal article (peer-reviewed)abstract
- We determined the genome-wide digital gene expression (DGE) profiles of primary acute lymphoblastic leukemia (ALL) cells from 21 patients taking advantage of `second-generation sequencing technology. Patients included in this study represent four cytogenetically distinct subtypes of B-cell precursor (BCP) ALL and T-cell lineage ALL (T-ALL). The robustness of DGE combined with supervised classification by nearest shrunken centroids (NSC) was validated experimentally and by comparison with published expression data for large sets of ALL samples. Genes that were differentially expressed between BCP ALL subtypes were enriched to distinct signaling pathways with dic(9;20) enriched to TP53 signaling, t(9;22) to interferon signaling, as well as high hyperdiploidy and t(12;21) to apoptosis signaling. We also observed antisense tags expressed from the non-coding strand of similar to 50% of annotated genes, many of which were expressed in a subtype-specific pattern. Antisense tags from 17 gene regions unambiguously discriminated between the BCP ALL and T-ALL subtypes, and antisense tags from 76 gene regions discriminated between the 4 BCP subtypes. We observed a significant overlap of gene regions with alternative polyadenylation and antisense transcription (Pless than1 x 10(-15)). Our study using DGE profiling provided new insights into the RNA expression patterns in ALL cells.
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| 4. |
- Staffas, Anna, 1982, et al.
(author)
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Presence of FLT3-ITD and high BAALC expression are independent prognostic markers in childhood acute myeloid leukemia.
- 2011
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In: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 118:22, s. 5905-5913
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Journal article (peer-reviewed)abstract
- Mutation status of the FLT3, NPM1, CEBPA, and WT1 genes and gene expression levels of ERG, MN1, BAALC, FLT3, and WT1 have been identified as possible prognostic markers in acute myeloid leukemia (AML). We have performed a thorough prognostic evaluation of these genetic markers in pediatric AML patients enrolled in the NOPHO 1993 or NOPHO 2004 protocols. Mutation status and expression levels were analyzed in 185 and 149 patients respectively. Presence of FLT3-ITD was associated with significantly inferior event-free survival (EFS), whereas presence of an NPM1 mutation in the absence of FLT3-ITD correlated with significantly improved EFS. Furthermore, high levels of ERG and BAALC transcripts were associated with inferior EFS. No significant correlation with survival was seen for mutations in CEBPA and WT1 or with gene expression levels of MN1, FLT3, and WT1. In multivariate analysis, the presence of FLT3-ITD and high BAALC expression were identified as independent prognostic markers of inferior EFS. We conclude that analysis of the mutational status of FLT3 and NPM1 at diagnosis is important for prognostic stratification of pediatric AML patients and that determination of the BAALC gene expression level can add valuable information.
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| 5. |
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| 6. |
- Zachariadis, V., et al.
(author)
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The frequency and prognostic impact of dic(9;20)(p13.2;q11.2) in childhood B-cell precursor acute lymphoblastic leukemia : results from the NOPHO ALL-2000 trial
- 2011
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In: Leukemia. - London : Springer Science and Business Media LLC. - 0887-6924 .- 1476-5551. ; 25:4, s. 622-628
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Journal article (peer-reviewed)abstract
- The dic(9;20)(p13.2;q11.2) is reported to be present in similar to 2% of childhood B-cell precursor acute lymphoblastic leukemia (BCP ALL). However, it easily escapes detection by G-banding analysis and its true prevalence is hence unknown. We performed interphase fluorescence in situ hybridization analyses-in a three-step manner-using probes for: (i) CDKN2A at 9p21, (ii) 20p and 20q subtelomeres and (iii) cen9 and cen20. Out of 1033 BCP ALLs diagnosed from 2001 to 2006, 533 were analyzed; 16% (84/533) displayed 9p21 deletions, of which 30% (25/84) had dic(9;20). Thus, dic(9;20)-positivity was found in 4.7% (25/533), making it the third most common genetic subgroup after high hyperdiploidy and t(12;21)(p13;q22). The dic(9;20) was associated with a female predominance and an age peak at 3 years; 18/25 (72%) were allocated to non-standard risk treatment at diagnosis. Including cases detected by G-banding alone, 29 dic(9;20)-positive cases were treated according to the NOPHO ALL 2000 protocol. Relapses occurred in 24% (7/29) resulting in a 5-year event-free survival of 0.69, which was significantly worse than for t(12;21) (0.87; P = 0.002) and high hyperdiploidy (0.82; P = 0.04). We conclude that dic(9;20) is twice as common as previously surmised, with many cases going undetected by G-banding analysis, and that dic(9;20) should be considered a non-standard risk abnormality.
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