Structural and numerical abnormalities resolved in one-step analysis: the most common chromosomal rearrangements detected by comparative genomic hybridization in childhood acute lymphoblastic leukemia

Cytogenetic abnormalities and TP53 and RAS gene profiles of childhood acute lymphoblastic leukemia in Morocco

BACKGROUND

Recurrent genetic abnormalities affecting pivotal signaling pathways are the hallmark of childhood acute lymphoblastic leukemia (ALL). The identification of these aberrations remains clinically important. Therefore, we sought to determine the cytogenetic profile and the mutational status of TP53 and RAS genes among Moroccan childhood cases of ALL.

METHODS

In total, 35 patients with childhood ALL were enrolled in the study. The diagnosis and treatment were established in the Pediatric Hematology and Oncology Center at the Children's Hospital of Rabat. Chromosome banding analysis and fluorescence in situ hybridization were used to detect genetic aberrations. Blood samples were screened for TP53 and RAS mutations using Sanger sequencing.

RESULTS

Of the 35 cases, 30 were B-lineage ALL (85.7 %). Moreover, a male predominance was observed. Cytogenetic analysis revealed chromosomal anomalies in 27 cases (77.1 %). The most frequent aberrations were high hyperdiploidy and BCR/ABL rearrangement. Interestingly, we found the rare t(15;16) and the t(8;14), which are uncommon translocations in pediatric B-ALL. The mutational analysis revealed Pro72Arg (rs1042522:C > G) and Arg213Arg (rs1800372:A > G) in TP53. In correlation with cytogenetic data, rs1042522:C > G showed a significant association with the occurrence of chromosomal translocations (p = 0.04). However, no variant was detected in NRAS and KRAS genes.

CONCLUSION

Our findings emphasize the significance of detecting chromosomal abnormalities as relevant prognostic markers. We also suggest a low occurrence of genetic variants among Moroccan children with ALL.

Comparative Genomic Hybridization and Transcriptome Sequencing Reveal Genes with Gain in Acute Lymphoblastic Leukemia: JUP Expression Emerges as a Survival-Related Gene

Acute lymphoblastic leukemia (ALL) in children or adults is characterized by structural and numeric aberrations in chromosomes; these anomalies strongly correlate with prognosis and clinical outcome. Therefore, this work aimed to identify the genes present in chromosomal gain regions found more frequently in patients with acute lymphoblastic leukemia (ALL) and ALL-derived cell lines using comparative genomic hybridization (CGH). In addition, validation of the genes found in these regions was performed utilizing RNAseq from JURKAT, CEM, and SUP-B15 cell lines, as well as expression microarrays derived from a MILE study. Chromosomes with common gain zones that were maintained in six or more samples were 14, 17, and 22, in which a total of 22 genes were identified. From them, NT5C3B, CNP, ACLY, and GNB1L maintained overexpression at the mRNA level in the cell lines and in patients with ALL. It is noteworthy that SALL2 showed very high expression in T-ALL, while JUP was highly expressed in B-ALL lineages. Interestingly, the latter correlated with worse survival in patients. This provided evidence that the measurement of these genes has high potential for clinical utility; however, their expressions should first be evaluated with a sensitive test in a more significant number of patients.

Genome-Wide DNA Copy Number Analysis of Acute Lymphoblastic Leukemia Identifies New Genetic Markers Associated with Clinical Outcome

Identifying additional genetic alterations associated with poor prognosis in acute lymphoblastic leukemia (ALL) is still a challenge. Aims: To characterize the presence of additional DNA copy number alterations (CNAs) in children and adults with ALL by whole-genome oligonucleotide array (aCGH) analysis, and to identify their associations with clinical features and outcome. Array-CGH was carried out in 265 newly diagnosed ALLs (142 children and 123 adults). The NimbleGen CGH 12x135K array (Roche) was used to analyze genetic gains and losses. CNAs were analyzed with GISTIC and aCGHweb software. Clinical and biological variables were analyzed. Three of the patients showed chromothripsis (cth6, cth14q and cth15q). CNAs were associated with age, phenotype, genetic subtype and overall survival (OS). In the whole cohort of children, the losses on 14q32.33 (p = 0.019) and 15q13.2 (p = 0.04) were related to shorter OS. In the group of children without good- or poor-risk cytogenetics, the gain on 1p36.11 was a prognostic marker independently associated with shorter OS. In adults, the gains on 19q13.2 (p = 0.001) and Xp21.1 (p = 0.029), and the loss of 17p (p = 0.014) were independent markers of poor prognosis with respect to OS. In summary, CNAs are frequent in ALL and are associated with clinical parameters and survival. Genome-wide DNA copy number analysis allows the identification of genetic markers that predict clinical outcome, suggesting that detection of these genetic lesions will be useful in the management of patients newly diagnosed with ALL.

Array-based comparative genomic hybridization detects copy number variations with prognostic relevance in 80% of ALL with normal karyotype or failed chromosome analysis

Pretreatment cytogenetics is an important parameter for risk stratification and therapy approach in acute lymphoblastic leukemia (ALL). However, in up to 30% of cases, chromosome banding analysis (CBA) fails or reveals a normal karyotype. To characterize the subset of ALL with normal karyotype or failed CBA, we performed fluorescence in situ hybridization (FISH) or PCR for BCR-ABL1 and MLL rearrangements as well as array comparative genomic hybridization (aCGH) in 186 adult patients. We further carried out FISH for MYC in cases with Burkitt leukemia phenotype. FISH or PCR revealed one of the respective rearrangements in 22% of patients. In 80% of cases, copy number variations (CNV) were identified by aCGH. In 22% of cases, all CNV were below the resolution of CBA. On the basis of results of FISH, RT-PCR and aCGH, patients were categorized into three groups. The novel subset of patients with submicroscopic CNV only showed an overall survival at 3 years of 84% compared with 64% for patients classified as adverse abnormalities and 77% for cases with other aberrations (P=0.046). Thus, ALL with non-informative CBA can be further classified by FISH and aCGH providing prognostic information, which may be useful for a more individualized therapy.