Abstract: Rearrangements in MLL (MLL-r) are common within very young children with leukemia and affect the prognosis and treatment. Previous studies have suggested the use of the NG2 molecule as a marker for MLL-r but these studies were performed using a small number of infants. We analyzed 148 patients (all less than 24 months, 86 less than 12 months) from various centers in Brazil to determine the predictive power of NG2 within that cohort. We show that NG2 can be used for MLL-r prediction; however, proper staff training and standardized sampling procedures are essential when receiving samples from multiple centers as the accuracy of the prediction varies greatly on a per center basis.
Abstract: Abstract Seven single nucleotide polymorphisms (SNPs) were genotyped in 535 Brazilian children (158 ALL, 74 AML and 303 controls). The subjects were classified as fast or slow acetylators based on their genotypic variants. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals. NAT2 SNP 341T>C frequency was higher among both leukemia subtypes compared to controls. There was also a significant difference in the frequency of SNP 590G>A in AML (OR, 1.57, 1.07-2.30). The haplotypes *14A, *5A, and *5C conferred an increased risk in ALL cases, while *14E, *6B, and *6F conferred an increased risk for AML. An age-dependent analysis demonstrated that the NAT2 slow-acetylators confer an increased risk association with leukemia in children ≤1 year-old (OR, 7.91, 3.87-16.16) and also in older children (1≥10 years-old) (OR, 1.53, 1.01-2.31), however in this last group the magnitude is reduced. The results demonstrate that the NAT2 different haplotypes contribute the risks of either ALL or AML.
Abstract: T-cell acute lymphoblastic leukemia (T-ALL) may affect children in very early age. However, the critical events leading to this brief latency is still unclear. We used standard methods to explore NOTCH1 mutations and other specific molecular markers in 15 early childhood T-ALL cases. Most of them consisted of immature differentiation subtype. Despite being found in a lower frequency than that described for overall pediatric T-ALL, NOTCH1 alterations were the most frequent ones. Other alterations included MLL(+) (n=4), SIL-TAL1(+) (n=3), FLT3 mutation (n=1) and HOX11L2(+) (n=1). Our results suggest that NOTCH1 and MLL abnormalities are primary leukemogenic hits in early T-ALL.
Abstract: Maternal exposure to dipyrone during pregnancy has been associated with risk of infant leukemia (IL). N-Acetyltransferase 2 (NAT2) enzyme acetylates dipyrone, resulting in a detoxified metabolite. We performed genotyping to identify the distribution of NAT2 polymorphisms in duo samples from mothers and children previously investigated in a case-controlled study of IL.
Abstract: In this concise report, we describe the history and evolution of childhood acute leukemia studies in Brazil, and the application if key biomarkers for clinical trials and epidemiological studies over the past 8 years. Highlights of each ongoing study are summarized. A Brazilian network integrating hospitals and scientific institutions from all country regions has been established. This organization is made possible through informatics and computer networking, and the standardization of pathological reviews including immunophenotyping and molecular characterization of childhood leukemias. The unique characteristics of the Brazilian population combined with a large clinical and epidemiologic framework for patient ascertainment has enabled large-scale epidemiological studies on childhood leukemia in Brazil.
Abstract: Acute lymphoblastic leukemia (ALL) in infants is characterized by a high frequency of MLL gene rearrangements. By contrast, the t(12;21) ETV6-RUNX1 fusion gene is typically detected in children older than 2 years. In a series of Brazilian infant leukemia cases, however, four younger cases harbored ETV6-RUNX1, at ages 2, 3, 5, and 7 months. This finding could represent a unique model for delineating the additional genomic hits required to accelerate the emergence of a frank leukemia in these t(12;21)-positive cases. We applied a whole-genome copy number analysis with single-nucleotide polymorphism (SNP) arrays, comparing t(12;21) infants with older pediatric age groups. Recurrent deletions, including 9p21.3 (CDKN2A, CKDN2B, and MTAP), 11p13 (CD44), 12p13.2 (ETV6), and patient-specific abnormalities were identified. Although infant cases with t(12;21) did not display specific genetic abnormalities explaining the short latency to overt leukemia, the frequency of copy number abnormalities increased proportionally with age. This novel SNP array analysis in an extremely rare series of cases opens new ideas about the etiology of ETV6-RUNX1-positive ALL.
Abstract: SIL-TAL1 fusion gene and the ectopic expression of HOX11L2 are common molecular abnormalities in T-cell acute lymphoblastic leukemia (T-ALL). To verify their influence on outcome, we analyzed a Brazilian pediatric T-ALL series of cases. One hundred and ninety two children, age ranged 0-21 years old, were consecutively diagnosed and treated. Reverse transcriptase-polymerase chain reaction (RT-PCR) technique was used to identify the molecular alterations. Kaplan-Meyer method was applied to estimate overall survival. The most frequent maturation stage was T-IV (40.1%), and 30.7% of cases were CD10(+). SIL-TAL1(+) and HOX11L2(+) accounted for 26.7% and 10.3% of the cases, respectively. The overall survival (OS) was 74% in 80-month follow-up. HOX11L2(+) was not predictive factor for outcome. Considering patients younger than nine years-old, those with SIL-TAL1(+) presented a poorer outcome (p = 0.02). The results of this study suggest that in the Brazilian population only the presence of SIL-TAL1 can predict outcome in a restricted group of patients.
Abstract: Down syndrome (DS) is an important risk factor associated with acute leukemia (AL). The presence of polymorphisms that reduce 5,10-methylenetetrahydrofolate reductase (MTHFR) activity has been linked to the multifactorial leukemogenic process. The authors have conducted a study to test whether 677C-->T and/or 1298A-->C polymorphisms of MTHFR would play an additional role in susceptibility of acute myeloid leukemia (AML) in DS children. They also verified whether any polymorphism in the MTHFR gene was associated with the risk of DS. Genetic polymorphisms determination was carried out in 248 samples from healthy individuals as controls and a total of 115 DS children (65 without leukemia and 50 with AML). The present study failed to reveal any association between these polymorphisms and risk of AML in DS children. The data also indicate that MTHFR polymorphisms are not associated with risk of being a DS child.
Abstract: Infant leukemia (IL) is characterised by the presence of MLL rearrangements and a poor outcome. FLT3 gene is consistently highly expressed in MLL+ patients. To correlate the clinical aspects of IL with FLT3 sequence alterations, we have analysed 159 children included in the Brazilian Collaborative Study Group of Infant Acute Leukemia. FLT3-D835 mutations and FLT3-ITD were detected by PCR-RFLP assay and standard PCR amplification, respectively. Mean age at diagnosis was 11.3 months. Overall, 7.5% (ITDs n=6 and D835 n=6) of patients contained FLT3 mutations. FLT3 mutated cases exhibited significantly higher white blood cells (WBC) than wild-type patients (p=0.013). Median overall survival time was 9.2 months (SE 3.3, 95% CI 2.8-15.6). Variables with significant poorer outcomes were age<6 months (p=0.0043), MLL+ (p=0.0292), AML subtype (p=0.0008), high WBC (p=0.0179) and FLT3-D835 mutation (p=0.042). The concomitant presence of FLT3 and MLL abnormalities displayed the worst survival (p=0.0032). Cox regression analysis, with survival as endpoint, showed that leukemia subtype and WBC were independent prognostic factors. Although FLT3 mutations were not a frequent genetic abnormality in this cohort, they might be prognostically important in IL, but this will need to be confirmed in the analyses of larger patient cohorts.
Abstract: Acute leukemia in early childhood is biologically and clinically distinct. The particular characteristics of this malignancy diagnosed during the first months of life have provided remarkable insights into the etiology of the disease. The pro-B, CD10 negative immunophenotype is typically found in infant acute leukemia, and the most common genetic alterations are the rearrangements of the MLL gene. In addition, the TEL/AML1 fusion gene is most frequently found in children older than 24 months. A molecular study on a Brazilian cohort (age range 0-23 months) has detected TEL/AML1+ve (N = 9), E2A/PBX1+ve (N = 4), PML/RARA+ve (N = 4), and AML1/ETO+ve (N = 2) cases. Undoubtedly, the great majority of genetic events occurring in these patients arise prenatally. The environmental exposure to damaging agents that give rise to genetic changes prenatally may be accurately determined in infants since the window of exposure is limited and known. Several studies have shown maternal exposures that may give rise to leukemogenic changes. The Brazilian Collaborative Study Group of Infant Acute Leukemia has found that mothers exposed to dipyrone, pesticides and hormones had an increased chance to give birth to babies with infant acute leukemia [OR = 1.48 (95%CI = 1.05-2.07), OR = 2.27 (95%CI = 1.56-3.31) and OR = 9.08 (95%CI = 2.95-27.96)], respectively. This review aims to summarize recent clues that have facilitated the elucidation of the biology of early childhood leukemias, with emphasis on infant acute leukemia in the Brazilian population.
Abstract: Infant acute lymphoblastic leukemia (IALL) is characterized by mixed lineage leukemia (MLL) gene rearrangements, unique gene expression profiles, poor prognosis, and drug resistance. One exception is cytosine arabinoside (Ara-C) to which IALL cells seem to be more sensitive. We quantified mRNA expression of Ara-C key enzymes in leukemic lymphoblasts from 64 Brazilian ALL children, 15 of them presenting MLL gene rearrangement, and correlated it with clinical and biological features. The diagnosis was based on morphological criteria and immunophenotyping using monoclonal antibodies. MLL gene rearrangements were detected by conventional cytogenetic analysis, RT-PCR and/or fluorescence in situ hybridization. The DCK and HENT1 expression levels were determined by real-time quantitative PCR using SYBR Green I. Relative quantification was made by the standard curve method. The results were analyzed by Mann-Whitney and Fisher exact tests. A P value of <or=0.05 was considered to be statistically significant. DCK and HENT1 expression levels were significantly lower in children with MLL gene-rearranged ALL compared to children with MLL germ line ALL (P = 0.0003 and 0.03, respectively). Our results differ from previous ones concerning HENT1 mRNA expression that observed a higher expression level in MLL gene-rearranged leukemias. In conclusion, the expression of the genes related to Ara-C metabolism was lower in MLL-positive children in the sample studied, suggesting the presence of population differences in the expression profile of these genes especially for HENT1.
Abstract: It has been reported that somatic mutations in the X-linked GATA1 gene are present in hematological clonal disorders in children with Down syndrome (DS). We analyzed retrospective samples of DS children with acute myeloid leukemia, transient leukemia (TL), and myelodysplastic syndrome (MDS) to test whether the specificity of GATA1 mutations can be helpful in distinguishing these hematopoietic disorders. A total of 49 samples were subjected to GATA1 mutation screening by direct sequencing and denaturing polyacrylamide gel electrophoresis (PAGE). Mutations in exon 2 of GATA1 were detected in six of eight DS-AML M7 samples and in four of six DS-TL; no mutation was detected in 13 children with acute lymphoblastic leukemia (DS-ALL), 6 with DS-AML (M0, M2, and M5), 6 with DS-MDS and in 8 DS infants without hematological disorders and 2 children with AML M7 without DS. Blast cells proportion in the sample represented a critical aspect on the sensitivity of mutation detection in GATA1, and a combination of sequence analysis and PAGE is necessary to detect mutations when blast percentage is low. The absence of detected mutations in any of the DS-MDS cases raises the question whether MDS in DS children is an intermediate stage between TL and AML M7, as previously suggested.
Abstract: Chromosome abnormalities often occur prenatally in childhood leukemia, characterizing an early event in leukemogenesis. The majority of the abnormalities occurring in infants involve the MLL gene on chromosome band 11q23. We describe the molecular cytogenetic findings of 207 infant acute leukemia (IAL) cases included in the Brazilian Collaborative Study Group of Infant acute leukemia.
Abstract: The polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene are associated with leukemogenesis. In order to investigate the influence of two polymorphisms in the MTHFR gene, 677C>T and 1298A>C, on the risk of acute lymphoblastic leukemia (ALL) we performed a case-control study in children from different Brazilians' regions. Genotyping of 176 ALL and 199 unselected healthy subjects was performed using PCR-RFLP assay. There was no association between the 677C>T or 1298A>C and risk of ALL in total case-control sample. However, 677T allele was linked to a decrease risk of ALL [odds ratio (OR), 0.43; 95% confidence interval (CI), 0.22-0.86], whereas the 1298A>C polymorphism presents an elevated risk factor [OR, 2.01; 95% CI, 1.01-3.99] in non-White children. Our investigation provides interesting data concerning the opposite effect of A1298C polymorphisms, particularly in the light of relatively scarce data regarding the MTHFR role in leukemia susceptibility in different populations.
Abstract: Transient myeloproliferative disorder is a form of self-limited leukemia that occurs almost exclusively in neonates with Down syndrome. The authors report an unusual case of a newborn without constitutional trisomy 21 who developed undifferentiated leukemia and subsequently achieved clinical and molecular remission without chemotherapy. Cytogenetics and molecular analysis have shown trisomy 21 and GATA1 mutation restricted to leukemic cells. G-to-T transversion was detected, which is predicted to result in a premature stop codon (c.119G>T; pGlu67X) in diagnosis samples. These findings emphasize that there must be a powerful interaction between GATA1 and trisomy 21 in leukemogenesis process.
