Gene-Environment Analyses Reveal Novel Genetic Candidates with Prenatal Tobacco Exposure in Relation to Risk for Childhood Acute Lymphoblastic Leukemia.

<div>AbstractBackground:<p>Associations between maternal tobacco exposure during pregnancy and childhood acute lymphoblastic leukemia (ALL) have yielded mixed results. This may be due to biases in self-reported smoking or other differences in individual-level risk factors. We utilized a biological marker of maternal tobacco exposure to evaluate the association between maternal tobacco exposure during pregnancy, genetics, and subsequent childhood ALL risk in two large population-based studies of childhood ALL in California.</p>Methods:<p>Maternal exposure to tobacco smoke was assessed with a validated methylation marker (cg05575921) of the aryl hydrocarbon receptor repressor (<i>AHRR</i>) gene in newborn dried blood spots. We adjusted for sex, birthweight, gestational age, mode of delivery, year of birth, <i>AHRR</i> quantitative trait locus (mQTL) rs77111113, and a polygenetic risk score for childhood ALL. We additionally adjusted for principal components in a gene–environment interaction testing method that incorporates gene-only and environment-only effects along with interactions.</p>Results:<p><i>AHRR</i> hypomethylation overall was not associated with childhood ALL. In gene–environment interaction testing, several genetic variants displayed significant interaction with <i>AHRR</i> hypomethylation and childhood ALL.</p>Conclusions:<p>Our results suggest that novel candidates in <i>PTPRK</i> and <i>DPP6</i> may play a role in tobacco-related leukemogenesis. Further research is necessary to better understand the effects of tobacco and these variants on childhood ALL risk.</p>Impact:<p>Despite the lack of an overall “main effect,” tobacco exposure during pregnancy affects childhood ALL risk depending on specific genetic variants.</p></div>

<div>AbstractBackground:<p>Associations between maternal tobacco exposure during pregnancy and childhood acute lymphoblastic leukemia (ALL) have yielded mixed results. This may be due to biases in self-reported smoking or other differences in individual-level risk factors. We utilized a biological marker of maternal tobacco exposure to evaluate the association between maternal tobacco exposure during pregnancy, genetics, and subsequent childhood ALL risk in two large population-based studies of childhood ALL in California.</p>Methods:<p>Maternal exposure to tobacco smoke was assessed with a validated methylation marker (cg05575921) of the aryl hydrocarbon receptor repressor (<i>AHRR</i>) gene in newborn dried blood spots. We adjusted for sex, birthweight, gestational age, mode of delivery, year of birth, <i>AHRR</i> quantitative trait locus (mQTL) rs77111113, and a polygenetic risk score for childhood ALL. We additionally adjusted for principal components in a gene–environment interaction testing method that incorporates gene-only and environment-only effects along with interactions.</p>Results:<p><i>AHRR</i> hypomethylation overall was not associated with childhood ALL. In gene–environment interaction testing, several genetic variants displayed significant interaction with <i>AHRR</i> hypomethylation and childhood ALL.</p>Conclusions:<p>Our results suggest that novel candidates in <i>PTPRK</i> and <i>DPP6</i> may play a role in tobacco-related leukemogenesis. Further research is necessary to better understand the effects of tobacco and these variants on childhood ALL risk.</p>Impact:<p>Despite the lack of an overall “main effect,” tobacco exposure during pregnancy affects childhood ALL risk depending on specific genetic variants.</p></div>

Objective:Tobacco smoke contains carcinogens known to damage somatic and germ cells. In this study, we investigated the effect of tobacco smoking on the risk of childhood acute lymphoblastic leukemia (ALL) and myeloid leukemia (AML).Methods:Information about tobacco smoking exposures of the mother before, during, and after pregnancy was collected via PubMed, Embase, and Web of Science databases through November 5, 2018. We performed to evaluate the association between smoking exposure and the risk of childhood ALL and AML. Study selection, data abstraction, and quality assessment were performed by 2 independent reviewers. Random effects models were used to obtain summary odds ratios (ORs) and 95% confidence intervals (CIs).Results:Nineteen case–control studies of childhood leukemia (age < 15 years) conducted in 9 countries from 1974 to 2018. Maternal smoking exposures did not a significant association with childhood ALL (OR = 1.004, 95% CI 0.953–1.058, P = .881) and AML (OR = 0.92, 95% CI 0.815–1.038, P = .177) during exposure time windows. However, there was an association with paternal smoking and ALL (OR = 1.15, 95% CI 1.038–1.275, P = .007). Paternal smoking in AML showed there was no association with smoking exposures and childhood AML (OR = 1.133, 95% CI 0.943–1.362, P = .181). Next, maternal daily cigarettes consumption showed no associations with ALL (OR = 1.08, 95% CI 1.000–1.168, P = .051) during pregnancy. No association with maternal daily smoking and AML (OR = 0.909, 95% CI 0.682–1.211, P = .514). Paternal daily cigarettes consumption was associated with increased risks of childhood ALL (OR = 1.200, 95% CI 1.112–1.302, P = .000). The higher consumption of paternal smoking (more than 10 per day) was significantly related to childhood ALL. Paternal daily smoking consumption also was related to AML (OR = 1.242, 95% CI 1.031–1.496, P = .022).Conclusion:Maternal smoking before, during, or after pregnancy was not associated with childhood ALL or AML. However, paternal smoking was related to a significantly elevated risk of childhood ALL during pregnancy, but not for AML. Maternal daily smoking consumption was not associated with ALL or AML during pregnancy. The higher consumption of paternal smoking were, the higher the risk of childhood ALL or AML.

BackgroundRecently, there have been a number of studies on the association between XRCC1 polymorphisms and childhood acute lymphoblastic leukemia (ALL) risk. However, the results of previous reports are inconsistent. Thus, we performed a meta-analysis to clarify the effects of XRCC1 variants on childhood ALL risk.MethodsA meta-analysis was performed to examine the association between XRCC1 polymorphisms (Arg399Gln, Arg194Trp, and Arg280His) and childhood ALL risk. We critically reviewed 7 studies with a total of 880 cases and 1311 controls for Arg399Gln polymorphism, 3 studies with a total of 345 cases and 554 controls for Arg280His polymorphism, and 6 studies with a total of 783 cases and 1180 controls for Arg194Trp polymorphism, respectively. Odds ratio (OR) and its 95% confidence interval (CI) were used.ResultsSignificant association between XRCC1 Arg399Gln polymorphism and childhood ALL risk was observed in total population analyses (ORadditive model = 1.501, 95% CI 1.112–2.026, POR = 0.008; ORdominant model = 1.316, 95% CI = 1.104–1.569, POR = 0.002) and Asian subgroup analyses (ORadditive model = 2.338, 95%CI = 1.254–4.359, POR = 0.008; ORdominant model = 2.108, 95%CI = 1.498–2.967, POR = 0.000). No association was detected in Caucasians, Metizo and mixed populations. Ethnicity was considered as a significant source of heterogeneity in the meta-regression model. For the other two XRCC1 polymorphisms, no association with childhood ALL risk was found.ConclusionsThe meta-analysis results suggested that XRCC1 Arg399Gln polymorphism might be associated with elevated childhood ALL risk among Asian population.

Surrogate measures of infectious exposures have been consistently associated with lower childhood acute lymphoblastic leukemia (ALL) risk. However, recent reports have suggested that physician-diagnosed early-life infections increase ALL risk, thereby raising the possibility that stronger responses to infections might promote risk. We examined whether medically diagnosed infections were related to childhood ALL risk in an integrated health-care system in the United States. Cases of ALL (n=435) diagnosed between 1994-2014 among children aged 0-14 years, along with matched controls (n=2,170), were identified at Kaiser Permanente Northern California. Conditional logistic regression was used to estimate risk of ALL associated with history of infections during first year of life and across the lifetime (up to diagnosis). History of infection during first year of life was not associated with ALL risk (odds ratio (OR)=0.85, 95% confidence interval (CI): 0.60, 1.21). However, infections with at least 1 medication prescribed (i.e., more "severe" infections) were inversely associated with risk (OR=0.42, 95% CI: 0.20, 0.88). Similar associations were observed when the exposure window was expanded to include medication-prescribed infections throughout the subjects' lifetime (OR=0.52, 95% CI: 0.32, 0.85).

Methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms have been implicated in childhood acute lymphoblastic leukemia (ALL) risk, but previously published studies were inconsistent and recent meta-analyses were not adequate. In a meta-analysis of 21 publications with 4,706 cases and 7,414 controls, we used more stringent inclusion method and summarized data on associations between MTHFR C677T and A1298C polymorphisms and childhood ALL risk. We found an overall association between 677T variant genotypes and reduced childhood ALL risk. Specifically, in the dominant genetic model, an association was found in a fixed-effect (TT + CT vs. CC: OR = 0.92; 95% CI = 0.85-0.99) but not random-effect model, whereas such an association was observed in both homozygote genetic model (TT vs. CC: OR = 0.80; 95% CI = 0.70-0.93 by fixed effects and OR = 0.78; 95% CI = 0.65-0.93 by random effects) and recessive genetic model (TT vs. CC + CT: OR = 0.83; 95% CI = 0.72-0.95 by fixed effects and OR = 0.84; 95% CI = 0.73-0.97 by random effects). These associations were also observed in subgroups by ethnicity: for Asians in all models except for the dominant genetic model by random effect and for Caucasians in all models except for the recessive genetic model. However, the A1298C polymorphism did not appear to have an effect on childhood ALL risk. These results suggest that the MTHFR C677T, but not A1298C, polymorphism is a potential biomarker for childhood ALL risk.

Accumulating evidence suggests that childhood acute lymphoblastic leukemia (ALL) may be initiated in utero or early in the postnatal period. High birth weight (or rapid fetal growth) is associated with risk of ALL, but the mechanisms are not understood. In a population-based epidemiologic study of childhood ALL, we utilized a haplotype-based approach to assess the role of eight genes involved in fetal growth and body size regulation in 377 childhood ALL cases and 448 controls. We found significant haplotype associations with risk of childhood ALL for IGF1 among non-Hispanics and Hispanics together (p = 0.002), for IGF2 among Hispanics (p = 0.040), and for IGF2R among Hispanics and non-Hispanics (p = 0.051 and 0.009, respectively). No haplotype associations were observed for IGF1R or the studied genes involved in body size regulation, including LEP, LEPR, GHRL, and NPY. Our study is the first to identify an association between the genes involved in the IGF axis and risk of childhood ALL. These findings for childhood ALL emphasize the importance of fetal growth, when lymphoid progenitor cells are not yet fully differentiated and therefore more susceptible to malignant transformation. Additional studies are needed to confirm these findings and identify specific causal variants.

Acute lymphoblastic leukemia (ALL) is the most common type of cancer among children. Tobacco exposure during gestation has been investigated as a potential risk factor, but its role remains undefined. Given tobacco's toxicologic profile as a DNA-damaging agent, we examined the impact of DNA repair gene variability as a source of vulnerability to tobacco exposure risk for ALL. Leveraging demographic and genotype data from two large California-based ALL epidemiology studies, we used logistic regression, MinimumP (minP) statistical method, and permutation tests to examine interactions between DNA repair genes and prenatal tobacco exposure. We found statistically significant interactions between prenatal tobacco exposure and DNA repair genes RECQL (minP = 1.00 × 10-4, FDR-P value = 1.86 × 10-2) and TDG (minP = 1.00 × 10-4, FDR-P value = 1.86 × 10-2) with regard to childhood ALL risk. Notable interactions in the homologous recombination pathway were observed among Latino children, whereas non-Latino White children displayed significant interactions in the base excision repair and nucleotide excision repair pathways. Our study highlights the significance of DNA repair genes and pathways when evaluating environmental exposure to tobacco smoke, suggesting that genetic variability within these pathways could impact vulnerability in the development of childhood ALL. This study highlights the significant impact of genetic variation interacting with prenatal tobacco exposure on ALL risk. Further research is needed to understand these interactions and their implications for ALL etiology. Expanding studies to other gene-environment interactions will aid in developing targeted prevention, diagnosis, and treatment strategies for pediatric oncology.

Genetic Polymorphisms in the Folate Pathway and Risk of Childhood Acute Lymphoblastic Leukemia (ALL): MTHFR, MTHFD1, RFC1 and TS.

Association of three polymorphisms in ARID5B, IKZF1and CEBPE with the risk of childhood acute lymphoblastic leukemia in a Chinese population

Genetic polymorphisms in the promoter regions of FAS, FASL and CASP8 involved in the apoptotic signaling pathway are thought to be associated with susceptibility to cancer. We hypothesized that these functional genetic variants might be associated with the risk of childhood acute lymphoblastic leukemia (ALL). A case–control study in a Chinese population with 361 cases of ALL and 519 controls was performed to evaluate the association between FAS, FASL and CASP8 variants and risk of childhood ALL. Individuals with FAS − 1377AG had an odds ratio (OR) of 0.72 for the risk of ALL compared to − 1377GG and the variant FASL − 844CC was associated with a statistically significantly decreased risk of childhood ALL (OR = 0.38). Furthermore, combined genotypes with 5–8 protective alleles were associated with a significantly decreased risk of childhood ALL compared with those with 0–4 variants, and this decreased risk was more pronounced among the subgroups of age < 6 years, female, parental never-drinking status and never house-painting. Our results provide evidence that FAS–FASL–CASP8 polymorphisms contributed to a reduced risk of childhood ALL in our population. Larger studies are warranted to validate our findings.

Microsomal epoxide hydrolase, EPHX1, plays a central role in the detoxification of potentially genotoxic epoxide intermediates. In this study, we firstly aimed to investigate the relationship between EPHX1 Tyr113His and His139Arg variants, and the risk of incidence of childhood acute lymphoblastic leukemia (ALL) in Turkish population, comprised of 190 healthy controls and 167 ALL patients. In exon 3 Tyr113His polymorphism, 113His/His homozygous mutant genotype with slow activity was 18.6% in ALL patients and 9% in controls, indicating 113His/His slow activity genotype was significantly associated with an increased risk of childhood ALL (OR: 2.3, 95% CI, 1.2-4.4, P = 0.01). No significant association was found between exon 4 His139Arg variant and the risk of ALL. When both exon 3 Tyr113His and exon 4 His139Arg polymorphisms were considered together, only the exon 3 113His/His, homozygous mutant, slow activity genotype with exon 4 wild-type genotype 139His/His was significantly increased the risk of ALL 2.4-fold (OR: 2.4, P = 0.02). We also evaluated whether haplotype analysis for EPHX1 Tyr113His polymorphism together with DNA protein XRCC1 Arg399Gln variant known for its deficient DNA repair capacity would represent more prominent risk factors for the development of childhood ALL. Accordingly, the co-presence of Tyr113His variant of EPHX1 and Arg399Gln variant of XRCC1 in the same individuals significantly increased the risk of childhood ALL up to 2.1-fold (OR = 2.1, P = 0.03). Moreover, homozygous mutant genotype for both genes significantly and considerably increased the risk of childhood ALL 8.5-fold (OR: 8.5, P = 0.03). In conclusion, individuals with EPHX1 113His/His slow activity genotype may not detoxify reactive carcinogenic epoxides efficiently, binding of reactive epoxides to DNA cause DNA damage. With the inadequate polymorphic DNA repair protein, XRCC1, this situation ultimately leads to significantly increased susceptibility for childhood ALL.

A role for folate in the etiology of childhood acute lymphoblastic leukemia (ALL) has long been suspected due to folate's dual role in control of DNA methylation as well as maintenance of DNA synthesis. Case-control studies examining self-reported maternal folate intake and supplementation during pregnancy have been inconclusive. Furthermore, while studies of children's own folate metabolism and transport genes have identified potential disease loci, the results have been mixed on the whole. A child's exposure to folate in utero is modulated by a number of factors, including maternal intake/supplementation, maternal genes, and child's genes. Therefore, we examined the role of folate in childhood ALL risk more directly by utilizing a quantitative microbiologic assay to measure newborn red blood cell folate levels in archived dried bloodspots collected at birth from 319 incident cases and 413 matched population-based controls who enrolled in the Northern California Childhood Leukemia Study between 1995 and 2002. After adjustment for income, race/ethnicity, gender, and age, we found no difference in newborn folate levels between cases and controls overall (971 vs. 968 nmol/L, p=0.94). In addition, no differences between cases and controls were observed after stratification by birth year to account for the start of folate fortification of grain products in the US (1982-1994: 953 vs. 952 nmol/L, p=0.98; 1995-1998: 1018 vs. 975 nmol/L, p=0.34; and 1999-2002: 878 vs. 990 nmol/L, p=0.23). Children whose mothers reported pre-pregnancy supplement use had somewhat higher newborn folate levels overall, but we observed no case-control differences in folate levels after stratification by supplement use. Our results do not support an association between folate levels at birth and risk of childhood ALL. However, our results do not rule out a role for folate exposures after birth. Future epidemiologic studies of childhood ALL should pay particular attention to post-natal folate exposures. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 676. doi:1538-7445.AM2012-676

Acute lymphoblastic leukemia (ALL) is the most common cancer in children, and efforts to understand its etiology has followed a paradigm that common genetic variation in the presence of modifiable environmental factors contribute to disease risk. To date, there are numerous reports of candidate gene association studies suggesting an involvement of genetic loci in childhood ALL risk, but the general lack of consistency in results has underscored the need for careful interpretation and confirmation in additional well-designed studies. Complementary efforts using the genome-wide association study approach have shown indisputable evidence that common low penetrance genetic polymorphisms contribute to childhood ALL risk. However, current calculations show that these established disease loci only explain a portion of the total estimated contribution of common genetic variation on childhood ALL risk. Certain candidate gene loci previously examined likely contribute to this unexplained variation in risk, but the challenge moving forward will be to establish which ones based on the accumulating evidence. In this review, we describe the results of the most recent gene association studies in childhood ALL and discuss options for future efforts to advance this area of research.

Acute lymphoblastic leukemia (ALL) is the most common type of cancer in children (age 0–14 years); however, the etiology remains incompletely understood. Several environmental exposures have been linked to risk of childhood ALL, including air pollution. Closely related to air pollution and human development is artificial light at night (ALAN), which is believed to disrupt circadian rhythm and impact health. We sought to evaluate outdoor ALAN and air pollution on risk of childhood ALL. The California Linkage Study of Early-Onset Cancers is a large population-based case–control in California that identifies and links cancer diagnoses from the California Cancer Registry to birth records. For each case, 50 controls with the same year of birth were obtained from birth records. A total of 2,782 ALL cases and 139,100 controls were identified during 2000–2015. ALAN was assessed with the New World Atlas of Artificial Night Sky Brightness and air pollution with an ensemble-based air pollution model of particulate matter smaller than 2.5 microns (PM2.5). After adjusting for known and suspected risk factors, the highest tertile of ALAN was associated with an increased risk of ALL in Hispanic children (odds ratio [OR] = 1.15, 95% confidence interval [CI] 1.01–1.32). There also appeared to be a borderline association between PM2.5 level and risk of ALL among non-Hispanic White children (OR per 10 µg/m3 = 1.24, 95% CI 0.98–1.56). We observed elevated risk of ALL in Hispanic children residing in areas of greater ALAN. Further work is needed to understand the role of ALAN and air pollution in the etiology of childhood ALL in different racial/ethnic groups.