Modification of the association between maternal smoke exposure and congenital heart defects by polymorphisms in glutathione S-transferase genes

Association of maternal phthalates exposure and metabolic gene polymorphisms with congenital heart diseases: a multicenter case-control study

BACKGROUND

The majority of congenital heart diseases (CHDs) are thought to result from the interactions of genetics and the environment factors. This study aimed to assess the association of maternal non-occupational phthalates exposure, metabolic gene polymorphisms and their interactions with risk of CHDs in offspring.

METHODS

A multicenter case-control study of 245 mothers with CHDs infants and 268 control mothers of health infant was conducted from six hospitals. Maternal urinary concentrations of eight phthalate metabolites were measured by ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). Twenty single nucleotide polymorphisms (SNPs) in cytochrome P450 family 2 subfamily C member 9 (CYP2C9) and 19 (CYP2C19), uridine diphosphate (UDP) glucuronosyl transferase family 1 member A7 (UGT1A7), family 2 member B7 (UGT2B7) and B15(UGT2B15) genes were genotyped. The multivariate logistic regressions were used to estimate the association between maternal phthalates exposure or gene polymorphisms and risk of CHDs. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the gene-gene and gene-phthalates exposure interactions.

RESULTS

There was no significant difference in phthalate metabolites concentrations between the cases and controls. No significant positive associations were observed between maternal exposure to phthalates and CHDs. The SNPs of UGT1A7 gene at rs4124874 (under three models, log-additive: aOR = 1.74, 95% CI:1.28-2.37; dominant: aOR = 1.86, 95% CI:1.25-2.78; recessive: aOR = 2.50, 95% CI: 1.26-4.94) and rs887829 (under the recessive model: aOR = 13.66, 95% CI: 1.54-121) were significantly associated with an increased risk of CHDs. Furthermore, the associations between rs4124874 (under log-additive and dominant models) of UGT1A7 were statistically significant after the false discovery rate correction. No significant gene-gene or gene-phthalate metabolites interactions were observed.

CONCLUSIONS

The polymorphisms of maternal UGT1A7 gene at rs4124874 and rs887829 were significantly associated with an increased risk of CHDs. More large-scale studies or prospective study designs are needed to confirm or refute our findings in the future.

Maternal Exposure to PM2.5 and the Risk of Congenital Heart Defects in 1.4 Million Births: A Nationwide Surveillance-Based Study

BACKGROUND

Evidence remains limited about the association of maternal exposure to ambient fine particulate matter (airborne particles with an aerodynamic diameter ≤2.5 µm [PM2.5]) with fetal congenital heart defects (CHDs) in highly polluted regions, and few studies have focused on preconception exposure.

METHODS

Using a nationwide surveillance-based case-control design in China, we examined the association between maternal exposure to PM2.5 during periconception (defined as 3 months before conception until 3 months into pregnancy) and risk of CHD in offspring. The study included 1 434 998 births involving 7335 CHDs from 2014 through 2017 on the basis of the National Population-Based Birth Defects Surveillance System, covering 30 provinces, municipalities, or municipal districts in China. We assigned maternal PM2.5 exposure during the periconception period to each participant using satellite-based PM2.5 concentrations at 1-km spatial resolution. Multilevel logistic regression models were used to calculate the multivariable-adjusted odds ratio and 95% CI for CHDs in offspring associated with maternal PM2.5 exposure, and the exposure-response association was investigated using restricted cubic spline analysis. Subgroup or sensitivity analyses were conducted to identify factors that may modify the association.

RESULTS

The average maternal exposure to PM2.5 levels across all participants was 56.51 μg/m3 (range, 10.95 to 182.13 μg/m3). For each 10 μg/m³ increase in maternal PM2.5 exposure, the risk of CHDs in offspring was increased by 2% (odds ratio, 1.02 [95% CI, 1.00 to 1.05]), and septal defect was the most influenced subtype (odds ratio, 1.04 [95% CI, 1.01 to 1.08]). The effect of PM2.5 on CHD risk was more pronounced during the preconception period. Mothers <35 years of age, those living in northern China, and those living in low-income areas were more susceptible to PM2.5 exposure than their counterparts (all P<0.05). PM2.5 exposure showed a linear association with total CHDs or specific CHD types.

CONCLUSIONS

High maternal PM2.5 exposure, especially during the preconception period, increases risk of certain types of CHD in offspring. These findings are useful for CHD prevention and highlight the public health benefits of improving air quality in China and other highly polluted regions.

Biomarkers for isolated congenital heart disease based on maternal amniotic fluid metabolomics analysis

INTRODUCTION

Congenital heart disease (CHD) is one of the most prevalent birth defects in the world. The pathogenesis of CHD is complex and unclear. With the development of metabolomics technology, variations in metabolites may provide new clues about the causes of CHD and may serve as a biomarker during pregnancy.

METHODS

Sixty-five amniotic fluid samples (28 cases and 37 controls) during the second and third trimesters were utilized in this study. The metabolomics of CHD and normal fetuses were analyzed by untargeted metabolomics technology. Differential comparison and randomForest were used to screen metabolic biomarkers.

RESULTS

A total of 2472 metabolites were detected, and they were distributed differentially between the cases and controls. Setting the selection criteria of fold change (FC) ≥ 2, P value < 0.01 and variable importance for the projection (VIP) ≥ 1.5, we screened 118 differential metabolites. Within the prediction model by random forest, PE(MonoMe(11,5)/MonoMe(13,5)), N-feruloylserotonin and 2,6-di-tert-butylbenzoquinone showed good prediction effects. Differential metabolites were mainly concentrated in aldosterone synthesis and secretion, drug metabolism, nicotinate and nicotinamide metabolism pathways, which may be related to the occurrence and development of CHD.

CONCLUSION

This study provides a new database of CHD metabolic biomarkers and mechanistic research. These results need to be further verified in larger samples.

Association between maternal smoke exposure and congenital heart defects from a case-control study in China

There is a gap in knowledge how maternal exposure to environmental tobacco smoke (ETS) is associated with offspring congenital heart defects (CHDs). In this case-control study, we collected data on 749 fetuses with CHDs and 880 fetuses without any congenital anomalies to examine the association of maternal ETS with fetal CHDs and the potentially moderating effect by maternal hazardous and noxious substances (HNS), periconceptional folate intake and paternal smoking. Maternal exposure to ETS in first trimester was associated with increased risk of CHDs in a dose-response gradient, with the AORs (95% CI) were1.38 (1.00-1.92), 1.60 (1.07-2.41), and 4.94 (2.43-10.05) for ETS < 1 h/day, 1-2 h/day, and ≥ 2 h/day, respectively. With the doubly unexposed group as reference categories, AORs for maternal ETS exposure ≥ 2 h/day in the absence of folate intake, in the presence of HNS exposure or paternal smoking, were 7.21, 11.43, and 8.83, respectively. Significant additive interaction between ETS exposure and maternal folate intake on CHDs was detected. Maternal ETS exposure during first trimester may increase the risk of offspring CHDs in a dose-response shape, and such effect may be modified by maternal folate intake or other potential factors.

Environmental Exposures and Congenital Heart Disease

Congenital heart disease (CHD) is the most common congenital abnormality worldwide, affecting 8 to 12 infants per 1000 births globally and causing >40% of prenatal deaths. However, its causes remain mainly unknown, with only up to 15% of CHD cases having a determined genetic cause. Exploring the complex relationship between genetics and environmental exposures is key in understanding the multifactorial nature of the development of CHD. Multiple population-level association studies have been conducted on maternal environmental exposures and their association with CHD, including evaluating the effect of maternal disease, medication exposure, environmental pollution, and tobacco and alcohol use on the incidence of CHD. However, these studies have been done in a siloed manner, with few examining the interplay between multiple environmental exposures. Here, we broadly and qualitatively review the current literature on maternal and paternal prenatal exposures and their association with CHD. We propose using the framework of the emerging field of the exposome, the environmental complement to the genome, to review all internal and external prenatal environmental exposures and identify potentiating or alleviating synergy between exposures. Finally, we propose mechanistic pathways through which susceptibility to development of CHD may be induced via the totality of prenatal environmental exposures, including the interplay between placental and cardiac development and the internal vasculature and placental morphology in early stages of pregnancy.

Parental risk factors associated with congenital heart disease in a Thai population: multivariable analysis

Background

Congenital heart diseases (CHDs) are the most common types of birth defects and contribute to a large proportion of infant morbidities and mortalities worldwide. These defects may require multiple surgical interventions impacting the infant's quality of life.

Objectives

To identify risk factors associated with CHD in a population of Thai children.

Methods

We conducted a case-control study of patients attending the Pediatric Clinic, Naresuan University Hospital, Thailand. We included data from pediatric patients diagnosed with CHDs as cases, and patients without cardiovascular abnormalities as controls. Risk data were collected from July 2019 to April 2020 using face-to-face interviews. Multiple logistic regression was used to analyze parental factors associated with CHDs.

Results

We included 249 cases classified into 2 groups according to severity and 304 patients as controls. For those less-severely affected (155 patients, 62.2%), ventricular septal defect (27.7%) was the most prevalent, whereas for those with severe CHDs, tetralogy of Fallot was the most prevalent (14.0%). There was no difference in sex distribution or maternal obstetric history between the groups. In multivariable analysis, a family history of CHDs (adjusted odds ratio [AOR] 4.67, 95% confidence interval (CI) 1.61-13.57, P = 0.005) and maternal exposure to second-hand cigarette smoke (AOR 1.58, 95% CI 1.03-2.42, P = 0.002) were identified as significant risk factors for CHDs.

Conclusion

A family history of CHDs and maternal exposure to second-hand cigarette smoke are associated with having offspring with CHDs in the population studied. These findings help us to encourage affected parents to obtain a fetal echocardiogram.

Maternal trichloroethylene exposure and metabolic gene polymorphisms may interact during fetal cardiovascular malformation

This study aimed to analyze the potential association between trichloroethylene (TCE) exposure and congenital heart disease (CHD) and to explore the effect of metabolic enzyme gene polymorphisms on heart development. A multicenter case-control study was conducted. The trichloroethylene concentrations were measured by UPLC-MSMS in urine. Fourteen SNPs in the GSTA1, GSTP1, MPO, NAT1, NAT2, CYP1A1, CYP1A2, CYP2E1 and EPHX1 genes were genotyped using an improved multiplex ligation detection reaction (iMLDR) technique. A total of 283 cases and 331 controls with maternal urine and/or venous blood were included in the present study. The median NAcDCVC was 7.65 ng/mL in the case group and 7.43 ng/mL in the control group. There was no significant difference in the NAcDCVC concentration between the CHD subtypes and controls (P > 0.05). The GA/AA of GSTA1 rs3957357 could increase the risk of CHDs under the dominant model (aOR = 2.26, 95 % CI: 1.31, 3.90), but other SNPs were not associated with CHDs (P > 0.05). GA or AA genotypes of GSTA1 rs3957357 with lower levels of TCE exposure were 3.53 times at risk relative to mothers carrying the wild type genotype. In conclusion, maternal exposure to trichloroethylene alone is not associated with the occurrence of fetal CHD and CHD subtypes. Maternal GSTA1 rs3957357 may increase the risk of CHD in offspring. TCE exposure and metabolic gene polymorphisms probably interact with each other to induce fetal cardiovascular malformation, but larger sample size studies are needed to confirm this hypothesis.

Genetic predisposition to the development of congenital heart diseases: Role of xenobiotic biotransformation genes

Congenital heart diseases are one of the most common multi-factorial fetal abnormalities caused by a complex of endo- and exogenous factors. It is known that mutations in xenobiotic biotransformation genes can be associated with the pathogenesis of congenital heart diseases. In the presented research, 131 children with congenital heart diseases and 101 women having children with this pathology were included in the study group. In control group, 103 healthy children and their mothers were included. Single-nucleotide polymorphisms in the xenobiotic biotransformation genes CYP1A1 (rs1048943), CYP1A2 (rs762551), GSTP1 (rs6591256, rs1871042 and rs17593068) were detected by the real-time polymerase chain reaction. Gene-gene interactions were determined using the Multifactor Dimensionality Reduction method. We obtained no difference in the frequency of CYP1A1, CYP1A2 and GSTP1 between the study and control groups. At the same time, the genetic combinations GSTP1 (rs6591256)-GSTP1 (rs1871042) and GSTP1 (rs6591256)-GSTP1 (rs1871042)-CYP1A1 (rs1048943) in women; and GSTP1 (rs1793068)-GSTP1 (rs6591256)-GSTP1 (rs1871042)-CYP1A1 (rs1048943)-CYP1A2 (rs762551) in children contribute to the pathogenesis of congenital heart diseases.

Risk factor analysis for congenital heart defects in children

Congenital heart defects (CHDs) are the most common malformations, occurring in almost 1.0 in 100 births. We investigated an association between risk factors and CHDs, because epidemiological studies have reported conflicting results regarding risk factors and CHDs recently. The study of CHD frequency was conducted in Chernivtsi region (Northern Bukovina) on the basis of the medical genetic center. A retrospective method of research by studying registration genetic maps was used to analyze risk factors. 91 cards of infants suffering from CHD (47 boys and 44 girls) aged 0–1 living in the territory of Northern Bukovina were selected. In order to identify risk factors, 133 cards of healthy infants (77 boys and 56 girls) were used. The analysis of risk factors revealed that the female gender of a child is a risk factor for CHD development. The analysis of the ordinal number of pregnancy revealed that the second and the third pregnancies are probable risk factors for the development of this pathology. It was found in our study that folic acid intake during the first trimester prevented CHD development (OR 2.33). The study revealed that among stressful risk factors are: unplanned pregnancy (OR 3.13); out-of-wedlock pregnancy and stress during pregnancy. Maternal CHD increased the CHD development in offspring approximately by two times. Some factors, such as a woman doing hard physical work during pregnancy, having sedentary work during pregnancy, the mother being a housewife or having an incomplete secondary education (OR 3.61), the mother’s secondary education, the father’s incomplete secondary education (OR 18.62), the father serving in the army (OR 2.15) or being a student at the time of woman’s pregnancy (OR 2.97) were significant for CHD development in the fetal stage. A young age of the father (up to 43 years) was also considered as one of the risk factors. This article is expected to provide timely information on risk factors for CHD development to a wide range of medical staff, including pediatric and adult cardiologists, pediatricians, thoracic surgeons, obstetricians, gynecologists, medical geneticists, genetic counselors and other relevant clinicians.

Association between prepregnancy body mass index and risk of congenital heart defects in offspring: an ambispective observational study in China

BACKGROUND

Congenital heart defects (CHDs) are the most common birth defect around the world. Maternal prepregnancy obesity has been proposed as a risk factor of CHDs, but the relationship of CHD risk with over- and underweight is controversial, especially because body mass index (BMI) distribution differs between Asia and the West. The study aimed to examine the potential associations of maternal over- and underweight on risk of offspring CHDs.

METHODS

An ambispective observational study involving 1206 fetuses with CHDs and 1112 fetuses without defects at seven hospitals in China was conducted. Standardized questionnaires were used to collect information on maternal prepregnancy weight and height, social demographic characteristics, living and occupational environments, and lifestyle behaviors. Univariate, multivariate and multilevel logistic regression as well as unrestricted cubic spline analysis were used to examine potential associations of prepregnancy BMI and offspring CHDs.

RESULTS

Prepregnancy maternal underweight (BMI<18.5) or low average BMI (18.5 ≤ BMI<21.25) was associated with significantly higher risk of CHD in offspring than high average BMI (21.25 ≤ BMI<24.0): multilevel logistic regression indicated adjusted odds ratios of 1.53 (95%CI 1.13, 2.08) for underweight, 1.44 (95%CI 1.10, 1.89) for low average BMI and 1.29 (95%CI 0.84, 1.97) for overweight or obesity (BMI ≥ 24.0). Mothers with prepregnancy BMI < 21.25 were at greater risk of offspring with septal defects, while mothers with low average BMI were at greater risk of offspring with conotruncal defects and septal defects.

CONCLUSIONS

Our findings suggest that underweight or low average BMI may be associated with higher risk of CHDs in offspring. Health professionals may wish to advise women planning to be pregnant to maintain or even gain weight to ensure adequate, balanced nutrition and thereby reduce the risk of CHDs in their offspring.

Influence of Second-Hand Smoke and Prenatal Tobacco Smoke Exposure on Biomarkers, Genetics and Physiological Processes in Children-An Overview in Research Insights of the Last Few Years

Children are commonly exposed to second-hand smoke (SHS) in the domestic environment or inside vehicles of smokers. Unfortunately, prenatal tobacco smoke (PTS) exposure is still common, too. SHS is hazardous to the health of smokers and non-smokers, but especially to that of children. SHS and PTS increase the risk for children to develop cancers and can trigger or worsen asthma and allergies, modulate the immune status, and is harmful to lung, heart and blood vessels. Smoking during pregnancy can cause pregnancy complications and poor birth outcomes as well as changes in the development of the foetus. Lately, some of the molecular and genetic mechanisms that cause adverse health effects in children have been identified. In this review, some of the current insights are discussed. In this regard, it has been found in children that SHS and PTS exposure is associated with changes in levels of enzymes, hormones, and expression of genes, micro RNAs, and proteins. PTS and SHS exposure are major elicitors of mechanisms of oxidative stress. Genetic predisposition can compound the health effects of PTS and SHS exposure. Epigenetic effects might influence in utero gene expression and disease susceptibility. Hence, the limitation of domestic and public exposure to SHS as well as PTS exposure has to be in the focus of policymakers and the public in order to save the health of children at an early age. Global substantial smoke-free policies, health communication campaigns, and behavioural interventions are useful and should be mandatory.

Mitochondrial impairment following neonatal overfeeding: A comparison between normal and ischemic-reperfused hearts

Overweight and obesity are established factors underpin several metabolic impairments, including the cardiovascular. Although the diversity of factors involved in overweight/obesity-induced cardiovascular diseases, mitochondria has been highlighted due to its role in cardiac metabolism. As obesity can be originated in early postnatal life, the current study evaluates the effects of neonatal overfeeding on the cardiac mitochondrial bioenergetics and oxidative balance in rats that underwent an ischemia-reperfusion insult. Seventy-two hours after delivery, Wistar rat litters were randomly assigned into the control (C; nine pups per mother) and the Overfed (OF; three pups per mother) groups throughout the lactation period. At weaning, male offspring were fed with laboratory chow ad libitum until sacrifice at 30 and 60 days of life. Mitochondrial heart bioenergetics and oxidative balance showed to be deeply affected by neonatal overfeeding at both ages. Interestingly, after ischemia-reperfusion insult I/R (Langendorff or mineral oil incubation), most parameters evaluated in OF animals were not influenced by additional ischemic-reperfusion injury. Our findings demonstrated that suckling overfeeding deregulates cardiac mitochondrial alike to ischemia-reperfusion insult by disengaging electrical mitochondrial coupling and potentiate oxidative stress, wherein the neonatal overfeeding shows to be so detrimental as I/R. Our findings support the concept that nutritional insults in the critical development periods increase the risk for cardiovascular disease and mitochondria impairments throughout life while oxidative damage change between molecular targets.

A Functional Aryl Hydrocarbon Receptor Genetic Variant, Alone and in Combination with Parental Exposure, is a Risk Factor for Congenital Heart Disease

Recent experimental studies showed that ablation of the aryl hydrocarbon receptor (AhR) as well as its activation by exogenous ligands disrupt the molecular networks involved in heart formation and function, leading to congenital heart disease (CHD). However, no evidence is available about the role of AhR in humans. We assessed the prevalence of a functional AhR genetic variant (p.Arg554Lys) in CHD patients as well as its joint effects with parental exposure. A total of 128 CHD patients (76 males; age 6.2 ± 6.7 years) and 274 controls (160 males; age at birth) were genotyped for the AhR polymorphism by using the TaqMan^® Drug Metabolism Genotyping assay. Both case and control parents completed a structured questionnaire on demographic, lifestyle and preconception exposures. Genotype (p = 0.001) and allele (p < 0.0001) distributions of AhR p.Arg554Lys differed significantly between patients and controls. A significant elevated CHD risk was found under dominant (OR = 2.9, 95% CI 1.9-4.6, p < 0.0001) and additive genetic models (OR = 6.2, 95% CI 2-19, p = 0.001). There was a significant interaction between 554-Lys allele and paternal smoking exposure (OR_smoking = 1.6, 95% CI = 0.9-2.9; OR_allele = 2.6, 95% CI = 1.3-5; OR_interaction = 4.9, 95% CI = 2.4-9.9, p _interaction < 0.0001). Additionally, 554-Lys allele exacerbated the effect of maternal periconceptional exposure (OR_exposure = 1.6, 95% CI = 0.8-3; OR_allele = 2.6, 95% CI = 1.5-4.5; OR_interaction = 5.7; 95% CI = 2.6-12, p _interaction < 0.0001). Our findings showed that the AhR p.Arg554Lys polymorphism, alone and in combination with parental exposures, is associated with the CHD risk, highlighting the significant role of AhR in the cardiovascular development.

Environmental Contaminants and Congenital Heart Defects: A Re-Evaluation of the Evidence

Congenital heart defects (CHDs) are a common birth defect of largely unknown etiology, with high fetal and neonatal mortality. A review of CHDs and environmental contaminant exposure found that meta-analyses showed only modest associations for smoking, vehicle exhaust components, disinfectant by-products and proximity to incinerators, with stronger results from the newer, larger and better quality studies masked by the typical absence of effect in older studies. Recent studies of exposure to agricultural pesticides, solvents, metals and landfill sites also showed associations. Certain contaminants have been associated with certain CHDs, with septal defects being the most common. Frequent methodological problems include failure to account for potential confounders or maternal/paternal preconception exposure, differences in diagnosing, defining and classifying CHDs, grouping of defects to increase power, grouping of contaminants with dissimilar mechanisms, exclusion of pregnancies that result in death or later life diagnosis, and the assumption that maternal residence at birth is the same as at conception. Furthermore, most studies use measurement estimates of one exposure, ignoring the many additional contaminant exposures in daily life. All these problems can distort and underestimate the true associations. Impaired methylation is a common mechanism, suggesting that supplementary folate may be protective for any birth defect.

Assessment of interaction between maternal polycyclic aromatic hydrocarbons exposure and genetic polymorphisms on the risk of congenital heart diseases

The major causes of congenital heart diseases (CHDs) are the interactions of genetic and environmental factors. We conducted a case–control study in 357 mothers of CHDs fetuses and 270 control mothers to investigate the association of maternal PAHs exposure, AHR, CYP1A1, CYP1A2, CYP1B1 and CYP2E polymorphisms, the interaction between PAHs exposure and genetic variants with the risk of CHDs. The higher level PAHs exposure was associated with the risk of CHDs (aOR = 2.029, 95% CI: 1.266, 3.251) or subtypes. The haplotypes of AHR or CYP1A2 were associated with the risk of CHDs: AHR: C-G-A-C: aOR = 0.765; T-A-G-A: aOR = 1.33; CYP1A2: A-T:aOR = 1.75; C-C: aOR = 0.706. When exposed to higher level PAHs, the risk of CHDs among the mothers carrying rs2158041 “C/T or T/T” genotype or rs7811989 “G/A or A/A” genotype in AHR was 1.724 (χ² = 7.209, P = 0.007) or 1.735 (χ² = 7.364, P = 0.007) times greater than the aOR in the mothers carrying wild genotype. The multiplicative-scale interactions between PAHs exposure and polymorphisms of CYP1A2 rs4646425 (P = 0.03) or CYP2E1 rs915908 (P = 0.0238) on the risk of CHDs were observed. Our study suggests that maternal AHR polymorphisms may modify the association of PAHs exposure with CHDs, CYP1A2 or CYP2E1 polymorphisms significantly interact with PAHs exposure on CHDs.

Congenital heart defects of fetus after maternal exposure to organic and inorganic environmental factors: a cohort study

Objective

Maternal exposure to various contaminants has been reported to be correlated with congetinal heart defects (CHDs). In this study, the effect of maternal exposure to organic and inorganic environmental factors upon the incidence of CHDs was investigated. We conducted a retrospective birth cohort study of infants born in the Maternal and Child Health Hospital of Panyu District in Guangzhou.

Materials and Methods

A total of 5381 cases with complete medical records, including mothers, fathers, and infants, were enrolled. The relationship between maternal occupational exposure to hazardous substances and strong noise during pregnancy and CHDs was analyzed. Occupational exposure to hazardous substances increased the incidence of CHDs.

Results

Forty-eight of 145 mothers (33.1%) in the CHDs group worked in hazardous and strong noise factories, while the corresponding percentage mothers in the control group was 22.8% (1193/5236). The percentage of mothers with a history of contact with organic solvents and exposure to strong noise in the CHDs group was significantly higher than the control group. There was no significant difference in the histories of contact with heavy metals, high temperatures, and other extreme environments between two groups.

Conclusions

Hazardous substances in factories, especially organic solvents, were identified as potential risk factors for CHDs. Besides, exposure to high noise also increased the incidence of CHDs.