• Congenital heart disease
• gene-environment interactions
• parental exposures

Congenital heart defects (CHDs) are the most prevalent of all birth defects, arising from the complex interplay of environmental exposures and genes. The molecular causes of most CHDs as well as the modifiable environmental risk factors, (especially for paternal exposure) remain largely unknown. Thus, there is an increasing interest in the study of gene-environment interaction in the pathogenesis of CHDs. The major aim of this project was to expand the knowledge of CHD etiology with specific attention at the identification of genetic and environmental risk factors. The effects of environmental factors might be modified by the genes responsible for the activation and detoxification of toxicant agents, contributing to an increased resistance (or sensitivity) to cardiac teratogenesis. Thus, the knowledge of genetic variants that can modify a person's risk of environmental exposure-induced disease may identify new potential therapeutic targets and appropriate preventive strategies.
In the first part of the study, we analyzed the association between different parental environmental exposures and CHD risk. Moreover, it has been investigated if the presence of specific polymorphisms in genes involved in toxicant metabolism, glutathione-S transferase: GSTM1 and GSTT1, in the children might modulate the risk of CHD associated to toxicant exposure. In a case-control study , 360 parents of a child with CHD and 360 parents of a child without any congenital malformations, were compared in terms of lifestyle habits and toxicant exposures.
The results showed that parental smoking (≥15 cigarettes/day) was significantly associated with CHD risk (OR 2.1, 95% CI 1.3-3.5, p=0.002). Moreover, both maternal (OR 2.6, 95% CI 1.6-4.2, p<0.0001) and paternal (OR 2.5, 95% CI 1.6-3.8, p<0.0001) occupational/environmental exposure to toxicants increased the risk of CHD. In addition, a significant additive risk (OR 4.5, 95% CI 2.5-8.3, p<0.0001) was found when both parents were exposed to toxicants. Regarding to genotype, GSTM1 and GSTT1 polymorphisms were investigated in 180 children with CHD. Both maternal (OR 3.6, 95% CI 1.1-11.2, p=0.03) and paternal (OR 3.3, 95% CI 1.0-10.8, p=0.03) exposure to toxicants increased the CHD risk in children who carried the combined null GST genotypes. The effect for the combined null genotypes was also stronger (OR 6.5, 95% CI 1.5-28.0, p=0.01) when both parents were exposed.
In the second part of the project, we analyzed the joint effect of the glutathione-S transferase P1 (GSTP1) genetic polymorphism (Ile105Val) and maternal environmental exposure, on CHD risk. The GSTP1 gene is highly expressed early in fetal life and is the most abundant phase II xenobiotic metabolism enzyme in a human placenta. Fetal inherited GSTP1 Ile105Val polymorphism may modify the metabolism and excretion of xenobiotics from fetal tissue and increase the risk of CHD. In a case-control study, 190 children with CHD and 190 healthy children were genotyped for the GSTP1 Ile105Val polymorphism. All the mothers completed a structured questionnaire on the demographic as well as the preconceptional and lifestyle exposures.
No significant differences in Ile105Val genotype frequencies were observed between CHD and healthy children (p=0.9) as well as no evidence of significant interaction between the maternal exposure and GSTP1 polymorphism was found.
In the last part of the project, we investigated whether the ISL1 (rs1017) single-nucleotide polymorphism, in 3’-UTR region, conferred susceptibility to CHD. Indeed, the LIM homeodomain transcriptor factor ISL1 is a known marker for undifferentiated cardiac progenitor cells that give rise to both the right ventricle and the inflow and outflow tracts. To date, contradictory findings about the role of the ISL1 rs1017 single-nucleotide polymorphism on increased risk of CHD have been reported.
In a case-control study, 309 patients with CHD and 500 healthy controls were genotyped for the ISL1 rs1017 polymorphism. No significant difference in the genotype and variant allele distribution was found between patients and controls. In addition, the ISL1 rs1017 polymorphism was not associated to the risk of CHD neither overall (p=0.7) nor stratifying the population by sex and CHD classification.
All these findings suggest that common genetic variants, not necessarily disease-causing, may contribute to increase the risk of CHD, especially interacting with environmental factors. Further studies are required to better define the role of genetic factors and their potential interaction with environmental factors on the risk of CHD.