Background: Complex diseases such as coronary artery disease (CAD), hypertension and diabetes are usually caused by individual susceptibility to multiple genes, environmental factors, and the interaction between them. The paraoxonase 1 (PON1) enzyme has been implicated in the pathogenesis of atherosclerosis and CAD. Two common polymorphisms in the coding region of the PON1 gene, which lead to a glutamine (Q)/arginine (R) substitution at position 192 and a leucine (L)/methionine (M) substitution at position 55, influence PON1 activity. Studies have investigated the association between these polymorphisms and CAD, but with conflicting results.
Aims: 1) To evaluate the association between PON1 polymorphisms and CAD risk; and 2) to study the interaction between PON1 polymorphisms and others in different candidate genes.
Methods: We evaluated the risk of CAD associated with PON1 Q192R and L55M polymorphisms in 298 CAD patients and 298 healthy individuals. We then evaluated the risk associated with the interaction of the PON1 polymorphisms with ACE DD, ACE 8 GG and MTHFR 1298AA. Finally, using a logistic regression model, we evaluated which variables (genetic, biochemical and environmental) were linked significantly and independently with CAD.
Results: We found that the PON1 55MM genotype was more common in the CAD population, but this did not reach statistical significance as a risk factor for CAD, while PON1 192RR presented an 80% higher relative risk compared to the population without this polymorphism. The interaction between PON1 192RR and MTHFR 1298AA, sited in different genes, increased the risk for CAD, compared with the polymorphisms in isolation (OR=2.76; 95% CI=1.20-6.47; p=0.009), as did the association of PON1 192RR with ACE DD, which presented a 337% higher risk compared to the population without this polymorphic association (OR=4.37; 95% CI=1.47-13.87; p=0.002). Similarly, the association between PON1 192RR and ACE 8 GG was linked to an even higher risk (OR=6.23; 95% CI=1.67-27.37; p<0.001). After logistic regression, smoking, family history, fibrinogen, diabetes, Lp(a) and the association of PON1 192RR + ACE 8 GG remained in the regression model and proved to be significant and independent risk factors for CAD. In the regression model the latter association had OR=14.113; p=0.018.
Conclusion: When analyzed separately, the PON1 192RR genotype presented a relative risk for CAD 80% higher than in the population without this genotype. Its association with other genetic polymorphisms sited in different genes, coding for different enzymes and belonging to different physiological systems, always increased the risk for CAD. After correction for other conventional and biochemical risk factors, the PON1 192RR + ACE 8 GG association remained a significant and independent risk factor for CAD.