Association of the insertion/deletion gene polymorphism of the apolipoprotein B signal peptide with myocardial infarction in Tunisian patients

Background: Numerous polymorphisms of the apolipoprotein B (APOB) gene have been described. Particularly, the insertion/deletion (Ins/Del) polymorphism located in the coding part of the signal peptide of apoB, associated with modification of lipid concentrations and the risk of coronary artery disease and/or myocardial infarction (MI), has been reported in the general population. Moreover, conflicting results emerge from the literature and suggest that the effect is context-dependent. In the present study, the first investigation of the Ins/Del polymorphism of the APOB gene in Tunisian patients with MI, we examined a possible association between this polymorphism and MI in a subgroup of the Tunisian population. Methods: A total of 318 Tunisian patients with MI and 368 healthy controls were included in the study. Genomic DNA was extracted from white blood cells, and the Ins/Del polymorphism was determined by electrophoresis in polyacrylamide gels after PCR amplification. A binary logistic regression analysis was performed to test how the association between MI and Ins/Del polymorphism is independent from confounding factors. Results: A significant difference in genotype distribution and allele frequency was observed between patients and controls. Patients with MI had a frequency of 7.2% for the Del/Del genotype, 39.6% for the Ins/Del genotype, and 53.1% for the Ins/Ins genotype. Controls had a frequency of 3.0% for the Del/Del, 32.1% for the Ins/Del and 64.9% for the Ins/Ins genotype (X-2 = 12.93, p = 0.002). The MI patient group showed a significantly higher frequency of the Del allele compared to controls (27.1% vs. 19.1%; X-2 = 12.50, p = 0.0004). In comparison to the Ins/Ins homozygotes, the odds ratio (95% confidence interval) for MI was 1.51 (1.09 - 2.07) for Ins/Del heterozy-gotes and 2.95 (1.40 - 6.22) for Del/Del homozygotes. In multivariate analysis, age (p = 0.001), smoking (p < 0.001), hypertension (p = 0.001), diabetes mellitus (p < 0.001), and dyslipidemia (p < 0.01) were independent correlates of the presence of MI, whereas the Ins/Del polymorphism (p = 0.330) was not an independent predictor of MI. Conclusions: The present study shows a significant but not independent association between the Ins/Del polymorphism of the APOB gene and MI in the Tunisian population.