Angiotensin converting enzyme gene polymorphism in coronary artery disease: the Indian scenario

Relationship between angiotensin-converting enzyme gene insertion/deletion polymorphism, angiographically defined coronary artery disease and myocardial infarction in patients with type 2 diabetes mellitus

INTRODUCTION

The insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene has been implicated in the pathogenesis of cardiovascular diseases. The objective of the present study was to investigate the influence of ACE gene I/D polymorphism on the development and progression of coronary artery disease (CAD) and myocardial infarction (MI) in type 2 diabetic (T2DM) patients.

MATERIALS AND METHODS

We screened 283 T2DM patients, inclusive of 160 patients with angiographically defined CAD, 73 patients with MI, 89 patients without MI and 121 T2DM individuals with no evidence of CAD for ACE gene I /D polymorphism.

RESULTS

There was no significant difference in the distribution of genotypes and alleles of ACE gene I/D polymorphism between T2DM+CAD and T2DM (non-CAD) groups. However, a significant association of this polymorphism with MI in T2DM+CAD patients (p=0.024) was observed. Further analysis revealed that the frequencies of the DD and ID genotypes increased with the number of stenosed coronary vessels (p=0.026). The DD genotype and the D allele were more frequent in the subgroup of T2DM patients with multivessel CAD (p=0.01) than in individuals with single vessel stenosis.

CONCLUSIONS

These findings reveal a significant relationship between ACE gene I/D polymorphism, multivessel CAD and also the occurrence of MI in T2DM individuals with significant coronary stenoses in our population.

Coronary heart disease, hypertension, and angiotensinogen gene variants in Indian population

Gene encoding components of the renin angiotensin system (RAS) have been implicated with the increased risk of cardiovascular disease (CVD). Two variants of the angiotensinogen (AGT) gene, M235T and T174M, have been shown to be associated with increased risk of hypertension. In the present study, we examined the association of these two polymorphisms and their synergistic interaction with the angiotensin I-converting enzyme (ACE) deletion homozygote genotype (D/D) on subjects with coronary heart disease (CHD) and hypertension. We studied 131 healthy individuals, 141 angiographically verified CHD patients, and 159 hypertensive subjects. The identification of the ACE and AGT gene polymorphisms was carried out using a PCR-based restriction endonuclease digestion method. There was no significant difference in the distribution of the M235T and T174M variants between the two test groups and the control group. Association was also not seen when analysis was carried out in patients when subgrouped according to the extent of the severity of the disease. In addition, the risk was not restricted to subjects carrying the D allele of the ACE gene and T235T of AGT. M235T and T174M variants do not contribute to the increased risk of CHD or hypertension in the Indian population.

Gene polymorphism and coronary risk factors in Indian population

Asian Indians who have settled overseas and those in urban India have increased risk of coronary events. Reasons for this increased risk are thought to be genetic but are yet unclear. Advances in molecular cardiology have revealed a number of single nucleotide polymorphisms associated with atherosclerosis. In this review, gene polymorphisms that have been associated with coronary diseases among Indians are discussed. Topics include the genes involved in hyperlipidemia, hypertension, and homocysteine. Mutations in the low-density lipoprotein receptor (LDLR) gene resulting in familial hypercholesterolemia have strong association with premature atherosclerosis. Common polymorphism of the apolipoproteins (apo) B-100 and E genes have been associated with variation in lipid and lipoprotein levels. Recently identified polymorphisms in the apoC3 (T-455C, C-482T), and cholesteryl ester transfer protein (CETP) (B1/B2 allele) genes are associated with increased triglycerides and reduced high-density lipoprotein (HDL)-levels, a feature now also common among Asian Indians. Angiotensin-converting enzyme-deletion (DD) polymorphism has been shown to influence beta-blocker therapy in heart failure. Mutations in methylenetetrahydrofolate reductase (C667T), cystathionine beta-synthase (T833C), and methionine synthase (A2756G) genes cause hyperhomocysteinemia, an independent risk factor for atherothrombosis. As the genetics of atherosclerosis continues to evolve, these factors along with the newer emerging factors may become a part of the routine assessment, aiding prediction of future coronary events.

Genes of renin angiotensin system and coronary heart disease

Coronary constriction, proliferation of smooth muscle cells and arrhythmia are involved in the pathophysiology of coronary heart disease and its complications such as myocardial infarction and sudden death. All these effects are favoured by high angiotensin II levels. Angiotensin II is the main effector molecule of the renin angiotensin system and it acts through angiotensin II type receptors. Genetically determined differences in the expression of the components of this system could adversely affect angiotensin II concentration and subsequently heart. Consequently each component of this system represents a potential candidate in the etiology of cardiovascular disease. In this article we review the variation of the angiotensin I converting enzyme, angiotensin II type I receptor and angiotensinogen genes and their association with cardiovascular disease.

Molecular basis of familial hypercholesterolemia: An Indian experience

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by a multitude of low-density lipoprotein (LDL) receptor gene mutations. The LDL receptor is a cell surface trans-membrane protein that mediates the uptake & lysosomal degradation of plasma LDI., thereby providing cholesterol to cells. Affected individuals have elevated plasma levels of LDL, which causes premature coronary atherosclerosis. FH has an estimated worldwide prevalence of 0.2%. In some subpopulations there is an increased frequency of FH and specific LDL receptor mutations are found to be common due to 'founder gene effect'. Overall, more than 300 naturally occurring LDL receptor mutations have been described. To data upto ten LDL receptor gene mutations have been identified in Indians in South Africa, suggesting increased incidence of FH among Indians. Most mutations have occurred at CpG dinucleotide, a mutational hotspot in human genetic disease. In our study in 25 hypercholesterolemic subjects we have identified two novel insertion mutations in two patients. But the mutations underlying FH are still undefined in the majority of cases. Mutational heterogeneity on the other-hand has complicated disease diagnosis at DNA level. These findings warrant application of a generalized mutation screening method in search for new LDL receptor gene defects.