Promoter polymorphisms in ACE (angiotensin I-converting enzyme) associated with clinical outcomes in hypertension.

Angiotensin I–converting enzyme (ACE) plays a key role in cardiovascular biology. Its functions are formation of angiotensin II and inactivation of bradykinin, resulting in vasoconstriction and increased blood pressure. ACE inhibitors are recommended as first-line agents in the treatment of hypertension and heart failure. Expressed in many tissues, ACE further affects a broad spectrum of physiological processes. As a result, the ACE gene has been implicated in susceptibility to hypertension, myocardial infarction (MI), renal pathophysiology, diabetes, and Alzheimer's disease. The suggestion of a heritable component to serum ACE activity1 led to extensive phenotype–genotype studies with ACE-related pathophysiology and response to ACE inhibitors.2 Numerous studies have focused on an insertion/deletion (I/D) polymorphism in intron 15. However, meta-analyses of phenotypic associations largely failed to confirm a role for I/D,3 and in vitro experiments did not reveal any effect on transcription4 or splicing.5 Therefore, genetic factors contributing to differential ACE expression remain unidentified. As ACE is one of the main therapeutic targets of antihypertensive therapies, a better understanding of genetic differences is required to assess disease risk and response to therapy. Genetic family studies map the heritable contribution to ACE activity and blood pressure to the region of the ACE gene, particularly in subjects of African ancestry.6,7 Moreover, allele frequencies at the ACE locus vary greatly between African Americans and European Americans.8 African Americans are at higher risk of hypertension9 and its target organ sequelae10 and less responsive to ACE inhibitors.11,12 In addition, African Americans are more likely to experience adverse drug effects.13 In this study, we searched for functional polymorphism in the ACE gene locus that might account for differences in disease susceptibility or response to therapy with ACE inhibitors. The ACE gene consists of 25 exons spanning ∼25 kb and encoding a soluble or a membrane-bound protein variant with two peptidase domains (Figure 1). ACE harbors a number of polymorphisms; however, frequent nonsynonymous single-nucleotide polymorphisms (SNPs) that affect the protein sequence are lacking, suggesting that regulatory polymorphisms that are yet to be discovered may contribute to genetic susceptibility in cardiovascular diseases involving ACE. To search for regulatory polymorphisms, we measured allelic mRNA expression of ACE in human cardiac tissues. In contrast to total mRNA levels, allelic mRNA ratios cancel out trans-acting factors, so that any detectable allelic expression imbalance (AEI) is a strong indicator of cis-acting regulatory factors.14–19 Allelic mRNA ratios, as the most proximate and accurate phenotype for SNP scanning, can then be exploited in a search for regulatory polymorphisms, followed by molecular genetic studies to address underlying mechanisms.14–16,19 Figure 1 ACE gene structure (University of California–Santa Cruz genome browser) and location of polymorphisms tested in this study. Overviews of HapMap linkage disequilibrium (LD) in the gene region for individuals from Utah of northern-European ancestry ... In this study, we report regulatory alleles affecting ACE expression that are common among African Americans, discovered in a screen of human myocardial tissues. To assess the clinical relevance of these alleles, we conducted a clinical genetic association study in the International Verapamil SR Trandolapril Study Genetic Substudy (INVEST-GENES).20