Angiotensin-converting enzyme gene polymorphism and allele frequencies in the lebanese population: prevalence and review of the literature
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- Sabbagh, A.S., Otrock, Z.K., Mahfoud, Z.R. et al. Mol Biol Rep (2007) 34: 47. doi:10.1007/s11033-006-9013-y
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We studied the distribution of the D/D, I/D, and I/I genotypes of the angiotensin-converting enzyme (ACE) in a sample of healthy Lebanese individuals to assess their prevalence and compare them with other populations. ACE genotypes were determined using the Cardiovascular Disease (CVD) StripAssay, which is based on a Polymerase Chain Reaction-Reverse hybridization technique. DNA from 133 unrelated healthy donors from our HLA-bank was used. The prevalence of D/D, I/D, and I/I genotypes was found to be 39.1, 45.1, and 15.8% respectively, with D and I allelic frequency of 61.7 and 38.3%, respectively. The sampled Lebanese population showed ACE genotypic distributions similar to Caucasians; however, with tendency towards harboring high D allele frequency together with a low I allele frequency just like the Spanish population. This first report from Lebanon will serve as a baseline statistical data for future investigations of the prevalence of ACE genotypes in association with various clinical entities notably cardiovascular diseases. The medical literature was also reviewed in this context.
During the last two decades there has been an increasing interest in the study of the angiotensin-converting enzyme (ACE) gene and its different polymorphisms. Both in vivo and in vitro studies suggest a role for the Renin-Angiotensin system in hemostasis-regulating mechanisms . Human ACE, present in the liver, kidney, and brain is a dipeptidyl carboxypeptidase that is located on the luminal surfaces of capillary endothelial cells in high concentrations and in the plasma at lower concentrations. ACE cleaves the carboxy-terminal dipeptide of angiotensin I, releasing the physiologically active octapeptide angiotensin II . The latter is a potent vasoconstrictive molecule that plays a key role in modulating vascular tone and is increased locally upon vascular injury . In addition, ACE degrades the vasodilator bradykinin , producing a synergistic effect with angiotensin II  and a reduction in tissue plasminogen activator production .
On the molecular level, the ACE gene is located on the long arm of chromosome 17 (17q23) and is characterized by a polymorphism resulting from the presence or absence of a 287 base pairs fragment of a repeated Alu sequence at intron 16 hence, the corresponding designation of I (for Insertion) or D (for Deletion) of the two resulting alleles [7, 8]. The literature states that as much as 47% of interindividual variability of plasma ACE concentration levels are genetically determined [7, 9, 10]. It is important to state that the level of plasma ACE has an important influence on the pathophysiology of cardiovascular disease and that its different polymorphisms affect the risk of hypertension [11, 12] and other cardiac disease [13, 14].
The three resulting ACE genotypes (D/D, I/D, and I/I) can cause a wide range of ACE activity, with the highest activity being associated with D/D and the lowest with I/I, while the I/D genotype shows intermediate levels. A possible explanation of the higher ACE levels associated with the D allele is that the I allele has a sequence similar to a silencer sequence .
To date, the ACE gene polymorphisms have not been studied yet in the Lebanese population. This is the first study that assesses the prevalence of the D and I alleles in addition to D/D, I/D, and I/I genotypes in our community establishing, therefore, a baseline data that may be important for future projects correlating ACE gene polymorphisms and variable clinical conditions.
Materials and methods
Samples and DNA extraction
This study was performed at the American University of Beirut Medical Center (AUBMC), which is a tertiary-care center in Lebanon accommodating patients from the different districts of the country. The Scientific Committee for Research Institutional Review Board at AUBMC approved this study involving the use of archived DNA material. We randomly selected 133 samples from donors logged into our HLA registry and representing healthy Lebanese people originating from different areas and religious communities of the country. Their DNA was originally extracted using the PEL-FREEZ extraction kit (PEL-FREEZ, DYNAL, USA) and stored at −80°C for later use.
PCR and reverse hybridization
Interpretation of results
For each polymorphic position, one of three possible patterns may be obtained: DD, ID, or II genotype.
Distribution of ACE genotypes with I and D allele frequencies in 133 unrelated healthy Lebanese individuals
Frequency of the various ACE genotypes and alleles as reported by selected studies from different population
Genotype Frequency (%)
Allele Frequency (%)
Wells et al.
Von Depka et al.
Hooper at al.
Uhm et al.
Bouba et al.
Bautista et al.
Jackson et al.
Fatini et al.
Gonzalez-Ordonez et al.
Rice et al.
Saeed et al.
Al-Eisa et al
The interaction between the renin-angiotensin system and fibrinolysis has been well established in the medical literature  including the prominent effect of the D allele [17, 18]. An interesting pattern of this effect is that it could be exerted according to a sex-specific pattern, for example, the ACE genotype and blood pressure seem to be strongly related in men than in women. Similarly, the D allele was related to venous thrombosis only in male African American subjects . Furthermore, the risk of hypertension is significantly associated with the ACE genotype  or the ACE levels , but only among males. It is important to note that several studies did not show any association of the ACE genotype neither with hypertension [10, 22, 23] nor with coronary artery disease [24, 25]. In Italian patients, the association between the ACE D/D genotype and coronary artery disease was observed as generally reported for the Caucasians [10, 26, 27] and the Japanese . On the other hand, two large prospective studies on the Danish population  and North American male physicians  failed to correlate the D allele and the D/D genotype with the incidence of coronary artery disease. Table 2 describes the prevalence of the different ACE genotypes and distribution of D and I alleles as reported in the literature by different investigators.
In a study by Leatham et al., it was found that increased ACE levels might result in a higher risk of acute myocardial infarction among subjects with the D/D genotype . However, in their meta-analysis of 15 studies (including a total of 3394 patients with myocardial infarction and 5479 controls) Samani et al. concluded that the ACE genotype might be associated with myocardial infarction; however, the effect of the D allele was not likely to be high . It is also worth noting that several studies suggested that the impact of the ACE gene polymorphism on the risk of acute myocardial infarction differs from one population to another . In order to explain this trend, some investigators suggested that the effect and impact of the ACE gene polymorphism greatly depend on the genetic make-up of the population under study [34, 35]. Schieffer et al. proposed that there are other existing genetic and environmental factors that could decrease the deleterious effect of the ACE gene in some populations, whereas accentuating it in others .
ACE gene polymorphisms and venous thromboembolism (VTE) have also been well studied in the literature with several conflicting results. Some studies showed a high prevalence of the ACE D/D genotype in VTE patients in the absence of hemostasis-related risk factors or in patients with hyperhomocysteinaemia and factor V Leiden mutation . Philipp et al. reported a high prevalence of ACE D/D genotype in patients with thrombosis after orthopedic surgery . The D/D genotype increased the thrombotic risk more than 11-fold while the I/D genotype increased the risk by around 5-fold . On the contrary, Della Valle et al. found that factor V Leiden and ACE I/D polymorphism were not associated with any increased risk of thromboembolic events after total joint arthroplasty in Caucasian subjects . In another study of patients with venous thrombosis after hip replacement surgery, the risk of deep vein thrombosis in those with the D/D genotype was increased more than 10-fold compared with patients with the I/I genotype .
Comparing our results with other studies done in the Arab world, we could find two studies from United Arab Emirates  and Kuwait . In both studies, the prevalence of the D/D and I/D polymorphisms was comparable to those in our population. However, we had more prevalent I/I polymorphism (Table 2). Our study is the first report from Lebanon that describes the prevalence of ACE gene polymorphisms and the frequency of its alleles. It is recommended that further larger studies be conducted in the Lebanese population based on ACE gene polymorphism and correlating its allele frequencies with the clinical entities notably cardiovascular diseases.