A population study of ethnic variations in the angiotensin-converting enzyme I/D polymorphism: relationships with gender, hypertension and impaired glucose metabolism

Aldosterone synthase gene (CYP11B2) C-344T polymorphism, plasma aldosterone, renin activity and blood pressure in a multi-ethnic population

BACKGROUND

The aldosterone synthase gene (CYP1B2) locus is a candidate region involved in the development of hypertension.

OBJECTIVE

To study the relationship between the C-344T CYP1B2 polymorphism, plasma aldosterone, renin activity and blood pressure in a multi-ethnic population.

DESIGN

Population-based, cross-sectional study of 1313 middle-aged men and women (456 white, 441 of African origin and 416 South Asian). Anthropometry, blood pressure, biochemistry, questionnaire data and timed urine collections were taken with standardized techniques. All were genotyped for the C-344T CYP11B2 polymorphism.

RESULTS

The frequency of the C allele was significantly lower in people of African origin (0.21) than in white (0.46) and South Asian (0.43) (P < 0.001). After adjustment for age, sex and ethnicity the TT genotype was associated with 14% higher plasma aldosterone levels, 3.7 mmHg higher systolic and 2.1 mmHg higher diastolic blood pressure than CC (P for linear trend < 0.05). No significant interactions with age, sex, ethnicity, body mass index (BMI) and fractional excretion of sodium were found in the associations between genotype and both blood pressure and aldosterone levels. In a sub-sample of participants in which plasma renin activity was measured (n = 457), a significant excess of T alleles was found in those with a raised (>/= 750) aldosterone-to-renin ratio (ARR).

CONCLUSION

In this multi-ethnic population, the C-344T CYP1B2 polymorphism is associated with blood pressure, plasma aldosterone levels and ARR. Although significant differences in allele frequencies were found between groups, ethnicity does not explain the results.

A cladistic model of ACE sequence variation with implications for myocardial infarction, Alzheimer disease and obesity

Sequence variation in ACE, which encodes angiotensin I converting enzyme, contributes to a large proportion of variability in plasma ACE levels, but the extent to which this impacts upon human disease is unresolved. Most efforts to associate ACE with other heritable traits have involved a single Alu insertion/deletion polymorphism, despite the probable existence of other functional sequence variants with effects that may not be consistently detectable by solely typing the Alu indel. Here, utilizing single nucleotide polymorphisms (SNPs) that differentiate major ACE clades in European populations, we demonstrate a number of significant phenotype associations across more than 4000 Swedish individuals. In a systematic analysis of metabolic phenotypes, effects were detected upon several traits, including fasting plasma glucose levels, insulin levels and measures of obesity (P-values ranging from 0.046 to 8.4 x 10(-6)). Extending cladistic models to the study of myocardial infarction and Alzheimer disease, significant associations were observed with greater effect sizes than those typically obtained in large-scale meta-analyses based on the Alu indel. Population frequencies of ACE genotypes were also found to change with age, congruent with previous data suggesting effects upon longevity. Clade models consistently outperformed those based upon single markers, reinforcing the importance of taking into consideration the possible confounding effects of allelic heterogeneity in this genomic region. Utilizing computational tools, potential functional variants are highlighted that may underlie phenotypic variability, which is discussed along with the broader implications these results may have for studies attempting to link variation in ACE to human disease.

Frequency of angiotensin-converting enzyme gene polymorphism in Turkish hypertensive patients

Hypertension is a multifactorial disease, in which genetic factors play an important role. This study was carried out to determine angiotensin-converting enzyme levels and angiotensin-converting enzyme gene polymorphism in Turkish hypertensive patients, and to establish whether there is an association of angiotensin-converting enzyme gene polymorphism with clinical and echocardiographic parameters. We have investigated the association among the allelic distribution of the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme gene identified by polymerase chain reaction, angiotensin-converting enzyme activity determined spectrophotometrically, cardiac morphology and function assessed by means of echocardiography. Distribution of angiotensin-converting enzyme gene I/D polymorphism and allele frequencies in hypertensive patients was not significantly different from controls. D allele frequency was 51.7% in hypertensives vs. 51.9% in controls and I allele 48.3 vs. 48.1%, respectively. The level of angiotensin-converting enzyme activity was significantly higher in the patients homozygotes for D allele (DD = 59.93 U/l) than in heterozygotes (ID = 39.49) and in homozygotes for I allele (II = 40.28 U/l). In addition to these, the level of angiotensin-converting enzyme activity was significantly lower in the ID and especially II patients receiving ACE inhibitors than the others. Also, it was determined that left atrium diameter was larger in the patients homozygotes for I allele than the others.

Molecular variants of the sodium/hydrogen exchanger type 3 gene and essential hypertension

OBJECTIVES

The objectives of this study were to identify polymorphic variants within the gene coding for the sodium/hydrogen exchanger type 3 (NHE3) and to examine their relationship with hypertension and biochemical indices of sodium balance.

DESIGN AND METHODS

Case-control comparisons on a total of 691 subjects of which 399 (68% with essential hypertension) were of African or Afro-Caribbean origin (blacks) and 292 (50% with essential hypertension) were of Caucasian origin (whites).

RESULTS

Eight exons of the C terminus of the NHE3 gene were screened systematically. A total of six variants were identified: (G1579A, G1709A, G1867A, C1945T, A2041G and C2405T). Further analyses in relation to essential hypertension and phenotypic characteristics were confined to the more frequent A2041G and the C2405T polymorphisms. The genotype frequencies of the A2041G polymorphism were significantly different between the whites and blacks, with the A allele being more frequent in the white population (0.43 for the whites and 0.14 for the blacks, respectively; P < 0.001). In contrast, there was no significant difference in the C2405T polymorphism between whites and blacks (C allele frequency: 0.86 for the whites and 0.88 for the blacks, respectively). In both the white and the black groups, there were no significant associations between these variants and essential hypertension (P > 0.05) or with serum electrolytes, creatinine or plasma renin activity (PRA) (ANOVA P > 0.05).

CONCLUSIONS

These results suggest a high degree of structural conservation of the NHE3 gene; however, the lack of association between these polymorphisms and blood pressure status does not necessarily eliminate the participation of this important sodium/hydrogen exchanger in the pathophysiology of essential hypertension, as we cannot exclude the existence of functionally important genetic variants in other sequences within the NEH3 gene.

Diabetic nephropathy: an inherited disease or just a diabetic complication?

Type 2 diabetic nephropathy is the most common cause of end-stage renal disease in western Europe and the United States. Although patients with overt nephropathy generally experience greater cumulative glycemic exposure, the difference in glycemic control between patients developing nephropathy and to those who did not could not be demonstrated. This observation is consistent with the finding that factors other than glycemic control are involved in the development of nephropathy. Genetic factors which specifically increase the susceptibility to nephropathy in patients with diabetes have been proposed. A range of linkage, association, and gene expression studies have been performed for revealing the genetic background of diabetic nephropathy but were not yet successful in identifying mutations which could explain the development of diabetic nephropathy in the majority of diabetic patients. Because of relatively small case numbers of all studies being performed so far, conclusions from those studies are limited. With the development of better technologies for an affordable genomewide association study using thousands of markers, it might become possible to unravel the genetic susceptibility factors for diabetic nephropathy. Comparing the expression levels of thousands of genes in patients and controls may identify key players in the pathogenesis of diabetic nephropathy and targets for pharmacologic intervention in the future.

Lack of association between polymorphisms in angiotensin-converting-enzyme and methylenetetrahydrofolate reductase genes and normal cognitive ageing in humans

The hypothesis that polymorphisms at two candidate genes that code for angiotensin-converting-enzyme (ACE) and methylenetetrahydrofolate reductase (MTHFR) are associated with normal cognitive ageing was tested using a sample (n=536) of healthy 80-year-old people who were born in 1921 and whose cognitive ability at age 11 was measured in the Scottish Mental Survey 1932. Cognitive ability at age 11 and age 80 was assessed using the Moray House Test. Cognitive ageing was defined as the change in IQ from age 11 to 80. There was no significant association between the tested ACE and MTHFR polymorphisms and IQ score at age 11, IQ at age 80, and IQ change (all P>0.05). The ACE genotypes deviated significantly from Hardy-Weinberg equilibrium proportions (P=0.02), which could indicate that this gene is under selection. Polymorphisms at the two studied genes are unlikely to be risk factors for normal cognitive ageing.

Genetic aspects of diabetic nephropathy

BACKGROUND

Diabetic nephropathy from type 2 diabetes mellitus is the most common cause of end-stage renal disease (ESRD) in the United States and in Western Europe. Although patients with overt nephropathy generally experience greater cumulative glycemic exposure, the difference in glycemic control between patients developing nephropathy compared to those who did not, could not be demonstrated. This observation is consistent with the notion that perhaps other factors, in addition to glycemic control, have a bearing on the development of nephropathy. Genetic factors, which specifically increase the susceptibility to nephropathy in patients with diabetes, have been proposed.

METHODS

A range of linkage and association studies has been performed for revealing the genetic background of diabetic nephropathy.

RESULTS

Until now, no mutation has been identified which could explain the development of diabetic nephropathy in the majority of diabetic patients.

CONCLUSIONS

Because of relatively small case numbers of all studies being performed so far, conclusions from those studies are limited. With the development of better technologies for an affordable genome-wide association study using thousands of markers, it might become possible to unravel the genetic causes of diabetic nephropathy.

Gender, ethnicity and genetics in cardiovascular disease: part 1: Basic principles

Prior to 1993, most drug efficacy and safety trials were conducted in white males, although gender and racial differences in pharmacodynamics and pharmacokinetics have been documented since the early 1900s. Over the last 2 decades, supported by the FDA and legislation, attempts to include more women and minorities in clinical drug trials have been made, with limited success. Yet, there are important differences in pathophysiology and pharmacogenetics, as well as pharmacotherapeutic effectiveness. This is the first of 2 articles that review the basic scientific principles of such differences. In particular, genetic polymorphisms of cardiovascular candidate genes and drug metabolism are described. The pharmacodynamic and pharmacokinetic variations among genders and ethnicities are summarized.

Renin-angiotensin gene polymorphism in children with uremia and essential hypertension

The M235T polymorphism of the angiotensinogen (ANG) gene, the I/D polymorphism of the angiotensin converting enzyme (ACE) gene, and the A1166C polymorphism of the angiotensin II type 1 receptor (AT1R) gene were identified in 70 patients with end-stage renal disease [20 pediatric ESRD, aged 14.9+/-3.1, years blood pressure (BP) 139+/-14/91+/-13 mmHg, 50 adult ESRD, aged 48.7+/-18.7 years, BP 149.1+/-24/96.9+/-12 mmHg], 35 with juvenile essential hypertension (JEHT, aged 14.4+/-2.7 years, 24-h mean BP 135.37+/-7.37/72.4+/-7.68 mmHg), 130 adult healthy normotensive controls (aged 34.9+/-8.1 years, BP 117.8+/-8.7/78.7+/-8.5 mmHg), and 20 pediatric controls (aged 13.2+/-1.2 years, BP 109+/-6.5/71+/-5.9 mmHg). The ACE gene polymorphism was determined by polymerase chain reaction and the ANG and AT1R gene polymorphisms by single-step LightCycler technology. The ACE gene distribution of the Hungarian controls did not differ from the results of the other Caucasian populations. In JEHT and pediatric ESRD patients, the MT genotype of ANG was more frequent than in controls (JEHT 80%, pediatric ESRD 74% versus controls 50%, P<0.02). The DD genotype of ACE was over-represented in pediatric ESRD compared with controls (ESRD 45% versus controls 22%, P<0.05). There was a non-significant increase in the CC genotype frequency of AT1R in adult patients with ESRD compared with controls. In conclusion, there was an increased frequency of the ACE DD genotype in pediatric ESRD, which could be a genetic risk factor for the development of ESRD. Furthermore, there was a significant increase in MT genotype frequency of ANG M235T polymorphism in pediatric ESRD and JEHT. The role of AT1R gene polymorphism needs further investigation.

Contrasting associations between aldosterone synthase gene polymorphisms and essential hypertension in blacks and in whites

BACKGROUND

Genetic variability in the gene for aldosterone synthase--a key enzyme in the production of aldosterone--can affect sodium homeostasis and thereby blood pressure. The possibility of impaired aldosterone production for the development of hypertension is of particular relevance in black Afro-Caribbeans exposed to a high dietary sodium intake.

OBJECTIVES

To compare the frequency of three variants (-344C/T, intron 2 conversion, and the K173R polymorphism) of the aldosterone synthase gene in blacks and whites, and to determine any association of the variants with hypertension.

DESIGN AND METHODS

We made case-control comparisons of the three gene variants in relation to ethnic background and to essential hypertension in 193 white (51% hypertensive) and 245 black individuals (59% hypertensive) living in south London.

RESULTS

The frequency of each of the variants was significantly different between the two ethnic groups. The T and the K alleles were more frequent in the black participants (79 compared with 50% for the -344T allele and 81 compared with 50% for K173 allele), whereas the frequency of the intron 2 conversion allele was much lower in that group (8 compared with 38%). None of these variants was associated with essential hypertension in the black participants. In contrast, in the white participants there was a significant and graded association between the intron 2 conversion allele and essential hypertension (odds ratio 1.86, 95% confidence interval 1.16 to 2.98; = 0.01). Moreover, among the white population, the presence of homozygosity both of the T allele and of the intron 2 conversion alleles was associated with a much greater frequency of hypertension (71 compared with 43%; chi(2) = 0.03).

CONCLUSIONS

The contrasting associations between these variants and essential hypertension do not necessarily exclude the possibility that other, as yet undefined, variants of the aldosterone synthase gene could be linked with hypertension in black people. Nonetheless, the strong association between the intron 2 conversion allele and essential hypertension in the white population reinforces the view that the increased blood pressure may be due, at least in part, to abnormal expression of enzymes involved in the metabolism of adrenal mineralocorticoids.

Characterization of high-altitude pulmonary hypertension in the Kyrgyz: association with angiotensin-converting enzyme genotype

Previous studies have suggested a genetic component in susceptibility to hypoxia-induced pulmonary hypertension. We therefore estimated the prevalence of high-altitude pulmonary hypertension (HAPH) in a Kyrgyz population and whether the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene associates with HAPH. An electrocardiographic survey of 741 highlanders demonstrated electrocardiogram signs of cor pulmonale in 14% of subjects. Pulmonary artery hemodynamics measured in an independent group of 136 male highlanders with symptoms of dyspnea at altitude revealed established pulmonary hypertension (mean pulmonary artery pressure [MPAP] > or = 25 mm Hg) in 20%. However, 26% of the normal subjects demonstrated an exaggerated response (twofold or greater increase in MPAP) to inhalation of 11% oxygen, and were classified as hyperresponsive. Ten-year follow-up of this group revealed increases in the MPAP, but not in normal subjects. Comparison of ACE I/D genotypes in the catheterized group revealed a threefold higher frequency of the I/I genotype in highlanders with HAPH, compared with normal highlanders (chi2 = 11.59, p = 0.003). In addition, MPAP was higher in highlanders with the I/I genotype (26.9 +/- 4.0 mm Hg) compared with the I/D genotype (20.6 +/- 1.2 mm Hg) or the D/D genotype (18.3 +/- 0.9 mm Hg) (p < 0.05). We conclude that HAPH is associated with ACE I/D genotype among Kyrgyz highlanders and the development of HAPH in this population and may be predicted by hyperresponsiveness to acute hypoxia.

Homocysteine levels in men and women of different ethnic and cultural background living in England

This population-based cross-sectional study in South London looks at the total homocysteine (tHcy) levels in groups of different ethnic background and the possible role of environmental factors and the 677C-->T genetic polymorphism of the methylenetetrahydrofolate reductase (MTHFR). Fasting plasma tHcy was measured in 1392 men and women, age 40-59 years; 475 were white, 465 of African origin (of whom 180 were West Africans and 280 Caribbeans) and 452 South Asian (of whom 222 were Hindus and 167 Muslims). The homozygous MTHFR TT variant had observed frequencies of 0.10 in whites, 0.01 in people of African origin and 0.02 in South Asians (P<0.001). tHcy levels were 16% (95% CI 8-26) higher amongst TT than CC. tHcy levels were 25% (21-29) higher in men than women. Levels were significantly higher in South Asians than whites (8% [3-13]). Vegetarians had higher levels than non-vegetarians (25% [18-33]). These differences were present after adjustments for age, sex, smoking, body mass index (BMI), MTHFR 677C-->T polymorphism and socio-economic status. Compared with whites (10.0 [9.7-10.3] micromol/l), and allowing for confounders, Hindus had significantly higher levels of tHcy (12.1 [11.6-12.6] micromol/l). This difference was attenuated by the inclusion of vegetarianism in the model (11.3 [10.8-11.9] micromol/l). In contrast Muslims had similar tHcy levels to whites while both West Africans and Caribbeans had slightly lower levels, though differences were not significant. The reported higher levels of tHcy in South Asians are due to high levels amongst Hindus only. They are in part accounted for by their vegetarianism. These differences in tHcy are large enough to be important contributors to the risk of vascular disease and may be preventable by simple targeted population strategies.

Angiotensin I-converting enzyme insertion/deletion polymorphism and cardiac mortality and morbidity after coronary artery bypass graft surgery

STUDY OBJECTIVES

This study was designed to evaluate whether the insertion (I)/deletion (D) polymorphism of the angiotensin I-converting enzyme (ACE) gene is associated with mortality and cardiac morbidity after coronary artery bypass graft surgery (CABG).

METHODS AND RESULTS

The ACE I/D genotype was determined in 249 consecutive patients who underwent CABG. Follow-up information (after 2 years) was obtained in 247 patients (99.2%). The primary end point was total mortality; the secondary end point was mortality from cardiac reasons, or the need for myocardial revascularization (coronary angioplasty or recurrent CABG) during follow-up. At follow-up, total mortality was 9.7% (all patients). None of the 51 patients with the ACE II genotype, 14 of 125 patients with the ACE ID genotype (11.2%), and 10 of 71 with the ACE DD genotype (14.1%) died during follow-up (p < 0.05). The ACE DD genotype, older age, diabetes mellitus, decreased left ventricular ejection fraction, and lack of internal mammary artery graft were independently related to an increased mortality after CABG. The incidence of the secondary end point was 14.5% (all patients): ACE II, 5.8%; ACE ID, 9.4%; ACE DD, 30.3% (p < 0.05). The ACE DD genotype and the presence of a left main coronary artery stenosis >or= 50% were independent predictors for the secondary end point.

CONCLUSION

The ACE DD genotype is associated with increased midterm mortality and cardiac morbidity after CABG.

No association between DCP1 genotype and late-onset Alzheimer disease

In a study of 261 patients with Alzheimer disease (AD) and 306 cognitively normal control subjects from Germany, Switzerland, and Italy, we found no association between genotype counts or allelic frequencies of DCP1, the gene encoding angiotensin-converting enzyme. In accordance with several other studies, our data could not confirm previous association findings. Critical review about all studies available on DCP1 genotyping and AD, age-associated cognitive decline, longevity, and other conditions revealed remarkable inconsistencies. Several studies showed significant deviations of genotype counts from Hardy Weinberg equilibrium (HWE). Deviations from HWE may limit the comparability of study results and require clarification before drawing conclusions with respect to disease risk, health conditions, or longevity in association with DCP1 genotype.

Angiotensin-converting enzyme gene polymorphism and its association with essential hypertension in a Tibetan population

There is strong evidence to support the idea that the renin-angiotensin system (RAS) plays an important role in the pathogenesis of essential hypertension (EH) and its complications. However, existing data about the association of angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism with blood pressure is conflicting, mainly due to racial differences and environmental exposure status. We therefore conducted a case control study to observe the relationship between ACE I/D polymorphism and EH in a Tibetan population who live in relatively isolated areas and are genetically homogeneous. The study was conducted at stable residential communities in the urban district of Lhasa, the capital of the Tibet autonomous region, China, and 106 unrelated EH patients and 135 normotensIve subjects were recruited. PCR, PCR/RFLP and PCR-SSCP were carried out to study the association between RAS genes and EH. Frequencies for the DD, ID and II genotypes were 27, 47 and 29 in hypertensive subjects, and 15, 60 and 48 in normotensive subjects, respectively. Derived allele frequencies for the I and D alleles were 0.51 and 0.49 in hypertensive subjects and 0.64 and 0.36 in normotensive subjects. There were significant differences in genotype distribution and derived allele frequency between these two groups. The genotype and allele frequencies of the ACE gene differed significantly between hypertensive and normotensive females (p>0.05), but there were no differences in males. In females, the DBP and MAP level were significantly higher for the DD than for the ID and II genotype, and SBP was significantly higher for the DD than for the II genotype. But in males, there were no significant differences in blood pressure among ACE genotypes. The results showed a significant association between the D allele of the ACE gene and hypertension in Tibetan women but not in Tibetan men.

[The involvement of the renin-angiotensin system gene polymorphisms in coronary heart disease]

INTRODUCTION AND OBJECTIVES

Previous studies angiotensin-converting enzyme gene insertion/deletion polymorphism ACE (I/D), angiotensinogen gene polymorphism, and angiotensin II AT1 receptor polymorphism in relation to coronary heart disease controversial results. This study was designed to analyze the association between these gene polymorphisms and the first coronary event in individuals residing on Grand Canary Island, Spain.

PATIENTS AND METHOD

Case-control study. Case subjects (n = 304) were recruited at the first coronary event; age-matched controls (n = 315) were randomly selected from the Grand Canary population. Participants were examined for the usual risk factors. Blood samples were obtained for biochemical analyses and DNA extraction. Genotyping was performed by PCR and restriction analysis.

RESULTS

Neither ACE (I/D) nor AT1 receptor polymorphism was associated with coronary heart disease, whereas the frequency distribution of AGT M235T genotypes among patients and control subjects (TT: 29% and 19%; MT: 48% and 50%; MM: 22% and 31%, respectively) was statistically different (p = 0.003). Multiple logistic regression analysis identified the TT genotype of the angiotensinogen gene (OR = 1.9; 95% CI 1.1-3.4), diabetes (OR = 4.4; 95% CI 2.0-9.4) and hypertension (OR = 2.1; 95% CI 1.3-3.3) as risk factors predicting the coronary event.

CONCLUSIONS

Our results provide no evidence of an association between ACE (I/D) or AT1 receptor polymorphism and coronary heart disease. However, homozygosity for the T allele of the angiotensinogen gene, diabetes and hypertension independently place individuals at higher risk of experiencing a coronary event on Grand Canary Island.

Variations in angiotensin-converting enzyme gene insertion/deletion polymorphism in Indian populations of different ethnic origins

The pattern of angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism in the Indian population is poorly known. In order to determine the status of the polymorphism, young unrelated male army recruits were screened. The population had cultural and linguistic differences and lived in an environment that varied significantly from one region to another. Analysis of the genotype, showed higher frequency of the insertion allele in four of the five groups i.e. I allele frequency was significantly higher (P < 0.05) in Dogras, Assamese and Kumaonese. The deletion allele frequency was comparatively higher in the fifth group that belonged to Punjab. A correlation was observed between the genotype and enzyme activity. Involvement of a single D allele in the genotype enhanced the activity up to 37.56 3.13%. The results suggested ethnic heterogeneity with a significant gene cline with higher insertion allele frequency. Such population-based data on various polymorphisms can ultimately be exploited in pharmacogenomics.

Angiotensin-converting enzyme (ACE) I/D genotype and renal ACE gene expression

BACKGROUND

The angiotensin-converting enzyme (ACE) I/D genotype affects serum ACE levels and the onset and progression of renal disease, but little is known about the mechanism. We investigated a possible association between the ACE I/D genotype and renal ACE mRNA levels in healthy subjects.

METHODS

Renal biopsy samples were obtained from 50 healthy kidney donors. The ACE I/D genotype was determined by polymerase chain reaction (PCR). Renal ACE mRNA quantification was performed by competitive RNA-PCR. In situ hybridization (ISH) for ACE mRNA on renal biopsy specimens was also performed.

RESULTS

The number of ACE transcripts in 100 ng of total RNA was significantly (P < 0.01) lower in subjects with II genotype (5.6 +/- 5.3 x 10(5), N = 20) compared with those with the ID (17.9 +/- 13.6 x 10(5), N = 23) or the DD genotype (36.9 +/- 14.6 x 10(5), N = 7) in healthy donors. The ISH studies showed that both tubular and glomerular ACE mRNA expressions were weak in subjects with the II genotype, intermediate in subjects with ID genotype, and strong in subjects with DD genotype.

CONCLUSIONS

It is suggested that renal ACE gene expression is associated with the ACE I/D genotype in healthy Japanese subjects.

Heart disease and vascular risk factors in the cognitively impaired elderly: implications for Alzheimer's dementia

The term "cardiogenic dementia" was introduced a few decades ago to indicate an alteration of consciousness and cognition due to heart disease. Although this term is now disused, the relationship between cardiovascular disease and cognitive impairment is currently of great interest, not only for its potential therapeutic implications. but also for the recently recognized important role that vascular factors appear to play in Alzheimer's disease. The aims of this review are therefore 1) to show data supporting the role of cardiac disease--namely congestive heart failure, myocardial infarction and atrial fibrillation--and other vascular risk factors--i.e., hypertension and diabetes--in the development or worsening of cognitive impairment; 2) to highlight recent observations on the relationship between presence and severity of congestive heart failure/ myocardial infarction/atrial fibrillation and Alzheimer's disease: and 3) to uncover the type of studies needed in this field in order to facilitate a more precise algorithm of dementia prevention as well as intervention in demented patients with cardiovascular disease.

T594M and G442V polymorphisms of the sodium channel beta subunit and hypertension in a black population

Polymorphisms of the epithelial sodium channel may raise blood pressure by increasing renal sodium reabsorption. This study examines frequency distributions and associations with hypertension of the T594M and of the G442V polymorphisms of the beta subunit of the epithelial sodium channel in a population-based sample. We studied a stratified random sample of 459 subjects (279 women), aged 40-59 years, of black African origin from general practices' lists within a defined area of South London. All were first generation immigrants. The polymorphic variants were detected using single strand conformational polymorphism technique (SSCP). The prevalence of hypertension (BP > or =160 and/or 95 mm Hg or on drug therapy) was 43%; of these, 76% were on drug therapy. The main analysis was carried out by three ordered blood pressure categories (I to III) according to increasing blood pressure and presence or absence of drug therapy. The frequency of the 594M variant (heterozygotes and homozygotes) was 4.6%; the frequency of the 442V variant was higher (27.0%). The frequency of the 594M variant increased with increasing blood pressure category (P = 0.05) and was more common in hypertensives than normotensives. By contrast the frequency of the 442V variant did not vary across increasing blood pressure categories (P = 0.62). No gender difference was observed. Adjustment for age, sex and body mass index did not alter these findings. These results suggest that the 594M variant may contribute to high blood pressure in black people of African origin whereas the G442V polymorphism is unlikely to influence blood pressure in this population.

Association of angiotensinogen M235T and A(-6)G gene polymorphisms with coronary heart disease with independence of essential hypertension: the PROCAGENE study. Prospective Cardiac Gene

OBJECTIVES

We examined the relationship between the angiotensinogen (AGT) gene M235T polymorphism, the variant promoter of the AGT gene A(-6)G and the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism and coronary heart disease (CHD) in native Gran Canaria Island habitants, who have the highest rates of CHD in Spain.

BACKGROUND

Some studies subject that the ACE (I/D) polymorphism could be associated with CHD, while AGT (M235T) has been related to essential hypertension.

METHODS

We studied 304 subjects with angiographic evidence of coronary artery disease and a clinical diagnosis of myocardial infarction or unstable angina and 315 age- and gender-matched controls. Blood was drawn and DNA extracted. Angiotensin-converting enzyme (I/D) gene polymorphism was analyzed by polymerase chain reaction (PCR) and AGT gene polymorphisms by restriction fragment length polymorphism-PCR and mutagenically-separated PCR.

RESULTS

The ACE (I/D) polymorphism showed no association with CHD, whereas the frequency distribution of AGT (M235T) genotypes among patients and controls (235T: 29.1% and 19.0%; M235T: 48.5% and 50.2%; M235: 22.4% and 30.8%, respectively) was statistically different (p = 0.005) and not related to the presence of essential hypertension. Similar results were observed with the AGT A(-6)G polymorphism. In multiple logistic regression analysis, CHD odds ratio associated with 235T and M235 homozygotes were 1.7 (1.1 to 2.6) and 0.54 (0.36 to 0.82), respectively.

CONCLUSIONS

This study shows that genetic variation of the AGT (M235T), but not the ACE (I/D), genotypes contributes to the presence of CHD independently of blood pressure profile in a subset of the Spanish population with a high prevalence of cardiovascular disease.

Angiogenin gene-race interaction for resting and exercise BP phenotypes: the HERITAGE Family Study

We examined the association between an angiogenin gene polymorphism and blood pressure (BP) at rest and in response to acute exercise before and after a 20-wk endurance-training program. Subjects were 737 normotensive and borderline hypertensive subjects (257 black and 480 white). The polymorphism was detected by PCR and digestion with AvaII, yielding an allele of 253 bp or a rare allele of 194 + 59 bp. Resting and exercise [50 W; 60, 80, and 100% of maximal O2 consumption (VO2 max)] systolic (SBP) and diastolic BP were determined before and after training. Among blacks, adjusted SBP in the sedentary state was significantly lower in carriers of the rare allele at rest and exercise intensities of 60, 80, and 100% of VO2 max. In the trained state, carriers of the rare allele had a significantly (P < 0.05) lower SBP than did noncarriers at rest and at 80 and 100% of VO2 max. The genotypic effect observed among blacks was not evident among whites. Furthermore, change in BP (after--before) was not significantly associated with the genotype. In conclusion, the angiogenin gene AvaII polymorphism is associated with a lower SBP at rest and in response to acute high-intensity exercise in blacks but not in whites.

Candidate gene polymorphisms in cardiovascular disease: a comparative study of frequencies between a French and an Italian population

A multilocus assay was used to genotype up to 27 variable sites in 15 genes in French and Italian, presumed to be healthy populations (n=1480, n=162, respectively). These genes are involved in lipid metabolism (APOE, APOB, APOC3, CETP, LPL, PON), homocysteine metabolism (CBS, MTHFR), blood viscosity (Fibrinogen, FV), platelet aggregation (GpIIIa), leukocyte adhesion (SELE), and renin-angiotensin system (AT1R, ACE, AGT). Allele frequencies for all the markers were compared between the two populations. Five allele frequencies differed between the two European countries: APOB 71Ile (p < 0.001), SELE 98T (p < 0.001), SELE 128Arg (p < or = 0.01), APOE E4 (p < or = 0.01) and MTHFR 677T (p < or = 0.01), suggesting the existence of a north-south gradient in European allele frequencies. The other allele frequencies : APOC3 -482T, -455C, 1100T, 3175G, 3206G; LPL -93G, 9Asn, 291Ser; CETP 405Val; PON 192Arg; ACE Del; AGT 235Thr; AT1R 1166C; CBS 278Thr, GpIIIa P1A2; Fibrinogen -455A, FV 506Gln and SELE 554Phe, were similar between the two populations. They were also similar to those observed in other European countries.

Risk of venous thromboembolism associated with the insertion/deletion polymorphism in the angiotensin-converting enzyme gene

The circulating levels of angiotensin I-converting enzyme (ACE) are linked with a 287-base pair insertion/deletion (I/D) polymorphism at intron 16 of the ACE gene. Thus, the homozygous deletion (D/D genotype) could cause chronic vasoconstriction, arterial hypertension and, possibly, coronary artery disease. Also, the increase in plasminogen activator inhibitor-1 level and impaired fibrinolysis were related with the D/D genotype. The D allele has been recently associated with venous thrombosis among African-American men as well as among patients that underwent elective total hip replacement. We assess the risk of venous thromboembolism (VTE) linked with each genotype of the I/D ACE gene polymorphism in a Caucasian population by means of a case-control study. We genotyped the ACE gene in a series of 148 patients aged 45.0 +/- 16.0 years (range, 11-80 years), objectively diagnosed in our centre of deep-vein thrombosis or pulmonary embolism, and in 240 thrombosis-free subjects (25-75 years) from the same geographic area. The observed difference in D allele frequencies between patients (0.56) and controls (0.62) was nonsignificant overall; however, statistical significance (P = 0.05) was found by considering the recessive hypothesis (D/D versus I/ D + I/I) [odds ratio (OR) = 0.64, 95% confidence interval (CI95) = 0.42-0.99]. The OR was 0.88 (CI95 = 0.51-1.53; P = 0.65) for the dominant hypothesis (D/D + I/D versus I/I genotypes). The relative risk for the D allele was close to 1 for the dominant hypothesis, both considering gender and recurrent tendency; however, it was protective in men regarding the recessive hypothesis (OR = 0.53, CI95 = 0.29-0.97, P = 0.04). The I/D ACE allele distribution was similar among the 46 thrombophilic patients (antithrombin, protein C or protein S deficiencies, factor V R506Q, factor II G20210A or lupus anticoagulant). In conclusion, among (Spanish) Caucasians, this study does not support the hypothesis that the deletion allele (D) of the ACE gene could be a significant risk factor for VTE, being protective in men.

Frequency and allelic association of common variants in the lipoprotein lipase gene in different ethnic groups: the Wandsworth Heart and Stroke Study

The lower serum triglyceride (Tg), higher high density cholesterol (HDL-C) levels and low coronary heart disease (CHD) mortality in black populations, contrast with that in whites. By comparison, South Asian populations display a higher mortality from CHD associated with increased Tg and low HDL-C levels. Lipoprotein lipase (LPL) plays a major role in Tg metabolism. To determine if variation in the LPL gene contributes to the differences in lipid levels, we studied the frequencies and allelic associations of five common variants in the lipoprotein lipase (LPL) gene (-93T/G, D9N, N291S, S447X, and the HinddIII RFLP in intron 8) with serum Tg and HDL-cholesterol concentrations in population samples of middle-aged men and women of whites, South Asians, and blacks of African origin co-resident in South London. Significantly higher frequencies of the H(-) (P < 0.00001), N9 (P < 0.001), and -93G (P < 10(-10)) alleles were seen in blacks compared to the other two groups. Allelic association between -93G and N9, and H(+) and X447 was strong in all three groups. However, no association was observed between serum Tg and HDL-cholesterol concentrations and these variants in the three ethnic groups. A single common polymorphism in the LPL gene is unlikely to account for the differences in fasting serum Tg in populations of different ethnic background. The importance of the differences in frequencies and the mechanism(s) whereby these may contribute towards a beneficial LPL genotype in black populations remain to be determined.

The role of cerebral ischemia in Alzheimer's disease

The Alzheimer type of dementia and stroke are known to increase at comparable rates with age. Recent advances suggest that vascular risk factors linked to cerebrovascular disease and stroke in the elderly significantly increase the risk of developing Alzheimer's disease (AD). These include atherosclerosis, atrial fibrillation, coronary artery disease, hypertension, and diabetes mellitus. Moreover, review of various autopsy series shows that 60-90% of AD cases exhibit variable cerebrovascular pathology. Although some vascular lesions such as cerebral amyloid angiopathy, endothelial degeneration, and periventricular white matter lesions are evident in most cases of AD, a third will exhibit cerebral infarction. Despite the interpretation of pathological evidence, longitudinal clinical studies suggest that the co-existence of stroke and AD occurs more than by chance alone. Strokes known to occur in patients with Alzheimer syndrome and most frequently in the oldest old substantially worsen cognitive decline and outcome, implicating some interaction between the disorders. Nevertheless, the nature of a true relationship between the two disorders seems little explored. What predisposes to strokes in underlying cognitive decline or AD? Is it possible that cerebral ischemia is a causal factor for AD? I examined several vascular factors and the vascular pathophysiology implicated in stroke and AD, and propose that cerebral ischemia or oligemia may promote Alzheimer type of changes in the aging brain. Irrespective of the ultimate pathogenetic mechanism, these approaches implicate that management of peripheral vascular disease is important in the treatment or prevention of Alzheimer's disease or mixed dementia.

Gender-specific association of the angiotensin converting enzyme gene with Alzheimer's disease

Epidemiological studies have demonstrated that risk factors for vascular disease are also risk factors for Alzheimer's disease (AD). The gene for the angiotensin converting enzyme (ACE) has recently been reported to be associated with risk for AD. We have investigated the possibility of such an association in 98 clinic-based and 73 community-based AD cases versus 175 community-based controls and find a gender-specific association of ACE genotype with AD in the female clinic population. These data suggest that gender may interact with genetic factors to influence risk for AD. Gender-specific risk for AD has been previously reported, and a biological rationale for involvement of ACE in the AD process is supported by studies exploring the relationship between AD and vascular risk factors such as hypertension. However, the results may also be a consequence of the known anomalies that arise in genetic association studies as a consequence of sample selection.

Association between the C825T polymorphism of the G protein beta3-subunit gene and hypertension in blacks

A polymorphism (C825T) of the G protein beta3-subunit gene has been associated with low renin hypertension in whites. The aim of this study was to examine the C825T polymorphism in relation to hypertension in a population-based study of black people of African origin who have high prevalence of low renin, salt-sensitive hypertension. A total of 428 men and women, aged 40 to 59 years (270 Caribbeans and 158 West Africans), who took part in a population-based survey were studied. All were blacks and first-generation immigrants. The C825T polymorphism was detected by polymerase chain reaction followed by restriction-enzyme digestion. The prevalence of hypertension (supine blood pressures >/=160 systolic and/or 95 mm Hg diastolic or on drug therapy) was 43%. The distribution of the genotypes (CC, CT, and TT) was in Hardy-Weinberg equilibrium with observed frequencies of 4.0% (n=17), 33.6% (n=144), and 62.4% (n=267), respectively. Allele frequencies were 20.8% for C and 79.2% for T. No difference was detected between Caribbeans and West Africans. A 3-fold higher risk of hypertension was found among the carriers of the T variant both as heterozygotes (odds ratio [OR], 3.43 [95% CI, 0.94 to 12.4]) and homozygotes (OR, 3.87 [95% CI, 1. 09 to 13.8]). The estimate of effect and the blood pressure values in the groups carrying the T variant suggested a dominant model for the T allele. This was confirmed by a significant association between the T allele and hypertension (OR, 3.71 [95% CI, 1.05 to 13. 1]), even when adjusted for age, sex, and body mass index (OR, 4.14 [95% CI, 1.11 to 15.4]). The study shows, for the first time, a high frequency of the 825T allele in black people, and it provides evidence that the T allele may be a susceptibility factor for the development of hypertension in blacks. Given the high frequency of the T allele, even a 2-fold increased risk of hypertension among the carriers of the T allele might account for 44% of the cases of hypertension in blacks.