Cardiovascular phenotype of young adults and angiotensinogen alleles

Heritability of left ventricular structure and function in Caucasian families

AIMS

The aim of this study was to investigate the heritability as well as genetic and environmental correlations of left ventricular (LV) structural and functional traits in complex pedigrees of a Caucasian population.

METHODS AND RESULTS

We randomly recruited 459 white European subjects from 52 families (50% women; mean age 45 years). LV structure was measured by M-mode and 2D echocardiography and LV function was measured by conventional Doppler and tissue Doppler imaging (TDI). Other measurements included blood pressure, anthropometric, and biochemical measurements. We estimated the heritability of LV traits while adjusting for covariables, including sex, age, body height and weight, systolic and diastolic blood pressures, and heart rate. With full adjustment, heritability of LV mass was 0.23 (P= 0.025). The TDI-derived mitral annular velocities Ea and Aa showed moderate heritability (h(2)= 0.36 and 0.53, respectively), whereas the mitral inflow A peak had weak heritability (h(2) = 0.25) and the E peak was not heritable (h(2) = 0.11). We partitioned the total phenotypic correlation when it reached significance, into a genetic and an environmental component. The genetic correlations were 0.61 between the E and Ea peaks and 0.90 between the A and Aa peaks.

CONCLUSION

Our study demonstrated moderate heritability for LV mass as well as the mitral annular Ea and Aa peaks. We also found significant genetic correlations between the E and Ea peaks and between the A and Aa peaks. Our current findings support the ongoing research to map and detect genetic variants that contribute to the variation in LV mass and other LV structural and functional phenotypes.

Carotid artery atherosclerosis in hypertensive patients with a functional LDL receptor-related protein 6 gene variant

BACKGROUND AND AIMS

Rare (611C) and common (1062V) variants of the Low-Density Lipoprotein Receptor-Related Protein 6 (LRP6) display reduced activation of Wnt/ß-catenin signaling. The rare gene variant was associated with hypertension, metabolic abnormalities, and early coronary artery disease. We investigated whether the common 1062V LRP6 variant was related to carotid artery atherosclerosis (CAA) in hypertensive patients.

METHODS AND RESULTS

Retrospective study of 334 hypertensive patients (<65 years old) who underwent carotid artery ultrasonography. Hypertension, type 2 diabetes, dyslipidemia, glomerular filtration rate, and smoking habit were evaluated. CAA was defined by the presence of atherosclerotic plaques (focal intima-media thickness ≥ 1.3 mm). Logistic regression models were used to estimate the independent effect of 1062V allele. The relationship between LRP6 genotypes and LRP6 gene expression in carotid plaques was also investigated. No difference was observed between genotypes in clinical variables except for a slightly higher fasting glucose in 1062V carriers. The 1062V LRP6 variant was an independent risk factor for CAA in both unadjusted (OR 2.08, 95%CI 1.27-3.41, p=0.003) and adjusted models (OR 1.92, 95%CI 1.09-3.39, p=0.02). LRP6 was expressed in carotid atherosclerotic plaques at significantly lower levels (p=0.015) in 1062V carriers.

CONCLUSION

Beside the role of established risk factors, 1062V variant of LRP6 and CAA are strongly associated in hypertensive patients, making LRP6 a novel relevant candidate gene for atherosclerosis in the presence of hypertension.

AGT M235T genotype/anxiety interaction and gender in the HyperGEN study

Background

Both anxiety and elevated heart rate (HR) have been implicated in the development of hypertension. The HyperGen cohort, consisting of siblings with severe and mild hypertension, an age-matched random sample of persons from the same base populations, and unmedicated adult offspring of the hypertensive siblings (N = 1,002 men and 987 women), was analyzed for an association of the angiotenisinogen AGTM235T genotype (TT, MT, MM) with an endophenotype, heart rate (HR) in high and low anxious groups.

Methodology

The interaction of AGTM genotype with anxiety, which has been independently associated with hypertension, was investigated adjusting for age, hypertension status, smoking, alcohol consumption, beta blocker medication, body mass index, physical activity and hours of television viewing (sedentary life style).

Principal Findings

Although there was no main effect of genotype on HR in men or women, high anxious men with the TT genotype had high HR, whereas high anxious men with the MM genotype had low HR. In women, HR was inversely associated with anxiety but there was no interaction with genotype.

Conclusion/Significance

The results suggest that high anxiety in men with the TT genotype may increase risk for hypertension whereas the MM genotype may be protective in high anxious men. This type of gene x environment interaction may be one reason why genome wide association studies sometimes fail to replicate. The locus may be important only in combination with certain environmental factors.

Angiotensinogen promoter variants influence gene expression in human kidney and visceral adipose tissue

Human angiotensinogen (AGT) gene promoter polymorphisms (G-217A; A-20C; G-6A) influence AGT transcription in vitro and have been implicated in the genetics of essential hypertension. We analysed the association among AGT promoter variants and AGT mRNA levels in human kidney and visceral adipose tissue (VAT) in vivo. Samples of kidney and VAT were obtained from 35 consecutive patients undergoing renal surgery. The AGT gene promoter of each patient was sequenced to identify variants. AGT gene expression was studied by real-time PCR TaqMan assay. Clinical data obtained before surgery were also considered in the statistical analysis. Two new polymorphisms at -175 and at -163 were identified. Although AGT expression was significantly higher in VAT than in the kidney, when both variants were present together AGT expression in VAT was about fivefold lower (P=0.033) than in the wild haplotype. This lower AGT expression in VAT suggests that the proximity and linkage of -175A and -163A variants might destabilize the binding of specific transcription factors to an acute-phase responsive element 3. Among the known AGT promoter variants, only -20C SNP has an important effect on tissue-specific differential AGT expression in the human tissues studied, inducing a 3.8-fold increase in AGT mRNA localized only in the kidney medulla (P=0.038). The other known polymorphisms (G-6A; G-217A) were not associated with different levels of AGT expression. Our results support the hypothesis that some human AGT promoter variants influence transcriptional activity in a tissue-specific way in humans.

Cardiovascular and metabolic effects of natriuretic peptides

Natriuretic peptides (NP) are essential in mammals to regulate blood volume and pressure. The functional roles of NP are not limited to natriuresis and diuresis. Several peripheral and central actions of the peptides have been characterized. Studies on transgenic mice have revealed their key function in the regulation of cardiomyocyte growth. Plasma NP levels increase in patients with cardiovascular disorders and heart failure. They represent useful clinical markers for clinicians to diagnose heart diseases. The recent discovery of their potent lipolytic action in adipose tissue is a breakthrough in cardiovascular medicine. This new function of NP in the regulation of lipid metabolism offers interesting questions in the field of obesity, diabetes and cardiovascular diseases. This review will briefly describe the effects of NP on the cardiovascular system and lipid metabolism.

The 460Trp allele of α-adducin increases carotid intima–media thickness in young adult males

BACKGROUND

The 460Trp allele of the alpha-adducin gene (ADD1), which is involved in a form of salt-sensitive hypertension, has been associated with patterns of target organ damage.

OBJECTIVES

As carotid artery intima-media thickness (IMT) largely depends upon unknown genetic factors, besides being associated to conventional risk factors, we tested the association of the 460Trp allele of ADD1 with IMT in a well-characterized sample of young healthy normotensive subjects, to assess the role of ADD1 polymorphism without overlapping effects of age or already elevated blood pressure.

METHODS

Anthropometric measurements, blood pressure (BP), and carotid artery wall IMT (high-resolution sonography and digitalized morphometry) were obtained in 420 healthy normotensive Caucasian university students. Genotypes for ADD1 were detected by automated genomic polymerase chain reaction (PCR).

RESULTS

ADD1 genotypes were evenly distributed between genders. IMT was significantly larger in carriers of the 460Trp allele of ADD1, while a significant gender x ADD1 interaction (P = 0.02) demonstrated that IMT was increased only in males carrying the 460Trp allele (P < 0.001). No significant association was found in females.

CONCLUSIONS

The 460Trp allele of ADD1 contributes substantially to increase carotid IMT, in a male hormonal milieu only, at least in the young age range.

Genetic variants predisposing to cardiovascular disease

PURPOSE OF REVIEW

The goal of this review is to provide an update on the most recent and relevant findings in the area of genotype-phenotype associations as well as the relationships between genetic factors and cardiovascular disease risk markers and events. In addition, emphasis will be placed on the methodological problems associated with studying the genetics of complex disorders, specifically cardiovascular diseases.

RECENT FINDINGS

Genes associated with cardiovascular disease predisposition have been examined, including traditional cardiovascular disease candidate genes, such as ACE, AGT, eNOS, PON and MTHFR, new loci that have recently been added to the growing list of cardiovascular disease candidate genes (i.e. MEF2A, ALOX5, LTA, APOM, PDE4D), and genes that have been shown to be at the intersection of several age-related disorders through interaction with one another or with environmental factors (i.e. APOA5, APOE, PPARgamma, LPL and LIPC).

SUMMARY

During the last year, tremendous effort has been made in elucidating new genes associated with cardiovascular disease predisposition. For the most part, however, major breakthroughs have not been made, primarily due to the poor replication of results among studies, as a consequence of poor experimental design. Nevertheless, we have increased our understanding of the complexity of cardiovascular disease and the relevance of gene-environment interactions as the ultimate drivers of the individual predisposition to the disease. It is essential, therefore, that present and future genetic studies in this area take into consideration the inclusion of high-quality environmental data in the analytical process to test the clinical usefulness of a genetic marker as a risk predictor.

Association analysis of genes in the renin-angiotensin system with subclinical cardiovascular disease in families with Type 2 diabetes mellitus: the Diabetes Heart Study

AIMS

Cardiovascular disease (CVD) is a major complication of Type 2 diabetes mellitus. The renin-angiotensin system (RAS) and nitric oxide production are both important regulators of vascular function and blood pressure. Genes encoding proteins involved in these pathways are candidates for a contribution to CVD in diabetic patients. We have investigated variants of the angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin type 1 receptor (AT1R) and endothelial nitric oxide synthase (NOS3) genes for association with subclinical measures of CVD in families with Type 2 diabetes mellitus (T2DM).

METHODS

Atherosclerosis was measured by carotid intima-media thickness and calcification of the carotid and coronary arteries in 620 European Americans and 117 African Americans in the Diabetes Heart Study. Because of the role of these systems in blood pressure regulation, blood pressure was also investigated.

RESULTS

Compelling evidence of association was not detected with any of the SNPs with any outcome measures after adjustments for covariates despite sufficient power to detect relatively small differences in traits for specific genotype combinations.

CONCLUSIONS

Genetic variation of the RAS and NOS3 genes do not appear to strongly influence subclinical cardiovascular disease or blood pressure in this diabetic population.

The genetics of stroke

PURPOSE OF REVIEW

Ischaemic stroke is a heterogeneous disease caused by different pathogenic mechanisms, of which small artery and large artery stroke are the most common. The identification of the genes involved is unclear. The likely candidate genes associated with stroke are those that are associated with matrix deposition (stromelysin-1, MMP3), inflammation (IL-6), and lipid metabolism (hepatic lipase, APOE, PON1) and clotting (factor V Leiden, fibrinogen).

RECENT FINDINGS

In this review we will only discuss those genes in which there has been a significant contribution to the understanding of stroke since October 2003.

SUMMARY

The published data were reviewed to determine the robustness of these associations and to examine whether there is any evidence of risk modification by factors such as smoking habit, known to be associated with stroke.

Genetic risk factors for stroke and carotid atherosclerosis: insights into pathophysiology from candidate gene approaches

Ischaemic stroke is the most common form of stroke and is caused by atherosclerosis in most patients. Several genetic determinants contribute to stroke risk. Of these, carotid intimal-medial wall thickness (IMT) is particularly relevant, because it is a surrogate measure of subclinical atherosclerosis and a strong predictor of future ischaemic stroke. Studies of twins, siblings, and families have provided significant evidence for heritability, but the genes involved have not been identified. Some researchers have reported that IMT is high in people with functional variants of genes related to matrix deposition (MMP3), inflammation (interleukin 6), and lipid metabolism (hepatic lipase, APOE, CETP, and PON1). In this review, we assess the robustness of these associations and examine whether there is any evidence of risk modification by factors, such as smoking.

Aldosterone synthase alleles and cardiovascular phenotype in young adults

The C(-344)T promoter polymorphism of the human aldosterone synthase (CYP11B2) gene has been associated with hypertension and cardiac hypertrophy, but there were contrasting data. We analysed the genotype/phenotype associations between this polymorphism and cardiovascular variables in a young adult population, where interactions among genes, gene-environment, and acquired ageing-related organ damage are reduced. Anthropometric measurements, blood pressure, heart rate, left ventricular variables (by echocardiography), and carotid artery wall intimal-media thickness (by high-resolution sonography and digitalized morphometry) were taken in 420 white Caucasian students (mean age 23.5 years, s.d. 2.5 years). CYP11B2 alleles were detected by genomic polymerase chain reaction followed by digestion. Taking into account the three possible models of inheritance, we found no differences in the considered variables, except for an independent effect of the C(-344) allele on SBP in males (TT 125.6 (1.6), TC 128.4 (1.2) and CC 130.5 (2.2), mmHg, media (ES), P=0.03), and on interventricular septum thickness in diastole in females (CC 6.98 (0.12) vs TT 6.87 (0.09) and TC 6.87 (0.07), mmHg, P<0.01), in the codominant model. In conclusion, the CYP11B2 C(-344)T polymorphism appears to have a slight role in the cardiovascular phenotype of young healthy adults, even if these genotype/phenotype relationships might change with ageing.

Allelic variants of natriuretic peptide receptor genes are associated with family history of hypertension and cardiovascular phenotype

OBJECTIVE

Abnormalities in the natriuretic peptide system could play a key role in the genesis of hypertension. We evaluated the associations between a family history of hypertension, cardiovascular phenotype and allelic variants of Npr1 and Npr3, two candidate genes that codify for natriuretic peptide receptors.

METHODS

We genotyped 45 young normotensive subjects (19 males, 26.8 +/- 3.7 years) with accurately assessed family history of hypertension (FH+) and 52 (26 males, 26.1 +/- 3.1 years) without (FH-) for the known variants of Npr1 and Npr3 genes, and for a novel length difference (3C/4C) polymorphism at position 15129 in the 3'-untranslated region of the Npr1 gene. Blood pressure, echocardiography and plasma brain natriuretic peptide were assessed.

RESULTS

Both the novel Npr1 3C allele (59 versus 33%, P < 0.001) and the 3C/3C genotype (31 versus 8%; P < 0.001) were significantly more frequent in FH+ than in FH-. The inverse distribution of the 4C/4C genotype suggested that a casual association was very unlikely. Moreover, the 3C/3C homozygous had significantly higher systolic blood pressure (121.1 +/- 6.3 versus 115.6 +/- 7.8 mmHg in 4C/4C; P < 0.05) and a longer left ventricular isovolumic relaxation time (67 +/- 10 versus 61 +/- 9 ms; P < 0.05). The Npr3 C(-55) allele variant was also more frequent in FH+ (88 versus 76%, P < 0.05), but was not associated with the cardiovascular phenotype.

CONCLUSIONS

The novel Npr1 gene 3C variant and the Npr3 gene C(-55) allele are associated with hypertensive family history. Moreover, the functional Npr1 3C variant, when homozygous, is also associated with higher systolic blood pressure and prolonged ventricular relaxation.

Genetics of intima-media thickness

PURPOSE OF REVIEW

Increased carotid artery intima-media thickness is associated with an increased risk of coronary heart disease or cerebrovascular disease and is a powerful predictor of cardiovascular and cerebrovascular outcomes. Consequently, the measurement is now used in a number of case control, cohort and familial and linkage studies as an intermediate phenotype for the investigation of the genetic and environmental determinants of atherosclerosis. The aim of this paper is to review the most recent available data on the genetic determinants of carotid intima-media thickness.

RECENT FINDINGS

Genes could account for a significant amount of variation in carotid intima-media thickness: up to 30-66%. Carotid intima-media thickness progressed more rapidly with age in familial hypercholesterolemia patients than in patients without his condition. Familial hypercholesterolemia patients with a null LDL receptor allele tended to have higher carotid intima-media thickness than patients carrying the LDL receptor defective allele. Small association studies showing positive or negative results with the angiotensinogen gene variants as well as with the angiotensin converting enzyme I/D polymorphism add to the confusion in this largely controversial area. Differing results may depend on the vascular territory and genetic background. New associations have been described in small studies.

SUMMARY

Studies on the association of polymorphisms and intima-media thickness are frequently disappointing and lead occasionally to conflicting results. Among study limitations is the fact that mostly single gene effects are considered; longitudinal cohort studies may be more appropriate than case control studies. Ongoing large prospective population studies and clinical trials have integrated the measurements of intima-media thickness and genotype determination with a genomic approach. As a result, in the near future we may see more important and robust results with significant consequences on our understanding of genetic determinants of atherosclerotic cardiovascular disease.