Renal function in relation to three candidate genes

A Mutation in γ-Adducin Impairs Autoregulation of Renal Blood Flow and Promotes the Development of Kidney Disease

BACKGROUND

The genes and mechanisms involved in the association between diabetes or hypertension and CKD risk are unclear. Previous studies have implicated a role for γ-adducin (ADD3), a cytoskeletal protein encoded by Add3.

METHODS

We investigated renal vascular function in vitro and in vivo and the susceptibility to CKD in rats with wild-type or mutated Add3 and in genetically modified rats with overexpression or knockout of ADD3. We also studied glomeruli and primary renal vascular smooth muscle cells isolated from these rats.

RESULTS

This study identified a K572Q mutation in ADD3 in fawn-hooded hypertensive (FHH) rats-a mutation previously reported in Milan normotensive (MNS) rats that also develop kidney disease. Using molecular dynamic simulations, we found that this mutation destabilizes a critical ADD3-ACTIN binding site. A reduction of ADD3 expression in membrane fractions prepared from the kidney and renal vascular smooth muscle cells of FHH rats was associated with the disruption of the F-actin cytoskeleton. Compared with renal vascular smooth muscle cells from Add3 transgenic rats, those from FHH rats had elevated membrane expression of BKα and BK channel current. FHH and Add3 knockout rats exhibited impairments in the myogenic response of afferent arterioles and in renal blood flow autoregulation, which were rescued in Add3 transgenic rats. We confirmed these findings in a genetic complementation study that involved crossing FHH and MNS rats that share the ADD3 mutation. Add3 transgenic rats showed attenuation of proteinuria, glomerular injury, and kidney fibrosis with aging and mineralocorticoid-induced hypertension.

CONCLUSIONS

This is the first report that a mutation in ADD3 that alters ACTIN binding causes renal vascular dysfunction and promotes the susceptibility to kidney disease.

Angiotensin-converting enzyme insertion/deletion polymorphism contributes high risk for chronic kidney disease in Asian male with hypertension--a meta-regression analysis of 98 observational studies

Background

Associations between angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphisms and chronic kidney disease (CKD) have been extensively studied, with most studies reporting that individuals with the D allele have a higher risk. Although some factors, such as ethnicity, may moderate the association between ACE I/D polymorphisms and CKD risk, gender-dependent effects on the CKD risk remain controversial.

Objectives

This study investigated the gender-dependent effects of ACE I/D polymorphisms on CKD risk.

Data sources

PubMed, the Cochrane library, and EMBASE were searched for studies published before January 2013.

Study eligibility criteria, participants, and interventions

Cross-sectional surveys and case–control studies analyzing ACE I/D polymorphisms and CKD were included. They were required to match the following criteria: age >18 years, absence of rare diseases, and Asian or Caucasian ethnicity.

Study appraisal and synthesis methods

The effect of carrying the D allele on CKD risk was assessed by meta-analysis and meta-regression using random-effects models.

Results

Ethnicity [odds ratio (OR): 1.24; 95% confidence interval (CI): 1.08–1.42] and hypertension (OR: 1.55; 95% CI: 1.04–2.32) had significant moderate effects on the association between ACE I/D polymorphisms and CKD risk, but they were not significant in the diabetic nephropathy subgroup. Males had higher OR for the association between ACE I/D polymorphisms and CKD risk than females in Asians but not Caucasians, regardless of adjustment for hypertension (p<0.05). In subgroup analyses, this result was significant in the nondiabetic nephropathy group. Compared with the I allele, the D allele had the highest risk (OR: 3.75; 95% CI: 1.84–7.65) for CKD in hypertensive Asian males.

Conclusions and implications of key findings

The ACE I/D polymorphisms may incur the highest risk for increasing CKD in hypertensive Asian males.

Genetic basis of the impaired renal myogenic response in FHH rats

This study examined the effect of substitution of a 2.4-megabase pair (Mbp) region of Brown Norway (BN) rat chromosome 1 (RNO1) between 258.8 and 261.2 Mbp onto the genetic background of fawn-hooded hypertensive (FHH) rats on autoregulation of renal blood flow (RBF), myogenic response of renal afferent arterioles (AF-art), K(+) channel activity in renal vascular smooth muscle cells (VSMCs), and development of proteinuria and renal injury. FHH rats exhibited poor autoregulation of RBF, while FHH.1BN congenic strains with the 2.4-Mbp BN region exhibited nearly perfect autoregulation of RBF. The diameter of AF-art from FHH rats increased in response to pressure but decreased in congenic strains containing the 2.4-Mbp BN region. Protein excretion and glomerular and interstitial damage were significantly higher in FHH rats than in congenic strains containing the 2.4-Mbp BN region. K(+) channel current was fivefold greater in VSMCs from renal arterioles of FHH rats than cells obtained from congenic strains containing the 2.4-Mbp region. Sequence analysis of the known and predicted genes in the 2.4-Mbp region of FHH rats revealed amino acid-altering variants in the exons of three genes: Add3, Rbm20, and Soc-2. Quantitative PCR studies indicated that Mxi1 and Rbm20 were differentially expressed in the renal vasculature of FHH and FHH.1BN congenic strain F. These data indicate that transfer of this 2.4-Mbp region from BN to FHH rats restores the myogenic response of AF-art and autoregulation of RBF, decreases K(+) current, and slows the progression of proteinuria and renal injury.

Upregulation of Na+/Ca2+ exchanger and TRPC6 contributes to abnormal Ca2+ homeostasis in arterial smooth muscle cells from Milan hypertensive rats

The Milan hypertensive strain (MHS) of rats is a model for hypertension in humans. Inherited defects in renal function have been well studied in MHS rats, but the mechanisms that underlie the elevated vascular resistance are unclear. Altered Ca(2+) signaling plays a key role in the vascular dysfunction associated with arterial hypertension. Here we compared Ca(2+) signaling in mesenteric artery smooth muscle cells from MHS rats and its normotensive counterpart (MNS). Systolic blood pressure was higher in MHS than in MNS rats (144 +/- 2 vs. 113 +/- 1 mmHg, P < 0.05). Resting cytosolic free Ca(2+) concentration (measured with fura-2) and ATP-induced Ca(2+) transients were augmented in freshly dissociated arterial myocytes from MHS rats. Ba(2+) entry activated by the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol (a measure of receptor-operated channel activity) was much greater in MHS than MNS arterial myocytes. This correlated with a threefold upregulation of transient receptor potential canonical 6 (TRPC6) protein. TRPC3, the other component of receptor-operated channels, was marginally, but not significantly, upregulated. The expression of TRPC1/5, components of store-operated channels, was not altered in MHS mesenteric artery smooth muscle. Immunoblots also revealed that the Na(+)/Ca(2+) exchanger-1 (NCX1) was greatly upregulated in MHS mesenteric artery (by approximately 13-fold), whereas the expression of plasma membrane Ca(2+)-ATPase was not altered. Ca(2+) entry via the reverse mode of NCX1 evoked by the removal of extracellular Na(+) induced a rapid increase in cytosolic free Ca(2+) concentration that was significantly larger in MHS arterial myocytes. The expression of alpha(1)/alpha(2) Na(+) pumps in MHS mesenteric arteries was not changed. Immunocytochemical observations showed that NCX1 and TRPC6 are clustered in plasma membrane microdomains adjacent to the underlying sarcoplasmic reticulum. In summary, MHS arteries exhibit upregulated TRPC6 and NCX1 and augmented Ca(2+) signaling. We suggest that the increased Ca(2+) signaling contributes to the enhanced vasoconstriction and elevated blood pressure in MHS rats.

alpha- and beta-Adducin polymorphisms affect podocyte proteins and proteinuria in rodents and decline of renal function in human IgA nephropathy

Adducins are cytoskeletal actin-binding proteins (α, β, γ) that function as heterodimers and heterotetramers and are encoded by distinct genes. Experimental and clinical evidence implicates α- and β-adducin variants in hypertension and renal dysfunction. Here, we have addressed the role of α- and β-adducin on glomerular function and disease using β-adducin null mice, congenic substrains for α- and β-adducin from the Milan hypertensive (MHS) and Milan normotensive (MNS) rats and patients with IgA nephropathy. Targeted deletion of β-adducin in mice reduced urinary protein excretion, preceded by an increase of podocyte protein expression (phospho-nephrin, synaptopodin, α-actinin, ZO-1, Fyn). The introgression of polymorphic MHS β-adducin locus into MNS (Add2, 529R) rats was associated with an early reduction of podocyte protein expression (nephrin, synaptopodin, α-actinin, ZO-1, podocin, Fyn), followed by severe glomerular and interstitial lesions and increased urinary protein excretion. These alterations were markedly attenuated when the polymorphic MHS α-adducin locus was also present (Add1, 316Y). In patients with IgA nephropathy, the rate of decline of renal function over time was associated to polymorphic β-adducin (ADD2, 1797T, rs4984) with a significant interaction with α-adducin (ADD1, 460W, rs4961). These findings suggest that adducin genetic variants participate in the development of glomerular lesions by modulating the expression of specific podocyte proteins.

Prevalence of metabolic syndrome and its association with obesity indices in a Chinese population

BACKGROUND

To investigate the prevalence of metabolic syndrome in an urbanizing community in Qingpu, a suburb of Shanghai, and to determine which obesity indices, including body mass index, waist circumference (WC), and waist:hip (WHpR), and waist:height (WHtR) ratios, are most closely associated with metabolic syndrome.

METHODS

We conducted a cross-sectional health survey of 1634 individuals (age 15-87 years) in the Jinhulu community located in Qingpu. The National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP ATP III) criteria were used to define metabolic syndrome, with central obesity defined according to Asia-Pacific (APC) region criteria.

RESULTS

The age-standardized prevalence of metabolic syndrome was 3.6% in men and 7.2% in women. Using the criterion of central obesity in the APC, the age-standardized prevalence of metabolic syndrome increased to 8.3% in men and 10.9% in women. Regardless of age, WHtR consistently showed a higher odd ratios (OR) after adjustment for confounding factors of 2.17 (95% confidence interval [CI] 1.12-4.20; P = 0.022) in subjects<52 years of age and 1.92 (95% CI 1.18-3.11; P = 0.008) in those ≥52 years of age. In men, the WHtR was the only significant predictor (OR 2.42; 95% CI 1.15-5.08; P = 0.02) of metabolic syndrome after adjustment, whereas in women WHtR (OR 1.87; 95% CI 1.37-2.85; P =0.0088) was slightly inferior to WHpR and WC.

CONCLUSION

Metabolic syndrome is prevalent in an urbanizing rural area in Qingpu. Of the anthropometric parameters commonly used to identify metabolic syndrome, WHtR may be the best.

Angiotensin converting enzyme insertion/deletion polymorphism and renoprotection in diabetic and nondiabetic nephropathies

Despite the huge amount of studies looking for candidate genes, the ACE gene remains the unique, well-characterized locus clearly associated with pathogenesis and progression of chronic kidney disease, and with response to treatment with drugs that directly interfere with the renin angiotensin system (RAS), such as angiotensin converting enzyme (ACE) inhibitors and angiotensin II receptor antagonists (ARA). The II genotype is protective against development and progression of type I and type II nephropathy and is associated with a slower progression of nondiabetic proteinuric kidney disease. ACE inhibitors are particularly effective at the stage of normoalbuminuria or microalbuminuria in both type I and type II diabetics with the II genotype, whereas the DD genotype is associated with a better response to ARA therapy in overt nephropathy of type II diabetes and to ACE inhibitors in male patients with nondiabetic proteinuric nephropathies. The role of other RAS or non-RAS polymorphisms and their possible interactions with different ACE I/D genotypes are less clearly defined. Thus, evaluating the ACE I/D polymorphism is a reliable tool to identify patients at risk and those who may benefit the most of renoprotective therapy with ACE inhibitors or ARA. This may guide pharmacologic therapy in individual patients and help design clinical trials in progressive nephropathies. Moreover, it might help optimize prevention and intervention strategies at population levels, in particular, in countries where resources are extremely limited and 1 million patients continue to die every year of cardiovascular or renal disease.

Conceptual basis and methodology of the SOPHIA study

To clarify the role of gene polymorphisms on the effect of losartan and losartan plus hydrochlorothiazide on blood pressure (primary end point) and on cardiac, vascular and metabolic phenotypes (secondary end point) after 4, 8, 12, 16 and 48 weeks treatment, an Italian collaborative study - The Study of the Pharmacogenomics in Italian hypertensive patients treated with the Angiotensin receptor blocker losartan (SOPHIA) - on never-treated essential hypertensives (n = 800) was planned. After an 8 week run-in, losartan 50 mg once daily will be given and doubled to 100 mg at week +4 if blood pressure is more than 140/90 mmHg. Hydroclorothiazide 25 mg once daily at week +8 and amlodipine 5 mg at week +16 will be added if blood pressure is more than 140/90 mmHg. Cardiac mass (echocardiography), carotid intima-media thickness, 24 h ambulatory blood pressure, homeostatic model assessment (HOMA) index, microalbuminuria, plasma renin activity and aldosterone, endogenous lithium clearance, brain natriuretic peptide and losartan metabolites will be evaluated. Genes of the renin-angiotensin-aldosterone system, salt sensitivity, the beta-adrenergic system and losartan metabolism will be studied (Illumina custom arrays). A whole-genome scan will also be performed in half of the study cohort (1M array, Illumina 500 GX beadstation).

Gly460Trp alpha-adducin gene polymorphism and endothelial function in untreated hypertensive patients

OBJECTIVES

Endothelium-dependent vasodilatation is impaired in essential hypertension. Besides traditional and emerging cardiovascular risk factors, genetic factors may also promote deleterious alterations of endothelial physiology. The aim of the present study was to investigate the relationship between the 460Trp allele of ADD1 and endothelium-dependent vasodilation in 110 never-treated hypertensive patients.

METHODS

Forearm blood flow (FBF) was measured during intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) at increasing doses. Analysis of endothelium-dependent and endothelium-independent vasodilation was tested according to ADD1 genotype.

RESULTS

The FBF values at the three incremental doses of ACh were 5.22 +/- 0.24 (+76%), 8.64 +/- 0.45 (+193%) and 14.74 +/- 0.71 (+395%) ml/100 ml of tissue per min for Gly460Gly and 4.63 +/- 0.20 (+51%), 6.84 +/- 0.36 (+123%) and 11.22 +/- 3.8 (+269%) ml/100 ml of tissue per min for 460Trp. Thus, ACh-stimulated FBF was significantly reduced in hypertensive subjects carrying the 460Trp allele of ADD1 (P < 0.001). SNP-stimulated FBF was not affected by ADD1.

CONCLUSIONS

The main finding in this study was that in essential hypertensives the 460Trp allele of ADD1 is strongly associated with an impaired endothelium-dependent vasodilation, a powerful predictor of cardiovascular risk.

Angiotensin-converting enzyme I/D and alpha-adducin Gly460Trp polymorphisms: from angiotensin-converting enzyme activity to cardiovascular outcome

The angiotensin-converting enzyme (ACE) I/D and the alpha-adducin (ADD1) Gly460Trp polymorphisms are associated with cardiovascular risk factors. In a prospective population study and in cell models, we investigated the combined effects of these 2 polymorphisms. We randomly recruited 1287 white subjects (women: 50.0%; mean age: 55.9 years). We obtained outcomes from registries and repeat examinations (median 3). Over 9.0 years (median), 178 fatal or nonfatal cardiovascular events occurred. In ADD1 Trp allele carriers, the multivariate-adjusted hazard ratios associated with ACE DD versus I were 1.72 (P=0.007) for total mortality, 2.35 (P=0.02) for cardiovascular mortality, 2.02 (P=0.005) for all cardiovascular events, and 2.59 (P=0.03) for heart failure. In contrast, these hazard ratios did not reach significance in ADD1 GlyGly homozygotes (0.08<or=P<or=0.90). The positive predictive value and attributable risk associated with ACE DD homozygosity combined with mutated ADD1 were 36.2% and 10.3%, respectively. To clarify our epidemiological observations, we investigated the effects of mutated human ADD1 on the membrane-bound ACE activity in fibroblasts from 51 volunteers and in transfected human embryonic kidney cells (31 experiments). In fibroblasts (5.10 versus 3.63 nanomoles of generated hippuric acid per milligram of protein per minute; P=0.0021) and human embryonic kidney cells (1.086 versus 0.081 nmol/mg per minute; P=0.017), the membrane-bound ACE activity increased in the presence but not absence of the ADD1 Trp allele. In conclusion, the combination of ACE DD homozygosity and mutated ADD1 worsened cardiovascular prognosis to a similar extent as classic risk factors, possibly because of increased membrane-bound ACE activity in subjects carrying the ADD1 Trp allele.

Association Between Arterial Properties and Renal Sodium Handling in a General Population

Mean arterial pressure drives pressure-natriuresis and determines arterial structure and function. In a population sample, we investigated the relation between arterial characteristics and renal sodium handling as assessed by the clearance of endogenous lithium. We ultrasonographically measured diameter, cross-sectional compliance (CC) and distensibility (DC) of the carotid, brachial, and femoral arteries in 1069 untreated subjects (mean age: 41.6 years; 50.1% women; 18.8% hypertensive subjects). While accounting for covariates and standardizing for the sodium excretion rate in both sexes, CC and DC of the femoral artery increased with higher fractional distal sodium reabsorption. Differences associated with a 1-SD change in fractional distal reabsorption of sodium were 51.7 mm(2)/kPax10(-3) (95% CI: 23.9 to 79.5; P=0.0002) and 0.56x10(-3)/kPa (95% CI: 0.17 to 0.94; P=0.004) for femoral CC and DC, respectively. In women as well as in men, a 1-SD increment in fractional proximal sodium reabsorption was associated with decreases in femoral and brachial diameter, amounting to 111.6 mum (95% CI: 38.2 to 185.1; P=0.003) and 52.5 mum (95% CI: 10.0 to 94.9; P=0.016), respectively. There was no consistent association between the properties of the elastic carotid artery and renal sodium handling. In conclusion, higher fractional sodium reabsorption in the distal nephron is associated with higher femoral CC and DC, and higher proximal sodium reabsorption is associated with decreased brachial and femoral diameters. These findings demonstrate that there might be an influence of renal sodium handling on arterial properties or vice versa or that common mechanisms might influence both arterial and renal function.

α-Adducin and angiotensin-converting enzyme polymorphisms in hypertension: evidence for a joint influence on albuminuria

BACKGROUND

A single-nucleotide polymorphism (Gly460Trp) within the alpha-adducin gene (ADD1) may influence several renal phenotypes, including salt sensitivity, susceptibility to renal failure, the renal haemodynamics and confer a worse cardiovascular risks profile. However, its relationship with microalbuminuria, a marker of early renal and cardiovascular damage and an independent predictor of morbid events in hypertension, is unknown. For this reason, we related the ADD1 genetic polymorphism to urine albumin levels and other clinical variables in essential hypertensive men. The angiotensin-converting enzyme (ACE) insertion/deletion (ID) polymorphism was also evaluated because of its interactive potential with the ADD1 genotype.

METHODS

Albuminuria (three overnight collections), echocardiographic left ventricular mass index, blood pressure, body mass index, renal function, glucose and lipids were measured in 238 genetically unrelated, never treated, uncomplicated Caucasian essential hypertensive men. Polymerase chain reaction or a 5' nuclease assay were used to characterize the ACE ID and ADD1 Gly460Trp variants, respectively.

RESULTS

Microalbuminuria (albuminuria >or= 15 microg/min) was more frequent in patients with the ACE DD variant, but only in those with a ADD1 Gly460Gly background. In contrast, urine albumin did not differ by ACE ID genotype in the presence of mutated ADD1 Trp alleles. ADD1 polymorphisms per se were not associated with albuminuria. Cardiovascular, renal, metabolic parameters were homogeneously distributed among different genetic backgrounds.

CONCLUSIONS

ACE DD and ADD1 Gly460Gly polymorphisms may jointly influence albuminuria in hypertensive men, 460Gly homozygosis facilitating or, possibly, the 460Trp allele mitigating the noxious renal impact of the ACE DD genotype. The data highlight further the complex pathophysiological implications of microalbuminuria in hypertension.

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 variations of tubular sodium reabsorption leading to “primary” hypertension: from gene polymorphism to clinical symptoms

The definition of the most appropriate strategy to demonstrate causation of a given genetic-molecular mechanism in a complex multifactorial polygenic disease like hypertension is hampered by the underestimation of the complexity arising from the genetic and environmental interactions. To disentangle this complexity, we developed a strategy based on six steps: 1) isolation of a rodent model of hypertension (Milan hypertensive strain and Milan normotensive strain) that shares some pathophysiological abnormalities with human primary hypertension; 2) definition in the model of the sequence of events linking these abnormalities to a genetic molecular mechanism; 3) determination of the polymorphism of the three adducin genes discovered in the model both in rats and in humans; 4) comparison at biochemical and physiological levels between the rodent models and the hypertensive carriers of the “mutated” gene variants; 5) evaluation of the impact of the adducin genes in hypertension and its organ complications with association and linkage studies in humans, also considering the genetic and environmental interactions; and 6) development of a pharmacogenomic approach aimed at establishing the therapeutic benefit of a drug interfering with the sequence of events triggered by adducin and their effect's size. The bulk of data obtained demonstrates the importance of a multidisciplinary approach considering a variety of genetic and environmental interactions. Adducin functions within the cells as a heterodimer composed of a combination of three subunits. Each of these subunits is coded by genes mapping to different chromosomes. Therefore, the interaction among these genes, taken together with the interactions with other modulatory genes or with the environment, is indispensable to establish the adducin clinical impact. The hypothesis that adducin polymorphism favors the development of hypertension via an increased tubular sodium reabsorption is well supported by a series of consistent experimental and clinical data. Many mechanistic aspects, underlying the link between these genes and clinical symptoms, need to be clarified. The clinical effect size of adducin must be established also with the contribution of pharmacogenomics with a drug that selectively interferes with the sequence of events triggered by the mutated adducin.

OASIS-HT: design of a pharmacogenomic dose-finding study

Experimental evidence and observations in humans strongly support an interactive role of mutated α-adducin, sodium (Na+)/potassium (K+)-adenosine triphosphatase (ATPase) activity and endogenous ouabain in Na+ homeostasis and the pathogenesis of hypertension. The Ouabain and Adducin for Specific Intervention on Sodium in HyperTension (OASIS-HT) trial is an early Phase II dose-finding study, which will be conducted across 39 European centers. Following a run-in period of 4 weeks without treatment, eligible patients will be randomized to one of five oral doses of rostafuroxin consisting of 0.05, 0.15, 0.5, 1.5, or 5.0 mg/day. Each dose will be compared to a placebo in a double-blind crossover experiment with balanced randomization. Treatment will be initiated with the active drug and continued with placebo or vice versa. Each double-blind period will last 5 weeks. The primary end point is the reduction in systolic blood pressure defined as the average of three clinic readings with the patient in the sitting position. Secondary end points include the reduction in diastolic blood pressure on clinic measurement, the decrease in the 24-h blood pressure, and the incidence of end points related to safety. Secondary objectives are to investigate the dependence of the blood pressure-lowering activity on the plasma concentration of endogenous ouabain and the genetic variation of the enzymes involved in the metabolism of this hormone, and the adducin cytoskeleton proteins. Eligible patients will have Grade I or II systolic hypertension without associated conditions and no more than two additional risk factors. In conclusion, OASIS-HT is a combination of five concurrent crossover studies, one for each dose of rostafuroxin to be studied. To our knowledge, OASIS-HT is the first Phase II dose-finding study in which a genetic hypothesis is driving primary and secondary end points.

Preventing end stage renal disease in diabetic patients--genetic aspect (part I)

Diabetic nephropathy is a major cause of diabetes- related morbidity and mortality; however the clinical course of the disease and the renal prognosis is highly variable among individuals. The current review will discuss the genetic influence on the development of end stage renal disease (ESRD) in diabetic patients and potential improvements to the current treatment strategy to slow the loss of kidney function in these patients. In this first part, the growing evidence that glucose-induced activation of the intra-renal and systemic renin-angiotensin systems plays an essential role in processes leading to destruction of renal function is summarised. Genetic variations, especially the angiotensin-converting enzyme (ACE)/ID polymorphisms in the gene coding for ACE, are involved in activation of the renin-angiotensin system and seem to influence the clinical course of diabetic nephropathy during treatment with ACE inhibitors. In addition, this polymorphism may interact with other polymorphisms within the renin-angiotensin system, leading to high risk of ESRD. As new genetic approaches and methods develop, further understanding of diabetic nephropathy will evolve and genotyping will help prevent ESRD in diabetic patients.

Cardiovascular risk in relation to alpha-adducin Gly460Trp polymorphism and systolic pressure: a prospective population study

Preliminary evidence from 1 case-control study suggested that in hypertensive patients, the alpha-adducin 460Trp allele might be associated with a 2-fold higher risk of coronary heart disease. In a prospective population study, we investigated whether the alpha-adducin Gly460Trp polymorphism predicted mortality and morbidity. From August 1985 until July 2003, we randomly recruited 2235 Belgian residents. We obtained information on vital status (until July 1, 2004) and the incidence of events via registries and repeat examinations (median 3). In Cox regression, before and after adjustment for other risk factors, we found strong interaction between systolic blood pressure at baseline, analyzed as a continuous variable, and the alpha-adducin polymorphism in relation to total (P=0.01) and cardiovascular mortality (P=0.007) and all cardiovascular (P=0.003), cardiac (P=0.001), and coronary events (P=0.03). The hazard ratio for total mortality associated with the Trp allele relative to GlyGly homozygosity was 2.30 (95% confidence interval, 1.12 to 4.72; P=0.02) in patients with stage-2 systolic hypertension (> or =160 mm Hg) and 0.88 (0.61 to 1.26; P=0.48) in the other participants. For all cardiovascular complications, these estimates were 2.94 (1.28 to 6.74; P=0.01) and 0.83 (0.58 to 1.20; P=0.32), respectively. For all cardiovascular events, the positive predictive value and the attributable risk associated with the Trp allele in patients with stage-2 systolic hypertension were 76.9% and 44.3%, respectively. In conclusion, the alpha-adducin Gly460Trp polymorphism, in combination with systolic blood pressure, is a strong predictor of cardiovascular mortality and morbidity.

Role of the adducin family genes in human essential hypertension

OBJECTIVE

In both humans and rats, polymorphisms of the alpha adducin (ADD1) gene are involved in renal sodium handling, essential hypertension and some of its organ complications. Adducin functions within cells as a heterodimer composed of various combinations of three subunits that are coded by three genes (ADD1, 2, 3) each located on a different chromosome.

DESIGN

These characteristics provide the biochemical basis for investigating epistatic interactions among these loci.

METHODS

We examined the three adducin gene polymorphisms and their association with ambulatory blood pressure (ABPM) and with plasma levels of renin activity (PRA), endogenous ouabain (EO), in 512 newly discovered and never-treated hypertensive patients.

RESULTS

Relative to carriers of the wild type (Gly/Gly) ADD1 gene, patients carrying the mutated Trp ADD1 allele had higher blood pressure (systolic blood pressure (SBP) 143.2 +/- 1.0 versus 140.6 +/- 0.6 mmHg P = 0.027 and diastolic blood pressure (DBP) 94.2 +/- 0.77 versus 92.3 +/- 0.5 mmHg, P = 0.03), lower PRA and EO, consistent with the hypothesis of the renal sodium retaining effect of the Trp allele. Polymorphisms in the ADD2 and ADD3 genes taken alone were not associated with these variables. However, the differences in SBP and DBP between the two ADD1 genotypes were greatest in carriers of the ADD3 G allele (around + 8 mmHg). The significance of the interaction between ADD1 and ADD3 ranged between P = 0.020 to P = 0.006 according to the genetic model applied.

CONCLUSIONS

The interaction of ADD1 and ADD3 gene variants in humans is statistically associated with variation in blood pressure, suggesting the presence of epistatic effects among these loci.

Epistatic interaction between α- and γ-adducin influences peripheral and central pulse pressures in white Europeans

BACKGROUND

Adducin is a membrane skeleton protein consisting of alpha- and beta- or alpha- and gamma-subunits. Mutations in alpha- and beta-adducin are associated with hypertension. In the European Project on Genes in Hypertension, we investigated whether polymorphisms in the genes encoding alpha-adducin (Gly460Trp), beta-adducin (C1797T) and gamma-adducin (A386G), alone or in combination, affected pulse pressure (PP), an index of vascular stiffness.

METHODS

We measured peripheral and central PP by conventional sphygmomanometry and applanation tonometry, respectively. We randomly recruited 642 subjects (162 nuclear families and 70 unrelated individuals) from three European populations. In multivariate analyses, we used generalized estimating equations and the quantitative transmission disequilibrium test.

RESULTS

Peripheral and central PP averaged 46.1 and 32.6 mmHg, respectively. Among carriers of the alpha-adducin Trp allele, peripheral and central PP were 5.8 and 4.7 mmHg higher in gamma-adducin GG homozygotes than in their AA counterparts, due to an increase in systolic pressure. gamma-Adducin GG homozygosity was associated with lower urinary Na/K ratio among alpha-adducin Trp allele carriers and with higher urinary aldosterone excretion among alpha-adducin GlyGly homozygotes. Sensitivity analyses in founders and offspring separately, and tests based on the transmission of the gamma-adducin G allele across families, confirmed the interaction between the alpha- and gamma-adducin genes.

CONCLUSIONS

In alpha-adducin Trp allele carriers, peripheral and central PP increased with the gamma-adducin G allele. This epistatic interaction is physiologically consistent with the heterodimeric structure of the protein and its influence on transmembranous sodium transport.

Adducin Polymorphism

Adducin is a heterodymeric cytoskeleton protein, the 3 subunits of which are encoded by genes ( ADD1 , ADD2 , ADD3 ) mapping to 3 different chromosomes. A long series of parallel studies in the Milan hypertensive rat strain model of hypertension and humans indicated that an altered adducin function may cause hypertension through an enhanced constitutive tubular sodium reabsorption. Six human linkage studies showed positive results when a DNA marker mapping to 30 kb from the ADD1 locus or single-nucleotide polymorphisms (SNPs) of 1 of the 3 adducin genes were considered either alone or in combination with each other or angiotensin-converting enzyme (ACE) D allele or salt intake. When DNA markers mapping at much larger distance from the ADD1 locus were used, negative results were found by 4 studies. Positive results were also obtained in 18 of 20 association studies that, in addition to blood pressure, investigated variables reflecting body sodium or the renin-angiotensin system. Mixed results regarded case-control studies or studies in predominantly normotensive populations that did not consider the above-mentioned variables. Four of 5 studies showed a selective beneficial effect of diuretics in carriers of the mutated ADD1. Twelve of 16 studies found that ADD1 polymorphism alone or in combination with that of ACE positively associates with stroke or coronary heart disease or renal or vascular dysfunctions. In conclusion, when context is taken into account, the impact of adducin in hypertension and its related disorders is clear.

Carotid artery intima-media thickness and angiotensin-converting enzyme gene polymorphism in the offspring of parents with premature stroke

AIM

To determine some common cardiovascular risk factors, alterations in the measurements of intima-media thickness (IMT) and the distribution of the angiotensin-converting enzyme (ACE) polymorphism in children of parents with premature stroke, and to investigate the cardiovascular risk of these children and the potential need for some preventive measures.

METHODS

A family history of cardiovascular disease represents a cardiovascular risk factor in the offspring. This association has not yet been clearly determined for cerebrovascular accidents. New technology allows us to investigate the risk for cardiovascular disease at an early presymptomatic stage. We applied the measurement of IMT of carotid arteries by ultrasound imaging and the determination of the ACE insertion/deletion (I/D) polymorphism in blood to evaluate the predisposition for cerebrovascular disease in the offspring of patients with previous stroke. We investigated 58 subjects whose parents had experienced a cerebrovascular accident before the age of 45 y and compared them with a matched control group whose parents had not suffered a stroke.

RESULTS

The results of IMT at various sites of the carotid arteries and the genotype distribution of the ACE gene were not significantly different between the study group and the control group. In addition, no differences were found in the serum levels of lipid fractions or other biochemical variables.

CONCLUSION

We conclude that determination of the carotid IMT and of the ACE I/D polymorphism do not permit discrimination of the cardiovascular risk in children of parents with or without premature stroke.

Blood pressure in relation to three candidate genes in a Chinese population

OBJECTIVE

In a prospective analysis of a Caucasian population, we recently found that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp) and aldosterone synthase (-344C/T) jointly influence the incidence of hypertension. We therefore investigated the association between blood pressure and these three genes in a Chinese population.

METHODS

We genotyped 479 Han Chinese from 125 nuclear families recruited in northern China via random sampling (approximately 75%) and at specialized hypertension clinics (approximately 25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and the quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables.

RESULTS

The participants included 239 (49.9%) women and 132 (27.6%) hypertensive patients, of whom 77 took antihypertensive drugs. The blood pressure, measured at the subjects' homes, averaged 126/80 mmHg. Mean values of urinary sodium, potassium and Na/K ratio were 226 mmol/day, 37 mmol/day and 6.31, respectively. In adjusted GEE analyses, systolic blood pressure was 9.3 mmHg (95% confidence interval 3.6-15.0 mmHg; P = 0.001) and 14.6 mmHg (95% confidence interval 3.4-25.8 mmHg; P = 0.01) higher in the ACE DD than II subjects among the alpha-adducin TrpTrp (n = 141) and aldosterone synthase CC (n = 33) homozygotes, respectively (P < or =0.05 for interactions of the ACE genotype with the alpha-adducin and aldosterone synthase polymorphisms). Among 40 informative offspring homozygous for the alpha-adducin Trp allele, systolic blood pressure was significantly associated with transmission of the ACE D allele (beta = 5.5 mmHg; P = 0.046).

CONCLUSIONS

The ACE I/D, alpha-adducin Gly460Trp and aldosterone synthase -344C/T polymorphisms interact to influence systolic blood pressure in Chinese, suggesting that these genes might indeed predispose to hypertension, especially in an ecogenetic context characterized by a high salt intake.

Effect of Add1 gene transfer on blood pressure in reciprocal congenic strains of Milan rats

Genetic variants of alpha adducin (ADD1) taken alone or in interaction with those of beta (ADD2) and gamma (ADD3) subunits have been associated with primary hypertension in humans and in Milan hypertensive (MHS) rats. In this study, we report the dissection of the individual contribution of each rat Add gene to blood pressure, by congenic substitution mapping. Congenic strains were developed by introgressing Add1, Add2, and Add3 genes (and chr14, chr4, and chr1 associated segments) of MHS in the Milan normotensive rat (MNS) genetic background (MNS.H-Add1, MNS.H-Add2, and MNS.H-Add3) and vice versa (MHS.N-Add1, MHS.N-Add2, and MHS.N-Add3). Systolic blood pressure (SBP) of MNS.H-Add1 rats was significantly higher (+10 mmHg) than that of MNS, whereas SBP of MHS.N-Add1 was significantly lower (-10 mmHg) than that of MHS. The differences account for 43% of the blood pressure differences between MHS and MNS. In contrast, SBPs of Add2 and Add3 congenic strains were not different from those of the correspondent recipient parental strain. The fine mapping of chr14 congenic segment supports the identity of blood pressure QTL with Add1 gene.

Renal function in relation to three candidate genes in a Chinese population

We recently found in a white population that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp), and aldosterone synthase (-344C/T) jointly influence renal function. We therefore investigated in a Chinese population the associations between the serum concentrations of creatinine and uric acid and these three genetic polymorphisms. We genotyped 471 ethnic Han Chinese subjects from 125 nuclear families recruited in northern China via random population sampling (75%) and at specialized hypertension clinics (25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables. The participants were 39.7 years old and included 235 women (49.9%). The blood pressure measured at the subjects' homes averaged 126/80 mmHg. Mean values were 71 micromol/l for serum creatinine, 111 ml min(-1) 1.73 m(-2) for calculated creatinine clearance, and 236 micromol/l for serum uric acid. With adjustment for covariables, GEE analyses of single genes demonstrated that serum uric acid, but not serum creatinine, was positively associated with the ACE D allele. Serum uric acid concentrations were 15.8 micromol/l (95% confidence interval 3.3-28.2) and 25.7 micromol/l (11.1-40.2) higher in DD homozygotes than in ID and II subjects, respectively. Further GEE analyses of the three genes combined showed that the association between serum uric acid and the ACE polymorphism was confined to carriers of the alpha-adducin Gly and/or aldosterone synthase C alleles. Sensitivity analyses in parents and offspring separately as well as QTDT analyses were confirmatory. Among 114 informative offspring carrying the alpha-adducin Gly allele serum uric acid was significantly and positively associated with the transmission of the ACE D allele (beta=20.7 micromol/l). In conclusion, the present study extends our previous findings on the combined effects of the three candidate genes and supports the concept that these genetic polymorphisms jointly influence renal function.

Pharmacogenomics and renal drug disposition in the newborn

Genetic polymorphisms in the genes coding for drug metabolizing enzymes, drug transporters, and drug receptors are major determinants of an individual's response to drugs. The potential interactions of pharmacogenomics of renal drug transporters and drug receptors with renal drug disposition and the immature kidneys are briefly reviewed. Examples of gene polymorphisms seen in the RAAS (renin angiotensin system), beta-adrenergic receptors, dopamine receptors and cytochrome P450 and their potential clinical impact are discussed. The human newborn has deficient hepatic and renal drug metabolism and disposition. This immaturity in drug-handling capacity may potentially be superimposed to genetic polymorphisms determining drug metabolism and transport thereby substantially increasing interpatient variability in drug dose requirements and in drug responses in the newborn. Pharmacogenomics is a tool that can be used to individualize drug therapy in newborns to minimize adverse drug effects and to optimize efficacy.

NPHS2 R229Q functional variant is associated with microalbuminuria in the general population

BACKGROUND

Microalbuminuria is a risk factor for developing end-stage renal disease and cardiovascular events. Mutations in NPHS2 have been shown to cause autosomal-recessive nephrotic syndrome. Recently, a functional polymorphism of this gene (R229Q) was described and associated with a maturity-onset form of nephrotic syndrome. We have investigated whether the carrier status of this novel genetic variant is associated with microalbuminuria in individuals from the general population.

METHODS

Demographic, cardiovascular risk factors, and renal phenotypes in 1577 individuals from a cross-sectional-based study were collected following the general guidelines of the WHO-MONICA project (monitoring trends and determinants in cardiovascular diseases). Blood and urine samples were obtained. Microalbuminuria was determined using a semiquantitative protocol, and DNA was extracted from peripheral lymphocytes.

RESULTS

A strong association was found between the 229Q allele and microalbuminuria (P= 0.008). The presence of the 229Q allele was still associated with a 2.77-fold increased risk of presenting microalbuminuria even after adjustment for age, ethnicity, hypertension, obesity, and diabetes in a multiple logistic regression model. In addition, a statistically significant interaction was identified between the presence of the 229Q allele and body mass index (BMI) (P= 0.01), suggesting an additive effect between the 229Q allele and other risk factors for microalbuminuria.

CONCLUSION

These data have important implications for the understanding of microalbuminuria in the general population and may contribute to better ways of disease prediction and prevention.

Expression analysis of the human adducin gene family and evidence of ADD2 beta4 multiple splicing variants

Adducin is a cytoskeleton heterodimeric protein. Its subunits are encoded by three related genes (ADD1, ADD2, and ADD3) which show alternative spliced variants. Adducin polymorphisms are involved in blood pressure regulation in humans and rats. We have analyzed mRNA distribution of ADD gene family in human tissues and cells with Real-Time TaqMan RT-PCR. Whereas ADD1 is ubiquitously distributed, ADD3 is more expressed in kidney medulla and cortex than in fetal kidney, while in adult liver it is less abundant than in fetal liver. ADD2 beta1 and beta4 variants show the same pattern of distribution with the highest expression in brain, fetal liver, and kidney. Conventional RT-PCR identified new beta4 variants. Beta4a is characterized by an in-frame insertion of 21 nucleotides upstream exon 15 predicting a 7 amino acids longer protein with a similar C-terminus region. It is coexpressed with beta1 and beta4 in several tissues. Fetal kidney shows further beta4b, beta4c and beta4d variants containing internal exon deletions that enormously modify the predicted NH(2) and central regions. Our findings could help one to understand the functional role of adducin variants in specific tissues and cells.

Essential hypertension

Hypertension is a frequent, chronic, age-related disorder, which often entails debilitating cardiovascular and renal complications. Blood pressure is usually noted in combination with other cardiovascular risk factors. Diagnosis of hypertension increasingly relies on automated techniques of blood pressure measurement. The pathophysiology of essential hypertension depends on the primary or secondary inability of the kidney to excrete sodium at a normal blood pressure. The central nervous system, endocrine factors, the large arteries, and the microcirculation also have roles in the disorder. Although monogenic forms of blood pressure dysregulation exist, hypertension mostly arises as a complex quantitative trait that is affected by varying combinations of genetic and environmental factors. Non-pharmacological strategies can reduce blood pressure. Antihypertensive drug treatment diminishes the complications of hypertension. The concept that a few major genes will provide the final clue to the pathogenesis of essential hypertension is an oversimplification that contradicts the heterogeneous nature of this disorder. Further integration of genetic, molecular, clinical, and epidemiological research could disclose subsets of patients in whom specific combinations of genetic and environmental factors raise blood pressure, and might lead to more individualised treatment.

Pharmacogenomics of primary hypertension--the lessons from the past to look toward the future

A number of recent reviews have addressed the issue of the pharmacogenomics of primary hypertension and related complications by considering the data on the genotype-drug response relationship. Here we mainly discuss the methodological aspects of this issue, trying to integrate 'traditional' clinical and experimental pathophysiology and therapy-pharmacology with the 'new' genetics. Such integration is indispensable to: a). define the appropriate 'context' (genetic background, environment, age, gender, phase of hypertension, previous therapy etc.) in which a given genotype-drug response relationship should be tested (it is indeed likely that many discrepancies among published data originate from context's interference); b). assign the correct clinical meaning to the results obtained by statistics and functional genetics methodologies; c). define a novel clinical entity caused by a disease favoring allele, alone or in combination with other alleles, with a consistent clinical picture, prognosis and responsiveness to the appropriate drug; d). estimate the size of the population target amenable to benefit from a therapeutic intervention developed according to the pharmacogenomics' principles; e). develop a novel drug that selectively interferes with the sequence of events triggered by the genetic mechanism(s) underlying the clinical entity. Peculiar to this strategy is to look for consistency among findings gathered from different 'contexts' after having properly accounted for the context's dependency of the results.

Genetics of hypertension: the adducin paradigm

The following were investigated: (1) how we became interested in studying adducin genes and what we know about adducin; (2) studies in animals and humans supporting the role of adducin polymorphisms in hypertension, including some methodological problems related to the dissection of the role of a given genetic molecular mechanism in a complex multifactorial polygenic disease like hypertension; (3) biochemical mechanisms underlying the effect of adducin and its interaction with the Na-K pump; and (4) future directions.

Antihypertensive compounds that modulate the Na-K pump

A primary impairment of the kidney sodium excretion has been documented both in hypertensive patients (EH) and genetic animal models (Milan hypertensive rat [MHS]) carrying mutations of the cytoskeletal protein adducin and/or increased plasma levels of endogenous ouabain (EO). Ouabain (OU) itself induces hypertension in rats and both OU and mutated adducin activate the renal Na/K-ATPase function both in vivo and in cultured renal cells (NRK). A new antihypertensive agent, PST 2238, able to selectively interact with these alterations has been developed. PST lowers blood pressure (BP) by normalizing the expression and activity of the renal Na-K pump selectively in those rat models carrying the adducin mutation (MHS) and/or increased EO levels (OS) at oral doses of 0.1-10 micro g/kg. In NRK cells either transfected with mutated adducin or incubated with 10(-9) M OU, PST normalizes the Na-K pump activity. Recently, an association between EO and cardiac complications has been observed in both EH and rat models consistent with a prohypertrophic activity of OU. OS rats showed a 10% increase of left ventricle and kidney weights as compared with controls, and PST 2238 (1 micro g/kg OS) prevented both ventricle and renal hypertrophy. This effect was associated with the ability of PST to antagonize the OU-dependent activation of growth-related genes, in the membrane subdomains of caveolae. In conclusion, PST is a new antihypertensive agent that may prevent cardiovascular complications associated with hypertension through the selective modulation of the Na-K pump function.

Tissue-specific modulation of beta-adducin transcripts in Milan hypertensive rats

Genetic variants in Adducins, a family of cytoskeleton proteins (alpha, beta, and gamma) encoded by three genes, have been associated with primary hypertension in humans and in Milan hypertensive (MHS) rats. The present paper describes the identification of a rat beta 4 alternative splicing isoform differing from beta subunit for an in-frame insertion of 18 amino acids and showing a polymorphic site (R592W) between MHS and its normotensive control (MNS). Furthermore, we established a quantitative real-time PCR assay for analyzing the tissue expression of adducin gene family and determining whether any subunit transcript demonstrates altered expression during the development of MHS hypertension, especially in tissues relevant for the control of cardiovascular phenotypes (i.e., kidney, left ventricle, and large arteries). Among the three adducins only beta transcripts were modulated, in a tissue-specific manner, during the development of hypertension in MHS, compared to age-matched MNS controls. A 43% decrease in renal outer medulla was already present at the prehypertensive phase; a 70% decrease in femoral artery and 66% increase in left ventricle were observed after the development of hypertension. Surprisingly beta 4-Add, which is a minor component of total beta transcripts, is drastically reduced up to 88% in all MHS tissues. Alteration in beta-Add expression levels may account, at least in part, for the observed phenotypic changes in MHS hypertension.

Carotid and femoral intima-media thickness in relation to three candidate genes in a Caucasian population

BACKGROUND

In a Caucasian population, the prevalence and incidence of hypertension, renal function and large artery stiffness were significantly correlated with polymorphisms in the genes encoding the angiotensin-converting enzyme (ACE I/D), aldosterone synthase (-C344T) and the cytoskeleton protein alpha-adducin (Gly460Trp).

OBJECTIVE

This study investigated intima-media thickening, a precursor of atherosclerosis, in relation to these genetic polymorphisms.

METHODS

Carotid and femoral intima-media thickness were assessed with a wall-track system in 380 subjects enrolled in a population study. Subjects were genotyped for the presence of the ACE D, aldosterone synthase -344T and alpha-adducin 460Trp alleles. The statistical analysis allowed for confounders, interactions among genes, and the non-independence of the phenotypes within families.

RESULTS

The sample included 188 men (49.5%). Mean age was 39.8 years. Intima-media thickness of the carotid and femoral arteries averaged 575 and 719 microm, respectively. Intima-media thickness of the femoral-but not carotid-artery increased with the number of ACE D alleles. The effect of ACE genotype on femoral intima-media thickness was confined to carriers of the 460Trp allele and the -344T allele. Expressed as a percentage of the population mean, the mean differences between II and DD homozygotes averaged 13.4% (95% CI 5.6-21.2%) in all subjects, 21.2% (8.0-34.5%) in carriers of the 460Trp allele, 15.4% (4.1-26.8%) in carriers of the -344T allele, and 25.2% (10.7-39.7%) if the 460Trp and -344T alleles were both present.

CONCLUSION

This study shows that a relationship exists between the intima-media thickness of the large muscular femoral artery and the ACE gene. This relationship is only apparent in the presence of either the alpha-adducin 460Trp or the aldosterone synthase -344T allele. These findings may have clinical implications for the assessment of genetic cardiovascular risk.