Analysis of promoter region polymorphism in the aldosterone synthase gene (CYP11B2) as a risk factor for myocardial infarction

Several polymorphisms in genes of the reninangiotensin-aldosterone system have been found to have pleiotropic effects on cardiovascular disorders. Recently, a polymorphism (-344 C/T) in the promoter region of the aldosterone synthase gene (CYP11B2), which may influence plasma aldosterone levels, has been reported to strongly influence left ventricular diameters and mass in young adults and arterial stiffness in essential hypertensives. We investigated any association with risk of myocardial infarction (MI). CYP11B2 -344 polymorphism genotypes were determined by polymerase chain reaction (PCR) in 542 acute MI cases and 500 control subjects without history of coronary disease. All subjects were white and <75 years old. There was no significant difference in either genotype distributions (cases CC 17%, CT 52%, TT 31%; controls CC 22%, CT 47%, TT 31%, P = .10) or allele frequencies (cases C/T 0.43/0.57, controls C/T 0.46/0.54, P = .39) between cases and controls. The odds ratio (OR) for MI associated with the CC genotype was 0.75 (0.54-1.05), and remained insignificant when analysis was restricted to the 129 (24%) cases and 193 (37%) controls < 55 years of age (OR 0.68 [0.36-1.27], P = .20). In further analyses, there was no interaction of the polymorphism with other cardiovascular risk factors (smoking, hypertension, diabetes, body mass index, or cholesterol level) in determining MI risk, and the polymorphism did not influence the frequency of these risk factors in either cases or controls. In the case cohort, age at MI was not significantly different in subjects with the three genotypes (CC 61.2 +/- 9.8 years, CT 61.8 +/- 9.1 years, TT 62.2 +/- 9.0 years, P = .69). We conclude that the aldosterone synthase -344 promoter region polymorphism does not significantly influence the risk of MI either directly or via interaction with other risk factors.     

Congenital hyperreninemic hypoaldosteronism unlinked to the aldosterone synthase (CYP11B2) gene.

Isolated hyperreninemic hypoaldosteronism presenting in infancy is usually caused by mutations in the CYP11B2 gene encoding aldosterone synthase. We studied five patients in four unrelated kindreds with hyperreninemic hypoaldosteronism, in whom we were unable to find such mutations. All presented in infancy with failure to thrive, hyponatremia, hyperkalemia, markedly elevated plasma renin activity, and low or inappropriately normal aldosterone levels. All had normal cortisol levels and no signs or symptoms of congenital adrenal hyperplasia. All responded to fludrocortisone treatment. There were no mutations detected in exons or splice junctions of CYP11B2. Linkage of the disorder to CYP11B2 was studied in two unrelated consanguineous patients and in an affected sib pair. The consanguineous patients were each heterozygous for at least one of three polymorphic microsatellite markers near CYP11B2, excluding linkage to CYP11B2. However, linkage of the disease to CYP11B2 could not be excluded in the affected sib pair. Genes involved in the regulation of aldosterone biosynthesis, including those encoding angiotensinogen, angiotensin-converting enzyme, and the AT1 angiotensin II receptor were similarly excluded from linkage. These results demonstrate the existence of an inherited form of hyperreninemic hypoaldosteronism distinct from aldosterone synthase deficiency. The affected gene(s) remain to be determined.     

Haplotype analysis of aldosterone synthase gene (CYP11B2) polymorphisms shows association with essential hypertension

OBJECTIVE: The CYP11B2 locus is an important candidate region in essential hypertension (HT). We therefore investigated CYP11B2 polymorphisms T-344C, T4986C and A6547G for association with essential HT. This included haplotype analysis and measurement of plasma aldosterone levels. METHODS: The three single nucleotide polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis of genomic DNA from 146 HT and 291 normotensive (NT) white subjects of Anglo-Celtic descent, in whom parental blood pressure status was the same as the subjects'. Genotype and allele frequencies in HTs and NTs were compared by chi2 analysis. Linkage disequilibrium and haplotype frequencies were estimated by the program 'snphap'. Phenotype-genotype relationships were tested using one-way analysis of variance. RESULTS: The T-344C variant was associated with HT (chi2 = 7.4, P = 0.0064). This association was confined to female HTs (P = 0.0061 for genotypes, P = 0.0013 for alleles). A strong association with HT was also seen for the A6547G variant (P = 0.0015), being greatest in females (P < 0.0001). No association was seen for the T4986C variant. Haplotype analysis of the three single nucleotide polymorphisms across eight different haplotype combinations showed a significant association with HT (chi2 = 24, seven degrees of freedom, P < 0.001). No significant tracking of plasma aldosterone with genotype was observed. CONCLUSION: The T-344C and A6547G, but not the T4986C, variants of the aldosterone synthase gene are associated with HT in females of the Anglo-Celtic population studied. This was reinforced by haplotype analysis.     

Effects of genetic variation in the aldosterone synthase (CYP11B2) gene on enzyme function

Objective  Evidence suggests that high levels of aldosterone lead to hypertension and increased risk of cardiovascular disease. Around 15% of patients with essential hypertension have a raised aldosterone to renin ratio (ARR) suggesting that aldosterone production is inappropriately high in relation to its principal agonist angiotensin II. This may be due to increased activity of aldosterone synthase caused by genetic variation in the CYP11B2 gene. We screened the coding region of human CYP11B2 for genetic variants and tested their effects on function in vitro .
Protocol  Normotensive subjects ( n  = 69) were screened for sequence variants in the coding region of CYP11B2 by single-stranded conformation polymorphism (SSCP) analysis and sequencing. The effects of nonsynonymous variants on enzyme activity were assessed in JEG-3 cells transiently transfected with wild-type or variant expression plasmids. The conversion of the substrate 11-deoxycorticosterone (DOC) to corticosterone (B) and aldosterone was measured.
Results  Twenty variants were detected in CYP11B2 and eight analysed functionally (Arg87Gly, Asn281Thr, Gly288Ser, Lys296Asn, Asp335Asn, Gln404Arg, Ala414Pro and His439Tyr). Corticosterone synthesis was unaltered and aldosterone synthesis reduced in variant Arg87Gly; Asn281Thr increased corticosterone and decreased aldosterone production; Gly288Ser increased corticosterone production and abolished aldosterone production; Lys296Asn reduced both corticosterone and aldosterone production; Asp335Asn increased corticosterone synthesis but did not affect aldosterone production. Variants Gln404Arg, Ala414Pro and His439Tyr showed increases in both corticosterone and aldosterone synthesis compared to the wild-type.
Conclusion  The study confirms the genetic variability of the CYP11B2 gene and provides us with additional valuable structure–function information.     

Promoter variants of aldosterone synthase gene (CYP11B2) and salt-sensitivity of blood pressure

The T(-344)C polymorphism in promoter of CYP11B2 gene encoding aldosterone synthase has been associated with differences in plasma aldosterone (ALDO) concentrations. In addition, the results of recent study carried out in Japan suggest that C(-344) allele of CYP11B2 may be a genetic marker of salt-sensitive hypertension characterized by low plasma renin activity (PRA) and high ALDO/PRA ratio. Therefore, it raises the question of whether the T(-344)C polymorphism of CYP11B2 gene may be associated with salt-sensitive hypertension in Caucasians. The DNA samples were obtained from 68 Polish hypertensives. During 3 subsequent 1-week periods each subject received diets of normal, low and high sodium content (120-140, 20-40 and 240-260 mmol Na+/day, respectively). Salt sensitivity was expressed as the difference between mean arterial pressure (MAP) on high salt diet and MAP on low salt one (delta MAPH-L). Genomic DNA isolated from peripheral blood nuclear cells was amplified by PCR method with primers flanking the polymorphic region and C(-344) allele was identified by gain of Hae III restriction site. There were 14 TT homozygotes (20.6%), 35 TC heterozygotes (51.5%) and 19 CC homozygotes (27.9%) in the studied group. No significant differences in delta MAPH-L, glomerular filtration rate, natriuresis, excreted fraction of filtered sodium, PRA, ALDO and ALDO/PRA ratio determined on each diet have been found in subjects according to CYP11B2 genotype. Our preliminary results suggest the lack of association of the T(-344)C CYP11B2 polymorphism with salt-sensitive hypertension as well as with activity of plasma renin-angiotensin-aldosterone system in Caucasian patients.     

Association between aldosterone synthase (CYP11B2) polymorphism and left ventricular mass in human essential hypertension

OBJECTIVES: The aim of our study was to evaluate the relationship between aldosterone synthase gene polymorphism and cardiac dimensions in essential hypertension. BACKGROUND: Higher aldosterone synthase messenger ribonucleic acid levels in the human heart are accompanied by increased intracardiac aldosterone production, a phenomenon that is associated with cardiac fibrosis and hypertrophy. Recent evidence suggests that a polymorphism (-344C/T) in the promoter region of the aldosterone synthase gene is associated with increased constitutive aldosterone production. METHOD: Relationships between M-mode echocardiographic cardiac dimensions and aldosterone synthase -344C/T polymorphism were studied in 210 never-treated, middle-aged patients (age 41.6 +/- 1.4 years) affected by mild to moderate essential hypertension. Among these patients, 48 had the genotype -C344C, 97 had -C344T, and 65 had -T344T. Patients in the three groups were similar in terms of age, gender, body mass index, and blood pressure. RESULTS: Left ventricular (LV) mass and thickness were positively correlated with the number of T alleles: LV mass (CC, CT, and TT, respectively: 168 +/- 6.9, 179 +/- 5.2, and 193 +/- 6.9 g; p = 0.03), LV septal thickness (0.99 +/- 0.02, 1.03 +/- 0.02, and 11.08 +/- 0.03 cm, p = 0.04), PWT (0.93 +/- 0.03, 0.95 +/- 0.01, and 1.03 +/- 0.02 cm; p = 0.002), and relative wall thickness (38.3 +/- 1.2%, 38.8 +/- 0.8%, and 42.8 +/- 1.1%; p = 0.004). This trend was confirmed by linear regression, suggesting a "major gene" behavior for the T allele. Multiple regression analysis showed that this effect was independent of anthropometric and clinical factors, including adrenal aldosterone. CONCLUSIONS: Our data suggest that -344C/T polymorphism affects LV mass and thickness in essential hypertension, independent of adrenal aldosterone. A role for intracardiac aldosterone synthesis is hypothesized.     

Mutations in the human CYP11B2 (aldosterone synthase) gene causing corticosterone methyloxidase II deficiency.

Corticosterone methyloxidase II (CMO-II) deficiency is an autosomal recessive disorder of aldosterone biosynthesis, characterized by an elevated ratio of 18-hydroxycorticosterone to aldosterone in serum. It is genetically linked to the CYP11B1 and CYP11B2 genes that, respectively, encode two cytochrome P450 isozymes, P450XIB1 and P450XIB2. Whereas P450XIB1 only catalyzes hydroxylation at position 11 beta of 11-deoxycorticosterone and 11-deoxycortisol, P450XIB2 catalyzes the synthesis of aldosterone from deoxycorticosterone, a process that successively requires hydroxylation at positions 11 beta and 18 and oxidation at position 18. To determine the molecular genetic basis of CMO-II deficiency, seven kindreds of Iranian-Jewish origin were studied in which members suffered from CMO-II deficiency. No mutations were found in the CYP11B1 genes, but two candidate mutations, R181W and V386A, were found in the CYP11B2 genes. When these mutations were individually introduced into CYP11B2 cDNA and expressed in cultured cells, R181W reduced 18-hydroxylase and abolished 18-oxidase activities but left 11 beta-hydroxylase activity intact, whereas V386A caused a small but consistent reduction in the production of 18-hydroxycorticosterone. All individuals affected with CMO-II deficiency were homozygous for both mutations, whereas eight asymptomatic subjects were homozygous for R181W alone and three were homozygous for V386A alone. These findings confirm that P450XIB2 is the major enzyme mediating oxidation at position 18 in the adrenal and suggest that a small amount of residual activity undetectable in in vitro assays is sufficient to synthesize normal amounts of aldosterone.     

新疆哈萨克族隔离群醛因合成酶基因CYP11B2T(-344)C多态性与高血压的关联性研究

目的探讨哈萨克族人群醛固酮合成酶基因CYP11B2T(-344)C多态性与原发性高血压关联性.方法应用聚合酶链反应、限制性内切酶方法检测了新疆巴里坤县186例哈萨克族原发性高血压患者和168例正常人群CYP11B2基因T(-344)C多态性.结果哈萨克族正常人群及高血压患者的CYP11B2基因T(-344)C多态CC、Ct、TT基因型频率分别为0.12,0.61 0.27,和0.20,0.50,0.30,C和T等位基因分布频率分别为0.43,0.57和0.45,0.55,符合Hardy-Weinberg平衡.群体相关分析结果表明CYP11B2基因的C及T等位基因分布在高血压病组及正常人群差异无显著性(x2=4.838,P=0.89).然而女性高血压组CC基因型频率(0.24)较正常人群(0.12)高(x2=6.104,P＜0.05)结论CYP11B2基因T(-344)C多态性可能与新疆巴里坤哈萨克族女性高血压有关.     

醛固酮合成酶基因多态性与小动脉顺应性的研究

目的探讨醛固酮合成酶（CYP11B2）基因-344C／T多态性与小动脉顺应性（C2）的关系及其临床意义。方法（1）用CVProfilorDO-2020动脉脉搏分析仪测量大小动脉顺应性,共224例,其中C2异常组123例,对照组101例。（2）用多聚酶链反应-限制性片段长度多态性分析方法检测CYP11B2基因-344C／T多态性。结果（1）C2异常组TT基因型、T等位基因频率均高于对照组,但差异无统计学意义（55．3％比41．6％,P〉0．05,75．6％比66．8％,P〉0．05）。（2）CC型与CT型合并分析,显示C2异常组TT型频率显著高于对照组（30．3％比18．8％,P〈0．05）。（3）协方差分析显示,与CT／CC型比较,TT型者C2显著降低。（4）Logistic回归分析表明,TT型是导致C2减退重要的基因型（P=0．043,OR=1．9395％ CI1．02～3．63）。结论CYP11B2基因-344C／T多态性与小动脉顺应性C2密切相关,TT型是C2减退的敏感基因型。     

Association of aldosterone synthase CYP11B2 (-344C/T) gene polymorphism with essential hypertension and left ventricular hypertrophy in the Egyptian population

ABSTRACT

Background and Objectives: Essential hypertension is a complex progressive cardiovascular disorder. Renin–angiotensin aldosterone system (RAAS) plays a major role in blood pressure regulation. Aldosterone, synthesized in the adrenal cortex by aldosterone synthase is encoded by the CYP11B2 gene. This case-control study was aiming to investigate the relationship between the aldosterone synthase gene (CYP11B2) biallelic polymorphism in the promoter at position ?344 (?344C/T) with essential hypertension and left ventricular hypertrophy in the Egyptian population.

Methods: This study was conducted on 100 hypertensive patients (group I) and 50 healthy control subjects (group II). Serum aldosterone, plasma renin, ARR levels were investigated. Echocardiography was done to evaluate LV dimensions. Genotyping of the CYP11B2 gene was performed by PCR/RFLP confirmed by direct sequencing.

Results: Our study revealed that CYP11B2 (?344T) allele was significantly higher than (?344C) allele in hypertensive patients as compared to healthy control (OR-2.51; 95% CI:1.3–3.5; P = 0.002) and ?344TT genotype was associated with increased LVMI as compared with ?344CC genotype (P = 0.001).

Conclusion: A Significant association was observed between the CYP11B2 (?344C/T) polymorphism and ?344T allele and essential hypertension in the Egyptian population. Also, we found that the CYP11B2 ?344C/T polymorphism and ?344T allele are associated with left ventricular hypertrophy which may predispose to cardiovascular complications of hypertension.     

Polymorphic differences from normal in the aldosterone synthase gene (CYP11B2) in patients with primary hyperaldosteronism and adrenal tumour (Conn's syndrome).

OBJECTIVE: The hypertension of Conn's syndrome is due to autonomous aldosterone production by a unilateral adrenocortical adenoma. The source of tumour initiation and the reasons for excess aldosterone production as opposed to cortisol are not known, although variations in the promoter region of the gene coding for aldosterone synthase (CYP11B2) might account for the altered rate of aldosterone secretion. DESIGN: In a series (n = 27) of well-characterized Conn's syndrome cases, the aldosterone synthase gene (CYP11B2) was screened by single-strand conformational polymorphism (SSCP) for differences from the consensus sequence. RESULTS: No new mutations were found. The frequencies of two previously described linked polymorphisms, one a change of -344C to T in a putative steroidogenic factor-1 (SF-1) binding site and the other an exchange of intron 2 for that of CYP11B1 (conversion) were measured in tumour and genomic DNA. The frequency of the SF-1 T allele (P < 0.0001) and the conversion allele (P < 0.001) were markedly different between the Conn's syndrome group and the normal controls. However, the frequency did not differ between tumour and genomic DNA in the patient group. CONCLUSION: While it is unlikely that this difference from normal is related to tumour growth, these genotypes may predispose the tumour to aldosterone production.     

Haplotypes of aldosterone synthase (CYP11B2) gene in the general population of Japan: the Ohasama study.

Since the identification of a chimeric aldosterone synthase which induces mendelian hypertension, polymorphisms in aldosterone synthase (CYP11B2) has been one of major targets for molecular analyses in association with hypertension. To date, four polymorphic variants of CYP11B2, -344T/C at promoter region, a gene conversion in intron 2, 2713A/G (in exon 3) which converts from Lys to Arg at codon 173 (K173R), and 4986T/C (in exon7) which converts from Val to Ala at codon 386 (V386A), have been identified in Caucasian population. Then, linkage disequilibrium between -344T/C polymorphism and a gene conversion in intron 2 or K173R mutation has been described, suggesting the presence of genetic haplotypes in Caucasians. Since the presence of a gene conversion in intron 2 or V386A mutation was still unknown in the Japanese population, all these polymorphisms were examined together to determine the CYP11B2 haplotypes of Japanese, using DNA samples from 1290 participants of the Ohasama study, who represent the general population of a rural community of northern Japan. Molecular analyses demon- strated the presence of a gene conversion of intron 2, but the absence of V386A mutation in Japanese population. The complete linkage disequilibrium between -344T/C polymorphism and K173R mutation was noted. Although -344T allele was linked either with a gene conversion in intron 2 or with normal intron 2, -344C allele was completely linked with normal intron 2. These results indicate the presence of 3 allelic haplotypes of CYP11B2, -344C with normal intron 2 and 173R, -344T with normal intron 2 and 173K, and -344T with converted intron 2 and 173K, in the general Japanese population. The frequency (total 1.0) was 0.35, 0.53, and 0.12, respectively. The presence of allelic haplotypes is considered to be an additional genetic information to individual polymorphism of CYP11B2 to determine the linkage between CYP11B2 polymorphisms and hypertension.     

A biallelic gene polymorphism of CYP11B2 predicts increased aldosterone to renin ratio in selected hypertensive patients

Altered control of aldosterone synthase (CYP11B2) gene expression may modulate aldosterone secretion, as suggested by a raised aldosterone to renin ratio (ARR) in some patients with essential hypertension. We compared the frequency of two linked CYP11B2 polymorphisms, one in the steroidogenic factor-1 (SF-1) binding site and the other an intronic conversion (Int2) in relation to ARR in 141 hypertensive patients. Patients were divided into groups with either normal or high supine ARR using a cut-off threshold of 145 pmol/liter per ng/liter. Supine ARR was normal in 104 patients and raised in 37 patients. The two polymorphisms were in strong linkage disequilibrium (chi(2) = 123.8; P < 0.0001). The SF-1 T and Int2 C alleles were more prevalent among patients with high ARR (46% and 43%, respectively) than with normal ARR (22% and 17%; P < 0.01 and P < 0.005, respectively). Odds ratios for raised ARR in subjects with a homozygous SF-1 T and Int2 C haplotype were 6.1 (95% confidence interval, 1.6-22.5; P < 0.005) when compared with the contrasting haplotype. Linear modeling of individual postural changes in renin and aldosterone showed a maximal achievable aldosterone increase of 110 pmol/liter with no mutated haplotype and 500 pmol/liter with two mutated haplotypes. These findings support the view of a molecular basis regulating aldosterone production.     

CYP2C19 gene polymorphism in patients with myocardial infarction who use clopidogrel

One of the foundations of the modern treatment of myocardial infarction (MI) is a combination antiplatelet therapy consisting of acetylsalicylic acid (ASA) and clopidogrel. Pharmacodynamic and clinical studies have demonstrated that the polymorphism CYP2C19 (CYP2C19*2 allele) is associated with a reduced antiplatelet effect of clopidogrel and an increase in the incidence of severe cardiovascular complications. The study included 97 patients with MI. Coronary angiography was performed with subsequent standard treatment of MI, including stenting of the infarct-related coronary artery. CYP2C19 polymorphism was determined by polymerase chain reaction. At 6months, outcomes were determined. The frequency of allele CYP2C19*2 was 22.7%. We found statistically insignificant differences in the prevalence of CYP2C19 gene polymorphism in different forms of myocardial infarction. In contrast to the authors, who previously published data on the effect of CYP2C19 gene polymorphism on cardiovascular complications, we found no differences according to genotype. CYP2C19 gene polymorphism does not influence the prognosis for the next six months, if to patient follow medical recommendations, including the regular use of clopidogrel.     

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.     

Aldosterone synthase gene (CYP11B2) C-344T polymorphism in Caucasians from the Berlin Salt-Sensitivity Trial (BeSST)

OBJECTIVE: Aldosterone synthase (CYP11B2) is a key enzyme in the biosynthesis of aldosterone. Recently, the T allele of a polymorphism in the 5'-flanking region of the CYP11B2 gene (C-344T) has been reported to be more frequent in hypertensives than in normotensives, and has also been associated with increased plasma aldosterone levels. We therefore hypothesized that this variant may be related to increased blood-pressure response to dietary salt intake. SUBJECTS AND METHODS: We genotyped 1 63 young normotensive men recruited within the framework of the Berlin Salt-Sensitivity Trial (BeSST) for the CYP11B2 C-344T polymorphism. Subjects were characterized for family history of hypertension, plasma parameters of the renin-angiotensin-aldosterone system and blood-pressure response to a high (220 mmol/day) and low (20 mmol/day) salt diet RESULTS: The frequency of the -344T allele (0.45) was similar to that reported previously and genotype distribution was in Hardy-Weinberg equilibrium (CC, n = 55; CT, n = 71; TT, n = 37). There was a trend towards a higher frequency of the T allele in subjects with a positive family history of hypertension (0.48 versus 0.42), but the C-344T genotype was not related to blood pressure under either diet Furthermore, when subjects were classified into salt-sensitive and salt-resistant groups, allelic distribution did not differ between the two groups (qT = 0.43 versus qT = 0.45). While renin activity and plasma aldosterone levels were not related to genotype, plasma angiotensinogen was significantly higher in T-allele carriers under both the high (P = 0.02) and low (P = 0.008) salt diet. CONCLUSION: Our findings do not support the hypothesis that the C-344T polymorphism of the CYP11B2 gene is associated with salt sensitivity or increased activity of the renin-angiotensin system in young normotensive subjects. It is, therefore, unlikely that the C-344T polymorphism is a genetic marker for salt sensitivity in young normotensive Caucasian men.