Structural analysis and evaluation of the aldosterone synthase gene in hypertension

Forms of mineralocorticoid hypertension

Hypertension with hypokalemia, metabolic alkalosis, and suppressed plasma renin activity defines mineralocorticoid hypertension. Mineralocorticoid hypertension is the consequence of an overactivity of the epithelial sodium channel expressed at the apical membrane of renal cells in the distal nephron. This is usually the case when the mineralocorticoid receptor is activated by its physiologic substrate aldosterone. The best known form of mineralocorticoid hypertension is an aldosterone-producing adrenal tumor leading to primary aldosteronism. Primary aldosteronism can also be caused by unilateral or bilateral adrenal hyperplasia and rarely adrenal carcinoma. Interestingly, most of the inherited monogenic disorders associated with hypertension involve an excessive activation of the mineralocorticoid axis. In some of these disorders, mineralocorticoid hypertension results from activation of the mineralocorticoid receptor by other steroids (cortisol, deoxycorticosterone), by primary activation of the receptor itself, or by constitutive overactivity of the renal epithelial sodium channel. The present review addresses the physiology and significance of the key players of the mineralocorticoid axis, placing emphasis on the conditions leading to mineralocorticoid hypertension.

Salt sensitivity of Japanese from the viewpoint of gene polymorphism

Excess salt intake is an important environmental risk for the predisposition to essential hypertension. Previous physiological studies have shown that salt sensitivity is associated with insulin resistance, enhancement of sympathetic nerve activity and decrease of blood pressure decline at night. We have been examining the genetic importance of candidate gene polymorphisms of salt-sensitive hypertension using several populations. The angiotensinogen gene (AGT) is a thrifty gene which increases the risk for common disease with growth of civilization via sodium and body fluid retention. The CC genotype of the AGT/T+31C polymorphism, which is in complete linkage disequilibrium with the TT genotype of the M235T polymorphism, was associated with a decrease of blood pressure decline at night in the Ohasama Study. On the other hand, the Gly460Trp genotype of the alpha-adducin gene (ADD1) is associated with erythrocyte sodium transport and increases tubular sodium reabsorption and risk for hypertension. We also revealed in the Ohasama Study that the Trp460 allele of ADD1 is associated with hypertension in young subjects with low renin activity. In addition to these polymorphisms, the T(-344)C polymorphism in the promoter of the aldosterone synthase gene (CYP11B2) and the C825T polymorphism of the G-protein beta3 subunit gene (GNB3) are considered candidates for the genetic risk of salt-sensitive hypertension. We compared the allele frequency of five candidate genes between Japanese and Caucasians; the results showed that the frequencies of all alleles were significantly higher in Japanese than in Caucasians. This interesting finding might suggest a feasible explanation for the huge interracial differences in the frequency of salt-sensitive hypertension.

Measured haplotype analysis of the aldosterone synthase gene and heart size

Gene-association studies of heart size and the aldosterone synthase (CYP11B2) gene have produced inconsistent results, possibly because of limitations in the sample size and/or the number and location of the polymorphisms. An analysis of six polymorphisms spanning 6 kb of the CYP11B2 gene in Caucasian British families revealed a limited number of haplotypes because of strong linkage disequilibrium over this small region. The genotype and haplotype information was used in an association study involving 955 members of 229 families phenotyped for echocardiographic measures of heart size. In a mixed effects linear modelling analysis, the G5937C polymorphism was associated with cardiac wall thickness (P=0.02), and the intron conversion and A4550C polymorphisms were associated with left ventricular cavity size (P=0.02 and 0.002, respectively). Measured haplotype analyses confirmed the association of alleles at the intron conversion and G5937C polymorphisms with cardiac wall thickness (P=0.02), and alleles at the intron conversion polymorphism with left ventricular cavity size (P=0.04). The polymorphisms contributed to 2.0-3.4% of the variability in these traits. In summary, genetic polymorphisms at the CYP11B2 gene make a small contribution to quantitative variation in echocardiographic measures of heart size. These results point to the importance of analysing the full extent of genetic variation that captures the haplotype structure of a locus in gene association studies.

Genetic variability and transplantation

PURPOSE OF REVIEW

The purpose of this review is to summarize recent advances within the area of genetic polymorphisms with a specific emphasis on renal transplantation, and to discuss the potential clinical applications.

RECENT FINDINGS

Due to recent advances in molecular techniques, there has been an abundance of publications describing genetic variability in molecules relevant to transplant outcome. Many studies are now demonstrating associations between polymorphisms in these candidate genes and outcomes in organ transplantation.

SUMMARY

These studies emphasize the potential role of genetic variability in transplantation, and provide the rationale for large prospective studies to clearly define the potential benefits of genotyping in the risk stratification of transplant recipients.

Renin-angiotensin-aldosterone system and G-protein beta-3 subunit gene polymorphisms in salt-sensitive essential hypertension

Approximately 50% of hypertensive patients are salt sensitive (they increase their Blood Pressure in response to sodium intake or volume expansion). Mechanisms underlying salt sensitivity are not completely elucidated although there is evidence that they may be genetically determined. The aim of this study is to establish the relation among some genetic polymorphisms of the renin-angiotensin system (RAAS) and the beta-3 subunit of the protein G and salt sensitivity. We studied 102 essential hypertensive patients, stage 1-2 and without target organ damage. Salt sensitivity was assessed by the rapid protocol of Weinberger. We determined by polymerase Chain reaction techniques the following polymorphisms: insertion/deletion (I/D) of the angiotensin-converting enzyme (ACE), A1166C of the angiotensin II type 1 receptor (AT1R), -344C/T and intron 2 conversion (IC) of the aldosterone synthase (CYP11B2), and C825T of the beta-3 subunit of the protein G (GNB3). 41 patients (40.19%) were salt sensitive. The distribution of the different polymorphisms was similar in both groups of patients, but subjects carriers of the W allele of the CYP11B2 IC polymorphism had a greater risk for salt sensitivity as compared with no carriers (37 of 41, 90.2% vs 4 of 41, 9.8%, OR 3.02, P<0.05). Although there is no association between salt sensitivity and the different studied genotypes of the RAAS and of the GNB3, our data show a greater risk for salt sensitivity among carriers of the W allele of the CYP11B2 1C polymorphism.

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

BACKGROUND

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

OBJECTIVES

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Genetics of blood pressure, hypertensive complications, and antihypertensive drug responses

Hypertension is the most prevalent, treatable risk factor for diseases of the heart, brain and kidneys. In this review, we discuss advances in understanding of the genetics of blood pressure regulation, the development of hypertensive complications and the pharmacodynamics of antihypertensive drug responses. Discovery of single gene mutations that cause hypertension or hypotension in humans suggests that the common final pathway for regulation of blood pressure level is via alterations in renal sodium handling. Based on a working hypothesis that common genetic variations contributing to blood pressure variation in the population may also act on this same pathway, we summarize supporting evidence emerging from linkage and selected association studies of candidate genes--including those encoding components of the renin-angiotensin-aldosterone system, the epithelial sodium channel, adrenoceptors, G protein subunits, and other cellular signaling mediators and modifiers. We proceed to distinguish ischemic target organ complications due to arteriolosclerotic changes of the microvasculature from those due to atherosclerosis involving larger conduit and capacitance arteries. Using the example of subcortical white matter ischemia of the brain, we propose that interindividual variation in the arteriolosclerotic complications is more likely than atherosclerotic complications to be related to the same genetic (and environmental) mechanisms that contribute to hypertension. We conclude by summarizing the state-of-the-art of antihypertensive pharmacogenetics, which has succeeded in rejecting the null hypothesis that genetic variation does not influence blood pressure or protective target organ responses to drug therapy. In each of the three areas covered in this review, we indicate the many remaining obstacles to the routine clinical use of genetic measurements in the diagnosis, evaluation and treatment of hypertension.

Dietary electrolytes and hypertension in the elderly

The effect of age on older hypertensive patient's blood pressure response to increased sodium intake is well known. Salt sensitivity which does increase with age and the decrease in renal function limiting the ability of aged kidney to excrete sodium load are major factors, responsible for rise in blood pressure during Na consumption in the elderly. Clinical studies encourage salt reduction with and without weight loss. Although potassium consumption is highly recommended, one should be aware of potassium overload in the elderly.

Positive association of CYP11B2 gene polymorphism with genetic predisposition to essential hypertension

Predispositions to essential hypertension and cardiovascular diseases are possibly associated with gene polymorphisms of the renin-angiotensin system. Gene polymorphisms of angiotensinogen and angiotensin-converting enzyme genes have been suggested to be risk factors for hypertension and myocardial infarction. Concerning the polymorphism of aldosterone synthase (CYP11B2) gene, earlier studies have shown inconsistent results in terms of its relation to hypertension. In the present case-control study, we investigated the association of -344T/C polymorphism in the promoter region of human CYP11B2 gene with genetic predisposition to hypertension. The genotype of -344T/C polymorphism was determined in essential hypertension subjects (n=250) and normotensive subjects (n=221). The distributions of three genotypes (TT, TC, and CC) were significantly different between the hypertensive and the normotensive groups (chi(2)=9.61, P=0.008). Namely, the frequency of C allele was higher in the hypertensive patients than in the normotensive subjects (34.2 vs 26.5%, P=0.010). Our data suggest that the -344C allele of CYP11B2 gene polymorphism is associated with the genetic predisposition to develop essential hypertension.

Genomics of steroid hormones: in silico analysis of nucleotide sequence variants (polymorphisms) of the enzymes involved in the biosynthesis and metabolism of steroid hormones

Alterations of steroid hormone biosynthesis and metabolism are suspected to be involved in the pathogenesis of several diseases. Several polymorphisms of the enzymes involved in these processes have already been described and some could be associated with certain diseases. We attempted to examine the sequence variants of these genes in order to find novel variants by an in silico analysis. We analyzed the known human nucleotide sequences of the enzymes p450 side-chain cleavage enzyme, steroid 17-alpha-hydroxylase/17,20-lyase, 3-beta-hydroxysteroid dehydrogenase types 1 and 2, 21-hydroxylase, 11-beta-hydroxylase, aldosterone synthase, aromatase, 11-beta-hydroxysteroid dehydrogenase types 1 and 2, steroid 5-alpha-reductase types 1 and 2, steroid 5-beta-reductase, dehydroepiandrosterone sulfotransferase, 17-beta-hydroxysteroid dehydrogenase types 1-3. The analysis was performed using the National Center for Biotechnology Information Database by the search tool blastn. We found numerous sequence variants in both coding and non-coding sequences. The majority of these sequence variants have already been described, nevertheless, some appear as novel variants. Some of these may also have functional significance. We hypothesize over the possible significance of these findings and briefly review the available literature.

Interaction between the C(-344)T polymorphism of CYP11B2 and age in the regulation of blood pressure and plasma aldosterone levels: cross-sectional and longitudinal findings of the Olivetti Prospective Heart Study

OBJECTIVE

To study the interaction between the C(-344)T polymorphism and known determinants (age, body mass and dietary sodium) of blood pressure and plasma aldosterone.

DESIGN

Cross-sectional and longitudinal (1980-1995) survey of male workers in southern Italy.

SETTING

Medical centre of the Olivetti factories.

PARTICIPANTS

In 1995, the C(-344)T polymorphism was characterized in 811 untreated men. A subgroup of 280 participants already seen in 1980 was the object of longitudinal analysis.

MAIN OUTCOME MEASURES

Blood pressure, demographic, anthropometric and biochemical variables (serum and urinary electrolytes and plasma aldosterone) and frequency of the C(-344)T polymorphism.

RESULTS

In the whole population, there was no difference among genotypes for any of the variables examined. However, multiple regression showed a significant interaction between age (but not body mass or sodium intake) and genotype with regard to systolic (P = 0.03) and diastolic ( P= 0.02) pressure variability independently of covariates. Diastolic pressure increased linearly with age in carriers of the T allele (TT, P<0.001 and TC, P= 0.005), but not in CC homozygotes ( P= 0.848). In T carriers - but not in CC homozygotes - blood pressure and serum potassium increased and plasma aldosterone and serum sodium decreased across quintiles of age (P< 0.001 for all trends). In the longitudinal study, diastolic pressure increased significantly over time only in T carriers (TC+TT: +2.6 +/- 0.6, versus CC: -0.4 +/- 1.5 mmHg, P= 0.04).

CONCLUSION

Inter-individual variation of blood pressure and plasma aldosterone is affected by the interaction of C(-344)T polymorphism and ageing, thus supporting a role for this variant in mechanisms affecting blood pressure regulation.

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.

Variants of the CYP11B2 gene predict response to therapy with candesartan

In a prospective trial, patients with an elevated diastolic blood pressure (above 95 mm Hg) received high-dose (16 mg) or low-dose (8 mg) candesartan in addition to standardised medication. A positive response to treatment was defined as a diastolic blood pressure <85 mm Hg at follow-up. Genotyping for two candidate genes was performed in 116 patients. Genotypes of the CYP11B2 promotor polymorphism significantly predicted a positive response to treatment (CC: 67%; TC: 34%; TT: 21%; p=0.005).

Polymorphisms in the angiotensinogen and angiotensin II type 1 receptor gene are related to change in left ventricular mass during antihypertensive treatment: results from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation versus Atenolol (SILVHIA) trial

BACKGROUND

Our aim was to determine if gene polymorphisms in the renin-angiotensin-aldosterone system (RAAS) were related to the degree of change in left ventricular hypertrophy (LVH) during antihypertensive treatment.

METHODS AND RESULTS

Patients with essential hypertension and echocardiographically diagnosed LVH were included in a double-blind study to receive treatment with either the angiotensin II type 1 receptor (AT1-receptor) antagonist irbesartan (n = 41), or the beta-1 adrenergic receptor blocker atenolol (n = 43) as monotherapy for 3 months. The angiotensinogen T174M and M235T, the angiotensin-converting enzyme I/D, the AT1-receptor A1166C and the aldosterone synthase (CYP11B2) -344 C/T polymorphisms were analysed and related to the change in left ventricular mass (LVM). Patients with the angiotensinogen 174 TM genotype treated with irbesartan responded with the greatest reduction in LVM (-23 +/- 31SD g/m2 for TM and +0.5 +/- 18 g/m2 for TT, P = 0.005), independent of blood pressure reduction. Both the angiotensinogen 235 T-allele (P = 0.02) and the AT1-receptor 1166 AC genotype responded with the greatest reduction in LVM when treated with irbesartan (-0.1 +/- 19 g/m2 for AA and -18 +/- 30 g/m2 for AC, P = 0.02), independent of blood pressure reduction. These polymorphisms were not associated with the change in LVM during treatment with atenolol.

DISCUSSION

The angiotensinogen T174M and M235T and the AT1-receptor A1166C polymorphisms were related to the change in LVH during antihypertensive treatment with an AT1-receptor antagonist; of these angiotensinogen T174M was the most powerful. This highlights the role of the RAAS for left ventricular hypertrophy and the potential of pharmacogenetics as a tool for guidance of antihypertensive therapy.

Recipient RAS gene variants and renal allograft function

BACKGROUND

Genetic variants of the renin-angiotensin system (RAS) have been implicated in the progression of native kidney diseases. A decreased long-term renal allograft function has also been associated with increased activity of RAS, which may be genetically determined.

METHODS

The effect of the angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin type 1 receptor (AGT1R), and aldosterone synthase (CYP11B2) genotypes on renal function was investigated in 223 first-allograft recipients. Graft function was estimated by yearly determinations of serum creatinine. Genotyping was performed for the M235T-AGT, the I/D-ACE, the A1166C-AGT1R, and the -344T/C-CYP11B2 gene polymorphisms using polymerase chain reaction.

RESULTS

The percentage of patients with preserved stable graft function up to 15 years after transplantation was higher when mean blood pressure was <97 mmHg, than when it was >117 mmHg (60 vs. 25% of patients). The CYP11B2 genotype predicted long-term stable graft function with more patients suffering from worsening renal function with the CYP11B2 TT than the CC genotype (P=0.002). There was a weak association between the AGT1R genotype (P=0.037), but not the AGT or ACE genotypes, and a preserved long-term graft function. Cox proportional hazards estimation showed no interactions between the observed effect of CYP11B2 genotype on renal function over time and the number of HLA class I and II matches, other RAS genotypes, graft function, or mean blood pressure at 1 year after transplantation.

CONCLUSIONS

The rate of decline in renal allograft function is strongly associated with the CYP11B2 but not AGT, ACE, or AGT1R genotypes. This finding suggests that certain genetic factors related to the RAS are important determinants of long-term renal allograft function.

The neurohormonal natural history of essential hypertension: towards primary or tertiary aldosteronism?

Use of the aldosterone-to-renin ratio has controversially suggested that approximately 10% of hypertensives have primary aldosteronism, and most of these individuals are thought to have idiopathic hyperaldosteronism. The usual renin-angiotensin system control is intact in these individuals and is similar to that in low renin and essential hypertensives, differing only in the degree of sensitivity. There is recent evidence suggesting that hyperaldosteronism relates to aldosterone synthase genetic polymorphism, and also that increased angiotensin II stimulation of the adrenal glands appears to paradoxically upregulate the receptors increasing angiotensin II sensitivity. Taken together, the possibility arises that, in susceptible hypertensives, hyperaldosteronism could be acquired. Indeed, it is well known that renin-driven renovascular hypertension is associated with the development of hyperaldosteronism. Hypothetically, within the wider hypertensive population, these findings set the scene that angiotensin II adrenal sensitivity increases over time until the secretion of aldosterone becomes "autonomous" and hence "tertiary" aldosteronism in a significant proportion of hypertensives.

Aldosterone synthase gene (CYP11B2) C-334T polymorphism, ambulatory blood pressure and nocturnal decline in blood pressure in the general Japanese population: the Ohasama Study

OBJECTIVE

The C-344T polymorphism in the 5'-flanking region of the aldosterone synthase (CYP11B2) gene has been suggested to be associated with hypertension and disturbed circadian blood pressure (BP) rhythm through its effect on aldosterone synthesis. However, previous findings on this topic have been inconsistent.

DESIGN

A cross-sectional study.

SUBJECTS AND METHODS

We investigated the CYP11B2 C-344T genotype in 802 subjects, aged 40 and over, in a Japanese community, who gave written informed consent and were monitored for 24 h ambulatory BP.

RESULTS

The frequencies of the CC, CT, and TT genotypes in these Japanese subjects were 0.14, 0.44, and 0.42, showing a higher frequency of the T allele (0.64) than in Caucasians. Although there was no significant difference in 24 h ambulatory BP levels among the genotypes, the nocturnal decline in BP was significantly greater in the CC homozygous subjects than in other subjects (P = 0.0065 for systolic and P = 0.031 for diastolic decline in nocturnal BP). Detailed analyses demonstrated that this association was significant only in aged (60 years and over) or male subjects. The prevalence of previous cardiovascular disease was significantly less in these subjects with the CC genotype than in those with the TC and TT genotypes, although age, body mass index, male gender, smoking, use of alcohol and antihypertensive medication did not differ among the three genotypes. There was no significant difference among the three genotypes in biochemical and hormonal parameters.

CONCLUSION

Although the C-344 T polymorphism of CYP11B2 did not directly influence the level of 24 h BP, the CC genotype was associated with decreased nocturnal BP in elderly or male Japanese. Since prevalence of previous cardiovascular disease was significantly less in homozygous CC subjects, greater nocturnal BP decline in this genotype appears to be beneficial in the circadian BP rhythm.

Renal function in relation to three candidate genes

We recently found that femoral intima media thickness, as well as the incidence of hypertension, is influenced by genes encoding the angiotensin-converting enzyme (ACE; insertion/deletion [I/D]) polymorphism, alpha-adducin (Gly460Trp), and aldosterone synthase (-344C/T). By interfering with blood pressure or sodium homeostasis, these genetic polymorphisms also may change renal function. We therefore investigated serum creatinine level, calculated and measured creatinine clearances, and 24-hour urinary protein excretion in subjects previously genotyped for these three polymorphisms. The 1,454 participants drawn at random from the population (64.3% of those invited) were aged 43.4 years and included 744 women (51.2%). Blood pressure, measured by study nurses at subjects' homes, averaged 123/76 mm Hg. Mean values were 90 micromol/L for serum creatinine; 84 and 88 mL/min/1.73 m(2) for calculated and measured (n = 855) creatinine clearances, respectively; and 90 mg/d of protein for proteinuria (n = 556). The prevalence of mild renal dysfunction (creatinine clearance </= 60 mL/min/1.73 m(2)) was nearly 11%. In single-gene analyses with adjustment for significant covariables, the risk for mild renal dysfunction was positively associated with the ACE D allele. However, multiple-gene analyses showed that these associations were restricted to carriers of the mutated alpha-adducin Trp allele (40.1% of all subjects). Findings remained similar after hypertensive patients and women on hormonal therapy were excluded. In this phenotypically more homogeneous subgroup, serum creatinine level was 3.6 micromol/L (P = 0.02) and relative risks for mild renal dysfunction and proteinuria were 1.7-fold (P < 0.001) and 26% (P = 0.02) greater in ACE D subjects than ACE II homozygotes, respectively. The aldosterone synthase T allele did not strengthen genetic associations with the ACE D allele considered alone or in combination with the alpha-adducin Trp allele. Thus, in the present cross-sectional analysis, renal function was slightly but consistently impaired when both the ACE D and alpha-adducin Trp alleles were present. These findings, together with experimental studies and our previous reports on femoral intima media thickness and the incidence of hypertension, constitute a growing body of evidence delineating a clinical entity genetically determined by the risk-carrying ACE D and alpha-adducin Trp alleles.

Genetic variation in aldosterone synthase predicts plasma glucose levels

The mineralocorticoid hormone, aldosterone, is known to play a role in sodium homeostasis. We serendipitously found, however, highly significant association between single-nucleotide polymorphisms in the aldosterone synthase gene and plasma glucose levels in a large population of Chinese and Japanese origin. Two polymorphisms--one in the putative promoter (T-344C) and another resulting in a lysine/arginine substitution at amino acid 173, which are in complete linkage disequilibrium in this population--were associated with fasting plasma glucose levels (P = 0.000017) and those 60 (P = 0.017) and 120 (P = 0.0019) min after an oral glucose challenge. A C/T variant in intron 1, between these polymorphisms, was not associated with glucose levels. Arg-173 and -344C homozygotes were most likely to be diabetic [odds ratio 2.51; 95% confidence interval (C.I.) 1.39-3.92; P = 0.0015] and have impaired fasting glucose levels (odds ratio 3.53; 95% C.I. 2.02-5.5; P = 0.0000036). These results suggest a new role for aldosterone in glucose homeostasis.

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.

Unequal crossing-over between aldosterone synthase and 11beta-hydroxylase genes causes congenital adrenal hyperplasia

Congenital adrenal hyperplasia is one of the most frequently inherited diseases. It is characterized by a severe decline in cortisol secretion, which results in a compensatory increase in ACTH and consequent adrenal growth (hyperplasia). Here we describe the first case of 11beta-hydroxylase deficiency that is caused by an unequal cross-over of the genes encoding aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1). CYP11B1 and CYP11B2 are located on chromosome 8q24 approximately 45 kb apart from each other. The investigated genetic recombination deleted the normal alleles of the two genes and created a chimeric fusion gene, which consists of the promotor and exons 1 through 4 of the aldosterone synthase gene plus intron 4 through exon 9 of the 11beta-hydroxylase gene. This recombination event subordinates any remaining 11beta-hydroxylase activity of the chimeric enzyme to the control mechanisms of CYP11B2, the expression of which is mainly regulated by angiotensin II and K(+). Normally the 11beta-hydroxylase activity is controlled by ACTH. The existence of the CYP11B2/CYP11B1 chimera was discovered by means of a PCR method and was confirmed with a Southern blot. Furthermore, by applying a minigene expression method we demonstrated a point mutation in intron 3 (IVS3+16G-->T) of the patient's second 11beta-hydroxylase allele that radically diminishes proper splicing of the pre-mRNA by giving rise to a new, highly preferred donor splice site.

Genetic alterations in patients with primary aldosteronism

The syndrome of primary aldosteronism is characterized by hypertension with excessive production of aldosterone, potassium loss, and suppression of the renin-angiotensin system. The most common clinical subtypes of primary aldosteronism are aldosterone-producing adrenocortical adenoma (APA) and bilateral adrenal cortical hyperplasia (idiopathic hyperaldosteronism, or IHA). It has been reported that renin suppression and aldosterone levels are lower and hypokalemia milder in patients with IHA than in patients with APA. In the present study, we investigated the genetic analysis of aldosterone synthase gene, CYP11B2 in patients with primary aldosteronism and review the recent studies. The chimeric CYP11B1/CYP11B2 gene, which is a candidate gene for glucocorticoid-remediable hyperaldosteronism, was not found in either the DNA from aldosteronoma or in the genomic DNA from patients with APA or IHA. Mutations in the CYP21 or CYP11B1 gene were not present in patients with APA. No mutations in the coding region of the CYP11B2 gene were found in patients with IHA or APA. The level of CYP11B2 messenger RNA (mRNA) was much higher in the aldosteronoma portion than in nonadenomatous portion. The overexpression of CYP11B2 mRNA seen in the mononuclear leukocytes of patients with IHA suggests that unidentified aldosterone-stimulating factors or abnormalities of the CYP11B2 promoter region may cause the overproduction of aldosterone characteristic of IHA. The variants of the CYP11B2 gene may also contribute to dysregulation of aldosterone synthesis and lead to susceptibility to IHA.

Effects of three candidate genes on prevalence and incidence of hypertension in a Caucasian population

BACKGROUND

The genes encoding angiotensin converting enzyme (ACE, I/D), alpha-adducin (ADD, Gly460Trp) and aldosterone synthase (AS, -344C/T) share the potential of influencing blood pressure (BP) via sodium homeostasis. However, most studies in humans focused on single-gene effects and disregarded epistasis, the suppression or potentiation of a gene by other non-allelic genes.

METHODS

We studied the singular and combined effects of the aforementioned candidate genes: (1) in relation to BP, plasma renin activity (PRA) and urinary aldosterone in 1461 subjects randomly selected from a Caucasian population; and (2) in relation to the incidence of hypertension in a subgroup of 678 initially normotensive subjects followed up for 9.1 years (median).

RESULTS

In cross-sectional analyses, AS/CC homozygosity was associated with slightly lower systolic BP (-1.32 mmHg; P = 0.08). AS/TT homozygotes showed both lower PRA and higher urinary aldosterone excretion (P < or = 0.05). In multiple-gene analyses, compared with the whole study population, ADD/Trp subjects had a higher relative risk of hypertension in the presence of the AS/T allele (1.29; P = 0.05), whereas in combination with AS/CC homozygosity ADD/Trp subjects had the smallest relative risk (0.48; P = 0.003). Hypertension developed in 229 subjects (36.6 cases per 1000 person-years). ACE/DD homozygosity, in comparison with the other ACE genotypes, was associated with increases in the incidence of hypertension, which amounted to 31% (P = 0.005) in single-gene analyses, to 59% (P = 0.004) in carriers of the ADD/Trp allele and to 122% (P = 0.0007) in AS/CC subjects. Among subjects who had both the ADD/Trp allele and the AS/CC genotype, ACE/DD homozygotes manifested a 252% (P = 0.001) higher incidence of hypertension.

CONCLUSIONS

Epistatic interactions between the ACE, ADD and AS genes contribute to the prevalence and incidence of hypertension in Caucasians. The clinical relevance of the risk-conferring haplotypes identified in our prospective study was underscored by their positive predictive values, which under the assumption of a 20% life-time risk of hypertension, ranged from 29.8-40.1%.

Genetic polymorphisms of the renin-angiotensin-aldosterone system in end-stage renal disease

BACKGROUND

Hypertension contributes to the progression to renal failure. A genetic susceptibility to hypertension may predispose to the development of end-stage renal disease (ESRD) and promote a more rapid progression to ESRD in patients with renal diseases. Genes encoding for angiotensinogen (AGT), angiotensin-converting enzyme (ACE), and aldosterone synthase (CYP11B2) are candidates for abnormal blood pressure regulation.

METHODS

Genotyping was performed in 327 control subjects and 260 ESRD patients for the M235T-AGT, the insertion/deletion (I/D)-ACE, and the -344T/C-CYP11B2 gene polymorphisms using polymerase chain reaction, gel analysis, and appropriate restriction digest when required.

RESULTS

Genotype frequencies did not differ significantly between ESRD patients and controls. When ESRD diabetic subjects were compared with diabetic patients without nephropathy, the prevalence of the AGT-MM genotype was lower (28.1 vs. 52.8%, P < 0.01), while the AGT-TT genotype was higher (15.6 vs. 2.7%, P < 0.05). The AGT-TT genotype was associated with a faster progression to ESRD in patients with glomerulonephritis (P < 0.05). In the total ESRD population, progression of renal disease was faster with the ACE-DD than with the DI and II alleles (P < 0.05). This association was particularly strong when the interaction with the AGT genotype was analyzed, with a rapid progression in ACE-DD as compared with ACE-DI and II in patients with the AGT-MM genotype (P < 0.01).

CONCLUSIONS

Susceptibility for ESRD and faster progression to ESRD are linked with the AGT genotype in diabetic patients. Faster progression to ESRD is associated with the ACE genotype when the total population with ESRD and with the AGT genotype when patients with glomerulonephritis are considered. Thus, genes of the renin-angiotensin-aldosterone system are candidate genes for further understanding of the interindividual differences in the development and course of ESRD.

An influence of variation in the aldosterone synthase gene (CYP11B2) on corticosteroid responses to ACTH in normal human subjects

OBJECTIVE

Previous evidence suggests that the efficiency of 11beta-hydroxylase is at least partly heritable and also that it may be mildly impaired in essential hypertension. In both cases, assessment of activity was based on the response of 11-deoxycorticosterone (DOC) and 11-deoxycortisol to ACTH. The gene (CYP11B1) coding for this enzyme is highly homologous with and lies a relatively short distance downstream from the gene coding for aldosterone synthase (CYP11B2) on chromosome 8. Two polymorphisms of CYP11B2 have been described. The first involves a change of -344C to T in a putative steroidogenic factor-1 (SF-1) binding site and the other, the intron conversion, an exchange of intron 2 for that of CYP11B1. These polymorphisms are in linkage dysequilibrium. Their effects on 11beta-hydroxylation were studied.

METHODS AND RESULTS

Normal subjects (n = 135) were genotyped and those homozygous for either or both the polymorphisms were given ACTH (250 microg, i.v.). Plasma was sampled before and 30 minutes after administration. Basal concentrations of DOC, corticosterone, 11-deoxycortisol and cortisol and responses of corticosterone and cortisol to ACTH were not affected by genotype. However, the responses of DOC (P = 0.002 and P = 0.001, respectively) and 11-deoxycortisol (P = 0.025 and P = 0.002, respectively) were significantly greater in subjects homozygous for SF-1 T and/or intron conversion than in those homozygous for SF-1 C and/or normal intron.

CONCLUSIONS

These results indicate different 11beta-hydroxylase efficiencies. Thus, variation in CYP11B2 appears to affect the product of CYP11B1. The mechanism is unclear. The close proximity of the two genes may lead to competition for transcription factors or specific differences in intron 2 may affect transcription. Alternatively, the polymorphisms may be acting as markers for adjacent functional genetic variations.

Polymorphisms in the renin-angiotensin system and endothelium-dependent vasodilation in normotensive subjects

BACKGROUND

Our aim was to test the hypothesis that genes encoding components in the renin-angiotensin system influence endothelial vasodilatory function.

METHODS

In 59 apparently healthy, normotensive individuals, endothelium-dependent vasodilation (EDV) and endothelial-independent vasodilation (EIDV) was evaluated by infusing metacholine and sodium nitroprusside into the brachial artery. Forearm blood flow was measured by venous occlusion plethysmography. The ACE insertion (I)/deletion (D) polymorphism, the T174M and M235T angiotensinogen restriction fragments length polymorphisms, the angiotensin II receptor type 1 (AT1R) A1166C, and the aldosterone synthase gene (CYP11B2) C-344T polymorphisms were analysed.

RESULTS

When analysing the ACE, the two angiotensinogen and the aldosterone synthase CYP11B2 genotypes independently, no significant association with endothelial vasodilatory function was found. However, a significant reduction in endothelium-dependent vasodilation was observed in the subjects (n=9) with the ACE D allele and the angiotensinogen T174M genotype (P<0.05). Subjects with the AT1R genotype AC showed a reduction in both EDV (P=0.05) and EIDV (P=0.04) when compared with those with the AA genotype.

CONCLUSIONS

The subjects with the ACE D allele in combination with the angiotensinogen T174M genotype are associated with a reduced EDV. This together with the observation that the AC AT1R genotype is associated with a reduction in both EDV and EIDV, supports the hypothesis that endothelial vasodilatory function is influenced by genes in the renin-angiotensinogen system.

Lack of association between genetic polymorphism of CYP11B2 and hypertension in Japanese: the Suita Study

Aldosterone synthase (CYP11B2) is a key enzyme in the biosynthesis of aldosterone. Recently, a polymorphism in the 5'-flanking region of the CYP11B2 gene [T(-344)C] has been reported to be associated with blood pressure and plasma aldosterone levels. We investigated the association between this polymorphism and hypertension in a large population-based sample of 4,000 Japanese. The genotype distribution in hypertensive subjects (n=1,535) was compared to that in normotensive subjects (n=2,514). In subjects not receiving antihypertensive medication, the influence of the genotype on blood pressure values adjusted for clinical covariates was analyzed. All analyses were performed separately for men and women. The genotype distribution did not differ between hypertensive and normotensive subjects in either men (frequency of C allele: 30.3% vs. 31.4%, p=0.48) or women (31.5% vs. 31.7%, p=0.93). There were no significant differences in systolic blood pressure, diastolic blood pressure, or pulse pressure among the three genotypes in either men or women who had not received hypertensive medication. Our data suggest that the T(-344)C polymorphism of CYP11B2 is unlikely to influence blood pressure status in the Japanese population.

Aldosterone synthase (CYP11B2) -344 C/T polymorphism is associated with left ventricular structure in human arterial hypertension

OBJECTIVES

This study examined the association between the -344 C/T polymorphism of the human aldosterone synthase promoter and left ventricular structure in arterial hypertension.

BACKGROUND

Because of conflicting results from different studies, the mechanism of such an association, if any, has not been determined.

METHODS

We examined the aldosterone synthase promoter genotype in 120 young (age: 26 +/- 3 years) male, white subjects with normal or mildly elevated blood pressure. Left ventricular structural parameters and urinary sodium excretion over 24 h before and after additional oral sodium load (6 g/day over 1 week) were determined.

RESULTS

Hypertensive subjects with the CC genotype had a greater left ventricular end-diastolic diameter but smaller relative wall thickness than those with the TT genotype (54 +/- 2 vs. 50 +/- 4 mm, and 0.37 +/- 0.07 vs. 0.44 +/- 0.06 mm, respectively; p < 0.05). Hypertensive subjects with the TT genotype (n = 15) had a greater increase in urinary sodium excretion after oral sodium load than those with the CC genotype (n = 11) (135 +/- 95 vs. 24 +/- 133 mmol/liter/day; p < 0.05). Serum aldosterone levels were found to be decreased after oral sodium load in hypertensive subjects with the TT and CT genotypes only (-37 +/- 45 and -38 +/- 51 pg/ml, respectively; all p < 0.01) but not in those with the CC genotype (-12 +/- 30 pg/ml, n.s.). Such differences were not found in normotensive subjects.

CONCLUSIONS

Hypertensive subjects with the -344 CC genotype of the aldosterone synthase promoter are characterized by a pattern of early eccentric left ventricular hypertrophy. Differences in renal sodium handling across the genotypes might contribute to this finding.

Molecular genetics of essential hypertension: recent results and emerging strategies

Efforts to identify hypertension-predisposition genetic loci have focused largely on candidate gene strategies, in which specific candidates have been tested for linkage and association with blood pressure or the diagnosis of hypertension. A variety of candidate genes have been investigated, including loci involving the renin-angiotensin-aldosterone system, sodium epithelial channel, catecholaminergic/adrenergic function, renal kallikrein system, alpha-adducin, and others involving lipoprotein metabolism, hormone receptors, and growth factors. These studies, and more recently, several genome-wide scans, have yielded highly promising results suggesting a number of potential candidate genes and genomic regions that may contribute to blood pressure variation. The results also point to the need for more robust phenotypes that are intermediate in the pathogenetic development of high blood pressure. Additional methods and strategies for improving genetic studies of human hypertension include comparative genomics, in which results from animal studies are used to target potential blood pressure loci, the use of newly developed quantitative tests of linkage and association, comprehensive single-nucleotide polymorphism discovery in candidate loci, and the use of single-nucleotide polymorphisms in cladistic/haplotype analyses and genome-wide searches.

Etiology and pathophysiology of stroke as a complex trait

Stroke (brain attack) is currently the third leading cause of death in Western societies. Recent advances in molecular genetics have finally demonstrated what has long been suggested by the clinical observation, that is, stroke is not only the complication of major pathologic conditions such as atherosclerosis, hypertension, or cardiac diseases, but rather it represents a complex trait itself. Thus, the pathogenesis of stroke is often the result of the combined effects of genes exerting a direct contributory role and of their interactions with several environmental determinants. A genetic dissection of stroke has been attempted in suitable animal models and in humans. With this approach, the genetic defects underlying monogenic disorders associated with stroke were identified. Moreover, important findings have recently highlighted the contribution of genes encoding cardiovascular hormones, such as the atrial natriuretic peptide, for the pathogenesis of multifactorial, polygenic forms of stroke. A more thorough understanding of the fine mechanisms, dependent from mutations within stroke susceptibility genes and underlying the disease pathogenesis, may help to introduce new specific tools to achieve better prevention and treatment of stroke.

Genetic determination of human essential hypertension

Recent advances in genetic determination of human essential hypertension (EHT) are discussed by reviewing the candidate genes. Candidate genes have been selected based on genetic information from classical linkage analysis (affected sib-pair analysis) or mendelian hypertension (autosomal dominant inheritance of hypertension). Most of these genes are, directly or indirectly, coupled to salt handling of the kidney, being included in the renin-angiotensin system (RAS), steroid-hormone metabolism, and renal sodium transporters. Angiotensinogen (AGT) gene in RAS was first described as a strong candidate associated with the onset of hypertension, since sib-pair linkage analysis has demonstrated the trait loci for hypertension which includes the coding region for AGT. M235T polymorphism of AGT has been studied extensively in many populations including Japanese, and the results suggest a weak, but significant linkage with hypertension. The presence (insertion [I]) or absence (deletion [D]) of 287bp in intron 16 of angiotensin converting enzyme gene has also been examined in RAS, and the results suggest D polymorphism as a risk factor for hypertension in men. Other components in RAS, such as renin, angiotensinogen II type I receptor, or kallikrein have also been studied, but the available information is still incomplete. Genetic investigations of mendelian hypertension has identified the genetic mechanisms for glucocorticoid remediable aldosteronism, apparent mineral corticoid excess, and Liddle's syndrome as chimeric gene duplications of CYP11B1 (aldosterone synthase gene) and CYP11B2 (11beta-hydroxylase gene), mutations in the gene of 11beta-hydroxysteroid dehydrogenase type 2 that catalyzes the conversion of cortisol to cortisone, and mutations in beta or gamma subunit of epithelial sodium channel (ENaC), respectively. Subsequently, genetic variants of CYP11B2 and beta or gamma subunit of ENaC have been found, suggesting the -344C polymorphism of CYP11B2, 594S variant of betaENaC, and two rare variants of gammaENaC as risk factors for EHT. In spite of the extensive research, haplotypes in individual populations remain to be elucidcated in most candidate genes. Even casual conclusions of possible linkage with EHT need to be further examined with better determinations of phenotypes, such as ambulatory and home blood pressure monitoring or identification of onset of hypertension in cohort studies.

Comprehensive analysis of the renin-angiotensin gene polymorphisms with relation to hypertension in the Japanese

BACKGROUND

Components of the renin-angiotensin (R-A) system have been repeatedly investigated as candidate genes for essential hypertension. In particular, suggestive or significant association has been detected in some studies for the angiotensinogen M235T, angiotensin I-converting enzyme I/D, angiotensin II type 1 receptor A1166C, and aldosterone synthase C-344T polymorphisms, although the results remain inconclusive.

OBJECTIVE AND METHODS

To evaluate the importance of these candidate genes for hypertension, we undertook an extensive association study in the Japanese. This case-control study was conducted in a total of 1476 individuals using the four R-A gene polymorphisms. In the assessment of genotyping data, 843 hypertensive subjects were divided into three case subgroups according to severity of hypertension, while 633 normotensive subjects divided into two control subgroups by the age of enrollment. Each subgroup was further divided by sex. Subsequently, the presence of synergy (or gene-gene interaction) was evaluated among four R-A gene polymorphisms.

RESULTS

No significant association was observed between the individual R-A gene polymorphisms and hypertension status in our case-control study. The results were almost unchanged when severity of hypertension, sex-specificity, and synergy were taken into account

CONCLUSIONS

Despite a relatively large number of subjects, we did not find significant evidence for disease association in the Japanese population. Given confounding factors in the case-control strategy, the lack of association does not exclude the relevance of the R-A genes to hypertension. Further investigation needs to be performed in large-scale populations, where the use of not only hypertension status, but also 'intermediate' phenotypes would be useful.

Genetic variation of the gamma subunit of the epithelial Na+ channel and essential hypertension. Relationship with salt sensitivity

We evaluated the association of a common polymorphism in gammaENaC, consisting in a C to G transversion in codon 649, with essential hypertension and to the pressor response to salt in whites. Two hundred fifteen essential hypertensive patients, and 137 normotensive controls were genotyped for the gamma649 ENaC polymorphism by polymerase chain reaction method and diagnostic restriction enzyme digestion. The genotype distribution of the gamma649 ENaC polymorphism in the hypertensives, 129 CC (60%) and 86 CG/GG (40%) was not significantly different from that of the control group, 84 CC (61%) and 53 CG/GG (39%) (P = .81). Salt sensitivity was assessed in a group of 48 patients by 24-h mean blood pressure response to changes in salt intake. Nineteen patients were diagnosed as salt sensitive, whereas 29 had salt-resistant hypertension. The gamma649 ENaC genotype distribution in salt-sensitive patients was 12 CC (63%) and 7 CG/GG (37%), not significantly different from the distribution in the salt-resistant group, 19 CC (65%) and 10 CG/GG (35%), P = .87. The changes in systolic, diastolic, and mean blood pressure as measured by ambulatory blood pressure monitoring, and in plasma renin activity and plasma aldosterone induced by high salt diet were not different among the gamma649 ENaC genotypes. In the present study we found no association between the gamma649 ENaC polymorphism and essential hypertension or salt sensitivity. Although these data do not support a major causative role for this polymorphism, we cannot exclude that a functional mutation elsewhere in ENaC might be associated with essential hypertension.

Amino acid residue 147 of human aldosterone synthase and 11beta-hydroxylase plays a key role in 11beta-hydroxylation

A number of amino acids differ between aldosterone synthase and 11beta-hydroxylase. To assess their importance in determining the different functional specificities, we substituted aldosterone synthase-specific (aspartate D147, isoleucine I248, glutamine Q43, and threonine T493) with 11beta-hydroxylase-specific amino acids (glutamate E147, threonine T248, arginine R43, and methionine M493), respectively. I248T, Q43R, and T493M had no effect on steroid production compared to wild-type aldosterone synthase. However, CYP11B2-D147E caused a significant increase in corticosterone production and a smaller increase in aldosterone production from 11-deoxycorticosterone (DOC). This appeared to be predominantly due to an increase in the 11beta-hydroxylation of DOC to corticosterone mediated by a decrease in Km, which was 1.4 micromol/L for the mutant compared with 5 micromol/L for the wild-type enzyme. CYP11B2-D147E had no effect on the conversion of 11-deoxycortisol to cortisol. The reverse construct (CYP11B1-E147D), substituting the 11beta-hydroxylase residue with the aldosterone synthase equivalent, decreased the conversion of DOC to corticosterone, which was mediated by an increase in Km that was 7.5 micromol/L for the mutant compared with 2.5 micromol/L for the wild-type enzyme. Again, the conversion of 11-deoxycortisol to cortisol was unimpaired. Thus, amino acid 147 is involved in the transformation of the 17-deoxysubstrate, but not the 17alpha-hydroxysubstrate. The results demonstrate that a conservative change in amino acid, even at some linear distance from known active centers, can significantly affect enzyme substrate affinity and subsequent steroid hormone production.

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.

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.

Genes and hypertension: where we are and where we should go

Our understanding of the genetics of hypertension is incomplete. A great deal has, however, been learned about the role of several <<candidate>> genes by altering their expression in transgenic and knockout models. Crosses of inbred strains, analyzed in F2 generations, have demonstrated consistent quantitative trait loci, particularly on chromosomes 1, 2 and 10, suggesting significant contributions of some genes in distinct models of rodent hypertension. The effect of these loci has been tested in congenic strains and their interaction underlined in double congenics. The weakness of testing individual animals from F2 crosses is overcome in recombinant inbred strains. In humans, Mendelian models of hypertension have contributed to progress in our understanding of this disease, but have not yet revealed any major gene of essential hypertension. Many association as well as linkage studies of humans have provided useful though somewhat contradictory data. Our renewed effort is oriented towards the discovery of genetic determinants of environmental interaction in hypertension as well as towards the future of pharmacogenomics. This progress will be the basis of future individualized treatment and prevention.

Genetic analysis of aldosterone synthase in patients with idiopathic hyperaldosteronism

Idiopathic hyperaldosteronism (IHA) is characterized by hypertension with excessive production of aldosterone, potassium loss, and suppression of the renin-angiotensin system. We compared activity of aldosterone synthase and expression of CYP11B2 messenger RNA (mRNA) in mononuclear leukocytes (MNL) from patients with IHA to findings in leukocytes from patients with aldosterone-producing adenoma and normal controls. Aldosterone synthase activity was estimated from conversion of [14C]deoxycorticosterone to [14C]aldosterone. Levels of CYP11B2 mRNA were determined by competitive PCR. In the same subjects, we sought the chimeric CYP11B1/CYP11B2 that is candidate gene for glucocorticoid-remediable hyperaldosteronism. Southern blot analysis and a long PCR method were used to detect the chimeric gene. Direct sequencing of the CYP11B2 also was performed. No chimeric genes or mutations in the coding region of the CYP11B2 were found in genomic DNA from these patients. However, both aldosterone synthase activity and CYP11B2 mRNA expression were greater in mononuclear leukocytes of patients with IHA than those of patients with aldosterone-producing adenoma or controls. These results suggest that regulatory factors of the CYP11B2 gene, e.g. unidentified aldosterone-stimulating substances or abnormalities in the promoter region of the CYP11B2 gene in patients with IHA resulting in oversecretion, may cause overexpression of mRNA of CYP11B2.

Nitric oxide, nitric oxide synthase, and hypertensive vascular disease

In normotension the endothelium produces mainly nitric oxide (NO) and prostacyclin, and the vasodilator and growth inhibitory influence predominates. Hypertension, however, is associated with a shift towards enhanced constriction and vascular hypertrophy. These effects are associated with an apparent decrease in the production of bioactive NO and concomitant increase in the generation of oxygen-derived free radicals, such as superoxide anions (O(2)-). While the enzymatic source of endothelial O(2)- has been debated intensely over the past few years, it may well turn out that the endothelial NO synthase is itself an important producer of O(2)-. Because the redox state of endothelial cells and, for example, the activation of redox-sensitive transcription factors is regulated by the balance between NO and O(2)- production, endothelial NO synthase may well be the most crucial enzyme determining the anti- or prohypertensive and eventually proatherogenic state of the vascular wall.

Cardiac genes and gene databases for cardiovascular disease genetics

Genes play a very important role in the etiology of hypertension. This paper reviews the current pool of candidate genes for human hypertension. Some of the genes studied in rat models of hypertension are also discussed. The methods for studying the genetics of hypertension are reviewed. A discussion of the role of cardiac gene libraries and gene databases in the characterization of cardiovascular disease is also included. This review is concluded by a discussion on the future role of genomics and cardiovascular gene databases in medical research.