Polymorphic Variation in the 11β-Hydroxylase Gene Associates With Reduced 11-Hydroxylase Efficiency

Altered glucocorticoid metabolism in girls with central obesity

BACKGROUND

Dysregulation of glucocorticoid metabolism is known to be a causative factor of obesity. However, only a few studies have evaluated the enzymatic activities involved in glucocorticoid metabolism in the pediatric population.

OBJECTIVE

To examine whether circulating glucocorticoid metabolites and their ratios reflecting the activities of metabolic enzyme are associated with obesity and body composition in girls.

METHODS

A total of 227 girls aged 7-13 years (131 control, 45 overweight, 51 obese) were enrolled in this study. Serum concentrations of glucocorticoids (11-deoxycortisol, cortisol, tetrahydrocortisol [THF], allo-THF, allo-dihydrocortisol [allo-DHF], and cortisone) were evaluated by gas chromatography-mass spectrometry. Enzyme activities corresponding to the ratios of cortisol and cortisone to their respective precursors and metabolites were also assessed.

RESULTS

Serum levels of allo-THF were significantly higher in obese girls compared with those in overweight and control girls (P = 0.018); however, concentrations of other cortisol metabolites were not significantly different between the groups studied. According to the severity of obesity, increasing trends in the metabolic ratios reflecting the activity of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) [(cortisol + allo-DHF + allo-THF + THF)/cortisone], relative 5α/5β-reductase [allo-THF/THF] activity, and 3α-HSD [allo-THF/allo-DHF] activity, were noted (P-for-trend <0.05). Body fat percentage and waist-to-height ratio positively correlated with the activities of 11β-HSD1 and 3α-HSD (P < 0.05). Following covariate control, girls with central obesity demonstrated significantly higher metabolic ratios reflecting 11β-HSD1, relative 5α/5β-reductase, and 3α-HSD activities (P < 0.05).

CONCLUSIONS

We found an altered glucocorticoid metabolism suggesting increased production of cortisol by 11β-HSD1 and increased metabolic clearance of cortisol catalyzed by 3α-HSD in girls with central obesity.

Association of the -344T/C polymorphism in aldosterone synthase gene promoter with left ventricular structure in Chinese Han: A meta-analysis

No consensus view has been published on the relationship between the aldosterone synthase gene (CYP11B2) -344C/T polymorphism and left ventricular hypertrophy (LVH) in Chinese Han. We undertook a meta-analysis to investigate the potential association of this polymorphism and left ventricular structure-related phenotypes, including left ventricular mass (LVM), left ventricular mass index (LVMI), left ventricular end systolic diameter (LVESD), left ventricular end diastolic dimension (LVEDD), left ventricular posterior wall thickness (LVPWT), and interventricular septal wall thickness (IVS). Studies in English and Chinese were found based on a systematic search of Medline, Embase, CNKI, and Wanfang databases. The dominant model (TT vs. TC+CC) and homozygote model (TT vs. CC) were selected to examine the association between the -344C/T polymorphism and LVH. The random-effects model was used to pool data. From a total of 3104 participants, despite the investigation of six echocardiographic indicators, we found no significant association between the -344C/T variant and LVH in the whole group and the subgroup analyses by blood pressure. However, in the subgroup of northern Han Chinese, TT genotype had higher LVPWT than CC genotype and TC genotype (p_{heterogeneity} = 0.4, p_value = 0.04, 95% CI 0.09 (0.00, 0.18)). In addition, no evidence of publication bias was observed. In conclusion, our meta-analysis indicated that subjects with TT genotype might have higher risk of developing LVH in northern Han Chinese.

ACTH and Polymorphisms at Steroidogenic Loci as Determinants of Aldosterone Secretion and Blood Pressure

The majority of genes contributing to the heritable component of blood pressure remain unidentified, but there is substantial evidence to suggest that common polymorphisms at loci involved in the biosynthesis of the corticosteroids aldosterone and cortisol are important. This view is supported by data from genome-wide association studies that consistently link the CYP17A1 locus to blood pressure. In this review article, we describe common polymorphisms at three steroidogenic loci (CYP11B2, CYP11B1 and CYP17A1) that alter gene transcription efficiency and levels of key steroids, including aldosterone. However, the mechanism by which this occurs remains unclear. While the renin angiotensin system is rightly regarded as the major driver of aldosterone secretion, there is increasing evidence that the contribution of corticotropin (ACTH) is also significant. In light of this, we propose that the differential response of variant CYP11B2, CYP11B1 and CYP17A1 genes to ACTH is an important determinant of blood pressure, tending to predispose individuals with an unfavourable genotype to hypertension.

Analysis of the Aldosterone Synthase (CYP11B2) and 11β-Hydroxylase (CYP11B1) Genes

The aldosterone synthase (CYP11B2) and 11β-hydroxylase (CYP11B1) enzymes are known to be important players in the development of hypertension. Sequencing of the CYP11B2 and CYP11B1 genes and quantification of their respective mRNAs is greatly complicated by their high degree of sequence similarity. The need to ensure gene specificity during such analysis has required the development of particular methods for the detection of key polymorphisms at these loci, which are detailed in this chapter.

Common Polymorphisms at the CYP17A1 Locus Associate With Steroid Phenotype: Support for Blood Pressure Genome-Wide Association Study Signals at This Locus

Genome-wide association studies implicate the CYP17A1 gene in human blood pressure regulation although the causative polymorphisms are as yet unknown. We sought to identify common polymorphisms likely to explain this association. We sequenced the CYP17A1 locus in 60 normotensive individuals and observed 24 previously identified single-nucleotide polymorphisms with minor allele frequency >0.05. From these, we selected, for further studies, 7 polymorphisms located ≤ 2 kb upstream of the CYP17A1 transcription start site. In vitro reporter gene assays identified 3 of these (rs138009835, rs2150927, and rs2486758) as having significant functional effects. We then analyzed the association between the 7 polymorphisms and the urinary steroid metabolites in a hypertensive cohort (n=232). Significant associations included that of rs138009835 with aldosterone metabolite excretion; rs2150927 associated with the ratio of tetrahydrodeoxycorticosterone to tetrahydrodeoxycortisol, which we used as an index of 17α-hydroxylation. Linkage analysis showed rs138009835 to be the only 1 of the 7 polymorphisms in strong linkage disequilibrium with the blood pressure-associated polymorphisms identified in the previous studies. In conclusion, we have identified, characterized, and investigated common polymorphisms at the CYP17A1 locus that have functional effects on gene transcription in vitro and associate with corticosteroid phenotype in vivo. Of these, rs138009835--which we associate with changes in aldosterone level--is in strong linkage disequilibrium with polymorphisms linked by genome-wide association studies to blood pressure regulation. This finding clearly has implications for the development of high blood pressure in a large proportion of the population and justifies further investigation of rs138009835 and its effects.

Plasma steroid profiling and response to trophins to illustrate intra-adrenal dynamics

The importance of corticosteroids in cardiovascular and other chronic disease is recognised. In addition, plasma steroid precursor-to-product ratios are useful and convenient indirect indicators of efficiency of key steroidogenic enzymes (aldosterone synthase, 11β-hydroxylase and 17α-hydroxylase). The use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) has enabled measurement of numerous corticosteroid compounds simultaneously. However, normal responses to trophins and variation in salt intake are not well described. This study examined these parameters in a large group of healthy volunteers. Sixty normotensive volunteers were recruited and underwent infusion of angiotensin II (AngII) and ACTH, following low- and high-salt diet. Measurement of plasma steroids at baseline and 30 min after infusion of trophin was carried out by LC-MS. As expected, plasma mineralocorticoid levels increased in response to salt restriction and were suppressed with salt loading; ACTH infusion increased all corticosteroids, while AngII increased mineralocorticoids and suppressed glucocorticoid production. ACTH increased S:F but decreased DOC:B, thus the S:F ratio is a more appropriate index of 11β-hydroxylase efficiency. The B:F ratio increased following ACTH treatment and salt restriction. A larger proportion of plasma B than generally accepted may be derived from the zona glomerulosa and this ratio may be most informative of 17α-hydroxylase activity in salt-replete subjects. Although DOC:aldosterone, B:aldosterone and 18-hydroxyB:aldosterone should provide indices of aldosterone synthase efficiency, responses of individual compounds to trophins suggest that none of them accurately reflect this. Based on these data, aldosterone synthase activity is most accurately reflected by aldosterone concentration alone.

Progress in the identification of responsible genes and molecular mechanisms in primary aldosteronism

Aldosterone, the mineralocorticoid hormone, plays an important role in blood regulation. Autonomous secretion of aldosterone is known as primary aldosteronism (PA), the most common cause of secondary hypertension. PA comprises a group of heterogenous disorders which makes their classification and management challenging. With the advent of the genomic era several germline and somatic mutations have been identified that are involved in the pathogenesis of primary aldosteronism. This article will review our current knowledge of the genetic mechanisms of familial hyperaldosterism, somatic mutations in genes encoding electrolyte channels and other potential genetic mechanisms implicated in the dysregulation of aldosterone production from in vitro and animal models. There is potential for novel targeted therapies and diagnosis for subsets of patient. The challenges to achieve them are highlighted in this review.

APEX1 regulation of aldosterone synthase gene transcription is disrupted by a common polymorphism in humans

RATIONALE

The genetic mechanisms underlying hypertension are unclear, but relative aldosterone excess, present in ≈10% of hypertensive patients, is known to be a heritable trait. This phenotype associates with a T/C single nucleotide polymorphism (SNP) at position -344 of the aldosterone synthase gene (CYP11B2). However, deletion of this SNP has no effect on gene transcription. We have identified another T/C SNP at -1651, in tight linkage disequilibrium with the -344 SNP and here investigate its functional effect on CYP11B2 transcription.

OBJECTIVE

We assessed the effect on transcriptional activity of the -1651 T/C SNP in vivo and in vitro and propose the mechanism by which transcriptional activity is altered.

METHODS AND RESULTS

We demonstrated that the SNP at -1651 exerts significant allele-dependent effects on CYP11B2 transcription. We confirm binding of the transcriptional repressor APEX1 to -1651T, which is associated with reduced transcriptional activity in relation to the less strongly bound -1651C. We show that inhibiting APEX1 by small molecule inhibition or small interfering RNA (SiRNA) leads to increased CYP11B2 transcription. In addition, overexpression of APEX1 is associated with reduced transcriptional activity. Finally, we also show that -1651T associates with lower excretion rates of aldosterone metabolites in human subjects.

CONCLUSIONS

We conclude that APEX1 is a novel transcriptional repressor of CYP11B2 and that differential APEX1 binding at -1651 of CYP11B2 results in altered gene expression. This mechanism may contribute to the observed relationship between CYP11B2 genotype and aldosterone phenotype in a subgroup of hypertensive patients.

Common Variation at the 11-β Hydroxysteroid Dehydrogenase Type 1 Gene Is Associated With Left Ventricular Mass

Background—

Polymorphisms in 11-β hydroxysteroid dehydrogenase type 1 (11β-HSD1, encoded by HSD11B1 ) have been reported to be associated with obesity-related cardiovascular risk factors, such as type II diabetes and hypertension. Left ventricular hypertrophy (LVH) is an independent risk factor for cardiovascular death associated with these factors but has significant additional heritability, the cause of which is undetermined. The 11β-HSD1 is believed to maintain tonic inhibition of the mineralocorticoid receptor in cardiomyocytes, and mineralocorticoid receptor activation is involved in the pathophysiology of LVH. We assessed the association between polymorphisms in the HSD11B1 gene and left ventricular mass (LVM) in 248 families ascertained through a proband with hypertension.

Methods and Results—

LVM was measured by electrocardiography and echocardiography in 868 and 829 participants, respectively. Single-nucleotide polymorphisms (SNPs) tagging common variation in the HSD11B1 gene were genotyped by mass spectrometry. The rs846910 SNP, which lies in the flanking region 5′ to exon 1B of HSD11B1 , was associated with LVM both by electrocardiography (≈5% lower LVM per copy of the rare allele, P =0.02) and by echocardiography (≈10% lower LVM per copy of the rare allele, P =0.003). Genotype explained 1% to 2% of the population variability in LVM, or approximately 5% of the heritable fraction. There were no significant associations between any HSD11B1 SNP and blood pressure or body mass index that could have confounded the association with LVM.

Conclusions—

Genotype at HSD11B1 has a small, but significant effect on LVM, apparently independently of any effect on obesity-related traits. These findings suggest a novel action of 11β-HSD1 in the human cardiomyocyte, which may be of therapeutic importance.

Primary aldosteronism: an update

Primary aldosteronism (PA) is common with an estimated prevalence rate of 10% in subjects with essential hypertension and higher in those with resistant hypertension. As well as contributing to hypertension, aldosterone has detrimental effects on the heart, vasculature and kidneys as well as adverse metabolic effects leading to an excess of cardiovascular morbidity. Therefore, recognition and appropriate treatment of PA is of increasing importance. However, the diagnosis of PA and determination of subtype can be problematic. The purpose of this review is to provide an overview of the evidence supporting this increased prevalence of PA, explore the metabolic and cardiovascular consequences of aldosterone excess and discuss optimal diagnostic and therapeutic strategies of PA.

Polymorphisms in CYP11B2 and CYP11B1 genes associated with primary hyperaldosteronism

Several frequent polymorphisms in the CYP11B2 gene are suggested to be associated with essential hypertension and aldosterone secretion. In this study, we investigated the association of polymorphisms in CYP11B2 and CYP11B1 genes with the risk of primary hyperaldosteronism (PH). Three polymorphisms in the CYP11B2 gene (intron 2 conversion, rs1799998 and rs4539) and two polymorphisms in the CYP11B1 gene (rs6410 and rs6387) were analyzed in patients with PH and in the normal population. The rs6410 allelic frequencies in patients with aldosterone-producing adenoma (APA) and idiopathic hyperaldosteronism (IHA) were significantly different from those in controls at P=1.09 x 10(-5) and 0.015, respectively. There was a relative excess of AA homozygotes and AG heterozygotes of the rs6410 allele in the APA group as compared with the control group (P=2.19 x 10(-4)). There were significantly different genotypes, AA and AG, of the rs6410 allele between the patients with IHA and the controls only after adjustments for age, gender and body mass index (odds ratio (OR)=4.06, 95% confidence interval (CI) 1.31-12.66; OR=2.41, 95% CI 1.02-5.72). One susceptible haplotype, AAAWT, was identified to be significantly associated with APA (OR=1.44, 95% CI 1.19-1.76), and three susceptible haplotypes, AAAWT, AGGWT and AGAWC, were identified to be significantly associated with IHA (OR=1.55, 95% CI 1.23-1.96; OR=1.49, 95% CI 1.17-1.89; OR=1.40, 95% CI 1.04-1.88). In contrast, one protective haplotype, GGAWT, showed a significant difference between the patients with APA and controls (OR=0.73, 95% CI 0.55-0.97). Several haplotypes were associated with ARR in both the controls and cases. Our data demonstrated that there was a significant association between polymorphisms in the CYP11B2 and CYP11B1 genes and a genetic predisposition to PH. The association with IHA seemed closer compared with APA.

Plasma corticosteroid profiling: brief opinion of its current status in clinical diagnosis and research

Adrenal steroid biosynthesis comprises a series of dynamically interrelated, enzyme-catalyzed reactions in two separate compartments, the zona glomerulosa and the zona fasciculata/reticularis. End products (cortisol, aldosterone and androgens), together with a proportion of the intermediate compounds, appear in the circulation as a characteristic profile. Rare deficiencies of individual enzymes modify this profile in a recognizable way. Previous exhaustive profiling suggests that their diagnosis can now often be made on the basis of single-compound analyses with concomitant genetic tests. However, high-capacity liquid chromatography coupled with tandem mass spectrometry-based methods are facilitating profiling of large population samples, revealing that smaller differences in enzyme efficiency, indicated by potentially more complex corticosteroid patterns, may be related to clinical wellbeing in a much larger proportion of the population.

Familial and phenotypic associations of the aldosterone Renin ratio

CONTEXT

The aldosterone to renin ratio (ARR) is a marker of aldosterone excess, widely used to screen for primary aldosteronism (PA). The significance of a raised ARR in normotensive and hypertensive subjects and the phenotypic and familial factors affecting it are unclear.

OBJECTIVE

We estimated the distribution and heritability of the ARR and tested for associations between ARR and blood pressure (BP) with 11 polymorphisms at the CYP11B1/CYP11B2 locus.

DESIGN AND SETTING

A total of 1172 individuals from 248 Caucasian families ascertained via a hypertensive proband were evaluated.

MAIN OUTCOME MEASURE

Plasma aldosterone was measured by RIA, and plasma renin concentration was measured by the LIAISON Direct Renin chemiluminescent immunoassay.

RESULTS

Unadjusted and adjusted ARR were continuously distributed in normotensives and hypertensives, with no evidence of a cutoff that would identify a separate population with PA. Median ARR was 4.19 ng/liter per mIU/liter (range, 0.04-253.16). ARR levels were higher in females and associated with age, body mass index, and potassium. Antihypertensive agents had significant predictable effects on the ARR. Renin was negatively associated, and ARR was positively associated with ambulatory BP readings (P < 0.001) in subjects not taking antihypertensives. The heritability of the ARR was 38.1% (P < 10(-8)). Plasma aldosterone, but not ARR, was influenced by the intron 2 conversion variation in the CYP11B2 gene (beta = -0.07; P = 0.04).

CONCLUSIONS

The ARR is continuously distributed, is influenced by genetic and environmental factors, and is not a marker of a distinct pathological abnormality but possibly reflects the long-term influence of aldosterone on cardiovascular homeostasis.

A novel locus for arterial hypertension on chromosome 1p36 maps to a metabolic syndrome trait cluster in the Sorbs, a Slavic population isolate in Germany

OBJECTIVE

Genome-wide linkage studies and genome-wide association studies have not as yet identified major genes contributing to primary hypertension in the general population. This state-of-affairs suggests considerable heterogeneity with small contributing effects for primary hypertension, or other complex genetic traits, in outbred populations. Isolated populations, as recent data from Iceland and French Canada suggest, could offer a solution to this problem.

METHODS

We studied a Slavic isolate in Germany, the Sorbs, and genotyped 1040 polymorphic microsatellite markers in 87 multigeneration families.

RESULTS

Our genome-wide linkage scan revealed a locus on chromosome 1p36.13 at D1S3669-D1S2826 (40.95 cM Marshfield coordinates; logarithm of the odds = 3.45, nominal P = 0.00003) that reached genome-wide significance (P = 0.004), indicating the increased power in isolated populations. The chromosome 1 locus maps to a region in which traits such as diabetes, hyperlipidemia, obesity and BMI cluster.

CONCLUSION

Our results suggest that this locus contributes to the metabolic syndrome, and that further attention in this and other populations is warranted.

Altered corticosteroid biosynthesis in essential hypertension: A digenic phenomenon

Aldosterone plays an important role in electrolyte and blood pressure homeostasis. Our studies have focused on the role of aldosterone in essential hypertension. We have shown that plasma aldosterone and ARR are heritable characteristics and that aldosterone concentrations in older subjects are inversely correlated with birthweight and positively correlated with blood pressure. Aldosterone levels are also associated with polymorphic variation in the CYP11B2 gene, which encodes aldosterone synthase, the enzyme responsible for aldosterone production. Interestingly, CYP11B2 polymorphisms are also associated with less efficient activity of 11beta-hydroxylase, encoded by the neighbouring, highly homologous CYP11B1 gene. We propose that a digenic effect leads to increased aldosterone production, with inefficient 11beta-hydroxylation causing a long-term increase in ACTH drive to the adrenal gland and enhanced expression of CYP11B2, thereby resulting in chronically raised aldosterone secretion in response to factors such as angiotensin II and potassium. In susceptible subjects this is likely, over many years, to result in hypertension with relative aldosterone excess.

Effect of variation in CYP11B1 and CYP11B2 on corticosteroid phenotype and hypothalamic-pituitary-adrenal axis activity in hypertensive and normotensive subjects

BACKGROUND

Aldosterone is important in the development of hypertension. We have shown that a single nucleotide polymorphism (SNP) (-344T) in the 5' regulatory region (UTR) of the gene encoding aldosterone synthase (CYP11B2) associates with aldosterone excess and hypertension as well as altered adrenal 11-hydroxylation efficiency (deoxycortisol to cortisol). This conversion is carried out by the enzyme 11beta-hydroxylase, encoded by the adjacent gene, CYP11B1. We proposed that the effects of CYP11B2 are explained by linkage disequilibrium (LD) across the CYP11B locus. We have demonstrated high LD across this locus and identified two SNPs in the 5' UTR of CYP11B1 (-1859 G/T, -1889 A/G) that associate with reduced transcription in vitro and altered 11-hydroxylation efficiency in vivo. Accordingly, we hypothesized that the reduced adrenal 11-hydroxylation may lead to chronic resetting of the pituitary-adrenal axis, with chronically increased ACTH drive resulting in aldosterone excess.

METHODS

To test this, we examined hypothalamic-pituitary-adrenal (HPA) axis activity in hypertensive and normotensive individuals stratified according to genotype at CYP11B2 (-344T/C) and CYP11B1 (-1859 G/T, -1889 A/G). Fifty-six subjects homozygous for CYP11B2 SNP (27 TT, 12 CC), and 38 homozygous for CYP11B1 SNPs (18 TTGG, 20 GGAA) were recruited. Diurnal variation and the effects of dexamethasone suppression and ACTH stimulation on plasma aldosterone, cortisol and ACTH under controlled conditions were studied.

RESULTS

Subjects with SNPs associated with reduced 11-hydroxylation efficiency (-344T CYP11B2; TTGG CYP11B1) showed reduced inhibition of ACTH after dexamethasone (P = 0.05) and an altered cortisol-ACTH relationship (decreased cortisol-ACTH ratio, P < 0.02). The same individuals also demonstrated close correlations between plasma cortisol and aldosterone (-344T CYP11B2 r = 0.508, P < 0.004; TTGG CYP11B1 r = 0.563, P < 0.003) suggesting that there was common regulation (possibly ACTH) of these hormones in genetically susceptible subjects.

CONCLUSIONS

Variation in CYP11B2 and CYP11B1 associates with chronic up-regulation of the HPA axis. These novel data support the suggestion that chronic aldosterone excess, in genetically susceptible individuals, may be a consequence of increased ACTH drive to the adrenal and identify novel molecular mechanisms that may lead to the development of hypertension within the general population.

Steroid 11beta- hydroxylase deficiency congenital adrenal hyperplasia

Congenital adrenal hyperplasia due to steroid 11beta-hydroxylase deficiency is a genetic disorder of steroidogenesis, transmitted as an autosomal recessive trait. It is associated with low renin hypertension, hypokalemia, hyperandrogenemia and genital ambiguity in affected females. Mutations in the CYP11B1 gene, causing 11beta-hydroxylase deficiency in the zona fasciculata in the adrenal cortex, have been identified. The indicators of congenital adrenal hyperplasia caused by 11beta-hydroxylase deficiency, include increased serum concentrations of desoxycorticosterone, 11 deoxycortisol and delta4-androstenedione, and suppressed plasma renin concentrations. The disorder is treated by administration of glucocorticoids.

A lifetime of aldosterone excess: long-term consequences of altered regulation of aldosterone production for cardiovascular function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Phenotypic consequences of variation across the aldosterone synthase and 11-beta hydroxylase locus in a hypertensive cohort: data from the MRC BRIGHT Study

BACKGROUND

Aldosterone is an important cardiovascular hormone; 15% of hypertensive subjects have alteration in aldosterone regulation, defined by a raised ratio of aldosterone to renin (ARR). Studies of the aldosterone synthase gene (CYP11B2) have focused on a single nucleotide polymorphism in the 5'promoter region (-344 C/T). In normotensive subjects, the T allele associates with raised levels of the 11-deoxysteroids, deoxycorticosterone and 11-deoxycortisol which are substrates for 11beta-hydroxylase, encoded by the adjacent and homologous gene, CYP11B1. We have speculated that this altered 11beta-hydroxylase efficiency leads to increased ACTH drive to the adrenal gland to maintain cortisol production and reported herein the association between the -344 C/T single nucleotide polymorphism (SNP) and adrenal steroid production in subjects with essential hypertension.

METHODS

The CYP11B2-344 C/T polymorphism was genotyped and urinary excretion of adrenal steroid metabolites was measured (by GCMS) in 511 unrelated hypertensives from the Medical Research Council (MRC) British Genetics of Hypertension (BRIGHT) study.

RESULTS

Thirty-five per cent of subjects were homozygous for the -344T allele whilst 16% were CC homozygotes. There was no difference in cortisol excretion rate between the two genotype groups but the index of adrenal 11beta-hydroxylation (ratio of tetrahydrodeoxycortisol/total cortisol) was significantly higher in the TT group (P < 0.005) than in the CC group. Excretion rates of the major urinary metabolite of aldosterone (tetrahydroaldosterone) correlated strongly with the ACTH-regulated steroids, cortisol (r = 0.437, P < 0.0001) and total androgen metabolites (r = 0.4, P < 0.0001) in TT but not CC subjects.

CONCLUSIONS

Hypertensives homozygous for the -344 T allele of CYP11B2 demonstrate altered 11beta-hydroxylase efficiency (CYP11B1); this is consistent with the hypothesis of a genetically determined increase in adrenal ACTH drive in these subjects. The correlation between excretion of aldosterone and cortisol metabolites and suggests that, in TT subjects, ACTH exerts an important common regulatory influence on adrenal corticosteroid production in subjects with hypertension.

A review of the genetics of essential hypertension

PURPOSE OF REVIEW

Essential hypertension affects more than 20% of the adult population, and has a multifactorial origin arising from an interaction between susceptibility genes and environmental factors. Several strategies have been used to identify hypertension susceptibility genes. This review highlights recent efforts in genetic dissection of essential hypertension.

RECENT FINDINGS

Recently, further chromosomal regions harboring blood pressure loci have emerged in genome-wide linkage studies. Findings from a new systematic two-dimensional genome scan are presented, as well as sex-specific loci linked to hypertension in inbred rodent models. Many case-control association studies have been carried out, but results so far have been equivocal. This review discusses some interesting studies combining linkage and association strategies using gene-gene interactions, and studies the use of haplotypes instead of SNPs. Two novel hypertension susceptibility genes are presented, and a short summary on new insights into genes of the renin-angiotensin and adrenergic systems is given.

SUMMARY

To date, linkage and association studies have not been convincing. Genome-wide association studies may prove to be an effective approach to the problems posed by complex traits. Combined with candidate gene approaches, it is hoped this strategy will yield convincing evidence for genes associated with essential hypertension.

Diagnosis and treatment of low-renin hypertension

Plasma renin levels can be used to classify hypertension. A significant proportion of hypertensive individuals display a low-renin profile and thus low-renin hypertension (LRH) requires appropriate diagnosis and treatment. LRH includes essential, secondary and genetic forms, the most common of which are low-renin essential hypertension and primary aldosteronism. Several studies have investigated the relationship between PRA status and clinical response to different antihypertensive therapies. The present review will discuss the differential diagnosis of LRH subtypes and the most appropriate treatment options based on the pathophysiological background of this condition.