Alan B. Weder

Patterns of single-nucleotide polymorphisms in candidate genes for blood-pressure homeostasis

Sequence variation in human genes is largely confined to single-nucleotide polymorphisms (SNPs) and is valuable in tests of association with common diseases and pharmacogenetic traits. We performed a systematic and comprehensive survey of molecular variation to assess the nature, pattern and frequency of SNPs in 75 candidate human genes for blood-pressure homeostasis and hypertension. We assayed 28 Mb (190 kb in 148 alleles) of genomic sequence, comprising the 5´ and 3´ untranslated regions (UTRs), introns and coding sequence of these genes, for sequence differences in individuals of African and Northern European descent using high-density variant detection arrays (VDAs). We identified 874 candidate human SNPs, of which 22% were confirmed by DNA sequencing to reveal a discordancy rate of 21% for VDA detection. The SNPs detected have an average minor allele frequency of 11%, and 387 are within the coding sequence (cSNPs). Of all cSNPs, 54% lead to a predicted change in the protein sequence, implying a high level of human protein diversity. These protein-altering SNPs are 38% of the total number of such SNPs expected, are more likely to be population-specific and are rarer in the human population, directly demonstrating the effects of natural selection on human genes. Overall, the degree of nucleotide polymorphism across these human genes, and orthologous great ape sequences, is highly variable and is correlated with the effects of functional conservation on gene sequences.

A BDNF Coding Variant Is Associated with the NEO Personality Inventory Domain Neuroticism, a Risk Factor for Depression

, but with traits, such as personality factors, that are themselves associated with risk for the disorder (Lander and Schork, 1994; Stolten-berg and Burmeister, 2000). Often such traits have a higher heritability than the disease status (Almasy and Blangero, 2001). Neuroticism, as measured by the NEO personality inventory (NEO-PI) (Costa and McCrae, 1997), a psycho-metrically sound and widely used instrument, is one such trait. High scorers on the Neuroticism domain are char-acterized by frequent experience of “negative emotional-ity” such as anxiety, low mood, and hostility. Converging lines of evidence point to brain-derived neurotrophic fac-tor (BDNF) as a factor in the pathophysiology of depres-sion. To explore the possibility that variation in the BDNF gene is, in part, responsible for the population variation in Neuroticism, we studied a community sample of 441 sub-jects, genotyping a G→A single-nucleotide polymorphism (SNP) responsible for a valine→methionine substitution in the prodomain of BDNF. The less common, nonconserved Met allele was associated with significantly lower mean Neuroticism scores (

Whole-genome association study identifies STK39 as a hypertension susceptibility gene

Hypertension places a major burden on individual and public health, but the genetic basis of this complex disorder is poorly understood. We conducted a genome-wide association study of systolic and diastolic blood pressure (SBP and DBP) in Amish subjects and found strong association signals with common variants in a serine/threonine kinase gene, STK39. We confirmed this association in an independent Amish and 4 non-Amish Caucasian samples including the Diabetes Genetics Initiative, Framingham Heart Study, GenNet, and Hutterites (meta-analysis combining all studies: n = 7,125, P < 10−6). The higher BP-associated alleles have frequencies > 0.09 and were associated with increases of 3.3/1.3 mm Hg in SBP/DBP, respectively, in the Amish subjects and with smaller but consistent effects across the non-Amish studies. Cell-based functional studies showed that STK39 interacts with WNK kinases and cation-chloride cotransporters, mutations in which cause monogenic forms of BP dysregulation. We demonstrate that in vivo, STK39 is expressed in the distal nephron, where it may interact with these proteins. Although none of the associated SNPs alter protein structure, we identified and experimentally confirmed a highly conserved intronic element with allele-specific in vitro transcription activity as a functional candidate for this association. Thus, variants in STK39 may influence BP by increasing STK39 expression and consequently altering renal Na+ excretion, thus unifying rare and common BP-regulating alleles in the same physiological pathway.

Admixture mapping for hypertension loci with genome-scan markers

Identification of genetic variants that contribute to risk of hypertension is challenging. As a complement to linkage and candidate gene association studies, we carried out admixture mapping using genome-scan microsatellite markers among the African American participants in the US National Heart, Lung, and Blood Institutes Family Blood Pressure Program. This population was assumed to have experienced recent admixture from ancestral groups originating in Africa and Europe. We used a set of unrelated individuals from Nigeria to represent the African ancestral population and used the European Americans in the Family Blood Pressure Program to provide estimates of allele frequencies for the European ancestors. We genotyped a common set of 269 microsatellite markers in the three groups at the same laboratory. The distribution of marker location–specific African ancestry, based on multipoint analysis, was shifted upward in hypertensive cases versus normotensive controls, consistent with linkage to genes conferring susceptibility. This shift was largely due to a small number of loci, including five adjacent markers on chromosome 6q and two on chromosome 21q. These results suggest that chromosome 6q24 and 21q21 may contain genes influencing risk of hypertension in African Americans.

Sex-specific determinants of increased left ventricular mass in the Tecumseh Blood Pressure Study.

BackgroundLeft ventricular hypertrophy (LVH) defined by either ECG or echocardiographic criteria is a risk factor for cardiovascular morbidity and mortality. A number of determinants of LVH have been described in previous studies, principally male sex, hypertension, obesity, and aortic valvular stenosis. We examined the distribution of LV mass (LVM) in a population of 18- to 42-year-old normotensive men and women who were free of valvular heart disease to establish sex-specific normal values for LVM index (LVMI) and to determine the correlates of LVMI. Methods and ResultsLVM was derived from measurements obtained by M-mode echocardiography. Average LVMI is significantly greater in men (102.9±0.7 g/m2) than women (88.2±0.7 g/m2). By defining LVH as an LVMI greater than the 90th percentile, we developed sex-specific criteria for LVH: men, >125.4 g/m2; women, >110 g/m2. We found that LVH in men is associated with indices of enhanced sympathetic nervous system reactivity and with elevated fasting insulin and triglyceride levels, which may be caused by insulin resistance. In women, LVH was associated with higher body weight and obesity. ConclusionsBefore the onset of hypertension, increased LVMI appears to have different determinants in men and women. We suggest that early LVH in young men is a manifestation of hyperkinetic borderline hypertension, a state previously shown to be associated with increased sympathetic nervous system activity and insulin resistance. The hyperkinetic state is less prevalent in young women, in whom increased adiposity seems to be the predominant factor associated with LVH.

Chlorthalidone Reduces Cardiovascular Events Compared With Hydrochlorothiazide A Retrospective Cohort Analysis

There is significant controversy around whether chlorthalidone (CTD) is superior to hydrochlorothiazide (HCTZ) in hypertension management. The objective of this analysis was to evaluate the effects of CTD compared with HCTZ on cardiovascular event (CVE) rates. We performed a retrospective observational cohort study from the Multiple Risk Factor Intervention Trial data set from the National Heart, Lung, and Blood Institute. The Multiple Risk Factor Intervention Trial was a cardiovascular primary prevention trial where participants were men 35 to 57 years of age enrolled and followed beginning in 1973. CVEs were measured yearly, and time to event was assessed by Cox regression. Systolic blood pressure, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglyceride, potassium, glucose, and uric acid were measured yearly. The difference between groups was evaluated by repeated-measures mixed modeling, and each model was adjusted for predictors of each variable. CVEs were significantly lower in those on CTD (adjusted hazard ratio: 0.51 [95% CI: 0.43 to 0.61]; P<0.0001) and on HCTZ (adjusted hazard ratio: 0.65 [95% CI: 0.55 to 0.75]; P<0.0001) compared with those who took neither drug. When comparing the 2 drugs, CTD had significantly fewer CVEs compared with HCTZ (P=0.0016). CTD displayed significantly lower SBP (P<0.0001), lower total cholesterol (P<0.0001), lower low-density lipoprotein cholesterol (P=0.0009), lower potassium (P=0.0003), and higher uric acid (P<0.0001) over time compared with HCTZ. In conclusion, both HCTZ and CTD reduce CVEs compared with neither drug. When comparing both drugs, CTD reduces CVEs more than HCTZ, suggesting that CTD may be the preferred thiazide-type diuretic for hypertension in patients at high risk of CVEs.

Normal limits in relation to age, body size and gender of two-dimensional echocardiographic aortic root dimensions in persons >15 years of age

Nomograms to predict normal aortic root diameter for body surface area (BSA) in broad ranges of age have been widely used but are limited by lack of consideration of gender effects, jumps in upper limits of aortic diameter among age strata, and data from older teenagers. Sinus of Valsalva diameter was measured by American Society of Echocardiography convention in normal-weight, nonhypertensive, nondiabetic subjects ≥15 years old without aortic valve disease from clinical or population-based samples. Analyses of covariance and linear regression with assessment of residuals identified determinants and developed predictive models for normal aortic root diameter. In 1,207 apparently normal subjects ≥15 years old (54% women), aortic root diameter was 2.1 to 4.3 cm. Aortic root diameter was strongly related to BSA and height (r = 0.48 for the 2 comparisons), age (r = 0.36), and male gender (+2.7 mm adjusted for BSA and age, p <0.001 for all comparisons). Multivariable equations using age, gender, and BSA or height predicted aortic diameter strongly (R = 0.674 for the 2 comparisons, p <0.001) with minimal relation of residuals to age or body size: for BSA 2.423 + (age [years] × 0.009) + (BSA [square meters] × 0.461) - (gender [1 = man, 2 = woman] × 0.267), SEE 0.261 cm; for height 1.519 + (age [years] × 0.010) + (height [centimeters] × 0.010) - (gender [1 = man, 2 = woman] × 0.247), SEE 0.215 cm. In conclusion, aortic root diameter is larger in men and increases with body size and age. Regression models incorporating body size, age, and gender are applicable to adolescents and adults without limitations of previous nomograms.

Serotonin Transporter and GABA(A) Alpha 6 Receptor Variants Are Associated with Neuroticism

BACKGROUND A tendency to experience negative affect, as measured by the neuroticism component of the Neuroticism, Extraversion, and Openness Personality Inventory (NEO-PI), is a trait marker for major depression. Epidemiologic studies indicate a strong genetic component, but to date few specific genetic variants have been definitively implicated. A serotonin transporter promoter polymorphism (5-HTTLPR) has been extensively studied in neuroticism and several psychiatric disorders, with inconclusive results. A GABA(A) receptor alpha6 subunit variant (Pro385Ser) has been associated with alcohol-related traits but has not been studied in neuroticism or depression. METHODS A total of 384 subjects who completed the NEO-PI were genotyped at 5-HTTLPR and Pro385Ser. Associations between polymorphisms and both alcohol use and personality domains were tested. RESULTS The 5-HTTLPR short allele (p =.008) and Pro385Ser Pro allele (p =.003) are associated with higher neuroticism scores. The 5-HTTLPR long allele (p =.006), but not Pro385Ser, is also associated with an increased presence of alcohol use. In addition, there is a nonsignificant suggestion of an interaction: the effect of 5-HTTLPR on neuroticism might be dependent on the Pro385Ser genotype. CONCLUSIONS These findings support a role for the serotonin transporter and GABA(A) alpha6 subunit in depression-related traits.

Associations Between Hypertension and Genes in the Renin-Angiotensin System

Abstract—The genes of the renin-angiotensin system have been subjected to intense molecular scrutiny in cardiovascular disease studies, but their contribution to risk is still uncertain. In this study, we sampled 192 African American and 153 European American families (602 and 608 individuals, respectively) to evaluate the contribution of variations in genes that encode renin-angiotensin system components of susceptibility to hypertension. We genotyped 25 single-nucleotide polymorphisms in the renin-angiotensin system genes ACE, AGT, AGTR1, and REN. The family-based transmission/disequilibrium test was performed with each single-nucleotide polymorphism and with the multilocus haplotypes. Two individual single-nucleotide polymorphisms were significantly associated with hypertension among African Americans, and this result persisted when both groups were combined. The associations were confirmed in haplotype analysis for REN, AGTR1, and ACE in African Americans. Consistent but less significant evidence was found in European Americans. We also randomly sampled unrelated individuals across families to obtain 84 cases and 108 controls among the African Americans and 41 cases and 113 controls in the European Americans. Single-nucleotide polymorphism and haplotype analyses again showed consistent, albeit weaker, results. Thus, in this biracial population sample, we find evidence that interindividual variation in the renin-angiotensin system genes contributes to hypertension risk.

Influence of Race and Dietary Salt on the Antihypertensive Efficacy of an Angiotensin-Converting Enzyme Inhibitor or a Calcium Channel Antagonist in Salt-Sensitive Hypertensives

Dietary salt restriction is a recommended adjunct with antihypertensive therapy. There may be racial differences in blood pressure response to salt restriction while on antihypertensive therapy. We performed a multicenter, randomized, double-blind, placebo-controlled, parallel-group clinical trial (black, n=96; Hispanic, n=63; white, n=232). Participants were initially preselected for stage I to III hypertension and then further selected for salt sensitivity (> or = 5 mm Hg increase in diastolic blood pressure after 3 weeks of low salt [< or = 88 mmol/d Na+] and high salt [>190 mmol/d Na+] diet). We compared the antihypertensive effect of an angiotensin-converting enzyme inhibitor (enalapril 5 or 20 mg BID) or a calcium channel antagonist (isradipine 5 or 10 mg BID) during alternating periods of high and low salt intake. The main outcome measure was blood pressure change and absolute blood pressure level achieved with therapy. During the high salt diet (314.7+/-107.5 mmol/d urinary Na+) there was greater downward change in blood pressure with both enalapril and isradipine compared with the low salt diet (90.1+/-50.8 mmol/d Na+); however, the absolute blood pressure achieved in all races was consistently lower on a low salt diet for both agents. Black, white, and Hispanic isradipine-treated salt-sensitive hypertensives demonstrated a smaller difference between high and low salt diets (black, -3.6/-1.6 mmHg; white, -6.2/-3.9 mmHg; Hispanic, -8.1/-5.3 mm Hg) than did enalapril-treated patients (black, -9.0/-5.3 mm Hg; white, -11.8/-7.0 mm Hg; Hispanic, -11.1/-5.6 mm Hg). On the low salt diet, blacks, whites, and Hispanics had similar blood pressure control with enalapril and isradipine. On the high salt diet, blacks had better blood pressure control with isradipine than with enalapril, whereas there was no difference in the blood pressure control in whites and Hispanics treated with either drug. Dietary salt reduction helps reduce blood pressure in salt-sensitive hypertensive blacks, whites, and Hispanics treated with enalapril or isradipine. These data demonstrate that controlling for salt sensitivity diminishes race-related differences in antihypertensive activity.