Boerwinkle, Eric

We conducted a genome-wide association study to identify novel genes influencing diastolic blood pressure (BP) response to hydrochlorothiazide, a commonly prescribed thiazide diuretic preferred for the treatment of high BP. Affymetrix GeneChip Human Mapping 100K Arrays were used to measure single nucleotide polymorphisms across the 22 autosomes in 194 non-Hispanic black subjects and 195 non-Hispanic white subjects with essential hypertension selected from opposite tertiles of the race- and sex-specific distributions of age-adjusted diastolic BP response to hydrochlorothiazide (25 mg daily, PO, for 4 weeks). The black sample consisted of 97 “good” responders (diastolic BP response [mean±SD]=−18.3±4.2 mm Hg; age=47.1±6.1 years; 51.5% women) and 97 “poor” responders (diastolic BP response=−0.18±4.3; age=47.4±6.5 years; 51.5% women). Haplotype trend regression identified a region of chromosome 12q15 in which haplotypes constructed from 3 successive single nucleotide polymorphisms (rs317689, rs315135, and rs7297610) in proximity to lysozyme ( LYZ ), YEATS domain containing 4 ( YEATS4 ), and fibroblast growth receptor substrate 2 ( FRS2 ) were significantly associated with diastolic BP response (nominal P =2.39×10 −7 ; Bonferroni corrected P =0.024; simulated experiment-wise P =0.040). Genotyping of 35 additional single nucleotide polymorphisms selected to “tag” linkage disequilibrium blocks in these genes provided corroboration that variation in LYZ and YEATS4 was associated with diastolic BP response in a statistically independent data set of 291 black subjects and in the sample of 294 white subjects. These results support the use of genome-wide association analyses to identify novel genes influencing antihypertensive drug responses.

Background and Purpose— Genetic factors that influence interindividual variation in levels of plasma homocysteine, a risk factor for vascular disease, are not fully understood. We performed linkage analyses to identify genomic regions that influence homocysteine levels in blacks and non-Hispanic whites. Methods— Subjects (n=2283) belonged to hypertensive sibships and included 1319 blacks (63±10 years, 70% women) and 964 non-Hispanic whites (61±7 years, 57% women). Fasting plasma homocysteine was measured by high-pressure liquid chromatography. Genotypes were measured at 366 microsatellite marker loci distributed across the 22 autosomes. Plasma homocysteine adjusted for age, sex, body mass index, serum creatinine, and estrogen use (in women) was used in the genetic analyses. Heritability and linkage analyses were performed using a variance components approach. Results— Mean (±SD) homocysteine levels were 10.4±5.27 μmol/L in blacks and 10.0±2.84 μmol/L in non-Hispanic whites ( P =0.58 for difference). Homocysteine levels were significantly ( P <0.0001) heritable in blacks ( h 2 =0.70) and in non-Hispanic whites ( h 2 =0.49). Linkage analyses demonstrated significant evidence of linkage (multipoint logarithm of odds≥3.0) for homocysteine on chromosomes 1q42, 14q32, and 19p13 in blacks and on chromosomes 9q34 and 12q24 in non-Hispanic whites. Tentative evidence of linkage (logarithm of odds 1.3 to 2.0) was present on chromosomes 2q32, 7p15, 8q24, 18q21, and 20p12 in blacks and chromosomes 6q26 and 18q21 in non-Hispanic whites. Four genes in the homocysteine metabolism pathway ( MTR , DNMT1 , GAMT , and CARM1 ) were present under 2 of the significant linkage signals in blacks (chromosomes 1q42 and 19p13). Conclusions— Plasma homocysteine is a significantly heritable trait. Linkage analyses reveal several unique genomic loci that may influence circulating levels of homocysteine and therefore susceptibility to vascular diseases including stroke.

Single nucleotide polymorphisms (SNPs) in genes encoding or influencing renal sodium transport systems were investigated as potential predictors of blood pressure (BP) response to a thiazide diuretic. A sample of 585 adults with essential hypertension (30 to 59.9 years of age; 50% blacks; 47% women) were treated with hydrochlorothiazide for 4 weeks (25 mg daily, orally) to determine office BP responses. Ambulatory BP responses were measured in a subset of 228 subjects. After adjustment for ethnicity, sex, age, and waist-to-hip ratio, 3 SNPs in WNK1 (rs2107614, rs2277869, and rs1159744), encoding a lysine-deficient protein kinase that regulates thiazide-sensitive sodium-potassium cotransport, made statistically significant contributions to predicting ambulatory BP responses, accounting for 2% to 4% of variation in systolic and diastolic responses ( P <0.05). SNPs in the β 2 -adrenoceptor (rs2400707) and the epithelial sodium channel γ-subunit (rs5723 and rs5729) were associated with similar magnitude of variation in ambulatory systolic BP response ( P =0.028) or office diastolic BP response ( P <0.05), respectively. However, SNPs evaluated in the furosemide-sensitive sodium-potassium chloride cotransporter, potassium inwardly rectifying channel, chloride channel, thiazide-sensitive sodium chloride cotransporter, epithelial sodium channel β-subunit, and the mineralocorticoid receptor were not associated with significant variation in ambulatory or office BP responses. Polymorphisms in genes regulating renal sodium transport, in particular WNK1 , predict interindividual differences in antihypertensive responses to hydrochlorothiazide.

We measured 366 microsatellite markers genome-wide to search for loci contributing to subcortical white matter ischemic damage (leukoariosis) and brain atrophy in 488 non-Hispanic white subjects (193 men, 295 women; mean age±SD=64.1±7.7 years; 79% hypertensive) from 223 sibships recruited through ≥2 members with essential hypertension diagnosed before age 60. Leukoariosis was quantitated by magnetic resonance imaging (MRI), brain atrophy by the difference between intracranial and brain volumes, and calculated mean arterial pressure and pulse pressure provided measures of steady-state level and pulsatile components of blood pressure. After adjustment for sex and age, variance components models estimated significant heritability of leukoariosis (0.72), brain atrophy (0.52), mean arterial pressure (0.084), and pulse pressure (0.294) ( P <0.0001 for each trait). Univariate maximum logarithm of odds scores (MLS) were observed for leukoariosis on chromosome 5 (MLS=1.91; P =0.00150); for brain atrophy on 1q and 17p (MLS=2.76, P =0.00018); for mean arterial pressure on 11p (MLS=1.57; P =0.00354); and for pulse pressure on 11p (MLS=3.02; P =0.00070). Bivariate linkage analyses provided evidence of loci with pleiotropic effects on brain atrophy and pulse pressure on chromosomes 11p (MLS = 5.07 at 16 cM; P =0.00001) and 16q (MLS of 4.56 at 124 cM; P =0.00003). These results demonstrate usefulness of multivariate linkage analyses to detect loci with pleiotropic effects on genetically correlated traits and suggest overlap between the genes influencing blood pressure and those contributing to brain atrophy.

Few studies have investigated whether ethnic groups differ in the prevalence of peripheral arterial disease (PAD). We compared the distribution of the ankle-brachial index (ABI), a measure of PAD, between African Americans and non-Hispanic white individuals. Subjects (n = 931) belonged to the Genetic Epidemiology Network of Arteriopathy (GENOA) study, a community-based study of hypertensive sibships, and included 453 African Americans from Jackson, Mississipi (mean age 72 6 years, 69% women) and 478 non-Hispanic white individuals from Rochester, Minnesota (mean age 58 7 years, 64% women). ABI was determined at two sites in each lower extremity and the lowest of four indices was used in the analyses. PAD was defined as an ABI of 0.95. Information about conventional risk factors was derived from interviews and from blood samples drawn at the study visit. The prevalence of diabetes and hypertension was significantly higher in African Americans than in non-Hispanic white individuals. After adjusting for age, African American subjects had a lower mean ABI (women 0.97 vs 1.04, p < 0.001; men 0.96 vs 1.12, p < 0.001) and a greater prevalence of PAD (women 34% vs 22%, p = 0.010; men 33% vs 11%, p < 0.001) than their non-Hispanic white counterparts. In multiple regression analyses, African American ethnicity was a predictor of a lower ABI and the presence of PAD in each sex after adjusting for age and other conventional risk factors. In conclusion, the lower ABI and greater prevalence of PAD in African Americans than in non-Hispanic white individuals is not explained by differences in conventional risk factors. Identifying additional ‘novel’ risk factors that account for the ethnic differences in PAD is an important next step towards understanding why such differences exist and developing more effective strategies to reduce the burden of PAD.

Ischemic damage to the subcortical white matter of the brain, referred to as leukoaraiosis, is a frequent complication of hypertension-related microvascular disease and contributes to the risk of stroke and vascular dementia. A large genetic contribution to this late-life form of target organ damage was suggested by a study of elderly male twins. As part of the Genetic Epidemiology Network of Arteriopathy (GENOA), 483 non-Hispanic white subjects were recruited to undergo MRI for determination of the brain volume of leukoaraiosis (291 women and 192 men from 210 sibships providing 434 sibling pairs; mean age±SD=65.2±7.3 years). The GENOA–Rochester sibships contain 2 or more siblings with essential hypertension diagnosed before age 60. The frequency distribution of the volume of leukoaraiosis was positively skewed, with a median value of 6.61 cm 3 (interquartile range: 4.77 to 9 0.83 cm 3 ). Variance component models were used to estimate the heritability (ie, the proportion of phenotypic variation caused by additive genetic factors). After logarithm transformation of the volume of leukoaraiosis, the estimated heritability (±SE) was 0.802±0.102 ( P <0.0001). Adjustments for sex, age, systolic blood pressure, and brain volume reduced the heritability estimate to 0.671±0.110 ( P <0.0001). This evidence of strong genetic influence on the susceptibility to leukoaraiosis justifies efforts to localize the responsible genes and characterize the predisposing genetic polymorphisms.

Background and Purpose— Hypertension is an important risk factor for stroke, and the 2 diseases may share susceptibility genes in common. We sought to identify genomic regions influencing susceptibility to both hypertension and stroke. Subjects and Methods— Genome-wide linkage scans were performed in samples of 338 white and 265 black hypertensive sibships recruited by the Genetic Epidemiology Network of Arteriopathy Study of the NHLBI Family Blood Pressure Program (FBPP). The hypertensive sibships were stratified by positive (+FH) or negative (−FH) family history of stroke. Genome-wide scans were repeated in each stratum, and the results were compared within each ethnic group by a regression-based analysis of heterogeneity. Results— In whites, the best evidence for linkage was found on chromosome 16 in the unstratified sample of hypertensive sibpairs (logarithm of odds [LOD]=1.85 at 71 cM). In blacks, the best evidence for linkage was found on chromosome 2 in the unstratified sample of hypertensive sibpairs (LOD=1.95 at 230 cM). Additional evidence for linkage (LOD ≥1.5) was observed among white hypertensive sibpairs with a −FH on chromosome 13 and among black hypertensive sibpairs with a +FH of stroke on chromosome 19. Conclusions— Significant evidence for linkage heterogeneity among hypertensive sibpairs stratified by family history of stroke suggests the presence of genes influencing susceptibility to both hypertension and stroke on chromosomes 13 (whites) and 19 (blacks). Although no significant evidence of heterogeneity was observed on chromosome 16 in whites and chromosome 2 in blacks, these chromosomes do provide evidence of linkage to hypertension.

Abstract— Coronary artery disease (CAD) is the leading cause of mortality in the developed world. Although several CAD risk factors, including measures of lipid metabolism, obesity, and blood pressure, have a genetic basis, many genes for CAD susceptibility have yet to be identified. Coronary atherosclerosis is the major cause of CAD, but many with coronary atherosclerosis lack symptoms. Thus, a major limitation of using symptomatic CAD endpoints (eg, sudden coronary death, myocardial infarction) as a study outcome is substantial disease misclassification. Coronary artery calcification (CAC) is part of the atherosclerotic process and is an independent predictor of CAD endpoints. In the present study, CAC was noninvasively quantified by electron beam computed tomography. We performed genome-wide multipoint mode-of-inheritance-free linkage analysis on affected sib pairs, defined as being ≥ the 70th sex- and age-specific percentile for CAC quantity, in a sample of 29 families enriched for hypertension. Almost 95% of participants were asymptomatic for CAD. Our LOD score (log 10 odds in favor of linkage) results provide evidence that chromosomal regions 6p21.3 (maximum LOD score=2.22, P =0.00070) and 10q21.3 (maximum LOD score=3.24, P =0.000057) may harbor genes associated with subclinical coronary atherosclerosis.