Genetic influences on aortic root size in American Indians: the Strong Heart Study

Ethnic Difference in Proximal Aortic Stiffness: An Observation From the Dallas Heart Study

OBJECTIVES

This study aims to compare ethnic difference in proximal aortic pulse wave velocity (PWV) and characteristic impedance (Zc).

BACKGROUND

Increased aortic stiffness is an independent predictor of target organ damage, incident hypertension, and all-cause mortality. However, previous studies have not directly assessed proximal aortic function in Blacks, the ethnic population with disproportionately high risk for incident hypertension and target organ complications.

METHODS

We evaluated the multiethnic, population-based DHS (Dallas Heart Study) participants (N = 2,544, 54.2% women, 49.7% Black) who underwent cardiac magnetic resonance at 1.5-T. Aortic stiffness and Zc were determined from aortic arch PWV and lumen area measurements. Linear regression was used to evaluate ethnic differences in proximal aortic wall stiffness using aortic arch PWV and Zc as dependent variables with and without adjustment for traditional cardiovascular risk factors. Because cardiac output was significantly higher in Blacks compared to Whites and Hispanics, additional comparisons of PWV and Zc were performed after adjustment for cardiac output and peripheral vascular resistance.

RESULTS

Compared with Whites, both Blacks and Hispanics had higher levels of aortic arch PWV (4.25, 95% confidence interval [CI]: 4.15 to 4.35 m/s, vs. 4.72, 95% CI: 4.64 to 4.81 m/s, vs. 4.48, 95% CI: 4.33 to 4.63 m/s, respectively, both p < 0.05 vs. White), and Zc (64.9, 95% CI: 63.3 to 66.6 dyne·s/cm⁵, vs. 75.6, 95% CI: 74.0 to 77.2 dyne·s/cm⁵, vs. 70.1, 95% CI: 67.6 to 72.8 dyne·s/cm⁵, respectively, both p < 0.01 vs. White) after adjustment for age, age squared, sex, body mass index, height, mean arterial blood pressure, antihypertensive treatment, heart rate, total cholesterol, diabetes mellitus, and smoking. Compared with Hispanics, Blacks also had higher level of both PWV and Zc (both p < 0.01). Ethnic differences in PWV and Zc persisted after adjustment for cardiac output and peripheral vascular resistance.

CONCLUSIONS

In a multiethnic population-based-sample, Blacks and Hispanics had higher proximal aortic stiffness compared with Whites independent of blood pressure and relevant risk factors.

Aortic root dimensions are predominantly determined by genetic factors: a classical twin study

OBJECTIVES

Previous studies using transthoracic echocardiography (TTE) observed moderate heritability of aortic root dimensions. Computed tomography angiography (CTA) might provide more accurate heritability estimates. Our primary aim was to assess the heritability of the aortic root with CTA. Our secondary aim was to derive TTE-based heritability and compare this with the CTA-based results.

METHODS

In the BUDAPEST-GLOBAL study 198 twin subjects (118 monozygotic, 80 dizygotic; age 56.1 ± 9.4 years; 126 female) underwent CTA and TTE. We assessed the diameter of the left ventricular outflow tract (LVOT), annulus, sinus of Valsalva, sinotubular junction and ascending aorta. Heritability was assessed using ACDE model (A additive genetic, C common environmental, D dominant genetic, E unique environmental factors).

RESULTS

Based on CTA, additive genetic effects were dominant (LVOT: A = 0.67, E = 0.33; annulus: A = 0.76, E = 0.24; sinus of Valsalva: A = 0.83, E = 0.17; sinotubular junction: A = 0.82, E = 0.18; ascending aorta: A = 0.75, E = 0.25). TTE-derived measurements showed moderate to no genetic influence (LVOT: A = 0.38, E = 0.62; annulus: C = 0.47, E = 0.53; sinus of Valsalva: C = 0.63, E = 0.37; sinotubular junction: C = 0.45, E = 0.55; ascending aorta: A = 0.67, E = 0.33).

CONCLUSION

CTA-based assessment suggests that aortic root dimensions are predominantly determined by genetic factors. TTE-based measurements showed moderate to no genetic influence. The choice of measurement method has substantial impact on heritability estimates.

KEY POINTS

• Aortic root dimensions are determined by genetic and environmental effects. • Transthoracic echocardiography (TTE) demonstrated moderate to no genetic effects on aortic root dimensions. • Computed tomography angiography might provide more accurate heritability estimates compared to TTE. • Three-dimensional imaging techniques are needed to reliably quantify aortic root dimensions.

Out of proportion proximal aortic remodeling: A subclinical marker of early vascular ageing? A systematic review

INTRODUCTION

Proximal aorta stiffens and dilates with aging. Aortic stiffening is a well known process, carrying prognostic implications. On the contrary, few data are available about proximal aorta dilatation. It is not known if "out of proportion" aortic remodeling, i.e. in excess for age, sex and body size, could be a marker of early vascular ageing; there is controversy on how it would be accelerated by classical risk factors or would associate with validated markers of cardiovascular organ damage.

AIM

We conducted a systematic review in order to evaluate the determinants of proximal aortic dimensions, focusing on the association with arterial hypertension, cardiovascular risk factors and markers of organ damage.

DETERMINANTS OF PROXIMAL AORTA REMODELING

Age, gender and body size explain 40-50% of the variability of aortic dimensions; genetic predisposition accounts for nearly 20%. Among cardiovascular risk factors obesity and hypertension seem to be associated with faster outward aortic remodeling. Arterial hypertension would account for a 0.60-0.78 mm greater diameter at the ascending aorta. Moreover, in hypertension, left ventricular mass showed a strict association with aortic diameter in nearly all studies. Other classical risk factors for atherogenesis such as dyslipidemia and smoking showed a weak influence on proximal aortic dimensions. No study reported a greater aortic remodeling in diabetics.

CONCLUSIONS

"Out of proportion" proximal aortic remodeling, could represent a subclinical marker of early vascular ageing, describing the cumulative influence of genetic predisposition, arterial hypertension and obesity.

Genetic and Environmental Effects on the Abdominal Aortic Diameter Development

Background

Configuration of the abdominal aorta is related to healthy aging and a variety of disorders.

Objectives

We aimed to assess heritable and environmental effects on the abdominal aortic diameter.

Methods

114 adult (69 monozygotic, 45 same-sex dizygotic) twin pairs (mean age 43.6 ± 16.3 years) underwent abdominal ultrasound with Esaote MyLab 70X ultrasound machine to visualize the abdominal aorta below the level of the origin of the renal arteries and 1-3 cm above the bifurcation.

Results

Age- and sex-adjusted heritability of the abdominal aortic diameter below the level of the origin of the renal arteries was 40% [95% confidence interval (CI), 14 to 67%] and 55% above the aortic bifurcation (95% CI, 45 to 70%). None of the aortic diameters showed common environmental effects, but unshared environmental effects were responsible for 60% and 45% of the traits, respectively.

Conclusions

Our analysis documents the moderate heritability and its segment-specific difference of the abdominal aortic diameter. The moderate part of variance was explained by unshared environmental components, emphasizing the importance of lifestyle factors in primary prevention. Further studies in this field may guide future gene-mapping efforts and investigate specific lifestyle factors to prevent abdominal aortic dilatation and its complications.

The Influence of Known Genetic Variants on Subclinical Cardiovascular Outcomes in Childhood

Background—

Genome-wide association studies have identified single-nucleotide polymorphisms (SNPs) for subclinical cardiovascular outcomes in adults. We examined the influence of these variants on the same outcomes in childhood.

Methods and Results—

In a population-based prospective cohort study among 4137 children, we examined the associations of SNPs, individually and incorporated in genetic risk scores, which were identified in adults for cardiac (2 SNPs for left ventricular end-diastolic diameter and 5 SNPs for aortic root diameter) and blood pressure outcomes (29 SNPs for systolic and diastolic blood pressure, 22 SNPs for mean arterial pressure, and 10 SNPs for pulse pressure) with the same outcomes in children (median age of 6.0 years [95% range, 4.5–8.7]). Weighted and unweighted risk scores for aortic root diameter were associated with childhood aortic root diameter (difference per additional average risk allele 0.09 mm [95% CI: 0.05, 0.13]). Weighted and unweighted risk scores for pulse pressure were associated with childhood pulse pressure (difference per additional average risk allele 0.22 mm Hg [95% CI: 0.08, 0.35] and 0.18 mm Hg [95% CI: 0.05, 0.31], respectively), but not with childhood systolic or diastolic blood pressure or mean arterial pressure. The risk scores for blood pressure and mean arterial pressure were not associated with any of the childhood blood pressure outcomes.

Conclusions—

Genetic risk scores based on SNPs for aortic root diameter and pulse pressure in adults are associated with the same outcomes in children. SNPs related to cardiovascular outcomes in adulthood at least partly influence cardiovascular development from early life onwards.

TGFβRIIb mutations trigger aortic aneurysm pathogenesis by altering transforming growth factor β2 signal transduction

BACKGROUND

Thoracic aortic aneurysm (TAA) is a common progressive disorder involving gradual dilation of the ascending and/or descending thoracic aorta that eventually leads to dissection or rupture. Nonsydromic TAA can occur as a genetically triggered, familial disorder that is usually transmitted in a monogenic autosomal dominant fashion and is known as familial TAA. Genetic analyses of families affected with TAA have identified several chromosomal loci, and further mapping of familial TAA genes has highlighted disease-causing mutations in at least 4 genes: myosin heavy chain 11 (MYH11), α-smooth muscle actin (ACTA2), and transforming growth factor β receptors I and II (TGFβRI and TGFβRII).

METHODS AND RESULTS

We evaluated 100 probands to determine the mutation frequency in MYH11, ACTA2, TGFβRI, and TGFβRII in an unbiased population of individuals with genetically mediated TAA. In this study, 9% of patients had a mutation in one of the genes analyzed, 3% of patients had mutations in ACTA2, 3% in MYH11, 1% in TGFβRII, and no mutations were found in TGFβRI. Additionally, we identified mutations in a 75 base pair alternatively spliced TGFβRII exon, exon 1a that produces the TGFβRIIb isoform and accounted for 2% of patients with mutations. Our in vitro analyses indicate that the TGFβRIIb activating mutations alter receptor function on TGFβ2 signaling.

CONCLUSIONS

We propose that TGFβRIIb expression is a regulatory mechanism for TGFβ2 signal transduction. Dysregulation of the TGFβ2 signaling pathway, as a consequence of TGFβRIIb mutations, results in aortic aneurysm pathogenesis.

Body surface area as a key determinant of aortic root and arch dimensions in a population-based study

The associations between the aortic dimensions (of the aortic sinus, aortic annulus and aortic arch) and physiological variables have not been established in the Chinese population. The present study examined the associations among physiological variables to determine the aortic root and arch dimensions echocardiographically. The diameters of the aortic sinus, annulus and arch were measured in 1,010 subjects via 2-D echocardiography with a 3.5-MHz transducer in a trans-thoracic position. The images of the aortic sinus and aortic annulus were obtained from a standard parasternal long-axis view. The maximum diameter of the valve orifice was measured at the end of systole. The aortic arch dimension was visualized in the long-axis using a suprasternal notch window and the maximum transverse diameter was measured. Epidata 3.0, Excel 2007 and SPSS version 17.0 were used to collect and analyze the data. A total of 1,010 subjects were enrolled. The mean age was 55.0±17.0 years (range of 18 to 90 years). The body surface area (BSA) was the best predictor of all the studied physiological variables and may be used to predict aortic sinus, annulus and arch dimensions independently (r=0.54, 0.37 and 0.39, respectively). Gender, blood pressure, age and BSA are significant predictors of the aortic dimensions. Of these, BSA was the best predictor.

Bicuspid aortic valve and thoracic aortic aneurysm: three patient populations, two disease phenotypes, and one shared genotype

Bicuspid aortic valve (BAV) and thoracic aortic aneurysm (TAA) are two discrete cardiovascular phenotypes characterized by latent progressive disease states. There is a clear association between BAV and TAA; however the nature and extent of this relationship is unclear. There are both distinct and overlapping developmental pathways that have been established to contribute to the formation of the aortic valve and the aortic root, and the mature anatomy of these different tissue types is intimately intertwined. Likewise, human genetics studies have established apparently separate and common contributions to these clinical phenotypes, suggesting complex inheritance and a shared genetic basis and translating 3 patient populations, namely, BAV, TAA, or both, into a common but diverse etiology. A better understanding of the BAV-TAA association will provide an opportunity to leverage molecular information to modify clinical care through more sophisticated diagnostic testing, improved counseling, and ultimately new pharmacologic therapies.

Aorta Measurements are Heritable and Influenced by Bicuspid Aortic Valve

Objectives: To determine whether the contributions of genetics and bicuspid aortic valve (BAV) independently influence aortic (Ao) dimensions. Background: Ao dilation is a risk factor for aneurysm, dissection, and sudden cardiac death. Frequent association of BAV with Ao dilation implicates a common underlying defect possibly due to genetic factors. Methods: Families enriched for BAV underwent standardized transthoracic echocardiography. In addition to BAV status, echocardiographic measures of Ao (annulus to descending Ao), pulmonary artery, and mitral valve annulus (MVA) diameters were obtained. Using variance components analysis, heritability was estimated with and without BAV status. Additionally, bivariate genetic analyses between Ao dimensions and BAV were performed. Results: Our cohort was obtained from 209 families enriched for BAV. After adjusting for age, body surface area, and sex, individuals with BAV had a statistically significant increase in all echocardiographic measurements (p < 0.006) except descending Ao and MVA. Individuals with BAV were at greater odds of having Ao dilation (OR = 4.44, 95% CI 2.93–6.72) than family members without BAV. All echocardiographic measurements exhibited moderate to strong heritability (0.25–0.53), and these estimates were not influenced by inclusion of BAV as a covariate. Bivariate genetic analyses supported that the genetic correlation between BAV and echo measures were not significantly different from zero. Conclusion: We show for the first time that echocardiographic measurements of Ao, pulmonary artery and MVA diameters are quantitative traits that exhibit significant heritability. In addition, our results suggest the presence of BAV independently influences the proximal Ao and pulmonary artery measures but not those in the descending Ao or MVA.

Measuring selection in contemporary human populations

Are humans currently evolving? This question can be answered using data on lifetime reproductive success, multiple traits and genetic variation and covariation in those traits. Such data are available in existing long-term, multigeneration studies - both clinical and epidemiological - but they have not yet been widely used to address contemporary human evolution. Here we review methods to predict evolutionary change and attempts to measure selection and inheritance in humans. We also assemble examples of long-term studies in which additional measurements of evolution could be made. The evidence strongly suggests that we are evolving and that our nature is dynamic, not static.

Genetic variants associated with cardiac structure and function: a meta-analysis and replication of genome-wide association data

CONTEXT

Echocardiographic measures of left ventricular (LV) structure and function are heritable phenotypes of cardiovascular disease.

OBJECTIVE

To identify common genetic variants associated with cardiac structure and function by conducting a meta-analysis of genome-wide association data in 5 population-based cohort studies (stage 1) with replication (stage 2) in 2 other community-based samples.

DESIGN, SETTING, AND PARTICIPANTS

Within each of 5 community-based cohorts comprising the EchoGen consortium (stage 1; n = 12 612 individuals of European ancestry; 55% women, aged 26-95 years; examinations between 1978-2008), we estimated the association between approximately 2.5 million single-nucleotide polymorphisms (SNPs; imputed to the HapMap CEU panel) and echocardiographic traits. In stage 2, SNPs significantly associated with traits in stage 1 were tested for association in 2 other cohorts (n = 4094 people of European ancestry). Using a prespecified P value threshold of 5 x 10(-7) to indicate genome-wide significance, we performed an inverse variance-weighted fixed-effects meta-analysis of genome-wide association data from each cohort.

MAIN OUTCOME MEASURES

Echocardiographic traits: LV mass, internal dimensions, wall thickness, systolic dysfunction, aortic root, and left atrial size.

RESULTS

In stage 1, 16 genetic loci were associated with 5 echocardiographic traits: 1 each with LV internal dimensions and systolic dysfunction, 3 each with LV mass and wall thickness, and 8 with aortic root size. In stage 2, 5 loci replicated (6q22 locus associated with LV diastolic dimensions, explaining <1% of trait variance; 5q23, 12p12, 12q14, and 17p13 associated with aortic root size, explaining 1%-3% of trait variance).

CONCLUSIONS

We identified 5 genetic loci harboring common variants that were associated with variation in LV diastolic dimensions and aortic root size, but such findings explained a very small proportion of variance. Further studies are required to replicate these findings, identify the causal variants at or near these loci, characterize their functional significance, and determine whether they are related to overt cardiovascular disease.

Genome-wide linkage analysis of pulse pressure in American Indians: the Strong Heart Study

BACKGROUND

Pulse pressure, a measure of central arterial stiffness and a predictor of cardiovascular mortality, has known genetic components.

METHODS

To localize the genetic effects of pulse pressure, we conducted a genome-wide linkage analysis of 1,892 American-Indian participants of the Strong Heart Family Study (SHFS). Blood pressure was measured three times and the average of the last two measures was used for analyses. Pulse pressure, the difference between systolic blood pressure (SBP) and diastolic blood pressure (DBP), was log-transformed and adjusted for the effects of age and sex within each study center. Variance component linkage analyses were performed using marker allele frequencies derived from all individuals and multipoint identity-by-descent matrices calculated in Loki.

RESULTS

We identified a quantitative-trait locus influencing pulse pressure on chromosome 7 at 37 cM (marker D7S493, LOD = 3.3) and suggestive evidence of linkage on chromosome 19 at 92 cM (marker D19S888, LOD = 1.8).

CONCLUSIONS

The signal on 7p15.3 overlaps positive findings for pulse pressure among Utah population samples, suggesting that this region may harbor gene variants for blood pressure related traits.

Genome-wide association of echocardiographic dimensions, brachial artery endothelial function and treadmill exercise responses in the Framingham Heart Study

BACKGROUND

Echocardiographic left ventricular (LV) measurements, exercise responses to standardized treadmill test (ETT) and brachial artery (BA) vascular function are heritable traits that are associated with cardiovascular disease risk. We conducted a genome-wide association study (GWAS) in the community-based Framingham Heart Study.

METHODS

We estimated multivariable-adjusted residuals for quantitative echocardiography, ETT and BA function traits. Echocardiography residuals were averaged across 4 examinations and included LV mass, diastolic and systolic dimensions, wall thickness, fractional shortening, left atrial and aortic root size. ETT measures (single exam) included systolic blood pressure and heart rate responses during exercise stage 2, and at 3 minutes post-exercise. BA measures (single exam) included vessel diameter, flow-mediated dilation (FMD), and baseline and hyperemic flow responses. Generalized estimating equations (GEE), family-based association tests (FBAT) and variance-components linkage were used to relate multivariable-adjusted trait residuals to 70,987 SNPs (Human 100K GeneChip, Affymetrix) restricted to autosomal SNPs with minor allele frequency > or =0.10, genotype call rate > or =0.80, and Hardy-Weinberg equilibrium p > or = 0.001.

RESULTS

We summarize results from 17 traits in up to 1238 related middle-aged to elderly men and women. Results of all association and linkage analyses are web-posted at http://ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?id=phs000007 webcite. We confirmed modest-to-strong heritabilities (estimates 0.30-0.52) for several Echo, ETT and BA function traits. Overall, p < 10(-5) in either GEE or FBAT models were observed for 21 SNPs (nine for echocardiography, eleven for ETT and one for BA function). The top SNPs associated were (GEE results): LV diastolic dimension, rs1379659 (SLIT2, p = 1.17*10(-7)); LV systolic dimension, rs10504543 (KCNB2, p = 5.18*10(-6)); LV mass, rs10498091 (p = 5.68*10(-6)); Left atrial size, rs1935881 (FAM5C, p = 6.56*10(-6)); exercise heart rate, rs6847149 (NOLA1, p = 2.74*10(-6)); exercise systolic blood pressure, rs2553268 (WRN, p = 6.3*10(-6)); BA baseline flow, rs3814219 (OBFC1, 9.48*10(-7)), and FMD, rs4148686 (CFTR, p = 1.13*10(-5)). Several SNPs are reasonable biological candidates, with some being related to multiple traits suggesting pleiotropy. The peak LOD score was for LV mass (4.38; chromosome 5); the 1.5 LOD support interval included NRG2.

CONCLUSION

In hypothesis-generating GWAS of echocardiography, ETT and BA vascular function in a moderate-sized community-based sample, we identified several SNPs that are candidates for replication attempts and we provide a web-based GWAS resource for the research community.

GENETIC INFLUENCES ON THE ARTERIAL WALL

1. Arterial stiffness, which has independent predictive value for cardiovascular events, seems to have a genetic component, largely independent of the influence of blood pressure and other cardiovascular risk factors. 2. In animal models of essential hypertension (stroke-prone spontaneously hypertensive rats and spontaneously hypertensive rats), structural modifications of the arterial wall include an increase in the number of elastin-smooth muscle cell connections and smaller fenestrations of the internal elastic lamina, possibility leading to redistribution of the mechanical load towards elastic materials. These modifications may give rise to mechanisms explaining why changes in arterial wall material accompanying wall hypertrophy in these animals are not associated with an increase in arterial stiffness. 3. In monogenic connective tissue diseases (Marfan, Williams and Ehlers-Danlos syndromes) and the corresponding animal models, precise characterization of the arterial phenotype makes it possible to determine the influence of abnormal, genetically determined, wall components on arterial stiffness. 4. Such studies have highlighted the role of extracellular matrix signalling in the vascular wall and have shown that elastin and collagen not only display elasticity or rigidity, but are also involved in the control of smooth muscle cell function. 5. These data provide strong evidence that arterial stiffness is affected by the amount and density of stiff wall material and the spatial organization of that material.

APOE alleles are not associated with calcific aortic stenosis

OBJECTIVES

To analyse the association of APOE alleles with aortic stenosis (AS) in a large study population.

METHODS

Patients with AS (n = 538) and a control group of the same age without heart disease (n = 536) were recruited. Left heart catheterisation was performed and mean gradient, aortic valve area, presence of stenotic coronary artery disease (CAD) and cardiovascular risk factors (hypercholesterolaemia, hypertension, smoking, diabetes mellitus and family history of CAD) were assessed. The frequency of the APOE major alleles e2, e3 and e4 was assessed by genotyping the polymorphisms APOE334 and APOE472 with a 5' exonuclease assay (TaqMan).

RESULTS

Mean gradient across the aortic valve in cases was 50 (SD 20) mm Hg corresponding to a mean aortic valve area of 0.84 (SD 0.34) cm(2). 270 patients with AS had stenotic CAD. Among patients with AS, the prevalence of hypercholesterolaemia (64% v 40%, p < 0.001), smoking (43% v 27%, p < 0.001), diabetes (27% v 17%, p < 0.01), family history of CAD (30% v 21%, p </= 0.05), and male sex (65% v 44%, p < 0.001) was higher in those with than in those without CAD. The frequency of the major alleles was not different between cases and controls (APOE e2: 104 (19.3%) v 94 (17.5%); APOE e3: 319 (59.3%) v 332 (61.9%); APOE e4: 115 (21.3%) v 110 (20.5%); all p > 0.10).

CONCLUSION

APOE e4 is not associated with AS, reflecting the different genetic backgrounds of CAD and AS.

Birth weight and cardiac structure in children

OBJECTIVE

Epidemiologic studies have shown associations between impaired fetal growth and risk for coronary heart disease in adults. The underlying mechanisms are unknown. We investigated whether restricted intrauterine growth affects cardiac structure.

METHODS

We performed echocardiography on 216 9-year-old children who were measured previously at birth. The diameter of the coronary left and right main branches was derived from the widest dimension; total coronary artery diameter was calculated by adding the diameters of the left and right coronary arteries. Aortic root diameter, left atrial diameter, left ventricular diameter, left ventricular outflow tract diameter, and left ventricular mass were measured.

RESULTS

On average, children who had weighed less at birth had a smaller total coronary artery diameter, aortic root diameter, and left ventricular outflow tract diameter after adjustment for gender, gestational age, current height and weight, and maternal height and prepregnant weight. For each SD increase in birth weight, total coronary diameter rose by 0.10 mm, log aortic root diameter rose by 1.5%, and log left ventricular outflow tract diameter rose by 1.6%.

CONCLUSION

Impaired fetal growth may have long-term effects on cardiac structure. This may help to explain why adults whose birth weight was low are at greater risk for coronary heart disease.

Inheritance analysis of congenital left ventricular outflow tract obstruction malformations: Segregation, multiplex relative risk, and heritability

The left ventricular outflow tract (LVOTO) malformations, aortic valve stenosis (AVS), coarctation of the aorta (COA), and hypoplastic left heart (HLH) constitute a mechanistically defined subgroup of congenital heart defects that have substantial evidence for a genetic component. Evidence from echocardiography studies has shown that bicuspid aortic valve (BAV) is found frequently in relatives of children with LVOTO defects. However, formal inheritance analysis has not been performed. We ascertained 124 families by an index case with AVS, COA, or HLH. A total of 413 relatives were enrolled in the study, of which 351 had detailed echocardiography exams for structural heart defects and measurements of a variety of aortic arch, left ventricle, and valve structures. LVOTO malformations were noted in 30 relatives (18 BAV, 5 HLH, 3 COA, and 3 AVS), along with significant congenital heart defects (CHD) in 2 others (32/413; 7.7%). Relative risk for first-degree relatives in this group was 36.9, with a heritability of 0.71-0.90. Formal segregation analysis suggests that one or more minor loci with rare dominant alleles may be operative in a subset of families. Multiplex relative risk analysis, which estimates number of loci, had the highest maximum likelihood score in a model with 2 loci (range of 1-6 in the lod-1 support interval). Heritability of several aortic arch measurements and aortic valve was significant. These data support a complex but most likely oligogenic pattern of inheritance. A combination of linkage and association study designs is likely to enable LVOTO risk gene identification. This data can also provide families with important information for screening asymptomatic relatives for potentially harmful cardiac defects.

Heritability of left ventricular dimensions and mass in American Indians: The Strong Heart Study

OBJECTIVE

We sought to determine the heritability of left ventricular dimensions and mass in adult American Indians.

METHODS

Echocardiograms were analysed in 1373 American Indian participants, from 445 families, in the Strong Heart Study (SHS) to determine the heritability of left ventricular dimensions and mass. Heritability calculations were performed using variance component analysis in SOLAR, a computer analysis program.

RESULTS

The SHS participants analysed in this study included 1305 relative pairs, predominantly (n = 1077) sib-pairs. After simultaneously adjusting for sex, age and centre, the proportion of the residual phenotypic variance due to additive genetic effects or heritability (h2) of left ventricular mass was 0.27 (SE = 0.08, P < 0.001). Addition of body weight, height, systolic blood pressure, heart rate, medications and diabetes into the polygenic model attenuated the residual h2 of left ventricular mass to 0.17 (SE = 0.09, P < 0.05). The residual h2 for left ventricular end-diastolic chamber diameter (LVID), after simultaneously adjusting for sex, age and centre was 0.36 (SE = 0.08, P < 0.001) for the analysed families. The residual h2 for interventricular septal wall thickness was 0.26 (SE = 0.07), while that of left ventricular posterior wall thickness was 0.19 (SE = 0.08, both P < 0.001). While adjustment for body weight, height, systolic blood pressure, heart rate, medications and diabetes reduced the h2 of LVID to 0.33 (SE = 0.09, P < 0.001), the h2 of septal (0.12, SE = 0.10) and posterior wall thickness (0.09, SE = 0.09) were no longer significant after similar adjustment. The residual h2 for relative wall thickness, a measure of left ventricular geometry, was 0.22 (SE = 0.07, P < 0.001) after adjusting for sex, age and centre, and 0.17 (SE = 0.08, P < 0.05) after additional adjustment for body weight, height, systolic blood pressure, heart rate, medications and diabetes.

CONCLUSIONS

A substantial proportion of the variance of left ventricular dimensions and mass can be explained by heredity, independent of the effects of sex, age, body size, blood pressure, heart rate, medications and diabetes. Identification of genes influencing left ventricular size and geometry may provide mechanistic and therapeutic targets to prevent left ventricular hypertrophy.

Is aortic dilatation an atherosclerosis-related process?

OBJECTIVES

The study determined, in a population-based setting, whether dilatation of the thoracic aorta is an atherosclerosis-related process.

BACKGROUND

The role of atherosclerosis in thoracic aortic dilatation and aneurysm formation is poorly defined.

METHODS

The dimensions of the thoracic aorta were measured with transesophageal echocardiography in 373 subjects participating in a population-based study (median age 66 years; 52% men). The associations between clinical and laboratory atherosclerosis risk factors, aortic atherosclerotic plaques, and aortic dimensions were examined.

RESULTS

Age, male gender, and body surface area (BSA) jointly accounted for 41%, 31%, 38%, and 47% of the variability in diameters of the sinuses of Valsalva, ascending aorta, aortic arch, and descending aorta, respectively. Adjusting for age, gender, and BSA: 1) smoking was associated with a greater aortic arch diameter, and diastolic blood pressure and diabetes were each associated with a greater descending aorta diameter (p < 0.05); 2) atherosclerotic plaques in the descending aorta were associated with a greater descending aorta diameter (0.18 +/- 0.08-mm increase in diameter per 1-mm increase in plaque thickness; p = 0.02); and 3) minor negative associations were noted between atherosclerotic plaques and risk factors for atherosclerosis and the dimensions of the proximal thoracic aorta. Notably, atherosclerosis risk factors and plaque variables each accounted for <2% of the variability in aortic dimensions, adjusting for age, gender, and BSA.

CONCLUSIONS

Age, gender, and BSA are major determinants of thoracic aortic dimensions. Atherosclerosis risk factors and aortic atherosclerotic plaques are weakly associated with distal aortic dilatation, suggesting that atherosclerosis plays a minor role in aortic dilatation in the population.