Heritability of left atrial size in the Tecumseh population

Cardiovascular Risk Factors Track From Mother to Child

Background

Cardiovascular risk factors can track from mother to child by several pathways: pregnancy complications, genetic inheritance, and shared environmental risk factors after pregnancy. The degree of tracking, and to which extent this is influenced by these pathways, is unknown. We hypothesized that cardiovascular risk factors track from mother to child regardless of pregnancy complications and environmental risk factors. We determined the degree of tracking between maternal and offspring micro‐ and macrovascular cardiovascular risk factors after pregnancy and the extent to which this is influenced by pregnancy complications and shared environmental risk factors.

Methods and Results

We included 5624 mother‐offspring pairs from The Generation R Study, an ongoing prospective, population‐based birth cohort. Information on pregnancy complications (preeclampsia, small for gestational age, and preterm birth) was obtained through hospital charts. Mother‐offspring associations were assessed 6 years after pregnancy (central retinal arteriolar and venular calibers, body mass index, blood pressure, left atrial diameter, aortic root diameter, left ventricular mass, fractional shortening, and pulse wave velocity) and 9 years after pregnancy (body mass index and blood pressure). We observed that worse cardiovascular parameters in mothers were associated with worse cardiovascular parameters in their offspring 6 and 9 years after pregnancy (P<0.001). Results were similar when mother‐offspring pairs with a previous pregnancy complication were excluded.

Conclusions

Six and 9 years after pregnancy, an adverse cardiovascular profile in mothers is strongly associated with an adverse cardiovascular profile in their offspring. Results were not attenuated by environmental exposures or a previous pregnancy complication. This supports the hypothesis that cardiovascular risk factors (micro‐ and macrovascular) track from mother to child, regardless of the course of pregnancy.

Clinical correlates and heritability of cardiac mechanics: The HyperGEN study

BACKGROUND

Indices of cardiac mechanics are sensitive markers of subclinical myocardial dysfunction. Improved understanding of the clinical correlates and heritability of cardiac mechanics could result in novel insight into the acquired and genetic risk factors for myocardial dysfunction. Therefore, we sought to determine the clinical correlates and heritability of indices of cardiac mechanics in whites and African Americans (AAs).

METHODS

We examined 2058 participants stratified by race (1104 whites, 954 AA) in the Hypertension Genetic Epidemiology Network (HyperGEN), a population- and family-based study, and performed digitization of analog echocardiograms with subsequent speckle-tracking analysis. We used linear mixed effects models to determine the clinical correlates of indices of cardiac mechanics (longitudinal, circumferential, radial strain; early diastolic strain rate; and early diastolic tissue velocities). Heritability estimates for cardiac mechanics were calculated using maximum-likelihood variance component analyses in Sequential Oligogenic Linkage Analysis Routine (SOLAR), with adjustment for clinical and echocardiographic covariates.

RESULTS

Several clinical characteristics and conventional echocardiographic parameters were found to be associated with speckle-tracking traits of cardiac mechanics. Male sex, blood pressure, and fasting glucose were associated with worse longitudinal strain (LS) (P < 0.05 for all) after multivariable adjustment. After adjustment for covariates, LS, e' velocity, and early diastolic strain rate were found to be heritable; LS and e' velocity had higher heritability estimates in AAs compared to whites.

CONCLUSIONS

Indices of cardiac mechanics are heritable traits even after adjustment for clinical and conventional echocardiographic correlates. These findings provide the basis for future studies of genetic determinants of these traits that may elucidate race-based differences in heart failure development.

A comprehensive genetic study on left atrium size in Caribbean Hispanics identifies potential candidate genes in 17p10

BACKGROUND

Left atrial (LA) enlargement is associated with cardiovascular disease and stroke. Genetic factors contributing to the LA dimension are poorly understood. We sought to map susceptibility genes for LA size in a large Dominican family data set and an independent population-based sample from the Northern Manhattan Study.

METHODS AND RESULTS

One hundred Dominican families comprising 1350 individuals were studied to estimate heritability and map quantitative trait loci for LA size using variance components analysis. LA dimension was measured by transthoracic echocardiography. A polygenic covariate screening was used to identify significant covariates. LA size had a moderate estimate of heritability (h(2)=0.42) after adjusting for significant covariates. Linkage analysis revealed suggestive evidence on chromosome 10p19 (D10S1423, MLOD=2.00) and 17p10 (D17S974, MLOD=2.05). Ordered subset analysis found significantly enhanced (P<0.05 for increase of LOD score) evidence for linkage at 17p10 (MLOD=2.9) in families with lower LDL level. Single nucleotide polymophisms (n=2233)were used to perform a peak-wide association mapping across 17p10 in 825 NOMAS individuals. Evidence for association were found in NTN1, MYH10, COX10, and MYOCD genes (P=0.00005 to 0.005).

CONCLUSIONS

Using nonbiased genome-wide linkage followed by peak-wide association analysis, we identified several possible susceptibility genes affecting LA size. Among them, MYOCD has been shown to serve as a key transducer of hypertrophic signals in cardiomyocytes. Our data support that polymorphisms in MYOCD modify LA size.

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 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.

Relationships of the appropriateness of left ventricular mass to left atrial size and function in arterial hypertension

OBJECTIVE

To investigate whether left ventricular mass (LVM) appropriateness may be related to left atrial changes in both size and performance in arterial hypertension.

METHODS

Three hundred and thirty-five hypertensive outpatients were studied by Doppler echocardiography and divided into two groups on the basis of LVM appropriateness. Left ventricular mass was defined inappropriate when greater than 128% of the value predicted from age, sex and stroke work (95th percentile of normal distribution) and appropriate for values <or= 128%. Left atrial volumes were obtained by two-dimensional echocardiography, left atrial ejection force was used as an index of systolic performance and calculated accordingly with Manning's formula.

RESULTS

Left ventricular mass was inappropriate in 58 patients (17%). Individuals with an inappropriate mass showed higher left atrial maximum and minimum volumes compared to those with appropriate mass (all P<0.001), independent of left ventricular geometry. Left atrial ejection fraction (44 +/- 13 versus 46 +/- 13%) and ejection force (8.4 +/- 4.8 versus 9.3 +/- 5.3 kdynes) were not statistically different between groups. In the whole group, left atrial volumes and stroke volume showed a close positive relationship with respect to crude values of LVM and inappropriate LVM, whereas left atrial ejection force was better related to left ventricular concentric geometry. This correlation was explained by the more pronounced diastolic dysfunction found in the highest quartile of left atrial ejection force.

CONCLUSIONS

In arterial hypertension, left atrial enlargement parallels an increase in LVM. Left atrial ejection force is at least in part independent of this mechanism, being mainly linked to concentric geometry and left ventricular diastolic function impairment.