Left ventricular mass (LVM) is an important risk factor for stroke and vascular disease. The genetic basis of LVM is unclear although a high heritability has been suggested. We sought to map quantitative trait loci (QTL) for LVM using large Dominican families.
Probands were selected from Dominican subjects of the population-based Northern Manhattan Study (NOMAS). LVM was measured by transthoracic echocardiography. A set of 405 microsatellite markers was used to screen the whole genome among 1360 subjects from 100 Dominican families who had complete phenotype data and DNA available. A polygenic covariate screening was run to identify the significant covariates. Variance components analysis was used to estimate heritability and to detect evidence for linkage, after adjusting for significant risk factors. Ordered-subset Analysis (OSA) was conducted to identify a more homogeneous subset for stratification analysis.
LVM had a heritability of 0.58 in the studied population (p < 0.0001). The most significant evidence for linkage was found at chromosome 12p11 (MLOD = 3.11, empirical p = 0.0003) with peak marker at D12S1042. This linkage was significantly increased in a subset of families with the high average waist circumference (MLOD = 4.45, p = 0.0045 for increase in evidence for linkage).
We mapped a novel QTL near D12S1042 for LVM in Dominicans. Enhanced linkage evidence in families with larger waist circumference suggests that gene(s) residing within the QTL interact(s) with abdominal obesity to contribute to phenotypic variation of LVM. Suggestive evidence for linkage (LOD = 1.99) has been reported at the same peak marker for left ventricular geometry in a White population from the HyperGEN study, underscoring the importance of this QTL for left ventricular phenotype. Further fine mapping and validation studies are warranted to identify the underpinning genes.
The aim of this study was to investigate the heritability as well as genetic and environmental correlations of left ventricular (LV) structural and functional traits in complex pedigrees of a Caucasian population.
Methods and results
We randomly recruited 459 white European subjects from 52 families (50% women; mean age 45 years). LV structure was measured by M-mode and 2D echocardiography and LV function was measured by conventional Doppler and tissue Doppler imaging (TDI). Other measurements included blood pressure, anthropometric, and biochemical measurements. We estimated the heritability of LV traits while adjusting for covariables, including sex, age, body height and weight, systolic and diastolic blood pressures, and heart rate. With full adjustment, heritability of LV mass was 0.23 (P= 0.025). The TDI-derived mitral annular velocities Ea and Aa showed moderate heritability (h2= 0.36 and 0.53, respectively), whereas the mitral inflow A peak had weak heritability (h2 = 0.25) and the E peak was not heritable (h2 = 0.11). We partitioned the total phenotypic correlation when it reached significance, into a genetic and an environmental component. The genetic correlations were 0.61 between the E and Ea peaks and 0.90 between the A and Aa peaks.
Our study demonstrated moderate heritability for LV mass as well as the mitral annular Ea and Aa peaks. We also found significant genetic correlations between the E and Ea peaks and between the A and Aa peaks. Our current findings support the ongoing research to map and detect genetic variants that contribute to the variation in LV mass and other LV structural and functional phenotypes.
Echocardiography; Heritability; Left ventricular phenotypes; Population science
Apolipoprotein (Apo) A1 is a protective factor for cardiovascular events. This study aimed to perform complex segregation analyses of Apo A1 levels in families of adolescents systematically ascertained from the junior high school students in a rural community. Both siblings and parents of the adolescent probands were recruited for the study. Apo A1 concentrations were measured by turbidimetric immunoassay methods. After adjustment for gender, age, body mass index, smoking and drinking status, residual values of Apo A1 were subjected to subsequent analyses.
Significant mother-father and parent-offspring correlations were found. Commingling analyses indicated that a four-component distribution model was needed to account for the Apo A1 variation. Segregation analysis using regressive models revealed that the best-fit model of Apo A1 was a model of environmental effect plus familial correlation (heritability = 23.9%), in which a significant mother-father correlation existed. Models containing major gene effect could be rejected.
These results suggest that variations of Apo A1 levels in the normal range, especially during adolescence, are likely to be influenced by multiple factors without significant contribution from major genes.
The genetic influences on bone mass likely change throughout the life span, but most genetic studies of bone mass regulation have focused on adults. There is, however, a growing awareness of the importance of genes influencing the acquisition of bone mass during childhood on lifelong bone health. The present investigation examines genetic influences on childhood bone mass by estimating the residual heritabilities of different measures of second metacarpal bone mass in a sample of 600 10-year-old participants from 144 families in the Fels Longitudinal Study. Bivariate quantitative genetic analyses were conducted to estimate genetic correlations between cortical bone mass measures, and measures of bone growth and development. Using a maximum likelihood-based variance components method for pedigree data, we found a residual heritability estimate of 0.71 for second metacarpal cortical index. Residual heritability estimates for individual measures of cortical bone (e.g., lateral cortical thickness, medial cortical thickness) ranged from 0.47 to 0.58, at this pre-pubertal childhood age. Low genetic correlations were found between cortical bone measures and both bone length and skeletal age. However, after Bonferonni adjustment for multiple testing, ρG was not significantly different from 0 for any of these pairs of traits. Results of this investigation provide evidence of significant genetic control over bone mass largely independent of maturation while bones are actively growing and before rapid accrual of bone that typically occurs during puberty.
bone size; genetics; radiography; maturation
C-reactive protein (CRP) largely has been studied in white non-Hispanic cohorts. There is limited information on CRP’s range of values, heritability and relation to cardiovascular disease (CVD) risk factors in African Americans. We sought to evaluate the distribution, clinical correlates, heritability and genetic linkage of log-transformed CRP in participants of the middle-aged to elderly African American community-based Jackson Heart Study. The distribution and correlates of CRP were analyzed for the entire study cohort who underwent the first examination (2001–2004). Heritability was estimated for the family cohort nested within the larger Jackson Heart Study (246 families, n=1,317). The relation between CRP and CVD risk factors were tested with multivariable stepwise regression analyses. Heritability was estimated using a variance components method. Linkage analysis was performed using the multipoint variance components approach. The study sample consisted of 4,919 participants (mean age 55±13 years, 63% women); median CRP concentration was 2.7 mg/L. In stepwise models traditional risk factors explained 23.8% of CRP’s variability, with body mass index (BMI, partial R2=13.6%) explaining 57.1% of the variability of CRP due to traditional risk factors. The heritability of CRP (adjusted for age, sex and BMI) was 0.45. The strongest linkage evidence for CRP was observed on chromosome 11 (11p13–11p11.2) with a logarithm of odds score of 2.72. In conclusion, in this large population-based cohort of African Americans, circulating CRP concentration was heritable and associated with several traditional cardiovascular risk factors, particularly BMI.
C-reactive protein; risk factors; genetics; heritability; blood pressure; cholesterol; body mass index; African Americans
Left ventricular (LV) hypertrophy is a strong independent predictor of increased cardiovascular morbidity and mortality in clinical and population-based samples. Clinical and hemodynamic stimuli to LV hypertrophy induce not only an increase in cardiac mass and wall thickness but also a fundamental reconfiguration of the protein, cellular and molecular components of the myocardium. Several studies have indicated that LV mass is influenced by genetic factors. The substantial heritability (h2) for LV mass in population-based samples of varying ethnicity indicates robust genetic influences on LV hypertrophy. Genome-wide linkage and association studies in diverse populations have been performed to identify genes influencing LV mass, and although several chromosomal regions have been found to be significantly associated with LV mass, the specific genes and functional variants contained in these chromosomal regions have yet to be identified. In addition, multiple studies have tried to link single-nucleotide polymorphisms (SNPs) in regulatory and pathway genes with common forms of LV hypertrophy, but there is little evidence that these genetic variations are functional. Up to this point in time, the results obtained in genetic studies are of limited clinical value. Much of the heritability remains unexplained, the identity of the underlying gene pathways, genes, and functional variants remains unknown, and the promise of genetically-based risk prediction and personalized medicine remain unfulfilled. However, molecular biological technologies continue to improve rapidly, and the long-term potential of sophisticated genetic investigations using these modern genomic technologies, coupled with smart study designs, remains intact. Ultimately, genetic investigations offer much promise for future prevention, early intervention and treatment of this major public health issue.
Left ventricular (LV) hypertrophy; genetic epidemiology; Genome-wide linkage and association studies
Left ventricular (LV) mass and related phenotypes are heritable, important predictors of cardiovascular disease, particularly in hypertensive individuals.
Identify genetic predictors of echocardiographic phenotypes in hypertensive families.
Methods & Results
A multi-stage genome-wide association study (GWAS) was conducted in hypertensive-ascertained African American families (HyperGEN, Stage I; GENOA, Stage II); findings were replicated in HyperGEN Caucasian families (Stage III). Echocardiograms were collected using a common protocol, and participants were genotyped with the Affymetrix Genome-Wide Human SNP 6.0 Array. In Stages I and II, 1258 and 989 African Americans, and Stage III 1316 Caucasians, were analyzed using mixed models adjusted for ancestry. Phenotypes included LV mass, LV internal dimension (LVID), wall thicknesses (posterior (PWT) and intraventricular septum (IVST)), and relative wall thickness (RWT). In Stage I, 5 single nucleotide polymorphisms (SNP) had P≤10−6. In Stage II, one SNP (rs1436109; NCAM1 intron 1) replicated with the same phenotype (PWT, P=0.025) in addition to RWT (P=0.032). In Stage III, rs1436109 was associated with RWT (P=5.47×10−4) and LVID (P=1.86×10−4). Fisher’s combined P-value for all stages was RWT=3.80×10−9, PWT=3.12×10−7, IVST=8.69×10−7, LV mass=2.52×10−3, and LVID=4.80×10−4.
This GWAS conducted in hypertensive families identified a variant in NCAM1 associated with LV wall thickness and RWT. NCAM is upregulated during the remodeling period of hypertrophy to heart failure in Dahl salt-sensitive rats. Our initial screening in hypertensive African-Americans may have provided the context for this novel locus.
GWAS; NCAM1; hypertrophy; genomics
To date, all known Alzheimer's disease genes influence amyloid beta (Aβ). The development of in vivo imaging of Aβ deposition in the human brain using Pittsburgh compound B (PIB) offers the possibility of using cortical PIB binding as a quantitative endophenotype for genetic studies of late-onset Alzheimer's disease (LOAD).
Heritability of Aβ deposition was determined using 82 elderly siblings from 35 families. Correlation with other Aβ related traits was determined using an unrelated sample of 112 individuals. For both samples, APOE ε4 was genotyped and PET imaging was performed using the PIB ligand. Mean cortical binding potential (MCBP) was computed from several regions-of-interest.
MCBP has a high heritability (0.61, p=0.043). Furthermore, most of the heritable component (74%) cannot be explained by APOE ε4 genotype. Analysis of the unrelated sample reveals that a third of the variance of MCBP cannot be predicted by other biological traits, including CSF Aβ42 levels.
These findings demonstrate that MCBP is a genetic trait and that other more easily measured Aβ related traits such as CSF Aβ42 do not fully explain the variance in MCBP. Thus, mean cortical PIB binding is a useful trait for large-scale genetic studies of LOAD.
It remains unclear whether the body mass index (BMI) and blood pressure (BP) profile are clustered within families in Chinese Han population. The aim of this study is to explore familial aggregation and parent-offspring correlations of BMI and blood pressure in Chinese Han population.
6,369 Han nucleus families, consisting of parents and at least one biological adult child who were living together, were enrolled from the nation-wide cross-sectional study (China National Nutrition and Health Survey) which was conducted in 2002, with a total number of 19,107 participants aged 18–64 years (6,369 sets of parents, 4,132 sons and 2,237 daughters). Family aggregation (Intra-class correlations, ICCs) and parent-offspring correlations in BMI, systolic BP (SBP) and diastolic BP (DBP) were estimated using linear mixed effect regression models.
BMI and BP levels in two generations and ICCs of BMI, SBP and DBP varied across the country. Familial aggregation of overweight/obesity was observed in rural area (ICC = 5.4%, p<0.05), and high BP (defined as SBP ≥ 120 mmHg or DBP ≥ 80 mmHg) was more common in low income families (ICC = 4.4%, p<0.05) compared to middle income (ICC = 1.9%) and high income families (ICC = 2.6%). Additionally, offspring with more parents being overweight/obese tend to have higher BMI. The similar trend was found for high BP. However, we did not observe that same-sex parent-offspring correlations of BMI and BP were stronger than the correlations for mother-son or father-daughter.
Our study suggested that familial environments, alongside the impact of genetic factors, could be important non-communicable chronic diseases (NCD) risk factors. Family-based intervention taking both mother and father into account might have great potential in NCD prevention for younger generation.
Body mass index; Blood pressure; Family aggregation; Parent-offspring correlation; Sex-specific
Obesity and obstructive sleep apnea each have a substantial genetic basis and commonly co-exist in individuals. The degree to which the genetic underpinnings for these disorders overlap has not been previously quantified.
A total of 1802 individuals from 310 families in the Cleveland Family Study underwent home sleep studies as well as standardized assessment of body mass index and circumferences at the waist, hip, and neck. In 713 participants with laboratory sleep studies, fasting blood samples were assayed for leptin, adiponectin, and resistin. Variance component models were used to estimate heritability and genetic correlations.
The heritability of the apnea hypopnea index was 0.37 ± 0.04 and 0.33 ± 0.07 for home and laboratory sleep studies respectively. The genetic correlations between apnea hypopnea index and anthropomorphic adiposity measures ranged from 0.57 to 0.61 suggesting obesity can explain nearly 40% of the genetic variance in sleep apnea. The magnitude of the genetic correlations between apnea severity and adipokine levels was substantially less than those with anthropomorphic measures, ranging from 0.11–0.46. After adjusting for body mass index, no significant genetic correlation with apnea severity was observed for any of the other adiposity measures.
Substantial but not complete overlap in genetic bases exist between sleep apnea and anthropomorphic indices of adiposity, and this overlap accounts for more than one third of the genetic variance in apnea severity. These findings suggest that genetic polymorphisms exist that importantly influence sleep apnea susceptibility through both obesity-dependent and obesity-independent pathways.
obesity; sleep apnea; genetics; heritability; genetic correlation
Rationale: Left ventricular hypertrophy (LVH) is a heritable predictor of cardiovascular disease, particularly in blacks. Objective: Determine the feasibility of combining evidence from two distinct but complementary experimental approaches to identify novel genetic predictors of increased LV mass. Methods: Whole-exome sequencing (WES) was conducted in seven African-American sibling trios ascertained on high average familial LV mass indexed to height (LVMHT) using Illumina HiSeq technology. Identified missense or nonsense (MS/NS) mutations were examined for association with LVMHT using linear mixed models adjusted for age, sex, body weight, and familial relationship. To functionally assess WES findings, human induced pluripotent stem cell-derived cardiomyocytes (induced pluripotent stem cell-CM) were stimulated to induce hypertrophy; mRNA sequencing (RNA-seq) was used to determine gene expression differences associated with hypertrophy onset. Statistically significant findings under both experimental approaches identified LVH candidate genes. Candidate genes were further prioritized by seven supportive criteria that included additional association tests (two criteria), regional linkage evidence in the larger HyperGEN cohort (one criterion), and publically available gene and variant based annotations (four criteria). Results: WES reads covered 91% of the target capture region (of size 37.2 MB) with an average coverage of 65×. WES identified 31,426 MS/NS mutations among the 21 individuals. A total of 295 MS/NS variants in 265 genes were associated with LVMHT with q-value <0.25. Of the 265 WES genes, 44 were differentially expressed (P < 0.05) in hypertrophied cells. Among the 44 candidate genes identified, 5, including HLA-B, HTT, MTSS1, SLC5A12, and THBS1, met 3 of 7 supporting criteria. THBS1 encodes an adhesive glycoprotein that promotes matrix preservation in pressure-overload LVH. THBS1 gene expression was 34% higher in hypertrophied cells (P = 0.0003) and a predicted conserved and damaging NS variant in exon 13 (A2099G) was significantly associated with LVHMT (P = 4 × 10−6). Conclusion: Combining evidence from cutting-edge genetic and cellular experiments can enable identification of novel LVH risk loci.
hypertrophy; left ventricular mass; cardiomyocyte; exome; genomics
The goal of this study is to assess the relationship between stress coping mechanisms and the risk of atherosclerosis in patients with Hwa-Byung.
The Korean version of the Ways of Coping Checklist (WOCC) was administered to 50 patients with Hwa-Byung (49.1±10.1 years, 6 males). Brachial-ankle pulse wave velocity (baPWV) and serum cholesterol level were assessed in all participants.
After controlling for age, sex, diagnosis of hypertension, Body Mass Index (BMI), and serum cholesterol level, the score of seeking social support in coping strategies was negatively correlated with right and left baPWV (r=-0.356, p=0.016; r=-0.373, p=0.012, respectively). In addition, the score of active coping mechanism was negatively correlated with both sides of baPWV (r=-0.383, p=0.009; r=-0.389, p=0.008, respectively).
The seeking social support and active coping mechanism were inversely related to the severity of arterial stiffness in Hwa-Byung patients. Therefore, our result may suggest a possibility that coping strategies in Hwa-Byung patients are associated with the risk of atherosclerosis.
Hwa-Byung; Coping mechanism; Atherosclerosis
This study was carried out to analyze the vertical transmission of Yq AZFc microdeletions from father to son in infertile Han Chinese families to investigate genetic factors and family background affecting fertility status. The peripheral blood of infertile males in 19 Han families was extracted and screened with modified multiplex polymerase chain reaction (PCR). Family trees were drawn according to fertility status and clinical characteristics of the subjects. The vertical transmission of Yq AZFc microdeletions was detected in six cases of 19 investigated families (31.6%, 6/19). Although both fathers and sons showed a similar type of Yq AZFc deletion, the fathers were fertile, whereas the sons were infertile and showed severe oligozoospermia. The vertical transmission of Yq AZFc microdeletion from fertile fathers to infertile sons over generations is not rare. This has different effects on fertility status in fathers and sons in Han Chinese families. Both genetic factors and family background affect spermatogenetic phenotypes.
infertility; microdeletion; vertical transmission; Y chromosome
Growth factors play an important role in regulating vascular function. Data are limited regarding clinical and genetic correlates of endothelial growth factors and their associations with vascular function.
Methods and results
We evaluated clinical and genetic correlates of circulating vascular endothelial growth factor A (VEGF), its soluble receptor sFlt-1, and hepatocyte growth factor (HGF) in 3754 Framingham Study participants. We also related the growth factors to measures of brachial artery function. Serum VEGF and HGF were higher and sFLt-1 was lower in women and smokers. VEGF and HGF were associated positively with body mass index; both displayed strong positive associations with the metabolic syndrome (P < 0.001) and its components. The heritabilities of VEGF, sFlt-1, and HGF were 78, 13, and 38%, respectively. VEGF and HGF were related positively to baseline brachial diameter (P < 0.01) and to baseline mean flow velocity (P < 0.001) in age- and sex-adjusted models, but the multivariable models failed to reach significance. None of the growth factors were related to flow-mediated dilation.
In our community-based sample, circulating VEGF and HGF demonstrated high heritabilities and a sexual dimorphism. Increased angiogenesis and greater endothelial cell turnover may underlie associations of these growth factors with risk factors including smoking.
Vascular growth factors; VEGF; SFlt-1; HGF; Vascular function; Heritability; Metabolic syndrome
Genetic studies on facial morphology targeting healthy populations are fundamental in understanding the specific genetic influences involved; yet, most studies to date, if not all, have been focused on congenital diseases accompanied by facial anomalies. To study the specific genetic cues determining facial morphology, we estimated familial correlations and heritabilities of 14 facial measurements and 3 latent factors inferred from a factor analysis in a subset of the Korean population. The study included a total of 229 individuals from 38 families. We evaluated a total of 14 facial measurements using 2D digital photographs. We performed factor analysis to infer common latent variables. The heritabilities of 13 facial measurements were statistically significant (p < 0.05) and ranged from 0.25 to 0.61. Of these, the heritability of intercanthal width in the orbital region was found to be the highest (h2 = 0.61, SE = 0.14). Three factors (lower face portion, orbital region, and vertical length) were obtained through factor analysis, where the heritability values ranged from 0.45 to 0.55. The heritability values for each factor were higher than the mean heritability value of individual original measurements. We have confirmed the genetic influence on facial anthropometric traits and suggest a potential way to categorize and analyze the facial portions into different groups.
facial bones; genetic research; statistical factor analysis
Evidence for a major role of genetic factors in the determination of body mass index (BMI) comes from studies of related individuals. Despite consistent evidence for a heritable component of BMI, estimates of BMI heritability vary widely between studies and the reasons for this remain unclear. While some variation is natural due to differences between populations and settings, study design factors may also explain some of the heterogeneity. We performed a systematic review that identified 88 independent estimates of BMI heritability from twin studies (total 140,525 twins) and 27 estimates from family studies (42,968 family members). BMI heritability estimates from twin studies ranged from 0.47 to 0.90 (5th/50th/95th centiles: 0.58/0.75/0.87) and were generally higher than those from family studies (range: 0.24–0.81; 5th/50th/95th centiles: 0.25/0.46/0.68). Meta-regression of the results from twin studies showed that BMI heritability estimates were 0.07 (P = 0.001) higher in children than in adults; estimates increased with mean age among childhood studies (+0.012/year, P = 0.002), but decreased with mean age in adult studies (−0.002/year, P = 0.002). Heritability estimates derived from AE twin models (which assume no contribution of shared environment) were 0.12 higher than those from ACE models (P < 0.001), whilst lower estimates were associated with self reported versus DNA-based determination of zygosity (−0.04, P = 0.02), and with self reported versus measured BMI (−0.05, P = 0.03). Although the observed differences in heritability according to aspects of study design are relatively small, together, the above factors explained 47% of the heterogeneity in estimates of BMI heritability from twin studies. In summary, while some variation in BMI heritability is expected due to population-level differences, study design factors explained nearly half the heterogeneity reported in twin studies. The genetic contribution to BMI appears to vary with age and may have a greater influence during childhood than adult life.
body mass index; twin study; family study; heritability
The ambulatory arterial stiffness index (AASI) can be used to predict cardiovascular morbidity and mortality in hypertensive patients. However, data on AASI in Chinese patients with chronic kidney disease (CKD) is not available.
This cross-sectional study enrolled 583 CKD patients. Univariate and multivariate analyses were used to evaluate the relationship between AASI and renal function and parameters of cardiovascular injury.
Patients with a higher AASI had a higher systolic blood pressure, a lower estimated glomerular filtration rate (eGFR), a higher serum cystatin C, a higher left ventricular mass index (LVMI) and carotid intima-media thickness (cIMT). Univariate analyses showed that AASI was positively correlated with serum cystatin C (r=0.296, P < 0.001), serum creatinine (r=0.182, P < 0.001), and LVMI (r = 0.205, P < 0.001) and negatively correlated with the eGFR (r = –0.200, P < 0.001). Multivariate analyses revealed that serum cystatin C, eGFR, serum creatinine and LVMI were independently correlated with AASI.
These data suggest that AASI was closely correlated with renal function and parameters of cardiovascular injury in Chinese CKD patients. Good quality, long-term, large longitudinal trials to validate the role of AASI in clinical practice for Chinese CKD patients.
Ambulatory arterial stiffness index; Chronic kidney disease; Renal function; Left ventricular mass index
In the HXB and BXH recombinant inbred strains derived from the spontaneously hypertensive rat and the normotensive Brown Norway rat, we determined the strain distribution patterns of 500 genetic markers to scan the rodent genome for quantitative trait loci regulating cardiac mass and blood pressure. The markers spanned approximately 1,139 cM of the genome and were tested for correlations with left ventricular mass adjusted for body weight, and with systolic, diastolic, and mean arterial pressures. The marker for the dopamine 1A receptor (Drd1a) on chromosome 17 showed the strongest correlation with left ventricular heart weight (P = .00038, r = -0.59) and the relationship to heart weight was independent of blood pressure. The markers showing the strongest correlations with systolic, diastolic, and mean arterial pressure were D19Mit7 on chromosome 19 (P = .0012, r = .55), D2N35 on chromosome 2 (P = .0008, r = .56), and Il6 on chromosome 4 (P = .0018, r = .53), respectively. These studies demonstrate that the HXB and BXH strains can be effectively used for genome scanning studies of complex traits and have revealed several chromosome regions that may be involved in the genetic control of blood pressure and cardiac mass in the rat.
Family studies of individual tissues have shown that gene expression traits are genetically heritable. Here, we investigate cis and trans components of heritability both within and across tissues by applying variance-components methods to 722 Icelanders from family cohorts, using identity-by-descent (IBD) estimates from long-range phased genome-wide SNP data and gene expression measurements for ∼19,000 genes in blood and adipose tissue. We estimate the proportion of gene expression heritability attributable to cis regulation as 37% in blood and 24% in adipose tissue. Our results indicate that the correlation in gene expression measurements across these tissues is primarily due to heritability at cis loci, whereas there is little sharing of trans regulation across tissues. One implication of this finding is that heritability in tissues composed of heterogeneous cell types is expected to be more dominated by cis regulation than in tissues composed of more homogeneous cell types, consistent with our blood versus adipose results as well as results of previous studies in lymphoblastoid cell lines. Finally, we obtained similar estimates of the cis components of heritability using IBD between unrelated individuals, indicating that transgenerational epigenetic inheritance does not contribute substantially to the “missing heritability” of gene expression in these tissue types.
An important goal in biology is to understand how genotype affects gene expression. Because gene expression varies across tissues, the relationship between genotype and gene expression may be tissue-specific. In this study, we used heritability approaches to study the regulation of gene expression in two tissue types, blood and adipose tissue, as well as the regulation of gene expression that is shared across these tissues. Heritability can be partitioned into cis and trans effects by assessing identity-by-descent (IBD) at the genomic location close to the expressed gene or genome-wide, respectively, and applying variance-components methods to partition the heritability of each gene. We estimated the proportion of gene expression heritability explained by cis regulation as 37% in blood and 24% in adipose tissue. Notably, the heritability shared across tissue types was primarily due to cis regulation. Thus, the relative contribution of cis versus trans regulation is expected to increase with the number of cell types present in the tissue being assayed, just as observed in our study and in a comparison to previous work on lymphoblastoid cell lines (LCL). We specifically ruled out a substantial contribution of transgenerational epigenetic inheritance to heritability of gene expression in these cohorts by repeating our heritability analyses using segments shared IBD in distantly related Icelanders.
A project of QTL detection was carried out in the French Holstein, Normande, and Montbéliarde dairy cattle breeds. This granddaughter design included 1 548 artificial insemination bulls distributed in 14 sire families and evaluated after a progeny-test for 24 traits (production, milk composition, persistency, type, fertility, mastitis resistance, and milking ease). These bulls were also genotyped for 169 genetic markers, mostly microsatellites. The QTL were analysed by within-sire linear regression of daughter yield deviations or deregressed proofs on the probability that the son receives one or the other paternal QTL allele, given the marker information. QTL were detected for all traits, including those with a low heritability. One hundred and twenty QTL with a chromosome-wise significance lower than 3% were tabulated. This threshold corresponded to a 15% false discovery rate. Amongst them, 32 were genome-wise significant. Estimates of their contribution to genetic variance ranged from 6 to 40%. Most substitution effects ranged from 0.6 to 1.0 genetic standard deviation. For a given QTL, only 1 to 5 families out of 14 were informative. The confidence intervals of the QTL locations were large and always greater than 20 cM. This experiment confirmed several already published QTL but most of them were original, particularly for non-production traits.
dairy cattle; QTL detection; genetic marker; granddaughter design
Cardiovascular disease-related traits, such as body mass index (BMI), systolic blood pressure (SBP), triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL), and glucose levels (GLUC), have moderate to high correlations with each other. We hypothesized that there might be some common factors underlying the correlations of these traits, and attempted to identify these factors and their genetic structures. Cross-sectional measurements from the 330 extended Framingham Heart Study families were used in this study. Principal component factor analysis was applied to obtain the factors that were then analyzed using variance components linkage analysis.
With the above six traits three factors were generated: BMI-SBP-GLUC, HDL-TG, and TC-TG. The heritabilities for these factors were 32%, 45%, and 49%, respectively. Comparing the linkage results of the factors with the results of their component traits, evidence for linkage was observed for the TC-TG factor to a locus on chromosome 2p23 with a two-point LOD score 2.73 (marker GATA8F07) and a multipoint LOD score 1.81 (at 54 cM), while the LOD scores for TC and TG did not exceed 1 at this region.
Our analysis showed a locus on chromosome 2 might have a pleiotropic effect on the cardiovascular disease-related traits TC and TG.
Integration of genetic and metabolic profiling holds promise for providing insight into human disease. Coronary artery disease (CAD) is strongly heritable, but the heritability of metabolomic profiles has not been evaluated in humans. We performed quantitative mass spectrometry-based metabolic profiling in 117 individuals within eight multiplex families from the GENECARD study of premature CAD. Heritabilities were calculated using variance components. We found high heritabilities for amino acids (arginine, ornithine, alanine, proline, leucine/isoleucine, valine, glutamate/glutamine, phenylalanine and glycine; h2=0.33–0.80, P=0.005–1.9 × 10−16), free fatty acids (arachidonic, palmitic, linoleic; h2=0.48–0.59, P=0.002–0.00005) and acylcarnitines (h2=0.23–0.79, P=0.05–0.0000002). Principal components analysis was used to identify metabolite clusters. Reflecting individual metabolites, several components were heritable, including components comprised of ketones, β-hydroxybutyrate and C2-acylcarnitine (h2=0.61); short- and medium-chain acylcarnitines (h2=0.39); amino acids (h2=0.44); long-chain acylcarnitines (h2=0.39) and branched-chain amino acids (h2=0.27). We report a novel finding of high heritabilities of metabolites in premature CAD, establishing a possible genetic basis for these profiles. These results have implications for understanding CAD pathophysiology and genetics.
acylcarnitines; amino acids; heritability; cardiovascular disease; metabolomics
There is a relationship between CD4-T-cell number and circulating interleukin 7 (IL-7) levels in human immunodeficiency virus (HIV)-positive individuals. Here, we show that IL-7 induced a dose-dependent production of CCL3 (MIP-1α), CCL4 (MIP-1β), and CCL5 (RANTES) in peripheral blood mononuclear cells (PBMC), ex vivo tonsil lymphoid tissue of HIV− individuals, and PBMC from HIV+ individuals, suggesting that IL-7 may regulate β-chemokine production in vivo. In a cross-sectional study of HIV+ individuals (n = 130), a weak but significant correlation between IL-7 and RANTES was noted (r = 0.379; P < 0.001). Remarkably, the correlation between IL-7 and RANTES increased to an r value of 0.798 (P < 0.001) if individuals with low CD4 cell counts (<200 cells/μl) were excluded from the analysis. Our results suggest that there is a relationship between IL-7 and the production of RANTES both in vitro and in vivo that is lost in immune-compromised patients (CD4 count of <200 cells/μl) but that could be restored by antiretroviral therapy. Unlike the case for IL-7, high levels of RANTES suggest an intermediate stage of HIV disease progression.
Background and Purpose
Reduced arterial distensibility has been introduced as a novel risk factor for atherosclerosis. The importance of the genetic contribution to variation in distensibility is largely unknown. The purpose of this study was to estimate heritability of carotid distensibility.
The ongoing Northern Manhattan Family Study recruits high-risk Caribbean Hispanic families to study genetic effects on stroke/cardiovascular risk factors. The distensibility metrics (strain, stiffness, distensibility, and elastic modulus) were measured from the right common carotid artery, and the heritability for each was estimated. Variance component methods were used to estimate age- and sex-adjusted heritability. Correlations were calculated to evaluate the relationship between distensibility phenotypes and intimamedia thickness (IMT) at each carotid segment.
The current data included 88 probands and 605 relatives from 88 families. Age- and sex-adjusted heritability was 25% for strain, 17% for distensibility, 20% for stiffness, and 20% for elastic modulus. Without adjustment for covariates, strong correlations were found between distensibility metrics and IMT: the absolute values of correlation coefficients were between 0.2 and 0.5, and all P values were <0.001. However, the correlation coefficients were reduced substantially after adjusting for age and sex.
These results suggested that genetic factors explained a moderate proportion of the variability of carotid distensibility. The correlations between distensibility and IMT were mainly attributable to age and sex effects. The regulation of carotid distensibility and IMT may reflect different underlying genetic and environmental mechanisms.
atherosclerosis; carotid arteries; genetics
Increasing left ventricular mass is a risk factor for cardiovascular morbidity and mortality.
To examine the possible association of smoking with the left ventricular growth response in men.
Left ventricular mass was measured in 309 army recruits before and after an identical 12‐week physical training programme. Left ventricular mass was determined using cardiovascular magnetic resonance.
Left ventricular mass increased with training (mean (standard deviation (SD)) 3.83 (10.81) g, p<0.001). By univariate analysis, exercise‐induced change in left ventricular mass was positively associated with cigarette smoking (mean (SD) 1.69 (11.10) g v 4.76 (10.23) g for non‐smokers v ex‐ and current smokers, respectively; p = 0.026), whereas age, height, diastolic and systolic blood pressure (SBP), alcohol consumption or indices of physical activity were not significantly associated with change in left ventricular mass. Multivariate analysis showed body weight, smoking status and SBP to be independent predictors of left ventricular mass (incremental R2 = 3.4%, p = 0.004; R2 = 4.9%, p = 0.024; and R2 = 1.7%, p = 0.041, respectively).
Cigarette smoking and SBP are associated with exercise‐induced left ventricular growth in young men. The positive association of smoking with changes in left ventricular mass is surprising, given the limited exposure of these subjects to smoking, and although these data do not prove causation, they are of great interest to those trying to uncover the drivers of left ventricular hypertrophy, as well as to those examining the possible ill‐effects of smoking in the young.