Heritabilities of Apolipoprotein and Lipid Levels in Three Countries

Co-methylation analyses identify CpGs associated with lipid traits in Chinese discordant monozygotic twins

To control genetic background and early life milieu in genome-wide DNA methylation analysis for blood lipids, we recruited Chinese discordant monozygotic twins to explore the relationships between DNA methylations and total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG). 132 monozygotic (MZ) twins were included with discordant lipid levels and completed data. A linear mixed model was conducted in Epigenome-wide association study (EWAS). Generalized estimating equation model was for gene expression analysis. We conducted Weighted correlation network analysis (WGCNA) to build co-methylated interconnected network. Additional Qingdao citizens were recruited for validation. Inference about Causation through Examination of Familial Confounding (ICE FALCON) was used to infer the possible direction of these relationships. A total of 476 top CpGs reached suggestively significant level (P < 10-4), of which, 192 CpGs were significantly associated with TG (FDR < 0.05). They were used to build interconnected network and highlight crucial genes from WGCNA. Finally, four CpGs in GATA4 were validated as risk factors for TC; six CpGs at ITFG2-AS1 were negatively associated with TG; two CpGs in PLXND1 played protective roles in HDL-C. ICE FALCON indicated abnormal TC was regarded as the consequence of DNA methylation in CpGs at GATA4, rather than vice versa. Four CpGs in ITFG2-AS1 were both causes and consequences of modified TG levels. Our results indicated that DNA methylation levels of 12 CpGs in GATA4, ITFG2-AS1, and PLXND1 were relevant to TC, TG, and HDL-C, respectively, which might provide new epigenetic insights into potential clinical treatment of dyslipidemia.

Association of epistatic effects of MTHFR, ACE, APOB, and APOE gene polymorphisms with the risk of myocardial infarction and unstable angina in Egyptian patients

Despite remarkable discoveries in the genetic susceptibility of coronary artery disease (CAD), a large part of heritability awaits identification. Epistasis or gene-gene interaction has a profound influence on CAD and might contribute to its missed genetic variability; however, this impact was largely unexplored. Here, we appraised the associations of gene-gene interactions and haplotypes of five polymorphisms, namely methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, angiotensin converting enzyme (ACE) insertion/deletion (I/D), apolipoprotein B (APOB) R3500Q, and apolipoprotein E (APOE) ε4 with the risk of myocardial infarction (MI) and unstable angina (UA). Gene-environment interactions with traditional risk factors and clinical data were also scrutinized. This study recruited 100 MI, 50 UA patients, and 100 apparently healthy controls. Logistic regression models were employed in association analyses. We remarked that the single locus effect of individual polymorphisms was relatively weak; however, a magnified effect of their combination via gene-gene interaction may predict MI risk after adjustment for multiple comparisons. Only MTHFR C677T, ACE I/D, and APOB R5300Q were associated with the risk of UA, and the ACE I/D-R3500Q interaction posed a decreased UA risk. APOB R3500Q was in strong linkage disequilibrium with MTHFR C677T, ACE I/D, and APE ε4 polymorphisms. The TCDGε3, CADGε4, and TADGε4-C677T-A1298C-ACE I/D-R3500Q-APOE haplotypes were associated with escalating MI risk, while the CDG or CIG-C677T-ACE I/D-R3500Q haplotype was highly protective against UA risk compared to controls. Interestingly, the CADGε4 and CAIGε3 haplotypes were strongly associated with the presence of diabetes and hypertension, respectively in MI patients; both haplotypes stratified patients according to the ECHO results. In UA, the CDG haplotype was negatively associated with the presence of diabetes or dilated heart. Conclusively, our results advocate that a stronger combined effect of polymorphisms in MTHFR, ACE, APOB, and APOE genes via gene-gene and gene-environment interactions might help in risk stratification of MI and UA patients.

Genetic Pathways Underlying Individual Differences in Regular Physical Activity

Twin and family studies show a strong contribution of genetic factors to physical activity (PA) assessed by either self-report or accelerometers. PA heritability is around 43% across the lifespan. Genome-wide association studies have implied biological pathways related to exercise ability and enjoyment. A polygenic score based on genetic variants influencing PA could help improve the success of intervention programs.

Utility of Genetically Predicted Lp(a) (Lipoprotein [a]) and ApoB Levels for Cardiovascular Risk Assessment

BACKGROUND

Current lipid guidelines suggest measurement of Lp(a) (lipoprotein[a]) and ApoB (apolipoprotein B) for atherosclerotic cardiovascular disease risk assessment. Polygenic risk scores (PRSs) for Lp(a) and ApoB may identify individuals unlikely to have elevated Lp(a) or ApoB and thus reduce such suggested testing.

METHODS

PRSs were developed using least absolute shrinkage and selection operator regression among 273 222 and 356 958 UK Biobank participants of white British ancestry for Lp(a) and ApoB, respectively, and validated in separate sets of 60 771 UK Biobank and 15 050 European Prospective Investigation into Cancer and Nutrition-Norfolk participants. We then assessed the proportion of participants who, based on these PRSs, were unlikely to benefit from Lp(a) or ApoB measurements, according to current lipid guidelines.

RESULTS

In the UK Biobank and European Prospective Investigation into Cancer and Nutrition-Norfolk cohorts, the area under the receiver operating curve for the PRS-predicted Lp(a) and ApoB to identify individuals with elevated Lp(a) and ApoB was at least 0.91 (95% CI, 0.90-0.92) and 0.74 (95% CI, 0.73-0.75), respectively. The Lp(a) PRS and measured Lp(a) showed comparable association with atherosclerotic cardiovascular disease incidence, whereas the ApoB PRS was in general less predictive of atherosclerotic cardiovascular disease risk than measured ApoB. In the context of the European Society of Cardiology/European Atherosclerosis Society lipid guidelines, at a 95% sensitivity to identify individuals with elevated Lp(a) and ApoB levels, at least 54% of Lp(a) and 24% of ApoB testing could be reduced by prescreening with a PRS while maintaining a low false-negative rate.

CONCLUSIONS

A substantial proportion of suggested testing for elevated Lp(a) and a modest proportion of testing for elevated ApoB could potentially be reduced by prescreening individuals with PRSs.

Association of Non-High-Density Lipoprotein Cholesterol Measured in Adolescence, Young Adulthood, and Mid-Adulthood With Coronary Artery Calcification Measured in Mid-Adulthood

Importance

Elevated non-high-density lipoprotein cholesterol (non-HDL-C) is associated with the presence of coronary artery calcification (CAC), a marker of heart disease in adulthood. However, the relative importance of non-HDL-C levels at specific life stages for CAC remains unclear.

Objective

To identify the relative association of non-HDL-C measured at distinct life stages (adolescence, young adulthood, mid-adulthood) with the presence of CAC measured in mid-adulthood.

Design, Setting, and Participants

The Cardiovascular Risk in Young Finns Study is a population-based prospective cohort study that started in 1980 with follow-up over 28 years. Participants from 3 population centers (Kuopio, Tampere, and Turku in Finland) represent a convenience sample drawn from the 3 oldest cohorts at baseline (aged 12-18 years in 1980). Data were collected from September 1980 to August 2008. Analysis began February 2020.

Exposures

Non-HDL-C levels were measured at 3 life stages including adolescence (aged 12-18 years), young adulthood (aged 21-30 years), and mid-adulthood (aged 33-45 years).

Main Outcomes and Measures

In 2008, CAC was determined from computed tomography and dichotomized as 0 (no CAC, Agatston score = 0) and 1 (presence of CAC, Agatston score ≥1) for analysis. Using a bayesian relevant life course exposure model, the relative association was determined between non-HDL-C at each life stage and the presence of CAC in mid-adulthood.

Results

Of 589 participants, 327 (56%) were female. In a model adjusted for year of birth, sex, body mass index, systolic blood pressure, blood glucose level, smoking status, lipid-lowering and antihypertensive medication use, and family history of heart disease, cumulative exposure to non-HDL-C across all life stages was associated with CAC (odds ratio [OR], 1.50; 95% credible interval [CrI], 1.14-1.92). At each life stage, non-HDL-C was associated with CAC and exposure to non-HDL-C during adolescence had the strongest association (adolescence: OR, 1.16; 95% CrI, 1.01-1.46; young adulthood: OR, 1.14; 95% CrI, 1.01-1.43; mid-adulthood: OR, 1.12; 95% CrI, 1.01-1.34).

Conclusions and Relevance

These data suggest that elevated non-HDL-C levels at all life stages are associated with coronary atherosclerosis in mid-adulthood. However, adolescent non-HDL-C levels showed the strongest association with the presence of CAC in mid-adulthood, and greater awareness of the importance of elevated non-HDL-C in adolescence is needed.

Candidate Gene Analysis Reveals Strong Association of CETP Variants With High Density Lipoprotein Cholesterol and PCSK9 Variants With Low Density Lipoprotein Cholesterol in Ghanaian Adults: An AWI-Gen Sub-Study

Variations in lipid levels are attributed partly to genetic factors. Genome-wide association studies (GWASs) mainly performed in European, African American and Asian cohorts have identified variants associated with LDL-C, HDL-C, total cholesterol (TC) and triglycerides (TG), but few studies have been performed in sub-Saharan Africans. This study evaluated the effect of single nucleotide variants (SNVs) in eight candidate loci (ABCA1, LCAT, LPL, PON1, CETP, PCSK9, MVK, and MMAB) on lipid levels among 1855 Ghanaian adults. All lipid levels were measured directly using an automated analyser. DNA was extracted and genotyped using the H3Africa SNV array. Linear regression models were used to test the association between SNVs and log-transformed lipid levels, adjusting for sex, age and waist circumference. In addition Bonferroni correction was performed to account for multiple testing. Several variants of CETP, LCAT, PCSK9, and PON1 (MAF > 0.05) were associated with HDL-C, LDL-C and TC levels at p < 0.05. The lead variants for association with HDL-C were rs17231520 in CETP (β = 0.139, p < 0.0001) and rs1109166 in LCAT (β = −0.044, p = 0.028). Lower LDL-C levels were associated with an intronic variant in PCSK9 (rs11806638 [β = −0.055, p = 0.027]) and increased TC was associated with a variant in PON1 (rs854558 [β = 0.040, p = 0.020]). In silico functional analyses indicated that these variants likely influence gene function through their effect on gene transcription. We replicated a strong association between CETP variants and HDL-C and between PCSK9 variant and LDL-C in West Africans, with two potentially functional variants and identified three novel variants in linkage disequilibrium in PON1 which were associated with increasing TC levels in Ghanaians.

Genetic and environmental determinants of variation in the plasma lipidome of older Australian twins

The critical role of blood lipids in a broad range of health and disease states is well recognised but less explored is the interplay of genetics and environment within the broader blood lipidome. We examined heritability of the plasma lipidome among healthy older-aged twins (75 monozygotic/55 dizygotic pairs) enrolled in the Older Australian Twins Study (OATS) and explored corresponding gene expression and DNA methylation associations. 27/209 lipids (13.3%) detected by liquid chromatography-coupled mass spectrometry (LC-MS) were significantly heritable under the classical ACE twin model (h2 = 0.28-0.59), which included ceramides (Cer) and triglycerides (TG). Relative to non-significantly heritable TGs, heritable TGs had a greater number of associations with gene transcripts, not directly associated with lipid metabolism, but with immune function, signalling and transcriptional regulation. Genome-wide average DNA methylation (GWAM) levels accounted for variability in some non-heritable lipids. We reveal a complex interplay of genetic and environmental influences on the ageing plasma lipidome.

Epigenetics, heritability and longitudinal analysis

BACKGROUND

Longitudinal data and repeated measurements in epigenome-wide association studies (EWAS) provide a rich resource for understanding epigenetics. We summarize 7 analytical approaches to the GAW20 data sets that addressed challenges and potential applications of phenotypic and epigenetic data. All contributions used the GAW20 real data set and employed either linear mixed effect (LME) models or marginal models through generalized estimating equations (GEE). These contributions were subdivided into 3 categories: (a) quality control (QC) methods for DNA methylation data; (b) heritability estimates pretreatment and posttreatment with fenofibrate; and (c) impact of drug response pretreatment and posttreatment with fenofibrate on DNA methylation and blood lipids.

RESULTS

Two contributions addressed QC and identified large statistical differences with pretreatment and posttreatment DNA methylation, possibly a result of batch effects. Two contributions compared epigenome-wide heritability estimates pretreatment and posttreatment, with one employing a Bayesian LME and the other using a variance-component LME. Density curves comparing these studies indicated these heritability estimates were similar. Another contribution used a variance-component LME to depict the proportion of heritability resulting from a genetic and shared environment. By including environmental exposures as random effects, the authors found heritability estimates became more stable but not significantly different. Two contributions investigated treatment response. One estimated drug-associated methylation effects on triglyceride levels as the response, and identified 11 significant cytosine-phosphate-guanine (CpG) sites with or without adjusting for high-density lipoprotein. The second contribution performed weighted gene coexpression network analysis and identified 6 significant modules of at least 30 CpG sites, including 3 modules with topological differences pretreatment and posttreatment.

CONCLUSIONS

Four conclusions from this GAW20 working group are: (a) QC measures are an important consideration for EWAS studies that are investigating multiple time points or repeated measurements; (b) application of heritability estimates between time points for individual CpG sites is a useful QC measure for DNA methylation studies; (c) drug intervention demonstrated strong epigenome-wide DNA methylation patterns across the 2 time points; and (d) new statistical methods are required to account for the environmental contributions of DNA methylation across time. These contributions demonstrate numerous opportunities exist for the analysis of longitudinal data in future epigenetic studies.

An exome-wide sequencing study of lipid response to high-fat meal and fenofibrate in Caucasians from the GOLDN cohort

Our understanding of genetic influences on the response of lipids to specific interventions is limited. In this study, we sought to elucidate effects of rare genetic variants on lipid response to a high-fat meal challenge and fenofibrate (FFB) therapy in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) cohort using an exome-wide sequencing-based association study. Our results showed that the rare coding variants in ITGA7, SIPA1L2, and CEP72 are significantly associated with fasting LDL cholesterol response to FFB (P = 1.24E-07), triglyceride postprandial area under the increase (AUI) (P = 2.31E-06), and triglyceride postprandial AUI response to FFB (P = 1.88E-06), respectively. We sought to replicate the association for SIPA1L2 in the Heredity and Phenotype Intervention (HAPI) Heart Study, which included a high-fat meal challenge but not FFB treatment. The associated rare variants in GOLDN were not observed in the HAPI Heart study, and thus the gene-based result was not replicated. For functional validation, we found that gene transcript level of SIPA1L2 is associated with triglyceride postprandial AUI (P < 0.05) in GOLDN. Our study suggests unique genetic mechanisms contributing to the lipid response to the high-fat meal challenge and FFB therapy.

Association between apolipoprotein B genetic polymorphism and the risk of calcific aortic stenosis in Chinese subjects, in Xinjiang, China

Background

Limited information is available when it comes to the impact of genetic on Calcific Aortic Stenosis (CAS). Apolipoprotein B (apoB) is a key component in lipid metabolism and plays an important role in the dynamic equilibrium of cholesterol. We performed a case–control study to explore the association of apoB genetic polymorphisms with CAS in Chinese subjects, in Xinjiang, China.

Methods

We designed a case-control study including 314 CAS patients and 652 age- and sex-matched control subjects. Using the polymerase chain reaction-restriction fragment length (PCR-RFLP) method, we genotyped two SNPs (rs6725189 and rs693) of apoB gene in all subjects.

Results

We found that the rs693 T allele was associated with a significantly elevated CAS risk [TT/CT vs. CC: adjusted odds ratio (AOR) = 1.58, 95% confidence interval (CI) = 1.82–2.10, P = 0.002] and the rs6725189 T allele was also associated with a significantly elevated CAS risk (GT vs. GG: AOR = 1.82, 95% CI = 1.14–2.92, P = 0.013). Furthermore, we also found that the TC levels were significantly higher in rs693 TT/CT genotypes than that in CC genotypes (P < 0.05).

Conclusions

Both rs693 and rs6725189 of the apoB gene are associated with CAS in Chinese subjects, in Xinjiang, China.

Genetic Effects on the Correlation Structure of CVD Risk Factors: Exome-Wide Data From a Ghanaian Population

Plasma concentration of plasminogen activator inhibitor-1 (PAI-1) is highly correlated with several cardiovascular disease (CVD) risk factors. It also plays a direct role in CVD, including myocardial infarction and stroke, by impeding the dissolution of thrombi in the blood. Insofar as PAI-1 links CVD's risk factors to its endpoints, genetic variants modulating the relationship between PAI-1 and risk factors may be of particular clinical and biological interest. The high heritability of PAI-1, which has not been explained by genetic association studies, may also, in large part, be due to this relationship with CVD risk factors. Using exome-wide data from 1,032 Ghanaian study participants, we tested for heterogeneity of correlation by genotype between PAI-1 and 4 CVD risk factors (body mass index, triglycerides, mean arterial pressure, and fasting glucose) under the hypothesis that loci involved in the relationship between PAI-1 and other risk factors will also modify their correlational structure. We found more significant heterogeneities of correlation by genotype than we found marginal effects, with no evidence of type I inflation. The most significant result among all univariate and multivariate tests performed in this study was the heterogeneity of correlation between PAI-1 and mean arterial pressure at rs10738554, near SLC24A2, a gene previously associated with high blood pressure in African Americans.

Maternal early pregnancy lipid profile and offspring's lipids and glycaemic control at age 5-6 years: The ABCD study

BACKGROUND & AIMS

Maternal early pregnancy lipid profile might influence offspring's lipids and glycaemic control, through an increased offspring's fat percentage. This explorative study investigates whether maternal early pregnancy lipid profile is associated with offspring's lipids and glycaemic control independently of offspring's fat percentage and if these associations are mediated by offspring's fat percentage. Possible sex differences in these associations are also examined.

METHODS

1133 mother-child pairs of the prospective ABCD-study were included. Maternal non-fasting lipids were collected in early pregnancy: triglycerides, total cholesterol (TC), Apolipoprotein A1 (ApoA1), Apolipoprotein B (ApoB) and free fatty acids (FFA). Fasting triglycerides, TC, high density lipoprotein (HDL), low density lipoprotein (LDL), glucose and C-peptide were assessed in offspring aged 5-6 years and HOMA2-IR was calculated.

RESULTS

After adjustment for covariates, strongest associations were found between maternal TC and offspring's TC (boys β(95%CI) = 0.141 (0.074-0.207); girls β(95%CI) = 0.268 (0.200; 0.336)) and LDL (boys β(95%CI) = 0.114 (0.052; 0.176); girls β(95%CI) = 0.247 (0.181-0.312)), maternal ApoB and offspring's TC (boys β(95%CI) = 0.638 (0.311-0.965); girls β(95%CI) = 1.121 (0.766-1.475)) and LDL (boys β(95%CI) = 0.699 (0.393-1.005); girls β(95%CI) = 1.198 (0.868-1.529)), and maternal ApoA1 and offspring's HDL (only boys β(95%CI) = 0.221 (0.101-0.341)). No significant association was found between maternal lipids and offspring's glycaemic control, and offspring's fat percentage played no mediating role.

CONCLUSIONS

Maternal early pregnancy lipid profile is associated with offspring's lipid profile in childhood, with overall stronger associations in girls. This study provides further evidence that lowering lipid levels during pregnancy might be beneficial for the long term health of the offspring.

The multifaceted interplay between lipids and epigenetics

PURPOSE OF REVIEW

The interplay between lipids and epigenetic mechanisms has recently gained increased interest because of its relevance for common diseases and most notably atherosclerosis. This review discusses recent advances in unravelling this interplay with a particular focus on promising approaches and methods that will be able to establish causal relationships.

RECENT FINDINGS

Complementary approaches uncovered close links between circulating lipids and epigenetic mechanisms at multiple levels. A characterization of lipid-associated genetic variants suggests that these variants exert their influence on lipid levels through epigenetic changes in the liver. Moreover, exposure of monocytes to lipids persistently alters their epigenetic makeup resulting in more proinflammatory cells. Hence, epigenetic changes can both impact on and be induced by lipids.

SUMMARY

It is the combined application of technological advances to probe epigenetic modifications at a genome-wide scale and methodological advances aimed at causal inference (including Mendelian randomization and integrative genomics) that will elucidate the interplay between circulating lipids and epigenetics. Understanding its role in the development of atherosclerosis holds the promise of identifying a new category of therapeutic targets, since epigenetic changes are amenable to reversal.

A nonsynonymous SNP in BANK1 is associated with serum LDL cholesterol levels in three Korean populations

Serum levels of lipids, such as cholesterol and triglycerides, are heritable risk factors for cardiovascular disease and targets for therapeutic intervention. Because previous genome-wide association studies (GWASs) did not target functional genetic variants, we employed an alternate approach using nonsynonymous single-nucleotide polymorphisms (SNPs) to identify functional genetic variants associated with the regulation of serum lipid levels. We selected 3667 healthy individuals from a rural community-based cohort (CAVAS; Cardio Vascular disease Association Study) of the Korean Genome and Epidemiology Study project. We analyzed demographic and lifestyle information, lipid measurements and genotypes using the Illumina-1M SNP chip. For genotyping, we isolated 11 558 nonsynonymous SNPs and conducted a linear regression analysis with four lipid traits (total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterols and triglycerides). Significantly associated SNPs were validated in two independent Korean populations, Korean Association Resource (KARE) (n=4116) and Health Examinee (HEXA) (n=2178). Of the 11 558 SNPs, one SNP (rs3733197) from the CAVAS was significantly associated with serum LDL cholesterols (beta±s.e.=4.67±0.94, P-value=1.0 × 10(-6 and) Bonferroni corrected P-value=0.012). The replication results of HEXA and KARE were beta±s.e.=2.88±1.12, P-value=0.016 and beta±s.e.=1.26±0.97, P-value=0.196, respectively. An overall meta-analysis of the three data sets revealed beta=2.98±0.57, P-value=6.19 × 10(-7). The rs3733197 is located in the coding region of BANK1 (B-cell scaffold protein with ankyrin repeats 1), and the minor allele (A) resulted in the replacement of the Alanine at position 383 with Threonine.

Genetic architecture of lipid traits changes over time and differs by race: Princeton Lipid Follow-up Study

Dyslipidemia is a major risk factor for CVD. Previous studies on lipid heritability have largely focused on white populations assessed after the obesity epidemic. Given secular trends and racial differences in lipid levels, this study explored whether lipid heritability is consistent across time and between races. African American and white nuclear families had fasting lipids measured in the 1970s and 22-30 years later. Heritability was estimated, and bivariate analyses between visits were conducted by race using variance components analysis. A total of 1,454 individuals (age 14.1/40.6 for offspring/parents at baseline; 39.6/66.5 at follow-up) in 373 families (286 white, 87 African American) were included. Lipid trait heritabilities were typically stronger during the 1970s than the 2000s. At baseline, additive genetic variation for LDL was significantly lower in African Americans than whites (P = 0.015). Shared genetic contribution to lipid variability over time was significant in both whites (all P < 0.0001) and African Americans (P ≤ 0.05 for total, LDL, and HDL cholesterol). African American families demonstrated shared environmental contributions to lipid variation over time (all P ≤ 0.05). Lower heritability, lower LDL genetic variance, and durable environmental effects across the obesity epidemic in African American families suggest race-specific approaches are needed to clarify the genetic etiology of lipids.

Polygenic risk for hypertriglyceridemia is attenuated in Japanese men with high fitness levels

High cardiorespiratory fitness (CRF) is associated with a reduced risk for dyslipidemia; however, blood lipid levels are also affected by individual genetic variations. We performed a cross-sectional study to determine whether CRF modifies polygenic risk for dyslipidemia. Serum levels of triglycerides (TG), LDL cholesterol (LDL-C), and HDL cholesterol (HDL-C) were measured in 170 Japanese men (age 20–79 yr). CRF was assessed by measuring maximal oxygen uptake (V̇o2max), and subjects were divided into low-fitness and high-fitness groups according to the reference V̇o2max value for health promotion in Japan. We analyzed 19 single nucleotide polymorphisms (SNPs) associated with TG, LDL-C, or HDL-C levels. Based on these SNPs, we calculated three genetic risk scores (GRSs: TG-GRS, LDL-GRS, and HDL-GRS), and subjects were divided into low, middle, and high groups according to the tertile for each GRS. Serum TG levels of low-fitness individuals were higher in the high and middle TG-GRS groups than in the low TG-GRS group ( P < 0.01 and P < 0.05, respectively), whereas no differences were detected in the TG levels of high-fitness individuals among the TG-GRS groups. In contrast, the high LDL-GRS group had higher LDL-C levels than did the low LDL-GRS group, and HDL-C levels were lower in the high HDL-GRS group than in the low HDL-GRS group regardless of the fitness level ( P < 0.05). These results suggest that high CRF attenuates polygenic risk for hypertriglyceridemia; however, high CRF may not modify the polygenic risk associated with high LDL-C and low HDL-C levels in Japanese men.

Genome-wide characterization of shared and distinct genetic components that influence blood lipid levels in ethnically diverse human populations

Blood lipid concentrations are heritable risk factors associated with atherosclerosis and cardiovascular diseases. Lipid traits exhibit considerable variation among populations of distinct ancestral origin as well as between individuals within a population. We performed association analyses to identify genetic loci influencing lipid concentrations in African American and Hispanic American women in the Women's Health Initiative SNP Health Association Resource. We validated one African-specific high-density lipoprotein cholesterol locus at CD36 as well as 14 known lipid loci that have been previously implicated in studies of European populations. Moreover, we demonstrate striking similarities in genetic architecture (loci influencing the trait, direction and magnitude of genetic effects, and proportions of phenotypic variation explained) of lipid traits across populations. In particular, we found that a disproportionate fraction of lipid variation in African Americans and Hispanic Americans can be attributed to genomic loci exhibiting statistical evidence of association in Europeans, even though the precise genes and variants remain unknown. At the same time, we found substantial allelic heterogeneity within shared loci, characterized both by population-specific rare variants and variants shared among multiple populations that occur at disparate frequencies. The allelic heterogeneity emphasizes the importance of including diverse populations in future genetic association studies of complex traits such as lipids; furthermore, the overlap in lipid loci across populations of diverse ancestral origin argues that additional knowledge can be gleaned from multiple populations.

Identification of a functional apolipoprotein E promoter polymorphism regulating plasma apolipoprotein E concentration

OBJECTIVE

There is compelling evidence that the plasma apolipoprotein E (APOE) concentration, in addition to the APOE ε2/ε3/ε4 genotype, influences plasma lipoprotein levels, but the functional genetic variants influencing the plasma APOE concentration have not been identified.

APPROACH AND RESULTS

Genome-wide association studies in 2 cohorts of healthy, middle-aged subjects identified the APOE locus as the only genetic locus showing robust associations with the plasma APOE concentration. Fine-mapping of the APOE locus confirmed that the rs7412 ε2-allele is the primary genetic variant responsible for the relationship with plasma APOE concentration. Further mapping of the APOE locus uncovered that rs769446 (-427T/C) in the APOE promoter is independently associated with the plasma APOE concentration. Expression studies in 199 human liver samples demonstrated that the rs769446 C-allele is associated with increased APOE mRNA levels (P=0.015). Transient transfection studies and electrophoretic mobility shift assays in human hepatoma HepG2 cells corroborated the role of rs769446 in transcriptional regulation of APOE. However, no relationships were found between rs769446 genotype and plasma lipoprotein levels in 2 cohorts (n=1648 and n=1039) of healthy middle-aged carriers of the APOE ε3/ε3 genotype.

CONCLUSIONS

rs769446 is a functional polymorphism involved in the regulation of the plasma APOE concentration.

A genome-wide association study of monozygotic twin-pairs suggests a locus related to variability of serum high-density lipoprotein cholesterol

Genome-wide association analysis on monozygotic twin-pairs offers a route to discovery of gene environment interactions through testing for variability loci associated with sensitivity to individual environment/lifestyle. We present a genome-wide scan of loci associated with intra-pair differences in serum lipid and apolipoprotein levels. We report data for 1,720 monozygotic female twin-pairs from GenomEUtwin project with 2.5 million SNPs, imputed or genotyped, and measured serum lipid fractions for both twins. We found one locus associated with intra-pair differences in high-density lipoprotein cholesterol, rs2483058 in an intron of SRGAP2, where twins carrying the C allele are more sensitive to environmental factors(P=3.98 x 10-8). We followed up the association in further genotyped monozygotic twins (N= 1,261),which showed a moderate association for the variant (P= 0.200, same direction of an effect). In addition,we report a new association on the level of apolipoprotein A-ll (P= 4.03 x 1 o-8).

Total ApoE and ApoE4 isoform assays in an Alzheimer's disease case-control study by targeted mass spectrometry (n=669): a pilot assay for methionine-containing proteotypic peptides

Allelic polymorphism of the apolipoprotein E (ApoE) gene (ApoE ε2, ApoE ε3 and ApoE ε4 alleles) gives rise to three protein isoforms (ApoE2, ApoE3 and ApoE4) that differ by 1 or 2 amino acids. Inheritance of the ApoE ε4 allele is a risk factor for developing Alzheimer's disease (AD). The potential diagnostic value of ApoE protein levels in biological fluids (i.e. cerebrospinal fluid, plasma and serum) for distinguishing between AD patients and healthy elderly subjects is subject to great controversy. Although a recent study reported subnormal total ApoE and ApoE4 levels in the plasma of AD patients, other studies have found normal or even elevated protein levels (versus controls). Because all previously reported assays were based on immunoenzymatic techniques, we decided to develop an orthogonal assay based on targeted mass spectrometry by tracking (i) a proteotypic peptide common to all ApoE isoforms and (ii) a peptide that is specific for the ε4 allele. After trypsin digestion, the ApoE4-specific peptide contains an oxidation-prone methionine residue. The endogenous methionine oxidation level was evaluated in a small cohort (n=68) of heterozygous ε3ε4 carriers containing both healthy controls and AD patients. As expected, the proportion of oxidized residues varied from 0 to 10%, with an average of 5%. We therefore developed a standardized strategy for the unbiased, absolute quantification of ApoE4, based on performic acid oxidization of methionine. Once the sample workflow had been thoroughly validated, it was applied to the concomitant quantification of total ApoE and ApoE4 isoform in a large case-control study (n=669). The final measurements were consistent with most previously reported ApoE concentration values and confirm the influence of the different alleles on the protein expression level. Our results illustrate (i) the reliability of selected reaction monitoring-based assays and (ii) the value of the oxidization step for unbiased monitoring of methionine-containing proteotypic peptides. Furthermore, a statistical analysis indicated that neither total ApoE and ApoE4 levels nor the ApoE/ApoE4 ratio correlated with the diagnosis of AD. These findings reinforce the conclusions of previous studies in which plasma ApoE levels had no obvious clinical significance.

Heritability of Longitudinal Measures of Body Mass Index and Lipid and Lipoprotein Levels in Aging Twins

Body-mass index (BMI), total cholesterol (TC), lowdensity lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) levels are known to be highly heritable. We evaluated the genetic and environmental relationships of these measures over time in an analysis of twin pairs. Monozygotic (235 pairs) and dizygotic (260 pairs) male twins were participants in the National Heart Lung and Blood Institute Veteran Twin Study, and were followed with three clinical exams from mean age 48 years to mean age 63 years. Structural equation modeling (SEM) with adjustment forAPOEgenotype (a significant contributor to TC and LDL-C) was used to assess longitudinal patterns of heritability. Results indicated a contribution of genetic factors to BMI, TC, LDL-C, HLD-C, and TG. Modest increases over time were observed in the heritability of BMI (from 0.48 to 0.61), TC (from 0.46 to 0.57), LDL-C (from 0.49 to 0.64), and HDL-C (from 0.50 to 0.62), but this trend was not present for TG. There was a corresponding decrease in shared environmental influences over time for these traits, although shared environment was a significant contributor only for HDL-C. Moreover, we observed that genetic influences for all measures were significantly correlated over time, and we found no evidence of age-specific genetic effects. In summary, longitudinal analyses of twin data indicate that genetic factors do not account for a significant proportion of the variation in age-related changes of BMI or lipid and lipoprotein levels.

A Longitudinal Genetic Study of Plasma Lipids in Adolescent Twins

Plasma lipids such as high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol and triglyceride levels contribute to variation in the risk of cardiovascular disease. The early stages of atherosclerosis in childhood have also been associated with changes in triglycerides, LDL and HDL. Heritability estimates for lipids and lipoproteins for adolescents are in the range .71 to .82, but little is known about changes of genetic and environmental influences over time in adolescence. We have investigated the contribution of genetic and environmental influences to variation in lipids in adolescent twins and their nontwin siblings using longitudinal twin and family data. Plasma HDL and LDL cholesterol, total cholesterol and triglycerides data from 965 twin pairs at 12, 14 and 16 years of age and their siblings have been analyzed. Longitudinal genetic models that included effects of age, sex and their interaction were fitted to assess whether the same or different genes influence each trait at different ages. Results suggested that more than one genetic factor influences HDL, LDL, total cholesterol and triglycerides over time at ages 12, 14 and 16 years. There was no evidence of shared environmental effects except for HDL and little evidence of long-term nonshared environmental effects was found. Our study suggested that there are developmental changes in the genes affecting plasma lipid concentrations across adolescence.

Genetic Dominance Influences Blood Biomarker Levels in a Sample of 12,000 Swedish Elderly Twins

In twin studies of cardiovascular disease biomarkers the dizygotic correlations are often estimated to be less than half of monozygotic correlations indicating a potential influence of nonadditive genetic factors. Using a large and homogenous sample, we estimated the additive and dominance genetic influences on levels of high density lipoprotein, low density lipoprotein, apolipoprotein A-I, apolipoprotein B, total cholesterol, triglycerides, glucose, hemoglobin Alc and c-reactive protein, all of which are biomarkers associated with cardiovascular disease. The blood biomarkers were measured on 12,000 Swedish twins born between 1911 and 1958. The large sample allowed us to obtain heritability estimates with considerable precision and provided adequate statistical power for estimation of dominance genetic components. Our study showed complete absence of the shared environment component for the investigated traits. Dominant genetic component was shown to be significant for low density lipoprotein (0.18), glucose (0.31), Hemoglobin Alc (0.55), and c-reactive protein (0.27). To our knowledge, this is the first statistically significant evidence for dominance genetic variance found for low density lipoprotein, glucose, hemoglobin Alc, and c-reactive protein in a population based twin sample. The study highlights the importance of acknowledging nonadditive genes underlying the risk of developing cardiovascular diseases.

Longitudinal Genetic Analysis of Plasma Lipids

The consensus from published studies is that plasma lipids are each influenced by genetic factors, and that this contributes to genetic variation in risk of cardiovascular disease. Heritability estimates for lipids and lipoproteins are in the range .48 to .87, when measured once per study participant. However, this ignores the confounding effects of biological variation measurement error and ageing, and a truer assessment of genetic effects on cardiovascular risk may be obtained from analysis of longitudinal twin or family data. We have analyzed information on plasma high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides, from 415 adult twins who provided blood on two to five occasions over 10 to 17 years. Multivariate modeling of genetic and environmental contributions to variation within and across occasions was used to assess the extent to which genetic and environmental factors have long-term effects on plasma lipids. Results indicated that more than one genetic factor influenced HDL and LDL components of cholesterol, and triglycerides over time in all studies. Nonshared environmental factors did not have significant long-term effects except for HDL. We conclude that when heritability of lipid risk factors is estimated on only one occasion, the existence of biological variation and measurement errors leads to underestimation of the importance of genetic factors as a cause of variation in long-term risk within the population. In addition our data suggest that different genes may affect the risk profile at different ages.

Heritabilities of Lipids in Young European American and African American Twins

Twin studies of lipids have almost exclusively involved Caucasians. People of African descent are known to show a healthier lipid profile, but relatively little is known about ethnic differences in genetic and environmental influences on lipids. One hundred and six African American (AA) and 106 European American (EA) twins (30 singletons and 91 complete pairs: 49 monozygotic, 21 dizygotic and 21 opposite-sex) from the south-eastern United States were studied (mean age 17.9 ± 3.2 years; 79% fasting). Lipids were assayed with the Cholestech LDX system. Analyses were adjusted for fasting status. Generalized estimating equations were used to test for the effects of sex and ethnicity on means, controlling for the dependence within twin pairs. Structural equation modeling was used to estimate genetic and environmental effects on each lipid variable. Females showed higher high-density lipoprotein (HDL) values than males (p< .001) and AAs showed higher HDL values than EAs (p< .001). EA males had higher triglyceride values than other groups (p= .02). All parameter estimates could be set equal across sex. Parameter estimates for total cholesterol, triglycerides and HDL could be set equal across ethnicity. The best fitting model for low- density lipoprotein (LDL) showed higher heritability in AAs (.92) than EAs (.69). Heritabilities ranged from 69% to 92%, with remaining variation explained by nonshared environmental effects. Adjustment for body mass index had virtually no effect on the heritability estimates. In this first twin study on lipids to include AAs, no ethnic differences in heritability were found except for LDL, where AAs exhibited higher estimates.

History, geography and population structure influence the distribution and heritability of blood and anthropometric quantitative traits in nine Sardinian genetic isolates

Isolated founder populations which exhibit great genetic and environmental homogeneity provide an attractive setting for the study of quantitative traits (QTs). Geneticists have repeatedly turned to population isolates and the past successes have prompted increased interest among medical researchers. We studied nine small isolated villages of a secluded area of Sardinia (Ogliastra), all of them characterized by a few founders, high endogamy rates, slow population expansion and a distinct genetic makeup. Anthropometric and blood parameters, 43 QTs in all, were analysed in about 9000 voluntary subjects for whom extended genealogical information was available. We explored the distribution and examined mean differences of each trait among villages by analysis of variance (ANOVA). A heritability analysis with the variance component (VC) method was performed. Results show significant differences in the distribution of most traits between groups of villages located in two distinct geographical areas already identified by a previous population structure analysis, thus supporting the existence of differentiation among sub-populations in the same region. Heritability estimates range between 30 and 89%, demonstrating that genetic effects substantially contribute to phenotypic variation of all investigated traits and that this population provides excellent research conditions for gene-mapping projects. Results suggest that history, geographic location and population structure may have influenced the genetic and phenotypic features of these isolates. Our findings may be useful for the ongoing linkage and association studies in these isolates and suggest that a thorough characterization of population is valuable to better identify genes or variants that may be rare in the population at large and peculiar to single villages.

Lipoprotein(a) predicts progression of carotid artery intima-media thickening in patients with type 2 diabetes: A four-year follow-up

BACKGROUND

The aim of the study was to establish whether increased levels of serum lipoprotein(a) significantly contribute to an increase in intima-media thickness and the number of carotid artery plaques, and consequently to cardiovascular risk in patients with type 2 diabetes mellitus.

METHODS

Lipoprotein(a) levels, intima-media thickness and the number of carotid artery plaques were determined at the beginning of the study in 146 patients with type 2 diabetes. Patients were divided into two groups according to serum lipoprotein(a) levels (> or <or=30 mg/dl). Intima-media thickness and the number of plaques were again determined after four years of follow-up. Intima-media thickness was assessed using high-resolution B-mode ultrasound.

RESULTS

The two groups of patients revealed no significant differences in baseline intima-media thickness (P = 0.112) in relation to lipoprotein(a) level. After follow-up, intima-media thickness was significantly greater in patients with higher lipoprotein(a) levels (1.24 + 0.22 vs. 1.15 + 0.17 mm, respectively; P = 0.005). The mean increase in thickness over four years was 0.12 mm (0.030 mm/year) in the group with low lipoprotein(a) levels and 0.17 mm (0.043 mm/year) in the group with high lipoprotein(a). Multivariate analysis indicated that intima-media thickness depended on lipoprotein(a), and not on triglyceride, HDL-cholesterol levels or waist-to-hip ratio. No significant difference in baseline and follow-up number of plaques was observed between the study groups (P = 0.276 vs. P = 0.355, respectively). Although the group with lipoprotein(a) >30 mg/dl had more cardiovascular events, the difference was not statistically significant.

CONCLUSIONS

These results indicate that lipoprotein(a) is an independent, genetically determined risk factor closely associated with progression of intima-media thickness in type 2 diabetes.

APOE/C1/C4/C2 gene cluster genotypes, haplotypes and lipid levels in prospective coronary heart disease risk among UK healthy men

The role of common APOE variants on plasma lipids, particularly low density lipoprotein (LDL) levels, and coronary heart disease (CHD) risk is well known; the influence of variation in the other nearby apolipoprotein genes APOC1, APOC4 and APOC2 is unclear. This study examines the association between APOE/C1/C4/C2 gene cluster variation using tagging SNPs and plasma lipid concentration along with risk of CHD in a prospective cohort. Genotypes for 11 common APOE/C1/C4/C2 SNPs were determined in 2,767 middle-aged (49 to 64 years) men from the Second Northwick Park Heart Study, with 275 CHD events over a 15-year follow-up period. Seven SNPs showed significant associations with one or more lipid trait in univariate analysis. Multivariate and haplotype analysis showed that the APOE genotypes are most strongly associated with effects on LDL-C and apoB concentration (explaining 3.4% of the LDL-C variance) while the other SNPs in this gene cluster explained an additional 1.2%. Haplotypes in APOC2 and APOC4 were associated with modest effects on HDL-C and apoAI (explaining respectively 1.4% and 1.2%). Carriers of the APOE ɛ2 SNP had a significantly lower risk of CHD hazard ratio (HR) of 0.63 (95% confidence interval [CI]: 0.42-0.95), as did carriers of the APOC2 SNP rs5127 (HR = 0.72, 95% CI: 0.56-0.93), while carriers of APOC1 SNP rs4803770 had higher risk of CHD (HR = 1.36, 95% CI: 1.04-1.78) compared with noncarriers. While the common APOE polymorphism explains the majority of the locus genetic determinants of plasma lipid levels, additional SNPs in the APOC1/C2 region may contribute to CHD risk, but these effects require confirmation.

Legacy of mutiny on the Bounty: founder effect and admixture on Norfolk Island

The population of Norfolk Island, located off the eastern coast of Australia, possesses an unusual and fascinating history. Most present-day islanders are related to a small number of the 'Bounty' mutineer founders. These founders consisted of Caucasian males and Polynesian females and led to an admixed present-day population. By examining a single large pedigree of 5742 individuals, spanning >200 years, we analyzed the influence of admixture and founder effect on various cardiovascular disease (CVD)-related traits. On account of the relative isolation of the population, on average one-third of the genomes of present-day islanders (single large pedigree individuals) is derived from 17 initial founders. The proportion of Polynesian ancestry in the present-day individuals was found to significantly influence total triglycerides, body mass index, systolic blood pressure and diastolic blood pressure. For various cholesterol traits, the influence of ancestry was less marked but overall the direction of effect for all CVD-related traits was consistent with Polynesian ancestry conferring greater CVD risk. Marker-derived homozygosity was computed and agreed with measures of inbreeding derived from pedigree information. Founder effect (inbreeding and marker-derived homozygosity) significantly influenced height. In conclusion, both founder effect and extreme admixture have substantially influenced the genetic architecture of a variety of CVD-related traits in this population.

Genetic influences on cardiovascular stress reactivity

Individual differences in the cardiovascular response to stress play a central role in the reactivity hypothesis linking frequent exposure to psychosocial stress to adverse outcomes in cardiovascular health. To assess the importance of genetic factors, a meta-analysis was performed on all published twin studies that assessed heart rate (HR) or blood pressure (BP) reactivity to the cold pressor test or various mental stress tasks. For reactivity to mental stress, the pooled heritability estimate ranged from 0.26 to 0.43. Reactivity to the cold pressor test yielded heritability estimates from 0.21 to 0.55. An ensuing review of genetic association studies revealed a number of genes, mostly within the sympathoadrenal pathway, that may account for part of the heritability of cardiovascular stress reactivity. Future progress in gene finding, that should include measures of sympathetic and vagal stress reactivity, may help uncover the molecular pathways from genetic variation to stress reactivity.

Heritability of insulin sensitivity and lipid profile depend on BMI: evidence for gene-obesity interaction

AIMS/HYPOTHESIS

Evidence from candidate gene studies suggests that obesity may modify genetic susceptibility to type 2 diabetes and dyslipidaemia. On an aggregate level, gene-obesity interactions are expected to result in different heritability estimates at different obesity levels. However, this hypothesis has never been tested.

METHOD

The present study included 2,180 British female twins. BMI was used as an index of general obesity. Outcome measures were insulin sensitivity (indexed by quantitative insulin-sensitivity check index [QUICKI]) and fasting plasma lipid profile. Structural equation modelling was used to test whether BMI interacted with latent genetic and environmental effects to impact on the outcome measures.

RESULTS

Genetic influences on triacylglycerol increased with BMI (p < 0.001) whereas the unique environmental influence on QUICKI decreased with BMI (p < 0.001), resulting in a higher heritability estimate for both measures at higher BMI levels. This was further illustrated by stratified analysis in twin pairs concordant for normal weight and twin pairs concordant for overweight. Heritability was 19 percentage points higher for triacylglycerol (p < 0.001) and 31 percentage points higher for QUICKI (p < 0.01) among twins concordant for overweight than among twins concordant for normal weight. BMI had no moderator effect on the latent genetic and environmental factors for total cholesterol and HDL-cholesterol.

CONCLUSIONS/INTERPRETATION

Our results suggest that the expression of genes influencing triacylglycerol and insulin sensitivity can vary as a function of obesity status. The substantial increases in the genetic contribution to the total variance in insulin sensitivity and triacylglycerols at higher BMIs may prove extremely valuable in the search for candidate genes.

Family-based mitochondrial association study of traits related to type 2 diabetes and the metabolic syndrome in adolescents

AIMS/HYPOTHESIS

There has been much focus on the potential role of mitochondria in the aetiology of type 2 diabetes and the metabolic syndrome, and many case-control mitochondrial association studies have been undertaken for these conditions. We tested for a potential association between common mitochondrial variants and a number of quantitative traits related to type 2 diabetes in a large sample of >2,000 healthy Australian adolescent twins and their siblings, many of whom were measured on more than one occasion.

METHODS

To the best of our knowledge, this is the first mitochondrial association study of quantitative traits undertaken using family data. The maternal inheritance pattern of mitochondria means established association methodologies are unsuitable for analysis of mitochondrial data in families. We present a methodology, implemented in the freely available program Sib-Pair for performing such an analysis.

RESULTS

Despite our study having the power to detect variants with modest effects on these phenotypes, only one significant association was found after correction for multiple testing in any of four age groups. This was for mt14365 with triacylglycerol levels (unadjusted p = 0.0006). This association was not replicated in other age groups.

CONCLUSIONS/INTERPRETATION

We find little evidence in our sample to suggest that common European mitochondrial variants contribute to variation in quantitative phenotypes related to diabetes. Only one variant showed a significant association in our sample, and this association will need to be replicated in a larger cohort. Such replication studies or future meta-analyses may reveal more subtle effects that could not be detected here because of limitations of sample size.

Heritability of serum apolipoprotein concentrations in middle-aged Japanese twins

Background

Studies of the genetic and environmental influences on apolipoproteins have been conducted, but few have used data from Japanese twins. The aim of this study was to quantify and compare the genetic and environmental causes of individual differences in the serum concentrations of apolipoproteins in Japanese middle-aged twins.

Methods

Apo A-I, apo A-II, apo B, apo C-II, apo C-III, and apo E were studied. A total of 142 twin pairs, aged 45 through 65 years, were enrolled: 85 monozygotic pairs (59 male, 26 female) and 57 same-sexed dizygotic pairs (43 male, 14 female). The intraclass correlation coefficient and structural equation modeling were used to estimate the best-fitting model and heritability.

Results

Sixteen percent to 75% of the total variances of apo A-I, apo C-II, and apo C-III were attributable to genetic influence; apo A-I and apo C-II were influenced by dominant genetic factors. Twenty percent to 73% of the total variances of apo A-II, apo B, and apo E were attributable to additive genetic influence; apo B was clearly influenced by common environmental factors. Furthermore, the heritability of all apolipoproteins was higher among females than among males.

Conclusions

Genetic factors, including additive genetic effects (A) and dominant effects (D), influence apolipoprotein levels. However, a common environment does not influence the variances of these apolipoproteins, with the exception of apo B. Furthermore, the heritability of apolipoprotein phenotypes differs by sex.

Genetic and environmental influences on serum lipids and the effects of puberty: a Chinese twin study

AIM

To study the contribution of genes and environment on the variation of serum lipids and the effects of puberty.

METHODS

In total, 314 same-sex twin pairs aged 5-18 years were studied. Puberty was marked physiologically by spermarche/menarche, and model fitting was used to analyse the genetic and environmental variance and its difference before and after puberty.

RESULTS

Lipid levels were different before and after puberty. The genetic factor had an important influence on lipid levels; the heritability estimates of total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), lipoprotein(a) (Lp(a)) and apolipoprotein E (ApoE) were between 49 and 86%. The total phenotypic variances of TC, HDL, LDL, Lp(a) and ApoE decreased after puberty, mainly as a result of decrease of genetic variance, even though the common environmental variance for HDL, Lp(a) and ApoE increased.

CONCLUSION

Genes and the environment have different effects on the levels of different lipids. The shared environmental effects on lipids are very important in children. The role of puberty on lipids deserves future study.

Linkage and association analyses of longitudinally measured lipid phenotypes in adolescence

The genetic basis of cardiovascular disease (CVD) is complex and still largely elusive. Plasma lipid concentrations are well-established risk factors for cardiovascular disease (CVD), and have adult heritabilities ranging from 0.48 to 0.87. Estimates for adolescents are slightly higher (range 0.71 to 0.82). To identify loci affecting lipid concentrations across adolescence, we analyzed longitudinal lipid data in a sample of 134 monozygotic and 626 dizygotic twin pairs at ages twelve, fourteen and sixteen, and their siblings, from 760 Australian families. Univariate linkage analysis for each phenotype and time point was supplemented by multivariate analysis across the time points. A genome-wide association scan was also performed on a subset of the subjects (N = 441). The strongest linkage was seen for triglycerides on chromosome 6p24.3 (multivariate -log(10) p = 6.81; equivalent LOD = 6.13; p = 1.55 x 10(-7)). Significant linkage was also found for LDL cholesterol on chromosome 2q35 (multivariate -log(10)p = 5.59; equivalent LOD = 4.53; p = 2.57 x 10(-6)). In the association analysis, rs10503840 on 8p21.1 was significantly associated with total cholesterol levels at age fourteen (p = 8.24 x 10(-7), estimated significance threshold 2.45 x 10(-6)). Association at p < 2.25 x 10(-6) was also found between triglycerides at age 12 and rs10507266, in an intron of THRAP2 (MIM 608771) on 12q24.21; and between HDL-C at age 14 and rs10506325 in an intergenic region of 12q13.13. Suggestive evidence of association at ages twelve and fourteen was found between HDL-C and rs10492859 on 16q23 (p = 2.42 x 10(-5) and 2.77 x 10(-4), respectively). Further longitudinal genetic studies of cardiovascular risk factors, focused on critical periods of development or change, are needed.

Genetic and environmental influences on factors associated with cardiovascular disease and the metabolic syndrome

The relative influence of genetics and the environment on factors associated with cardiovascular disease (CVD) and metabolic syndrome (MetS) remains unclear. We performed model-fitting analyses to quantify genetic, common environmental, and unique environmental variance components of factors associated with CVD and MetS [waist circumference, blood pressure, fasting plasma glucose and insulin, homeostatic model assessment of insulin resistance (HOMA-IR), and fasting plasma lipids] in adult male and female monozygotic twins reared apart or together. We also investigated whether MetS components share common influences. Plasma cholesterol and triglyceride concentrations were highly heritable (56-77%, statistically significant). Waist circumference, plasma glucose and insulin, HOMA-IR, and blood pressure were moderately heritable (43-57%, statistically significant). Unique environmental factors contributed to the variance of all variables (20-38%, perforce statistically significant). Common environmental factors contributed 23, 30, and 42% (statistically significant) of the variance of waist circumference, systolic blood pressure, and plasma glucose, respectively. Two shared factors influenced MetS components; one influenced all components except HDL cholesterol, another influenced only lipid (triglyceride and HDL cholesterol) concentrations. These results suggest that genetic variance has a dominant influence on total variance of factors associated with CVD and MetS and support the proposal of one or more underlying pathologies of MetS.

Genetics of hemostasis: differential effects of heritability and household components influencing lipid concentrations and clotting factor levels in 282 pediatric stroke families

BACKGROUND

The identification of heritable and environmental factors possibly influencing a condition at risk should be a prerequisite for the search for the proportion of variance attributable for shared environmental effects (c(2)) modulating the risk of disease. Such epidemiologic approaches in families with a first acute ischemic stroke during early childhood are lacking.

OBJECTIVES

Our goal was to estimate the phenotypic variation within lipid concentrations and coagulation factor levels and to estimate the proportions attributable to heritability (h(2)r) and c(2) in pediatric stroke families.

METHODS

Blood samples were collected from 1,002 individuals from 282 white stroke pedigrees. We estimated h(2)r and c(2) for lipoprotein (a) [Lp(a)], cholesterol, high-density lipoprotein, low-density lipoprotein (LDL), fibrinogen, factor (F) II, FV, FVIIIC, von Willebrand factor (vWF), antithrombin, protein C, protein S, plasminogen, protein Z, total tissue factor pathway inhibitor (TFPI), prothrombin fragment F1.2, and D-dimer, using the variance component method in sequential oligogenetic linkage analysis routines.

RESULTS

When incorporating h(2)r and c(2) in one model adjusted for age, blood group, sex, smoking, and hormonal contraceptives, significant h(2)r estimates were found for Lp(a), LDL, fibrinogen, protein C, and protein Z. In addition to the significant h(2)r estimates, c(2) showed a significant effect on phenotypic variation for fibrinogen, protein C, and protein Z. A significant c(2) effect was found for cholesterol, and plasma levels of FII, FV, vWF, antithrombin, protein S, plasminogen, and TFPI, ranging from 9.3% to 33.2%.

CONCLUSIONS

Our research stresses the importance of research on the genetic variability and lifestyle modifications of risk factors associated with pediatric stroke.

Genome-wide search for QTLs for apolipoprotein A-I level in elderly Swedish DZ twins: evidence of female-specific locus on 15q11-13

The effect of genetic variants underlying atherosclerosis is thought to be mediated through intermediate phenotypes such as serum cholesterol levels. Localization of quantitative trait loci influencing levels of serum lipids and (apo)lipoproteins may aid in the search for determinants of susceptibility to atherosclerotic diseases. Since apolipoprotein A-I is the primary protein constituent of high-density lipoprotein, it is considered to be critical for the antiatherogenic effect of high-density lipoproteins. We describe here an effort to map loci influencing apolipoprotein A-I levels. Measurements of apolipoprotein A-I levels and genome scans with more than 1000 microsatellite markers were successfully performed in both members of 501 pairs of fraternal twins from Sweden. Variance component linkage analysis was undertaken to map quantitative trait loci. In the total study sample, two loci showed comparable suggestive evidence of linkage, 6p21-12 (LOD=2.4) and 12q23 (LOD=2.4). Sex-limited analyses revealed significant female-specific linkage at marker D15S156 on 15q11-13 (LOD=4.1). The loci on 12q and 15q in the present study confirm previously reported loci for apolipoprotein A-I, while the peak on chromosome 6p lends further support to a locus influencing several phenotypes related to atherosclerosis. Intriguingly, the presence of genes belonging to the phospholipase A2 superfamily under three out of four observed linkage peaks would lend some support to the view that this group of genes might collectively represent candidates as apolipoprotein A-I level regulators.

Common and rare alleles in apolipoprotein B contribute to plasma levels of low-density lipoprotein cholesterol in the general population

CONTEXT

We have previously shown that rare mutations in the apolipoprotein B gene (APOB) may result in not only severe hypercholesterolemia and ischemic heart disease but also hypocholesterolemia. Despite this, common single-nucleotide polymorphisms (SNPs) in APOB have not convincingly been demonstrated to affect low-density lipoprotein (LDL) cholesterol levels.

OBJECTIVE

We tested the hypothesis that nonsynonymous SNPs in three important functional domains of APOB and APOB tag SNPs predict levels of LDL cholesterol and apolipoprotein B and risk of ischemic heart disease.

DESIGN

This was a prospective study with 25 yr 100% follow up, The Copenhagen City Heart Study.

SETTING

The study was conducted in the Danish general population.

PARTICIPANTS

Participants included 9185 women and men aged 20-80+ yr.

MAIN OUTCOME MEASURES

Levels of LDL cholesterol and apolipoprotein B and risk of ischemic heart disease and myocardial infarction were measured. The hypothesis was formulated before genotyping.

RESULTS

We genotyped 9185 individuals for APOB T71I (minor allele frequency: 0.33), Ivs4+171c>a (0.14), A591V (0.47), Ivs18+379a>c (0.30), Ivs18+1708g>t (0.45), T2488Tc>t (0.48), P2712L (0.21), R3611Q (0.09), E4154K (0.17), and N4311S (0.21). SNPs were associated with increases (T71I, Ivs181708g>t, T2488Tc>t, R3611) or decreases (Ivs4+171c>a, A591V, Ivs18+379a>c, P2712L, E4154, N4311S) in LDL cholesterol from -4.7 to +8.2% (-0.28 to 0.30 mmol/liter; P<or=0.002), and corresponding effects on cholesterol and apolipoprotein B levels. However, as predicted from the magnitude of the observed LDL cholesterol effects, none of these SNPs predicted risk of ischemic heart disease prospectively in the general population, in a case-control study, or as haplotypes.

CONCLUSIONS

Multiple common and rare alleles in APOB contribute to plasma levels of LDL cholesterol in the general population, although the effects of common alleles and haplotypes are modest.

Genetic and non-genetic correlates of vitamins K and D

OBJECTIVE

To assess the genetic and nongenetic correlates of circulating measures of vitamins K and D status in a community-based sample of men and women.

SUBJECTS/METHODS

A cross-sectional study of 1762 participants of the Framingham Offspring Study (919 women; mean age 59 years). Vitamin K status was measured as plasma phylloquinone and serum percent undercarboxylated osteocalcin (ucOC), and vitamin D was measured using plasma 25-hydroxyvitamin D (25(OH)D). Associations between vitamin K status and vitamin D status with biologically plausible nongenetic factors were assessed using stepwise regression. Heritability and linkage were determined using Sequential Oligogenic Linkage Analysis Routines (SOLAR).

RESULTS

Nongenetic factors accounted for 20.1 and 12.3% of the variability in plasma phylloquinone in men and women respectively, with triglycerides and phylloquinone intake being the primary correlates. In men 12.2% and in women 14.6% of the variability in %ucOC was explained by nongenetic factors in our models. Heritability estimates for these vitamin K status biomarkers were nonsignificant. Season, vitamin D intake, high-density lipoprotein (HDL) cholesterol and waist circumference explained 24.7% (men) and 24.2% (women) of the variability in plasma 25(OH)D. Of the three vitamins examined, only 25(OH)D was significantly heritable (heritability estimate=28.8%, P<0.01), but linkage analysis of 25(OH)D did not achieve genome-wide significance.

CONCLUSIONS

Variability in biomarkers of vitamin K status was attributed to nongenetic factors, whereas plasma 25(OH)D was found to be significantly heritable. Further studies are warranted to investigate genetic loci influencing vitamin D status.

European guidelines on cardiovascular disease prevention in clinical practice: executive summary. Fourth Joint Task Force of the European Society of Cardiology and other societies on cardiovascular disease prevention in clinical practice (constituted by representatives of nine societies and by invited experts)

Other experts who contributed to parts of the guidelines: Edmond Walma, Schoonhoven (The Netherlands), Tony Fitzgerald, Dublin (Ireland), Marie Therese Cooney, Dublin (Ireland), Alexandra Dudina, Dublin (Ireland) European Society of Cardiology (ESC) Committee for Practice Guidelines (CPG):, Alec Vahanian (Chairperson) (France), John Camm (UK), Raffaele De Caterina (Italy), Veronica Dean (France), Kenneth Dickstein (Norway), Christian Funck-Brentano (France), Gerasimos Filippatos (Greece), Irene Hellemans (The Netherlands), Steen Dalby Kristensen (Denmark), Keith McGregor (France), Udo Sechtem (Germany), Sigmund Silber (Germany), Michal Tendera (Poland), Petr Widimsky (Czech Republic), José Luis Zamorano (Spain)

Document reviewers: Irene Hellemans (CPG Review Coordinator) (The Netherlands), Attila Altiner (Germany), Enzo Bonora (Italy), Paul N. Durrington (UK), Robert Fagard (Belgium), Simona Giampaoli(Italy), Harry Hemingway (UK), Jan Hakansson (Sweden), Sverre Erik Kjeldsen (Norway), Mogens Lytken Larsen (Denmark), Giuseppe Mancia (Italy), Athanasios J. Manolis (Greece), Kristina Orth-Gomer (Sweden), Terje Pedersen (Norway), Mike Rayner (UK), Lars Ryden (Sweden), Mario Sammut (Malta), Neil Schneiderman (USA), Anton F. Stalenhoef (The Netherlands), Lale Tokgözoglu (Turkey), Olov Wiklund (Sweden), Antonis Zampelas (Greece)

An apolipoprotein A-II polymorphism (-265T/C, rs5082) regulates postprandial response to a saturated fat overload in healthy men

Apolipoprotein (Apo) A-II is an apolipoprotein with an unknown role in lipid metabolism. It has been suggested that the presence of the less frequent allele of a single nucleotide polymorphism (Apo A-II -265T/C, rs5082) reduces the transcription rate of Apo A-II and enhances VLDL postprandial clearance in middle-aged men. To further investigate the role of Apo A-II -265T/C on lipid metabolism, we studied 88 normolipidemic young men. The participants were given a fatty meal containing 1 g fat and 7 mg cholesterol/kg weight and capsules containing 60,000 IU vitamin A (retinyl palmitate, 15.15 mg RE) per square meter body surface area. Postprandial lipemia was assessed during the 11 h following the meal. Total cholesterol (Chol) and triacylglycerols (TG) in plasma and TG-rich lipoproteins (TRL) (large TRL and small TRL) were measured, as well as HDL, Apo A-I, Apo B, Apo B-48, and Apo B-100. Postprandial responses were higher in the TT group than in carriers of the minor allele (CC/TC) for total TG in plasma (21.37% of change of area under curve, P = 0.014), large TRL-TG (24.75% change, P = 0.017) and small TRL-Chol (26.63% change, P = 0.003). Our work shows that carriers of the minor allele for Apo A-II -265T/C (CC/TC) have a lower postprandial response compared with TT homozygotes. This finding may partially explain the role of Apo A-II in lipid metabolism and can identify a population with a decreased risk of cardiovascular disease, as corresponds to the lower level of postprandial hypertriglyceridemia.

Genetic determinants of HDL: monogenic disorders and contributions to variation

PURPOSE OF REVIEW

This review focuses on recent progress towards the characterization of genetic variations that contribute to interindividual variation in plasma high-density lipoprotein cholesterol levels in the general population.

RECENT FINDINGS

Many of the genes that harbor rare mutations leading to extreme high-density lipoprotein cholesterol levels contain common variation that influences plasma high-density lipoprotein cholesterol in several study populations. Candidate gene association studies provide evidence that some of these variations have an effect on high-density lipoprotein cholesterol, dependent on epistatic interactions or environmental context. Both rare and common variations contribute to interindividual high-density lipoprotein cholesterol variation. Recent comparisons of candidate gene sequences between individuals in the tails of the high-density lipoprotein cholesterol distributions (the upper or lower 1-5%) of several study populations indicate that as many as 20% of individuals with low high-density lipoprotein cholesterol harbor a rare mutation in an investigated gene. For example, the ABCA1 gene region harbors rare mutations and common variants that contribute to interindividual high-density lipoprotein cholesterol variation in the general population.

SUMMARY

The genetic control of high-density lipoprotein cholesterol level is complex. Maximizing the utility of genetic knowledge for predicting an individual's high-density lipoprotein cholesterol level or response to intervention will require a better understanding of the action of combinations of genetic variants and environmental exposures.

Bivariate genetic modeling of cardiovascular stress reactivity: does stress uncover genetic variance?

OBJECTIVE

To test the existence of gene-by-stress interaction by assessing cardiovascular stress reactivity in monozygotic and dizygotic twins.

METHODS

We studied 160 adolescent (mean age 16.7 +/- 2.0 years; range 13-22 years) and 212 middle-aged twin pairs (mean age 44.2 +/- 6.7 years; range 34-63 years). Systolic (SBP) and diastolic (DBP) blood pressure, heart rate (HR), pre-ejection period (PEP), and respiratory sinus arrhythmia (RSA) were measured at rest and during a choice reaction time and a mental arithmetic task. We used a bivariate analysis of the resting and mean stress levels to test for gene-by-stress interaction, which can be caused by the emergence of new genetic variance specific to stress or by stress-induced amplification of the existing genetic variance at rest.

RESULTS

Genetic factors significantly contributed to individual differences in resting SBP, DBP, HR, PEP, and RSA levels in the adolescent (heritability range 0.31-0.70) and middle-aged (heritability range 0.32-0.64) cohorts. The effect of these genetic factors was amplified by stress for all variables in the adolescent cohort, and for SBP in the middle-aged cohort. In addition, stress-specific genetic variation emerged for HR in both cohorts and for PEP and SBP in the adolescent cohort. Heritability of stress levels of SBP, DBP, HR, PEP, and RSA ranged from 0.54 to 0.74 in the adolescents and from 0.44 to 0.64 in the middle-aged cohort.

CONCLUSIONS

Stress uncovers genetic variance in BP, HR, and cardiac sympathovagal balance through the emergence of new stress-specific genetic effects and the amplification of existing genetic effects that also affect the resting values.

Genome-wide linkage scans for loci affecting total cholesterol, HDL-C, and triglycerides: the Family Blood Pressure Program

Atherosclerosis accounts for 75% of all deaths from cardiovascular disease and includes coronary heart disease (CHD), stroke, and other diseases of the arteries. More than half of all CHD is attributable to abnormalities in levels and metabolism of lipids. To locate genes that affect total cholesterol, high density lipoprotein cholesterol (HDL-C), and triglycerides, genome-wide linkage scans for quantitative trait loci were performed using variance components methods as implemented in SOLAR on a large diverse sample recruited as part of the Family Blood Pressure Program. Phenotype and genetic marker data were available for 9,299 subjects in 2,953 families for total cholesterol, 8,668 subjects in 2,736 families for HDL, and 7,760 subjects in 2,499 families for triglycerides. Mean lipid levels were adjusted for the effects of sex, age, age2, age-by-sex interaction, body mass index, smoking status, and field center. HDL-C and triglycerides were further adjusted for average total alcoholic drinks per week and estrogen use. Significant linkage was found for total cholesterol on chromosome 2 (LOD=3.1 at 43 cM) in Hispanics and for HDL-C on chromosome 3 (LOD=3.0 at 182 cM) and 12 (LOD=3.5 at 124 cM) in Asians. In addition, there were 13 regions that showed suggestive linkage (LOD >or= 2.0); 7 for total cholesterol, 4 for HDL, and 2 for triglycerides. The identification of these loci affecting lipid phenotypes and the apparent congruence with previous linkage results provides increased support that these regions contain genes influencing lipid levels.

Evidence of age-dependent genetic influences on plasma total cholesterol

BACKGROUND

Causes of variation in cardiovascular risk factors include biological variation within individuals, and more permanent differences between individuals, which are at least partly genetic in origin. We have compared the magnitude of genetic and non-genetic factors within and across occasions through repeated measures of plasma cholesterol in twin subjects, and have also determined how far the same genes affect cholesterol levels at different ages.

METHODS

Data on plasma total cholesterol were extracted for 208 twin pairs who had provided blood on up to six occasions across a period of 17 years. They were aged 18-30 years at the time of first study and 30-47 at the time of the last. Multivariate models of variation due to genetic, shared environmental and unique environmental factors were fitted to the multi-occasion data and the proportions of variation due to these factors were estimated.

RESULTS

One genetic factor influenced plasma cholesterol on all occasions and a second genetic factor only influenced cholesterol results on the fifth and sixth occasions 10-17 years after the first. Environmental factors did not have significant long-term effects.

CONCLUSIONS

We conclude that individuals' long-term mean plasma cholesterol values are strongly genetically determined, but that some of these genes are age-specific in their effects.