Philippa J. Talmud

Nonfasting Apolipoprotein B and Triglyceride Levels as a Useful Predictor of Coronary Heart Disease Risk in Middle-Aged UK Men

Objective—The Apolipoprotein-related Mortality Risk (AMORIS) study concluded that the apolipoprotein (apo)B/apoA-I ratio was the best predictor of coronary heart disease (CHD) risk. We have compared the pairwise combinations of total cholesterol, triglycerides (TGs), apoB, high density lipoprotein (HDL) cholesterol, low density lipoprotein cholesterol, and apoA-I on CHD risk prediction in middle–aged men. Methods and Results—Healthy middle-aged men (n=2508), free of CHD at baseline, were examined prospectively. Over 6 years of follow-up, there were 163 CHD events (including acute myocardial infarction, coronary artery surgery, and ECG evidence of silent myocardial infarction). The relative risk (RR) of CHD associated with cholesterol, TGs, apoB, apoA-I, apoB/apoA-I, low density lipoprotein cholesterol, and HDL cholesterol were examined by survival analysis. The apoB/apoA-I ratio was associated with the strongest effect on the RR (3.58, 95% CI 2.08 to 6.19). In multivariate analysis, apoA-I had no significant effect on risk. Examining RR by quartiles, apoB and HDL in combination (RR 8.38, 95% CI 3.21 to 21.92) were better predictors of CHD risk than apoB and TGs (RR 4.05, 95% CI 1.57 to 6.23). However, apoB and TGs in combination added risk information over and above lifestyle factors, whereas apoB and HDL cholesterol did not. Conclusions—The combined evaluation of apoB with TGs provides useful diagnostic criteria for CHD risk.

Association of telomere length with type 2 diabetes, oxidative stress and UCP2 gene variation

Objective High oxidative stress potentially leads to accelerated telomere shortening and consequent premature cell senescence, implicated in type 2 diabetes (T2D) development. Therefore, we studied the association of leukocyte telomere length (LTL) with the presence of T2D, as well as the effect on the patients’ LTL of plasma oxidative stress and of variation in UCP2, a gene involved in the mitochondrial production of reactive oxygen species. Methods Mean LTL was determined in 569 Caucasian, 103 South Asian and 70 Afro-Caribbean T2D patients aged from 24 to 92 years, 81 healthy Caucasian male students aged from 18 to 28 years and 367 healthy Caucasian men aged from 40 to 61 years by real-time PCR. Plasma total antioxidant status (TAOS) was measured in the T2D patients by a photometric microassay. The patients were also genotyped for the UCP2 functional variants −866G>A and A55V. Results Afro-Carribeans had 510 bp longer mean length compared to Caucasians (p < 0.0001) and 500 bp longer than South Asians (p = 0.004). T2D subjects displayed shorter age-adjusted LTL compared to controls [6.94(6.8–7.03) vs. 7.72(7.53–7.9), p < 0.001] with subjects in the middle and the lowest tertile of LTL having significantly higher odds ratios for T2D compared to those in the highest tertile [1.50(1.08–2.07) and 5.04(3.63–6.99), respectively, p < 0.0001]. In the patients, LTL was correlated negatively with age (r = −0.18, p < 0.0001) and positively with TAOS measures (r = 0.12, p = 0.01) after adjusting for age, while carriers of the UCP2 −866A allele had shorter age-adjusted LTL than common homozygotes [6.86(6.76–6.96) kb vs. 7.03(6.91–7.15) kb, p = 0.04]. Conclusion The present data suggest that shorter LTL is associated with the presence of T2D and this could be partially attributed to the high oxidative stress in these patients. The association of the UCP2 functional promoter variant with the LTL implies a link between mitochondrial production of reactive oxygen species and shorter telomere length in T2D.

Contribution of APOA5 gene variants to plasma triglyceride determination and to the response to both fat and glucose tolerance challenges

The aim of this study was to investigate the influence of APOA5 variants on fasting lipids and to the response to both an oral fat tolerance test (OFTT) and an oral glucose tolerance test (OGTT). The association of two APOA5 SNPs [S19W (SNP5), -1131T>C (SNP3)] and an APOA4/A5 intergenic SNP [-12238T>C (SNP4)] were examined in healthy young men (n=774) who had undergone both an OFTT and an OGTT. Both -1131T>C and S19W rare alleles were associated with triglyceride (TG)-raising effects (11%, P=0.008; 21% (in cases), P<0.026, respectively) and showed additive effects on TG. None of the variants influenced the responsiveness to the OFTT after correcting for baseline TG. Homozygosity for the -12238T>C rare allele was associated with higher waist to hip ratio (P<0.0006), systolic blood pressure (P=0.012) and AUC and peak of insulin after OGTT (P=0.003 and P=0.027, respectively), traits that define the metabolic syndrome. Our results strongly support the role of APOA5 in determining plasma TG levels in an age-independent manner and highlight the importance of the APOC3/A4/A5 gene cluster in both TG and metabolic homeostasis.

Genetic and environmental determinants of plasma high density lipoprotein cholesterol and apolipoprotein AI concentrations in healthy middle-aged men.

The effects of common variants of cholesteryl ester transfer protein (CETP) (TaqIB), hepatic lipase (HL) (−514C>T), lipoprotein lipase (LPL) (S447X) and lecithin cholesterol acyl transferase (LCAT) (S208T) on the determination of high density lipoprotein cholesterol (HDL‐C) and apolipoprotein AI (apoAI) levels were examined in 2773 healthy middle‐aged men participating in the second Northwick Park Heart Study. The extent of gene:gene, gene:smoking and gene:alcohol interactions were determined. For HDL‐C levels, only CETP genotype was associated with significant effects (p<0·0001), with the B2 allele being associated with higher levels in both smokers and non‐smokers. This interaction was significant at the lowest tertile of TG, suggesting that TG levels were rate limiting. As previously reported, CETP, LPL and HL genotypes were all associated with significant effects on apoAI levels (all p<0·01), with carriers of the rare alleles having higher levels and with no evidence of heterogeneity of effects in smokers and non‐smokers. LCAT genotype was not associated with significant effects on either trait. There was no significant interaction between any of the genotypes and alcohol consumption on either HDL‐C or apoAI levels. All genotypic effects were additive for HDL‐C and apoAI. Environmental and TG levels explained more than 20% and 5·5% of the variance in HDL‐C and apoAI, respectively. The novel aspect of this finding is that genetic variation at these loci explained in total only 2·5% of the variance in HDL‐C and 1·89% of the variance in apoAI levels. Thus despite the key roles played by these enzymes in HDL metabolism, variation at these loci, at least as detected by these common genotypes, contributes minimally to the variance in HDL‐C and apoAI levels in healthy men, highlighting the polygenic and multifactorial control of HDL‐C.

Association between the Ala379Val variant of the lipoprotein associated phospholipase A2 and risk of myocardial infarction in the north and south of Europe.

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) has been identified as a coronary heart disease (CHD) risk predictor. Both its anti-inflammatory role by hydrolysing platelet activating factor, and pro-inflammatory generation of atherogenic mediators may influence CHD risk. We investigated the association of the activity-reducing A379V variant with risk of myocardial infarction (MI) in a large European case-control study, which compared 527 post-MI men with 566 age-matched controls from north and south Europe. Overall, the frequency of the V379 allele was 0.24 (95%CI 0.21-0.26), with no evidence for differences between centres. Homozygosity for the V379 allele was associated with lower risk of MI, (Odds Ratio (OR) 0.56, 95%CI 0.32-0.98), maintained after adjustment for lifestyle factors and levels of inflammatory risk factors (C-reactive protein, fibrinogen, IL-6) (OR 0.46, 0.22-0.93). There was no evidence of heterogeneity of effect between the centres in the north and south of Europe (P-value for interaction=0.80). Since homozygosity for V379 occurs in only 5-6% of subjects, this genotype is not a major determinant of population genetic risk of CHD, but the association of this genotype with low levels of Lp-PLA(2), strongly support the pro-inflammatory causative, and not consequential, role of Lp-PLA(2) in CHD.

Refinement of Variant Selection for the LDL Cholesterol Genetic Risk Score in the Diagnosis of the Polygenic Form of Clinical Familial Hypercholesterolemia and Replication in Samples from 6 Countries

BACKGROUNDnFamilial hypercholesterolemia (FH) is an autosomal-dominant disorder caused by mutations in 1 of 3 genes. In the 60% of patients who are mutation negative, we have recently shown that the clinical phenotype can be associated with an accumulation of common small-effect LDL cholesterol (LDL-C)-raising alleles by use of a 12-single nucleotide polymorphism (12-SNP) score. The aims of the study were to improve the selection of SNPs and replicate the results in additional samples.nnnMETHODSnWe used ROC curves to determine the optimum number of LDL-C SNPs. For replication analysis, we genotyped patients with a clinical diagnosis of FH from 6 countries for 6 LDL-C-associated alleles. We compared the weighted SNP score among patients with no confirmed mutation (FH/M-), those with a mutation (FH/M+), and controls from a UK population sample (WHII).nnnRESULTSnIncreasing the number of SNPs to 33 did not improve the ability of the score to discriminate between FH/M- and controls, whereas sequential removal of SNPs with smaller effects/lower frequency showed that a weighted score of 6 SNPs performed as well as the 12-SNP score. Metaanalysis of the weighted 6-SNP score, on the basis of polymorphisms in CELSR2 (cadherin, EGF LAG 7-pass G-type receptor 2), APOB (apolipoprotein B), ABCG5/8 [ATP-binding cassette, sub-family G (WHITE), member 5/8], LDLR (low density lipoprotein receptor), and APOE (apolipoprotein E) loci, in the independent FH/M- cohorts showed a consistently higher score in comparison to the WHII population (P < 2.2 × 10(-16)). Modeling in individuals with a 6-SNP score in the top three-fourths of the score distribution indicated a >95% likelihood of a polygenic explanation of their increased LDL-C.nnnCONCLUSIONSnA 6-SNP LDL-C score consistently distinguishes FH/M- patients from healthy individuals. The hypercholesterolemia in 88% of mutation-negative patients is likely to have a polygenic basis.

Population Genomics of Cardiometabolic Traits: Design of the University College London-London School of Hygiene and Tropical Medicine-Edinburgh-Bristol (UCLEB) Consortium

Substantial advances have been made in identifying common genetic variants influencing cardiometabolic traits and disease outcomes through genome wide association studies. Nevertheless, gaps in knowledge remain and new questions have arisen regarding the population relevance, mechanisms, and applications for healthcare. Using a new high-resolution custom single nucleotide polymorphism (SNP) array (Metabochip) incorporating dense coverage of genomic regions linked to cardiometabolic disease, the University College-London School-Edinburgh-Bristol (UCLEB) consortium of highly-phenotyped population-based prospective studies, aims to: (1) fine map functionally relevant SNPs; (2) precisely estimate individual absolute and population attributable risks based on individual SNPs and their combination; (3) investigate mechanisms leading to altered risk factor profiles and CVD events; and (4) use Mendelian randomisation to undertake studies of the causal role in CVD of a range of cardiovascular biomarkers to inform public health policy and help develop new preventative therapies.

APOE, CETP and LPL genes show strong association with lipid levels in Greek children.

Background and aims Studies have consistently demonstrated that variants in a number of candidate genes are significant determinants of lipid levels in adults. However, few studies have investigated the impact of these variants in children. Therefore, in the present investigation we examined the influence of ten common variants in the genes for lipoprotein lipase (LPL – S447X), cholesterol ester transfer protein (CETP – Taq1B) apolipoprotein (APO) E (ɛ2, ɛ3, ɛ4), APOA5 (−1131C > T and S19W), APOA4 (S347T) and APOC3 (−482C > T; 1100C > T and 3238G > C) on lipoprotein levels children from the Gene–Diet Attica Investigation on childhood obesity (GENDAI). Methods and results The ten variants selected were genotyped in 882 Greek children, mean age: 11.2 ± 0.7 years (418 females and 464 males). Genotypes were assessed using TaqMan technology. Significantly higher total cholesterol (TC) (p = 0.0001) and low-density lipoprotein cholesterol (LDL-C) (p < 0.0001) were observed in APOE ɛ4 carriers compared to ɛ3/ɛ3 homozygotes and ɛ2 carriers. The association of APOE genotype with TC and high-density lipoprotein cholesterol (HDL-C) ratio (p = 0.0008) was further modulated by body mass index. Carriers of the CETP TaqIB B2 allele had significantly higher HDL-C (p < 0.0001) and significantly lower TC: HDL-C ratio (p < 0.0001) compared to B1/B1 individuals. No significant associations were observed between APOA4, APOA5 and APOC3 variants and serum lipids. Conclusion This study demonstrates that these common variants are associated with lipid levels in this healthy paediatric cohort, suggesting that even in these young children there may be potential in predicting their lifelong exposure to an adverse lipid profile.

Lipoprotein lipase gene variants and the effect of environmental factors on cardiovascular disease risk

Coronary heart disease (CHD) is a major cause of mortality in the Western world. CHD risk is known to be modified by both genetic and environmental factors. In this review, we look at the role of lipoprotein lipase (LPL) gene variants in predisposing to CHD risk and the important interaction between these genotypes and environmental factors (e.g. smoking). Gene–environmental interactions result in a greater than additive effect on risk and understanding these gene–environmental interactions has the potential not only for improving our understanding of the pathophysiology of the disease, but also in the development of new therapies and the targeting of specific therapies. For example, if a genotype increases risk in a particular environment, then those subjects would be encouraged to change their lifestyles more aggressively. Similarly at‐risk subjects could be targeted with available therapies more appropriately.

The lipoprotein lipase gene serine 447 stop variant influences hypertension-induced left ventricular hypertrophy and risk of coronary heart disease

LVH [LV (left ventricular) hypertrophy] is an independent risk factor for CHD (coronary heart disease). During LVH, the preferred cardiac energy substrate switches from FAs (fatty acids) to glucose. LPL (lipoprotein lipase) is the key enzyme in triacylglycerol (triglyceride) hydrolysis and supplies FAs to the heart. To investigate whether substrate utilization influences cardiac growth and CHD risk, we examined the association between the functional LPL S447X (rs328) variant and hypertension-induced LV growth and CHD risk. LPL-X447 has been shown to be more hydrolytically efficient and would therefore release more free FAs than LPL-S477. In a cohort of 190 hypertensive subjects, LPL X447 was associated with a greater LV mass index [85.2 (1.7) in S/S compared with 91.1 (3.4) in S/X+X/X; P=0.01], but no such association was seen in normotensive controls (n=60). X447 allele frequency was higher in hypertensives with than those without LVH {0.14 [95% CI (confidence interval), 0.08-0.19] compared with 0.07 (95% CI, 0.05-0.10) respectively; odds ratio, 2.52 (95% CI, 1.17-5.40), P=0.02}. The association of LPL S447X with CHD risk was then examined in a prospective study of healthy middle-aged U.K. men (n=2716). In normotensive individuals, compared with S447 homozygotes, X447 carriers were protected from CHD risk [HR (hazard ratio), 0.48 (95% CI, 0.23-1.00); P=0.05], whereas, in the hypertensives, X447 carriers had increased risk [HR, 1.54 (95% CI, 1.13-2.09) for S/S (P=0.006) and 2.30 (95% CI, 1.53-3.45) for X447+ (P<0.0001)] and had a significant interaction with hypertension in CHD risk determination (P=0.007). In conclusion, hypertensive LPL X447 carriers have increased risk of LVH and CHD, suggesting that altered FA delivery constitutes a mechanism through which LVH and CHD are associated in hypertensive subjects.