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Philippa J Talmud

Publications and source records attributed to Philippa J Talmud.

At least 37 records · Page 2Linked to original sources
PubMed2004

APOA5 gene variants, lipoprotein particle distribution, and progression of coronary heart disease: results from the LOCAT study.

Animal and human studies support a role for apolipoprotein A-V (apoA-V) in triglyceride (TG) metabolism. We examined the relationship of APOA5 -1131T>C and S19W with lipid subfractions and progression of atherosclerosis in the Lopid Coronary Angiography Trial. Compared with -1131TT men (n = 242), carriers of the -1131C allele (n = 54) had significantly higher total TG (P = 0.03), reflected in significantly increased VLDL mass [higher VLDL-TG, VLDL-cholesterol, VLDL-protein, and surface lipids (all P < 0.05)]. Because apoB levels were unaffected by genotype, this suggests an increase in VLDL size and not number. Compared with 19SS men (n = 268), 19W carriers (n = 44) had higher intermediate density lipoprotein (IDL)-TG, IDL-cholesterol (P = 0.04), and IDL-surface components [free cholesterol (P = 0.005) and phospholipids (P = 0.017)] but not protein content, suggesting an increase in IDL lipid enrichment resulting in an increase in IDL size. 19W carriers also showed a trend toward increased progression of atherogenesis, as measured by change in average diameter of segments (-0.46 +/- 0.011 mm compared with -0.016 +/- 0.006 mm) in 19SS men (P = 0.08). There was no effect of genotype on the response of these parameters to gemfibrozil treatment. These results shed new light on the role of APOA5 variants in TG metabolism and coronary heart disease risk.

Aged↗
PubMed2004

Genetic testing for cardiovascular disease susceptibility: a useful clinical management tool or possible misinformation?

Genetic susceptibility tests are already advertised on the Internet to identify individuals at above average risk for cardiovascular disease (CVD), such as deep vein thrombosis, hyperlipidemia, or atherosclerosis, whereas other tests claim to predict response to a particular drug treatment. Some kits are available to the public directly, bypassing a doctor. Their value, however, must be considered carefully, because although a genotype may be strongly and consistently associated with an intermediate trait, and because the intermediate trait is a strong predictor of CVD risk, there may be little or no association of genotype with risk over and above that of the measured trait. This is because multigenic effects and environmental modification (context dependency) of genotype effects determine CVD risk. An individual's personal characteristics and plasma risk-trait levels (which reflect both genotype and exposure) at present are the best predictors of clinical outcome. Only when genetic tests surpass this, possibly by the inclusion of many functional common variants, in conjunction with their context-dependent effects on risk, might their usefulness in clinical management be realized. Here we review some of the particular issues and concerns raised by CVD-risk genetic testing, and suggest areas of further research to address these issues.

Apolipoproteins E↗
PubMed2004

No APOEepsilon4 effect on coronary heart disease risk in a cohort with low smoking prevalence: the Whitehall II study.

Carriers of the APOEepsilon4 allele have consistently shown higher, and epsilon2 carriers have lower, plasma cholesterol and coronary heart disease (CHD) risk compared with epsilon3 homozygotes. An epsilon4:smoking interaction was observed in NPHSII, consistent with context dependency of the epsilon4 effect on CHD risk. In this study, APOE genotype was determined in 3787 male British civil servants followed for fatal and non-fatal myocardial infarction for median of 5.8 years, with 159 validated CHD events. APOE genotype was associated with expected effects on lipid traits (all P <0.0001). We tested the hypothesis that APOEepsilon4 was not a risk factor for CHD among non-smokers. In non-smokers, the odds ratio (OR) for epsilon2 and epsilon4 carriers were 0.51 (0.27, 0.97) and 0.70 (0.46, 1.08), respectively, compared with epsilon3 homozygotes. Thus epsilon2 carriers showed expected risk-protection, but despite 80% power to detect an OR in epsilon4 subjects of 1.71 (i.e. of magnitude increase reported in prospective studies), the epsilon4 non-smokers showed no increased risk compared with epsilon3 homozygotes. Smoking prevalence in this study was low (12.8%), but smokers had higher CHD risk which was of similar magnitude in risk in all genotypes [(OR 1.57 (1.03, 2.40)]. These data, therefore, provide strong corroborative evidence that there is no elevated risk of CHD in epsilon4 non-smokers, but failed to confirm the epsilon4:smoking interaction on risk. This supports the context dependency of the epsilon4 risk effect, but the low smoking incidence in the Whitehall men reduced our ability to examine a smoking:genotype interaction.

Adult↗
PubMed2004

How to identify gene-environment interactions in a multifactorial disease: CHD as an example.

CHD is a multifactorial disease, caused by both genetic and environmental factors. The inherited 'defective' genes will vary from individual to individual, and any single mutation is likely to be making only a small contribution to risk. The context dependency, i.e. the importance of environmental factors in influencing genetic risk, is now becoming evident. Thus, a mutation may have a modest effect on risk in individuals who maintain a low environmental risk, but a major effect in a high-risk environment. Methods of analysing gene-environment interactions on CHD risk will be discussed and illustrated with several examples. APOE has three common alleles, epsilon2, epsilon3 and epsilon4. The epsilon4 allele has consistently been associated with CHD risk, which has been confirmed by meta-analysis. However, when the effect of genotype on risk was considered in smokers and non-smokers separately, risk in non-smokers was similar in all APOE genotypes. By comparison, in the smokers, epsilon3 homozygotes, as expected, had an approximately 2-fold higher risk, while for epsilon4 carriers there was a significantly greater than additive effect of genotype and smoking on risk (P<0.007). Thus, the impact of the epsilon4 allele on CHD risk appears to be confined to current smokers, an effect that has been confirmed in several studies. Another example is the interaction between the alcohol dehydrogenase 3 gene variant and alcohol consumption on CHD risk (P<0.001), showing the context dependency of the effect. Thus, the importance of considering environmental factors as potential genotype-risk modifiers has major public health implications.

Alcohol Dehydrogenase↗
PubMed2004

Response to micronized fenofibrate treatment is associated with the peroxisome-proliferator-activated receptors alpha G/C intron7 polymorphism in subjects with type 2 diabetes.

OBJECTIVE: The association between polymorphisms in candidate genes related to lipoprotein metabolism and the reduction in plasma triglyceride (TG) in response to fenofibrate treatment was evaluated in subjects with type 2 diabetes treated with micronized fenofibrate (200 mg/day) for at least 3 years in the Diabetes Atherosclerosis Intervention Study. METHODS: The cholesteryl ester transfer protein Taq1B, LPL S447X, hepatic lipase -514 C-->T, peroxisome-proliferator-activated receptors alpha (PPARA) L162V and G/C intron 7 polymorphisms and the apolipoprotein E2/E3/E4 alleles were genotyped using PCR and restriction enzyme digestion. Subjects were divided into high TG-responders (with > 30% TG relative reduction after treatment) and low TG-responders. RESULTS: The frequency of the PPARA intron 7 G/G genotype was higher in high TG-responders than in low TG-responders (85% vs. 69%, P < 0.05). There was no significant difference between the percentage of high TG-responders and low TG-responders for any of the other genetic polymorphisms examined. In stepwise logistic regression, baseline TG and only the PPARA intron 7 polymorphism among the others were selected in the model as significant predictors of TG-response (odds ratio: 3.10, 95% CI: 1.28-7.52, P = 0.012 for PPARA polymorphism). With age, gender, body mass index, smoking status and HbA1c as additional factors, baseline TG (P< 0.0001), intron 7 (P = 0.013), body mass index (P = 0.040) and LPL-S447X (P = 0.084) were significant predictors of TG-response. CONCLUSION: These results indicate that elevated baseline TG levels and PPARA gene intron 7 G/G genotype were associated with TG reduction > 30% after fenofibrate treatment in patients with type 2 diabetes.

Apolipoprotein E2↗
PubMed2004

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.

Coronary Disease↗
PubMed2004

Evidence of admixture from haplotyping in an epidemiological study of UK Caucasian males: implications for association analyses.

OBJECTIVE: Cohort and case-control genetic association studies offer the greatest power to detect small genotypic influences on disease phenotypes, relative to family-based designs. However, genetic subdivisions could confound studies involving unrelated individuals, but the topic has been little investigated. We examined geographical and interallelic association of SNP and microsatellite haplotypes of the Y chromosome, of regions of chromosome 11, and of autosomal SNP genotypes relevant to cardiovascular risk traits in a UK-wide epidemiological survey. RESULTS: We show evidence (p = 0.00001) of the Danelaw history of the UK, marked by a two-fold excess of a Viking Y haplotype in central England. We also found evidence for a (different) single-centre geographical over-representation of one haplotype, both for APOC3-A4-A5 and for IGF2. The basis of this remains obscure but neither reflect genotyping error nor correlate with the phenotypic associations by centre of these markers. A panel of SNPs relevant to cardiovascular risks traits showed neither association with geographical location nor with Y haplotypes. CONCLUSION: Combinations of Y haplotyping, autosomal haplotyping, and genome-wide SNP typing, taken together with phenotypic2 associations, should improve epidemiological recognition and interpretation of possible confounding by genetic subdivision.

Alleles↗
PubMed2004

Heritability of multivariate factors of the metabolic syndrome in nondiabetic Japanese americans.

A rapidly growing body of evidence demonstrates important associations between the metabolic syndrome, characterized by a cluster of risk factors or phenotypes that include dyslipidemia, central obesity, hypertension, and hyperinsulinemia, and both cardiovascular disease and type 2 diabetes. The purpose of the present study was to characterize the metabolic syndrome in a sample of 432 individuals from 68 Japanese-American families, using factor analysis of quantitative phenotypes, and to estimate the heritability of these independent factors. Using nine characteristic phenotypes that included LDL particle size and C-reactive protein (CRP), factor analysis identified three multivariate factors interpreted as lipids, body fat/insulin/glucose/CRP, and blood pressure, explaining 65% of the variance. Heritability analysis revealed significant genetic effects on all of the factors: lipids (h(2) = 0.52, P < 0.001), body fat/insulin/glucose/CRP (h(2) = 0.27, P = 0.016), and blood pressure (h(2) = 0.25, P = 0.026). This analysis shows that independent, multivariate factors of the metabolic syndrome are heritable, demonstrating genetic influences on the underlying pathophysiological mechanisms of the syndrome.

Asian People↗
PubMed2003

Human paraoxonase gene cluster polymorphisms as predictors of coronary heart disease risk in the prospective Northwick Park Heart Study II.

The anti-atherogenic effect of HDL has been suggested to be partly due to the action of HDL-associated paraoxonase (PON). Three distinct enzymes have been identified, encoded by PON1, PON2 and PON3, clustered on chromosome 7q21-q22. Two cSNPs in PON1 (L55M and Q192R) and one in PON2 (S311C) have been implicated as independent risk factors for coronary heart disease (CHD) in some, but not all, studies. A PON3 SNP (A99A) was identified and the effect of these four PON SNPs on HDL levels and CHD risk was examined in the prospective Northwick Park Heart Study II (NPHSII). Genotype frequencies did not differ between cases and controls but the CHD risk associated with smoking was significantly modified by PON1 L55M genotype. Compared to LL non-smokers, LL smokers had a hazard ratio (HR) of 1.30 (95% CI 0.81-2.06) while M-allele carriers had a HR of 1.76 (1.17-2.67). When genotypes were analysed in combination, men with the genotype PON1 55 LM/MM+PON2 311 CC, had HR of 3.54 (1.81-6.93) compared to PON1 LL+PON2 SS/SC men (interaction P=0.004). These effects were independent of classical risk factors. These data demonstrate the importance of stratifying by environmental factors and the use of multiple SNPs for genetic analysis.

Amino Acid Substitution↗
PubMed2003

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.

Adult↗
PubMed2003

Apolipoprotein AIV gene variant S347 is associated with increased risk of coronary heart disease and lower plasma apolipoprotein AIV levels.

The impact of common variants in the apolipoprotein gene cluster (APOC3-A4-A5) on prospective coronary heart disease (CHD) risk was examined in healthy UK men. Of the 2808 men followed over 9 years, 187 had a clinically defined CHD event. Examination of 9 single nucleotide polymorphisms (SNPs) in this group revealed that homozygotes for APOA4 S347 had significantly increased risk of CHD [hazard ratio (HR) of 2.07 (95%CI 1.04 to 4.12)], whereas men homozygous for APOC3 1100T were protected [HR 0.28 (95%CI 0.09 to 0.87)]. In stepwise multiple regression analysis, after entering all the variants and adjusting for established risk factors APOA4 T347S alone remained in the model. Using all nine SNPs, the highest risk-estimate haplotypes carried APOA4 S347 and rare alleles of the two flanking intergenic markers. The protective effect of APOC3 1100T could be explained by negative linkage disequilibrium with these alleles. To determine the association of APOA4 T347S with apoAIV levels, the relationship was examined in 1600 healthy young European men and women. S347 homozygotes had significantly lower apoAIV plasma levels (13.64+/-0.59 mg/dL) compared with carriers of the T347 allele (14.90+/-0.12 mg/dL) (P=0.035). These results demonstrate that genetic variation in and around APOA4, independent of the effects of triglyceride, is associated with risk of CHD and apoAIV levels, supporting an antiatherogenic role for apoAIV.

Adolescent↗
PubMed2003

Progression of atherosclerosis is associated with variation in the alpha1-antitrypsin gene.

OBJECTIVE: Alpha1-Antitrypsin (AAT) protects elastic tissue and may play a role in atherogenesis. The association of atherosclerosis progression with common AAT variants was considered in 2 clinical trials. METHODS AND RESULTS: We examined the association of AAT V213A, S and Z deficiency alleles, and the functional 3' UTR 11478G>A with change in minimal luminal diameter, a measure of focal disease, in the Lopid Coronary Angiography Trial gemfibrozil study of post-bypass men. S or Z carriers (n=14) showed strong progression of disease on placebo (11.5%) but responded well to treatment (3% regression). 11478A carriers treated with placebo or gemfibrozil showed significantly more disease progression (n=8, -14.5% and n=16, -4.0%, respectively) than 11478GG men (n=107, -7.0% and n=108, -1.4%, respectively; overall, P=0.003). VV213 men treated with gemfibrozil (n=68) showed -4.8% progression, whereas A213 carriers (n=55) showed +1.4% regression of disease (P=0.001). No V213A effect was seen on placebo (P=0.11). In the Diabetes Atherosclerosis Intervention Study fenofibrate trial of angiographic progression in type 2 diabetes, the association of 11478A with increased disease progression was confirmed in the treatment group, but not the gemfibrozil-treated A213 association with regression, suggesting a pharmacogenetic difference. CONCLUSIONS: Disease progression is associated with variation in AAT, and low AAT levels promote atherogenesis.

3' Untranslated Regions↗
PubMed2003

Polymorphisms in CYP-7A1, not APOE, influence the change in plasma lipids in response to population dietary change in an 8 year follow-up; results from the Czech MONICA study.

OBJECTIVES: To evaluate the influence of variation in the genes for apolipoprotein E (APOE; epsilon2, epsilon3, epsilon4) and cholesterol-7alpha hydroxylase (CYP-7A1; -204A-->C) on plasma lipid level changes. DESIGN AND METHODS: 131 males for whom dietary composition markedly changed and total cholesterol decreased (from 6.21 +/- 1.31 mmol/L in 1988 - 5.43 +/- 1.06 mmol/L in 1996) over an 8 yr follow-up study. Polymorphisms were investigated using PCR. RESULTS: APOE genotype influenced plasma total and LDL cholesterol, with carriers of the epsilon4 having the highest and epsilon2 carriers the lowest levels, this reached borderline significance for cholesterol in 1988 (p = 0.06) and strongly affected the 1996 levels of LDL cholesterol (p = 0.008). However, APOE did not influence the change in these measures over time. In contrast, the CYP-7A1 -204A-->C polymorphism did not affect lipid measures per se but was strongly associated with a decrease in plasma total cholesterol [AA -0.38 (+/- 0.20) mmol/L, AC -0.65 +/- (0.08), CC -1.33 (+/- 0.3) mmol/L, p = 0.01] over the 8 yr time period. CONCLUSIONS: Variation in the CYP-7A1 gene may play an important role in an individual's sensitivity to dietary composition.

Adult↗
PubMed2003

Enhanced bridging function and augmented monocyte adhesion by lipoprotein lipase N9: insights into increased risk of coronary artery disease in N9 carriers.

Lipoprotein lipase (LPL) is central to triacylglycerol (TG) metabolism, having both hydrolytic and bridging functions. The common LPL gene variant D9N is associated with raised TG, reduced HDL-cholesterol concentrations and increased risk of coronary artery disease (CAD). To investigate the functional basis for the phenotype in N9 carriers, CHO K1 cells were stably transfected with wild type (D9) or mutant (N9) LPL cDNA. LPL RNA expression levels, monomer-to-dimer ratios, and dimer specific activities were similar in D9 and N9 cells. Significantly enhanced binding (4.6-fold) and internalisation (2.6-fold) of 125I-LDL by N9 compared with D9 cells was eradicated by pre-treatment with either heparin or heparinase, confirming involvement of LPL and cell surface proteoglycans. N9 cells bound and internalised 3.8- and 4.4-fold more oxidised 125I-LDL, respectively, than D9 cells (both P<0.0001). Binding of monocytes was 7-fold greater to plates coated with purified LPL-N9 dimer compared with LPL-D9 (P<=0.005). Thus once on the cell surface, LPL-N9 enhances bridging, as assessed both by LDL binding and internalisation, and monocyte adhesion. This augmented LPL-N9 bridging provides a mechanism for the reported increased CAD risk in N9 carriers.

Base Sequence↗
PubMed2003

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.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed2002

Relative contribution of variation within the APOC3/A4/A5 gene cluster in determining plasma triglycerides.

Since triglycerides (TG) are a major independent risk factor for coronary heart disease, understanding their genetic and environmental determinants is of major importance. Mouse models indicate an inverse relationship between levels of the newly identified apolipoprotein AV (APOAV) and TG concentrations. We have examined the relative influence of human APOA5 variants on plasma lipids, compared to the impact of variation in APOC3 and APOA4 which lie in the same cluster. Single nucleotide polymorphisms (SNPs) in APOA5 (S19W, -1131T>C) and APOA4 (T347S, Q360H) and an APOA4/A5 intergenic T>C SNP were examined in a large study of healthy middle-aged men (n=2808). APOA5 19WW and -1131CC men had 52% and 40% higher TG (P<0.003) compared to common allele homozygotes, respectively, effects which were independent and additive. APOA4 347SS men had 23% lower TG compared to TT men (P<0.002). Haplotype analysis was carried out to identify TG-raising alleles and included, in addition, four previously genotyped APOC3 SNPs (-2845T>G, -482C>T, 1100C>T, and 3238C>G). The major TG-raising alleles were defined by APOA5 W19 and APOC3 -482T. This suggests that the TG-lowering effect of APOA4 S347 might merely reflect the strong negative linkage disequilibrium with the common alleles of these variants. Thus variation in APOA5 is associated with differences in TGs in healthy men, independent of those previously reported for APOC3, while association between APOA4 and TG reflects linkage disequilibrium with these sites. The molecular mechanisms for these effects remain to be determined.

Apolipoprotein A-V↗