Effect of omega-3 fatty acid supplementation on arterial elasticity in patients with familial hypercholesterolaemia on statin therapy.

BACKGROUND AND AIMS: Increased arterial stiffness is closely linked with raised blood pressure that contributes substantially to enhanced risk of coronary heart disease in high risk individuals with familial hypercholesterolaemia (FH). Omega-3 fatty acid (ω3-FA) supplementation has been demonstrated to lower blood pressure in subjects with a high cardiovascular disease risk. Whether ω3-FA supplementation improves arterial stiffness in FH subjects, on background statin therapy, has yet to be investigated. METHOD AND RESULTS: We carried out an 8-week randomized, crossover intervention trial to test the effect of 4 g/d ω3-FA supplementation (46% eicosapentaenoic acid and 38% docosahexaenoic acid) on arterial elasticity in 20 adults with FH on optimal cholesterol-lowering therapy. Large and small artery elasticity were measured by pulse contour analysis of the radial artery. ω3-FA supplementation significantly (P < 0.05 in all) increased large artery elasticity (+9%) and reduced systolic blood pressure (-6%) and diastolic blood pressure (-6%), plasma triglycerides (-20%), apoB concentration (-8%). In contrast, ω3-FAs had no significant effect on small artery elasticity. The change in large artery elasticity was not significantly associated with changes in systolic blood pressure or plasma triglyceride concentration. CONCLUSIONS: ω3-FA supplementation improves large arterial elasticity and arterial blood pressure independent of statin therapy in adults with FH. CLINICAL TRIAL REGISTRATION: https://www.clinicaltrials.com/NCT01577056.

Homocysteine, methylenetetrahydrofolate reductase C677T polymorphism and cognitive impairment: the health in men study.

High total plasma homocysteine (tHcy) has been associated with cognitive impairment in later life, but it is unclear if this association is causal or is due to confounding. The C677T polymorphism of the 5,10 methylenetetrahydrofolate reductase gene (MTHFR) increases basal tHcy, but its contribution to cognitive impairment has not been established. We designed this study to determine if tHcy is causally related to cognitive impairment in later life by investigating its association with high tHcy and the MTHFR-C677T polymorphism. We recruited 1778 older men from the Health in Men Study cohort and established caseness on the basis of the participants' scores on a Telephone Interview for Cognitive Status score 27 in 2008. Exposure to tHcy, gene status and other variables of interest were obtained from assessments 4-7 years earlier. Multivariate logistic regression showed that the odds of cognitive impairment increased with a doubling of tHcy (adjusted odds ratio, OR 1.36; 95% confidence interval, 95% CI 1.02-1.82). Compared with the wild CC genotype, participants with the MTHFR-TT genotype had 46% greater odds of cognitive impairment (OR 1.46, 95% CI 1.01-2.11, P=0.043). The results of this study are consistent with, but do not prove the hypothesis that high tHcy causes cognitive impairment in later life.

Matrix metalloproteinase-2 gene variants and abdominal aortic aneurysm.

OBJECTIVE: To investigate associations between two polymorphisms of the matrix metalloproteinase-2 gene (MMP2) and the incidence and progression of abdominal aortic aneurysm (AAA). METHODS: Cases and controls were recruited from a trial of screening for AAAs. The association between two variants of MMP2 (-1360C>T, and +649C>T) in men with AAA (n=678) and in controls (n=659) was examined using multivariate analyses. The association with AAA expansion (n=638) was also assessed. RESULTS: In multivariate analyses with adjustments for multiple testing, no association between either SNP and AAA presence or expansion was detected. CONCLUSION: MMP2 -1360C>T and +649C>T variants are not risk factors for AAA.

Polymorphisms of the matrix metalloproteinase 9 gene and abdominal aortic aneurysm.

BACKGROUND: Increased matrix metalloproteinase (MMP) 9 activity has been implicated in the formation of abdominal aortic aneurysm (AAA). The aim was to explore the association between potentially functional variants of the MMP-9 gene and AAA. METHODS: The -1562C > T and -1811A > T variants of the MMP-9 gene were genotyped in 678 men with an AAA (at least 30 mm in diameter) and 659 control subjects (aortic diameter 19-22 mm) recruited from a population-based trial of screening for AAA. Levels of MMP-9 were measured in a random subset of 300 cases and 84 controls. The association between genetic variants (including haplotypes) and AAA was assessed by multivariable logistic regression. RESULTS: There was no association between the MMP-9-1562C > T (odds ratio (OR) 0.70 (95 per cent confidence interval (c.i.) 0.27 to 1.82)) or -1811A > T (OR 0.71 (95 per cent c.i. 0.28 to 1.85)) genotypes, or the most common haplotype (OR 0.81 (95 per cent c.i. 0.62 to 1.05)) and AAA. The serum MMP-9 concentration was higher in cases than controls, and in minor allele carriers in cases and controls, although the differences were not statistically significant. CONCLUSION: In this study, the genetic tendency to higher levels of circulating MMP-9 was not associated with AAA.

The relationship between ApoE, TNFA, IL1a, IL1b and IL12b genes and HIV-1-associated dementia.

OBJECTIVES: Host genetic factors implicated in AIDS dementia complex (ADC) were studied. METHODS: DNA from ADC patients (n=56), unselected HIV-seropositive patients (n=112, 171, 185 and 204) and HIV-seronegative controls (n=204, 60, 60, 96 and 624) were typed for polymorphic loci in genes encoding tumour necrosis factor (TNF)-alpha, interleukin (IL)-1alpha, IL-1beta, IL-12 and Apolipoprotein E (ApoE). Diagnosis of ADC was based on neurological symptoms, signs and neuroimaging findings with other causes of dementia excluded. Patients selected had ADC stage > or =1 and CD4 counts of <500 cells/microL. RESULTS: Allele 2 of TNFA-308 was more common in ADC patients compared to HIV-positive or HIV-negative controls (P=0.005, 0.024). No other differences between ADC patients and control groups were significant. Meta-analyses confirmed these results. CONCLUSIONS: This study suggests that TNFA-308 allele 2 or an allele in linkage disequilibrium with this locus influences ADC.

Familial lipoprotein lipase deficiency caused by known (G188E) and novel (W394X) LPL gene mutations.

Lipoprotein lipase (LPL) is the key enzyme in the catabolism of triglyceride-rich lipoproteins in the circulation. Familial LPL deficiency is characterized by hypertriglyceridaemia and absence of LPL activity. We report a case of LPL deficiency in a 43-year-old woman, who initially presented in childhood with chylomicronaemia syndrome. At that time, her plasma triglyceride concentration was approximately 30 mmol/L and post-heparin lipolytic activity was very low. In addition to having the known missense mutation LPL G188E, the patient was also found to have a novel nonsense mutation in exon 8, namely LPL W394X. The novel substitution in exon 8 (c.1262G > A) predicts a truncated protein product of 393 amino acids that lacks the carboxylterminal 12% of the mature LPL. Trp(394) is part of a cluster of exposed tryptophan residues in the carboxyl-terminal domain of LPL important for binding lipid substrate. Of 11 members from her three-generation family, three were heterozygotes for G188E (mean plasma triglyceride, 3.5 +/- 2.0 mmol/L), whereas six were heterozygotes for W394X (triglyceride, 4.3 +/- 1.8 mmol/L). In summary, we describe a case of familial LPL deficiency caused by compound heterozygosity for known (G188E) and novel (W394X) LPL gene mutations.

Polymorphisms of the interleukin-6 gene promoter and abdominal aortic aneurysm.

BACKGROUND: Elevated levels of circulating interleukin-6 (IL-6) have been reported in patients with abdominal aortic aneurysms (AAAs). Although this implicates inflammation as a cause of AAAs, there is also evidence that the aneurysmal aorta may secrete IL-6 into the circulation as a result of aortic proteolysis. Genetic association studies are one means of trying to clarify the role of specific mediators in the causal pathway. The aim of the present study was to examine the association between variants of the IL-6 gene and AAAs. METHODS: An association study involving 677 men with screen-detected AAAs and 656 age-matched controls was performed. Three variants in the IL-6 promoter region were analysed: IL-6-174G>C (rs1800795), IL-6-572G>C (rs1800796) and IL-6-597G>A (rs1800797). Univariate regression of SNP genotype on AAA as a binary outcome was initially performed under a range of genetic models (additive, dominant and recessive). This was followed by multivariate analyses, testing the same models but including risk factors known to be associated with AAAs. All analyses and haplotype estimation were performed under a generalized linear model framework. RESULTS: IL-6-572G>C polymorphism (frequency 1.5% in cases) was identified as an independent risk factor for AAA with an odds ratio (OR) of 6.00 (95%CI: 1.22, 29.41) when applied to the recessive model. No association was seen in the additive or dominant models. In a multivariate analysis using the most common haplotype (h.111, frequency 48.7%) as a reference, h.211 (frequency 4.4%) was an independent risk factor for AAA (OR 1.56, 95%CI: 1.02, 2.39). CONCLUSION: The IL-6 572G>C polymorphism (and h.211 haplotype) is associated with AAA, however it is too rare to be an important cause of most AAAs. This does not support the concept that the elevated level of IL-6 reported in patients with AAAs is a primary cause of the aneurysmal process.

The relationship between ACE genotype and risk of severe hypoglycaemia in a large population-based cohort of children and adolescents with type 1 diabetes.

AIMS/HYPOTHESIS: Genetic factors may account for familial clustering related to diabetes complications. Studies have shown a significant relationship between the presence of the deletion (D) allele of the gene encoding ACE and risk of severe hypoglycaemia. This large prospective cohort study assesses this relationship in a large sample of children and adolescents with type 1 diabetes. SUBJECTS AND METHODS: We studied 585 children and adolescents (mean age 11.9 +/- 4 years, 48.4% males). The frequency of severe hypoglycaemia (an event leading to loss of consciousness or seizure) was prospectively assessed over the 13-year period 1992-2004. Patients were seen with their parents every 3 months and data recorded at each visit. The ACE gene was detected using PCR. RESULTS: In our cohort of 585 children, 186 (31.8%) had at least one episode of severe hypoglycaemia, and of these 28.0% had the II genotype, 48.9% had the ID genotype and 23.1% had the DD genotype. This was in agreement with the Hardy-Weinberg proportion. A total of 477 severe hypoglycaemic episodes was recorded with a total of 3,404 person-years of follow-up, giving a total incidence of 14 per 100 patient-years. No significant increase in risk for DD genotype (incidence rate ratio = 0.97, 95% CI 0.61-1.55) relative to II genotype was observed. CONCLUSIONS/INTERPRETATION: This large prospective study concludes that the presence of the D allele of the ACE gene does not predict a significantly higher risk of severe hypoglycaemia in type 1 diabetic children and adolescents.

Homocysteine-lowering treatment with folic acid, cobalamin, and pyridoxine does not reduce blood markers of inflammation, endothelial dysfunction, or hypercoagulability in patients with previous transient ischemic attack or stroke: a randomized substudy of the VITATOPS trial.

BACKGROUND AND PURPOSE: Epidemiological and laboratory studies suggest that increasing concentrations of plasma homocysteine (total homocysteine [tHcy]) accelerate cardiovascular disease by promoting vascular inflammation, endothelial dysfunction, and hypercoagulability. METHODS: We conducted a randomized controlled trial in 285 patients with recent transient ischemic attack or stroke to examine the effect of lowering tHcy with folic acid 2 mg, vitamin B12 0.5 mg, and vitamin B6 25 mg compared with placebo on laboratory markers of vascular inflammation, endothelial dysfunction, and hypercoagulability. RESULTS: At 6 months after randomization, there was no significant difference in blood concentrations of markers of vascular inflammation (high-sensitivity C-reactive protein [P=0.32]; soluble CD40L [P=0.33]; IL-6 [P=0.77]), endothelial dysfunction (vascular cell adhesion molecule-1 [P=0.27]; intercellular adhesion molecule-1 [P=0.08]; von Willebrand factor [P=0.92]), and hypercoagulability (P-selectin [P=0.33]; prothrombin fragment 1 and 2 [P=0.81]; D-dimer [P=0.88]) among patients assigned vitamin therapy compared with placebo despite a 3.7-micromol/L (95% CI, 2.7 to 4.7) reduction in total homocysteine (tHcy). CONCLUSIONS: Lowering tHcy by 3.7 micromol/L with folic acid-based multivitamin therapy does not significantly reduce blood concentrations of the biomarkers of inflammation, endothelial dysfunction, or hypercoagulability measured in our study. The possible explanations for our findings are: (1) these biomarkers are not sensitive to the effects of lowering tHcy (eg, multiple risk factor interventions may be required); (2) elevated tHcy causes cardiovascular disease by mechanisms other than the biomarkers measured; or (3) elevated tHcy is a noncausal marker of increased vascular risk.

ATP-binding cassette transporter G8 gene as a determinant of apolipoprotein B-100 kinetics in overweight men.

OBJECTIVE: We examined the influence of genetic variation of the ATP-binding cassette (ABC) transporter G8 on apolipoprotein B (apoB) kinetics in overweight/obese men. METHODS AND RESULTS: Very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) apoB kinetics were determined in 47 men (body mass index 32+/-3 kg/m2) using stable isotope and multicompartmental modeling to estimate production rate (PR), fractional catabolic rate (FCR), and VLDL to LDL-apoB conversion. Relative to the wild-type (400TT), subjects carrying the ABCG8 400K allele had significantly decreased plasma concentrations of triglycerides, sitosterol, and campesterol, lower PR of VLDL-apoB, and higher VLDL to LDL-apoB conversion (P<0.05). The PR and FCR of LDL-apoB were also significantly higher with 400K allele (P<0.05). No association was found with ABCG8 D19H. Compared with APOE2 or APOE3, APOE4 carriers had significantly higher plasma LDL-cholesterol concentrations and lower LDL-apoB FCR. During multiple regression analysis including age, homeostasis model assessment score, plasma concentrations of sitosterol, and lathosterol, ABCG8 and apoE genotypes were independent determinants of VLDL-apoB PR and LDL-apoB FCR, respectively (P<0.05). CONCLUSIONS: Variation in the ABC transporter G8 appears to independently influence the metabolism of apoB-containing lipoproteins in overweight/obese subjects. This may have therapeutic implications for the management of dyslipidemia in these subjects.

Four novel mutations in APOB causing heterozygous and homozygous familial hypobetalipoproteinemia.

Familial hypobetalipoproteinemia (FHBL) is a rare codominant disorder of lipoprotein metabolism characterized by low levels of low-density lipoprotein (LDL) cholesterol and apolipoprotein (apo) B. Heterozygotes for FHBL have less-than-half normal LDL-cholesterol and apoB concentrations, whereas homozygotes have extremely low or undetectable LDL-cholesterol and apoB levels. These reductions in LDL-cholesterol and apoB have been suggested to provide FHBL subjects with resistance to atherosclerosis. FHBL can be caused by mutations in the APOB gene on chromosome 2. We present four novel mutations and one previously described mutation in APOB causing FHBL in five families. Immunoblotting and DNA sequencing were used to characterize the novel mutation apoB-40.3 (c.5564_5565insC) and the previously reported mutation apoB-80.5 (c.11040T>G). The apoB-6.9 (c.1018_1025del) and apoB-25.8 (c.3600T>A) mutations were identified by DNA sequence analysis, as variants shorter than apoB-31 are not detectable in plasma. A fifth mutation, the splice variant c.82+1G>A, was identified by sequencing and was found in a homozygous subject. In approximately 50% of the FHBL subjects, plasma alanine aminotransferase concentrations were mildly increased, suggestive of fatty liver. All affected FHBL subjects had low to low-normal serum vitamin E concentrations, highlighting the important and recognized relationship between lipid and vitamin E concentrations.

Association between the endothelin-1 gene Lys198Asn polymorphism blood pressure and plasma endothelin-1 levels in normal and pre-eclamptic pregnancy.

OBJECTIVE: This study examined the frequency of the Lys198Asn polymorphism in the endothelin-1 (ET-1) gene in women with pre-eclampsia and normal pregnancy; and its contribution to levels of plasma ET-1 and blood pressure. DESIGN AND METHODS: This was a retrospective study examining the frequency of the ET-1 Lys198Asn polymorphism in 72 proteinuric pre-eclamptics and 81 normal pregnant women. Height, weight, blood pressure and plasma ET-1 were measured antenatally and at 6 weeks post-partum. Using specific mutagenic primers, the frequency of the G/G (normal), G/T heterozygote and T/T (mutant) genotypes of the Lys198Asn polymorphism were examined. RESULTS: The polymorphism was not associated with pre-eclampsia. However, in the combined pregnant groups after correction for BMI and group, a significant effect of the T-allele (T/T,G/T) on systolic blood pressure was found (121 +/- 1.5 mmHg compared with 116 +/- 1.3 mmHg in the G/G homozygotes). A significant interaction was found between the T-allele and pregnancy in determining systolic blood pressure, so that the effect was no longer seen post-partum. Pregnant women with the T/T genotype had significantly elevated plasma ET-1 levels 5.8 pg/ml [confidence interval (CI) 3.7-9.1] compared with 3.1 pg/ml (CI 2.6-3.8) in the G/T heterozygotes and 3.6 pg/ml (CI 3.0-4.1) in the normal G/G homozygotes. CONCLUSION: The Lys198Asn polymorphism does not directly contribute to the incidence of pre-eclampsia. However, the association of the T-allele with raised blood pressure and the T/T genotype with increased plasma ET-1 levels suggest that this polymorphism may interact with other genes or environmental factors to sensitize pregnant women to develop pre-eclampsia.

Lack of evidence for association between endothelial nitric oxide synthase gene polymorphisms and coronary artery disease in the Australian Caucasian population.

BACKGROUND: Genetic polymorphism in the gene for endothelial nitric oxide synthase (eNOS) has been identified as a potential risk factor for the development of premature coronary artery disease (CAD). We determined whether the eNOS 4ab, G894T, and T-786C polymorphisms are associated with premature coronary artery disease. DESIGN: A case-control study. METHODS: PCR-based assays were used to compare the frequency of eNOS gene polymorphisms in 573 Caucasian subjects aged under 50 years presenting with symptomatic CAD and documented by coronary angiography, with or without myocardial infarction, to that of 624 similarly aged community controls without a history of symptomatic CAD. RESULTS: We found no difference in the frequency of 4ab genotypes between cases and controls: in the CAD subjects, the 4aa, 4ab, and 4bb genotype frequencies were 1.9%, 24.3% and 73.8% respectively, compared to 2.2%, 25.5% and 72.3% respectively for the controls. There was also no significant difference between cases and controls in the frequency of any allele (4a/4b, 894G/894T, -786C/-786T), or genotype for any of the polymorphisms. Similarly, logistic regression analysis showed no evidence for an association of the polymorphisms with premature CAD or myocardial infarction or any indication of an interaction between the polymorphisms and other CAD risk factors, including smoking. CONCLUSIONS: In a large case-control study, and in contrast to some earlier positive findings by others, we have found no evidence for an association between several eNOS gene polymorphisms and premature CAD in an Australian Caucasian population.

Inherited thrombophilia in ischemic stroke and its pathogenic subtypes.

BACKGROUND AND PURPOSE: One or more of the inherited thrombophilias may be causal risk factor for a proportion of ischemic strokes, but few studies have addressed this association or the association between thrombophilia and pathogenic subtypes of stroke. METHODS: We conducted a case-control study of 219 hospital cases with a first-ever ischemic stroke and 205 randomly selected community control subjects stratified by age, sex, and postal code. With the use of established criteria, cases of stroke were classified by pathogenic subtype in a blinded fashion. The prevalence of conventional vascular risk factors; fasting plasma levels of protein C, protein S, antithrombin III; and genetic tests for the factor V Leiden and the prothrombin 20210A mutation were determined in cases and control subjects. RESULTS: The prevalence of any thrombophilia was 14.7% (95% CI, 9.9% to 19.5%) among cases and 11.7% (95% CI, 7.4% to 17.0%) among control subjects (OR, 1.3; 95% CI, 0.7% to 2.3%). The prevalence of individual thrombophilias among cases ranged from 0.9% (95% CI, 0.1% to 3.4%) for protein S deficiency to 5.2% (95% CI, 0.3% to 9.1%) for antithrombin III deficiency; among control subjects, the prevalence ranged from 1.0% (95% CI, 0.1% to 3.6%) for protein S deficiency to 4.1% (95% CI, 0.2% to 7.8%) for antithrombin III deficiency. There were no significant differences in the prevalence of thrombophilia between cases and control subjects or between pathogenic subtypes of ischemic stroke. CONCLUSIONS: One in 7 patients with first-ever acute ischemic stroke will test positive for one of the inherited thrombophilias, but the relation is likely to be coincidental rather than causal in almost all cases, irrespective of the pathogenic subtype of the ischemic stroke. These results suggest that routine testing for thrombophilia in most patients with acute ischemic stroke may be unnecessary. Whether the thrombophilias may still be important in younger patients with ischemic stroke or in predicting complications (eg, venous thrombosis) and stroke outcome remains uncertain.

Lipoprotein lipase D9N, N291S and S447X polymorphisms: their influence on premature coronary heart disease and plasma lipids.

Lipoprotein lipase (LPL) plays a pivotal role in lipoprotein metabolism. Three recently described exonic polymorphisms of the gene, D9N, N291S and S447X, have been variably found to influence plasma lipids while effects on coronary heart disease (CHD) are less well documented. Two predominantly Caucasian groups were studied: CHD patients <50 years of age, with angiographically documented CHD; and a randomly recruited community control group without a history of heart disease. The 9N allele of the D9N polymorphism was present in 25 of 428 (5.8%) of Caucasian males with CHD and in seven of 291 (2.4%) of corresponding community subjects (odds ratio, 2.5; 95% confidence interval (CI), 1.1-5.9; P=0.03) and was also significantly over-represented in the Caucasian males with myocardial infarction (MI) (21 of 308 or 6.8%; odds ratio, 2.6; 95% CI, 1.1-5.9; P=0.01). The distributions of the other two polymorphisms were similar in the CHD and community groups. In multivariate models adjusted for age, sex, diabetes, body mass index, smoking, lipid levels and race, the D9N polymorphism remained significantly related to both CHD and MI, with an odds ratio >2. There were, generally, trends to more adverse fasting plasma high-density lipoprotein (HDL) cholesterol and triglycerides in carriers of the 291S and 9N alleles, and the opposite trends for triglycerides in 447X carriers. In the community group, male carriers of 291S (n=13) had significantly (20%) lower HDL cholesterol than corresponding non-carriers (n=323), 0.98+/-0.07 mmol/l (mean+/-S.E.) versus 1.22+/-0.02 mmol/l (P<0.005), while HDL cholesterol was not different in male carriers (n=8) and non-carriers (n=296) of 9N (1.23+/-0.13 mmol/l versus 1.22+/-0.02 mmol/l). Multivariate analysis confirmed that the 291S allele carrier status conferred a significantly lower HDL cholesterol (P=0.001) and the 447X allele lower triglyceride (P<0.01) in the community group. In conclusion, LPL 9N carrier status was unequivocally related to premature CHD and to MI in males, strongly supporting recent results in older aged males. The somewhat different effects of the D9N and N291S polymorphisms on plasma lipids, and the absence of a clear effect of the N291S on CHD, raise the possibility that the effect of 9N carrier status might be mediated through effects on LPL function in addition to those influencing fasting plasma lipids.

Duplication and diversification of the apolipoprotein CI (APOCI) genomic segment in association with retroelements.

We have previously shown that several multicopy gene families within the major histocompatibility complex (MHC) arose from a process of segmental duplication. It has also been observed that retroelements play a role in generating diversity within these duplicated segments. The objective of this study was to compare the genomic organization of a gene duplication within another multicopy gene family outside the MHC. Using new continuous genomic sequence encompassing the APOE-CII gene cluster, we show that APOCI and its pseudogene, APOCI', are contained within large duplicated segments which include sequences from the hepatic control region (HCR). Flanking Alu sequences are observed at both ends of the duplicated unit, suggesting a possible role in the integration of these segments. As observed previously within the MHC, the major differences between the segments are the insertion of sequences (approximately 200-1000 bp in length), consisting predominantly of Alu sequences. Ancestral retroelements also contribute to the generation of sequence diversity between the segments, especially within the 3' poly(A) tract of Alu sequences. The exonic and regulatory sequences of the APOCI and HCR loci show limited sequence diversity, with exon 3 being an exception. Finally, the typing of pre- and postduplication Alus from both segments indicates an estimated time of duplication of approximately 37 million years ago (mya), some time prior to the separation of Old and New World monkeys.

Genotypic associations of the hepatic secretion of VLDL apolipoprotein B-100 in obesity.

We examined the effect of genetic polymorphisms of proteins regulating intrahepatic processing of apolipoprotein B-100 (apoB) and the supply of neutral lipids to the liver on the hepatic secretion of very low density lipoprotein (VLDL) apoB in obesity. Hepatic secretion of very low density apolipoprotein B-100 (VLDL apoB) was measured using an infusion of [1-(13)C]leucine in 29 obese men. Isotopic enrichment and turnover of VLDL apoB was determined using gas chromatography-mass spectrometry and multi-compartmental modelling, respectively. Visceral fat was measured by magnetic resonance imaging. Genotypes for the apoB signal peptide (SP27/SP24 alleles), microsomal triglyceride transfer protein promoter (MTP, -493 G/T alleles), apoE (E2, E3, E4 alleles), hepatic lipase promoter (-514 C/T alleles), and cholesteryl ester transfer protein (CETP, Taq1B B1/B2 alleles) were determined using polymerase chain reaction. Statistically significant associations were found between hepatic secretion of apoB and allelic combinations of i) apoB SP with apoE (P = 0.02), hepatic lipase (P = 0.02), and CETP (P = 0. 006) genes, ii) MTP promoter with CETP genes (P = 0.03); the association with apoBSP/MTP promoter allelic combinations just failed to reach significance (P = 0.06), however. The CETP/apoBSP allelic combination was the most significant predictor of apoB secretion, and this was independent of visceral fat, plasma lathosterol and insulin levels, and dietary fat. SP24 carriers who were homozygous for CETP B1 had 60% lower apoB secretion than B2 heterozygotes who were non-carriers of SP24 (10.5 +/- 1.74 mg/kg fat free mass/day, n = 7 vs. 26.1 +/- 3.16, n = 22). The data suggest that variation in both the apoB and CETP genes may be a major genetic determinant of the hepatic secretion of apoB in men with visceral obesity.