Gene–gene interaction of PPARγ and ApoE affects coronary heart disease risk

The Correlation Between Peroxisome Proliferator-Activated Receptor Alpha and Gamma Polymorphisms and Acute Coronary Syndrome

Objective: This study aims to evaluate the relationship between peroxisome proliferator-activated receptor (PPAR) alpha and gamma gene polymorphisms and acute coronary syndrome (ACS) clinically.

Subject and methods: Peripheral blood samples were collected from a total of 200 people, including 100 acute coronary syndrome patients and 100 controls aged 19 to 93 years, admitted to the Pamukkale University Emergency Medicine Department. The healthy volunteers had no known chronic or acute diseases, no history of drug use, and no recent history of coronary artery disease (CAD). PPAR alpha L162V and PPAR gamma C161T gene polymorphic regions were detected using DNA sequencing analyses. In addition, data collected from the hemogram and biochemical parameters and comorbidities of the patients were statistically analyzed.

Results: PPAR gamma C161T polymorphisms were compared between groups. The CT heterozygous rate in the patient group (74%) was higher than in the control group (7%). The T allele was more common in the patient group (0.37) compared to the control group (0.03). When PPAR alpha L162V polymorphism was compared, VV homozygous individuals were %19 in the patient group and none in the control group. The V allele was found to be statistically higher in patients with ACS (p<0.01).

Conclusion: The findings revealed that elevated PPAR alpha L162V and PPAR gamma C161T gene polymorphisms were associated with a progressive risk of ACS.

PPARγ Gene Polymorphisms, Metabolic Disorders, and Coronary Artery Disease

Being activated by endogenous and exogenous ligands, nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) enhances insulin sensitivity, promotes adipocyte differentiation, stimulates adipogenesis, and has the properties of anti-atherosclerosis, anti-inflammation, and anti-oxidation. The Human PPARγ gene (PPARG) contains thousands of polymorphic loci, among them two polymorphisms (rs10865710 and rs7649970) in the promoter region and two polymorphisms (rs1801282 and rs3856806) in the exonic region were widely reported to be significantly associated with coronary artery disease (CAD). Mechanistically, PPARG polymorphisms lead to abnormal expression of PPARG gene and/or dysfunction of PPARγ protein, causing metabolic disorders such as hypercholesterolemia and hypertriglyceridemia, and thereby increasing susceptibility to CAD.

Polymorphisms and Gene-Gene Interaction in AGER/IL6 Pathway Might Be Associated with Diabetic Ischemic Heart Disease

Background: Although the genetic susceptibility to diabetes and ischemic heart disease (IHD) has been well demonstrated, studies aimed at exploring gene variations associated with diabetic IHD are still limited; Methods: Our study included 204 IHD cases who had been diagnosed with diabetes before the diagnosis of IHD and 882 healthy controls. Logistic regression was used to find the association of candidate SNPs and polygenic risk score (PRS) with diabetic IHD. The diagnostic accuracy was represented with AUC. Generalized multifactor dimensionality reduction (GMDR) was used to illustrate gene-gene interactions; Results: For IL6R rs4845625, the CT and TT genotypes were associated with a lower risk of diabetic IHD than the CC genotype (OR = 0.619, p = 0.033; OR = 0.542, p = 0.025, respectively). Haplotypes in the AGER gene (rs184003-rs1035798-rs2070600-rs1800624) and IL6R gene (rs7529229-rs4845625-rs4129267-rs7514452-rs4072391) were both significantly associated with diabetic IHD. PRS was associated with the disease (OR = 1.100, p = 0.005) after adjusting for covariates, and the AUC were 0.763 (p < 0.001). The GMDR analysis suggested that rs184003 and rs4845625 were the best interaction model after permutation testing (p = 0.001) with a cross-validation consistency of 10/10; Conclusions: SNPs and haplotypes in the AGER and IL6R genes and the interaction of rs184003 and rs4845625 were significantly associated with diabetic IHD.

Statistical Learning Methods Applicable to Genome-Wide Association Studies on Unbalanced Case-Control Disease Data

Despite the fact that imbalance between case and control groups is prevalent in genome-wide association studies (GWAS), it is often overlooked. This imbalance is getting more significant and urgent as the rapid growth of biobanks and electronic health records have enabled the collection of thousands of phenotypes from large cohorts, in particular for diseases with low prevalence. The unbalanced binary traits pose serious challenges to traditional statistical methods in terms of both genomic selection and disease prediction. For example, the well-established linear mixed models (LMM) yield inflated type I error rates in the presence of unbalanced case-control ratios. In this article, we review multiple statistical approaches that have been developed to overcome the inaccuracy caused by the unbalanced case-control ratio, with the advantages and limitations of each approach commented. In addition, we also explore the potential for applying several powerful and popular state-of-the-art machine-learning approaches, which have not been applied to the GWAS field yet. This review paves the way for better analysis and understanding of the unbalanced case-control disease data in GWAS.

The hepatoprotective effects of Salvia plebeia R. Br. extract in zebrafish (Danio rerio)

Salvia plebeia R. Br. is a traditional Chinese medicinal herb that has been widely used for the treatment of many inflammatory diseases such as hepatitis. However, the underlying molecular mechanism about the hepatoprotective effects of S. plebeia remains largely unknown. Here, we investigated the antioxidant activities and anti-inflammatory effects of ethanol extracts of S. plebeia (SPEE) in the zebrafish model. Firstly, we determined the chemical compositions of SPEE and identified three major constituents by using GC-MS analysis. After that, SPEE exhibited significantly antioxidant properties in the LPS-induced zebrafish embryos, and the enzyme activities of ROS, CAT and SOD were obviously inhibited in a dose-dependent manner. Secondly, SPEE greatly reduced fat vacuoles (HE staining), lipid accumulation (Oil O staining) and hepatocyte fibrosis (Gemori staining) in the thioacetamide (TAA)-induced hepatocyte injury of adult zebrafish. Meanwhile, the NO contents and lipid metabolism-related genes were substantially down-regulated after SPEE exposure. Thirdly, we used RNA-Seq analysis to identify the differentially expressed genes (DEGs) after SPEE exposure in adult zebrafish liver. The results showed that 1289 DEGs including 558 up-regulated and 731 down-regulated were identified between the TAA + SPEE and TAA groups. KEGG pathway and GO functional analysis revealed that steroid biosynthesis, oxidation-reduction and innate immunity were significantly enriched. Mechanistically, SPEE can considerably reduce the cell apoptosis of hepatocytes and promote the translocation of Nrf2 protein from the nucleus to the cytoplasm in TAA-induced zebrafish. Moreover, SPEE can modulate various inflammatory cytokines and immune genes both in the control and H₂O₂-stimulated conditions. The pro-inflammatory cytokines such as IL-1β and TNF-α was markedly up-regulated but the anti-inflammatory cytokines such as TGF-β was greatly down-regulated after SPEE treatment. In addition, some key genes in the TLR signaling were also activated in the H₂O₂-stimulated conditions. In summary, our results suggested that SPEE had an important role in the antioxidant and anti-inflammatory effects in zebrafish in the near future. Some of the components identified in this study may be served as potential sources of new hepatoprotective compounds for the treatment of inflammatory diseases.

PPARG and FTO polymorphism can modulate the outcomes of a central European diet and a Mediterranean diet in centrally obese postmenopausal women

The aim of this study was to test the hypothesis that polymorphism of genes with the biggest effects on body mass (FTO and PPARG) can affect the results of dieting in centrally obese postmenopausal women. A total of 144 volunteers were randomized to a 16-week intervention with two hypocaloric diets: either a Mediterranean diet (MED) moderate in fat (37% total energy as fat) or the Central European diet (CED) moderate in carbohydrates (55% total energy as carbohydrates). The associations between FTO and PPARG polymorphism on the baseline body mass, body composition, blood pressure, lipid and non-lipid parameters, and their changes after the trial were analyzed. None of the examined baseline outcomes differed in the rs9939609 FTO subgroups; abdominal fat was higher in the minor (G) allele carriers of the PPARG rs1801282. After the intervention, in the CED group, the PPARG G allele carriers showed greater reductions in weight (-6.58 ± 0.61 vs -9.58 ± 0.83; P < .01), lean mass (-0.38 ± 0.29 vs -1.79 ± 0.38; P < .05) and high-density lipoprotein (HDL) cholesterol (-0.46 ± 0.77 vs -5.25 ± 1.49; P < .01) than the CC homozygotes, and the TT individuals of the rs9939609 FTO had greater reductions in diastolic blood pressure (-9.03 ± 1.78 vs. -7.58 ± 1.50; P < .05). In the MED group, greater reductions in abdominal fat were observed in the G allele carriers than in the CC homozygotes (-3.31 ± 0.26 vs. -4.23 ± 0.41; P < .05). PPARG and FTO polymorphism may affect the outcomes of the diets aimed at weight reduction in postmenopausal women.

Exosomal microRNA-122 mediates obesity-related cardiomyopathy through suppressing mitochondrial ADP-ribosylation factor-like 2

Emerging studies have demonstrated that microRNAs (miRs) participate in the development of multiple metabolic complications including cardiovascular diseases. Among them, circulating level of liver-secreted miR-122 was closely correlated with several consequence of heart diseases in clinical studies, and overexpression of miR-122 impaired cardiomyocyte function. However, it was unknown whether miR-122 could regulate cardiac biology in obesity. Therefore, present study was to disclose the role of miR-122 in cardiac metabolic disorders and potential molecular mechanisms. Through utilizing clinical samples and high fat diet-fed mice, we investigated the physiological roles of miR-122 in obesity-related cardiomyopathy. Besides, present study explored the mitochondrial function under exosomal miR-122 stimulation in mouse primary cardiomyocytes. In clinical samples and obese mice, the circulating level of exosomal miR-122 was positively correlated with cardiac dysfunctional parameters, including reduction in ejection fraction (EF) and increased levels of NT-proBNP. Human plasma exosomes transported miR-122 into mouse primary cardiomyocytes, and impaired mitochondrial ATP production and oxygen consumption, whereas miR-122 sponge improved these inhibitory effects. In dietary-induced mice, increased hepatic and circulating exosomal miR-122 deteriorated cardiac structure and functional index, and inhibited mitochondrial function. Liver-specific blockage of miR-122 attenuated abnormal cardiac remodeling. Mechanistically, miR-122 directly bound and suppressed mitochondrial protein ADP-ribosylation factor-like 2 (Arl-2) in vitro and in vivo Knockdown of Arl-2 abolished the mitochondrial benefits of miR-122 sponge in exosome-treated mouse primary cardiomyocytes.In conclusions, our present study firstly showed that liver-secreted exosomal miR-122 played a critical role in the development of metabolic cardiomyopathy, and miR-122/mitochondrial Arl-2 signaling affected cardiac energy homeostasis.

Antiobesity, Regulation of Lipid Metabolism, and Attenuation of Liver Oxidative Stress Effects of Hydroxy-α-sanshool Isolated from Zanthoxylum bungeanum on High-Fat Diet-Induced Hyperlipidemic Rats

Zanthoxylum bungeanum is a traditional Chinese medicine (TCM) used to relieve pain, dispel dampness, stop diarrhea, and prevent itching. The aim of this study was to investigate the antiobesity and hypolipidemic effects of hydroxy-α-sanshool (HAS) isolated from Z. bungeanum on hyperlipidemic rats. Wistar rats (n = 48) were randomly divided into six groups: (1) normal diet rats (ND), (2) high-fat diet- (HFD-) treated rats, (3) HFD+fenofibrate-treated rats (HFD+FNB), (4) HFD+low dose of HAS-treated rats (HFD+LD, 9 mg/kg), (5) HFD+middle dose of HAS-treated rats (HFD+MD, 18 mg/kg), and (6) HFD+high dose of HAS-treated rats (HFD+HD, 36 mg/kg). The body weight and food intake of the rats were recorded during the treatment period. After 4 weeks of HAS treatment, abdominal adipose tissues were observed and total cholesterol (T-CHO), triglycerides (TG), high-density lipoprotein (HDL) cholesterol (HDL-C), and low-density lipoprotein (LDL) cholesterol (LDL-C) of serum and liver tissues were determined. Furthermore, histochemical examinations using oil red O and hematoxylin-eosin staining (H&E) were carried out and levels of malondialdehyde (MDA) and glutathione (GSH) and activities of superoxide dismutase (SOD) in the liver were determined. After HFD feeding, the body weight gain and food efficiency ratio of HFD rats were significantly enhanced (p < 0.05vs. ND rats) and HAS treatment (18 and 36 mg/kg) significantly decreased the body weight gain and food efficiency ratio (p < 0.05vs. HFD rats). In addition, HAS treatment could decrease the abdominal adipose tissues and liver adipocytes. Furthermore, HAS treatment significantly decreased the T-CHO, TG, and LDL-C, whereas it increased HDL-C (p < 0.05vs. HFD rats) in serum and the liver. HAS treatment increased the GSH level and SOD activity in the liver (p < 0.05vs. HFD rats), whereas it decreased the levels of MDA (p < 0.05vs. HFD rats). mRNA analyses suggested that HAS treatment increases the expression of Pparg (proliferator-activated receptor γ) and Apoe (peroxisome apolipoprotein E). Immunohistochemistry and Western blotting indicated that HAS stimulation increased the levels of PPARγ and APOE in the liver, as a stress response of the body defense system. These results revealed that HAS exerts antiobesity and hypolipidemic activities in HFD rats by reducing liver oxidative stress and thus could be considered as a potential candidate drug to cure or prevent obesity and hyperlipidemia.

PON2 and PPARG polymorphisms as biomarkers of risk for coronary heart disease

Aim: Investigate the correlation between paraoxonase 2 (PON2) Ser311Cys polymorphism as well as the peroxisome proliferator-activated receptor gamma (PPARG) His477His polymorphism and the susceptibility to development of coronary heart diseases (CHD) through a meta-analysis. Methods: Odds ratio and the corresponding 95% CI were used to assess the results. We included 7476 CHD patients and 8504 healthy controls. All the statistical analyses were performed by Comprehensive Meta-Analysis software (CMA, version 2.0). Results: The Ser311Cys polymorphism decreased susceptibility in the overall population and Asian population to CHD. The His477His polymorphism has a protective role in the overall population; however, the subgroup analysis by ethnicity suggested that in Asian population, His477His might increase the risk of CHD. Conclusion: These polymorphisms constitute important predictive indicators of CHD susceptibility.

Different Susceptibilities between Apoe- and Ldlr-Deficient Mice to Inflammation-Associated Colorectal Carcinogenesis

Hypercholesterolemia resulting in atherosclerosis is associated with an increased risk of ischemic heart disease and colorectal cancer (CRC). However, the roles of apoliprotein (Apo) E (Apoe) and low-density lipoprotein (Ldl) receptor (Ldlr) in colorectal carcinogenesis have not yet been investigated. In this study, we examined the susceptibility of Apoe-deficient and Ldlr-deficient mice, which are genetic animal models of atherosclerosis to azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced colorectal carcinogenesis. In Experiment 1, male Apoe-deficient (n = 20) and wild type (WT) mice (C57BL/6J, n = 21) were treated with a single intraperitoneal (i.p.) injection of AOM (10 mg/kg body weight) and then given 1.5% DSS in drinking water for seven days. They were maintained up to week 20 and sacrificed for the histopathological examination of colorectal tumors. The mRNA expression of cyclooxygenase (Cox)-2, inducible nitric oxide synthase (Nos2), tumor necrosis factor (Tnf)-α interleukin (Il)-1β, and Il-6 was assayed in the colorectal mucosa. In Experiment 2, male Ldlr-deficient (n = 14) and WT mice (C57BL/6J, n = 10) were given a single i.p. injection of AOM (10 mg/kg body weight) and then given 2% DSS in drinking water for seven days. They were sacrificed at week 20 to evaluate their colorectum histopathologically. In Experiment 1, the multiplicity of CRCs was significantly higher in the Apoe-deficient mice (2.75 ± 1.48) than in the WT mice (0.62 ± 0.67). The serum lipoprotein levels in the Apoe-deficient mice were also significantly higher than in the WT mice. In Experiment 2, the incidence (29%) and multiplicity (0.50 ± 0.94) of CRCs in the Ldlr mice were significantly lower than in the WT mice (80% incidence and 3.10 ± 2.38 multiplicity). The mRNA expression of two inducible enzymes and certain pro-inflammatory cytokines in the colorectum of each genotype was greater than in the respective WT mice. The values in the Apoe-deficient mice were much greater than in the Ldlr mice. These findings suggest that Apoe-deficient mice showed increased susceptibility to inflammation-associated colorectal carcinogenesis due to their high reactivity to inflammatory stimuli.

Apolipoprotein E Gene Variants and Risk of Coronary Heart Disease: A Meta-Analysis

Objectives. Apo E genes involved in lipoprotein synthesis and metabolism are considered one of the candidates to CHD. However, the results remain conflicting. Methods. We performed this meta-analysis based on 30 published studies including 11,804 CHD patients and 17,713 controls. Results. Compared with the wild genotype E3/3, the variant genotypes ApoEE3/4 and E4/4 were associated with 22% and 45% increased risk of CHD, respectively (E3/4 versus E3/3: OR = 1.22, 95% CI = 1.15–1.29; E4/4 versus E3/3: OR = 1.45, 95% CI = 1.23–1.71). Besides, compared with ε3 allele, carriers with the ε4 allele had a 46% increased risk of CHD (OR = 1.46, 95% CI = 1.28–1.66), while the ε2 had no significantly decreased risk of CHD. In the subgroup analysis by ethnicity, ε4 had a 25% increased risk of CHD in Caucasians (OR = 1.25, 95% CI = 1.11–1.41), and the effects were more evident in Mongolians (OR = 2.29, 95% CI = 1.89–2.77). The ε2 allele had a decreased risk of CHD in Caucasians (OR = 0.84, 95% CI = 0.74–0.96), but not in Mongolians. Conclusions. The analysis suggested that ApoEε4 mutation was associated with the increased risk of CHD, while ApoEε2 allele had a decreased risk of CHD just in Caucasians.

Association between peroxisome proliferator-activated receptor-alpha, delta, and gamma polymorphisms and risk of coronary heart disease: A case-control study and meta-analysis

OBJECTIVES

Risk of coronary heart disease (CHD) has been suggested to be associated with polymorphisms of peroxisome proliferator-activated receptors (PPARs), while the results were controversial. We aimed to systematically assess the association between PPAR polymorphisms and CHD risk.

METHODS

A case-control study with 446 subjects was conducted to evaluate the association between CHD risk and C161T polymorphism, which was of our special interest as this polymorphism showed different effects on risks of CHD and acute coronary syndrome (ACS). Meta-analyses were conducted to assess all PPAR polymorphisms. Either a fixed- or a random-effects model was adopted to estimate overall odds ratios (ORs).

RESULTS

In the case-control study, T allele carriers of C161T polymorphism were not significantly associated with CHD risk (Odds ratio (OR) = 0.74, 95% confidence interval (CI) 0.47-1.15, P = 0.19), while T allele carriers showed higher risk of ACS (OR = 1.63, 95% CI 1.00-2.65, P = 0.048). The meta-analysis indicated that compared with CC homozygous, T allele carriers had lower CHD risk (OR = 0.69, 95% CI 0.59-0.82, P < 0.001) but higher ACS risk (OR = 1.43, 95% CI 1.09-1.87, P = 0.010). Three other polymorphisms were also found to be significantly associated with CHD risk under dominant model: PPAR-alpha intron 7G/C polymorphism (CC+GC vs GG, OR 1.42, 95% CI 1.13-1.78, P = 0.003), L162V polymorphism (VV+LV vs LL, OR 0.74, 95% CI 0.56-0.97, P = 0.031), and PPAR-delta +294T/C polymorphism (CC+TC vs TT, OR 1.51, 95% CI 1.12-2.05, P = 0.007).

CONCLUSIONS

The results suggested that PPAR-alpha intron 7G/C and L162V, PPAR-delta +294T/C and PPAR-gamma C161T polymorphisms could affect CHD susceptibility, and C161T polymorphism might have different effects on CHD and ACS.

SNP-SNP Interaction between TLR4 and MyD88 in Susceptibility to Coronary Artery Disease in the Chinese Han Population

The toll-like receptor 4 (TLR4)-myeloid differentiation factor 88 (MyD88)-dependent signaling pathway plays a role in the initiation and progression of coronary artery disease (CAD). We investigated SNP-SNP interactions between the TLR4 and MyD88 genes in CAD susceptibility and assessed whether the effects of such interactions were modified by confounding risk factors (hyperglycemia, hyperlipidemia and Helicobacter pylori (H. pylori) infection). Participants with CAD (n = 424) and controls (n = 424) without CAD were enrolled. Polymerase chain restriction-restriction fragment length polymorphism was performed on genomic DNA to detect polymorphisms in TLR4 (rs10116253, rs10983755, and rs11536889) and MyD88 (rs7744). H. pylori infections were evaluated by enzyme-linked immunosorbent assays, and the cardiovascular risk factors for each subject were evaluated clinically. The significant interaction between TLR4 rs11536889 and MyD88 rs7744 was associated with an increased CAD risk (p value for interaction = 0.024). In conditions of hyperglycemia, the interaction effect was strengthened between TLR4 rs11536889 and MyD88 rs7744 (p value for interaction = 0.004). In hyperlipidemic participants, the interaction strength was also enhanced for TLR4 rs11536889 and MyD88 rs7744 (p value for interaction = 0.006). Thus, the novel interaction between TLR4 rs11536889 and MyD88 rs7744 was related with an increased risk of CAD, that could be strengthened by the presence of hyperglycemia or hyperlipidemia.

Association between Peroxisome Proliferator-activated Receptor Gamma Gene Polymorphisms and Atherosclerotic Diseases: A Meta-analysis of Case-control Studies

AIM

The aim of this study was to perform a meta-analysis to investigate the association between PPARγ rs1801282/rs3856806 polymorphisms and atherosclerotic diseases.

METHODS

The meta-analysis was performed by searching the PubMed, Embase and Web of Science databases from the first available year to September 10, 2013. Additionally, reference lists from the identified articles, reviews and abstracts presented at the meetings of related scientific societies were also checked. All case-control studies investigating the association between PPARγ rs1801282/rs3856806 polymorphisms and the risk of atherosclerotic disease were included. The association was assessed according to the odds ratio (OR) with a 95% confidence interval (CI). Publication bias was analyzed using Begg's funnel plot and Egger's regression test.

RESULTS

A total of 29 studies reporting PPARγ rs1801282/rs3856806 polymorphism were included in the final meta-analysis. Neither the rs1801282 (Pro12Ala) nor rs3856806 (C161T) polymorphisms showed any significant associations with susceptibility to atherosclerotic diseases. In the meta-analysis performed to assess the association between the rs3856806 gene polymorphism and atherosclerotic disease based on ethnicity and the type of disease, significant associations were found in the Caucasian subgroup, Asian, CAD and MI subgroups.

CONCLUSIONS

The present data suggest that there is no statistical evidence of a significant association between the PPARγ gene rs1801282/rs3856806 polymorphism and the risk of atherosclerotic disease. In contrast, the rs3856806 polymorphism was associated with an increased risk in the Caucasian and MI subgroups, whereas decreased risks were noted in the Asian and CAD subgroups. Due to significant between-study heterogeneity, further studies with a larger sample size involving homogeneous AS patients and well-matched controls are required in the future.

Association between apolipoprotein E gene polymorphism and the risk of coronary artery disease in Chinese population: evidence from a meta-analysis of 40 studies

Background

Epidemiological studies have evaluated the association between apolipoprotein E (ApoE) gene polymorphism and coronary artery disease (CAD) risk which developed inconsistent conclusions. To derive a more precise estimation of the relationship in Chinese population, we performed this meta-analysis.

Methods

Databases, including PubMed, EMbase, Web of Science, CBMdisc and CNKI, were searched to get the genetic association studies. Additionally, hand searching of the references of identified articles were performed. All the statistical tests were performed using Review Manager 5.1.2 and Stata 11.0.

Results

We identified a total of 40 studies, including 4,564 CAD cases and 3,985 controls. The results showed evidence for significant association between ApoE ε4 allele and CAD risk (for ε2/ε4 vs. ε3/ε3: OR = 1.86, 95% CI = 1.42–2.43, p<0.00001; for ε3/ε4 vs. ε3/ε3: OR = 2.34, 95% CI = 2.07–2.65, p<0.00001; for ε4/ε4 vs. ε3/ε3: OR = 2.89, 95% CI = 1.87–4.47, p<0.00001; for ε4 allele vs. ε3 allele: OR = 2.11, 95% CI = 1.91–2.35, p<0.00001).

Conclusions

The present meta-analysis suggests an association between ApoE ε4 allele and increased risk of CAD in Chinese population. However, due to the small sample size in most of the included studies and the selection bias existed in some studies, the results should be interpreted with caution.

The C161T polymorphism in the peroxisome proliferator-activated receptor gamma gene (PPARγ) is associated with risk of coronary artery disease: a meta-analysis

The researches attempting to associate the PPARγ C161T polymorphism with coronary artery disease (CAD) yielded complicated and contradictory results. We aimed for more precise estimate of the relationship and conducted a comprehensive meta-analysis. Publications written in English or Chinese were screened in MEDLINE, Embase, CNKI, Wanfang and CBM. Data on 11 studies including 3,020 cases and 2,853 controls were extracted. A random-effects model was available to synthesize the inconsistent outcomes of the individual studies, while addressing between-study heterogeneity and publication bias. The PPARγ C161T polymorphism followed Hard-Weinberg Equilibrium for all studies (P > 0.05).Overall, there was no evidence for a significant association under all genetic models but with distinct heterogeneity (T vs. C: P = 0.29, OR = 0.91, 95 %CI 0.77-1.08, P heterogeneity = 0.004, I (2) = 61.2 %). However, in the subgroup analysis by ethnicity, the T allele carriers showed a prominent 26 % risk reduction of CAD among Chinese (dominant genetic model: P = 0.03, 95 %CI 0.57-0.97, P heterogeneity = 0.03, I (2) = 56.1 %). After dividing into population source, the significance of CAD risk reduction was strengthened in hospital-based studies (allele comparison: P = 0.04, OR = 0.82, 95 %CI 0.67-1.00, P heterogeneity = 0.04, I (2) = 52.5 %; dominant model: P = 0.01, OR = 0.73, 95 %CI 0.57-0.92, P heterogeneity = 0.05, I (2) = 50.8 %). There was no obvious publication bias verified in the method of funnel plot and Egger's linear regression test (t = -0.11, P = 0.913). Taken together, our results revealed the PPARγ C161T polymorphism might play a moderate protective effect on developing CAD among Chinese, but not among Caucasians.

The effect of PPARG gene polymorphisms on the risk of coronary heart disease: a meta-analysis

The peroxisome proliferator-activated receptor-γ (PPARG) is a member of the nuclear hormone receptor superfamily that has attracted considerable attention as a candidate gene for coronary heart disease (CHD) based on its function as a key factor involved in the regulation of lipid and glucose metabolism. In the past decade, a number of case-control studies have been carried out to investigate the relationship between the PPARG polymorphisms and CHD. However, these studies have yielded contradictory results. To derive a more precise estimation of the relationship, a meta-analysis of 33 studies including a total of 12,340 cases and 17,471 controls on 3 PPARG polymorphisms (Pro12Ala, C161T and C1431T) was performed. In a combined analysis, the summary per-allele odds ratio for CHD was 1.02 (95 % CI: 0.93-1.13), 0.86 (95 % CI: 0.72-1.02), and 0.92 (95 % CI: 0.74-1.16) for PPARG 12Ala, 161T and 1431T alleles, respectively. No significant results were observed under dominant or recessive genetic models for these polymorphisms in almost all comparisons. In the stratified analyses according to ethnicity, sample size, CHD endpoints and HWE status, no evidence of any gene-disease association was obtained. Our results suggest that the Pro12Ala, C161T and C1431T polymorphisms of PPARG gene are not associated with CHD susceptibility.

The meta-analysis of the association of PPARG P12A, C161T polymorphism and coronary heart disease

OBJECTIVE

Two common variations of peroxisome proliferator-activated receptor γ (PPARG), P12A (Pro12Ala, rs1801282), and C161T (His447His, rs3856806), are thought to have an effect on susceptibility to coronary heart disease (CHD), but the results are inconsistent. Therefore, a meta-analysis of published studies was performed.

METHODS

The electronic databases, PubMed, Embase, Web of Science, and CNKI (China National Knowledge Infrastructure) were searched for studies to include in the present meta-analysis (last search was updated on 30 Aug. 2011). Twenty studies testing the association between PPARG gene polymorphisms and CHD were examined: 12 studies of P12A; 8 studies of C161T. Overall and ethnicity-specific summary odds ratios and corresponding 95 % confidence intervals for CHD associated with these polymorphisms were estimated using fixed- and random-effects models. Heterogeneity and publication bias were evaluated. A total of 20 studies including 5,795 cases and 9,069 controls were included in this meta-analysis.

RESULTS

No significant associations were found in carriers of the rare Ala allele of the P12A polymorphism versus the common Pro/Pro genotype among the studies with both of the fixed-effect and random-effect model. In the subgroup analyses by ethnicity, source of control and type of study, no significant risks were found. For PPARG C161T, carriers of the T variant of C161T polymorphism were associated with an increased risk of CHD (OR = 1.182, 95 % CI: 1.023-1.341, P(heterogeneity) = 0.002), and in the stratified analysis by ethnicity and source of controls, the contrast of CT + TT vs. CC all produced significant association in Asian and hospital-based controls (OR = 1.276, 95 % CI: 1.084-1.468, P(heterogeneity) = 0.055; OR = 1.164, 95 % CI: 1.001-1.326, P(heterogeneity) = 0.002),when the fixed-effect model was used. But they were all insignificant with the random-effect model.

CONCLUSION

This meta-analysis suggests that the PPARG C161T polymorphism marginally contributes to increased susceptibility to CHD and marginally increased association between PPARG H477H polymorphism and CHD also appeared in Asian and hospital-based controls. But PPARG P12A polymorphism is not associated with CHD risk.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Investigation of polymorphic variants of PPARD and APOE genes in Turkish coronary heart disease patients

The aim of this study was to determine the role of polymorphic variants of apolipoprotein E (APOE) and peroxisome proliferator-activated receptor delta (PPARD) genes in the development of coronary heart disease (CHD), and the PPARD and APOE gene-gene interaction in a Turkish population. This study was carried out using a sample of 223 patients with CHD (103 with diabetes and 120 without diabetes) and 101 controls. PPARD +294T/C and APOE genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism technique. The PPARD and APOE genotype distributions were the same between study groups (p>0.05). In the nondiabetic CHD patients, the PPARD +294 C allele showed higher serum low-density lipoprotein cholesterol (LDL-C) level than the common +294 TT homozygote genotype (3.83 ± 1.01 vs. 3.33 ± 1.14, p=0.015). In addition, a significant association between APOE 4 and PPARD +294 C alleles was detected based on their effects on LDL-C in the nondiabetic CHD patients (+294 C/APOE4: 4.43 ± 0.88 vs. +294 TT/nonAPOE 4: 3.48 ± 1.09, p = 0.009). This association indicated the interaction of two genes on plasma LDL-C levels ascended in the order +294 T<+294 T-APOE 4<+294 C<APOE 4<+294 C-APOE 4. The PPARD +294 C allele was associated with higher incidence of left ventricular hypertrophy (LVH) in all male patients with body mass index >27. In addition, the CHD patients who were +294 C allele carriers had a 2.48-fold higher risk of LVH than subjects homozygous for the T allele. An increasing effect of the PPARD +294 C allele was shown on serum LDL-C levels in nondiabetic CHD patients. In addition, the results suggested that the +294 C allele might be associated with an increased LVH risk especially in male CHD patients. Furthermore, gene-gene interaction between the PPARD +294T/C and the APOE polymorphisms was observed regarding LDL-C concentrations.

Impaired adipogenic response to thiazolidinediones in mice expressing human apolipoproteinE4

Thiazolidinediones (TZDs) are insulin sensitizers used to treat patients with insulin resistance. To assess potential gene-drug interactions, mice expressing human apolipoprotein E3 or E4 (APOE3 or APOE4) were fed a Western-type high-fat diet for 12 wk, at which time they developed similarly impaired glucose tolerance. Supplementing the diet with rosiglitazone (1.5 mg/g body weight) for an additional 4 wk improved plasma lipid profiles in both APOE3 and APOE4 mice. However, glucose tolerance improved only in APOE3 mice. Induction of adipogenesis and lipogenesis was severely blunted in adipose tissues, but not in the livers, of APOE4 mice. Consequently, lipids were channeled to the liver, causing marked steatosis in these mice. Impaired glucose tolerance was not a prerequisite for this adverse effect, and long-term treatment with rosiglitazone altered liver enzymes and caused hepatic fibrosis in APOE4 mice. Finally, TZDs failed to stimulate PPARγ activation and adipocyte differentiation in preadipocytes and embryonic fibroblasts isolated from APOE4 mice compared to those from APOE3 mice. We conclude that the effects of TZDs are APOE isoform dependent, and that the metabolic damage observed in APOE4 mice is rooted in an impaired activation of the adipogenic program in the adipose tissues expressing APOE4.

Three novel SNPs in the coding region of PPARγ gene and their associations with meat quality traits in cattle

The peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear hormone receptor that regulates adipogenesis and many other biological processes. In the present study, we carried out PCR-SSCP and DNA sequencing analyses to examine SNPs in coding region of the PPARγ gene. A total of 660 individuals from five Chinese cattle breeds were genotyped. We identified three SNPs and their associations with meat quality traits were analyzed in 108 Qinchuan cattle. Two missense mutations and one synonymous mutation were found: 200 A>G (genotypes AA, AB and BB) resulting in D7G change, the silent substitution 42895 C>T (genotypes JJ and JI) and 72472 G>T (genotypes CC, DC and DD) producing Q448H change, respectively. The frequencies of PPARγ-A allele were 0.86, 0.83, 0.80, 0.72 and 0.87 for Qinchuan, Nanyang, Jiaxian, Luxi and Xianan populations, respectively. The frequencies of PPARγ-J allele varied from 0.87 to 0.96 in the five populations. In the 72472 G>T locus, the frequencies of PPARγ-C allele were higher than PPARγ-D allele in the five populations, and ranged from 0.58 to 0.82. Least squares analysis revealed that in 42895 C>T locus, there was a significant effect on tenderness in 18-20 months Qinchuan cattle (P<0.01), and in the 72472 G>T locus, animals with the genotype DC had lower mean values than these with genotype CC (P<0.01) for back fat thickness in 18-20 months, and animals with the genotype DD had lower mean values than these with genotypes CC and DC (P<0.01) for water holding capacity in 21-24 months (P<0.01). The SNPs we have identified may contribute to establishing a more efficient selection program for improving of genetic characteristics in indigenous Chinese cattle.

Lack of association of the APOE epsilon 4 allele with the risk of obstructive sleep apnea: meta-analysis and meta-regression

STUDY OBJECTIVES

Reports on the association of polymorphisms in the gene encoding apolipoprotein E (APOE)--a vital macromolecule in cholesterol metabolism--with obstructive sleep apnea (OSA) have provided conflicting results. Our objective was to meta-analytically synthesize the existing evidence for the association of the APOE epsilon4 allele with the risk of OSA.

DESIGN

Random effects meta-analysis and meta-regression.

SETTING

Genetic epidemiological studies reporting the association of APOE epsilon4 allele with OSA susceptibility.

PATIENTS OR PARTICIPANTS

Synthesis of APOE epsilon4 allele data from 6,508 subjects including 1,901 cases of OSA and 4,607 controls.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Eight studies were included in the random effects meta-analysis; the summary effect size measured as odds ratio (OR) for association of the APOE epsilon4 allele with the risk of OSA was found to be 1.13 (95% confidence interval 0.86-1.47). There was a statistically significant heterogeneity (I2 = 72%, P = 0.001) across study results that was not explained by the mean age, proportion of males, or the proportion possessing the APOE epsilon4 allele or when grouped based on the geographic location of the study.

CONCLUSIONS

The hypothesis that the APOE epsilon4 allele may be causally associated with OSA cannot be supported on the basis of published literature.

Sex-specific interaction between APOE and APOA5 variants and determination of plasma lipid levels

The APOA5 and APOE genes play an important role in determination of plasma levels of triglycerides (TG) and total cholesterol (TC). We have analyzed APOA5 (T-1131>C and Ser19>Trp) and APOE (e2/e3/e4) variants in 2500 representatively selected Caucasians (1168 men, 1332 women). In female subjects (but not in male) an association between APOE polymorphism and TC was observed on the background of the common APOA5 haplotype (TT-1131/SerSer19) - APOE2 carriers have the lowest (5.12 (1.15) mmol/l) and the APOE4 carriers have the highest (6.05 (1.06) mmol/l) levels of plasma TC (P<0.001). If at least one APOA5 C-1131 or Trp19 allele was present, APOE exhibits no significant effect on plasma TC. APOA5 did not affect plasma TG levels, if APOE4 allele was present. In the presence of APOE2 or APOE3, carriers of the APOA5 alleles, C-1131 and/or Trp19, have higher TG levels (1.64 (1.05) mmol/l) than others (1.37 (0.75) mmol/l) (P<0.01). In male subjects, the same, but non-significant trend was observed. In female subjects, we have detected an interaction between APOE and APOA5 variants and plasma lipid levels.

No Association of Pro12Ala Polymorphism of PPAR-.GAMMA. Gene With Coronary Artery Disease in Korean Subjects

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)-gamma, a member of the nuclear hormone receptor family, which is involved in the differentiation of adipose tissue, is reported to be associated with the pathogenesis of type 2 diabetes mellitus, insulin resistance and atherosclerosis. Whether the prevalence of coronary artery disease (CAD) is associated with Pro12Ala polymorphism in exon B of PPAR-gamma was investigated in Korean adults.

METHODS AND RESULTS

The study was conducted in 267 subjects (158 males, 109 females, mean age 58 years) who underwent coronary angiography because of chest pain. Cardiovascular risk factors, such as blood pressure, body mass index (BMI), fasting blood sugar and serum lipid profiles, were assessed in all subjects, who were divided into 4 groups according to the number of stenosed coronary arteries: normal, 1-vessel, 2-vessel and 3-vessel disease. Genotyping of Pro12Ala polymorphism was done with real-time polymerase chain reaction. Allelic frequency for proline was 0.955 and 0.045 for alanine, which was in Hardy-Weinberg equilibrium (p=0.74). One hundred and seventeen subjects (43.8%) had normal coronary arteries, 88 (33%) had 1-vessel disease, 39 (14.6%) had 2-vessel disease and 23 (8.6%) had 3-vessel disease. When the cardiovascular risk factors were compared among the 4 groups, there were no meaningful differences except for age and FBG levels, which were significant even after adjustment for age and BMI. There were no significant differences in the prevalence or severity of CAD according to the different genotypes of Pro12Ala, and in logistic regression analysis Pro12Ala polymorphism was not a predictor for CAD.

CONCLUSIONS

There was no significant association between Pro12Ala polymorphism in exon B of PPAR-gamma and prevalence or severity of CAD in Korean adults. Further studies on the correlation between Pro12Ala polymorphism and CAD should be carried out in a larger Korean population in the future.

Pro12Ala Sequence Variant of the PPARG Gene Is Associated with Postprandial Hypertriglyceridemia in Non-E3/E3 Patients with the Metabolic Syndrome

Background: Postprandial hypertriglyceridemia, a component of the metabolic syndrome, has varied etiology and involves many genes related to triglyceride metabolism. Variations in these genes may affect postprandial hypertriglyceridemia in the context of the metabolic syndrome.

Methods: We orally administered 60 g of fat overload to 74 patients with the metabolic syndrome. We then measured baseline concentrations of cholesterol, triglycerides, HDL cholesterol, apolipoprotein AI, apolipoprotein B, uric acid, and uric acid excretion; we also performed homeostasis model assessments of insulin resistance and insulin sensitivity. At 3 h, we measured triglycerides, cholesterol, apolipoprotein AI, and apolipoprotein B. Patients were considered to have postprandial hypertriglyceridemia if the difference in plasma triglycerides between baseline and 3 h after the test was 1.71 mmol/L or more. We also measured anthropometrical variables and classified the patients according to their peroxisome proliferative activated receptor, gamma (PPARG) gene and apolipoprotein E (APOE) genotype.

Results: Postprandial hypertriglyceridemia occurred in 64.7% of patients with the Ala12 allele vs 19.9% of the Pro12Pro patients, (P = 0.00032; odds ratio, 7.6), and in 87.5% of the patients with both the Ala12 allele and the non-E3/E3 APOE genotype (odds ratio, 23.8). Logistic regression analysis showed that PPARG and APOE sequence variants were associated with the presence of postprandial hypertriglyceridemia.

Conclusion: The Pro12Ala PPARG sequence variant together with a non-E3/E3 APOE genotype is associated with a high risk for postprandial hypertriglyceridemia in patients with the metabolic syndrome, indicating a close association between these genes and the regulation of lipoproteinase clearance.

Effects of two common polymorphisms of peroxisome proliferator-activated receptor-gamma gene on metabolic syndrome

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)gamma is involved mainly in adipocyte differentiation and has been suggested to play an important role in the pathogenesis of insulin resistance and atherosclerosis. We investigated the frequencies of two common polymorphisms of PPARgamma gene, exon 6 C-->T substitution and exon B Pro12Ala in healthy subjects and analyzed the correlations between the different genotypes and insulin resistance, metabolic syndrome and cardiovascular risk factors.

METHODS

Anthropometric measurements, fasting glucose, insulin and lipid profiles were measured in 253 Korean females. Homeostatic model assessments and quantitative insulin sensitivity check indices were calculated. Metabolic syndrome was diagnosed according to the NCEP-ATP III guidelines and the Western Pacific Region of WHO for obesity criteria for waist circumference. Polymerase chain reaction (PCR)-restriction fragment-length polymorphism and real-time PCR were performed for genotyping of the DNAs.

RESULTS

For C161T polymorphism, allele frequencies were 0.804 and 0.196 for T allele, and 0.947 for proline and 0.053 for alanine. There was no Ala12Ala homozygote in the population. No differences were seen in the mean values of age, body mass index (BMI), blood pressure, fasting blood glucose level, fasting insulin levels, HOMA and QUICKI among different genotypes when analyzed as a whole, except that subjects with Pro12Ala had significantly higher body weight than those with Pro12Pro genotype. However, mean BMI, percent body fat and weight showed significant differences between genotypes in younger age group (< or =50 years). Although overall prevalence of metabolic syndrome had no association with the genotypes, the prevalence of decreased high-density lipoprotein cholesterol component was lower in those with the T allele than in those with the CC genotype. There was no association of the genotypes with glucose tolerance status. When the subjects were divided into four groups according to the combination of the genetic alleles of the two polymorphisms, subjects having Pro12Ala and T allele, simultaneously, showed significantly higher mean weight than those without Ala allele. Pro12Ala polymorphism seems to affect body weight, similar to the previous studies, and the effect was potentiated with the presence of T allele of C161T polymorphism.

CONCLUSIONS

Although either polymorphism failed to show significant association with insulin resistance, the fact that the prevalence of decreased HDL-C was lower in those with the T allele of C161T polymorphism suggests that this polymorphism might have a protective effect on atherosclerotic lipid profiles, which needs further investigation.

Genetic variants predisposing to cardiovascular disease

PURPOSE OF REVIEW

The goal of this review is to provide an update on the most recent and relevant findings in the area of genotype-phenotype associations as well as the relationships between genetic factors and cardiovascular disease risk markers and events. In addition, emphasis will be placed on the methodological problems associated with studying the genetics of complex disorders, specifically cardiovascular diseases.

RECENT FINDINGS

Genes associated with cardiovascular disease predisposition have been examined, including traditional cardiovascular disease candidate genes, such as ACE, AGT, eNOS, PON and MTHFR, new loci that have recently been added to the growing list of cardiovascular disease candidate genes (i.e. MEF2A, ALOX5, LTA, APOM, PDE4D), and genes that have been shown to be at the intersection of several age-related disorders through interaction with one another or with environmental factors (i.e. APOA5, APOE, PPARgamma, LPL and LIPC).

SUMMARY

During the last year, tremendous effort has been made in elucidating new genes associated with cardiovascular disease predisposition. For the most part, however, major breakthroughs have not been made, primarily due to the poor replication of results among studies, as a consequence of poor experimental design. Nevertheless, we have increased our understanding of the complexity of cardiovascular disease and the relevance of gene-environment interactions as the ultimate drivers of the individual predisposition to the disease. It is essential, therefore, that present and future genetic studies in this area take into consideration the inclusion of high-quality environmental data in the analytical process to test the clinical usefulness of a genetic marker as a risk predictor.

Gene polymorphism association studies in dialysis: cardiovascular disease

Cardiovascular disease (CVD) is the most important cause of morbidity and mortality in dialysis patients. The high prevalence of CVD is due to the cumulative effects of multiple risk factors from the early stages of chronic kidney disease (CKD). Familial predispositions to CVD, CKD, and their respective risk factors are well known, and it is likely that genetic factors determine the interindividual variability in risks for disease. Advances in genomic technology have facilitated the study of genetic variation--most commonly single nucleotide polymorphisms (SNPs) in candidate genes--and their associations with disease. This review examines CVD in dialysis patients as a model of a complex disease, discusses the approach to gene polymorphism association studies, including the roles of gene-environment and gene-gene interactions and provides an overview of available studies.

Single nucleotide variants in the beta2-adrenergic and beta3-adrenergic receptor genes explained 18.3% of adolescent obesity variation

Associations of obesity with its candidate genes, beta-adrenergic receptor genes (ADRBs), peroxisome proliferator-activated receptor-gamma (PPARgamma), and uncoupling proteins (UCPs) were studied in Korean adolescents. We analyzed the obesity-related phenotypes body mass index (BMI), percentage of body fat, plasma leptin and insulin levels, fasting glucose concentration, and plasma lipid profile in 329 teenagers to investigate the effects of seven single nucleotide variants 252G/A, 523C/A and 1053G/C in ADRB2; Trp64Arg in ADRB3; 161C/T in PPARgamma; Ala55Val in UCP2; and 210C/T in UCP3. The 1053G/C polymorphism (P < 0.05) in the ADRB2 gene and the Trp64Arg polymorphism (P < 0.01) in the ADRB3 gene were associated with BMI after adjustment for dietary energy intake. Trp64Arg polymorphism also influenced percentage of body fat (P < 0.01) and plasma leptin level (P < 0.05). Furthermore, significant interaction effects between the 1053G/C and Trp64Arg polymorphisms were observed on BMI (P < 0.01). The polymorphisms of the ADRB2 and ADRB3 genes explained 4.3% and 10.1% of the variation on BMI, and the two loci effect, including their epistasis, explained 18.3%. We concluded that 1053G/C and Trp64Arg polymorphisms of the ADRB genes additively and interactively contributed to the variation of complex adolescent obesity.

Analysis of separate and combined effects of common variation in KCNJ11 and PPARG on risk of type 2 diabetes

The separate and combined effects of the PPARG Pro(12)Ala polymorphism and the KCNJ11 Glu(23)Lys polymorphisms on risk of type 2 diabetes were investigated in relatively large-scale, case-control studies. Separate effects of the variants were examined among 1187/1461 type 2 diabetic patients and 4791/4986 middle-aged, glucose-tolerant subjects. The combined analysis involved 1164 type 2 diabetic patients and 4733 middle-aged, glucose-tolerant subjects. In the separate analyses, the K allele of the KCNJ11 Glu(23)Lys associated with type 2 diabetes (odds ratio, 1.19; P = 0.0002), whereas the PPARG Pro(12)Ala showed no significant association with type 2 diabetes. The combined analysis indicated that the two polymorphisms acted in an additive manner to increase the risk of type 2 diabetes, and we found no evidence for a synergistic interaction between them. Analysis of a model with equal additive effects of the two variants showed that the odds ratio for type 2 diabetes increased with 1.14/risk allele (P = 0.003). Together, the two polymorphisms conferred a population-attributable risk for type 2 diabetes of 28%. In conclusion, our results showed no evidence of a synergistic interaction between the KCNJ11 Glu(23)Lys and PPARG Pro(12)Ala polymorphisms, but indicated that they may act in an additive manner to increase the risk of type 2 diabetes.

Associations between apoE genotype and colon and rectal cancer

Apolipoprotein E (apoE) plays a major role in the metabolism of bile acids, cholesterol and triglycerides, and has recently been proposed as being involved in the carcinogenic process. Given the potential role of bile acids in colorectal cancer etiology, it is reasonable that colorectal cancer risk might be modified by apoE genotype. We used data collected from a case-control study of colon cancer (n=1556 cases and 1948 controls) and rectal cancer (n=777 cases and 988 controls). The absence of an e3 apoE allele significantly increased the risk of colon cancer (OR=1.37 95% CI 1.00-1.87), particularly among those diagnosed when older than 64 years (OR=1.88 95% CI 1.17-3.04; P interaction between age and apoE genotype equal to 0.05). A significant three-way interaction was detected for family history of colorectal cancer, age at diagnosis and apoE genotype (P = 0.05), in those diagnosed when older, not having an e3 allele and having a significantly increased risk of colon cancer with family history of colorectal cancer (OR=3.93 95% CI 1.23-12.6). This was compared with the risk associated with family history of colorectal cancer among those diagnosed when older, with an e3 allele of 1.61 (95% CI 1.17-2.23) or those diagnosed when younger without an e3 allele (OR=2.40 95% CI 0.56-10.3). Among those diagnosed when older than 64 years, associations of BMI and prudent diet with colon cancer were stronger among individuals without an e3 allele, although the P for interaction was not significant. We did not detect any significant associations between apoE genotype and rectal cancer, survival after diagnosis with colorectal cancer, stage of disease at diagnosis or type of tumor mutation. These findings suggest those apoE genotypes that do not include the e3 allele, the same genotypes that are associated with increased risk of coronary heart disease, may influence development of colon cancer among those who are older at diagnosis.