Heterogeneous effect of peroxisome proliferator-activated receptor gamma2 Ala12 variant on type 2 diabetes risk

Target gene variations of PPAR isoforms may contribute to MODY heterogeneity: A preliminary comparative study with type 2 diabetes

AIMS

The objective of this study was to evaluate the associations of several genetic variants of peroxisome proliferator-activated receptors (PPARs) on clinical and laboratory parameters in patients with maturity-onset diabetes of the young (MODY), and possible contribution to heterogeneity of the disease.

METHODS

The study groups comprised patients with MODY (genetically confirmed (n = 28), clinically relevant but genetically unconfirmed; MODYX (n = 56)), type 2 diabetes mellitus (T2DM; n = 94) and healthy controls (n = 153). PPARA-L162V-(rs1800206), PPARG-C161T-(rs3856806), P12A-(rs1801282), and PPARB/D + 294 T/C-(rs2016520) polymorphisms were genotyped by real-time-PCR.

RESULTS

The results demonstrated that the frequencies of PPARA-LL162 (p = 0.002), PPARG-CC161 (p = 0.002), and PPARG-ProPro (p = 0.012) genotypes were significantly higher in the MODY group compared to the controls. Furthermore, total-MODY and MODYX groups had a higher frequency of PPARA-LL162 genotype than T2DM (p = 0.005 and p = 0.006, respectively). The frequency of the PPARB/D + 294 T allele was significantly higher in individuals with T2DM than in genetically-determined MODY group (p = 0.019). The PPARA-LL162 genotype was associated with early-onset diabetes in total-MODY (p = 0.022) and T2DM (p < 0.05) groups.

CONCLUSIONS

The association of PPARA-L162V polymorphism with early-onset diabetes in both T2DM and MODY is a noteworthy finding. Considering these results, we suggested that genetic polymorphisms in PPAR isoforms may contribute to the clinical and metabolic heterogeneity of MODY.

Splice variants of metabolic nuclear receptors: Relevance for metabolic disease and therapeutic targeting

Metabolic nuclear receptors are ligand-activated transcription factors which control a wide range of metabolic processes and signaling pathways in response to nutrients and xenobiotics. Targeting these NRs is at the forefront of our endeavours to generate novel treatment options for diabetes, metabolic syndrome and fatty liver disease. Numerous splice variants have been described for these metabolic receptors. Structural changes, as a result of alternative splicing, lead to functional differences among NR isoforms, resulting in the regulation of different metabolic pathways by these NR splice variants. In this review, we describe known splice variants of FXR, LXRs, PXR, RXR, LRH-1, CAR and PPARs. We discuss their structure and functions, and elaborate on the regulation of splice variant abundance by nutritional signals. We conclude that NR splice variants pose an intriguing new layer of complexity in metabolic signaling, which needs to be taken into account in the development of treatment strategies for metabolic diseases.

The Pro12Ala polymorphism of PPARγ2 modulates beta cell function and failure to oral glucose-lowering drugs in patients with type 2 diabetes

BACKGROUND

We evaluate whether the Pro12Ala polymorphism of peroxisome proliferator-activated receptor γ2 (PPARγ2) has a role in the progression of diabetes by modulating the occurrence of treatment failure to glucose-lowering drugs.

METHODS

We studied 215 patients with type 2 diabetes participating in the Thiazolidinediones Or Sulphonylureas and Cardiovascular Accidents Intervention Trial study. All participants were insufficiently controlled (glycated haemoglobin [HbA_1c ] 7.0%-9.0%) with metformin 2 g/day and were randomly allocated to add-on pioglitazone or a sulfonylurea. Treatment failure was defined as HbA_1c ≥8% on two consecutive visits, 3 months apart.

RESULTS

Carriers or non-carriers of the polymorphism had similar age, body mass index, and diabetes duration. Ala carriers had lower fasting plasma insulin, better insulin sensitivity (Homeostasis Model Assessment [HOMA]2-%S), and worse beta cell secretion (HOMA2-%B) than non-carriers. During 24 months of follow-up, 32.5% among the Ala carriers and 8.6% among non-carriers (P < 0.001) developed treatment failure with a cumulative incidence of 18.6 vs 4.6/100 person-years. Those patients who developed treatment failure were older, had a younger age at diabetes diagnosis (48 ± 10 vs 52 ± 7 years; P = 0.032), higher HbA_1c (8.1 ± 0.5 vs 7.7 ± 0.5%; P < 0.001), and lower HOMA2-%B (30 ± 12 vs 46 ± 29; P = 0.015) at study entry, as compared to those who did not develop treatment failure. At multivariate analysis, the Pro12Ala polymorphism was significantly associated with treatment failure (hazard ratio [HR] 4.45; 95% confidence interval [CI] 1.79-11.1; P < 0.001); HbA_1c at study entry was the other independent predictor of failure in this study population.

CONCLUSION

The Pro12Ala polymorphism is associated with a greater insulin sensitivity, reduced beta cell function and a substantially increased risk of treatment failure.

PPARG (Pro12Ala) genetic variant and risk of T2DM: a systematic review and meta-analysis

Type 2 diabetes mellitus (T2DM) is a complex disease caused by the interaction between genetic and environmental factors. A growing number of evidence suggests that the peroxisome proliferator-activated receptor gamma (PPARG) gene plays a major role in T2DM development. Meta-analysis of genetic association studies is an efficient tool to gain a better understanding of multifactorial diseases and potentially to provide valuable insights into gene-disease interactions. The present study was focused on assessing the association between Pro12Ala variation in the PPARG and T2DM risk through a comprehensive meta-analysis. We searched PubMed, WoS, Embase, Scopus and ProQuest from 1990 to 2017. The fixed-effect or random-effect model was used to evaluate the pooled odds ratios (ORs) and 95% confidence intervals (CIs) depending on the heterogeneity among studies. The sources of heterogeneity and publication bias among the included studies were assessed using I² statistics and Egger's tests. A total of 73 studies, involving 62,250 cases and 69,613 controls were included. The results showed that the minor allele (G) of the rs1801282 variant was associated with the decreased risk of T2DM under different genetic models. Moreover, the protective effect of minor allele was detected to be significantly more in some ethnicities including the European (18%), East Asian (20%), and South East Asian (18%). And the reduction of T2DM risk in Ala12 carriers was stronger in individuals from North Europe rather than Central and South Europe. Our findings indicated that the rs1801282 variant may contribute to decrease of T2DM susceptibility in different ancestries.

PPARG Pro12Ala Ala carriers exhibit greater improvements in peripheral insulin sensitivity in response to 12 weeks of aerobic exercise training

The Ala allele of PPARG Pro12Ala ( rs1801282 ) is associated with greater improvements to the glucose metabolism in exercise studies, but whether this extends to peripheral insulin sensitivity is unknown. Our objective was to investigate the effect of PPARG Pro12Ala on exercise-induced changes in peripheral insulin sensitivity. A total of 124 (91 Pro homozygotes and 33 Ala carriers) previously physically inactive healthy young men and women with overweight or class 1 obesity who completed a 12 wk aerobic exercise intervention were included in the analysis. All participants underwent a hyperinsulinemic euglycemic clamp before and after the 12 wk intervention. The prescribed exercise frequency was 5–7 days/wk, and the exercise energy expenditure was 2,100 4,200 kcal/wk for men and 1,600 kcal/wk for women. Insulin sensitivity improved significantly in both genotype groups. However, Ala carriers had a 1.13-fold (95% confidence interval 1.01; 1.26, P = 0.032) greater improvement in insulin sensitivity from baseline compared with Pro homozygotes. Our data support that PPARG Pro12Ala modifies the effect of aerobic exercise on peripheral insulin sensitivity.

Pharmacogenetics of type 2 diabetes mellitus, the route toward tailored medicine

Type 2 diabetes mellitus (T2DM) is a chronic disease that has reached the levels of a global epidemic. In order to achieve optimal glucose control, it is often necessary to rely on combination therapy of multiple drugs or insulin because uncontrolled glucose levels result in T2DM progression and enhanced risk of complications and mortality. Several antihyperglycemic agents have been developed over time, and T2DM pharmacotherapy should be prescribed based on suitability for the individual patient's characteristics. Pharmacogenetics is the branch of genetics that investigates how our genome influences individual responses to drugs, therapeutic outcomes, and incidence of adverse effects. In this review, we evaluated the pharmacogenetic evidences currently available in the literature, and we identified the top informative genetic variants associated with response to the most common anti-diabetic drugs: metformin, DPP-4 inhibitors/GLP1R agonists, thiazolidinediones, and sulfonylureas/meglitinides. Overall, we found 40 polymorphisms for each drug class in a total of 71 loci, and we examined the possibility of encouraging genetic screening of these variants/loci in order to critically implement decision-making about the therapeutic approach through precision medicine strategies. It is possible then to anticipate that when the clinical practice will take advantage of the genetic information of the diabetic patients, this will provide a useful resource for the prevention of T2DM progression, enabling the identification of the precise drug that is most likely to be effective and safe for each patient and the reduction of the economic impact on a global scale.

Effects Of PPARγ2 Pro12Ala Variant On Adipocyte Phenotype Dependent Of DHA

BACKGROUND

Peroxisome proliferator-activated receptor γ2 (PPARγ2) plays a critical role in the regulation of adipocyte differentiation and adipocytokine production. The Pro12Ala variant is the most common mutation in the PPARγ2 gene. Its effect appears to be sensitive to dietary factors, such as docosahexaenoic acid (DHA) level. The purpose of this study was to investigate the interaction effect between PPARγ2 Pro12Ala variant and DHA on the phenotypes of adipocytes.

METHODS

We generated stable 3T3-L1 cell lines expressing wild-type PPARγ2 or PPARγ2 Pro12Ala variant. These two cell lines were cultured with different concentrations of DHA (0, 50, 200 umol/L). Then Oil red O staining was used to observe cell differentiation and the degree of lipid accumulation, TUNNEL assay was used to detect cell apoptosis, and ELISA assays were used to detect the changes of TNF-α, resistin and adiponectin levels in cell culture supernatant.

RESULTS

PPARγ2 Pro12Ala variant reduced lipid droplet accumulation in 3T3-L1 preadipocytes treated with or without 50 μmol/L DHA, but not with 200 μmol/L DHA, compared to that of wild-type PPARγ2. PPARγ2 reduced resistin production and increased adiponectin production in 3T3-L1 adipocytes, whereas PPARγ2 Pro12Ala variant diminished these effects. However, the absence of DHA blocked PPARγ2 Ala12 variant-induced effects on adiponectin production. There was no significant difference in TNF-α secretion between wild-type PPARγ2 and PPARγ2 Pro12Ala cells whether with or without DHA.

CONCLUSION

These results indicated that the effects of PPARγ2 Pro12Ala variant were dependent on DHA concentration.

The rs12917707 polymorphism at the UMOD locus and glomerular filtration rate in individuals with type 2 diabetes: evidence of heterogeneity across two different European populations

Background

UMOD variability has been associated at a genome-wide level of statistical significance with glomerular filtration rate (GFR) in Swedish individuals with type 2 diabetes (T2D; n = 4888). Whether this finding is extensible also to diabetic patients from other populations deserves further study. Our aim was to investigate the relationship between UMOD variability and GFR in patients with T2D from Italy.

Methods

Genotyping of the single nucleotide polymorphism (SNP) rs12917707 at the UMOD locus has been carried out in 3087 individuals from four independent Italian cohorts of patients with T2D by TaqMan allele discrimination.

Results

In none of the four study cohorts was rs12917707 significantly associated with GFR (P > 0.05 for all). Similar results were obtained when the four samples were pooled and analyzed together (β = 0.83, P = 0.19). Such effect was strikingly smaller than that previously reported in Swedish patients (P for heterogeneity = 1.21 × 10-7).

Conclusions

The previously reported strong association between rs12917707 and GFR in diabetic patients from Sweden is not observed in Italian diabetic patients, thus clearly pointing to a heterogeneous effect across the two different samples. This suggests that UMOD is a strong genetic determinant of kidney function in patients with T2D in some, but not all, populations.

The PPARγ2 P12A polymorphism is not associated with all-cause mortality in patients with type 2 diabetes mellitus

The high mortality risk of patients with type 2 diabetes mellitus may well be explained by the several comorbidities and/or complications. Also the intrinsic genetic component predisposing to diabetes might have a role in shaping the risk of diabetes-related mortality. Among type 2 diabetes mellitus SNPs, rs1801282 is of particular interest because (i) it is harbored by peroxisome proliferator-activated receptor-γ2 (PPARγ2), which is the target for thiazolidinediones which are used as antidiabetic drugs, decreasing all-cause mortality in type 2 diabetes mellitus, and (ii) it is associated with insulin resistance and related traits, risk factors for overall mortality in type 2 diabetes mellitus. We investigated the role of PPARγ2 P12A, according to a dominant model (PA + AA vs. PP individuals) on incident all-cause mortality in three cohorts of type 2 diabetes mellitus, comprising a total of 1672 patients (462 deaths) and then performed a meta-analysis of ours and all available published data. In the three cohorts pooled and analyzed together, no association between PPARγ2 P12A and all-cause mortality was observed (HR 1.02, 95 % CI 0.79-1.33). Similar results were observed after adjusting for age, sex, smoking habits, and BMI (HR 1.09, 95 % CI 0.83-1.43). In a meta-analysis of ours and all studies previously published (n = 3241 individuals; 666 events), no association was observed between PPARγ2 P12A and all-cause mortality (HR 1.07, 95 % CI 0.85-1.33). Results from our individual samples as well as from our meta-analysis suggest that the PPARγ2 P12A does not significantly affect all-cause mortality in patients with type 2 diabetes mellitus.

Phenotyping, Etiological Factors, and Biomarkers: Toward Precision Medicine in Autism Spectrum Disorders

Despite the progress made in understanding the biology of autism spectrum disorder (ASD), effective biological interventions for the core symptoms remain elusive. Because of the etiological heterogeneity of ASD, identification of a "one-size-fits-all" treatment approach will likely continue to be challenging. A meeting was convened at the University of Missouri and the Thompson Center to discuss strategies for stratifying patients with ASD for the purpose of moving toward precision medicine. The "white paper" presented here articulates the challenges involved and provides suggestions for future solutions.

The perilipin 2 (PLIN2) gene Ser251Pro missense mutation is associated with reduced insulin secretion and increased insulin sensitivity in Italian obese subjects

BACKGROUND

Perilipin 2 (PLIN2), a member of the family of perilipin lipid droplets coating proteins, is very widely expressed. The Ser251Pro (rs35568725) missense mutation in exon 6 of PLIN2 gene was previously associated with increased lipid accumulation, decreased lipolysis and increased number of small lipid droplets per cell. Furthermore, the Pro251 mutation was associated with decreased plasma triglyceride and very low density lipoprotein concentrations in population studies. The aim of this study was to evaluate the effect of the Ser251Pro mutation of PLIN2 gene in a cohort with a higher predisposition to obesity-associated metabolic alterations, such as insulin resistance, decreased insulin-secretion, hyperglycaemia, and dyslipidaemia.

METHODS

A large cohort (N = 1692) of Italian obese subjects (mean body mass index = 41 kg/m(2) ) was genotyped for the Ser251Pro mutation. All participants underwent oral glucose tolerance tests (OGTT), with measurement of glucose and insulin levels. Indices of insulin resistance and of insulin secretion were also calculated. Clinical and biochemical parameters were collected for all participants.

RESULTS

We observed that insulin concentration was significantly reduced at 120 min after the administration of glucose in Pro251 allele carriers, whereas glucose levels were similar in Pro251 allele carriers and non-carriers throughout the OGTT. Furthermore, the CIR120 index of insulin secretion was significantly lower (P < 0.035) and the ISI index of insulin-sensitivity was significantly higher (P < 0.031) in carriers of the Pro251 allele. When we analysed men and women separately to test for gender-specific associations, we observed that in women insulin levels were significantly lower in Pro251 allele carriers compared with wild-type subjects throughout the whole OGTT. In men, we confirmed a significant reduction in insulin concentration only at 120 min after the OGTT. No significant differences between genotype groups regarding triglyceride levels and anyother clinical and metabolic parameters were observed.

CONCLUSION

We observed a strong significant association between the PLIN2 Pro251 mutation and lower insulin secretion associated with an increased insulin sensitivity. Copyright © 2015 John Wiley & Sons, Ltd.

Genetic variants associated with lean and obese type 2 diabetes in a Han Chinese population: A case-control study

Type 2 diabetes (T2D) is highly phenotypically heterogeneous. Genetics of the heterogeneity of lean and obese T2D is not clear. The aim of the present study was to identify the associations of T2D-related genetic variants with the risks for lean and obese T2D among the Chinese Han population. A case-control study consisting of 5338 T2D patients and 4663 normal glycemic controls of Chinese Han recruited in the Chinese National Diabetes and Metabolic Disorders Study was conducted. T2D cases were identified according to the 1999 World Health Organization criteria. Lean T2D was defined as T2D patient with a body mass index (BMI) <23 kg/m, whereas obese T2D was defined as T2D patient with a BMI ≥28 kg/m. Twenty-five genome-wide association studies previously validated T2D-related single-nucleotide polymorphisms (SNPs) were genotyped. A genotype risk score (GRS) based on the 25 SNPs was created. After adjusting for multiple covariates, SNPs in or near CDKAL1, CDKN2BAS, KCNQ1, TCF7L2, CDC123/CAMK1D, HHEX, and TCF2 were associated with the risk for lean T2D, and SNPs in or near KCNQ1 and FTO were associated with the risk for obese T2D. The results showed that the GRS for 25 T2D-related SNPs was more strongly associated with the risk for lean T2D (Ptrend = 2.66 × 10) than for obese T2D (Ptrend = 2.91 × 10) in our study population. Notably, the T2D GRS contributed to lower obesity-related measurements and greater β-cell dysfunction, including lower insulin levels in oral glucose tolerance test, decreased insulinogenic index, and Homeostasis Model Assessment for β-cell Function. In conclusion, our findings identified T2D-related genetic loci that contribute to the risk of lean and obese T2D individually and additively in a Chinese Han population. Moreover, the study highlights the contribution of known T2D genomic loci to the heterogeneity of lean and obese T2D in Chinese Hans.

Genotype Phenotype Correlation of Genetic Polymorphism of PPAR Gamma Gene and Therapeutic Response to Pioglitazone in Type 2 Diabetes Mellitus- A Pilot Study

INTRODUCTION

Pro12Ala polymorphism is a missense mutation at codon 12 in peroxisome proliferator-activated receptor γ gene (PPARG). This polymorphism is known to be associated with increased insulin sensitivity. Pioglitazone, a thiazolidinedione, is an anti-diabetic drug which acts as an agonist at PPAR γ receptor.

AIM

To determine the association between Pro12Ala polymorphism of the PPARG and variation in therapeutic response to the PPARγ agonist, pioglitazone.

MATERIALS AND METHODS

The study was done as a hospital based pilot project in 30 patients with type 2 diabetes mellitus, on treatment with sulfonylurea or metformin but without adequate glycaemic control. They were started on pioglitazone as add on therapy for a period of 12 weeks. The participants were categorized as responders and non-responders based on the change in HbA1C level after 12 weeks. Pro12Ala polymorphism was analysed by polymerase chain reaction-restriction fragment length polymorphism.

STATISTICAL ANALYSIS

Logistic regression analysis was done to evaluate the associations between age, baseline body weight, BMI, waist circumference, waist-hip ratio and Pro12Ala variants with the response to pioglitazone. The p-value< 0.05 was considered significant.

RESULTS

The frequency distributions of PPAR gamma genotypes were 80% for Pro/Pro and 20% for Pro/Ala in the study population. Among the study participants, 30% were non-responders and 70% responders to pioglitazone. A significantly higher frequency of the polymorphism was detected in the responders (p=0.005) compared to non-responders group.

CONCLUSION

Our study suggests that there is a potential association between Pro12Ala polymorphism and glycaemic response to pioglitazone.

IGF2, LEPR, POMC, PPARG, and PPARGC1 gene variants are associated with obesity-related risk phenotypes in Brazilian children and adolescents

Association studies of genetic variants and obesity and/or obesity-related risk factors have yielded contradictory results. The aim of the present study was to determine the possible association of five single-nucleotide polymorphisms (SNPs) located in the IGF2, LEPR, POMC, PPARG, and PPARGC1 genes with obesity or obesity-related risk phenotypes. This case-control study assessed overweight (n=192) and normal-weight (n=211) children and adolescents. The SNPs were analyzed using minisequencing assays, and variables and genotype distributions between the groups were compared using one-way analysis of variance and Pearson's chi-square or Fisher's exact tests. Logistic regression analysis adjusted for age and gender was used to calculate the odds ratios (ORs) for selected phenotype risks in each group. No difference in SNP distribution was observed between groups. In children, POMC rs28932472(C) was associated with lower diastolic blood pressure (P=0.001), higher low-density lipoprotein (LDL) cholesterol (P=0.014), and higher risk in overweight children of altered total cholesterol (OR=7.35, P=0.006). In adolescents, IGF2 rs680(A) was associated with higher glucose (P=0.012) and higher risk in overweight adolescents for altered insulin (OR=10.08, P=0.005) and homeostasis model of insulin resistance (HOMA-IR) (OR=6.34, P=0.010). PPARG rs1801282(G) conferred a higher risk of altered insulin (OR=12.31, P=0.003), and HOMA-IR (OR=7.47, P=0.005) in overweight adolescents. PARGC1 rs8192678(A) was associated with higher triacylglycerols (P=0.005), and LEPR rs1137101(A) was marginally associated with higher LDL cholesterol (P=0.017). LEPR rs1137101(A) conferred higher risk for altered insulin, and HOMA-IR in overweight adolescents. The associations observed in this population suggested increased risk for cardiovascular diseases and/or type 2 diabetes later in life for individuals carrying these alleles.

Genetic Determinants of Type 2 Diabetes in Asians

Type 2 diabetes (T2D) has become a major health problem throughout the world and the epidemic is particularly severe in Asian countries. Compared with European populations, Asians tend to develop diabetes at a younger age and at much higher incidence rates given the same amount of weight gain. Genome-wide association studies (GWAS) have identified over 70 loci associated with T2D. Although the majority of GWAS results were conducted in populations of European ancestry, recent GWAS in Asians have made important contributions to the identification of T2D susceptibility loci. These studies not only confirmed T2D susceptibility loci initially identified in European populations, but also identified novel susceptibility loci that provide new insights into the pathophysiology of diseases. In this article, we review GWAS results of T2D conducted in East and South Asians and compare them to those of European populations. Currently identified T2D genetic variants do not appear to explain the phenomenon that Asians are more susceptible to T2D than European populations, suggesting further studies in Asian populations are needed.

Association of IRS1, CAPN10, and PPARG gene polymorphisms with type 2 diabetes mellitus in the high-risk population of Hyderabad, India

BACKGROUND

We attempted to validate earlier findings on the nature of the association of the IRS1, CAPN10, and PPARG genes with type 2 diabetes mellitus (T2DM) in the high-risk population of Hyderabad, India.

METHODS

A sample of 1379 subjects (758 T2DM patients, 621 controls) was genotyped for single nucleotide polymorphisms (SNPs) of the IRS1 (rs1801278), CAPN10 (rs3792267, rs5030952), and PPARG (rs1801282) genes.

RESULTS

The allele and genotype frequencies of IRS1 (rs1801278) and CAPN10 (rs3792267) SNPs differed significantly between the patient and control groups. Logistic regression analysis suggested a significant association of these two SNPs (P ≤ 0.007) with T2DM and the strength of association did not alter when adjusted for age, gender, body mass index, and the waist : hip ratio as covariates. The same two SNPs showed significant association in multivariate logistic regression analyses, even after Bonferroni correction for multiple testing, suggesting an independent nature of the role of these genes in the manifestation of T2DM in our population.

CONCLUSIONS

We replicated the significant association of rs1801278 and rs3792267 SNPs of the IRS1 and CAPN10 genes with T2DM in the population of Hyderabad. Despite the known biological significance of the PPARG gene and a sufficient statistical power of the present study, we could not replicate the association of PPARG with T2DM in our high-risk population. Given the vast ethnic, geographic, and genetic heterogeneity of the Indian population, many more studies are needed covering the ethnic and geographic heterogeneity of India to enable identification of an Indian-specific profile of genes associated with T2DM.

No evidence for a role of the peroxisome proliferator-activated receptor gamma (PPARG) and adiponectin (ADIPOQ) genes in antipsychotic-induced weight gain

Antipsychotics frequently cause changes in glucose metabolism followed by development of weight gain and/or diabetes. Recent findings from our group indicated an influence of glucose-related genes on this serious side effect. With this study, we aimed to extend previous research and performed a comprehensive study on the peroxisome proliferator-activated receptor gamma (PPARG) and the adiponectin (ADIPOQ) genes. In 216 schizophrenic patients receiving antipsychotics for up to 14 weeks, we investigated single-nucleotide polymorphisms in or near PPARG (N=24) and ADIPOQ (N=18). Statistical analysis was done using ANCOVA in SPSS. Haplotype analysis was performed in UNPHASED 3.1.4 and Haploview 4.2. None of the PPARG or ADIPOQ variants showed significant association with antipsychotic-induced weight gain in our combined sample or in a refined subsample of patients of European ancestry treated with clozapine or olanzapine after correction for multiple testing. Similarly, no haplotype association could withstand multiple test correction. Although we could not find a significant influence of ADIPOQ and PPARG on antipsychotic-induced weight gain, our comprehensive examination of these two genes contributes to understanding the biology of this serious side effect. More research on glucose metabolism genes is warranted to elucidate their role in metabolic changes during antipsychotic treatment.

PPARγ2 Pro12Ala polymorphism was associated with favorable cardiometabolic risk profile in HIV/HCV coinfected patients: a cross-sectional study

Background

Peroxisome proliferator-activated receptor gamma-2 gene (PPARγ2) rs1801282 (Pro12Ala) polymorphism has been associated with lower risk of metabolic disturbance and atherosclerosis. The aim of this study was to analyze the association between the Pro12Ala polymorphism and cardiometabolic risk factors in human immunodeficiency virus (HIV)/Hepatitis C virus (HCV)-coinfected patients.

Methods

We carried out a cross-sectional study on 257 HIV/HCV coinfected patients. PPARγ2 polymorphism was genotyped by GoldenGate® assay. The main outcome measures were: i) serum lipids (cholesterol, triglycerides, high-density lipoprotein (HDL-C), low-density lipoprotein (LDL-C), LDL-C/HDL-C, and atherogenic index (AI)); ii) homeostatic model assessment (HOMA-IR) values; iii) serum adipokines (leptin, adiponectin, resistin, plasminogen activator inhibitor-1(PAI-1), hepatic growth factor (HGF), and nerve growth factor (NGF)). Generalized Linear Models (GLM) with gamma distribution (log-link) were used to investigate the association between PPARγ2 polymorphism and continuous outcome variables. This test gives the differences between groups and the arithmetic mean ratio (AMR) in continuous outcome variables between groups.

Results

The rs1801282 CG/GG genotype was associated with low values of cholesterol (adjusted arithmetic mean ratio (aAMR) = 0.87 (95% of confidence interval (95% CI) = 0.79; 0.96); p = 0.004) and LDL-C (aAMR = 0.79 (95% CI = 0.68; 0.93); p = 0.004). Furthermore, rs1801282 CG/GG was associated with low values of HOMA-IR (aAMR = 0.69 (95% CI = 0.49; 0.98); p = 0.038) among patients with significant liver fibrosis (F ≥ 2). Moreover, rs1801282 CG/GG was also associated with low serum values of hepatic growth factor (HGF) (aAMR = 0.61 (95% CI = 0.39; 0.94); p = 0.028), and nerve growth factor (NGF) (aAMR = 0.47 (95% CI = 0.26; 0.84); p = 0.010). The serum levels of leptin, adiponectin, resistin, and PAI-1 did not show significant differences.

Conclusions

The presence of PPARγ2 rs1801282 G allele (Ala variant) was associated with a protective cardiometabolic risk profile versus CC genotype in HIV/HCV-coinfected patients. Thus, PPARγ2 rs1801282 polymorphism may play a significant role in the development of metabolic disorders in HIV/HCV coinfected patients, and might have an influence on the cardiovascular risk.

Proliferator-activated receptor gamma Pro12Ala interacts with the insulin receptor substrate 1 Gly972Arg and increase the risk of insulin resistance and diabetes in the mixed ancestry population from South Africa

BACKGROUND

The peroxisome proliferator-activated receptor gamma (PPARG), Pro12Ala and the insulin receptor substrate (IRS1), Gly972Arg confer opposite effects on insulin resistance and type 2 diabetes mellitus (T2DM). We investigated the independent and joint effects of PPARG Pro12Ala and IRS1 Gly972Arg on markers of insulin resistance and T2DM in an African population with elevated risk of T2DM. In all 787 (176 men) mixed-ancestry adults from the Bellville-South community in Cape Town were genotyped for PPARG Pro12Ala and IRS1 Gly972Arg by two independent laboratories. Glucose tolerance status and insulin resistance/sensitivity were assessed.

RESULTS

Genotype frequencies were 10.4% (PPARG Pro12Ala) and 7.7% (IRS1 Gly972Arg). Alone, none of the polymorphisms predicted prevalent T2DM, but in regression models containing both alleles and their interaction term, PPARG Pro12 conferred a 64% higher risk of T2DM. Furthermore PPARG Pro12 was positively associated in adjusted linear regressions with increased 2-hour post-load insulin in non-diabetic but not in diabetic participants.

CONCLUSION

The PPARG Pro12 is associated with insulin resistance and this polymorphism interacts with IRS1 Gly972Arg, to increase the risk of T2DM in the mixed-ancestry population of South Africa. Our findings require replication in a larger study before any generalisation and possible application for risk stratification.

The SH2B1 obesity locus and abnormal glucose homeostasis: lack of evidence for association from a meta-analysis in individuals of European ancestry

BACKGROUND/AIMS

The development of type 2 diabetes (T2D) is influenced both by environmental and by genetic determinants. Obesity is an important risk factor for T2D, mostly mediated by obesity-related insulin resistance. Obesity and insulin resistance are also modulated by the genetic milieu; thus, genes affecting risk of obesity and insulin resistance might also modulate risk of T2D. Recently, 32 loci have been associated with body mass index (BMI) by genome-wide studies, including one locus on chromosome 16p11 containing the SH2B1 gene. Animal studies have suggested that SH2B1 is a physiological enhancer of the insulin receptor and humans with rare deletions or mutations at SH2B1 are obese with a disproportionately high insulin resistance. Thus, the role of SH2B1 in both obesity and insulin resistance makes it a strong candidate for T2D. However, published data on the role of SH2B1 variability on the risk for T2D are conflicting, ranging from no effect at all to a robust association.

METHODS

The SH2B1 tag SNP rs4788102 (SNP, single nucleotide polymorphism) was genotyped in 6978 individuals from six studies for abnormal glucose homeostasis (AGH), including impaired fasting glucose, impaired glucose tolerance or T2D, from the GENetics of Type 2 Diabetes in Italy and the United States (GENIUS T2D) consortium. Data from these studies were then meta-analyzed, in a Bayesian fashion, with those from DIAGRAM+ (n = 47,117) and four other published studies (n = 39,448).

RESULTS

Variability at the SH2B1 obesity locus was not associated with AGH either in the GENIUS consortium (overall odds ratio (OR) = 0.96; 0.89-1.04) or in the meta-analysis (OR = 1.01; 0.98-1.05).

CONCLUSION

Our data exclude a role for the SH2B1 obesity locus in the modulation of AGH.

Association of genetic polymorphism of PPARγ-2, ACE, MTHFR, FABP-2 and FTO genes in risk prediction of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a non-autoimmune, complex, heterogeneous and polygenic metabolic disease condition characterized by persistent elevated blood glucose levels (hyperglycemia). India as said to be the diabetic capital of the world is likely to experience the largest increase in T2DM and a greater number of diabetic individuals in the world by the year 2030. Identification of specific genetic variations in a particular ethnic group has a critical role in understanding the risk of developing T2DM in a much efficient way in future. These genetic variations include numerous types of polymorphisms among which single nucleotide polymorphisms (SNPs) is the most frequent. SNPs are basically located within the regulatory elements of several gene sequences. There are scores of genes interacting with various environmental factors affecting various pathways and sometimes even the whole signalling network that cause diseases like T2DM. This review discusses the biomarkers for early risk prediction of T2DM. Such predictions could be used in order to understand the pathogenesis of T2DM and to better diagnostics, treatment, and eventually prevention.

The association between the Pro12Ala variant in the PPARγ2 gene and type 2 diabetes mellitus and obesity in a Chinese population

BACKGROUND

Conflicting results have been reported on the association of the Pro12Ala polymorphism of the PPARγ2 gene with the risk of type 2 diabetes or obesity.

METHODS AND FINDINGS

A total of 3146 subjects with 1145 cases of type 2 diabetes and 2001 healthy controls were included in the study. Genomic DNA was obtained from blood samples and the screening for the gene polymorphisms was done using an allelic discrimination assay-by-design TaqMan method. Overall, the Ala allele frequency was 5.6% in control subjects and 3.9% in diabetes subjects (P = 0.023). We found a statistically significant association of carriers of the Ala allele with greater homoeostasis model assessment of beta cell function index in all subjects (P = 0.046). After controlling for confounders, carriers of the Ala allele had a decreased risk of diabetes compared with noncarriers [odds ratio (OR) 0.64, 95% confidence interval (CI) 0.49-0.83; P = 0.001]. A beneficial effect of the Ala allele was also observed for obesity (OR 0.64, 95% CI 0.42-0.96; P = 0.030).

CONCLUSION

Our results suggested that the presence of the Ala allele may contribute to improved insulin secretory capacity and may confer protection from type 2 diabetes and obesity in the Chinese population.

Peroxisome proliferator-activated receptors alpha and gamma2 polymorphisms in nonalcoholic fatty liver disease: a study in Brazilian patients

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) refers to the accumulation of hepatic steatosis in the absence of excess alcohol consumption. The pathogenesis of fatty liver disease and steatohepatitis (NASH) is not fully elucidated, but the common association with visceral obesity, hyperlipidemia, hypertension and type 2 diabetes mellitus (T2DM) suggests that it is the hepatic manifestation of metabolic syndrome. Peroxisome proliferator-activated receptor PPARα and PPARγ are members of a family of nuclear receptors involved in the metabolism of lipids and carbohydrates, adipogenesis and sensitivity to insulin. The objective of this study was to analyze the polymorphisms Leu162Val of PPARα and Pro12Ala of PPARγ as genetic risk factors for the development and progression of NAFLD.

METHODS

One hundred and three NAFLD patients (89 NASH, 14 pure steatosis) and 103 healthy volunteers were included. Single nucleotide polymorphisms (SNPs) Leu162Val and Pro12Ala were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP).

RESULTS

NASH patients presented higher BMI, AST and prevalence of T2DM than patients with pure steatosis. A higher prevalence of 12Ala allele was observed in the NASH Subgroup when compared to Control Group. When we grouped NASH and Steatosis Subgroups (NAFLD), we found lower serum glucose and more advanced fibrosis in the Leu162Val SNP. On the other hand, there was no statistical difference in clinical, laboratorial and histological parameters according to the Pro12Ala SNP.

CONCLUSIONS

We documented a lower prevalence of 12Ala allele of gene PPARγ in the NASH Subgroup when compared to Control Group. In NAFLD patients, there were no associations among the occurrence of Pro12Ala SNP with clinical, laboratorial and histological parameters. We also documented more advanced fibrosis in the Leu162Val SNP. The obtained data suggest that Pro12Ala SNP may result in protection against liver injury and that Leu162Val SNP may be involved in the progression of NAFLD.

PPARG2 Pro12Ala and ADAMTS9 rs4607103 as "insulin resistance loci" and "insulin secretion loci" in Italian individuals. The GENFIEV study and the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 4

We investigated cross-sectionally whether the type 2 diabetes (T2DM) risk alleles of rs1801282 (PPARG2) and rs4607103 (ADAMTS9) were associated with T2DM and/or insulin sensitivity (IS) and beta cell function (βF) in Italians without and with newly diagnosed T2DM. In 676 nondiabetic subjects (336 NGR and 340 IGR) from the GENFIEV study and in 597 patients from the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS), we (1) genotyped rs1801282 and rs4607103, (2) assessed βF by C-peptide/glucose modeling after OGTT, and (3) assessed IS by HOMA-IR in both studies and by euglycemic insulin clamp in VNDS only. Logistic, linear, and two-stage least squares regression analyses were used to test (a) genetic associations with T2DM and with pathophysiological phenotypes, (b) causal relationships of the latter ones with T2DM by a Mendelian randomization design. Both SNPs were associated with T2DM. The rs4607103 risk allele was associated to impaired βF (p < 0.01) in the GENFIEV study and in both cohorts combined. The rs1801282 genotype was associated with IS both in the GENFIEV study (p < 0.03) and in the VNDS (p < 0.03), whereas rs4607103 did so in the VNDS only (p = 0.01). In a Mendelian randomization design, both HOMA-IR (instrumental variables: rs1801282, rs4607103) and βF (instrumental variable: rs4607103) were related to T2DM (p < 0.03-0.01 and p < 0.03, respectively). PPARG2 and ADAMTS9 variants are both associated with T2DM and with insulin resistance, whereas only ADAMTS9 may be related to βF. Thus, at least in Italians, they may be considered bona fide "insulin resistance genes".

PPAR-γ2 and PTPRD gene polymorphisms influence type 2 diabetes patients' response to pioglitazone in China

AIM

To investigate the influence of peroxisome proliferator-activated receptor γ2 (PPAR-γ2) gene polymorphism rs1801282 and protein tyrosine phosphatase receptor type D (PTPRD) gene polymorphism rs17584499 on the occurrence of type 2 diabetes and pioglitazone efficacy in a Chinese Han population.

METHODS

One hundred ninety seven type 2 diabetes patients and 212 healthy controls were enrolled. Among them, 67 type 2 diabetes patients were administered pioglitazone (30 mg/d, po) for 3 months. All the subjects were genotyped for genetic variants in PPAR-γ2 and PTPRD using MALDI-TOF mass spectrometry. Fasting plasma glucose, postprandial plasma glucose, glycated hemoglobin, serum triglyceride, total cholesterol, low-density and high-density lipoprotein-cholesterol were determined.

RESULTS

The PPAR-γ2 gene rs1801282 polymorphism was significantly associated with type 2 diabetes susceptibility (OR=0.515, 95% CI 0.268-0.990) and the PTPRD gene rs17584499 polymorphism was also significantly associated with type 2 diabetes (OR=1.984, 95% CI 1.135-3.469) in a dominant model adjusted for age, gender and BMI. After pioglitazone treatment for 3 months, the type 2 diabetes patients with PPAR-γ2 rs1801282 CG genotypes significantly showed higher differential values of postprandial plasma glucose and serum triglyceride compared with those with rs1801282 CC genotype. The patients with PTPRD rs17584499 CT+TT genotypes showed significantly lower differential value of postprandial plasma glucose compared to those with rs17584499 CC genotype.

CONCLUSION

Diabetes risk alleles in PPAR-γ2 (rs1801282) and PTPRD (rs17584499) are associated with pioglitazone therapeutic efficacy.

A genome-wide approach accounting for body mass index identifies genetic variants influencing fasting glycemic traits and insulin resistance

Recent genome-wide association studies have described many loci implicated in type 2 diabetes (T2D) pathophysiology and β-cell dysfunction but have contributed little to the understanding of the genetic basis of insulin resistance. We hypothesized that genes implicated in insulin resistance pathways might be uncovered by accounting for differences in body mass index (BMI) and potential interactions between BMI and genetic variants. We applied a joint meta-analysis approach to test associations with fasting insulin and glucose on a genome-wide scale. We present six previously unknown loci associated with fasting insulin at P < 5 × 10(-8) in combined discovery and follow-up analyses of 52 studies comprising up to 96,496 non-diabetic individuals. Risk variants were associated with higher triglyceride and lower high-density lipoprotein (HDL) cholesterol levels, suggesting a role for these loci in insulin resistance pathways. The discovery of these loci will aid further characterization of the role of insulin resistance in T2D pathophysiology.

Genetics of adipose tissue biology

Adipose tissue morphology and release of free fatty acids, as well as peptide hormones, are believed to contribute to obesity and related metabolic disorders. These adipose tissue phenotypes are influenced by adiposity, but there is also a strong hereditary impact. Polymorphisms in numerous adipose-expressed genes have been evaluated for association with adipocyte and clinical phenotypes. In our opinion, some results are convincing. Thus ADRB2 and GPR74 genes are associated with adipocyte lipolysis, GPR74 also with BMI; PPARG and SREBP1, which promote adipogenesis and lipid storage, are associated with T2D and possible adiposity; ADIPOQ and ARL15 are associated with circulating levels of adiponectin, ARL15 also with coronary heart disease. We anticipate that the use of complementary approaches such as expression profiling and RNAi screening, and studies of additional levels of gene regulation, that is, miRNA and epigenetics, will be important to unravel the genetics of adipose tissue function.

Lack of effect of apolipoprotein C3 polymorphisms on indices of liver steatosis, lipid profile and insulin resistance in obese Southern Europeans

Background

Apolipoprotein C3 (APOC3) is a component of triglyceride-rich lipoproteins, and APOC3 rs2854116 and rs2854117 polymorphisms have been associated with non-alcoholic fatty liver disease, hypertriglyceridaemia, and insulin-resistance.

Objective

To determine if the APOC3 variants alter the susceptibility of obese subjects to develop liver damage, hypertrigliceridaemia, and insulin-resistance.

Methods

The study was carried out on 585 unrelated obese Italians (median body mass index BMI = 41 kg/m²) who were genotyped for the rs2854116 and rs2854117 variants. All participants underwent oral glucose tolerance tests (OGTT), with measurement of glucose, insulin, lipid parameters. Indices of insulin-resistance (HOMA and ISI) were calculated. Alanine transaminase (ALT) and aspartate transaminase (AST) were used as markers of liver injury.

Results

The study subjects were divided into two groups: those homozygous for the wild-type alleles at both SNPs (-482C and -455T alleles) and those who were carriers of at least one variant allele or both (-482T, -455C or both). Also each SNP was analysed independently. No significant differences were found in ALT and AST levels and in the lipid profile between the two groups. Insulin concentrations, glucose tolerance and insulin sensitivity were similar in the two groups.

Conclusion

We did not identify any significant association between APOC3 polymorphisms and fatty liver disease, lipids, and insulin-resistance in obese subjects, thus not confirming the suggested role of these APOC3 gene sequence variants.

Genetic variants in peroxisome proliferator-activated receptor-γ and retinoid X receptor-α gene and type 2 diabetes risk: a case-control study of a Chinese Han population

BACKGROUND

The serum levels of adiponectin are paradoxically decreased in obesity and may play important roles in the development of type 2 diabetes mellitus (T2DM). Potentially functional polymorphisms in the peroxisome proliferator-activated receptor-γ (PPAR-γ) and retinoid X receptor-α (RXR-α) genes may alter T2DM risks by increasing the human adiponectin promoter activity in cells. Therefore, we hypothesized that single nucleotide polymorphisms (SNPs) in PPAR-γ and RXR-α were associated with risk of T2DM. To test this hypothesis, three potentially functional SNPs of PPAR-γ and four of RXR-α with a minor allele frequency of ≥ 0.05 in the Chinese Han population were identified from the National Center for Biotechnology Information dbSNPs database to evaluate their association with T2DM.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism was performed to test the genotypes in T2DM patients (n = 540) and normal controls (n = 604).

RESULTS

The variant genotypes rs2920502CC, rs3856806CT, rs3856806CT/TT, and rs4240711AG/GG were associated with T2DM. Furthermore, the prevalences of haplotype GTC and CTG in PPAR-γ and GTAC in RXR-α were less frequent in cases (17.1%, 2.6%, and 2.4%, respectively) than in controls (22.3%, 3.8%, and 6.6%, respectively), whereas GTGT in RXR-α was more frequent in cases (6.9%) than in controls (4.4%) (P < 0.05 for both two-sided χ(2) test and thousand times permutation tests). Patients with genotype CT/TT of rs3856806 and genotype AG/GG of rs4240711 had higher levels of serum adiponectin than those with the genotype CC and genotype AA (P = 0.026 and 0.021, respectively). Model X2 X5 X6 X7 (rs3856806, rs3132291, rs4240711, and rs4842194) was the best model with the highest test balanced accuracy (0.5764) (cross-validation consistency = 10/10) in the multifactor dimensionality reduction method.

CONCLUSIONS

The PPAR-γ and RXR-α gene variants associated with the development of T2DM in this study must be investigated in a larger population to reveal any potential effects on metabolism.

Meta-analysis of gene-environment interaction: joint estimation of SNP and SNP × environment regression coefficients

INTRODUCTION

Genetic discoveries are validated through the meta-analysis of genome-wide association scans in large international consortia. Because environmental variables may interact with genetic factors, investigation of differing genetic effects for distinct levels of an environmental exposure in these large consortia may yield additional susceptibility loci undetected by main effects analysis. We describe a method of joint meta-analysis (JMA) of SNP and SNP by Environment (SNP × E) regression coefficients for use in gene-environment interaction studies.

METHODS

In testing SNP × E interactions, one approach uses a two degree of freedom test to identify genetic variants that influence the trait of interest. This approach detects both main and interaction effects between the trait and the SNP. We propose a method to jointly meta-analyze the SNP and SNP × E coefficients using multivariate generalized least squares. This approach provides confidence intervals of the two estimates, a joint significance test for SNP and SNP × E terms, and a test of homogeneity across samples.

RESULTS

We present a simulation study comparing this method to four other methods of meta-analysis and demonstrate that the JMA performs better than the others when both main and interaction effects are present. Additionally, we implemented our methods in a meta-analysis of the association between SNPs from the type 2 diabetes-associated gene PPARG and log-transformed fasting insulin levels and interaction by body mass index in a combined sample of 19,466 individuals from five cohorts.

Evaluation of single nucleotide polymorphisms of Pro12Ala in peroxisome proliferator-activated receptor-γ and Gly308Ala in tumor necrosis factor-α genes in obese Asian Indians: a population-based study

BACKGROUND

A population-based case control study was performed to determine the associations of Pro12Ala polymorphism in peroxisome proliferator-activated receptor-γ (PPARG) and Gly308Ala polymorphism in tumor necrosis factor-α (TNFA) genes in obese subjects.

PATIENTS AND METHODS

Of 1,400 eligible subjects, ≧20 years, we recruited only 1,127. For extreme phenotype case-control design, we evaluated 201 subjects with body mass index (BMI) ≧30 kg/m(2) (Group 1) and 143 with BMI <20 kg/m(2) (Group 2). Clinical, anthropometric, biochemical, and nutritional details and polymorphisms were estimated.

RESULTS

In Group 1, the dietary intake of calories and fats was higher, physical activity was lower, and prevalence of truncal obesity, hypertension, high total cholesterol, low high-density lipoprotein cholesterol, and diabetes was greater than in Group 2. There were no homozygous polymorphisms of either gene. Heterozygous Pro12Ala polymorphism in PPARG was found in 15 (7.5%) subjects in Group 1 and 3 (2.1%) subjects in Group 2 (P = 0.028), and heterozygous Gly308Ala polymorphism in TNFA was found in 19 (9.5%) in Group 1 and 7 (4.9%) in Group 2 (P = 0.115). Presence of heterozygous polymorphism in PPARG and TNFA-predicted obesity with univariate odds ratio ([OR], 95% confidence intervals) of 2.25 (1.32-3.84, P = 0.003) and 1.48 (1.10-1.99, P = 0.009) and with multivariate OR 1.74 (1.03-2.93, P = 0.038) and 1.46 (1.05-2.03, P = 0.024), respectively. The addition of dietary and physical activity variables did not result in significant change.

CONCLUSION

Obese Asian Indians have greater prevalence of heterozygous polymorphisms of Pro12Ala in PPARG and Gly308Ala in TNFA genes.

Common polymorphisms of the peroxisome proliferator-activated receptor-gamma (Pro12Ala) and peroxisome proliferator-activated receptor-gamma coactivator-1 (Gly482Ser) and the response to pioglitazone in Chinese patients with type 2 diabetes mellitus

We investigated the effects of the common polymorphisms in the peroxisome proliferator-activated receptor-gamma (PPAR-gamma; Pro12Ala) and in PPAR-gamma coactivator-1(PGC-1; Gly482Ser) genes on the response to pioglitazone in Chinese with type 2 diabetes mellitus. A total of 250 patients with type 2 diabetes mellitus were treated with pioglitazone (30 mg/d) for 24 weeks without a change in previous medications. All patients were genotyped for the PPAR-gamma Pro12Ala and PGC-1 Gly482Ser polymorphisms. The Ala12Ala and Pro12Ala genotypes (26.0% vs 13.5%, P = .025) and Ala allele (15.6% vs 7.3%, P = .008) were significantly more frequent in pioglitazone responders than in nonresponders. The distribution of PGC-1 genotypes and alleles was not significantly different between responders and nonresponders. The decrease in fasting glucose (50.4 +/- 52.2 vs 43.3 +/- 51.7 mg/dL, P < .001) and hemoglobin A(1c) (0.57% +/- 1.44% vs 0.35% +/- 1.10%, P = .004) levels was significantly greater in subjects with the Ala12 carriers (Pro12Ala and Ala12Ala) than in those without the allele (Pro12Pro). Baseline fasting glucose and triglyceride levels were related to the response of pioglitazone. Only the PPAR-gamma Pro12Ala polymorphism was found to be associated with the response of pioglitazone by multiple logistic regression analysis. The PPAR-gamma Pro12Ala gene polymorphism is associated with the response to pioglitazone in Chinese patients with type 2 diabetes mellitus. These findings may be helpful for targeted treatment of diabetes by identifying patients who are likely to respond to pioglitazone.

Improvements in glucose homeostasis in response to regular exercise are influenced by the PPARG Pro12Ala variant: results from the HERITAGE Family Study

AIMS/HYPOTHESIS

Exercise training improves glucose homeostasis, but large inter-individual differences are reported, suggesting a role of genetic factors. We investigated whether variants either confirmed or newly identified as diabetes susceptibility variants through genome-wide association studies (GWAS) modulate changes in phenotypes derived from an IVGTT in response to an endurance training programme.

METHODS

We analysed eight polymorphisms in seven type 2 diabetes genes (CDKAL1 rs7756992; CDKN2A and CDKN2B rs10811661 and rs564398; HHEX rs7923837; IGF2BP2 rs4402960; KCNJ11 rs5215; PPARG rs1801282; and TCF7L2 rs7903146) in a maximum of 481 sedentary, non-diabetic white individuals, who participated in a 20-week endurance training programme. Associations were tested between the variants and changes in IVGTT-derived phenotypes.

RESULTS

The only evidence of association with training response was found with PPARG rs1801282 (Pro12Ala). We observed that Ala carriers experienced greater increase in overall glucose tolerance (Deltaglucose disappearance index Ala/Ala 0.22 +/- 0.22, Pro/Ala 0.14 +/- 0.06, Pro/Pro 0.004 +/- 0.03; p = 0.0008), glucose effectiveness (Ala/Ala 0.28 +/- 0.41, Pro/Ala 0.44 +/- 0.14, Pro/Pro 0.09 +/- 0.06; p = 0.004), acute insulin response to glucose (Ala/Ala 64.21 +/- 37.73, Pro/Ala -11.92 +/- 40.30, Pro/Pro -46.30 +/- 14.70; p = 0.03) and disposition index (Ala/Ala 551.8 +/- 448.5, Pro/Ala 534.6 +/- 218.3, Pro/Pro -7.44 +/- 88.18; p = 0.003).

CONCLUSIONS/INTERPRETATION

Compared with Pro/Pro individuals, PPARG Ala carriers experienced greater improvements in glucose and insulin metabolism in response to regular endurance training. However, we did not find evidence of association between type 2 diabetes susceptibility variants recently identified through GWAS and glucose homeostasis response to exercise. Our results extend those of previous studies showing that Ala carriers appear to be more responsive to beneficial health effects of lifestyle interventions.

The association between the peroxisome proliferator-activated receptor-gamma2 (PPARG2) Pro12Ala gene variant and type 2 diabetes mellitus: a HuGE review and meta-analysis

The peroxisome proliferator-activated receptor-γ gene (PPARG) has been implicated in the etiology of type 2 diabetes mellitus and has been investigated in numerous epidemiologic studies. In this Human Genome Epidemiology review, the authors assessed this relation in an updated meta-analysis of 60 association studies. Electronic literature searches were conducted on September 14, 2009. Population-based cohort, case-control, cross-sectional, or genome-wide association studies reporting associations between the PPARG Pro12Ala gene variant (rs1801282) and type 2 diabetes were included. An updated literature-based meta-analysis involving 32,849 type 2 diabetes cases and 47,456 controls in relation to the PPARG Pro12Ala variant was conducted. The combined overall odds ratio, calculated by per-allele genetic model random-effects meta-analysis for type 2 diabetes and the Pro12Ala polymorphism, was 0.86 (95% confidence interval: 0.81, 0.90). The analysis indicated a moderate level of heterogeneity attributable to genuine variation in gene effect size (I² = 37%). This may reflect the variation observed between ethnic populations and/or differences in body mass index. Work on PPARG Pro12Ala should now focus on the observed heterogeneity in the magnitude of the association between populations. Further investigations into gene-gene and gene-environment interactions may prove enlightening.

IL-1beta-511 and IL-1RN*2 polymorphisms in inflammatory bowel disease: An Italian population study and meta-analysis of European studies

BACKGROUND

Several studies have tried to find possible associations between genetic polymorphisms and inflammatory bowel disease prevalence and/or phenotype. Our objectives were to test the frequency and phenotypic association of two polymorphisms of the interleukin-1 pathway, IL-1beta-511 and IL-1RN*2, in inflammatory bowel disease patients and controls from an Italian population, and to compare our data with previously published similar studies in Europe.

METHODS

We screened 290 inflammatory bowel disease patients (178 ulcerative colitis and 112 Crohn's disease) and 106 controls for IL-1beta-511 and IL-1RN*2 polymorphisms by polymerase chain reaction (PCR)-based methods. The prevalence of the IL-1beta-511 and IL-1RN*2 polymorphisms in European inflammatory bowel disease patients was calculated by a meta-analysis of previously published studies using the Mantel-Haenszel method.

RESULTS

No correlation between the IL-1 polymorphisms and inflammatory bowel disease prevalence was found in our study population. Crohn's disease patients with the IL-1beta-511 mutation had a higher rate of complicated disease. A trend for an association between the IL-1RN*2 mutation and a higher risk for inflammatory bowel disease has been found only in studies with Northern European populations.

CONCLUSIONS

The IL-1beta-511 mutation can be associated with complex disease behaviour in Italian Crohn's disease patients. The IL-1RN*2 mutation may play a role in Northern European people with inflammatory bowel disease.

Novel biological insights emerging from genetic studies of type 2 diabetes and related metabolic traits

PURPOSE OF REVIEW

In the past 3 years, genome-wide association studies have identified many tens of common genetic variants associated with metabolic diseases and traits. Although much further research is needed to identify the target genes, the associations between gene variants and diseases are already providing biological insights. The purpose of this review is to update the reader with the most relevant findings, with a particular emphasis on type 2 diabetes (T2D) and glucose metabolism, and discuss some of the biological implications of the genetic findings.

RECENT FINDINGS

Largely through recent genome-wide association studies, we now know of approximately 20 gene variants associated with T2D, 10 with body mass index (BMI) and obesity, four with fasting glucose levels in the normoglycaemic population and over 30 with lipid levels. These findings are stimulating many new important areas of research related to metabolic diseases. For T2D and glucose metabolism, we discuss a number of aspects and implications of the genetic findings, including the observations that T2D gene variants are not usually in or near obvious candidate genes, highlighting the poor prior knowledge of the biology of the disease; most T2D gene variants are associated with beta-cell function rather than insulin resistance; there is a difference between genes that influence variation in normal glucose levels compared with those influencing onset and progression of diabetes; and there is a genetic link between diabetes and foetal growth.

SUMMARY

Genetic studies in the past 3 years have provided a greatly increased knowledge of the regions of the genome involved in adverse metabolic consequences. There are now over 100 common genetic variants reproducibly associated with metabolic traits, including reduced beta-cell function, obesity, increased lipid levels and increased glucose levels. These genetic findings are already altering perceptions of how these traits develop and interact to result in diseases such as T2D.

Insulin signaling regulating genes: effect on T2DM and cardiovascular risk

Type 2 diabetes mellitus (T2DM) is a complex disorder that has a heterogeneous genetic and environmental background. In this Review, we discuss the role of relatively infrequent polymorphisms of genes that regulate insulin signaling (including the K121Q polymorphism of ENPP1, the G972R polymorphism of IRS1 and the Q84R polymorphism of TRIB3) in T2DM and other conditions related to insulin resistance. The biological relevance of these three polymorphisms has been very thoroughly characterized both in vitro and in vivo and the available data indicate that they all affect insulin signaling and action as well as insulin secretion. They also affect insulin-mediated regulation of endothelial cell function. In addition, several reports indicate that the effects of all three polymorphisms on the risk of T2DM and cardiovascular diseases related to insulin resistance depend on the clinical features of the individual, including their body weight and age at disease onset. Thus, these polymorphisms might be used to demonstrate how difficult it is to ascertain the contribution of relatively infrequent genetic variants with heterogeneous effects on disease susceptibility. Unraveling the role of such variants might be facilitated by improving disease definition and focusing on specific subsets of patients.

Impact of the PPAR-gamma2 Pro12Ala polymorphism and ACE inhibitor therapy on new-onset microalbuminuria in type 2 diabetes: evidence from BENEDICT

OBJECTIVE

Cross-sectional studies found less microalbuminuria in type 2 diabetic patients with the Ala12 allele of the peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) Pro12Ala polymorphism. We prospectively evaluated the association between Pro12Ala polymorphism (rs1801282) and new-onset microalbuminuria.

RESEARCH DESIGN AND METHODS

Pro12Ala polymorphism was genotyped by TaqMan-based assay in genomic DNA of 1,119 consenting patients from BErgamo NEphrologic DIabetic Complications Trial (BENEDICT)-a prospective, randomized trial evaluating ACE inhibition effect on new-onset microalbuminuria (albuminuria 20-200 microg/min in at least two of three consecutive overnight urine collections in two consecutive visits) in hypertensive type 2 diabetes with albuminuria <20 microg/min at inclusion.

RESULTS

Baseline characteristics of Ala (Ala/Ala or Ala/Pro) carriers and Pro/Pro homozygotes were similar, with a nonsignificant trend to lower albuminuria (P = 0.1107) in the 177 Ala carriers. Over a median (interquartile range) of 44.0 (17.1-51.9) months, 7 (4%) Ala carriers and 86 (9.1%) Pro/Pro homozygotes developed microalbuminuria (hazard ratio [HR] 0.45 [95% CI 0.21-0.97]; P = 0.042). Final albuminuria was significantly lower in Ala carriers than Pro/Pro homozygotes (7.3 +/- 9.1 vs. 10.5 +/- 24.9 microg/min, respectively), even after adjustment for baseline albuminuria (P = 0.048). Baseline and follow-up blood pressure and metabolic control were similar in both groups. Incidence of microalbuminuria was significantly decreased by ACE versus non-ACE inhibitor therapy in Pro/Pro homozygotes (6.3 vs. 11.9%, respectively, HR 0.46 [0.29-0.72]; P < 0.001).

CONCLUSIONS

In type 2 diabetes, the Ala allele protects from worsening albuminuria and new-onset microalbuminuria, and ACE inhibition blunts the excess risk of microalbuminuria associated with the Pro/Pro genotype. Evaluating Pro12Ala polymorphism may help identifying patients at risk who may benefit the most from early renoprotective therapy.

The clinical application of genetic testing in type 2 diabetes: a patient and physician survey

AIMS/HYPOTHESIS

Advances in type 2 diabetes genetics have raised hopes that genetic testing will improve disease prediction, prevention and treatment. Little is known about current physician and patient views regarding type 2 diabetes genetic testing. We hypothesised that physician and patient views would differ regarding the impact of genetic testing on motivation and adherence.

METHODS

We surveyed a nationally representative sample of US primary care physicians and endocrinologists (n = 304), a random sample of non-diabetic primary care patients (n = 152) and patients enrolled in a diabetes pharmacogenetics study (n = 89).

RESULTS

Physicians and patients favoured genetic testing for diabetes risk prediction (79% of physicians vs 80% of non-diabetic patients would be somewhat/very likely to order/request testing, p = 0.7). More patients than physicians (71% vs 23%, p < 0.01) indicated that a 'high risk' result would be very likely to improve motivation to adopt preventive lifestyle changes. Patients favoured genetic testing to guide therapy (78% of patients vs 48% of physicians very likely to request/recommend testing, p < 0.01) and reported that genetic testing would make them 'much more motivated' to adhere to medications (72% vs 18% of physicians, p < 0.01). Many physicians (39%) would be somewhat/very likely to order genetic testing before published evidence of clinical efficacy.

CONCLUSIONS/INTERPRETATION

Despite the paucity of current data, physicians and patients reported high expectations that genetic testing would improve patient motivation to adopt key behaviours for the prevention or control of type 2 diabetes. This suggests the testable hypothesis that 'genetic' risk information might have greater value to motivate behaviour change compared with standard risk information.

Functional implications of genetic variation in human PPARgamma

The peroxisome proliferator-activated receptor gamma (PPARgamma) plays a key role in the regulation of lipid and glucose metabolism. Human genetic evidence supporting this view comes from the study of both common (e.g. the Pro12Ala polymorphism) and rare (loss-of-function mutations) variants in the gene encoding PPARgamma. Indeed, patients harbouring mutant PPARgamma exhibit familial partial lipodystrophy type 3 and an extreme monogenic form of the metabolic syndrome. The recent elucidation of the crystal structure of the full-length PPARgamma-RXRalpha heterodimer bound to DNA has shed new light on the functional consequences of these genetic PPARgamma alterations and provides novel insights as to why different perturbations of receptor function unite in a common pathway of metabolic dysfunction.

Pharmacogenomics in type II diabetes mellitus management: Steps toward personalized medicine

Advances in genotype technology in the last decade have put the pharmacogenomics revolution at the forefront of future medicine in clinical practice. Discovery of novel gene variations in drug transporters, drug targets, effector proteins and metabolizing enzymes in the form of single-nucleotide polymorphisms (SNPs) continue to provide insight into the biological phenomena that govern drug efficacy and toxicity. To date, novel gene discoveries extracted from genome-wide association scans and candidate gene studies in at least four antidiabetic drug classes have helped illuminate possible causes of interindividual variability in response. Inadequate protocol guidelines for pharmacogenomics studies often leads to poorly designed studies, making it hard to formulate a definitive conclusion regarding the clinical relevance of the information at hand. These issues, along with the ethical, social, political, legislative, technological, and economic challenges associated with pharmacogenomics have only delayed its entry to mainstream clinical practice. On the other hand, these issues are being actively pursued and rapid progress is being made in each area which assures the possibility of gaining widespread acceptance in clinical practice.

Disparities in allele frequencies and population differentiation for 101 disease-associated single nucleotide polymorphisms between Puerto Ricans and non-Hispanic whites

Background

Variations in gene allele frequencies can contribute to differences in the prevalence of some common complex diseases among populations. Natural selection modulates the balance in allele frequencies across populations. Population differentiation (F_ST) can evidence environmental selection pressures. Such genetic information is limited in Puerto Ricans, the second largest Hispanic ethnic group in the US, and a group with high prevalence of chronic disease. We determined allele frequencies and population differentiation for 101 single nucleotide polymorphisms (SNPs) in 30 genes involved in major metabolic and disease-relevant pathways in Puerto Ricans (n = 969, ages 45–75 years) and compared them to similarly aged non-Hispanic whites (NHW) (n = 597).

Results

Minor allele frequency (MAF) distributions for 45.5% of the SNPs assessed in Puerto Ricans were significantly different from those of NHW. Puerto Ricans carried risk alleles in higher frequency and protective alleles in lower frequency than NHW. Patterns of population differentiation showed that Puerto Ricans had SNPs with exceptional F_ST values in intronic, non-synonymous and promoter regions. NHW had exceptional F_ST values in intronic and promoter region SNPs only.

Conclusion

These observations may serve to explain and broaden studies on the impact of gene polymorphisms on chronic diseases affecting Puerto Ricans.