The Pro12Ala polymorphism of PPARgamma2 gene and susceptibility to type 2 diabetes mellitus in a Polish population

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.

Is the rs1801282 (G/C) Polymorphism of PPAR - Gamma Gene Associated with T2DM in Iraqi People?

BACKGROUND

Pro12Ala (rs1801282) is a common polymorphism of the human PPAR-γ gene. Studies have demonstrated conflicting results about its association with T2DM worldwide. There are no reports about such possible association among Iraqi people.

OBJECTIVES

This study aims at finding out whether having the mutant allele (Ala12) might be associated with T2DM among Iraqi people.

METHODS

One hundred and ninety-two Arabic Iraqi adult subjects (97 with T2DM and 95 controls) were genotyped using PCR- RFLP. Clinical, anthropometrical and biochemical variables were compared regarding the Pro12Ala genotypes.

RESULTS

About 5.67% of people with diabetes were carriers of the (Ala12) allele versus 9.47% of controls. Allelic and genotypic frequencies were not statistically different among diabetics and controls [(χ2= 1.99, p= 0.16) and (χ2= 2.17, p= 0.14)]. Age, BMI and smoking- but not Pro12Ala - were independent risk factors for T2DM in our subjects. Pro12Ala was not associated with T2DM (Odd's ratio 0.55, 95% CI 0.23- 1.32, p= 0.14).

CONCLUSIONS

Our study revealed a relatively high frequency of the Ala12 allele among Arabic Iraqis. These frequencies did not significantly differ between diabetics and controls indicating the absence of association of Pro12Ala with T2DM among Iraqis.

Peroxisome proliferator-activated receptor-γ polymorphism (rs1801282) is associated with obesity in Egyptian patients with coronary artery disease and type 2 diabetes mellitus

OBJECTIVE

Peroxisome Proliferator-Activated Receptor-γ (PPAR-γ) gene is one of the possible genes linking diabetes mellitus (DM) with coronary artery disease (CAD). The aim of this study is to clarify whether PPAR-γ Pro12Ala polymorphism is associated with the development of CAD in type 2 diabetic patients and to evaluate PPAR-γ Pro12Ala polymorphism genetic distribution in type 2 DM (T2DM) Egyptian subjects.

METHODS

PPAR-γ Pro12Ala polymorphism was determined by Real-Time PCR in serum of 405 subjects classified into 4 groups; T2DM patients (n = 105), T2DM with CAD (n = 100), CAD patients (n = 100) and healthy controls (n = 100).

RESULTS

The PPAR-γ Pro12Ala polymorphism was associated significantly with T2DM with CAD (group2) (OR = 3, 95% CI = (1.5-6); p = 0.001). In this study, T2DM with CAD complications carrying the PPAR-γ Pro12Ala polymorphism had higher BMI than those without the PPAR-γ Pro12Ala polymorphism (p < 0.0001). CAD patients carrying PPAR-γ Pro12Ala polymorphism had considerable insulin resistance features. Plasma paraoxanase 1(PON1) level was considerably reduced among our 3 studied groups in comparison to control group (p < 0.001).

CONCLUSIONS

PPAR-γ Pro12Ala polymorphism might represent a novel risk factor for CAD in T2DM.

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.

Association between PRO12ALA polymorphism of the PPAR-γ2 gene and type 2 diabetes mellitus in Iranian patients

BACKGROUND:

Peroxisome proliferator-activated receptor (PPARs) have been identified as ligand-activated transcription factors that belong to the nuclear receptor superfamily. It has been shown that an association exists between Proline 12 alanine (Pro12Ala) polymorphism of PPAR-GAMMA2 (PPAR-γ2) gene and increased risk of type 2 diabetes mellitus (T2DM) in different populations. Therefore, the present study was designed to investigate the association between Pro12Ala polymorphism of PPAR-γ2 gene and T2DM in an Iranian population.

MATERIALS AND METHODS:

Two hundred unrelated people, including 100 healthy controls and 100 diabetic patients were recruited diagnosed based on American Diabetes Association criteria. Blood samples were used for isolation of genomic deoxyribonucleic acid (DNA). Having extracted the genomic DNA from human blood leukocytes by means of High Pure polymerase chain reaction (PCR) Template preparation kit, we carried out polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on each blood sample. Then, Genomic DNA was digested by BstU-I restriction enzyme. Thereafter, restriction products were analyzed by means of Polyacrylamide gel electrophoresis and stained by Ethidium Bromide.

RESULTS:

We found that the frequency of Ala allele in healthy subjects was significantly higher than in diabetic subjects (P = 0003). Moreover, the genotype frequency of Ala/Ala in healthy subjects was significantly higher than in diabetic subjects (P < 0.001). However, the genotype frequency of Ala/Pro in diabetic subjects was significantly higher than in healthy subjects (P < 0.001).

CONCLUSION:

The present study suggests that polymorphism of PPAR-γ2 gene is associated with T2DM. Furthermore, Ala allele is significantly found in non-diabetic individual’s Iranian population.

Does Pro(12)Ala Polymorphism Enhance the Physiological Role of PPARγ2?

Obesity and type 2 diabetes mellitus (T2D) are two major public health problems that have motivated the scientific community to investigate the high contribution of genetic factors to these disorders. The peroxisome proliferator activated by gamma 2 (PPARγ2) plays an important role in the lipid metabolism. Since PPARγ2 is expressed mainly in adipose tissue, a moderate reduction of its activity influences the sensitivity to insulin, diabetes, and other metabolic parameters. The present study aims to contribute to the elucidation of the impact of the Pro(12)Ala polymorphism associated with T2D and obesity through a meta-analysis study of the literature that included approximately 11500 individuals, from which 3870 were obese and 7625 were diabetic. Statistical evidence supports protective effect in T2D of polymorphism Pro(12)Ala of PPARγ2 (OR = 0.702 with 95% CI: 0.622; 0.791, P < 0.01). Conversely the same polymorphism Pro(12)Ala of PPARγ2 seems to favor obesity since 1.196 more chance than nonobese was found (OR = 1.196 with 95% CI: 1.009; 1.417, P < 0.004). Our results suggest that Pro(12)Ala polymorphism enhances both adipogenic and antidiabetogenic physiological role of PPARγ. Does Pro(12)Ala polymorphism represent an evolutionary step towards the stabilization of the molecular function of PPARγ transcription factor signaling pathway?

ACE I/D and MTHFR C677T polymorphisms are significantly associated with type 2 diabetes in Arab ethnicity: a meta-analysis

In this meta-analysis study, SNPs were investigated for their association with type 2 diabetes (T2D) in both Arab and Caucasian ethnicities. A total of 55 SNPs were analyzed, of which 11 fulfilled the selection criteria, and were used for analysis. It was found that TCF7L2 rs7903146 was significantly associated with a pooled OR of 1.155 (95%C.I.=1.059-1.259), p<0.0001 and I(2)=78.30% among the Arab population, whereas among Caucasians, the pooled OR was 1.45 (95%C.I.=1.386-1.516), p<0.0001 and I(2)=77.20%. KCNJ11 rs5219 was significantly associated in both the populations with a pooled OR of 1.176(1.092-1.268), p<0.0001 and I(2)=32.40% in Caucasians and a pooled OR of 1.28(1.111-1.475), p=0.001 among Arabs. The ACE I/D polymorphism was found to be significantly associated with a pooled OR of 1.992 (95%C.I.=1.774-2.236), p<0.0001 and I(2)=83.20% among the Arab population, whereas among Caucasians, the pooled OR was 1.078 (95%C.I.=0.993-1.17), p=0.073 and I(2)=0%. Similarly, MTHFR C677T polymorphism was also found to be significantly associated among Arabs with a pooled OR of 1.924 (95%C.I.=1.606-2.304), p<0.0001 and I(2)=27.20%, whereas among Caucasians, the pooled OR was 0.986 (95%C.I.=0.868-1.122), p=0.835 and I(2)=0%. Meanwhile PPARG-2 Pro12Ala, CDKN2A/2B rs10811661, IGF2BP2 rs4402960, HHEX rs7923837, CDKAL1 rs7754840, EXT2 rs1113132 and SLC30A8 rs13266634 were found to have no significant association with T2D among Arabs. In conclusion, it seems from this study that both Arabs and Caucasians have different SNPs associated with T2D. Moreover, this study sheds light on the profound necessity for further investigations addressing the question of the genetic components of T2D in Arabs.

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.

Genetic polymorphisms of peroxisome proliferator-activated receptors and the risk of cardiovascular morbidity and mortality in a community-based cohort in washington county, Maryland

The primary aim of this study was to examine prospectively the associations between 5 peroxisome proliferator-activated receptor (PPAR) single nucleotide polymorphisms (SNPs) and cardiovascular morbidity and mortality in a community-based cohort study in Washington County, Maryland. Data were analyzed from 9,364 Caucasian men and women participating in CLUE-II. Genotyping on 5 PPAR polymorphisms was conducted using peripheral DNA samples collected in 1989. The followup period was from 1989 to 2003. The results showed that there were no statistically significant associations between the PPAR SNPs and cardiovascular deaths or events. In contrast, statistically significant age-adjusted associations were observed for PPARG rs4684847 with both baseline body mass and blood pressure, and for PPARG rs709158, PPARG rs1175543, and PPARD rs2016520 with baseline cholesterol levels. Future studies should be conducted to confirm these findings and to explore the associations in populations with greater racial and ethnic diversity.

Pro12Ala gene polymorphism in the peroxisome proliferator-activated receptor gamma as a risk factor for the onset of type 2 diabetes mellitus in the Serbian population

The peroxisome proliferator-activated receptor gamma (PPAR?) is a gene candidate for the onset of type 2 diabetes mellitus (T2DM). We investigated the association of the PPAR? Pro12Ala gene with the onset of T2DM for the first time in the Serbian population. The study population consisted of 197 controls and 163 T2DM patients. The 12Ala allele tended to be more frequent in the group of T2DM patients (0.11) compared to the control subjects (0.09). The results from this study indicate that the PPAR?2 12Ala allele presents a non-significant risk factor for T2DM development in the Serbian population.

The PPARgamma Pro12Ala variant is associated with insulin sensitivity in Russian normoglycaemic and type 2 diabetic subjects

The second isoform of the PPARgamma2 is specific for adipose tissue. In adipocytes, this isoform is involved in the regulation of adipogenesis and lipid storage, insulin and glucose metabolism. Pro12Ala, a missense mutation in exon 2 of PPARG, reduces transcriptional activity of PPARgamma2 and is shown to be associated with increased insulin sensitivity and protection from T2D. Previously, this polymorphism has never been assessed in a Russian population for its relationship to T2D, insulin resistance, and diabetes-related metabolic traits. In this study, we tested 588 Russian T2D patients and 597 normoglycaemic controls. Carriers of the Pro12 allele and subjects homozygous for Pro/Pro had significantly increased risk of developing T2D (OR 1.43 and 2.04, respectively). In Pro/Pro homozygotes, adjustment for potential confounding risk factors resulted in reducing the OR value from 2.04 to 1.69, but the association remained significant (p=0.046).The Pro/Pro genotype also showed association with increased levels of fasting insulin (p=0.019) in non-diabetic controls and elevated serum triglycerides (p=0.019) in T2D patients. Compared with other genotypes, non-diabetic and diabetic subjects homozygous for Pro/Pro had a significantly higher HOMA-IR score and reduced ISI value. This observation strongly supports the implication of the PPARG Pro12Ala in insulin resistance and T2D in a Russian population.

PPARγ2 polymorphism and human health

The nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARγ) is an important transcription factor regulating adipocyte differentiation, lipid and glucose homeostasis, and insulin sensitivity. Numerous genetic mutations of PPARγ have been identified and these mutations positively or negatively regulate insulin sensitivity. Among these, a relatively common polymorphism of PPARγ, Pro12Ala of PPARγ2, the isoform expressed only in adipose tissue has been shown to be associated with lower body mass index, enhanced insulin sensitivity, and resistance to the risk of type 2 diabetes in human subjects carrying this mutation. Subsequent studies in different ethnic populations, however, have revealed conflicting results, suggesting a complex interaction between the PPARγ2 Pro12Ala polymorphism and environmental factors such as the ratio of dietary unsaturated fatty acids to saturated fatty acids and/or between the PPARγ2 Pro12Ala polymorphism and genetic factors such as polymorphic mutations in other genes. In addition, this polymorphic mutation in PPARγ2 is associated with other aspects of human diseases, including cancers, polycystic ovary syndrome, Alzheimer disease and aging. This review will highlight findings from recent studies.

Alanine variant of the Pro12Ala polymorphism of the PPARgamma gene might be associated with decreased risk of diabetic retinopathy in type 2 diabetes

OBJECTIVE

Molecular background of diabetic retinopathy (DR) remains unknown. An interesting group of candidate genes encode proteins involved in insulin resistance.

AIM

To search for association between the PPARgamma, calpain 10, PTPN1 genes and DR in type 2 diabetes mellitus (T2DM).

METHODS

We examined 238 T2DM subjects without DR (NDR) and 121 with DR (mean diabetes duration: 9.1+/-6.8 and 15.1+/-7.7, respectively). The subjects were genotyped for four markers: Pro12Ala of PPARgamma, SNP43 of calpain 10, rs3787345 and rs754118 of PTPN1. The distributions of the genotypes were compared using the chi(2)-test and Fisher exact test.

RESULTS

The alleles and genotypes were not associated with DR in non-stratified analysis. To investigate the impact of T2DM duration, we performed analysis that excluded short duration NDR subjects and long-duration DR subjects. It allowed obtaining groups with similar T2DM duration but different DR status (DR: 88 individuals, 11.4+/-5.3 years; NDR: 136 individuals, 13.2 years+/-6.2, respectively). This analysis suggested that the alanine variant of Pro12Ala might be associated with decreased risk of DR (p=0.026 for alleles, p=0.038 and p=0.014 for genotypes in additive and dominant models, respectively). In multivariable logistic regression that included non-genetic parameters, Pro12Ala was not an independent risk factor (p=0.28). Further analysis showed, however, that Pro12Ala remained significant when urea level was excluded from the model.

CONCLUSION

The alanine variant of the Pro12Ala polymorphism of PPARgamma might be associated with decreased risk of DR in T2DM. This effect may be indirect, at least in part, due to diabetic kidney disease.

Association of the peroxisome proliferator-activated receptor-gamma2 Pro12Ala but not the C1431T gene variants with lower body mass index in Type 2 diabetes

The peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear receptor involved in lipid metabolism, adipocyte differentiation and regulation of insulin sensitivity, and is associated with Type 2 diabetes (T2DM). The association of the C1431T silent mutation and the Pro12Ala missense transversion within the PPARgamma gene with the development of T2DM or obesity has often yielded contradictory results. We examined the association of the PPARgamma Pro12Ala and C1431T gene variants and their haplotypes with the susceptibility to T2DM. This was a retrospective study involving 491 T2DM patients and 400 age- and gender-matched controls. Pro12Ala and C1431T genotyping was done by PCR-RFLP analysis. Comparable frequencies of the mutant 12Ala (0.07 vs 0.08, p=0.216) and 1431T (0.12 vs 0.10, p=0.189) alleles, and Pro12Ala (p=0.218) and C1431T (p=0.421) genotypes were seen between patients and in nondiabetic control subjects. While no difference was noted in the distribution of Pro12Ala- C1431T haplotypes and genotypes between patients and controls, the PPARgamma 12Ala, but not 1431T, allele was significantly associated with lower body mass index (BMI) (< or =25.0) among patients. Regression analysis confirmed the association of the Pro12Ala (odds ratio =5.340; 95% confidence interval =1.044-27.311) with normal (BMI<25.0) but not with overweight/obesity among T2DM patients. Despite its association with lower BMI among T2DM patients, the PPARgamma gene does not appear to markedly influence Type 2 diabetes among Tunisian subjects.

An analysis of peroxisome proliferator-activated receptor gamma (PPAR-gamma 2) Pro12Ala polymorphism distribution and prevalence of type 2 diabetes mellitus (T2DM) in world populations in relation to dietary habits

BACKGROUND AND AIM

The human peroxisome proliferator-activated receptor gamma (PPAR-gamma) is involved in lipid storage, glucose homeostasis and adipocyte differentiation. The Ala allele of the Pro12Ala polymorphism has been associated with a protective effect against T2DM. Ala allele frequencies are known for many populations, but data are absent for other interesting human groups.

METHODS AND RESULTS

We examined samples from Ethiopia, Benin, Ecuador and Italy. In addition, we performed an analysis of the Pro12Ala polymorphism distribution in world populations, also in relation to T2DM prevalence and the diet lipid content. In the European populations, the Ala allele frequencies are distributed according to a latitudinal trend, with the highest in the northern and central European populations and the lowest in the Mediterranean populations. Considering the world populations, a significant inverse relationship between Ala frequency and T2DM prevalence was observed mainly in populations where energy from lipids exceeded 30% of the total energy intake.

CONCLUSION

Northern Europe's cold climate has been hypothesised to have played a role in contributing to the present pattern. Moreover our analysis appears to confirm, at a population level, the protective effect of Ala allele against T2DM, already observed in case-control studies, but only in populations with a diet rich in lipids.

Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-gamma2 (PPARgamma-2) gene is associated with greater insulin sensitivity and decreased risk of type 2 diabetes in an Iranian population

BACKGROUND

The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-gamma2 (PPARgamma-2) gene has been variably associated with insulin resistance, obesity and type 2 diabetes in several populations. However, this association has not been studied in Iranian subjects and we hypothesized that this variation might be associated with insulin resistance, type 2 diabetes and related metabolic traits in this population.

METHODS

The Pro12Ala genotypes were determined by PCR-restriction fragment length polymorphism in 696 unrelated subjects including 412 non-diabetic controls and 284 type 2 diabetic patients.

RESULTS

The frequency of the Ala allele was 9.4% and 5.9% in controls and type 2 diabetic subjects, respectively [adjusted odds ratio (OR) 0.457, p=0.005]. The Ala allele did not show a significant effect on anthropometric and biochemical parameters in the type 2 diabetic group, whereas in non-diabetic subjects, carriers of the Ala allele had significantly lower fasting insulin (p=0.007) and homeostasis model assessment of insulin resistance (HOMA-IR) (p=0.009) levels compared to Pro/Pro subjects. Multivariate logistic regression analysis showed that Pro12Ala polymorphism was an independent determinant of type 2 diabetes in this population.

CONCLUSIONS

Our results for a sample of Iranian type 2 diabetes cases and controls provide evidence that the Pro/Ala genotype of the PPARgamma-2 gene is associated with insulin sensitivity and may also have protective role against type 2 diabetes.

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

Conflicting results have been reported regarding whether the PPARgamma2 Pro12Ala polymorphism plays a role in the risk of type 2 diabetes (T2D), suggesting genetic heterogeneity. To investigate this issue, a meta-analysis of 41 published and 2 unpublished studies (a total of 42,910 subjects) was conducted. Ala12 carriers had a 19% T2D risk reduction, but this association was highly heterogeneous (p = 0.005). A great proportion (48%) of heterogeneity was explained by the controls' BMI, with risk reduction being greater when BMI was lower. Risk reduction of Ala12 carriers in Asia (35%) was higher than in Europe (15%, p = 0.02) and tended to be higher than in North America (18%, p = 0.10). Difference between Asians and Europeans was no longer significant (p = 0.15) after adjusting for the controls' BMI. Studies from Europe were still heterogeneous (p = 0.02) with risk reduction in Ala12 carriers being progressively smaller (test for trend in the odds ratios, p = 0.02) from Northern (26% reduction, p < 0.0001) to Central (10%, p = 0.04) and Southern (0%, p = 0.94) Europe. In conclusion, in our meta-analysis, the reduced risk of T2D in Ala12 carriers is not homogeneous. It is greater in Asia than in Europe and, among Europeans, it is higher in Northern Europe, barely significant in Central Europe, and nonexistent in Southern Europe.

Effects of the type 2 diabetes-associated PPARG P12A polymorphism on progression to diabetes and response to troglitazone

CONTEXT

The common P12A polymorphism in PPARG (a target for thiazolidinedione medications) has been consistently associated with type 2 diabetes.

OBJECTIVE

We examined whether PPARG P12A affects progression from impaired glucose tolerance to diabetes, or responses to preventive interventions (lifestyle, metformin, or troglitazone vs. placebo).

PATIENTS

This study included 3548 Diabetes Prevention Program participants.

DESIGN

We performed Cox regression analysis using genotype at PPARG P12A, intervention, and their interactions as predictors of diabetes incidence. We also genotyped five other PPARG variants implicated in the response to troglitazone and assessed their effect on insulin sensitivity at 1 yr.

RESULTS

Consistent with prior cross-sectional studies, P/P homozygotes at PPARG P12A appeared more likely to develop diabetes than alanine carriers (hazard ratio, 1.24; 95% confidence interval, 0.99-1.57; P=0.07) with no interaction of genotype with intervention. There was a significant interaction of genotype with body mass index and waist circumference (P=0.03 and 0.002, respectively) with the alanine allele conferring less protection in more obese individuals. Neither PPARG P12A nor five other variants significantly affected the impact of troglitazone on insulin sensitivity in 340 participants at 1 yr.

CONCLUSIONS

The proline allele at PPARG P12A increases risk for diabetes in persons with impaired glucose tolerance, an effect modified by body mass index. In addition, PPARG P12A has little or no effect on the beneficial response to troglitazone.

Lack of association between the Pro12Ala polymorphism in PPAR-gamma2 gene and body weight changes, insulin resistance and chronic diabetic complications in obese patients with type 2 diabetes

BACKGROUND

It is generally accepted that the Pro12Ala polymorphism in peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) is associated with an increased risk of type 2 diabetes. However, studies on an association between the polymorphism and obesity have yielded inconsistent findings. Also, a role of PPAR-gamma receptors in development of chronic diabetic complications cannot be excluded. The aim of this study was to investigate an association between Pro12Ala polymorphism and body weight changes, insulin resistance, insulin secretion and incidence of diabetic complications in obese patients with long-lasting type 2 diabetes.

METHODS

In 216 obese patients with at least a 10-year history of type 2 diabetes, a detailed medical history was taken and a physical examination with assessment of diabetic complications was performed as well as evaluation of insulin resistance (homeostatic model assessment-HOMA), insulin secretion and other biochemical parameters. PCR-RFLP was used to assess Pro12Ala polymorphism. Two subgroups of patients were compared: homozygotic Pro/Pro and Ala allele carriers (Ala/Ala + Ala/Pro).

RESULTS

No differences between the analyzed groups in body weight changes, insulin resistance and insulin secretion were found, but Ala allele was significantly more frequent in males than in females. There was no difference in incidence and progression of diabetic complications with only a trend towards higher incidence of diabetic retinopathy in patients with Ala allele.

CONCLUSIONS

There is no association between Pro12Ala PPAR-gamma2 polymorphism and body mass changes observed during a course of type 2 diabetes, differences in peripheral insulin resistance and incidence and progression of diabetic complications in obese patients with long-lasting type 2 diabetes.

New polymorphism of ENPP1 (PC-1) is associated with increased risk of type 2 diabetes among obese individuals

The K121Q polymorphism in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is associated with type 2 diabetes and obesity. The possibility of other ENPP1 polymorphisms influencing these phenotypes has received little attention. Our aim was to examine the associations of tagging single nucleotide polymorphisms (SNPs) and haplotypes of the linkage disequilibrium (LD) block containing K121Q polymorphism with type 2 diabetes in a Polish population, controlling for any effect of obesity. We genotyped 426 type 2 diabetic case and 370 control subjects for seven SNPs in ENPP1. In the total group, neither type 2 diabetes nor obesity was significantly associated with any SNP. However, in obese subjects, two SNPs were significantly associated with type 2 diabetes: the Q allele of K121Q (odds ratio 1.6 [95% CI 1.003-2.6]) and T allele of rs997509 (4.7 [1.6-13.9]). In the LD block, four SNPs plus the K121Q polymorphism distinguished six haplotypes, three of which carried the Q allele. Interestingly, the T allele of rs997509 sufficed to distinguish a 121Q-carrying haplotype that was significantly more associated with type 2 diabetes than the other two (4.2 [1.3-13.5]). These other two 121Q-carrying haplotypes were not associated with type 2 diabetes. In conclusion, we found a new SNP, rs997509, in intron 1 that is strongly associated with risk of type 2 diabetes in obese individuals. The molecular mechanisms underlying this association are unknown.

Polymorphisms in the gene encoding hepatocyte nuclear factor-4alpha and susceptibility to type 2 diabetes in a Polish population

Recently, several association studies of type 2 diabetes mellitus (T2DM) and the hepatocyte nuclear factor (HNF)-4alpha gene were reported with conflicting results. Our aim was to search for association between two polymorphisms of HNF-4alpha and T2DM in Polish Caucasians. The study groups comprised of 461 T2DM cases and 366 controls. Genotype-quantitative trait analyses were based on the oral glucose tolerance test (OGTT), glucose and insulin results, and comprised 310 glucose-tolerant subjects. All individuals were genotyped for two HNF-4alpha polymorphisms. The frequencies of the minor alleles were as follows: 19.2% in T2DM vs. 17.6% in controls for rs2144908; and 20.6% vs. 20.1% for rs4810424, respectively. The distributions of alleles, genotypes, and haplotypes of the HNF-4alpha polymorphisms did not differ between the study groups (lowest P = 0.41). None of the examined SNPs showed an association in control subjects with quantitative traits of fasting plasma glucose, fasting insulin, as well as plasma glucose and insulin 2 hours after glucose load in OGTT. We conclude that both examined polymorphisms in HNF-4alpha are not associated with T2DM and prediabetic phenotypes in Polish Caucasian study groups of this size.

PPAR gamma and human metabolic disease

The nuclear receptor family of PPARs was named for the ability of the original member to induce hepatic peroxisome proliferation in mice in response to xenobiotic stimuli. However, studies on the action and structure of the 3 human PPAR isotypes (PPARalpha, PPARdelta, and PPARgamma) suggest that these moieties are intimately involved in nutrient sensing and the regulation of carbohydrate and lipid metabolism. PPARalpha and PPARdelta appear primarily to stimulate oxidative lipid metabolism, while PPARgamma is principally involved in the cellular assimilation of lipids via anabolic pathways. Our understanding of the functions of PPARgamma in humans has been increased by the clinical use of potent agonists and by the discovery of both rare and severely deleterious dominant-negative mutations leading to a stereotyped syndrome of partial lipodystrophy and severe insulin resistance, as well as more common sequence variants with a much smaller impact on receptor function. These may nevertheless have much greater significance for the public health burden of metabolic disease. This Review will focus on the role of PPARgamma in human physiology, with specific reference to clinical pharmacological studies, and analysis of PPARG gene variants in the abnormal lipid and carbohydrate metabolism of the metabolic syndrome.

The PPARG Pro12Ala polymorphism is associated with a decreased risk of developing hyperglycemia over 6 years and combines with the effect of the APM1 G-11391A single nucleotide polymorphism: the Data From an Epidemiological Study on the Insulin Resistance Syndrome (DESIR) study

Although cross-sectional studies have associated the Pro12Ala polymorphism of PPARG with type 2 diabetes, prospective studies offer more opportunities to investigate genetic variants. Associations between PPARG polymorphisms with insulin resistance parameters and with the 6-year incidence of impaired fasting glucose or type 2 diabetes were tested in 3,914 French Caucasians from the DESIR (Data From an Epidemiological Study on the Insulin Resistance Syndrome) cohort. In subjects normoglycemic at baseline (n = 3,498), the 6-year risk of hyperglycemia was lower in PPARG Ala carriers (odds ratio [OR] vs. ProPro = 0.66 [95% CI 0.44-0.99], P = 0.046 adjusted for sex, age, and BMI). Similar results were found with the PPARG C1431T single nucleotide polymorphism (SNP; adjusted OR = 0.65 [0.44-0.96], P = 0.036). Both alleles are in strong linkage disequilibrium (D' = 0.669, P < 0.001). The baseline mean fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) were lower in Ala carriers compared with ProPro homozygotes (P = 0.001 for both), with smaller increases in mean insulin and HOMA-IR during follow-up (P = 0.007 and 0.018, respectively). No association with insulin levels or HOMA-IR was found with C1431T. In this cohort, the APM1 G-11391A SNP is associated with the development of hyperglycemia. The combined effects of PPARG Pro12Ala and APM1 G-11391A SNPs showed no interaction on the risk of 6-year hyperglycemia. The PPARG Ala allele showed a relatively high protective effect in developing hyperglycemia and hyperinsulinemia during a 6-year period. Cumulative rather than synergistic effects of PPARG Pro12Ala and APM1 SNPs on diabetes risk are suggested.

Impact of genetic variation of PPARgamma in humans

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor with a key role in adipocyte differentiation. Since 1997, studies of rare mutations and common polymorphisms of the PPARgamma gene have enabled us to expand our knowledge of the role of this transcription factor in humans. Rare monogenic mutations in PPARgamma have a limited impact on the health of the population due to their low frequency but are associated with severe phenotypes such as severe insulin resistance, partial lipodystrophy, type 2 diabetes and hypertension. Conversely, common polymorphisms of PPARgamma with a relatively high frequency can have a significant impact on the general population. Although they may modulate the risk of developing type 2 diabetes, obesity and cardiovascular diseases, the data remains controversial. This review details and discusses results obtained for PPARgamma variants, whose effects sometimes appear discordant.