C Allele of the PPARδ+294T>C Polymorphism Confers a Higher Risk of Hypercholesterolemia, but not Obesity and Insulin Resistance: A Systematic Review and Meta-Analysis

The relationships of the PPARa Leu162Val and PPARd+294 T>C polymorphisms with metabolic indexes have been reported to be inconsistent and even contradictory. The meta-analysis was conducted to clarify the relationships between the two variants and the indexes of obesity, insulin resistance, and blood lipids. PubMed, Google Scholar, Embase, and Cochrane Library were searched for eligible studies. Standardized mean difference with 95% confidence interval was calculated to estimate the differences in the metabolic indexes between the genotypes of the Leu162Val and+294 T>C polymorphisms. Heterogeneity among studies was assessed by Cochran's x2-based Q-statistic test. Publication bias was identified by using Begg's test. Forty-one studies (44 585 subjects) and 33 studies (23 018 subjects) were identified in the analyses for the Leu162Val and+294 T>C polymorphisms, respectively. C allele carriers of the+294 T>C polymorphism had significantly higher levels of total cholesterol and low-density lipoprotein cholesterol than TT homozygotes in the whole population. Notably, C allele carriers of the+294 T>C polymorphism had significantly higher levels of triglycerides and total cholesterol in East Asians, but lower levels of triglycerides in West Asians than TT homozygotes. Regarding the Leu162Val polymorphism, it was found that Val allele carriers had significantly higher levels of blood glucose than Leu/Leu homozygotes only in European Caucasians. The meta-analysis demonstrates that C allele of the+294 T>C polymorphism in PPARd gene confers a higher risk of hypercholesterolemia, which may partly explain the relationship between this variant and coronary artery disease.