Objective: The provariant of the Pro12Ala polymorphism in peroxisome proliferator-activated receptor (PPAR)gamma has been identified as a risk allele for type 2 diabetes. The purpose of the present study was to reveal a significant association with pre-diabetic phenotypes in nondiabetic individuals based on a systematic meta-analysis of all available published evidence.
Research design and methods: We performed a classical meta-analysis of data from approximately 32,000 nondiabetic subjects in 57 studies to assess the effect of the Pro12Ala polymorphism on pre-diabetic traits.
Results: In the global comparison, there were no differences in BMI, glucose, insulin, or homeostasis model assessment of insulin resistance between the Pro/Pro and X/Ala genotype. However, in the Caucasian subgroup, the X/Ala genotype was associated with significantly increased BMI. In the obese subgroup (BMI >30 kg/m(2)), fasting glucose (P = 0.041) and insulin resistance (by homeostasis model analysis) (P = 0.020) were significantly greater in the Pro/Pro group. In subjects with the homozygous Ala/Ala genotype, fasting insulin was significantly lower compared with the Pro/Pro genotype (P = 0.040, N(Ala/Ala) = 154).
Conclusions: Across all studies, the Pro12Ala polymorphism had no significant effect on diabetes-related traits. Only in selected subgroups, such as Caucasians and obese subjects, did we see an association of the Ala allele with greater BMI and greater insulin sensitivity. This demonstrates the importance for appropriate stratification of analyses by environmental or other genetic factors. Meta-analysis of Ala/Ala homozygotes more clearly demonstrated the association with greater insulin sensitivity of carriers of the Ala allele.