Among several genetic variants of the PPARγ2 gene, two polymorphisms; Pro12Ala of the exon B (rs1801282) and the C1431T silent substitution (rs3856806) in the exon 6, are the most frequently occurring SNPs and have been associated with various diseases [13-21]. The association of Pro12Ala polymorphism with T2D, insulin resistance, obesity and metabolic disorders has been reported in several studies [24-26]. The C1431T polymorphism has also been studied in relation to obesity, diabetes and coronary heart disease [18,25-27]. After a meticulous review of the literature, we were able to find a single association study conducted on Egyptian individuals to explore the relation between Pro12Ala PPARγ2 variant and T2D risk . However, to our knowledge, no association studies, evaluating the role of the C1431T variant in T2D, or investigating the associations of PPARγ2 variants with DR, have been published.
In the present study, we investigated the impact of Pro12Ala and C1431T PPARγ2 polymorphisms on the risk to develop T2D and DR and we came out with two important findings. The first is the significantly higher risk for diabetes among carriers of the T allele of the C1431T polymorphism. The second finding is that the frequency of the Ala12 allele of PPARγ2 in the Egyptian sample studied was very high (~38% in T2D cases and ~39% in controls) compared to that reported for Caucasians [14,16,29,30]. However, the protective association of the “Ala” allele with T2D was not confirmed in the present work. In addition, our study failed to find any significant association of the two studied polymorphisms with the risk of DR among T2D patients.
The PPARγ2 Pro12Ala variant was not associated with either T2D or DR in the current study. In previous studies, the association between the Pro12Ala polymorphism and fasting glucose or insulin concentrations have yielded conflicting results [14,16,17,26]. Overall, combined evidences suggest that the Ala12 allele exerts a protective effect with carriers of this allele causing a decreased diabetes risk [13,15,17,24,26,31,32]. However, several reports from different ethnic origins failed to reproduce a significant association [16,19,23,33,34]. Nevertheless, some studies have even found an increased risk for T2D in subjects with the Ala12 variant [35,36]. The results of the previous Egyptian study supported an association between Pro allele of PPARγ2 gene and T2D . It is noteworthy that the unexplained high frequencies of the Ala allele observed among the Egyptian control subjects, in the previous study (53%)  and also in the current work (~39%), exceed any frequency reported.
Regarding the relation between the PPARγ2 Pro12Ala variant and DR, few reports are available and results were also controversial. Our findings are consistent with Petrovic et al., and Costa et al., [37,38], but contradict others who reported a protective role of the 12Ala polymorphism against proliferative DR in individuals with T2D [39,40].
In the present study, despite the increased frequency of the T allele of C1431T polymorphism and the strong association with T2D, we did not find any significant difference of this variant between the DR and DWR subgroups, indicating that it confers risk for the development T2D but not for the DR complications. The CT and TT genotype of C1431T were significantly present in diabetic patients as a whole, but no genotype was significantly higher in patients with DR. Instead, the T allele was slightly higher in the DWR subgroup. A contradicting finding was reported by Tai et al., , they described a reduced risk of diabetes in carriers of the T allele of the C1431T polymorphism. In fact, only few studies [18,20,26,41] have analyzed the effects of the C1431T polymorphism, and none of them found a significant association of this variant with glucose or lipid-related variables. These inconsistencies may be attributable to the fact that this polymorphism is silent at the amino acid level and is unlikely to have any direct mechanistic link with specific phenotypes. Instead, it might be in linkage disequilibrium with an unidentified functional variation either within or flanking the PPARγ2 gene or in another gene at this locus.
We ensued to compare our results regarding the distribution of the PPARγ2 polymorphisms with the available reports from different Arab populations. In agreement with our finding, Badii et al.,  could not confirm the potential association between this polymorphism and T2D among Qataris subjects but they reported a low frequency of the Ala allele (5.5% for diabetic and 5.9% for non diabetics) as compared to ours and to the previous reports in various Caucasians. In Tunisia, several researchers examined the association of the genetic variation of the PPARγ2 with the susceptibility to T2D and concluded that the PPARγ2 is unlikely to be responsible for T2D in the Tunisian population [43-45].
These discrepancies between studies related to these polymorphisms may be partly explained by the presence of a gene-gene or gene-environment interaction. The controversial findings may also be related to information bias caused by the studies design and the selection criteria of patients. In addition, the prevalence of these polymorphisms; which varies greatly among populations, and may be very low in some of them, may contribute to the inconsistent results by affecting the statistical power of the comparisons.
In conclusion, the present study describes a significantly higher risk for diabetes among carriers of the T allele of the C1431T polymorphism, while it reports lack of association of the Pro12Ala variants with T2D. We also found no evidence of an association between the studied variants of PPARγ2 gene with DR in the T2D patients. Thus, the PPARγ2 C1431T variant seems to confer risk for the development of T2D but not for its chronic complications. Finally, since the lack of association might come from the small sample size, further studies on larger sample sizes are required to verify the present observation.