Polymorphisms within exon 9 but not intron 8 of the vitamin D receptor are associated with the nephropathic complication of type-2 diabetes.

The impact of several environmental and genetic factors on diabetes and its complications is well documented but there is an urgent need to understand more about genetic risk factors associated with this disease. The present study was aimed at examining the two single nucleotide polymorphisms (SNP) in intron 8 and exon 9 of the vitamin D receptor (VDR) gene in nephropathic and non-nephropathic type-2 diabetic patients. In this clinical study, peripheral blood samples were obtained from 100 type-2 diabetic patients, 100 nephropathic type-2 diabetic patients and 100 healthy controls. DNA was extracted and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed to examine two SNP polymorphisms within the VDR gene. Our results showed a significant difference in the Taq-1 evaluated genotypes of exon 9 in the VDR gene of diabetic individuals with (P=0.012) and without (P ≤ 0.001) nephropathy. Analysis of the Taq-1 evaluated alleles of nephropathic (P=0.917) and non-nephropathic (P=1.000) did not show a significant difference. We also evaluated the intron 8 Apa-1 alleles in patients with (P=0.480) and without nephropathy (P=0.543) and determined there were no differences between these groups. Our results also showed that the frequency of Apa-1 genotypes did not differ in nephropathic (P=0.224) and non-nephropathic (P=0.236) diabetic patients. Based on our results, it can be concluded that VDR and its functional polymorphism in exon 9 may play an important role in pathogenesis of type-2 diabetes and more investigations are required to clarify their role in nephropathy.