Amino acid variants of the vitamin D-binding protein and risk of diabetes in white Americans of European origin

Abstract

Background: Genetic variants of vitamin D-binding protein (DBP) have been reported to be associated, not only with diabetes, but also with prediabetic traits, in several populations. There are two known polymorphisms in exon 11 of the DBP gene that result in amino acid variants: at codons 416 GAT → GAG (Asp→Glu) and 420 ACG → AAG (Thr → Lys). Objective: To examine the association of these polymorphisms with diabetes in white Americans of European origin. Methods: We studied unrelated individuals: 181 with type 1 diabetes, 215 with type 2 diabetes, and 163 healthy controls. Exon 11 was amplified using polymerase chain reaction and the two alleles were determined by digestion with specific endonucleases: HaeIII and StyI, respectively. Results: At codon 416, Asp/Glu allele frequencies were 45%/55% in patients with type 1 diabetes, 43%/57% in patients with type 2 diabetes, and 46%/54% in controls (x2=0.69, 2 d.f., P<0.71). At codon 420, corresponding Lys/Thr frequencies were 27%/73%, 30%/70%, and 30%/70% (x2 = 1.25, 2 d.f., P=0.53). Distributions of genotypes at both loci, and the haplotypes defined by the two loci, were also very similar in all groups. Conclusion: DNA polymorphisms in the DBP gene are not associated with diabetes in white Americans of European origin.