Role of polymorphism in vitamin D receptor gene on diabetic foot ulcer: A systematic review and meta-analysis

Abstract

Context: Once vitamin D is converted to its active form, the molecule binds to its receptor (VDR) and performs its function as a transcription factor in modulating immune response, inflammation cascade, and insulin signaling. Among diabetic individuals, these activities are thought to be correlated with foot ulceration. Gene polymorphisms could change the function of VDR, thereby affecting the development of foot ulceration among individuals with diabetes. Aims: To construct evidence on the role of VDR gene variants or single nucleotide polymorphisms (SNPs) on diabetic foot ulcers. Methods: Records reporting the distribution of genotypes and/or alleles among diabetic foot ulcer (DFU) patients and published until 10 March 2023 were retrieved from 12 major databases using predetermined keywords. The original research articles included in the study were assessed for reporting quality using the Newcastle Ottawa Scale. The quality of genotypic and allelic data was appraised by Hardy-Weinberg equilibrium (HWE). A quantitative analysis-based fixed-effects model was performed to estimate the proportion of genotype and allele frequencies among DFU patients. Results: Three studies were included in the systematic review reporting the FokI (rs2228570), TaqI (rs731236), BsmI (rs1544410), and ApaI (rs7975232) SNPs. Based on pooled estimates, among DFU patients CC, CT, and TT genotypes of VDR FokI SNPs had a prevalence of 45%, 43%, and 12%, respectively, without significant heterogeneity found in the reported data (p-Het<0.001; I2>0%). ApaI and FokI were associated with DFU, while no association in all genotypic and allelic models was found between TaqI or BsmI and DFU. CC genotype of BsmI and T allele of FokI was associated with oxidative stress (one of the underlying factors in DFU). Conclusions: Certain genotypes and alleles of FokI and ApaI SNPs could act as the risk factor for foot ulceration among diabetic individuals. More high-quality studies are still needed to draw solid conclusions on the role of VDR SNPs among DFU patients.