Altered Vitamin D Receptor Expression in Apa-I (rs7975232) Allelic Variants-A Probable Risk Factor for Susceptibility to Hepatitis B Virus Infection and Disease Progression

Vitamin D exerts its antiviral effect through vitamin D receptor (VDR)/retinoid X receptor-mediated host immunomodulation. Besides the downregulation of VDR expression, its polymorphism was also observed among hepatitis B virus (HBV)-positive patients. To understand the possible link between VDR polymorphism and its altered expression during HBV infection and disease progression, VDR Apa-I [rs7975232 (C>A)] single nucleotide polymorphism (SNP) was analyzed in a case-control manner. VDR Apa-I (rs7975232, C>A) polymorphism was studied using 340 HBV patients and 102 healthy controls. Genotype analysis and gene expression study was performed using restriction fragment length polymorphism and quantitative polymerase chain reaction, respectively. Statistical analysis was performed using SPSS (IBM) considering p-value <0.05 as significant for comparing the differences between the groups. Significant mean difference in VDR expression was observed between HBV-positive patients (1.6 ± 0.94) and controls (0.69 ± 0.73). Furthermore, the mean fold change of Healthy control with CC genotype (1.92 ± 0.99) was found to be marginally significant compared with mutant genotype (CA/AA) (1.08 ± 0.43/0.59 ± 0.56, p = 0.045). In HBV+ patients, the mean fold change in the CC genotype was 0.88 ± 0.38, which exhibits a significant mean difference upon comparison with other genotypes (0.52 ± 0.49, 0.113 ± 0.34; p = 0.018, p = 0.048). However, the fold change value does not differ between CA and AA genotypes. Further comparative analysis of VDR expression between the control and case also exhibits significant differences (p = 0.001) among allelic variants. Observed genotype distribution frequency exhibits a significant association with disease type. The mutant genotype was found to be significantly associated with HBV infection and disease progression, (odds ratio = 0.730, 95% confidence interval = 0.462-1.152, p = 0.06). VDR SNP rs7975232 (C>A) may affect VDR expression by controlling several other variables and suggest that deviation from wild-type genotype (CC) is associated with downregulation of expression, which in turn involved in host immunomodulation in favor of HBV infection and disease progression.