FokI vitamin D receptor polymorphism as a protective factor in intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis in pregnancy (ICP) is a pregnancy-specific liver disorder. Its etiology is not fully understood. Increasing evidence indicates the important role of vitamin D and the vitamin D receptor (VDR) in this disorder. The presence of polymorphic variants in the VDR gene could influence its activity and susceptibility to ICP development. The goal of the study was to investigate the role of four genetic polymorphisms of the VDR gene - Fok (rs731236), Bsm (rs1544410), Apa (rs7975232), and Taq (rs731236) - in the etiology of ICP in Polish women.

Ninety-eight women with confirmed ICP and 215 healthy pregnant women as a control group were recruited to the study. We examined four SNPs of the VDR gene: BsmI (rs7975232), TaqI (rs1544410), ApaI (rs228570), FokI (rs731236). Genotyping was performed using the PCR/RFLP method.

We observed higher frequency (borderline significant) of the Ff-ff genotypes containing at least one mutated allele of the VDR FokI polymorphism in the control group compared to the ICP group (p = 0.045, OR = 1.71, 95% CI 1.01-2.88). The frequency of the mutated f allele was slightly higher in controls (49.1%) than in the ICP group (43.4%) (OR = 1.26, 95% CI 0.90-1.77), but the difference was not statistically significant (p = 0.196).

Our results showed that the maternal VDR FokI polymorphism could play a protective role in ICP development and probably modulate the risk of ICP occurrence in pregnant women in the Polish population. In the future, to confirm these observations, research in larger, ethnically stratified and clinically analyzed groups is necessary.