Abstract
BackgroundIt remains unclear whether genetic factors may explain the reported variation in the levels of biochemical markers of chronic kidney disease mineral and bone disorders (CKD- MBD) across ethnic groups. Therefore, the aim of this study was to examine the influence of vitamin D receptor (VDR) polymorphisms on secondary hyperparathyroidism and its association with vitamin D levels in black and white South African study participants.MethodsThis was a cross sectional study involving 272 CKD stage 3- 5D patients and 90 healthy controls. The four major VDR polymorphisms (Bsm 1, Fok 1, Taq 1, and Apa1) were genotyped using the polymerase chain reaction- restriction fragment length polymorphism (PCR –RFLP) method. In addition, biochemical markers of CKD-MBD were measured to determine their associations with the four VDR polymorphisms.ResultsWith the exception of Taq I polymorphism, the distribution of the VDR polymorphisms differed significantly between blacks and whites. In hemodialysis patients, the Bb genotype was significantly associated with moderate secondary hyperparathyroidism (OR, 3.88; 95 CI 1.13–13.25, p = 0.03) and severe hyperparathyroidism (OR, 2.54; 95 CI 1.08–5.96, p = 0.03). This was consistent with the observed higher levels of median parathyroid hormone, fibroblast growth factor 23 and mean phosphate in patients with Bb genotype. This candidate risk genotype (Bb) was over represented in blacks compared to whites (71.0% versus 55.6%, p < 0.0001). In an unadjusted regression model, FokFf genotype was found to be significantly associated with the risk of developing severe vitamin D deficiency < 15 ng/ml (OR, 1.89; 95 CI 1.17–3.07, p = 0.01).ConclusionThe VDR Bb genotype is an independent predictor of developing secondary hyperparathyroidism in patients with end stage kidney disease. In addition, study participants with FokFf genotype are at increased of developing severe 25 -hydroxyvitamin D [25(OH)D] deficiency.
Highlights
It remains unclear whether genetic factors may explain the reported variation in the levels of biochemical markers of chronic kidney disease mineral and bone disorders (CKD- Chronic kidney disease- mineral and bone disorder (MBD)) across ethnic groups
BsmI polymorphism (BB genotype) has been associated with slower progression of secondary hyperparathyroidism and Waziri et al BMC Nephrology (2018) 19:30 normal levels of calcitriol in pre dialysis CKD patients, and lower levels of parathyroid hormone (PTH) in hemodialysis, and a greater reduction in PTH levels in response to a single bolus of calcitriol therapy compared to patients with bb genotype [8, 9]
In line with ongoing efforts to greater understanding of the mechanisms behind racial disparities in markers of CKD- MBD, we aimed to explore the variations in the vitamin D receptor (VDR) polymorphisms between black and white African CKD patients and their relationship with markers of mineral bone disorders
Summary
It remains unclear whether genetic factors may explain the reported variation in the levels of biochemical markers of chronic kidney disease mineral and bone disorders (CKD- MBD) across ethnic groups. The aim of this study was to examine the influence of vitamin D receptor (VDR) polymorphisms on secondary hyperparathyroidism and its association with vitamin D levels in black and white South African study participants. Contrary to earlier studies, findings from subsequent studies on the associations between VDR polymorphisms and markers of mineral bone disease have been inconsistent. Some studies have linked other VDR polymorphisms to mineral bone metabolism in hemodialysis patients. The VDR Fok I polymorphism (FF genotype) was reported to be associated with higher PTH levels [13]
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