Does the vitamin D receptor genotype predict bone mineral loss in haemodialysed patients?

Association of Vitamin D Receptor Gene Polymorphisms with Hypercalcemia in Peritoneal Dialysis Patients

♦ Background

Some polymorphisms at the human vitamin D receptor (VDR) gene locus may influence calcium and bone metabolism. We investigated the roles of the BsmI and TaqI VDR gene polymorphisms in the development of hypercalcemia in Turkish peritoneal dialysis (PD) patients.

♦ Methods

We enrolled 132 PD patients treated with dialysate containing 1.75 mmol/L calcium. Serum levels of calcium, phosphorus, albumin, and intact parathyroid hormone (iPTH), and the cumulative doses of calcium-based phosphate binders and calcitriol were recorded every 3 months. The VDR BsmI and TaqI genotypes were determined by polymerase chain reaction.

♦ Results

When the patients were categorized according to these VDR genotypes, serum levels of phosphorus and iPTH and cumulative doses of calcium-based phosphate binders and calcitriol were similar across groups. The corrected serum calcium levels tended to increase in the patients with BsmI non- BB (Bb + bb) variants, but were significantly decreased in the BB variants (9.9 ± 0.7 vs 9.1 ± 0.6 mg/dL, p < 0.05). Hypercalcemia appeared in 21.2% of the patients during the follow-up period. The hypercalcemic patients had a significantly higher prevalence of the BsmI non- BB genotype than the normocalcemic patients (85.7% vs 59.6%, p < 0.007). On the contrary, the serum calcium levels were not affected by the TaqI VDR gene polymorphism ( p > 0.05).

♦ Conclusions

These findings suggest that the non- BB variants of the BsmI VDR gene polymorphism are associated with increased risk of developing hypercalcemia in PD patients.

Effects of genetic variants on serum parathyroid hormone in hyperparathyroidism and end-stage renal disease patients: A systematic review and meta-analysis

BACKGROUND

Parathyroid hormone (PTH) is one of the principal regulators of calcium homeostasis, crucial for normal functioning of the kidneys, bones, heart, and nervous system. Different pathologic conditions can affect serum PTH level resulting in hyperparathyroidism or hypoparathyroidism. Our study assessed the association of previously reported polymorphisms with the level of PTH (expressed in pg/mL) among individuals with different pathologic conditions affecting PTH level.

METHODS

We searched Web of Science, MEDLINE, and Scopus to identify relevant articles published up to July 2017. The search yielded 6967 publications of which 44 fulfilled the inclusion criteria. We conducted meta-analyses for calcium-sensing receptor gene (CaSR) rs1801725 polymorphism in patients with primary hyperparathyroidism and vitamin D receptor gene (VDR) rs1544410 polymorphism in patients with end-stage renal disease (ESRD).

RESULTS

None of the polymorphisms were significantly associated with PTH levels in the overall population. In subgroup analysis by ethnicity for VDR rs1544410 gene polymorphism, we found significant differences under dominant model (SMD: -0.18 [-0.32, -0.05], P < .01) and AA versus GG comparison (SMD: -0.29 [-0.52, -0.06], P < .01) in Asian patients with ESRD, while nominally significant results (P < .05) were observed for AG versus GG and AA versus GG comparisons in European individuals with ESRD.

CONCLUSION

Scientific evidence of genetic association of serum PTH level among individuals with different pathologic conditions remains deficient and published results provide weak evidence. Further well-conducted studies on larger sample sets designed according to evidence-based principles are warranted to assure clinically applicable findings.

Association of vitamin D receptor BsmI (rs1544410) gene polymorphism with the intact parathyroid hormone (iPTH) level among patients with end-stage renal disease

Association of vitamin D receptor (VDR) BsmI (rs1544410) gene polymorphism with the intact parathyroid hormone (iPTH) level among patients with end-stage renal disease (ESRD) from the published reports is still conflicting. This meta-analysis was performed to evaluate the relationship between VDR BsmI (rs1544410) gene polymorphism and the iPTH level among patients with ESRD. The association studies were identified from PubMed, and Cochrane Library on 1 March 2014, and eligible investigations were included and synthesized using meta-analysis method. Six reports were recruited into this meta-analysis for the association of VDR BsmI gene polymorphism with iPTH level among patients with ESRD. In this meta-analysis, the iPTH level in ESRD patients carrying BsmI Bb genotype was higher than that in ESRD patients carrying bb genotype in overall populations (Bb versus bb: OR = 61.40, 95% CI: 19.65-103.16, p = 0.004). However, the iPTH level in ESRD patients carrying BB genotype was not significant different from that in ESRD patients with Bb genotype and bb genotype in overall populations (BB versus Bb: OR = -18.30, 95% CI: -126.28-89.69, p = 0.74; BB versus bb: OR = 22.85, 95% CI: -70.81-116.51, p = 0.63). Furthermore, the results for Caucasians were similar to those in overall populations. In conclusion, the iPTH level in ESRD patients carrying BsmI Bb genotype was higher than that in ESRD patients carrying bb genotype in overall populations and in Caucasians. However, more studies should be conducted to confirm it.

Determinants of bone mineral density in patients on haemodialysis or peritoneal dialysis--a cross-sectional, longitudinal study

INTRODUCTION

The aim of the study was to identify biomarkers of alteration in bone mineral density (BMD) in patients on haemodialysis (HD) and peritoneal dialysis (PD).

MATERIALS AND METHODS

In a cross-sectional, longitudinal study dual-energy X-ray absorptiometry scans were performed in 146 HD-patients and 28 PD-patients. Follow-up after 14 months (mean) was conducted in 73 patients. As potential biomarkers we investigated parathyroid hormone (PTH), 25-hydroxy vitamin-D, ionised calcium, albumin, phosphate, and total alkaline phosphatases (t-ALP).

RESULTS

Both groups of dialysis patients had lower BMD in the femoral neck (BMD(neck)) (P < 0.001) and forearm (BMD(forearm)) (P < 0.001) compared to healthy controls, but comparable BMD in the lumbar spine (BMD(spine)). BMD did not differ between dialysis types, but patients ever-treated with glucocorticoids had significantly lower BMD, while patients with polycystic kidney disease had higher BMD. BMD correlated with body weight, actual age, age at initiation of dialysis, duration of dialysis and levels of PTH and t-ALP. However, t-ALP only remained associated with low BMD(spine) after adjusting for other factors (P = 0.001). In the follow-up study all patients had decreased BMD in all three locations, but only for the lumbar spine there was a significant association between BMD and the bone markers t-ALP (P = 0.009) and PTH (P = 0.013).

CONCLUSIONS

Both HD and PD patients have low BMD, and increased concentrations of t-ALP is associated BMD(spine) after adjustment, while PTH and t-ALP is associated with decrease in BMD(spine) over time. This substantiates the use of these biomarkers in both types of dialysis patients.

Association analysis of clinical aspects and vitamin D receptor gene polymorphism with external apical root resorption in orthodontic patients

INTRODUCTION

Vitamin D is responsible for the regulation of certain genes at the transcription level, via interaction with the vitamin D receptor, and influences host immune responses and aspects of bone development, growth, and homeostasis. Our aim was to investigate the association of TaqI vitamin D receptor gene polymorphism with external apical root resorption during orthodontic treatment.

METHODS

Our subjects were 377 patients with Class II Division 1 malocclusion, divided into 3 groups: (1) 160 with external apical root resorption ≤1.43 mm, (2) 179 with external apical root resorption >1.43 mm), and (3) 38 untreated subjects. External apical root resorption of the maxillary incisors was evaluated on periapical radiographs taken before and after 6 months of treatment. After DNA collection and purification, vitamin D receptor TaqI polymorphism analysis was performed by polymerase chain reaction-restriction fragment length polymorphism. Univariate and multivariate analyses were performed to verify the association of clinical and genetic variables with external apical root resorption (P <0.05).

RESULTS

There was a higher proportion of external apical root resorption in orthodontically treated patients compared with the untreated subjects. In patients orthodontically treated, age higher than 14 years old, initial size of the maxillary incisor root superior to 30 mm, and premolar extraction were associated with increased external apical root resorption. Genotypes containing the C allele were weakly associated with protection against external apical root resorption (CC + CT × TT [odds ratio, 0.29; 95% confidence interval, 0.07-1.23; P = 0.091]) when treated orthodontic patients were compared to untreated individuals.

CONCLUSIONS

Clinical factors and vitamin D receptor TaqI polymorphism were associated with external apical root resorption in orthodontic patients.

Vitamin D receptor gene, biochemical bone markers and bone mineral density in Mexican women on dialysis

BACKGROUND

The influence of the Bsm1 polymorphism of the vitamin D receptor (VDR) gene on mineral and bone disorders in chronic kidney disease (CKD) is still under discussion. The aim of this study was to analyse the relationship between VDR polymorphism, bone mineral density (BMD), biochemical bone markers and clinical factors in women on peritoneal dialysis (PD) and haemodialysis (HD).

METHODS

In a cross-sectional study, 197 women (42 +/- 10 years; 25% with diabetes mellitus (DM); body mass index (BMI) 25.26 +/- 4.77 kg/m(2)) treated by PD (72%) or HD (28%) underwent measurements of BMD (measured at the calcaneus by quantitative ultrasound; expressed as T- and Z-scores) and plasma total calcium (tCa), intact parathyroid hormone 1-84 (iPTH), phosphorus, albumin, glucose, osteoprotegerin (OPG), fetuin-A, intact osteocalcin-49 and N-MID fragment 1-43 aa (N-MID osteocalcin) N-terminal propeptide of type 1 procollagen (PINP) and C-terminal telopeptide-beta aspartic acid (BCL). DNA was extracted from peripheral blood. PCR products were digested with Bsm1 to analyse VDR polymorphism.

RESULTS

The Z-score of BMD was -1.1 +/- 1.03. According to the values of osteopenia (T-score = -1.0), patients with higher BMD were younger, had lower frequency of amenorrhoea and diabetes and had higher serum creatinine and fetuin levels as well as lower levels of PINP. In a stepwise multivariate logistics analysis, osteopenia was associated with presence of genotype BB+Bb (OR = 3.26, P < or = 0.003) and age (OR = 0.95, P = 0.050). According to the B allele, bb: n = 126 (64%) and BB+Bb: n = 71(36%), group bb had significantly higher mean Z-scores (-0.97 +/- 1.0 vs -1.3+/-0.92; P < or = 0.021).

CONCLUSIONS

The high frequency of osteopenia observed in female CKD patients on dialysis is associated with age and genetic predisposition as revealed by its association to the Bsm1 VDR polymorphism.

Gene polymorphism association studies in dialysis: bone and mineral metabolism

Abnormalities in bone and mineral metabolism have a significant impact on morbidity and mortality among patients with end-stage renal disease (ESRD). In addition to confounding environmental factors, genetic susceptibility factors may also influence the occurrence and severity of these abnormalities and account for interindividual variability among patients. Indeed, polymorphisms involving genes of the calcium/parathyroid hormone/calcitriol axis have been associated with bone and mineral metabolism abnormalities. This review summarizes studies involving polymorphisms of candidate genes and their effects on the development of complications related to bone and mineral metabolism abnormalities among patients with ESRD.

Vitamin D receptor polymorphisms and diseases

The vitamin D endocrine system is central to the control of bone and calcium homeostasis. Thus, alterations in the vitamin D pathway lead to disturbances in mineral metabolism. Furthermore, a role for vitamin D has been suggested in other diseases, like cancer, diabetes and cardiovascular disease. Expression and nuclear activation of the vitamin D receptor (VDR) are necessary for the effects of vitamin D. Several genetic variations have been identified in the VDR. DNA sequence variations, which occur frequently in the population, are referred to as "polymorphisms" and can have biological effects. To test whether there is a linkage between VDR polymorphisms and diseases, epidemiological studies are performed. In these studies, the presence of a variation of the gene is studied in a population of patients, and then compared to a control group. Thus, association studies are performed, and a link among gene polymorphisms and diseases can be established. Since the discovery of VDR polymorphisms a number of papers have been published studying its role in bone biology, renal diseases, diabetes, etc. The purpose of this review is to summarize the vast amount of information regarding vitamin D receptor polymorphisms and human diseases, and discuss its possible role as diagnostic tools.

Osseous complications of pediatric transplantation

Adult stature and peak bone mass are achieved through childhood growth and development. Multiple factors impair this process in children undergoing solid organ transplantation, including chronic illness, pretransplant osteodystrophy, use of medications with negative impact on bone, and post-transplant renal dysfunction. While growth delay and short stature remain common, the most severe forms of transplant-related bone disease, fracture and avascular necrosis, appear to have become less common in the pediatric age group. Osteopenia is very prevalent in adult transplant recipients and probably also in pediatrics, but its occurrence and sequelae are difficult to study in these groups due to methodological shortfalls of planar densitometry related to short stature and altered patterns of growth and development. Although the effect on lifetime peak bone mass is not clear, data from adult populations suggest an elevated long-term risk of bone disease in children receiving transplants. Optimal management of pretransplantation osteodystrophy, attention to post-transplant renal insufficiency among both renal and non-renal transplant patients, reduction of steroid dose in select patients, and supplementation with calcium plus vitamin D during expected periods of maximal bone loss may improve bone health. Careful research is required to determine the role of bisphosphonate therapy in pediatric transplantation.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

The vitamin D receptor gene variant is associated with the prevalence of type 2 diabetes mellitus and coronary artery disease

AIMS

Vitamin D can influence lipolysis and insulin secretion. A common genetic polymorphism of the vitamin D receptor, which has been found to be associated with bone mineral density, has also been reported to be associated with insulin-dependent diabetes mellitus. To test the influence of the vitamin D receptor polymorphism on the prevalence of Type 2 diabetes mellitus and coronary artery disease we studied a population of high-risk patients, who were referred to our clinic for diagnostic coronary angiography.

METHODS

A total of 293 patients considered at high risk for coronary artery disease because of angina pectoris and known hypercholesterolaemia underwent diagnostic coronary angiography. The BsmI vitamin D receptor polymorphism was analysed by polymerase chain reaction.

RESULTS

Prevalence of Type 2 diabetes mellitus and coronary artery disease was gradually dependent on the number of B alleles (BB 28%, Bb 13%, bb 8% for Type 2 diabetes mellitus, P = 0.002; BB 88% Bb 72%, bb 66% coronary artery disease, P = 0.01). Patients with the BB genotype had an odds ratio of 3.64 (95% confidence interval 1.53-8.55, P = 0.002) to have Type 2 diabetes mellitus compared with patients with the bb genotype.

CONCLUSIONS

The genotype of the vitamin D receptor polymorphism determines the prevalence of Type 2 diabetes mellitus and coronary artery disease in a high-risk cohort population.

The vitamin D receptor genotype predisposes to the development of calcific aortic valve stenosis

OBJECTIVE

To test the hypothesis that vitamin D receptor polymorphism is associated with calcific aortic valve stenosis.

DESIGN

The distribution of one polymorphism of the vitamin D receptor (BsmI B/b) was examined in 100 consecutive patients with calcific valvar aortic stenosis and compared with a control group of 100 patients (paired match for age, sex, and the presence of coronary artery disease from a total of 630 patients without calcified aortic valves). Polymerase chain reaction and restriction fragment length polymorphism were used to determine genotypes.

RESULTS

There was a significant difference in vitamin D receptor allele and genotype frequencies between the two groups. The allele B had a higher prevalence in patients with calcific aortic stenosis (B = 0.56, b = 0.44) than in the control cohort (B = 0.40, b = 0.60) (p = 0.001).

CONCLUSIONS

There is a significant association of vitamin D receptor polymorphism with calcific aortic valve stenosis. The B allele of the vitamin D receptor is more common in patients with calcific aortic valve stenosis. It now needs to be evaluated whether other genes that control calcium homeostasis are involved in the pathogenesis of this disorder.