CYP2R1 mutations causing vitamin D-deficiency rickets

Application of small interfering RNA technology in cytochrome P450 gene modulation

Cytochrome P450 plays key roles in the biotransformation of endogenous and exogenous chemicals including drugs and environmental pollutants. The inhibition and downregulation of P450s can have therapeutic effects, and/or modulate drug metabolism. P450s are largely inhibited by small molecules; however, this strategy is often hampered by intrinsic toxicity and drug-drug interactions. Furthermore, it is challenging for small molecules to exhibit high selectivity and inhibitory efficiencies. Recently, small interfering RNA (siRNA) technology has demonstrated the potential for P450 modulation. Examples of recent applications of siRNAs in P450 gene modulation, in vitro and in vivo, are highlighted in this review. The necessity of siRNA techniques and their advantages as P450 modulators are discussed, along with a review of current obstacles and a perspective on future advancements. SIGNIFICANCE STATEMENT: This article reviews studies on the application of small interfering RNA technology to cytochrome P450 gene modulation. The necessity of siRNA methods and the benefits of their use as P450 modulators have been suggested by comparison with small-molecule drugs. Additionally, the challenges that presently limit the broader implementation of this topic are examined, and a perspective for future developments is proposed.

Vitamin D Enhancement of Adipose Biology: Implications on Obesity-Associated Cardiometabolic Diseases

Vitamin D is activated into 1α,25(OH)2D through two hydroxylation steps that are primarily catalyzed by 25-hydroxylase in the liver and 1α-hydroxylase in the kidneys. The active form of vitamin D regulates myriads of cellular functions through its nuclear receptor, vitamin D receptor (VDR). Vitamin D metabolizing enzymes and VDR are expressed in adipose tissues and vitamin D regulates multiple aspects of adipose biology including the recruitment and differentiation of adipose stem cells into adipocytes and metabolic, endocrine, and immune properties. Obesity is associated with low vitamin D status, which is thought to be explained by its sequestration in large mass of adipose tissues as well as dysregulated vitamin D metabolism. Low vitamin D status in obesity may negatively impact adipose biology leading to adipose tissue dysfunctions, the major pathological factors for cardiometabolic diseases in obesity. In this review, the current understanding of vitamin D metabolism and its molecular mechanisms of actions, focusing on vitamin D-VDR regulation of adipose biology with their implications on obesity-associated diseases, is discussed. Whether improving vitamin D status leads to reductions in adiposity and risks for cardiometabolic diseases is also discussed.

Association of vitamin D deficiency and insufficiency with uncontrolled type 1 diabetes Mellitus among Saudi pediatric patients; a hospital-based retrospective study

Background

The association between 25-hydroxy-vitamin D [25(OH)D] levels and glycemic control in pediatric patients with type 1 diabetes mellitus (T1DM) is unclear. In this study, we aimed to investigate the association between 25(OH)D levels and glycemic control in Saudi pediatric patients' with T1DM in a region that is sunny year-round.

Materials and methods

A retrospective study was conducted in the Pediatric Department of King Saud Hospital in Unaizah, Saudi Arabia. A total of 218 children with T1DM were enrolled in the study and grouped according to their glycated hemoglobin (HbA1C) levels into the controlled T1DM (HbA1C ≤ 7.5%) and the uncontrolled T1DM (HbA1C > 7.5%). Their 25(OH)D levels and thyroid function were measured using standard methods.

Results

Of the 218 children in this study, 182 (83.5%) had uncontrolled T1DM, while only 36 (16.5%) had controlled T1DM. The median (interquartile range) of 25(OH)D levels was significantly lower in the uncontrolled T1DM group compared with the controlled group [45.4 (31.2-59.7) nmol/L vs. 56.1 (37.5-77.6) nmol/L; p = 0.007], respectively. Vitamin D deficiency (<50.0 nmol/L) and insufficiency (50-74 nmol/L) were detected in 55.0% and 31.1% of all the enrolled children, respectively. Vitamin D deficiency was detected in 86.6% of the uncontrolled T1DM patients and in 16.5% of the controlled T1DM patients (p = 0.012). The multivariable analysis showed that both vitamin D deficiency [adjusted odds ratio (aOR) = 2.92, p = 0.048] and insufficiency [aOR = 3.17, p = 0.042] were risk factors for uncontrolled diabetes.

Conclusion

Vitamin D deficiency was highly prevalent in the studied group. Both vitamin D deficiency and insufficiency are associated with uncontrolled T1DM. Further study is needed.

CYP4A22 loss-of-function causes a new type of vitamin D-dependent rickets (VDDR1C)

Vitamin D-dependent rickets (VDDR) is a group of genetic disorders characterized by early-onset rickets due to deficiency of active vitamin D or a failure to respond to activated vitamin D. VDDR is divided into several subtypes according to the corresponding causative genes. Here we described a new type of autosomal dominant VDDR in a Chinese pedigree. The proband and his mother had severe bone malformations, dentin abnormalities, and lower serum 25 hydroxyvitamin D3 (25[OH]D3) and phosphate levels. The proband slightly responded to a high dose of vitamin D3 instead of a daily low dose of vitamin D3. Whole-exome sequencing, bioinformatic analysis, PCR, and Sanger sequencing identified a nonsense mutation in CYP4A22 (c.900delG). The overexpressed wild-type CYP4A22 mainly localized in endoplasmic reticulum and Golgi apparatus, and synthesized 25(OH)D3 in HepG2 cells. The overexpressed CYP4A22 mutant increased the expression of CYP2R1 and produced little 25(OH)D3 with vitamin D3 supplementation, which was reduced by CYP2R1 siRNA treatment. We concluded that CYP4A22 functions as a new kind of 25-hydroxylases for vitamin D3. Loss-of-function mutations in CYP4A22 lead to a new type of VDDR type 1 (VDDR1C). CYP2R1 and CYP4A22 may have some genetic compensation responding to nonsense-mediated mRNA decay effect of each other.

Genetic causes of hypophosphatemia

Phosphate is a key component of mineralized tissues and is also part of many organic compounds. Phosphorus homeostasis depends especially upon intestinal absorption, and renal excretion, which are regulated by various hormones, such as PTH, 1,25-dihydroxyvitamin D, and fibroblast growth factor 23. In this review we provide an update of several genetic disorders that affect phosphate transporters through cell membranes or the phosphate-regulating hormones, and, consequently, result in hypophosphatemia.

Physiology of Vitamin D-Focusing on Disease Prevention

Vitamin D is a crucial micronutrient, critical to human health, and influences many physiological processes. Oral and skin-derived vitamin D is hydroxylated to form calcifediol (25(OH)D) in the liver, then to 1,25(OH)2D (calcitriol) in the kidney. Alongside the parathyroid hormone, calcitriol regulates neuro-musculoskeletal activities by tightly controlling blood-ionized calcium concentrations through intestinal calcium absorption, renal tubular reabsorption, and skeletal mineralization. Beyond its classical roles, evidence underscores the impact of vitamin D on the prevention and reduction of the severity of diverse conditions such as cardiovascular and metabolic diseases, autoimmune disorders, infection, and cancer. Peripheral target cells, like immune cells, obtain vitamin D and 25(OH)D through concentration-dependent diffusion from the circulation. Calcitriol is synthesized intracellularly in these cells from these precursors, which is crucial for their protective physiological actions. Its deficiency exacerbates inflammation, oxidative stress, and increased susceptibility to metabolic disorders and infections; deficiency also causes premature deaths. Thus, maintaining optimal serum levels above 40 ng/mL is vital for health and disease prevention. However, achieving it requires several times more than the government's recommended vitamin D doses. Despite extensive published research, recommended daily intake and therapeutic serum 25(OH)D concentrations have lagged and are outdated, preventing people from benefiting. Evidence suggests that maintaining the 25(OH)D concentrations above 40 ng/mL with a range of 40-80 ng/mL in the population is optimal for disease prevention and reducing morbidities and mortality without adverse effects. The recommendation for individuals is to maintain serum 25(OH)D concentrations above 50 ng/mL (125 nmol/L) for optimal clinical outcomes. Insights from metabolomics, transcriptomics, and epigenetics offer promise for better clinical outcomes from vitamin D sufficiency. Given its broader positive impact on human health with minimal cost and little adverse effects, proactively integrating vitamin D assessment and supplementation into clinical practice promises significant benefits, including reduced healthcare costs. This review synthesized recent novel findings related to the physiology of vitamin D that have significant implications for disease prevention.

Pleiotropy of Progesterone Receptor Membrane Component 1 in Modulation of Cytochrome P450 Activity

Progesterone receptor membrane component 1 (PGRMC1) is one of few proteins that have been recently described as direct modulators of the activity of human cytochrome P450 enzymes (CYP)s. These enzymes form a superfamily of membrane-bound hemoproteins that metabolize a wide variety of physiological, dietary, environmental, and pharmacological compounds. Modulation of CYP activity impacts the detoxification of xenobiotics as well as endogenous pathways such as steroid and fatty acid metabolism, thus playing a central role in homeostasis. This review is focused on nine main topics that include the most relevant aspects of past and current PGRMC1 research, focusing on its role in CYP-mediated drug metabolism. Firstly, a general overview of the main aspects of xenobiotic metabolism is presented (I), followed by an overview of the role of the CYP enzymatic complex (IIa), a section on human disorders associated with defects in CYP enzyme complex activity (IIb), and a brief account of cytochrome b5 (cyt b5)'s effect on CYP activity (IIc). Subsequently, we present a background overview of the history of the molecular characterization of PGRMC1 (III), regarding its structure, expression, and intracellular location (IIIa), and its heme-binding capability and dimerization (IIIb). The next section reflects the different effects PGRMC1 may have on CYP activity (IV), presenting a description of studies on the direct effects on CYP activity (IVa), and a summary of pathways in which PGRMC1's involvement may indirectly affect CYP activity (IVb). The last section of the review is focused on the current challenges of research on the effect of PGRMC1 on CYP activity (V), presenting some future perspectives of research in the field (VI).

Hereditary Rickets: A Quick Guide for the Pediatrician

With the increased discovery of genes implicated in vitamin D metabolism and the regulation of calcium and phosphate homeostasis, a growing number of genetic forms of rickets are now recognized. These are categorized into calciopenic and phosphopenic rickets. Calciopenic forms of hereditary rickets are caused by genetic mutations that alter the enzymatic activity in the vitamin D activation pathway or impair the vitamin D receptor action. Hereditary forms of phosphopenic rickets, on the other hand, are caused by genetic mutations that lead to increased expression of FGF23 hormone or that impair the absorptive capacity of phosphate at the proximal renal tubule. Due to the clinical overlap between acquired and genetic forms of rickets, identifying children with hereditary rickets can be challenging. A clear understanding of the molecular basis of hereditary forms of rickets and their associated biochemical patterns allow the health care provider to assign the correct diagnosis, avoid non-effective interventions and shorten the duration of the diagnostic journey in these children. In this mini-review, known forms of hereditary rickets listed on the Online Mendelian Inheritance in Man database are discussed. Further, a clinical approach to identify and diagnose children with hereditary forms of rickets is suggested.

Association between Vitamin D Levels, Puberty Timing, and Age at Menarche

Pubertal development represents the process of physical maturation where an adolescent reaches sexual maturity and attains reproductive function. The effects of vitamin D are mainly mediated by the vitamin D receptor (VDR), which is expressed in almost all body cells, including the ovary and human pituitary gland and animal hypothalamus. Thus, vitamin D has gained great interest as pathogenic factor of pubertal disorders and fertility. This narrative review aimed to provide a broad overview of the available literature regarding the association between vitamin D levels, puberty timing, and age at menarche. A review of the data on the involvement of micronutrient deficiency, as a modifiable cause of pubertal disorders, is important for the prediction and prevention of deficiencies as well as for fertility protection and should be considered a public health priority. Reported data support that vitamin D is a regulator of neuroendocrine and ovarian physiology and, more in detail, a deficiency of vitamin D is involved in altered pubertal timing. Considering the long-term consequences of early pubertal development and early menarche, the detection of modifiable causes is crucial in preventive strategies. Future studies in humans and with an increased scale are needed to elucidate the vitamin D role in sexual maturation and puberty development.

Dietary Vitamin D Intake in Italian Subjects: Validation of a Frequency Food Questionnaire (FFQ)

Vitamin D plays a crucial role in calcium and phosphate metabolism, relating to bone health and preventing metabolic bone disorders such as rickets and osteomalacia. Vitamin D deficiency (serum 25-OH-D values <20 ng/mL or 50 nmol/L) is common also in Italian people; it is recommended to maintain levels above 30 ng/mL (75 nmol/L) in categories at risk. Supplementation and/or fortification with either ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3) aimed to modify this condition have commonly been proposed. Studies about vitamin D intake are numerous in the literature but not adequately designed and are very often incomplete in Mediterranean Countries such as in the Italian population. On these bases, we performed a survey to validate a frequency food questionnaire (FFQ) specifically created to rapidly assess dietary vitamin D intake in Italian people. For this aim, the data of questionnaires were compared with results derived in the same population from a designed 14-day frequency food diary (FFD). Overall, a good correlation between FFQ and FFD was observed (r = 0.89, p < 0.001), both demonstrating a remarkably low vitamin D intake, irrespective of age and gender. Our data confirm that the vitamin D intake is very low in Italy, which likely contributes to hypovitaminosis D.

Enzymatic activation in vitamin D signaling - Past, present and future

Vitamin D signaling is important in regulating calcium homeostasis essential for bone health but also displays other functions in cells of several tissues. Disturbed vitamin D signaling is linked to a large number of diseases. The multiple cytochrome P450 (CYP) enzymes catalyzing the different hydroxylations in bioactivation of vitamin D₃ are crucial for vitamin D signaling and function. This review is focused on the progress achieved in identification of the bioactivating enzymes and their genes in production of 1α,25-dihydroxyvitamin D₃ and other active metabolites. Results obtained on species- and tissue-specific expression, catalytic reactions, substrate specificity, enzyme kinetics, and consequences of gene mutations are evaluated. Matters of incomplete understanding regarding the physiological roles of some vitamin D hydroxylases are critically discussed and the authors will give their view of the importance of each enzyme for vitamin D signaling. Roles of different vitamin D receptors and an alternative bioactivation pathway, leading to 20-hydroxylated vitamin D₃ metabolites, are also discussed. Considerable progress has been achieved in knowledge of the vitamin D₃ bioactivating enzymes. Nevertheless, several intriguing areas deserve further attention to understand the pleiotropic and diverse activities elicited by vitamin D signaling and the mechanisms of enzymatic activation necessary for vitamin D-induced responses.

Comparison of calcifediol with vitamin D for prevention or cure of vitamin D deficiency

Vitamin D deficiency remains prevalent, with about 7% of the world's population living with severe vitamin D deficiency and about one third with mild deficiency. We compare the relative merits of calcifediol or 25-hydroxyvitamin D (25OHD) compared to vitamin D itself for supplementation as to prevent or cure vitamin D deficiency. The intestinal absorption of calcifediol is nearly 100% and thus higher than that of vitamin D itself. Moreover, calcifediol is absorbed by the intestinal cells and transported through the portal vein and thus immediately accessible to the circulation, while vitamin D is transported with chylomicrons through the lymph system. Therefore, in case of fat malabsorption or after bariatric surgery, calcifediol is much better absorbed in comparison with vitamin D itself. Serum 25OHD increases linearly with increasing doses of calcifediol, whereas serum 25OHD reaches a plateau when higher oral doses of vitamin D are used. Calcifediol, on a weight basis, is about 3 times more potent than vitamin D in subjects with mild vitamin D deficiency. This potency is even 6-8 times higher than vitamin D when baseline serum 25OHD is higher or when large doses are compared. In conclusion, calcifediol is an alternative option to correct vitamin D deficiency and may even be the preferred strategy in case of intestinal fat malabsorption, after bariatric surgery or in case of other conditions with suspected impaired 25-hydroxylase activity in the liver.

Approach to Hypophosphatemic Rickets

Hypophosphatemic rickets typically presents in infancy or early childhood with skeletal deformities and growth plate abnormalities. The most common causes are genetic (such as X-linked hypophosphatemia), and these typically will result in lifelong hypophosphatemia and osteomalacia. Knowledge of phosphate metabolism, including the effects of fibroblast growth factor 23 (FGF23) (an osteocyte produced hormone that downregulates renal phosphate reabsorption and 1,25-dihydroxyvitamin-D (1,25(OH)2D) production), is critical to determining the underlying genetic or acquired causes of hypophosphatemia and to facilitate appropriate treatment. Serum phosphorus should be measured in any child or adult with musculoskeletal complaints suggesting rickets or osteomalacia. Clinical evaluation incudes thorough history, physical examination, laboratory investigations, genetic analysis (especially in the absence of a guiding family history), and imaging to establish etiology and to monitor severity and treatment course. The treatment depends on the underlying cause, but often includes active forms of vitamin D combined with phosphate salts, or anti-FGF23 antibody treatment (burosumab) for X-linked hypophosphatemia. The purpose of this article is to explore the approach to evaluating hypophosphatemic rickets and its treatment options.

Association of CYP2R1 and VDR Polymorphisms with Metabolic Syndrome Components in Non-Diabetic Brazilian Adolescents

Associations between vitamin D deficiency and metabolic syndrome (MS) have been reported; however, the underlying biological mechanisms remain controversial. The aim of this study was to investigate the associations of CYP2R1 and VDR variants with MS and MS components in non-diabetic Brazilian adolescents. This cross-sectional study included 174 adolescents who were classified as overweight/obese. Three CYP2R1 variants and four VDR variants were identified by allelic discrimination. The CYP2R1 polymorphisms, rs12794714 (GG genotype) (odds ratio [OR] = 3.54, 95% confidence interval [CI] = 1.24–10.14, p = 0.023) and rs10741657 (recessive model—GG genotype) (OR = 3.90, 95%CI = 1.18–12.92, p = 0.026) were significantly associated with an increased risk of MS and hyperglycemia, respectively. The AG + GG genotype (dominant model) of the rs2060793 CYP2R1 polymorphism was associated with hyperglycemia protection (OR = 0.28, 95%CI = 0.08–0.92, p = 0.037). Furthermore, the CC genotype (recessive model) of the rs7975232 VDR polymorphism was significantly associated with a risk of hypertension (OR = 5.91, 95%CI = 1.91–18.32, p = 0.002). In conclusion, the CYP2R1 rs12794714 polymorphism could be considered a possible new molecular marker for predicting the risk of MS; CYP2R1 rs10741657 polymorphism and VDR rs7975232 polymorphism are associated with an increased risk of diabetes and hypertension in adolescents with overweight/obesity.

Clinical presentation and molecular genetic analysis of a Sudanese family with a novel mutation in the CYP2R1 gene

The aim of this study was to identify the genetic basis of two female siblings - born to consanguineous Sudanese parents - diagnosed clinically as having the rare condition of 25-hydroxylase deficiency (vitamin D-dependent rickets type 1B). The initial diagnosis was established based on clinical data, laboratory and radiological findings retrospectively. Primers for all exons (5) of human CYP2R1 (NM_024514) were generated followed by Sanger sequencing on exons 1-5 for both girls and their parents. Homozygosity for a point mutation (c.85C > T) was detected, leading to a nonsynonymous variant at position 29 in exon 1, resulting in a premature stop codon (p.Q29X). This is a previously unknown variant that leads to a severely truncated protein and predicted to be among the 0.1 % most deleterious genomic variants(CADD score 36). To our knowledge, this family represents the first case series from Sudan with a confirmed CYP2R1 gene mutation and the 6th world-wide. With the lack of genetic facilities, diagnosis should be suspected by the persistently low 25 hydroxyvitamin D level in spite of proper treatment and after ruling out liver disease and malabsorption. Patients in this case series showed healing of rickets when treated with high doses of 1,25-dihydroxyvitamin D₃ (1,25(OH)D₃; calcitriol) and oral calcium.

Haplotypes in the GC, CYP2R1 and CYP24A1 Genes and Biomarkers of Bone Mineral Metabolism in Older Adults

Candidate gene studies have analyzed the effect of specific vitamin D pathway genes on vitamin D availability; however, it is not clear whether genetic variants also affect overall bone metabolism. This study evaluated the association between genetic polymorphisms in GC, CYP2R1 and CYP24A1 and serum levels of total 25(OH)D, iPTH and other mineral metabolism biomarkers (albumin, total calcium and phosphorus) in a sample of 273 older Spanish adults. We observed a significant difference between CYP2R1 rs10741657 codominant model and total 25(OH)D levels after adjusting them by gender (p = 0.024). In addition, the two SNPs in the GC gene (rs4588 and rs2282679) were identified significantly associated with iPTH and creatinine serum levels. In the case of phosphorus, we observed an association with GC SNPs in dominant model. We found a relationship between haplotype 2 and 25(OH)D levels, haplotype 4 and iPTH serum levels and haplotype 7 and phosphorus levels. In conclusion, genetic variants in CYP2R1 and GC could be predictive of 25(OH)D and iPTH serum levels, respectively, in older Caucasian adults. The current study confirmed the role of iPTH as one of the most sensitive biomarkers of vitamin D activity in vivo.

Genetic Polymorphism of Vitamin D Family Genes CYP2R1, CYP24A1, and CYP27B1 Are Associated With a High Risk of Non-alcoholic Fatty Liver Disease: A Case-Control Study

Background

Previous studies have highlighted the important role of vitamin D and calcium pathway genes in immune modulation, cell differentiation and proliferation, and inflammation regulation, all closely implicated in the pathogenesis of non-alcoholic fatty liver disease (NAFLD).

Objective

This study aims to investigate whether 11 candidate single nucleotide polymorphisms (SNPs) in vitamin D and calcium pathway genes (CYP2R1, CYP24A1, and CYP27B1) are associated with the risk of NAFLD.

Methods

In this case-control study, a total of 3,023 subjects were enrolled, including 1,114 NAFLD cases and 1,909 controls. Eleven genetic variants in CYP2R1, CYP24A1, and CYP27B1 genes were genotyped. Logistic regression analysis was used to assess the effects of these variants on NAFLD risk. The functional annotations of positive SNPs were further evaluated by bioinformatics analysis.

Results

After adjusting for age, gender, and metabolic measures, we identified that CYP24A1 rs2296241 variant genotypes (recessive model: OR, 1.316; 95% CI, 1.048–1.653; p = 0.018), rs2248359 variant genotypes (recessive model: OR, 1.315; 95% CI, 1.033–1.674; p = 0.026), and CYP27B1 rs4646536 variant genotypes (additive model: OR, 1.147; 95% CI, 1.005–1.310; p = 0.042) were associated with an elevated risk of NAFLD. In combined effects analysis, we found that NAFLD risk significantly increased among patients carrying more rs2296241-A, rs2248359-T, and rs4646536-T alleles (p_trend = 0.049). Multivariate stepwise analysis indicated that age, visceral obesity, ALT, γ-GT, hypertriglyceridemia, hypertension, low HDL-C, hyperglycemia, and unfavorable alleles were independent predictors of NAFLD (all p < 0.05). The area under the receiver operating characteristic curve was 0.789 for all the above factors.

Conclusion

The polymorphisms of vitamin family genes CYP24A1 (rs2296241, CYP24A1, and rs2248359) and CYP27B1 (rs4646536) were associated with NAFLD risk in Chinese Han population, which might provide new insight into NAFLD pathogenesis and tools for screening high-risk population.

A Mendelian randomization study on the role of serum parathyroid hormone and 25-hydroxyvitamin D in osteoarthritis

OBJECTIVE

Serum parathyroid hormone (PTH) and 25-hydroxyvitamin D [25(OH)D] have been demonstrated to be associated with pathogenesis and progression of osteoarthritis (OA). This study aimed to determine the potential causal relationship between serum PTH and 25(OH)D levels and risk of OA.

DESIGN

We applied the two-sample Mendelian randomization (MR) approach to estimate the causal roles of serum PTH and 25(OH)D on OA. The instrumental variables for serum PTH and 25(OH)D were derived from two large genome-wide association studies (GWAS), which included 29,155 and 79,366 individuals, respectively. Summary-level data for overall, hip and knee OA were extracted from a GWAS meta-analysis, including 455,221 individuals. All participants included in this study were from the European population.

RESULTS

An inverse association was observed between serum PTH levels and risk of OA (random-effects: Effect = 0.71; 95% CI: 0.54 to 0.92; fixed-effects: Effect = 0.71; 95% CI: 0.61 to 0.82). Stratified by site, serum PTH levels were found to be inversely associated with knee OA (random-effects: Effect = 0.53; 95% CI: 0.41 to 0.68; fixed-effects: Effect = 0.53; 95% CI: 0.41 to 0.68). However, there was no evidence of the causal effect of serum 25(OH)D levels on OA.

CONCLUSIONS

The present study indicates an inverse causal relationship between serum PTH concentrations and development of OA. Moreover, a site-specific association was also observed between serum PTH levels and knee OA. The potential mechanisms by which serum PTH affects OA need to be further investigated.

High Fat Diet and High Cholesterol Diet Reduce Hepatic Vitamin D-25-Hydroxylase Expression and Serum 25-Hydroxyvitamin D3 Level through Elevating Circulating Cholesterol, Glucose, and Insulin Levels

SCOPE

Low circulating 25-hydroxyvitamin D (25(OH)D) levels associate with obesity, diabetes, and hyperlipidemia, but the underlying mechanisms remain uncertain. As energy-dense diet contributes to these disorders, this study investigates whether diet could impair vitamin D metabolism.

METHODS AND RESULTS

Compared with control chow-fed mice, high fat diet (HFD)-fed mice show lower serum 25(OH)D₃ and 1,25(OH)₂ D₃ levels, lower hepatic vitamin D 25-hydroxylase Cyp2r1 expression but comparable renal vitamin D metabolic enzymes expression. Time course studies show that after HFD feeding, the serum concentrations of cholesterol, triglycerides, fatty acids, glucose, and insulin elevate sequentially and before the reduction of hepatic Cyp2r1 expression and serum 25(OH)D₃ levels. Hepatic Cyp2r1 expression also reduces after consuming high fat and high sucrose diet. After high cholesterol diet feeding, serum total cholesterol rises and hepatic Cyp2r1 expression decreases ahead of the reduction of serum 25(OH)D₃ . In vitro studies demonstrate that high concentrations of cholesterol, glucose, and insulin significantly inhibit Cyp2r1expression in primary murine hepatocytes. Further studies show that dietary restriction in HFD-fed mice ameliorates hypercholesterolemia, hyperglycemia, and hypertriglyceridemia, and elevates hepatic Cyp2r1 expression and serum 25(OH)D₃ level.

CONCLUSION

These findings suggest that diet-induced elevation of circulating cholesterol, glucose, and insulin reduces serum 25(OH)D₃ level through suppressing hepatic Cyp2r1 expression.

1α,25-dihydroxyvitamin D3 promotes early osteogenic differentiation of PDLSCs and a 12-year follow-up case of early-onset vitamin D deficiency periodontitis

Periodontitis is a chronic periodontal disease that contributes to tooth loss. In recent years, many animal studies have reported that vitamin D (VitD) deficiency results in chronic periodontitis. However, no studies have reported cases of early-onset periodontitis with VitD deficiency. This study reports a 5-year-old male patient with early-onset periodontitis, VitD deficiency and VitD receptor (VDR) mutation. The patient was treated with VitD and calcium, and received systematic periodontal treatment. During the 12-year treatment, the periodontal conditions of this patient were stable. Our in vitro study found that VitD could promote the expression of alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), bone morphogenetic protein 2 (BMP2), bone gamma-carboxyglutamate protein (BGLAP), and VDR in the early osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Meanwhile, VitD could downregulate mRNA expression levels of Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-1β (IL-1β) and protein levels of IL-6 in the tumor necrosis factor-α (TNF-α) -induced inflammation of PDLSCs. Therefore, sufficient VitD supply can be a potential treatment for VitD deficiency induced early-onset periodontitis.

SNP rs12794714 of CYP2R1 is associated with serum vitamin D levels and recurrent spontaneous abortion (RSA): a case-control study

PURPOSE

Vitamin D (VD) deficiency seems to be associated with the risk of recurrent spontaneous abortion (RSA). Vitamin D receptor (VDR) and cytochrome P450 family 2 subfamily R member 1 (CYP2R1) are two genes which are vital for VD metabolism and actions. However, whether single-nucleotide polymorphisms (SNPs) in these genes are correlated with the risk of RSA are poorly understood. Therefore, we aimed to characterize the relationships among VDR SNPs, CYP2R1 SNPs and RSA.

METHODS

This case-control study enrolled 75 RSA patients and 83 controls. Serum VD and some cytokines were detected with LC-MS/MS and flow cytometry, respectively. Genotyping for three SNPs of CYP2R1 (rs10741657, rs10766197 and rs12794714) and five SNPs of VDR (rs7975232, rs1544410, rs2189480, rs2228570 and rs2239179) was done with polymerase chain reaction (PCR) and high-throughput sequencing. All the data were analyzed with appropriate methods and in different models.

RESULTS

The results revealed a significant correlation between the AG genotype of CYP2R1 rs12794714 and VD levels (OR 0.686; 95% CI 0.49-0.96; p = 0.028). Besides, the AG and GG genotypes of CYP2R1 rs12794714 were markedly related to the risk of RSA (OR 52.394, 59.497; 95% CI 2.683-1023.265, 3.110-1138.367; p = 0.009, 0.007, respectively).

CONCLUSION

Our results indicate that CYP2R1 rs12794714 might be a risk factor for RSA. Hence, early screening of pregnant women for CYP2R1 rs12794714 is necessary to warrant proactive counseling and treatment against RSA.

Cholecalciferol (vitamin D3) has a direct protective activity against interleukin 6-induced atrophy in C2C12 myotubes

We previously determined that different vitamin D metabolites can have opposite effects on C2C12 myotubes, depending on the sites of hydroxylation or doses. Specifically, 25(OH)D₃ (25VD) has an anti-atrophic activity, 1,25(OH)₂D₃ induces atrophy, and 24,25(OH)₂D₃ is anti-atrophic at low concentrations and atrophic at high concentrations. This study aimed to clarify whether cholecalciferol (VD3) too, the non-hydroxylated upstream metabolite, has a direct effect on muscle cells.

Assessing the effects of VD3 treatment on mouse C2C12 skeletal muscle myotubes undergoing atrophy induced by interleukin 6 (IL6), we demonstrated that VD3 has a protective action, preserving C2C12 myotubes size, likely through promoting the differentiation and fusion of residual myoblasts and by modulating the IL6-induced autophagic flux. The lack, in C2C12 myotubes, of the hydroxylase transforming VD3 in the anti-atrophic 25VD metabolite suggests that VD3 may have a direct biological activity on the skeletal muscle. Furthermore, we found that the protective action of VD3 depended on VDR, implying that VD3 too might bind to and activate VDR. However, despite the formation of VDR-RXR heterodimers, VD3 effects do not depend on RXR activity.

In conclusion, VD3, in addition to its best-known metabolites, may directly impact on skeletal muscle homeostasis.

Probing the Scope and Mechanisms of Calcitriol Actions Using Genetically Modified Mouse Models

Genetically modified mice have provided novel insights into the mechanisms of activation and inactivation of vitamin D, and in the process have provided phenocopies of acquired human disease such as rickets and osteomalacia and inherited diseases such as pseudovitamin D deficiency rickets, hereditary vitamin D resistant rickets, and idiopathic infantile hypercalcemia. Both global and tissue-specific deletion studies leading to decreases of the active form of vitamin D, calcitriol [1,25(OH)2D], and/or of the vitamin D receptor (VDR), have demonstrated the primary role of calcitriol and VDR in bone, cartilage and tooth development and in the regulation of mineral metabolism and of parathyroid hormone (PTH) and FGF23, which modulate calcium and phosphate fluxes. They have also, however, extended the spectrum of actions of calcitriol and the VDR to include, among others: modulation, jointly and independently, of skin metabolism; joint regulation of adipose tissue metabolism; cardiovascular function; and immune function. Genetic studies in older mice have also shed light on the molecular mechanisms underlying the important role of the calcitriol/VDR pathway in diseases of aging such as osteoporosis and cancer. In the course of these studies in diverse tissues, important upstream and downstream, often tissue-selective, pathways have been illuminated, and intracrine, as well as endocrine actions have been described. Human studies to date have focused on acquired or genetic deficiencies of the prohormone vitamin D or the (generally inactive) precursor metabolite 25-hyrodxyvitamin D, but have yet to probe the pleiotropic aspects of deficiency of the active form of vitamin D, calcitriol, in human disease. © 2020 American Society for Bone and Mineral Research © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Clinical Significance of Analysis of Vitamin D Status in Various Diseases

Vitamin D plays a role not only in the proper functioning of the skeletal system and the calcium-phosphate equilibrium, but also in the immune system, the cardiovascular system and the growth and division of cells. Although numerous studies have reported on the analysis of vitamin D status in various groups of patients, the clinical significance of measurements of vitamin D forms and metabolites remains ambiguous. This article reviews the reports analyzing the status of vitamin D in various chronic states. Particular attention is given to factors affecting measurement of vitamin D forms and metabolites. Relevant papers published during recent years were identified by an extensive PubMed search using appropriate keywords. Measurement of vitamin D status proved to be a useful tool in diagnosis and progression of metabolic syndrome, neurological disorders and cancer. High performance liquid chromatography coupled with tandem mass spectrometry has become the preferred method for analyzing the various forms and metabolites of vitamin D in biological fluids. Factors influencing vitamin D concentration, including socio-demographic and biochemical factors as well as the genetic polymorphism of the vitamin D receptor, along with vitamin D transporters and enzymes participating in vitamin D metabolism should be considered as potential confounders of the interpretation of plasma total 25(OH)D concentrations.

Rickets in association with skin diseases and conditions: A review with emphasis on screening and prevention

BACKGROUND

Rickets is a common disease worldwide. In the developed world, its prevalence dramatically decreased but still diagnosed in at-risk populations. The skin plays a critical role in vitamin D synthesis. Therefore, several skin diseases, especially keratinization disorders, could lead to impaired vitamin D metabolism and vitamin D deficient rickets.

OBJECTIVE

The article aimed to summarize the current knowledge of skin diseases and conditions associated with rickets.

METHODS

To examine the association between rickets and skin diseases, we performed a systematic review of the literature using PubMed database. The search included studies published from the database inception to August 2019.

RESULTS

A total number of 75 articles were included. Identified conditions associated with rickets were ichthyosis being a more common skin diseases, alopecia, epidermal and melanocytic nevi, xeroderma pigmentosum, mastocytosis, psoriasis, and atopic dermatitis. Three types of rickets were identified: vitamin D-dependent rickets, hypocalcemic vitamin D-dependent rickets type 2, and hypophosphatemic rickets. Cutaneous skeletal hypophosphatemia syndrome is a newly described and under-recognized condition. It is defined by the association of epidermal or melanocytic nevi, hypophosphatemic rickets, and elevated levels of fibroblast growth factor 23. Rickets in patients with ichthyosis was mainly due to impaired ability of ichthyotic skin to synthesize vitamin D, poor UV penetration of the skin caused by keratinocyte proliferation, and dark phototype. The latter may be considered a risk factor for rickets in patients with ichthyosis.

CONCLUSION

Despite its rarity, these associations should be properly recognized by dermatologists. Early diagnosis of rickets is important to prevent growth retardation and skeletal deformities.

The Role of Polymorphisms in Vitamin D-Related Genes in Response to Vitamin D Supplementation

Background. Vitamin D deficiency represents a major healthcare problem. Vitamin D status is influenced by genetic and environmental determinants. Several observational studies have evaluated the association of single-nucleotide polymorphisms (SNPs) in vitamin D-related genes and vitamin D levels. Nevertheless, little is known about the role of these SNPs in the response to vitamin D supplementation. We conducted an interventional study to define the association between SNPs in vitamin D-related genes and the response to vitamin D supplementation in 100 self-reported healthy women of Arab ancestry for the majority. Methods. A total of 100 healthy female subjects received a weekly oral dose of 50,000 IU vitamin D for 12 weeks. Serum vitamin D concentration and metabolic profiles were measured at baseline and 12 weeks post-vitamin D supplementation. The genotypes of 37 SNPs selected from previously reported vitamin D-related genes have been assessed by Fluidigm genotyping assay. Results. Rs731236 (VDR gene) and rs7116978 (CYP2R1 gene) showed a significant association with vitamin D status. The rs731236 GG genotype and the rs7116978 CC genotype were associated with a “vitamin D sufficiency” state. Rs731236 GG and rs7116978 CC genotypes showed a higher response to vitamin D supplementation. Transcription factor binding site prediction analysis showed altered binding sites for transcription factors according to the different rs7116978 alleles. Interestingly, the 37 SNPs previously established to play a role in vitamin D-related pathways explained very little of the response to vitamin D supplementation in our cohort, suggesting the existence of alternative loci whose number and effect size need to be investigated in future studies. Conclusion. In this paper, we present novel data on vitamin D-related SNPs and response to vitamin D supplementation demonstrating the feasibility of applying functional genomic approaches in interventional studies to assess individual-level responses to vitamin D supplementation.

Vitamin D regulation of adipogenesis and adipose tissue functions

Vitamin D insufficiency is associated with obesity and its related metabolic diseases. Adipose tissues store and metabolize vitamin D and expression levels of vitamin D metabolizing enzymes are known to be altered in obesity. Sequestration of vitamin D in large amount of adipose tissues and low vitamin D metabolism may contribute to the vitamin D inadequacy in obesity. Vitamin D receptor is expressed in adipose tissues and vitamin D regulates multiple aspects of adipose biology including adipogenesis as well as metabolic and endocrine function of adipose tissues that can contribute to the high risk of metabolic diseases in vitamin D insufficiency. We will review current understanding of vitamin D regulation of adipose biology focusing on vitamin D modulation of adiposity and adipose tissue functions as well as the molecular mechanisms through which vitamin D regulates adipose biology. The effects of supplementation or maintenance of vitamin D on obesity and metabolic diseases are also discussed.

Prolonged 25-OH Vitamin D Deficiency Does Not Impair Bone Mineral Density in Adult Patients With Vitamin D 25-Hydroxylase Deficiency (CYP2R1)

Vitamin D-dependent rickets type 1B (VDDR1B) is an autosomal semidominant genetic disorder caused by a deficiency in CYP2R1, which encodes vitamin D 25-hydroxylase, an enzyme that plays a crucial role in the conversion of vitamin D to 25-dihydroxyvitamin D₃. VDDR1B is a severe form of rickets that occurs during infancy and which is responsive to 25-OH vitamin D supplementation. We studied three adult patients from a multi-consanguineous family with VDDR1B. They have been diagnosed with pseudo-nutritional rickets and treated during their adolescence with 25-OH vitamin D. These patients stopped their treatments at the end of adolescence and were contacted 14 to 17 years later when VDDR1B diagnosis was carried out in their niece and nephews. These three patients had undetectable 25-OH vitamin D, but normal levels of plasma 1-25(OH)₂ vitamin D. All patients had a hip bone mineral density and a normal vertebral despite osteoarthritis degenerative lesions which may impact BMD evaluation. These findings show that vitamin D supplementation has a questionable effect, if any, for osteoporosis prevention in adulthood in contrast to its crucial importance during infancy and adolescence.

The measurement of vitamin D metabolites part II-the measurement of the various vitamin D metabolites

Today, the possibility exists to measure a number of different vitamin D metabolites with accurate and precise methods. The most abundant vitamin D metabolite, 25(OH)D, is considered the best marker for estimating vitamin D status and is therefore the most commonly measured in clinical practice. There is no consensus on the added value of measuring other metabolites beyond 25-hydroxyvitamin D, although, in some special clinical scenarios and complicated cases, these metabolites may provide just the information needed for an accurate diagnosis. The problem this review addresses is which metabolite to measure and when and how to measure it.

CYP2R1 and CYP27A1 genes: An in silico approach to identify the deleterious mutations, impact on structure and their differential expression in disease conditions

Mutations in CYP2R1 and CYP27A1 involved in the conversion of Cholecalciferol into Calcidiol were associated with the impaired 25-hydroxylase activity therefore affecting the Vitamin D metabolism. Hence, this study attempted to understand the influence of genetic variations at the sequence and structural level via computational approach. The non-synonymous mutations retrieved from dbSNP database were assessed for their pathogenicity, stability as well as conservancy using various computational tools. The above analysis predicted 11/260 and 35/489 non-synonymous mutations to be deleterious in CYP2R1 and CYP27A1 genes respectively. Native and mutant forms of the corresponding proteins were modeled. Further, interacting native and mutant proteins with cholecalciferol showed difference in hydrogen bonds, hydrophobic bonds and their binding affinities suggesting the possible influence of these mutations in their function. Also, expression of these genes in various disease conditions was investigated using GEO datasets which predicted that there is a differential expression in cancer and arthritis.

Identification and analysis of 35 genes associated with vitamin D deficiency: A systematic review to identify genetic variants

Vitamin D deficiency is a public health concern associated with, but not limited to, skeletal anomalies, chronic diseases, immune conditions, and cancer, among others. Hypovitaminosis D is mainly associated with environmental and lifestyle factors that affect sunlight exposure. However, genetic factors also influence 25-hydroxyvitamin D (25[OH]D) serum concentration. Although there is available information of genes with clear biological relevance or markers identified by Genome-Wide Association Studies, an overall view and screening tool to identify known genetic causes of altered serum levels of 25(OH)D is lacking. Moreover, there are no studies including the total genetic evidence associated with abnormal serum concentration of 25(OH)D. Therefore, we conducted a de-novo systematic literature review to propose a set of genes comprehensive of all genetic variants reported to be associated with deficiency of vitamin D. Abstracts retrieved from PubMed search were organized by gene and curated one-by-one using the PubTerm web tool. The genes identified were classified according to the type of genetic evidence associated with serum 25(OH)D levels and were also compared with the few commonly screened genes related to vitamin D status. This strategy allowed the identification of 35 genes associated with serum 25(OH)D concentrations, 27 (75%) of which are not commercially available and are not, therefore, analyzed in clinical practice for genetic counseling, nor are they sufficiently studied for research purposes. Functional analysis of the genes identified confirmed their role in vitamin D pathways and diseases. Thus, the list of genes is an important source to understand the genetic determinants of 25(OH)D levels. To further support our findings, we provide a map of the reported functional variants and SNPs not included in ClinVar, minor allelic frequencies, SNP effect sizes, associated diseases, and an integrated overview of the biological role of the genes. In conclusion, we identified a comprehensive candidate list of genes associated with serum 25(OH)D concentrations, most of which are not commercially available, but would prove of importance in clinical practice in screening for patients that should respond to supplementation because of alterations in absorption, patients that would have little benefit because alterations in the downstream metabolism of vitamin D, and to study non-responsiveness to supplementation with vitamin D.

Circulating levels of free 25(OH)D increase at the onset of rheumatoid arthritis

OBJECTIVE

Epidemiological studies suggest vitamin D deficiency as a potential risk factor for rheumatoid arthritis (RA) development, a chronic autoimmune disorder highly prevalent in indigenous North American (INA) population. We therefore profiled the circulating levels of 25-hydroxyvitaminD [25(OH)D], an active metabolite of vitamin D, in a cohort of at-risk first-degree relatives (FDR) of INA RA patients, a subset of whom subsequently developed RA (progressors).

METHODS

2007 onward, serum samples from INA RA patients and FDR were collected at the time of a structured baseline visit and stored at -20°C. Anti-citrullinated protein antibodies (ACPA), 25(OH)D, hs-CRP, vitamin-D binding protein (VDBP) and parathyroid hormone (PTH) levels were determined using ELISA and rheumatoid factor (RF) seropositivity was determined by nephelometry.

RESULTS

We demonstrate that 25 (OH) D concentrations were lower in winter than summer (P = 0.0538), and that serum 25(OH)D levels were higher in samples collected and stored after 2013 (P<0.0001). Analysis of samples obtained after 2013 demonstrated that 37.6% of study participants were 25(OH)D insufficient (<75nmol/L). Also, seropositive RA patients and FDR had lower 25(OH)D levels compared to ACPA-/FDR (P<0.05, P<0.01 respectively). Linear regression analysis showed 25(OH)D insufficiency was inversely associated with presence of RA autoantibodies. Longitudinal samples from 14 progressors demonstrated a consistent increase in 25(OH)D levels at the time they exhibited clinically detectable joint inflammation, without any significant change in VDBP or PTH levels. Spearman rank correlation analysis showed significant association between 25(OH)D and PTH levels, both in RA patients and progressors at RA onset time.

CONCLUSION

We demonstrate that 25(OH)D levels in serum increased at RA onset in progressors. The potential role that vitamin D metabolites and their downstream effects play in RA transition requires further investigation.

Evaluation of vitamin D biosynthesis and pathway target genes reveals UGT2A1/2 and EGFR polymorphisms associated with epithelial ovarian cancer in African American Women

An association between genetic variants in the vitamin D receptor (VDR) gene and epithelial ovarian cancer (EOC) was previously reported in women of African ancestry (AA). We sought to examine associations between genetic variants in VDR and additional genes from vitamin D biosynthesis and pathway targets (EGFR, UGT1A, UGT2A1/2, UGT2B, CYP3A4/5, CYP2R1, CYP27B1, CYP24A1, CYP11A1, and GC). Genotyping was performed using the custom-designed 533,631 SNP Illumina OncoArray with imputation to the 1,000 Genomes Phase 3 v5 reference set in 755 EOC cases, including 537 high-grade serous (HGSOC), and 1,235 controls. All subjects are of African ancestry (AA). Logistic regression was performed to estimate odds ratios (OR) and 95% confidence intervals (CI). We further evaluated statistical significance of selected SNPs using the Bayesian False Discovery Probability (BFDP). A significant association with EOC was identified in the UGT2A1/2 region for the SNP rs10017134 (per allele OR = 1.4, 95% CI = 1.2-1.7, P = 1.2 × 10-6 , BFDP = 0.02); and an association with HGSOC was identified in the EGFR region for the SNP rs114972508 (per allele OR = 2.3, 95% CI = 1.6-3.4, P = 1.6 × 10-5 , BFDP = 0.29) and in the UGT2A1/2 region again for rs1017134 (per allele OR = 1.4, 95% CI = 1.2-1.7, P = 2.3 × 10-5 , BFDP = 0.23). Genetic variants in the EGFR and UGT2A1/2 may increase susceptibility of EOC in AA women. Future studies to validate these findings are warranted. Alterations in EGFR and UGT2A1/2 could perturb enzyme efficacy, proliferation in ovaries, impact and mark susceptibility to EOC.

Fasting-Induced Transcription Factors Repress Vitamin D Bioactivation, a Mechanism for Vitamin D Deficiency in Diabetes

Low 25-hydroxyvitamin D levels correlate with the prevalence of diabetes; however, the mechanisms remain uncertain. Here, we show that nutritional deprivation-responsive mechanisms regulate vitamin D metabolism. Both fasting and diabetes suppressed hepatic cytochrome P450 (CYP) 2R1, the main vitamin D 25-hydroxylase responsible for the first bioactivation step. Overexpression of coactivator peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), induced physiologically by fasting and pathologically in diabetes, resulted in dramatic downregulation of CYP2R1 in mouse hepatocytes in an estrogen-related receptor α (ERRα)-dependent manner. However, PGC-1α knockout did not prevent fasting-induced suppression of CYP2R1 in the liver, indicating that additional factors contribute to the CYP2R1 repression. Furthermore, glucocorticoid receptor (GR) activation repressed the liver CYP2R1, suggesting GR involvement in the regulation of CYP2R1. GR antagonist mifepristone partially prevented CYP2R1 repression during fasting, suggesting that glucocorticoids and GR contribute to the CYP2R1 repression during fasting. Moreover, fasting upregulated the vitamin D catabolizing CYP24A1 in the kidney through the PGC-1α-ERRα pathway. Our study uncovers a molecular mechanism for vitamin D deficiency in diabetes and reveals a novel negative feedback mechanism that controls crosstalk between energy homeostasis and the vitamin D pathway.

A genetic variant of CYP2R1 identified in a cat with type 1B vitamin D-dependent rickets: a case report

Background

Vitamin D-dependent rickets is rare in animals and humans. Several types of this condition are associated with genetic variants related to vitamin D metabolism. This is the first report of type 1B vitamin D-dependent rickets in a cat.

Case presentation

Here, we describe the case of a 3-month-old female domestic short-haired cat previously fed on commercial kitten food that presented at our clinic with seizures, lethargy, and generalized pain. Serum and ionized calcium concentrations and 1,25-dihydroxycholecalciferol in this cat were low, and radiographs showed skeletal demineralization and abnormally wide growth plates on the long bones. Initially, simple vitamin D deficiency was suspected; however, the cat’s profile, which included fed a well-balanced commercial diet, together with the findings of additional laboratory tests and the cat’s unresponsiveness to various treatments, raised the suspicion of vitamin D-dependent rickets. Examination of the DNA sequences of CYP2R1 and CYP27B1 genes, which are genes linked with vitamin D metabolism, showed a CYP2R1 frameshift mutation in exon 5 (where T is deleted at position c.1386). This mutation alters the amino acid sequence from position 462, while the stop codon introduced at position 481 prematurely truncates the 501 amino acid full-length protein. With this knowledge, a new treatment regime based on a standard dose of calcitriol was started and this markedly improved the cat’s condition.

Conclusions

To the best of our knowledge, the present case is the first description of type 1B vitamin D-dependent rickets linked with a genetic variant of CYP2R1 in a cat.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1784-1) contains supplementary material, which is available to authorized users.

Shedding Light on Vitamin D Status and Its Complexities during Pregnancy, Infancy and Childhood: An Australian Perspective

Ensuring that the entire Australian population is Vitamin D sufficient is challenging, given the wide range of latitudes spanned by the country, its multicultural population and highly urbanised lifestyle of the majority of its population. Specific issues related to the unique aspects of vitamin D metabolism during pregnancy and infancy further complicate how best to develop a universally safe and effective public health policy to ensure vitamin D adequacy for all. Furthermore, as Australia is considered a “sunny country”, it does not yet have a national vitamin D food supplementation policy. Rickets remains very uncommon in Australian infants and children, however it has been recognised for decades that infants of newly arrived immigrants remain particularly at risk. Yet vitamin D deficiency rickets is entirely preventable, with the caveat that when rickets occurs in the absence of preexisting risk factors and/or is poorly responsive to adequate treatment, consideration needs to be given to genetic forms of rickets.

Physiological regulation of phosphate by vitamin D, parathyroid hormone (PTH) and phosphate (Pi)

Inorganic phosphate (Pi) is an abundant element in the body and is essential for a wide variety of key biological processes. It plays an essential role in cellular energy metabolism and cell signalling, e.g. adenosine and guanosine triphosphates (ATP, GTP), and in the composition of phospholipid membranes and bone, and is an integral part of DNA and RNA. It is an important buffer in blood and urine and contributes to normal acid-base balance. Given its widespread role in almost every molecular and cellular function, changes in serum Pi levels and balance can have important and untoward effects. Pi homoeostasis is maintained by a counterbalance between dietary Pi absorption by the gut, mobilisation from bone and renal excretion. Approximately 85% of total body Pi is present in bone and only 1% is present as free Pi in extracellular fluids. In humans, extracellular concentrations of inorganic Pi vary between 0.8 and 1.2 mM, and in plasma or serum Pi exists in both its monovalent and divalent forms (H2PO4- and HPO42-). In the intestine, approximately 30% of Pi absorption is vitamin D regulated and dependent. To help maintain Pi balance, reabsorption of filtered Pi along the renal proximal tubule (PT) is via the NaPi-IIa and NaPi-IIc Na+-coupled Pi cotransporters, with a smaller contribution from the PiT-2 transporters. Endocrine factors, including, vitamin D and parathyroid hormone (PTH), as well as newer factors such as fibroblast growth factor (FGF)-23 and its coreceptor α-klotho, are intimately involved in the control of Pi homeostasis. A tight regulation of Pi is critical, since hyperphosphataemia is associated with increased cardiovascular morbidity in chronic kidney disease (CKD) and hypophosphataemia with rickets and growth retardation. This short review considers the control of Pi balance by vitamin D, PTH and Pi itself, with an emphasis on the insights gained from human genetic disorders and genetically modified mouse models.

Haplotypes in the CYP2R1 gene are associated with levels of 25(OH)D and bone mineral density, but not with other markers of bone metabolism (MrOS Sweden)

Objective

Polymorphisms in the CYP2R1 gene encoding Vitamin D 25-hydroxylase have been reported to correlate with circulating levels of 25-OH vitamin D3 (25(OH)D). It is unknown whether these variations also affect overall bone metabolism. In order to elucidate the overall associations of polymorphisms in the CYP2R1, we studied haplotype tagging single nucleotide polymorphisms (SNPs) in the gene and serum levels of 25(OH)D, calcium, phosphate, parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF23), as well as bone mineral density (BMD).

Methods

Baseline data on serum parameters and BMD from MrOS Sweden, a prospective population-based cohort study of elderly men (mean age 75 years, range 69–81), were analyzed. Genotyping was performed for eight SNPs covering the CYP2R1 gene in 2868 men with available samples of DNA. Subjects were followed up concerning incidence of fracture during five years.

Results

There was a significant genetic association with circulating levels of 25(OH)D (4.6–18.5% difference in mean values between SNP alleles), but there were no correlations with levels of calcium, phosphate, PTH or FGF23 for any genetic variant. No differences were found in fracture incidence between the variants. There was an inverse relationship between lower BMD and concomitant higher 25(OH)D for three of the haplotypes (p < 0.005).

Conclusions

Common variants in the CYP2R1 gene encoding Vitamin D 25-hydroxylase correlate with levels of circulating 25(OH)D but do not otherwise associate with measures of calcium and phosphate homeostasis. Presence of the specific haplotypes may be an indicator of risk for low 25(OH)D levels, and may in addition be correlated to bone mineral density.

MANAGEMENT OF ENDOCRINE DISEASE: Therapeutics of Vitamin D

OBJECTIVE

The central role of vitamin D in bone health is well recognized. However, controversies regarding its clinical application remain. We therefore aimed to review the definition of hypovitaminosis D, the skeletal and extra-skeletal effects of vitamin D and the available therapeutic modalities.

DESIGN

Narrative and systematic literature review.

METHODS

An international working group that reviewed the current evidence linking bone and extra-skeletal health and vitamin D therapy to identify knowledge gaps for future research.

RESULTS

Findings from observational studies and randomized controlled trials (RCTs) in vitamin D deficiency are discordant, with findings of RCTs being largely negative. This may be due to reverse causality with the illness itself contributing to low vitamin D levels. The results of many RCTs have also been inconsistent. However, overall evidence from RCTs shows vitamin D reduces fractures (when administered with calcium) in the institutionalized elderly. Although controversial, vitamin D reduces acute respiratory tract infections (if not given as bolus monthly or annual doses) and may reduce falls in those with the lowest serum 25-hydroxyvitamin D (25OHD) levels. However, despite large ongoing RCTs with 21 000–26 000 participants not recruiting based on baseline 25OHD levels, they will contain a large subset of participants with vitamin D deficiency and are adequately powered to meet their primary end-points.

CONCLUSIONS

The effects of long-term vitamin D supplementation on non-skeletal outcomes, such as type 2 diabetes mellitus (T2DM), cancer and cardiovascular disease (CVD) and the optimal dose and serum 25OHD level that balances extra-skeletal benefits (T2DM) vs risks (e.g. CVD), may soon be determined by data from large RCTs.

Effects of CYP2R1 gene variants on vitamin D levels and status: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

CYP2R1 is a key gene in the vitamin D metabolic pathway. It has been suggested that CYP2R1 gene variants in European populations are associated with concentrations of 25(OH)D, a biomarker of vitamin D levels and status in peripheral blood. However, a comprehensive meta-analysis of this effect including different ethnicities has never been conducted. The objective of this meta-analysis was to evaluate the association between CYP2R1 gene variants and 25(OH)D levels and vitamin D status.

METHODS

PubMed, EMBASE, Web of Science, CNKI and Wanfang databases were systematically searched up to May 2018. Reporting followed PRISMA guidelines. The quality of the evidence was assessed using the STREGA system. Random or fixed effects model combined estimates and sub-group tested for ethnic differences. The I² statistic quantified between-study variation due to heterogeneity.

RESULTS

Sixteen articles with a total of 52,417 participants met the inclusion criteria and were included in the meta-analysis. For rs10741657, GG genotype was associated with a clear descending trend of 25(OH)D levels when compared with the AA genotype [SMD = -2.32, 95% CI (-4.42, -0.20); SMD = -3.46, 95% CI (-6.60, -0.33) and SMD = -0.24, 95% CI (-0.51, -0.03) for total, Caucasian and Asian groups, respectively] with the following heterogeneities I² = 37.9%, 69.2% and 24.5%, respectively. However, under the AG/AA genetic model, significant changes in 25(OH)D levels [SMD and 95% CI: -1.27(-2.32, -0.23)] were only evident in the Caucasian population. The meta-analysis on vitamin D deficiency showed that the risk-allele G was associated with an increased risk of vitamin D deficiency (OR = 1.09; 95% CI = 1.03-1.15, P = 0.002). The association between rs10741657 and increased risk of vitamin D deficiency was significant (OR = 1.42; 95% CI = 1.11-1.83, P = 0.006) under the dominant model (GG + AG/AA), but not under the recessive model (GG/AG + AA), (OR = 1.28; 95% CI = 0.89-1.84, P = 0.181). There was no evidence of publication bias.

CONCLUSION

Published articles provide evidence supporting a major role for the rs10741657 polymorphism of the CYP2R1 gene in determining 25(OH)D levels and the presence of vitamin D deficiency.

Is calcifediol better than cholecalciferol for vitamin D supplementation?

Modest and even severe vitamin D deficiency is widely prevalent around the world. There is consensus that a good vitamin D status is necessary for bone and general health. Similarly, a better vitamin D status is essential for optimal efficacy of antiresorptive treatments. Supplementation of food with vitamin D or using vitamin D supplements is the most widely used strategy to improve the vitamin status. Cholecalciferol (vitamin D₃) and ergocalciferol (vitamin D₂) are the most widely used compounds and the relative use of both products depends on historical or practical reasons. Oral intake of calcifediol (25OHD₃) rather than vitamin D itself should also be considered for oral supplementation. We reviewed all publications dealing with a comparison of oral cholecalciferol with oral calcifediol as to define the relative efficacy of both compounds for improving the vitamin D status. First, oral calcifediol results in a more rapid increase in serum 25OHD compared to oral cholecalciferol. Second, oral calcifediol is more potent than cholecalciferol, so that lower dosages are needed. Based on the results of nine RCTs comparing physiologic doses of oral cholecalciferol with oral calcifediol, calcifediol was 3.2-fold more potent than oral cholecalciferol. Indeed, when using dosages ≤ 25 μg/day, serum 25OHD increased by 1.5 ± 0.9 nmol/l for each 1 μg cholecalciferol, whereas this was 4.8 ± 1.2 nmol/l for oral calcifediol_. Third, oral calcifediol has a higher rate of intestinal absorption and this may have important advantages in case of decreased intestinal absorption capacity due to a variety of diseases. A potential additional advantage of oral calcifediol is a linear dose-response curve, irrespective of baseline serum 25OHD, whereas the rise in serum 25OHD is lower after oral cholecalciferol, when baseline serum 25OHD is higher. Finally, intermittent intake of calcifediol results in fairly stable serum 25OHD compared with greater fluctuations after intermittent oral cholecalciferol.

Using stable isotope tracers to study bone metabolism in children

Skeletal mineralization is initiated in utero and continues throughout childhood and adolescence. During these key periods of the life cycle, calcium retention must increase significantly to provide sufficient mineral for bone deposition and skeletal growth. Stable calcium isotopes have served as a fundamental tool to non-invasively characterize the dynamic changes in calcium physiology that occur from infancy through adolescence. These approaches have helped define the dynamics of calcium absorption and utilization in healthy children and in children with chronic diseases. As data in this area have accumulated, new areas of emphasis are beginning to characterize the determinants of variability in mineral retention, the genetic determinants of bone turnover and calcium flux and the impact of the gut microbiome on whole body and niche specific calcium dynamics. Advances in these areas will help define calcium utilization in paediatric populations and provide information that may be useful in maximizing bone acquisition across this critical phase of the life cycle.

Inherited Variation in Vitamin D Genes and Type 1 Diabetes Predisposition

The etiology and pathophysiology of type 1 diabetes remain largely elusive with no established concepts for a causal therapy. Efforts to clarify genetic susceptibility and screening for environmental factors have identified the vitamin D system as a contributory pathway that is potentially correctable. This review aims at compiling all genetic studies addressing the vitamin D system in type 1 diabetes. Herein, association studies with case control cohorts are presented as well as family investigations with transmission tests, meta-analyses and intervention trials. Additionally, rare examples of inborn errors of vitamin D metabolism manifesting with type 1 diabetes and their immune status are discussed. We find a majority of association studies confirming a predisposing role for vitamin D receptor (VDR) polymorphisms and those of the vitamin D metabolism, particularly the CYP27B1 gene encoding the main enzyme for vitamin D activation. Associations, however, are tenuous in relation to the ethnic background of the studied populations. Intervention trials identify the specific requirements of adequate vitamin D doses to achieve vitamin D sufficiency. Preliminary evidence suggests that doses may need to be individualized in order to achieve target effects due to pharmacogenomic variation.

Osteocalcin, a bone-derived hormone with important andrological implications

Increasing evidence disclosed the existence of a novel multi-organ endocrine pathway, involving bone, pancreas and testis, of high penetrance in energy metabolism and male fertility. The main mediator of this axis is undercarboxylated osteocalcin (ucOC), a bone-derived protein-exerting systemic effects on tissues expressing the metabotropic receptor GPRC6A. The recognized effects of ucOC are the improvement of insulin secretion from the pancreas, the amelioration of systemic insulin sensitivity, in particular in skeletal muscle, and the stimulation of the global endocrine activity of the Leydig cell, including vitamin D 25-hydroxylation and testosterone production. The supporting evidence of this circuit in both animal and human models is here reviewed, with particular emphasis on the role of ucOC on testis function. The possible pharmacological modulation of this hormonal circuit for therapeutic aims is also discussed.

The Biphasic Effect of Vitamin D on the Musculoskeletal and Cardiovascular System

This narrative review summarizes beneficial and harmful vitamin D effects on the musculoskeletal and cardiovascular system. Special attention is paid to the dose-response relationship of vitamin D with clinical outcomes. In infants and adults, the risk of musculoskeletal diseases is highest at circulating 25-hydroxyvitamin D (25OHD) concentrations below 25 nmol/L and is low if 40-60 nmol/L are achieved. However, evidence is also accumulating that in elderly people the risk of falls and fractures increases again at circulating 25OHD levels > 100 nmol/L. Cohort studies report a progressive increase in cardiovascular disease (CVD) events at 25OHD levels < 50 nmol/L. Nevertheless, meta-analyses of randomized controlled trials suggest only small beneficial effects of vitamin D supplements on surrogate parameters of CVD risk and no reduction in CVD events. Evidence is accumulating for adverse vitamin D effects on CVD outcomes at 25OHD levels > 100 nmol/L, but the threshold may be influenced by the level of physical activity. In conclusion, dose-response relationships indicate deleterious effects on the musculoskeletal system and probably on the cardiovascular system at circulating 25OHD levels < 40-60 nmol/L and >100 nmol/L. Future studies should focus on populations with 25OHD levels < 40 nmol/L and should avoid vitamin D doses achieving 25OHD levels > 100 nmol/L.