Synergism of CYP2R1 and CYP27B1 polymorphisms and susceptibility to type 1 diabetes in Egyptian children

Evaluation of serum vitamin D metabolites, phagocytosis, and biomarkers of inflammation in dogs with naturally occurring diabetes mellitus

Naturally occurring diabetes mellitus (NODM) is one of the most common endocrine disorders in dogs and its etiology closely resembles type 1 diabetes mellitus (T1DM) in people. Human patients with T1DM commonly have cellular derangements consistent with inflammation, impaired immune function, and hypovitaminosis D. There is little information available regarding inflammatory biomarkers, immune function, and vitamin D status in diabetic dogs. Therefore, our objectives were to assess inflammatory biomarkers, vitamin D metabolites, and phagocytic capacity in diabetic dogs and determine whether associations exist with these variables and the level of clinical control or vitamin D metabolites. This was a prospective case-control study that included 20 otherwise healthy diabetic dogs (clinically controlled, n = 10; uncontrolled, n = 10) and 20 non-diabetic, healthy, age (± 2 years), breed, and sex matched controls. Complete blood count, biochemical panel, urinalysis, and fructosamine were performed at a single commercial reference laboratory. Basal plasma tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8, and IL-10 were measured using a canine-specific multiplex bead-based assay. Serum C-reactive protein (CRP) was measured using a commercially available ELISA kit. Serum 25-hydroxyvitamin (OH)D3 and 24,25-dihydroxyvitamin (OH)2D3 were measured with HPLC. Phagocytosis of opsonized-Escherichia coli (E. coli) was evaluated with flow cytometry. Diabetic dogs had higher serum CRP concentrations than controls (p = 0.02). Plasma IL-8 concentrations were higher in diabetic dogs with uncontrolled clinical disease compared to controls (p = 0.02). Diabetic dogs had a lower percentage of leukocytes that phagocytized opsonized-E. coli (p = 0.02), but an increased number of bacteria phagocytized per cell (p < 0.001) compared to controls. No between-group differences were identified in vitamin D metabolites, nor were associations found between vitamin D and any variables. Fructosamine had a positive association with serum CRP concentration (rho = 0.35, p = 0.03) and number of bacteria phagocytized per cell (rho = 0.45, p = 0.004) in our cohort (n = 40). Like people with T1DM, diabetic dogs have a proinflammatory phenotype and phagocytic dysregulation that may be correlated with glycemic control.

CTSG polymorphisms in Chinese children with type 1 diabetes mellitus

Cathepsin G (CTSG) plays an important role in the regulation of immune processes. Accumulated studies show that CTSG is involved in the onset and development of type 1 diabetes mellitus (T1DM). As the genetic background of T1DM varies widely among populations, we aimed to study the relationship between genetic polymorphisms in CTSG and T1DM susceptibility in Chinese populations. A total of 141 patients with T1DM and 200 healthy controls were enrolled in the study. Serum CTSG expression was detected using enzyme-linked immunosorbent assay (ELISA). Genotyping of two selected single nucleotide polymorphisms (SNPs) (rs2236742 and rs2070697) of CTSG was performed using PCR and Sanger sequencing. CTSG expression in patients with T1DM was significantly higher than in the control group. Alleles C and T of CTSG SNP rs2236742 were increased in T1DM. No significant associations were found for the SNP rs2070697. Our results indicate that the CTSG rs2236742 allele (C/T) is associated with T1DM in Chinese children and may serve as a new biomarker for predicting T1DM susceptibility.

Exploring the link between vitamin D deficiency and obstructive sleep apnea: A comprehensive review

Despite the high prevalence and significant health burden of obstructive sleep apnea (OSA), its underlying pathophysiology remains incompletely understood. This comprehensive review explores the emerging connection between vitamin D deficiency and OSA, discusses potential mechanisms underlying this association, and explores the therapeutic implications of these findings. Recent research has consistently highlighted the high incidence of vitamin D deficiency among patients with OSA, which often occurs independently of geographical location. This suggests that factors beyond lack of sunlight exposure may be involved. This review also discusses how reduced vitamin D may be associated with more severe manifestations of OSA. In addition, it explores the potentiality of using vitamin D supplements as a therapeutic strategy for OSA, noting that some studies have found improvements in sleep quality and a reduction in OSA severity. Potential mechanisms are proposed, including the role of vitamin D deficiency in promoting inflammation, oxidative stress, hypoxia, impairing immune function, muscle function, and gene polymorphism of vitamin D receptors, all of which could contribute to the pathogenesis of obstructive sleep apnea. The paper underscores the need for future research to validate these observations, to determine optimal vitamin D supplementation dosage and duration, to explore potential side effects and risks, and to investigate potential interactions with other treatments.

Analysis of single nucleotide polymorphisms associated with the vitamin D pathway in the placentas of women with gestational diabetes mellitus: a laboratory study

BACKGROUND

The aim of this study was to analyze the single nucleotide polymorphisms (SNPs) of genes known to be involved in vitamin D metabolism in the placenta using the placental tissue of mothers diagnosed with gestational diabetes mellitus (GDM) to determine whether the SNPs and occurrence of GDM are related.

METHODS

We enrolled 80 women of the same gestational age, 40 with and 40 without GDM. The placenta was obtained from each woman after delivery and SNP genotyping was performed on seven SNPs in the CYP27B1 (rs10877012), CYP24A1 (rs2248359, rs6013897, and rs2209314), and GC (rs2282679, rs16847024, and rs3733359) genes. Maternal serum 25-hydroxyvitamin D levels were measured during the first trimester of pregnancy and before delivery.

RESULTS

At the time of delivery, vitamin D levels were lower (21.05±12.05 mg/dL vs. 31.31±20.72 mg/dL, p=0.012) and the frequency of vitamin D deficiency was higher (60.7% vs. 32.5%, p=0.040) in the GDM group. In women with GDM, the G allele of rs10877012 was more common (86.3% vs. 65.0%, p=0.002). The rs10877012 GG genotype was more common in the GDM group (72.5% vs. 42.5%, p=0.007) and the rs10877012 TT genotype was more common in the control group (12.5% vs. 0%, p=0.007).

CONCLUSION

Mothers with GDM have lower serum concentrations of vitamin D before delivery than healthy controls and vitamin D deficiency is common. A polymorphism in CYP27B1 (rs10877012), is considered to be a cause of GDM pathogenesis.

Single nucleotide polymorphisms in vitamin D binding protein and 25-hydroxylase genes affect vitamin D levels in adolescents of Arab ethnicity in Kuwait

Vitamin D deficiency (VDD) is widespread in the Arab world despite ample sunshine throughout the year. In our previous study, lifestyle and socio-demographic factors could explain only 45% of variability in vitamin D levels in Kuwaiti adolescents, suggesting that genetics might contribute to VDD in this region. Single nucleotide polymorphisms (SNP) in the 25-hydroxylase (CYP2R1) and the GC globulin (GC) genes have been reported to affect vitamin D levels in various ethnic groups in adults. In this study, we investigated the association of two SNPs from GC (rs4588 and rs7041) and three SNPs from CYP2R1 (rs10741657, rs11023374 and rs12794714) with vitamin D levels and VDD in a nationally representative sample of adolescents of Arab ethnicity from Kuwait. Multivariable linear regression, corrected for age, sex, parental education, governorate, body mass index, and exposure to sun, demonstrated that each of the 5 study variants showed significant associations with plasma 25(OH)D levels in one or more of the additive, recessive, and dominant genetic models - the rs10741657 under all the three models, rs12794714 under both the additive and recessive models, rs7041 under the recessive model; and rs4588 and rs11023374 under the dominant model. Minor alleles at rs4588 (T), rs7041 (A), rs11023374 (C), and rs12794714 (A) led to a decrease in plasma 25(OH)D levels - rs4588:[β (95%CI) = -4.522 (-8.66,-0.38); p=0.033]; rs7041:[β (95%CI) = -6.139 (-11.12,-1.15); p=0.016]; rs11023374:[β (95%CI) = -4.296 (-8.18,-0.40); p=0.031]; and rs12794714:[β (95%CI) = -3.498 (-6.27,-0.72); p=0.014]. Minor allele A at rs10741657 was associated with higher levels of plasma 25(OH)D levels [β (95%CI) = 4.844 (1.62,8.06); p=0.003)] and lower odds of vitamin D deficiency (OR 0.40; p=0.002). These results suggest that the CYP2R1 and GC SNP variants are partly responsible for the high prevalence of VDD in Kuwait. Genotyping these variants may be considered for the prognosis of VDD in Kuwait.

Single-nucleotide polymorphisms as important risk factors of diabetes among Middle East population

Diabetes is a chronic metabolic disorder that leads to the dysfunction of various tissues and organs, including eyes, kidneys, and cardiovascular system. According to the World Health Organization, diabetes prevalence is 8.8% globally among whom about 90% of cases are type 2 diabetes. There are not any significant clinical manifestations in the primary stages of diabetes. Therefore, screening can be an efficient way to reduce the diabetic complications. Over the recent decades, the prevalence of diabetes has increased alarmingly among the Middle East population, which has imposed exorbitant costs on the health care system in this region. Given that the genetic changes are among the important risk factors associated with predisposing people to diabetes, we examined the role of single-nucleotide polymorphisms (SNPs) in the pathogenesis of diabetes among Middle East population. In the present review, we assessed the molecular pathology of diabetes in the Middle East population that paves the way for introducing an efficient SNP-based diagnostic panel for diabetes screening among the Middle East population. Since, the Middle East has a population of 370 million people; the current review can be a reliable model for the introduction of SNP-based diagnostic panels in other populations and countries around the world.

Progress in the Relationship between Vitamin D Deficiency and the Incidence of Type 1 Diabetes Mellitus in Children

Type 1 diabetes mellitus (T1DM) is an autoimmune disease, due to a large number of islet β cells damaged, resulting in an absolute lack of insulin, ultimately relying on insulin therapy. Vitamin D is a fat-soluble sterol derivative that not only participates in calcium and phosphorus metabolism but also acts as an immunomodulatory role by binding to nuclear vitamin D receptors to regulate the expression of transcription factors. Increasing evidence has shown that vitamin D has immunoregulation and anti-inflammatory effects, and it may play a role in T cell regulatory responses due to downregulation in the expression of cathepsin G and inhibition of CD4+ T cell activation and protection of β cells from immune attack and is beneficial in decreasing oxidative stress in T1DM patients. Epidemiologic evidence demonstrates involvement of vitamin D deficiency in T1DM pathogenesis, with the immune system improperly targeting and destroying its own islet β cells. In addition, polymorphisms in genes critical for vitamin D metabolism may increase the risk of islet autoimmunity and T1DM. In this paper, the relationship between vitamin D deficiency and the molecular mechanism of T1DM was discussed.

Vitamin D levels and Vitamin D-related gene polymorphisms in Chinese children with type 1 diabetes

Low vitamin D levels may play a role in type 1 diabetes (T1D) susceptibility. Since 25(OH)D synthesis is genetically regulated, single nucleotide polymorphisms (SNPs) of important genes have also been shown to modulate the risk of T1D, so this study aimed to investigate the relationship between five SNPs in CYP2R1, DHCR7, CYP24A1, VDR genes, serum 25(OH)D levels and T1D in Chinese children. This case-control study included 141 T1D patients and 200 age-matched healthy children.25 (OH) D concentration was determined, genotyping was performed by High resolution melting (HRM). There was a significant difference in the prevalence of vitamin D deficiency, insufficiency, and sufficiency between T1D and healthy controls. (χ ² = 10.86, p = 0.004), however no evidence of the association between any group of SNPs and circulating 25(OH) D levels was observed. The allele distribution of CYP2R1(rs1993116) was significantly different between T1D and control group (p = 0.040), and the C allele carriers of rs1993116 had a higher risk of T1D than the T allele carriers, Carriers of the CC and CT genotypes of rs1993116 have higher T1D risk than those carrying the TT genotype. GMDR analysis revealed a significant interaction between CYP2R1(rs12794714) and CYP2R1(rs1993116) in the risk of T1D with a maximum testing balance accuracy of 60.39%.

Integrated bioinformatics analysis reveals novel key biomarkers in diabetic nephropathy

Objectives:

The underlying molecular mechanisms of diabetic nephropathy have yet not been investigated clearly. In this investigation, we aimed to identify key genes involved in the pathogenesis and prognosis of diabetic nephropathy.

Methods:

We downloaded next-generation sequencing data set GSE142025 from Gene Expression Omnibus database having 28 diabetic nephropathy samples and nine normal control samples. The differentially expressed genes between diabetic nephropathy and normal control samples were analyzed. Biological function analysis of the differentially expressed genes was enriched by Gene Ontology and REACTOME pathways. Then, we established the protein–protein interaction network, modules, miRNA-differentially expressed gene regulatory network and transcription factor-differentially expressed gene regulatory network. Hub genes were validated by using receiver operating characteristic curve analysis.

Results:

A total of 549 differentially expressed genes were detected including 275 upregulated and 274 downregulated genes. The biological process analysis of functional enrichment showed that these differentially expressed genes were mainly enriched in cell activation, integral component of plasma membrane, lipid binding, and biological oxidations. Analyzing the protein–protein interaction network, miRNA-differentially expressed gene regulatory network and transcription factor-differentially expressed gene regulatory network, we screened hub genes MDFI, LCK, BTK, IRF4, PRKCB, EGR1, JUN, FOS, ALB, and NR4A1 by the Cytoscape software. The receiver operating characteristic curve analysis confirmed that hub genes were of diagnostic value.

Conclusions:

Taken above, using integrated bioinformatics analysis, we have identified key genes and pathways in diabetic nephropathy, which could improve our understanding of the cause and underlying molecular events, and these key genes and pathways might be therapeutic targets for diabetic nephropathy.

Vitamin D and Type 1 Diabetes Risk: A Systematic Review and Meta-Analysis of Genetic Evidence

Several observational studies have examined vitamin D pathway polymorphisms and their association with type 1 diabetes (T1D) susceptibility, with inconclusive results. We aimed to perform a systematic review and meta-analysis assessing associations between selected variants affecting 25-hydroxyvitamin D [25(OH)D] and T1D risk. We conducted a systematic search of Medline, Embase, Web of Science and OpenGWAS updated in April 2021. The following keywords “vitamin D” and/or “single nucleotide polymorphisms (SNPs)” and “T1D” were selected to identify relevant articles. Seven SNPs (or their proxies) in six genes were analysed: CYP2R1 rs10741657, CYP2R1 (low frequency) rs117913124, DHCR7/NADSYN1 rs12785878, GC rs3755967, CYP24A1 rs17216707, AMDHD1 rs10745742 and SEC23A rs8018720. Seven case-control and three cohort studies were eligible for quantitative synthesis (n = 10). Meta-analysis results suggested no association with T1D (range of pooled ORs for all SNPs: 0.97–1.02; p > 0.01). Heterogeneity was found in DHCR7/NADSYN1 rs12785878 (I²: 64.8%, p = 0.02). Sensitivity analysis showed exclusion of any single study did not alter the overall pooled effect. No association with T1D was observed among a Caucasian subgroup. In conclusion, the evidence from the meta-analysis indicates a null association between selected variants affecting serum 25(OH)D concentrations and T1D.

Identification of hub genes related to the progression of type 1 diabetes by computational analysis

BACKGROUND

Type 1 diabetes (T1D) is a serious threat to childhood life and has fairly complicated pathogenesis. Profound attempts have been made to enlighten the pathogenesis, but the molecular mechanisms of T1D are still not well known.

METHODS

To identify the candidate genes in the progression of T1D, expression profiling by high throughput sequencing dataset GSE123658 was downloaded from Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) were identified, and gene ontology (GO) and pathway enrichment analyses were performed. The protein-protein interaction network (PPI), modules, target gene - miRNA regulatory network and target gene - TF regulatory network analysis were constructed and analyzed using HIPPIE, miRNet, NetworkAnalyst and Cytoscape. Finally, validation of hub genes was conducted by using ROC (Receiver operating characteristic) curve and RT-PCR analysis. A molecular docking study was performed.

RESULTS

A total of 284 DEGs were identified, consisting of 142 up regulated genes and 142 down regulated genes. The gene ontology (GO) and pathways of the DEGs include cell-cell signaling, vesicle fusion, plasma membrane, signaling receptor activity, lipid binding, signaling by GPCR and innate immune system. Four hub genes were identified and biological process analysis revealed that these genes were mainly enriched in cell-cell signaling, cytokine signaling in immune system, signaling by GPCR and innate immune system. ROC curve and RT-PCR analysis showed that EGFR, GRIN2B, GJA1, CAP2, MIF, POLR2A, PRKACA, GABARAP, TLN1 and PXN might be involved in the advancement of T1D. Molecular docking studies showed high docking score.

CONCLUSIONS

DEGs and hub genes identified in the present investigation help us understand the molecular mechanisms underlying the advancement of T1D, and provide candidate targets for diagnosis and treatment of T1D.

Association of Vitamin D Pathway Gene CYP27B1 and CYP2R1 Polymorphisms with Autoimmune Endocrine Disorders: A Meta-Analysis

BACKGROUND

Studies on organ-specific autoimmune endocrine disorders showed correlations between disease risks and vitamin D pathways gene variants, such as CYP27B1 rs10877012 and rs4646536, or CYP2R1 rs10741657 single nucleotide polymorphisms. However, previous works presented inconsistent conclusions. Our study aimed at assessing the association of CYP27B1 and CYP2R1 polymorphisms with autoimmune endocrine disorder susceptibility using the meta-analysis method.

METHODS

Case-control studies of the subject of interest were identified from the databases Pubmed, Embase, Cochrane Library, and China National Knowledge Infrastructure. Studies that met inclusion and quality criteria were pooled. Observational outcomes were diagnosis of autoimmune Addison's disease, Graves disease, Hashimoto thyroiditis, or type 1 diabetes mellitus. Statistical analysis was performed using software STATA 16.0.

RESULTS

A total of 14 studies involving 12 929 patients (2243 autoimmune Addison disease, 1253 Graves disease, 612 Hashimoto thyroiditis, 8821 type 1 diabetes), and 12 907 healthy control subjects were pooled for meta-analysis. The rs10877012 minor allele A and its homozygote and heterozygote conferred low overall disease risk (OR [odds ratio] = 0.748, 95% CI [confidence interval] 0.620-0.902 in dominant model; OR = 0.709, 95% CI 0.571-0.879 in recessive model; OR = 0.777, 95% CI 0.674-0.895 in the allele model). The population carrying rs4646536 minor allele C and its homozygote and heterozygote showed decreased overall autoimmune endocrine disorders risk (OR = 0.849, 95% CI 0.748-0.963; OR = 0.868, 95% CI 0.790-0.955; OR = 0.915, 95% CI 0.875-0.957 in the dominant, recessive, and allele model, respectively). No significant genetic association was found for rs10741657.

CONCLUSION

Our study suggested CYP27B1 polymorphisms rs10877012 minor allele A and rs4646536 minor allele C were negatively related to susceptibilities of organ-specific autoimmune endocrine diseases.

Autoimmune thyroid disease and type 1 diabetes mellitus: same pathogenesis; new perspective?

Autoimmune thyroid disease (AITD) and type 1 diabetes mellitus (T1DM) are two common autoimmune diseases that can occur concomitantly. In general, patients with diabetes have a high risk of AITD. It has been proposed that a complex genetic basis together with multiple nongenetic factors make a variable contribution to the pathogenesis of T1DM and AITD. In this paper, we summarize current knowledge in the field regarding potential pathogenic factors of T1DM and AITD, including human leukocyte antigen, autoimmune regulator, lymphoid protein tyrosine phosphatase, forkhead box protein P3, cytotoxic T lymphocyte-associated antigen, infection, vitamin D deficiency, and chemokine (C-X-C motif) ligand. These findings offer an insight into future immunotherapy for autoimmune diseases.

Association study between genetic variants in vitamin D metabolism related genes and childhood autism spectrum disorder

Vitamin D deficiency has been implicated as a risk factor for autism spectrum disorder (ASD). This case-controlled study was to determine the association between single nucleotide polymorphisms (SNPs) in genes encoding vitamin D metabolism related enzymes and childhood ASD in a Chinese Han population. Both autistic children and age-and gender-matched healthy controls were recruited from September 2012-November 2017. The severity of ASD was evaluated by the childhood autism rating scale (CARS). Taqman probe based real-time PCR was applied to examine genotypes. The association between SNPs and the risk of ASD or the disease severity was examined through the logistic regression. This study recruited 249 children with ASD and 353 healthy controls. The G/A genotype (P = 0.0112) or the G allele (P = 0.0117) of CYP24A1 rs17219315, and the G/A genotype of CYP27B1 rs4646536 (P = 0.0341) were significantly associated with an increased risk of ASD. In addition, multivariate analysis found that A allele of both CYP2R1 rs12794714 (P = 0.0159) and CYP27B1 rs4646536 (P = 0.0268) were significantly associated with the severity of ASD. Genetic polymorphisms in vitamin D metabolism related enzymes are associated with the risk of childhood ASD and the severity of the disease.

Vitamin D in Type 2 Diabetes: Genetic Susceptibility and the Response to Supplementation

Variants of vitamin D metabolism-genes may predispose to type 2 diabetes (T2D). This study investigated the impact of these variants on disease susceptibility, Vitamin D, parathyroid hormone, C-peptide and HbA1c levels before and after cholecalciferol supplementation in patients with T2D.Twelve polymorphisms within CYP2R1, CYP27B1, DBP, VDR and CYP24A1 were genotyped in 553 T2D patients and 916 controls. In addition 65 patients receiving either cholecalciferol or placebo were analyzed during 6 months intervention and 6 months follow-up.T2D risk alleles are VDR rs7975232 "G" (p_c=0.031), rs1544410 "G" (p_c=0.027) and CYP2R1 rs10741657 "A" (p_c=0.016). Patients with genotypes CYP27B1 rs10877012 "CC" (p_c=4x10^-5), DBP rs7041 "GG" (p_c=0.003), rs4588 "CC" (p_c = 3x10^-4), CYP24A1 rs2585426 "CG" (p_c=0.006) and rs2248137 "CG" (p_c=0.001) showed lower 25(OH)D3 and DBP rs4588 "CC" lower 1,25(OH)2D3 levels (p_c=0.005). Whereas DBP rs4588 "CC" (p_c=0.009), CYP27B1 rs10877012 "AC" (p_c=0.059), VDR rs7975323 "AG" (p_c=0.033) and rs1544410 "GG" (p_c=0.013) are associated with higher 25(OH)D3 levels at 6 months' follow-up. Significant PTH suppression was detected for CYP2R1 "AG" (p_c=0.002), DBP rs4588 "CC" (p_c<0.001), VDR rs110735810 "CT" (p_c<0.001) and CYP24A1 rs2248137 "GG" (p_c=0.021).Genetic variants of the vitamin D system predispose to type 2 diabetes and regulate - partially - vitamin D metabolism, concentrations and the vitamin D status. Vitamin D insufficiency is a T2D risk factor. The response to cholecalciferol supplementation can be measured as 25(OH)D3 increment and PTH suppression. This process is regulated by genes of the vitamin D system conferring modest T2D risk.

Vitamin D effects and endocrine diseases

A lack of vitamin D has been linked to autoimmune diseases including type 1 diabetes, autoimmune thyroiditis and to obesity. The prevalence of vitamin D deficiency is higher in diabetic or obese children and patients with thyroiditis compared to healthy controls. Moreover, low vitamin D values seem to be associated with major complications and poor glycemic control, in particular in obese children. Supplementation with vitamin D, which has immune-regulatory properties, may support our therapies and improve the outcomes in different diseases. Although some studies suggest a possible role of vitamin D in the etiology of autoimmune diseases and obesity, data on supplementation benefits are inconclusive and further studies are needed. In this paper, we focus on the current evidence regarding vitamin D function in endocrine diseases and possible benefits of its supplementation in pediatric age.

Influence of Vitamin D on Islet Autoimmunity and Beta-Cell Function in Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease leading to immune-mediated destruction of pancreatic beta cells, resulting in the need for insulin therapy. The incidence of T1D is increasing worldwide, thus prompting researchers to investigate novel immunomodulatory strategies to halt autoimmunity and modify disease progression. T1D is considered as a multifactorial disease, in which genetic predisposition and environmental factors interact to promote the triggering of autoimmune responses against beta cells. Over the last decades, it has become clear that vitamin D exerts anti-inflammatory and immunomodulatory effects, apart from its well-established role in the regulation of calcium homeostasis and bone metabolism. Importantly, the global incidence of vitamin D deficiency is also dramatically increasing and epidemiologic evidence suggests an involvement of vitamin D deficiency in T1D pathogenesis. Polymorphisms in genes critical for vitamin D metabolism have also been shown to modulate the risk of T1D. Moreover, several studies have investigated the role of vitamin D (in different doses and formulations) as a potential adjuvant immunomodulatory therapy in patients with new-onset and established T1D. This review aims to present the current knowledge on the immunomodulatory effects of vitamin D and summarize the clinical interventional studies investigating its use for prevention or treatment of T1D.

Vitamin D level and gene polymorphisms in Korean children with type 1 diabetes

BACKGROUND

Vitamin D metabolism has been associated with type 1 diabetes.

OBJECTIVE

We aimed to clarify the association of 25-hydroxylase (CYP2R1) and 1α-hydroxylase (CYP27B1) with risk of developing type 1 diabetes in Korean children.

METHODS

In total, 252 children (96 type 1 diabetes and 156 healthy controls) under the age of 20 years were recruited. Serum 25-hydroxyvitamin D (25OHD) and 1α,25-dihydroxyvitamin D [1α,25(OH)₂ D] levels were determined. Allelic, genotypic, and haplotypic distribution of CYP2R1 (rs12794714, rs10766196, rs10741657, rs2060793, and rs10766197) and CYP27B1 (rs4646536, rs10877012, and rs3782130) polymorphisms were determined. Clinical and biochemical data were analyzed according to genotype.

RESULTS

Mean vitamin D level was considerably lower, and vitamin D deficiency was more prevalent in children with type 1 diabetes than in healthy controls. The GG genotype of CYP2R1 rs12794714 and AA genotype of CYP2R1 rs10766196 were significantly associated with risk of developing type 1 diabetes (odds ratio 2.00, 95% confidence interval 1.176-3.413 and odds ratio 1.88, 95% confidence interval 1.103-3.195, respectively). The GG+GA genotype of CYP2R1 rs12794714 and AA+AG genotype of CYP2R1 rs10766196 were associated with prevalent vitamin D deficiency in children with type 1 diabetes. These genotypes did not differ with respect to glycosylated hemoglobin and daily insulin requirement.

CONCLUSIONS

Serum 25OHD and 1α,25(OH)₂ D levels were lower in children with type 1 diabetes than in healthy controls. CYP2R1 rs12794714 and rs10766196 polymorphisms were associated with a higher risk of type 1 diabetes. Thus, polymorphisms in vitamin D metabolism may contribute to susceptibility to type 1 diabetes in Korean children.

Role of cytochrome P450 polymorphisms and functions in development of ulcerative colitis

Cytochromes P450s (CYPs) are terminal enzymes in CYP dependent monooxygenases, which constitute a superfamily of enzymes catalysing the metabolism of both endogenous and exogenous substances. One of their main tasks is to facilitate the excretion of these substances and eliminate their toxicities in most phase 1 reactions. Endogenous substrates of CYPs include steroids, bile acids, eicosanoids, cholesterol, vitamin D and neurotransmitters. About 80% of currently used drugs and environmental chemicals comprise exogenous substrates for CYPs. Genetic polymorphisms of CYPs may affect the enzyme functions and have been reported to be associated with various diseases and adverse drug reactions among different populations. In this review, we discuss the role of some critical CYP isoforms (CYP1A1, CYP2D6, CYP2J2, CYP2R1, CYP3A5, CYP3A7, CYP4F3, CYP24A1, CYP26B1 and CYP27B1) in the pathogenesis or aetiology of ulcerative colitis concerning gene polymorphisms. In addition, their significance in metabolism concerning ulcerative colitis in patients is also discussed showing a clear underestimation in genetic studies performed so far.

The role of vitamin D in the pathogenesis and treatment of diabetes mellitus: a narrative review

Diabetes mellitus, a metabolic disorder associated with chronic complications, is traditionally classified into two main subtypes. Type 1 diabetes mellitus (T1DM) results from gradual pancreatic islet β cell autoimmune destruction, extending over months or years. Type 2 diabetes mellitus (T2DM) is a heterogeneous disorder, with both insulin resistance and impairment in insulin secretion contributing to its pathogenesis. Vitamin D is a fat-soluble vitamin with an established role in calcium metabolism. Recently, several studies have provided evidence suggesting a role for it in various non-skeletal metabolic conditions, including both types of diabetes mellitus. Preclinical studies of vitamin D action on insulin secretion, insulin action, inflammatory processes, and immune regulation, along with evidence of an increase of hypovitaminosis D worldwide, have prompted several epidemiological, observational, and supplementation clinical studies investigating a potential biological interaction between hypovitaminosis D and diabetes. This narrative review aims to summarize current knowledge on the effect of vitamin D on T1DM and T2DM pathogenesis, prevention, and treatment, as well as on micro- and macrovascular complications of the disease. Furthermore, on the basis of current existing evidence, we aim to highlight areas for potential future research.

Molecular evidence of role of vitamin D deficiency in various extraskeletal diseases

BACKGROUND

Role of vitamin D is not only limited to skeletal system but various other systems of the body, such as immune system, endocrine system, and cardiopulmonary system.

MATERIALS AND METHODS

It is supported by the confirmations of systems-wide expression of vitamin D receptor (VDR), endocrinal effect of calcitriol, and its role in immune responses.

RESULTS

Expression of VDR in various systems, immunoregulatory and hormonal response of vitamin D and deficiency of vitamin D may establish various pathologies in the body.

CONCLUSION

This review provides molecular evidence of relation of vitamin D with extra skeletal.

Vitamin D and Type I Diabetes

Vitamin D is a fat-soluble vitamin that plays an important role in bone metabolism but is also endowed with the capability of modulating inflammatory and immune function. Recent studies reported a relationship between low vitamin D levels and several autoimmune diseases such as Type 1 Diabetes. Vitamin D regulates the expression of over 200 genes, also related to immune modulation, suggesting a putative role in these diseases pathogenesis. This review overviews the most recent advances on the association between vitamin D and increased risk of Type 1 Diabetes as well as between vitamin D and either glucose homeostasis or insulin sensitivity. The effects of vitamin D in modulating the immune response and balancing anti-inflammatory cytokines, suggest that vitamin D system may represent an unforeseen target for the design of novel strategies for the treatment of patients with autoimmune diseases and in particular Type 1 Diabetes.

Immunomodulatory Effect of Vitamin D and Its Potential Role in the Prevention and Treatment of Type 1 Diabetes Mellitus-A Narrative Review

Type 1 diabetes mellitus is a chronic autoimmune disease associated with degeneration of pancreatic β-cells that results in an inability to produce insulin and the need for exogenous insulin administration. It is a significant global health problem as the incidence of this disorder is increasing worldwide. The causes are still poorly understood, although it certainly has genetic and environmental origins. Vitamin D formed profusely in the skin upon exposure to sunlight, as well as from dietary sources, exhibits an immunomodulatory effect based on gene transcription control. Indeed, vitamin D can downregulate mechanisms connected with adaptive immunity, induce immunological tolerance and decrease auto-aggression-related inflammation. These properties provide the basis for a preventive and therapeutic role of vitamin D. As many studies have demonstrated, appropriate supplementation with vitamin D reduces the risk of autoimmune diseases, including type 1 diabetes mellitus, and alleviates disease symptoms in patients. The aim of this narrative review is to present the molecular mechanisms for the vitamin D immunomodulatory effect as well as review human clinical studies on the use of vitamin D as adjuvant therapy in type 1 diabetes mellitus.

Triangular relationship between CYP2R1 gene polymorphism, serum 25(OH)D3 levels and T2DM in a Chinese rural population

BACKGROUND

A low serum vitamin D concentration is associated with an increased risk of type 2 diabetes mellitus (T2DM). Recently, several single nucleotid polymorphisms (SNPs) have been identified which influence vitamin D levels. If a causal relationship exists between vitamin D concentrations and T2DM, one would expect a similar association between the newly identified SNPs and T2DM risk. Therefore, this study investigated the association between four SNPs of cytochrome P450 family 2, subfamily R, peptide 1 (CYP2R1) gene, serum 25(OH)D₃ levels and T2DM.

METHODS

Three hundred and ninety-seven patients with confirmed T2DM, as well as 397 age- and gender-matched controls were enrolled in this case-control study. Genotyping was performed by TaqMan probe assays. Kruskal-Wallis one-way analysis and muitiple logistic regression analysis were performed to identify the possible risk genotype for vitamin D levels and T2DM, respectively. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the gene-gene and gene-environment interactions.

RESULTS

The serum 25(OH)D₃ levels were significant lower in the T2DM group. Significant differences were observed between patients and controls in terms of the genotype distributions of rs1993116 (P = 0.048) and rs10766197 (P = 0.024). Similarly, rs1993116 and rs10766197 polymorphisms were found to be significantly associated with T2DM risk. AG + GG genotype carriers of the rs1993116 and rs10766197 polymorphisms could have an increased risk of developing T2DM compared with AA carriers, the OR and 95% CI were 1.64 (1.09-2.46) and 1.76 (1.18-2.65), respectively. However, none of the tested SNPs were independently associated with serum 25(OH)D₃ levels (P > 0.059). Gene-gene and gene-environment interaction analyses indicated that rs12794714-rs10766197 and rs12794714-vitamin D deficiency (VDD) models successfully predicted T2DM risk (P < 0.001).

CONCLUSIONS

Rs1993116 and rs10766197 polymorphisms of CYP2R1 gene may be novel genetic markers for T2DM in China. Given the lack of association between SNPs and serum 25(OH)D₃ levels, well-designed future studies should be conducted with larger sample sizes in rural areas of China.

Genetic polymorphisms of CYP2S1, CYP2J2 and CYP2R1 genes in three Chinese populations: Han, Tibetan and Uighur

AIM

Cytochrome P450 enzymes CYP2S1, CYP2J2 and CYP2R1 are of interest due to their unknown enzymatic function and disease-specific expression property. The aim of this study was to investigate the genetic variations of CYP2S1, CYP2J2 and CYP2R1 genes, and their polymorphic distribution in different Chinese populations.

MATERIALS & METHODS

All of the exons, exon-intron boundaries and 1 kb 5'-flanking region of the three genes were sequenced in 150 Chinese subjects.

RESULTS

There were 21, 15 and nine genetic variants identified in CYP2S1, CYP2J2 and CYP2R1 genes, respectively. The genetic polymorphisms of CYP2S1 and CYP2J2 showed significant difference. Thr353Ala variant in CYP2S1 protein was predicted to be consistently damaged. The hydrogen bond interactions were decreased in two mutants: Thr353Ala and Cys372Ser. -177C >T in CYP2S1 affected transcription factor EGR1 binding site.

CONCLUSION

This study highlights the importance of genetic polymorphism information on the CYP2S1, CYP2J2  and CYP2R1 genes in Chinese populations.

Genetic polymorphisms of vitamin D3 metabolizing CYP24A1 and CYP2R1 enzymes in Turkish patients with ischemic stroke

Objective Vitamin D deficiency is known as an important risk factor in pathogenesis of atherosclerosis, which contributes to stroke development. Genetic variations including single nucleotide polymorphisms (SNPs) in enzymes involved in vitamin D metabolism can affect susceptibility to the development of stroke. Therefore, the objective of this study was to investigate the association between polymorphisms of vitamin D metabolizing enzymes (rs927650 SNP in CYP24A1, and rs10741657 SNP in CYP2R1 genes,) and ischemic stroke risk in Turkish population. Materials and methods To test this hypothesis, we designed a case-control study which consisted of 256 ischemic stroke patients and 132 controls. Genotypes were determined by PCR-RFLP technique. Results No significant differences were found between patients and controls in terms of CYP24A1 rs927650 and CYP2R1 rs10741657 genotype frequencies. Polymorphic allele frequencies of CYP24A1 rs927650 and CYP2R1 rs10741657 were 0.414 and 0.660 in stroke patients, respectively. Conclusion This is the first study conducted regarding the association of CYP24A1 rs927650 and CYP2R1 rs10741657 genetic polymorphisms and ischemic stroke risk. The polymorphic genotypes of these polymorphisms, together with hypertension, diabetes, smoking, and obesity, were found as significant risk factors for ischemic stroke.

Regulation of Immune Function by Vitamin D and Its Use in Diseases of Immunity

Evidence exists for a role for vitamin D and its active metabolites in modulating immune functions. In animal models, vitamin D deficiency is associated with a higher risk for autoimmunity in genetically predisposed subjects and increases in susceptibility to infections. In addition, high-dose vitamin D can improve immune health, prevent autoimmunity, and improve defense against infections. In humans, evidence exists on associations between vitamin D deficiency and impaired immune function, leading to autoimmunity in genetically predisposed people and increased risk for infections; data on therapeutic immune effects of vitamin D supplementation when vitamin D levels are already sufficient are lacking.

Vitamin D and diabetes mellitus: Causal or casual association?

The incidence of both type 2 and type 1 diabetes mellitus has been increasing worldwide. Vitamin D deficiency, or the awareness of its prevalence, has also been increasing. Vitamin D may have a role in the pathogenic mechanisms predisposing to type 2 diabetes by modulating insulin resistance and/or pancreatic β-cell function. Vitamin D status or elements involved in its activation or transport may also be involved in the development of type 1 diabetes mellitus through immunomodulatory role . Based on these observations a potential association between vitamin D and diabetes has been hypothesized. In this review we discuss up to date evidence linking vitamin D with the development of diabetes. Moreover, the role of vitamin D supplementation in the prevention of both types of diabetes is analysed together with its role in improving glycemic control in diabetic patients. We also address the potential role of vitamin D deficiency in the development of macro- and microvascular complications in diabetes. Finally, we provide recommendation for Vitamin D therapy in diabetes in view of current evidence and highlight areas for potential future research in this area.

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.

SNP rs11185644 of RXRA gene is identified for dose-response variability to vitamin D3 supplementation: a randomized clinical trial

The level of serum 25-Hydroxyvitamin D [25(OH)D] has high heritability, suggesting that genes may contribute to variations in serum 25(OH)D level and vitamin D dose-response. As vitamin D deficiency has been linked to numerous diseases, understanding how genetic variation contributes to vitamin D dose-response is important for personalized vitamin D treatment and cost-effective disease prevention. To identify genetic variants responsible for vitamin D status and dose-response, we performed two vitamin D3 and calcium clinical supplementation trials in 2,207 postmenopausal Caucasian women. We examined the association of 291 SNPs with baseline serum 25(OH)D levels and 25(OH)D dose-response. Five SNPs, rs10500804 (P = 4.93 × 10⁻⁷), rs2060793 (P = 6.63 × 10⁻⁷), rs10741657 (P = 1.49 × 10⁻⁶), rs10766197 (P = 1.05 × 10⁻⁵) and rs11023380 (P = 7.67 × 10⁻⁵) in the CYP2R1 gene, as well as 6 SNPs, rs4588 (P = 7.86 × 10⁻⁷), rs2298850 (P = 1.94 × 10⁻⁶), rs1155563 (P = 6.39 × 10⁻⁶), rs705119 (P = 2.80 × 10⁻⁵), rs705120 (P = 1.08 × 10⁻⁴) and rs222040 (P = 1.59 × 10⁻⁴) in the GC gene were associated with baseline serum 25(OH)D levels. SNP rs11185644 near the RXRA was significantly associated with 25(OH)D dose-response (P = 1.01 × 10⁻⁴). Our data suggest that polymorphisms in the CYP2R1 and GC gene may contribute to variation in baseline serum 25(OH)D concentration, and that polymorphism rs11185644 may contribute to variation in 25(OH)D dose-response in healthy postmenopausal Caucasian women.

Are low sun exposure and/or vitamin D risk factors for type 1 diabetes?

Ultraviolet radiation and vitamin D, with their known immunosuppressive effects, have the potential to delay or inhibit type 1 diabetes.

Genetic Variation in CYP2R1 and GC Genes Associated With Vitamin D Deficiency Status

This cross-sectional study enrolled 180 patients at a private family practice in Virginia. Total serum vitamin D concentrations were obtained weekly from January 30, 2013, through March 30, 2013, in consecutive patients regularly scheduled for laboratory work at the practice. Patients were categorized into 2 groups and analyzed for variant alleles in vitamin D receptor ( VDR; rs2228570), cytochrome P450 2R1 ( CYP2R1; rs10741657), 7-dehydrocholesterol reductase ( DHCR7; rs12785878), and group-specific component ( GC; rs2282679) to determine whether variants of those alleles influenced total serum 25(OH)D concentrations. One-hundred and eighty patients were enrolled, with 40 (22%) being sufficient, 25-hydroxy vitamin D level 25(OH)D ≥ 30 ng/mL, and 140 (78%) being insufficient, 25(OH)D < 30 ng/mL. Of the 4 genes, 2 genes, CYP2R1 (rs10741657) and GC (rs2282679), demonstrated a significant association related to vitamin D status. Subjects with 1 or more variant alleles at rs10741657 were almost 3.7 (odds ratio [OR] 3.67; 95% confidence interval [CI]: 1.35-9.99) times more likely be insufficient in vitamin D and subjects with 1 or more variant alleles at rs2282679 were about half (OR 0.42; 95% CI: 0.18-0.93) as likely to be insufficient in vitamin D. Allelic variations in CYP2R1 (rs10741657) and GC (rs2282679) affect vitamin D levels, but variant alleles on VDR (rs2228570) and DHCR7 (rs12785878) were not correlated with vitamin D deficiency, 25(OH)D < 30 ng/mL.

Association of rs7041 and rs4588 Polymorphisms of the Vitamin D Binding Protein and the rs10741657 Polymorphism of CYP2R1 with Vitamin D Status Among Jordanian Patients

AIM

Previous studies have shown a high prevalence of vitamin D deficiency among Jordanians despite adequate exposure to sunlight, suggesting the presence of other causes for this deficiency. The aim of this study was to identify the relationship between 25-hydroxyvitamin D [25-(OH) VD] status and the nonsynonymous single-nucleotide polymorphisms (SNPs) (rs7041 and rs4588) of the GC gene, which encodes the vitamin D binding protein, and one SNP (rs10741657) near the CYP2R1 gene.

METHODS

Blood samples from 381 subjects (74 males and 307 females, 18-60 years of age) were obtained from the "National Center for Diabetes, Endocrinology and Genetics" (Amman, Jordan). The subjects were classified as "apparently healthy" if they did not suffer from chronic diseases and as "unhealthy" if they suffered from certain chronic diseases. Subjects' genotypes for GC; rs7041 and rs4588; CYP2R1; rs10741657 were determined by the polymerase chain reaction-restriction fragment length polymorphism assay method.

RESULTS

Apparently, healthy subjects had significantly higher 25-(OH) VD levels than unhealthy patients. In apparently healthy subjects, the rs10743657 genotypes containing the variant allele A (AA, GA) were associated with higher 25-(OH) VD levels than the homozygous wild-type genotype (GG). The genotypes containing the variant allele of rs7041 (TT, TG) and rs4588 (AA, AC) were associated with lower 25-(OH) VD levels than the wild-type genotypes (GG and CC, respectively). Haplotype analysis of rs7041 and rs4588 revealed that the haplotypes GC1S and GC1S/S were associated with 25-(OH) VD sufficiency, whereas haplotypes GC1F/S, GC1F/2, GC1S/2, GC2, and GC2/2 were associated with 25-(OH) VD deficiency. In unhealthy patients, only the homozygous genotype of the variant allele of rs7041 (TT) was associated with higher 25-(OH) VD levels, which is the reverse of what had been observed in apparently healthy subjects.

CONCLUSIONS

The rs70141657G/A of CYP2R1 and rs7041T/G and rs4588C/A of vitamin D binding protein genetic polymorphisms were associated with increased risk of vitamin D deficiency among apparently healthy Jordanians.

Vitamin D Actions on CD4(+) T Cells in Autoimmune Disease

This review summarizes and integrates research on vitamin D and CD4⁺ T-lymphocyte biology to develop new mechanistic insights into the molecular etiology of autoimmune disease. A deep understanding of molecular mechanisms relevant to gene–environment interactions is needed to deliver etiology-based autoimmune disease prevention and treatment strategies. Evidence linking sunlight, vitamin D, and the risk of multiple sclerosis and type 1 diabetes is summarized to develop the thesis that vitamin D is the environmental factor that most strongly influences autoimmune disease development. Evidence for CD4⁺ T-cell involvement in autoimmune disease pathogenesis and for paracrine calcitriol signaling to CD4⁺ T lymphocytes is summarized to support the thesis that calcitriol is sunlight’s main protective signal transducer in autoimmune disease risk. Animal modeling and human mechanistic data are summarized to support the view that vitamin D probably influences thymic negative selection, effector Th1 and Th17 pathogenesis and responsiveness to extrinsic cell death signals, FoxP3⁺CD4⁺ T-regulatory cell and CD4⁺ T-regulatory cell type 1 (Tr1) cell functions, and a Th1–Tr1 switch. The proposed Th1–Tr1 switch appears to bridge two stable, self-reinforcing immune states, pro- and anti-inflammatory, each with a characteristic gene regulatory network. The bi-stable switch would enable T cells to integrate signals from pathogens, hormones, cell–cell interactions, and soluble mediators and respond in a biologically appropriate manner. Finally, unanswered questions and potentially informative future research directions are highlighted to speed delivery of etiology-based strategies to reduce autoimmune disease.

[The role of vitamin D3 in the regulation of the mineral metabolism in experimental type 1 diabetes]

Diabetes was shown to be associated with a considerable lowering of 25(OH)D3 in blood serum of mice. Vitamin D3 deficiency was correlated with impaired mineral metabolism in bone tissue, indicating the development of secondary osteoporosis. A decrease in weight, length and diameter (diaphysis, proximal metaepiphysis) of tibia in diabetic animals was observed as compared with control. Diabetes caused hypocalcemia, hypophosphatemia and increased enzymatic activity of alkaline phosphatase (ALP) and its isoenzymes in serum. This changes were accompanied by the impairments of vitamin D3 25-hydroxylase isoforms (CYP27A1 and CYP2R1) expression, which are the main enzymes of cholecalciferol biotransformation to 25(OH)D3 - precursor of hormonally active form of vitamin D3. A decrease in bone resorption processes was established after vitamin D3 administration as it is evident from normalization of bone morphometrical parameters and mineral metabolism in diabetic mice. Vitamin D3 ability to counter diabetes-induced alterations in bone tissue can be ascribed, at least in part, to its positive effects on the formation of vitamin D3 hormonally active forms.

Triangular relationship between single nucleotide polymorphisms in the CYP2R1 gene (rs10741657 and rs12794714), 25-hydroxyvitamin d levels, and coronary artery disease incidence

OBJECTIVE

To investigate the relationship between the rs10741657 and rs12794714 polymorphisms in the CYP2R1 gene, 25(OH)D levels, and coronary artery disease (CAD) incidence.

METHODS

In total, 134 male patients with verified CAD were recruited, alongside 109 age- and sex-matched controls. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism, using the corresponding restriction enzyme for each polymorphism, whereas 25(OH)D levels were analyzed by HPLC-UV.

RESULTS

25(OH)D levels were significantly lower in patients. The genotypic and allelic distributions of the rs10741657 polymorphism were significantly different between patients and controls, whereas insignificant results were obtained for the rs12794714 polymorphism. Furthermore, rs10741657, but not rs12794714, predicted 25(OH)D levels.

CONCLUSION

The rs10741657 polymorphism is a novel genetic marker for CAD.

CYP2R1 is a major, but not exclusive, contributor to 25-hydroxyvitamin D production in vivo

Bioactivation of vitamin D consists of two sequential hydroxylation steps to produce 1α,25-dihydroxyvitamin D3. It is clear that the second or 1α-hydroxylation step is carried out by a single enzyme, 25-hydroxyvitamin D 1α-hydroxylase CYP27B1. However, it is not certain what enzyme or enzymes are responsible for the initial 25-hydroxylation. An excellent case has been made for vitamin D 25-hydroxylase CYP2R1, but this hypothesis has not yet been tested. We have now produced Cyp2r1 (-/-) mice. These mice had greater than 50% reduction in serum 25-hydroxyvitamin D3. Curiously, the 1α,25-dihydroxyvitamin D3 level in the serum remained unchanged. These mice presented no health issues. A double knockout of Cyp2r1 and Cyp27a1 maintained a similar circulating level of 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3. Our results support the idea that the CYP2R1 is the major enzyme responsible for 25-hydroxylation of vitamin D, but clearly a second, as-yet unknown, enzyme is another contributor to this important step in vitamin D activation.