Search Results (13)

There is evidence that calcitriol is the only biologically active vitamin D metabolite. This review summarizes data on the regulation of renal and extrarenal synthesis of calcitriol by nutritional, physiologic, mechanical, genetic, and disease-related factors. Relatively low circulating calcitriol due to low substrate availability, i.e., low circulating 25-hydroxyvitamin D, has been reported in nutritional rickets, osteomalacia, obesity, and preeclampsia. In these situations, vitamin D supplementation can increase circulating calcitriol and, together with calcium, prevent rickets/osteomalacia and reduce the risk of preeclampsia and obesity-related type 2 diabetes mellitus. However, the correction of low circulating calcitriol due to mechanical unloading/immobilization by vitamin D supplementation is not effective in preventing osteoporotic fractures. Circulating calcitriol is also low in diseases such as cardiac and renal failure. Both illnesses share some other similarities regarding dysregulated calcium/phosphate metabolism, including elevated parathyroid hormone and fibroblast growth factor-23, suggesting similar treatment strategies. Genetic disorders of vitamin D metabolism are rare and can affect circulating calcitriol differently. Calcitriol synthesis in immune cells is obviously not primarily dependent on circulating 25-hydroxyvitamin D, which challenges the use of vitamin D for infection prevention. Since various factors can differently influence calcitriol regulation, more personalized preventive/therapeutic strategies of targeting calcitriol synthesis are necessary. Full article

Background: Vitamin D-dependent rickets type 1A (VDDR1A) is a rare autosomal recessive disorder caused by mutations in the CYP27B1 gene, leading to a deficiency in active vitamin D (1,25-dihydroxyvitamin D). This study examines the genotypic and phenotypic characteristics of VDDR1A in Vietnamese children. Patients and Methods: A retrospective analysis was conducted on 19 Vietnamese children diagnosed with VDDR1A. Clinical, radiological, biochemical, and molecular data were collected. Rickets Severity Scores (RSSs), biochemical parameters, and height standard deviation scores (HtSDSs) were used to assess the severity of the condition. Results: The study included 19 children from 17 families (ten males and nine females). The median age of rickets diagnosis was 19.2 months, while with VDDR1A, the median time of diagnosis was 7.5 months. Common symptoms among the children included thickened wrists and ankles (19/19), genu varum or genu valgum (18/19), failure to thrive (18/19), rachitic rosary (12/19), and delayed walking (11/19). The radiographic features showed that all children had cupping, splaying, and fraying, twelve children had rachitic rosary, and six exhibited pseudofractures. The biochemical findings showed severe hypocalcemia, normal or mildly low serum phosphate, elevated alkaline phosphatase and parathyroid hormone levels, and normal serum 25-hydroxyvitamin D levels. Genetic analysis identified biallelic CYP27B1 variants, including one known pathogenic frameshift mutation, c.1319_1325dup p.(Phe443Profs*24), one novel likely pathogenic missense variant, c.616C>T p.(Arg206Cys), and one novel pathogenic frameshift mutation, c.96_97del p.(Ala33Thrfs*299). The c.1319_1325dup p.(Phe443Profs*24) variant was the most common, present in 18 out of 19 children. Conclusions: The children with VDDR1A in this study presented with growth failure and skeletal deformities. Key findings included severe hypocalcemia, elevated alkaline phosphatase and parathyroid hormone levels, normal or elevated 25(OH)D, and high RSSs. Predominant frameshift mutations in CYP27B1, especially c.1319_1325dup, highlighted the importance of early genetic diagnosis for optimal management. Additionally, two novel CYP27B1 variants were identified, expanding the known mutation spectrum of VDDR1A. Full article

Background: Vitamin D-dependent rickets type 1A (VDDR1A) is a rare autosomal recessive disorder caused by pathogenic variants in the CYP27B1 gene, typically characterized by growth failure, rickets, leg bowing, fracture, seizures, hyperparathyroidism, hypocalcemia, high-alkaline phosphatase, high or normal 25(OH)D3, and low 1,25(OH)2D3. Methods: We studied two siblings in a Mexican family with an atypical form of VDDR1A. In addition to the typical features of VDDR1A, the proband showed cafe au lait spots, small teeth, and grayish sclera, with hypophosphatemia, normocalcemia, and normal 25(OH)D3; the proband’s brother showed grayish sclera. The proband underwent next generation sequencing. Sanger sequencing was performed in the proband, his brother, the parents, and 100 healthy controls validate the detected variant. Results: Both brothers presented with a recurrent variant NM_000785.3; c.1319_1325dupCCCACCC and a novel nonsense variant NM_000785.3; c.227G>A in the CYP27B1 gene. Conclusions: Calcitriol treatment had a better response in proband´s younger brother. We describe the first Mexican family with an atypical form of VDDR1A associated with a novel nonsense variant, the results contribute to the phenotypic spectrum and increase the pool of pathogenic variants in CYP27B1. Data suggest that nonsense-truncating variants play a significant role in the severity of VDDR1A. Full article

Vitamin D hydroxylation in the liver/kidney results in conversion to its physiologically active form of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃]. 1,25(OH)₂D₃ controls gene expression through the nuclear vitamin D receptor (VDR) mainly expressed in intestinal epithelial cells. Cytochrome P450 (CYP) 24A1 is a catabolic enzyme expressed in the kidneys. Interestingly, a recently identified mutation in another CYP enzyme, CYP3A4 (gain-of-function), caused type III vitamin D-dependent rickets. CYP3A are also expressed in the intestine, but their hydroxylation activities towards vitamin D substrates are unknown. We evaluated CYP3A or CYP24A1 activities on vitamin D action in cultured cells. In addition, we examined the expression level and regulation of CYP enzymes in intestines from mice. The expression of CYP3A or CYP24A1 significantly reduced 1,25(OH)₂D₃-VDRE activity. Moreover, in mice, Cyp24a1 mRNA was significantly induced by 1,25(OH)₂D₃ in the intestine, but a mature form (approximately 55 kDa protein) was also expressed in mitochondria and induced by 1,25(OH)₂D₃, and this mitochondrial enzyme appears to hydroxylate 25OHD₃ to 24,25(OH)₂D₃. Thus, CYP3A or CYP24A1 could locally attenuate 25OHD₃ or 1,25(OH)₂D₃ action, and we suggest the small intestine is both a vitamin D target tissue, as well as a newly recognized vitamin D-metabolizing tissue. Full article

Vitamin D has been known to exert a wide range of physiological effects, including calcemic, osteogenic, anticancer, and immune responses. We previously generated genetically modified (GM) rats and performed a comparative analysis of their physiological properties to elucidate the roles of vitamin D and vitamin D receptor (VDR). In this study, our primary goal was to investigate the manifestations of type II rickets in rats with the VDR(H301Q) mutation, analogous to the human VDR(H305Q). Additionally, we created a double-mutant rat with the VDR(R270L/H301Q) mutation, resulting in almost no affinity for 1,25-dihydroxy-vitamin D3 (1,25D3) or 25-hydroxy-vitamin D3 (25D3). Notably, the plasma calcium concentration in Vdr(R270L/H301Q) rats was significantly lower than in wild-type (WT) rats. Meanwhile, Vdr(H301Q) rats had calcium concentrations falling between those of Vdr(R270L/H301Q) and WT rats. GM rats exhibited markedly elevated plasma parathyroid hormone and 1,25D3 levels compared to those of WT rats. An analysis of bone mineral density in the cortical bone of the femur in both GM rats revealed significantly lower values than in WT rats. Conversely, the bone mineral density in the trabecular bone was notably higher, indicating abnormal bone formation. This abnormal bone formation was more pronounced in Vdr(R270L/H301Q) rats than in Vdr(H301Q) rats, highlighting the critical role of the VDR-dependent function of 1,25D3 in bone formation. In contrast, neither Vdr(H301Q) nor Vdr(R270L/H301Q) rats exhibited symptoms of alopecia or cyst formation in the skin, which were observed in the Vdr-KO rats. These findings strongly suggest that unliganded VDR is crucial for maintaining the hair cycle and normal skin. Our GM rats hold significant promise for comprehensive analyses of vitamin D and VDR functions in future research. Full article

Phosphorus is essential for all living organisms. It plays an important role in maintaining biological functions, such as energy metabolism, cell membrane formation, and bone mineralization. Various factors in the intestine, kidneys, and bones regulate the homeostasis of the inorganic phosphate (Pi) concentration in the body. X-linked hypophosphatemia (XLH), the most common form of hereditary hypophosphatemic rickets, is characterized by an impaired mineralization of the bone matrix, hypertrophic chondrocytes with hypophosphatemia, and active vitamin D resistance in childhood. Phosphate-regulating gene with homologies to endopeptidases on the X chromosome was recognized as the responsible gene for XLH. XLH is classified as fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets. The enhanced FGF23 stimulates renal phosphate wasting by downregulating sodium-dependent Pi cotransporters, NaPi2a and NaPi2c proteins, in the proximal tubules. Recently, transmembrane protein (Tmem) 174 has been identified as a novel regulator of phosphate transporters. This review introduces the role of Tmem174 in the Pi homeostasis in the body. Full article

Background: Vitamin D has a role in the pathogenesis of many medical disorders, especially those of the central nervous system. It is essential in maintaining the bone health of children. However, patients with epilepsy are at high risk of developing vitamin D deficiency due to antiseizure medications (ASMs). Therefore, we aimed to assess the prevalence of vitamin D deficiency and related risk factors in children with epilepsy. Methods: This is the baseline report of a pragmatic, randomized, controlled, open-label trial that assessed the impact of vitamin D supplementation in preventing vitamin D deficiency (NCT03536845). We included children with epilepsy aged 2–16 years who were treated with ASMs from December 2017 to March 2021. Children with preexisting vitamin D metabolism problems, vitamin-D-dependent rickets, malabsorption syndromes, renal disease, and hepatic disease were excluded. The baseline demographic data, anthropometric measurements, seizure types, epilepsy syndromes, ASMs, and seizure control measures were recorded. Blood tests for vitamin D (25-hydroxyvitamin D [25(OH)D), serum calcium, serum phosphorus, and parathyroid hormone levels were performed. Based on vitamin D concentration, patients were categorized as deficient (<50 nmol/L), insufficient (74.9–50 nmol/L), or normal (>75 nmol/L). Results: Of 159 recruited children, 108 (67.92%) had generalized seizures, 44 (27.67%) had focal seizures, and 7 (4.4%) had unknown onset seizures. The number of children receiving monotherapy was 128 (79.0%) and 31 (19.1%) children were receiving polytherapy. The mean vitamin D concentration was 60.24 ± 32.36 nmol/L; 72 patients (45.28%) had vitamin D deficiency and 45 (28.3%) had vitamin D insufficiency. No significant difference in vitamin D concentration was observed between children receiving monotherapy and those receiving polytherapy. The main risk factors of vitamin D deficiency were obesity and receiving enzyme-inducer ASMs. Conclusions: The prevalence of vitamin D deficiency was high among children with epilepsy. Obese children with epilepsy and those on enzyme-inducer ASMs were at increased risk for vitamin D deficiency. Further studies are needed to establish strategies to prevent vitamin D deficiency. Full article

Hereditary metabolic bone diseases are characterized by genetic abnormalities in skeletal homeostasis and encompass one of the most diverse groups among rare diseases. In this review, we examine 25 selected hereditary metabolic bone diseases and recognized genetic variations of 78 genes that represent each of the three groups, including sclerosing bone disorders, disorders of defective bone mineralization and disorder of bone matrix and cartilage formation. We also review pathophysiology, manifestation and treatment for each disease. Advances in molecular genetics and basic sciences has led to accurate genetic diagnosis and novel effective therapeutic strategies for some diseases. For other diseases, the genetic basis and pathophysiology remain unclear. Further researches are therefore crucial to innovate ways to overcome diagnostic challenges and develop effective treatment options for these orphan diseases. Full article

Vitamin D is essential for the normal mineralization of bones during childhood. Although diet and adequate sun exposure should provide enough of this nutrient, there is a high prevalence of vitamin D deficiency rickets worldwide. Children with certain conditions that lead to decreased vitamin D production and/or absorption are at the greatest risk of nutritional rickets. In addition, several rare genetic alterations are also associated with severe forms of vitamin-D-resistant or -dependent rickets. Although vitamin D3 is the threshold nutrient for the vitamin D endocrine system (VDES), direct measurement of circulating vitamin D3 itself is not a good marker of the nutritional status of the system. Calcifediol (or 25(OH)D) serum levels are used to assess VDES status. While there is no clear consensus among the different scientific associations on calcifediol status, many clinical trials have demonstrated the benefit of ensuring normal 25(OH)D serum levels and calcium intake for the prevention or treatment of nutritional rickets in childhood. Therefore, during the first year of life, infants should receive vitamin D treatment with at least 400 IU/day. In addition, a diet should ensure a normal calcium intake. Healthy lifestyle habits to prevent vitamin D deficiency should be encouraged during childhood. In children who develop clinical signs of rickets, adequate treatment with vitamin D and calcium should be guaranteed. Children with additional risk factors for 25(OH)D deficiency and nutritional rickets should be assessed periodically and treated promptly to prevent further bone damage. Full article

Classically, a secosteroid hormone, vitamin D, has been implicated in calcium and phosphate homeostasis and has been associated with the pathogenesis of rickets and osteomalacia in patients with severe nutritional vitamin D deficiency. The spectrum of known vitamin D-mediated effects has been expanded in recent years. However, the mechanisms of how exactly this hormone elicits its biological function are still not fully understood. The interaction of this metabolite with the vitamin D receptor (VDR) and, subsequently, with the vitamin D-responsive element in the region of specific target genes leading to the transcription of genes whose protein products are involved in the traditional function of calcitriol (known as genomic actions). Moreover, in addition to these transcription-dependent mechanisms, it has been recognized that the biologically active form of vitamin D₃, as well as its immediate precursor metabolite, calcifediol, initiate rapid, non-genomic actions through the membrane receptors that are bound as described for other steroid hormones. So far, among the best candidates responsible for mediating rapid membrane response to vitamin D metabolites are membrane-associated VDR (VDRm) and protein disulfide isomerase family A member 3 (Pdia3). The purpose of this paper is to provide an overview of the rapid, non-genomic effects of calcifediol and calcitriol, whose elucidation could improve the understanding of the vitamin D₃ endocrine system. This will contribute to a better recognition of the physiological acute functions of vitamin D₃, and it could lead to the identification of novel therapeutic targets able to modulate these actions. Full article

We have developed an in vitro system to easily examine the affinity for vitamin D receptor (VDR) and CYP24A1-mediated metabolism as two methods of assessing vitamin D derivatives. Vitamin D derivatives with high VDR affinity and resistance to CYP24A1-mediated metabolism could be good therapeutic agents. This system can effectively select vitamin D derivatives with these useful properties. We have also developed an in vivo system including a Cyp27b1-gene-deficient rat (a type I rickets model), a Vdr-gene-deficient rat (a type II rickets model), and a rat with a mutant Vdr (R270L) (another type II rickets model) using a genome editing method. For Cyp27b1-gene-deficient and Vdr mutant (R270L) rats, amelioration of rickets symptoms can be used as an index of the efficacy of vitamin D derivatives. Vdr-gene-deficient rats can be used to assess the activities of vitamin D derivatives specialized for actions not mediated by VDR. One of our original vitamin D derivatives, which displays high affinity VDR binding and resistance to CYP24A1-dependent metabolism, has shown good therapeutic effects in Vdr (R270L) rats, although further analysis is needed. Full article

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. Full article

Objective: Clarify the concept of vitamin D sufficiency, the relationship between efficacy and vitamin D status and the role of Vitamin D supplementation in the management of non-skeletal diseases. We outline reasons for anticipating different serum vitamin D levels are required for different diseases. Method: Review the literature for evidence of efficacy of supplementation and minimum effective 25-hydroxyvitamin D (25-OHD) levels in non-skeletal disease. Results: Evidence of efficacy of vitamin supplementation is graded according to levels of evidence. Minimum effective serum 25-OHD levels are lower for skeletal disease, e.g., rickets (25 nmol/L), osteoporosis and fractures (50 nmol/L), than for premature mortality (75 nmol/L) or non-skeletal diseases, e.g., depression (75 nmol/L), diabetes and cardiovascular disease (80 nmol/L), falls and respiratory infections (95 nmol/L) and cancer (100 nmol/L). Conclusions: Evidence for the efficacy of vitamin D supplementation at serum 25-OHD levels ranging from 25 to 100 nmol/L has been obtained from trials with vitamin D interventions that change vitamin D status by increasing serum 25-OHD to a level consistent with sufficiency for that disease. This evidence supports the hypothesis that just as vitamin D metabolism is tissue dependent, so the serum levels of 25-OHD signifying deficiency or sufficiency are disease dependent. Full article