Mutations in CYP24A1 and idiopathic infantile hypercalcemia

Hypervitaminosis D is correlated with adverse dental implant outcomes: A retrospective case-control study

OBJECTIVES

To investigate vitamin-D levels effect on the survival/success and on marginal bone levels of dental implants.

METHODS

Patients with peri-implant disease and healthy control patients with functionally loaded dental implants were included in this retrospective case-control study. Forty patients with 201 implants were in the diseased-cohort, while thirty-three patients with 90 implants were in the control-cohort. Patient blood 25(OH)D levels were assessed through quantitative blood test. The correlation between abnormal 25(OH)D levels and disease status of each patient was assessed using Fisher's exact tests. The correlation of each implant's outcomes with vitamin-D status was assessed using Kaplan-Meier survival analysis and Mann-Whitney U tests.

RESULTS

Patients with blood 25(OH)D levels >70 ng/mL (hypervitaminosis-D) had a 21.1-fold increase in the risk of implant failure or severe peri-implant bone loss regarding patients with intermediate (>30, ≤70 ng/mL) levels. Kaplan-Meier survival analysis revealed that implants in the hypervitaminosis-D cohort had a survival probability of 73.7 % (95 % CI:56.5-84.5 %) at 19-years after surgery, compared to 95 % for implants in patients with intermediate 25(OH)D levels (95 % CI:88.3-97.9 %). Additionally, implants in the hypervitaminosis-D cohort lost bone faster than implants in the intermediate cohort. These results were specific to the patient cohort with elevated blood 25(OH)D levels and not observed in patients taking vitamin-D supplementation. The impact of hypervitaminosis-D was enriched for implants in the maxilla, and not as apparent for implants in the mandible.

CONCLUSIONS

Blood 25(OH)D levels >70 ng/mL were correlated with adverse implant outcomes, including implant failure and peri-implant bone loss, especially in the maxilla.

CLINICAL RELEVANCE

These results suggest that hypervitaminosis D may be a previously unidentified risk factor for dental implant complications and should be further investigated to elucidate the underlying mechanism.

A novel transgenic mouse model highlights molecular disruptions involved in the pathogenesis of Dent disease 1

Dent disease (DD) is a hereditary renal disorder characterized by low molecular weight (LMW) proteinuria and progressive renal failure. Inactivating mutations of the CLCN5 gene encoding the 2Cl-/H+exchanger ClC-5 have been identified in patients with DD type 1. ClC-5 is essentially expressed in proximal tubules (PT) where it is thought to play a role in maintaining an efficient endocytosis of LMW proteins. However, the exact pathological roles of ClC-5 in progressive dysfunctions observed in DD type 1 are still unclear. To address this issue, we designed a mouse model carrying the most representative type of ClC-5 missense mutations found in DD patients. These mice showed a characteristic DD type 1 phenotype accompanied by altered endo-lysosomal system and autophagy functions. With ageing, KI mice showed increased renal fibrosis, apoptosis and major changes in cell metabolic functions as already suggested in previous DD models. Furthermore, we made the interesting new discovery that the Lipocalin-2-24p3R pathway might be involved in the progression of the disease. These results suggest a crosstalk between the proximal and distal nephron in the pathogenesis mechanisms involved in DD with an initial PT impairment followed by the Lipocalin-2 internalisation and 24p3R overexpression in more distal segments of the nephron. This first animal model of DD carrying a pathogenic mutation of Clcn5 and our findings pave the way aimed at finding therapeutic strategies to limit the consequences of ClC-5 disruption in patients with DD type 1 developing chronic kidney disease.

Significance of vitamin D responsiveness on the etiology of vitamin D-related diseases

Vitamin D resistance (VDRES) explains the necessity for higher doses of Vitamin D (VD) than those recommended for treatment success. VD receptor (VDR) signaling blockade, such as that caused by infections and poisons, is one basis for VDRES etiology. Mutations within genes affecting the VD system cause susceptibility to developing low VD responsiveness and autoimmunity. In contrast, VD hypersensitivity (VDHY) occurs if there is extra VD in the body; for example, as a result of an overdose of a VD supplement. Excess 1,25(OH)2D3 is produced in lymphomas and granulomatous diseases. The placenta produces excess 1,25(OH)2D3. Gene mutations regulating the production or degradation of 1,25(OH)2D3 enhance the effects of 1,25(OH)2D3. Increased 1,25(OH)2D3 levels stimulate calcium absorption in the gut, leading to hypercalcemia. Hypercalcemia can result in the calcification of the kidneys, circulatory system, or placenta, leading to kidney failure, cardiovascular disease, and pregnancy complications. The primary treatment involves avoiding exposure to the sun and VD supplements. The prevalence rates of VDRES and VDHY remain unclear. One estimate was that 25%, 51%, and 24% of the patients had strong, medium, and poor responses, respectively. Heavy-dose VD therapy may be a promising method for the treatment of autoimmune diseases; however, assessing its potential side effects is essential. To avoid VD-mediated hypercalcemia, responsiveness must be considered when treating pregnancies or cardiovascular diseases associated with VD. Furthermore, how VD is associated with the related disorders remains unclear. Investigating responsiveness to VD may provide more accurate results.

Infantile hypercalcemia type 1 (HCINF1): a rare disease resulting in nephrolithiasis and nephrocalcinosis caused by mutations in the vitamin D catabolic enzyme, CYP24A1

Infantile hypercalcemia type 1 (HCINF1), formerly known as Lightwood syndrome, is a subtype of hypercalcemia caused by loss-of-function biallelic mutations in the vitamin D catabolic enzyme, CYP24A1, which 24-hydroxylates the hormone 1,25-(OH)2D3. This short review focuses on the main features of the HCINF1 disease; emerging knowledge of the structure and function of the cytochrome P450, CYP24A1 and the location of inactivating mutations; the development of a rapid LC-MS/MS-based laboratory test for defective 24-hydroxylation; and future implications for bioanalytical assay and treatment of all types of vitamin D-related hypercalcemic conditions.

Vitamin D and bone health: What vitamin D can and cannot do

Historically vitamin D deficiency had devastating consequences for children causing rickets resulting in severe bone deformities often leading to death. The mystery of the cause of rickets finally came to light when it was observed that cod liver oil and sunlight could prevent and cure rickets. The first vitamin D to be discovered was vitamin D2 from ergosterol in ultraviolet irradiated yeast. Vitamin D3 was discovered from UV exposure to the skin. Investigations revealed the two major functions of vitamin D were to increase intestinal calcium and phosphate absorption and mobilize calcium from the skeleton to maintain calcium and phosphorus homeostasis. Later studies demonstrated that vitamin D does not have an active role in bone mineralization. Vitamin D deficiency results in secondary hyperparathyroidism increasing bone resorption. As a result, this decreases bone mineral content and compromises the architectural integrity increasing risk for fracture. Vitamin D deficiency has also been shown to enhance aging of the bone causing cracks and enhancing bone fractures. Vitamin D deficiency also causes osteomalacia. Therefore, vitamin D sufficiency is extremely important to maximize bone health throughout life. It helps to prevent bone loss, but it cannot restore bone loss due to increased bone resorption that can occur under a variety of circumstances including menopause. The Endocrine Society Guidelines recommends for all ages that adequate vitamin D obtained from the sun, foods and supplements is necessary in order to maintain a circulating concentration of 25-hydroxyvitamin D of at least 30 ng/mL for maximum bone health.

Loss of 24-hydroxylated catabolism increases calcitriol and fibroblast growth factor 23 and alters calcium and phosphate metabolism in fetal mice

Calcitriol circulates at low levels in normal human and rodent fetuses, in part due to increased 24-hydroxylation of calcitriol and 25-hydroxyvitamin D by 24-hydroxylase (CYP24A1). Inactivating mutations of CYP24A1 cause high postnatal levels of calcitriol and the human condition of infantile hypercalcemia type 1, but whether the fetus is disturbed by the loss of CYP24A1 is unknown. We hypothesized that loss of Cyp24a1 in fetal mice will cause high calcitriol, hypercalcemia, and increased placental calcium transport. The Cyp24a1+/- mice were mated to create pregnancies with wildtype, Cyp24a1+/-, and Cyp24a1 null fetuses. The null fetuses were hypercalcemic, modestly hypophosphatemic (compared to Cyp24a1+/- fetuses only), with 3.5-fold increased calcitriol, 4-fold increased fibroblast growth factor 23 (FGF23), and unchanged parathyroid hormone. The quantitative RT-PCR confirmed the absence of Cyp24a1 and 2-fold increases in S100g, sodium-calcium exchanger type 1, and calcium-sensing receptor in null placentas but not in fetal kidneys; these changes predicted an increase in placental calcium transport. However, placental 45Ca and 32P transport were unchanged in null fetuses. Fetal ash weight and mineral content, placental weight, crown-rump length, and skeletal morphology did not differ among the genotypes. Serum procollagen 1 intact N-terminal propeptide and bone expression of sclerostin and Blgap were reduced while calcitonin receptor was increased in nulls. In conclusion, loss of Cyp24a1 in fetal mice causes hypercalcemia, modest hypophosphatemia, and increased FGF23, but no alteration in skeletal development. Reduced incorporation of calcium into bone may contribute to the hypercalcemia without causing a detectable decrease in the skeletal mineral content. The results predict that human fetuses bearing homozygous or compound heterozygous inactivating mutations of CYP24A1 will also be hypercalcemic in utero but with normal skeletal development.

Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows

The 6th International Conference, "Controversies in Vitamin D," was convened to discuss controversial topics, such as vitamin D metabolism, assessment, actions, and supplementation. Novel insights into vitamin D mechanisms of action suggest links with conditions that do not depend only on reduced solar exposure or diet intake and that can be detected with distinctive noncanonical vitamin D metabolites. Optimal 25-hydroxyvitamin D (25(OH)D) levels remain debated. Varying recommendations from different societies arise from evaluating different clinical or public health approaches. The lack of assay standardization also poses challenges in interpreting data from available studies, hindering rational data pooling and meta-analyses. Beyond the well-known skeletal features, interest in vitamin D's extraskeletal effects has led to clinical trials on cancer, cardiovascular risk, respiratory effects, autoimmune diseases, diabetes, and mortality. The initial negative results are likely due to enrollment of vitamin D-replete individuals. Subsequent post hoc analyses have suggested, nevertheless, potential benefits in reducing cancer incidence, autoimmune diseases, cardiovascular events, and diabetes. Oral administration of vitamin D is the preferred route. Parenteral administration is reserved for specific clinical situations. Cholecalciferol is favored due to safety and minimal monitoring requirements. Calcifediol may be used in certain conditions, while calcitriol should be limited to specific disorders in which the active metabolite is not readily produced in vivo. Further studies are needed to investigate vitamin D effects in relation to the different recommended 25(OH)D levels and the efficacy of the different supplementary formulations in achieving biochemical and clinical outcomes within the multifaced skeletal and extraskeletal potential effects of vitamin D.

Persistent hypercalcaemia associated with two pathogenic variants in the CYP24A1 gene and a parathyroid adenoma-a case report and review

Introduction

24-Hydroxylase, encoded by the CYP24A1 gene, is a crucial enzyme involved in the catabolism of vitamin D. Loss-of-function mutations in CYP24A1 result in PTH-independent hypercalcaemia with high levels of 1,25(OH)2D3. The variety of clinical manifestations depends on age, and underlying genetic predisposition mutations can lead to fatal infantile hypercalcaemia among neonates, whereas adult symptoms are usually mild.

Aim of the study

We report a rare case of an adult with primary hyperparathyroidism and loss-of-function mutations in the CYP24A1 gene and a review of similar cases.

Case presentation

We report the case of a 58-year-old woman diagnosed initially with primary hyperparathyroidism. Preoperatively, the suspected mass adjoining the upper pole of the left lobe of the thyroid gland was found via ultrasonography and confirmed by 99mTc scintigraphy and biopsy as the parathyroid gland. The patient underwent parathyroidectomy (a histopathology report revealed parathyroid adenoma), which led to normocalcaemia. After 10 months, vitamin D supplementation was introduced due to deficiency, and the calcium level remained within the reference range. Two years later, biochemical tests showed recurrence of hypercalcaemia with suppressed parathyroid hormone levels and elevated 1,25(OH)2D3 concentrations. Further investigation excluded the most common causes of PTH-independent hypercalcaemia, such as granulomatous disease, malignancy, and vitamin D intoxication. Subsequently, vitamin D metabolites were measured using LC-MS/MS, which revealed high levels of 25(OH)D3, low levels of 24,25(OH)2D3 and elevated 25(OH)2D3/24,25(OH)2D3 ratios, suggesting a defect in vitamin D catabolism. Molecular analysis of the CYP24A1 gene using the NGS technique revealed two pathogenic variants: p.(Arg396Trp) and p.(Glu143del) (rs114368325 and rs777676129, respectively).

Conclusions

The diagnostic process for hypercalcaemia becomes complicated when multiple causes of hypercalcaemia coexist. The measurement of vitamin D metabolites using LC-MS/MS may help to identify carriers of CYP24A1 mutations. Subsequent molecular testing may contribute to establishing the exact frequency of pathogenic variants of the CYP24A1 gene and introducing personalized treatment.

The Vitamin D Metabolite Diagnostic Ratio Associates With Phenotypic Traits of Idiopathic Hypercalciuria

Introduction

Underlying mechanisms for hypercalciuria remain unknown in most cases; thus, the designation "idiopathic." We hypothesized that the vitamin D-inactivating enzyme, CYP24A1 contributes to the pathogenesis of hypercalciuria in kidney stone formers.

Methods

We conducted association analyses between CYP24A1 activity, estimated by the vitamin D metabolite diagnostic ratio (25(OH) vitamin D3/total 24,25 (OH)2 vitamin D ratio; VMDR), and the phenotype of participants in 2 observational cohorts of kidney stone formers, the Swiss Kidney Stone Cohort (SKSC) and the Bern Kidney Stone Registry (BKSR). Circulating 25(OH)- and 24,25 (OH)2 vitamin D were quantified using a validated liquid chromatography tandem mass spectrometry assay.

Results

A total of 974 participants were included in the analysis. We found a positive association of VMDR (and hence negative association of CYP24A1 activity) with total (β 0.009 mmol/l; 95% confidence interval [CI]: 0.002, 0.016; P = 0.02) and ionized plasma calcium (β 0.005 mmol/l; 95% CI: 0.002, 0.008; P < 0.01), absolute and fractional excretion of urinary calcium (β 0.054 mmol/24h; 95% CI: 0.010, 0.097; P = 0.02 and β 0.046%; 95% CI: 0.018, 0.074; P < 0.01, respectively). Further, VMDR was associated with an increased likelihood of forming calcium oxalate dihydrate stones (Odds ratio [OR] 1.64; 95% CI: 1.22, 2.35; P < 0.01) and reduced bone mineral density (BMD) at the femoral neck (β -0.005 g/cm2; 95% CI: -0.010, -0.001; P = 0.04). The described associations became stronger when the analysis was confined to idiopathic calcium stone formers.

Conclusion

Our study reveals that CYP24A1 activity, estimated by VMDR, is associated with clinical traits previously linked to idiopathic hypercalciuria.

Review of childhood genetic nephrolithiasis and nephrocalcinosis

Nephrolithiasis (NL) is a common condition worldwide. The incidence of NL and nephrocalcinosis (NC) has been increasing, along with their associated morbidity and economic burden. The etiology of NL and NC is multifactorial and includes both environmental components and genetic components, with multiple studies showing high heritability. Causative gene variants have been detected in up to 32% of children with NL and NC. Children with NL and NC are genotypically heterogenous, but often phenotypically relatively homogenous, and there are subsequently little data on the predictors of genetic childhood NL and NC. Most genetic diseases associated with NL and NC are secondary to hypercalciuria, including those secondary to hypercalcemia, renal phosphate wasting, renal magnesium wasting, distal renal tubular acidosis (RTA), proximal tubulopathies, mixed or variable tubulopathies, Bartter syndrome, hyperaldosteronism and pseudohyperaldosteronism, and hyperparathyroidism and hypoparathyroidism. The remaining minority of genetic diseases associated with NL and NC are secondary to hyperoxaluria, cystinuria, hyperuricosuria, xanthinuria, other metabolic disorders, and multifactorial etiologies. Genome-wide association studies (GWAS) in adults have identified multiple polygenic traits associated with NL and NC, often involving genes that are involved in calcium, phosphorus, magnesium, and vitamin D homeostasis. Compared to adults, there is a relative paucity of studies in children with NL and NC. This review aims to focus on the genetic component of NL and NC in children.

Genetic profile of a large Spanish cohort with hypercalcemia

Introduction

The disorders in the metabolism of calcium can present with manifestations that strongly suggest their diagnosis; however, most of the time, the symptoms with which they are expressed are nonspecific or present only as a laboratory finding, usually hypercalcemia. Because many of these disorders have a genetic etiology, in the present study, we sequenced a selection of 55 genes encoding the principal proteins involved in the regulation of calcium metabolism.

Methods

A cohort of 79 patients with hypercalcemia were analyzed by next-generation sequencing.

Results

The 30% of our cohort presented one pathogenic or likely pathogenic variant in genes associated with hypercalcemia. We confirmed the clinical diagnosis of 17 patients with hypocalciuric hypercalcemia (pathogenic or likely pathogenic variants in the CASR and AP2S1 genes), one patient with neonatal hyperparathyroidism (homozygous pathogenic variant in the CASR gene), and another patient with infantile hypercalcemia (two pathogenic variants in compound heterozygous state in the CYP24A1 gene). However, we also found variants in genes associated with primary hyperparathyroidism (GCM2), renal hypophosphatemia with or without rickets (SLC34A1, SLC34A3, SLC9A3R1, VDR, and CYP27B1), DiGeorge syndrome (TBX1 and NEBL), and hypophosphatasia (ALPL). Our genetic study revealed 11 novel variants.

Conclusions

Our study demonstrates the importance of genetic analysis through massive sequencing to obtain a clinical diagnosis of certainty. The identification of patients with a genetic cause is important for the appropriate treatment and identification of family members at risk of the disease.

Biallelic and monoallelic pathogenic variants in CYP24A1 and SLC34A1 genes cause idiopathic infantile hypercalcemia

OBJECTIVE

Idiopathic infantile hypercalcemia (IIH) is a rare disorder of PTH-independent hypercalcemia. CYP24A1 and SLC34A1 gene mutations cause two forms of hereditary IIH. In this study, the clinical manifestations and molecular aspects of six new Chinese patients were investigated.

METHODS

The clinical manifestations and laboratory study of six patients with idiopathic infantile hypercalcemia were analyzed retrospectively.

RESULTS

Five of the patients were diagnosed with hypercalcemia, hypercalciuria, and bilateral medullary nephrocalcinosis. Their clinical symptoms and biochemical abnormalities improved after treatment. One patient presented at age 11 years old with arterial hypertension, hypercalciuria and nephrocalcinosis, but normal serum calcium. Gene analysis showed that two patients had compound heterozygous mutations of CYP24A1, one patient had a monoallelic CYP24A1 variant, and three patients had a monoallelic SLC34A1 variant. Four novel CYP24A1 variants (c.116G > C, c.287T > A, c.476G > A and c.1349T > C) and three novel SLC34A1 variants (c.1322 A > G, c.1697_1698insT and c.1726T > C) were found in these patients.

CONCLUSIONS

A monoallelic variant of CYP24A1 or SLC34A1 gene contributes to symptomatic hypercalcemia, hypercalciuria and nephrocalcinosis. Manifestations of IIH vary with onset age. Hypercalcemia may not necessarily present after infancy and IIH should be considered in patients with nephrolithiasis either in older children or adults.

Critical Role for 24-Hydroxylation in Homeostatic Regulation of Vitamin D Metabolism

Context

The body has evolved homeostatic mechanisms to maintain free levels of Ca+2 and 1,25-dihydroxyvitamin D [1,25(OH)2D] within narrow physiological ranges. Clinical guidelines emphasize important contributions of PTH in maintaining this homeostasis.

Objective

To investigate mechanisms of homeostatic regulation of vitamin D (VitD) metabolism and to apply mechanistic insights to improve clinical assessment of VitD status.

Design

Crossover clinical trial studying participants before and after VitD3-supplementation.

Setting

Community.

Participants

11 otherwise healthy individuals with VitD-deficiency (25-hydroxyvitamin D [25(OH)D] ≤20 ng/mL).

Interventions

VitD3-supplements (50,000 IU once or twice a week depending on BMI, for 4-6 weeks) were administered to achieve 25(OH)D≥30 ng/mL.

Results

VitD3-supplementation significantly increased mean 25(OH)D by 2.7-fold and 24,25-dihydroxyvitamin D [24,25(OH)2D] by 4.3-fold. In contrast, mean levels of PTH, FGF23, and 1,25(OH)2D did not change. Mathematical modeling suggested that 24-hydroxylase activity was maximal for 25(OH)D≥50 ng/mL and achieved a minimum (~90% suppression) with 25(OH)D<10-20 ng/mL. The 1,25(OH)2D/24,25(OH)2D ratio better predicted modeled 24-hydroxylase activity (h) (ρ=-0.85; p=0.001) compared to total plasma 25(OH)D (ρ=0.51; p=0.01) and the 24,25(OH)2D/25(OH)D ratio (ρ=0.37; p=0.3).

Conclusions

Suppression of 24-hydroxylase provides a first line of defense against symptomatic VitD-deficiency by decreasing metabolic clearance of 1,25(OH)2D. The 1,25(OH)2D/24,25(OH)2D ratio provides a useful index of VitD status since it incorporates 24,25(OH)2D levels and therefore, provides insight into 24-hydroxylase activity. When VitD availability is limited, this suppresses 24-hydroxylase activity - thereby decreasing the level of 24,25(OH)2D and increasing the 1,25(OH)2D/24,25(OH)2D ratio. Thus, an increased 1,25(OH)2D/24,25(OH)2D ratio signifies triggering of homeostatic regulation, which occurs at early stages of VitD-deficiency.

Inherited non-FGF23-mediated phosphaturic disorders: A kidney-centric review

Phosphate is freely filtered by the glomerulus and reabsorbed exclusively in the proximal tubule by two key transporters, NaPiIIA and NaPiIIC, encoded by SLC34A1 and SLC34A3, respectively. Regulation of these transporters occurs primarily through the hormone FGF23 and, to a lesser degree, PTH. Consequently, inherited non-FGF23 mediated phosphaturic disorders are due to generalised proximal tubular dysfunction, loss-of-function variants in SLC34A1 or SLC34A3 or excess PTH signalling. The corresponding disorders are Renal Fanconi Syndrome, Infantile Hypercalcaemia type 2, Hereditary Hypophosphataemic Rickets with Hypercalciuria and Familial Hyperparathyroidism. Several inherited forms of Fanconi renotubular syndrome (FRTS) have also been described with the underlying genes encoding for GATM, EHHADH, HNF4A and NDUFAF6. Here, we will review their pathophysiology, clinical manifestations and the implications for treatment from a kidney-centric perspective, focussing on those disorders caused by dysfunction of renal phosphate transporters. Moreover, we will highlight specific genetic aspects, as the availability of large population genetic databases has raised doubts about some of the originally proposed gene-disease associations concerning phosphate transporters or their associated proteins.

When to suspect infantile hypercalcemia-1?

PURPOSE

The screening test to suspect infantile hypercalcemia-1 (HCINF1) is the measure of 25(OH)D3/24,25(OH)2D3 ratio at mass spectroscopy (MS). When the ratio is > 80, the gold standard for the diagnosis is genetic analysis. Given its limited availability, MS may not represent a screening test and most cases of HCINF1 remain undiagnosed. Aim of the study is to identify cut-offs of serum calcium and PTH useful to suspect patients with HCINF1.

METHODS

We compared the levels of total serum calcium and PTH of 6 patients with HCINF1 harboring biallelic CYP24A1 pathogenic variants with 3 different control groups: (1) 12 subjects wild type for CYP24A1; (2) 12 subjects matched for age and sex; (3) 12 subjects matched for vitamin D levels. We validated the cut-offs, testing the number of adult patients affected by HCINF1 reported in the literature that could be identified using these cut-offs.

RESULTS

A serum calcium level > 9.6 mg/dL showed the highest sensitivity (100%) and specificity (91%) in the comparison between homozygous and wild-type subjects. A serum PTH index < 0.315 showed the highest sensitivity (100%) and specificity (83.3%). A serum calcium level > 9.6 mg/dL was able to identify all adult HCINF1 patients whereas a PTH ratio < 0.315 identified 89.8% of the cases. Superimposable results were obtained using the other control groups.

CONCLUSION

Patients with serum calcium levels higher than 9.6 mg/dL and a PTH index lower than 0.315 are likely to be affected by HCINF1. Their diagnosis may be confirmed using MS and genetic analysis.

Nephrocalcinosis in Neonates

Nephrocalcinosis occurs in as many as 40% of preterm neonates. Many causes and contributors predispose neonates to develop nephrocalcinosis, including metabolic, genetic, and iatrogenic factors. Because nephrocalcinosis can be a manifestation of an underlying genetic disorder, neonates with nephrocalcinosis must undergo an evaluation to identify and address contributors, to prevent further renal calcium deposition that can potentially lead to renal dysfunction. In this article, we review the epidemiology, pathogenesis, diagnosis, and evaluation of nephrocalcinosis in neonates. We also summarize the natural history of nephrocalcinosis of prematurity as well as the management of this condition.

Clinical heterogeneity and therapeutic options for idiopathic infantile hypercalcemia caused by CYP24A1 pathogenic variant

OBJECTIVES

Infantile hypercalcemia-1 (HCINF1) is a rare disease caused by pathogenic variants in the CYP24A1 gene, resulting in the inability to metabolize active vitamin D. This leads to hypercalcemia and severe complications.

CONTENT

On December 8th, 2022, a systematic literature search was conducted in PubMed, Wanfang, and CNKI using the keywords "hypercalcemia" and "CYP24A1". Data extraction included patient demographics, clinical presentation, treatment medications, and outcomes. The findings were synthesized to identify common patterns and variations among cases and to assess the efficacy of different therapies in reducing serum calcium. Our findings revealed two distinct peaks in the incidence of HCINF1 caused by CYP24A1 pathogenic variant. Kidney stones or renal calcifications were the most common clinical manifestations of the disease, followed by polyuria and developmental delay. Laboratory investigations showed hypercalcemia, elevated vitamin D levels, hypercalciuria, and low parathyroid hormone. Genetic analysis remains the only reliable diagnostic tool. Although there is no definitive cure for HCINF1, multiple drugs, including bisphosphonates, calcitonin, and rifampicin, have been used to control its symptoms. Blocking the production and intake of vitamin D is the preferred treatment option.

SUMMARY AND OUTLOOK

Our review highlights the basic clinical and biochemical features of HCINF1 and suggests that targeted diagnostic and therapeutic strategies are needed to address the clinical heterogeneity of the disease. The insights gained from this study may facilitate the development of innovative treatments for HCINF1.

Functional Assessment of Vitamin D Status by a Novel Metabolic Approach: The Low Vitamin D Profile Concept

BACKGROUND

Determining serum 25-hydroxyvitamin D [25(OH)D], 24,25-dihydroxyvitamin D [24,25(OH)2D] and the vitamin D metabolite ratio (VMR) allows the identification of individuals with a low vitamin D metabolite profile. Here, we evaluated if such a functional approach provides superior diagnostic information to serum 25(OH)D alone.

METHODS

25(OH)D, 24,25(OH)2D, and the VMR were determined in participants of the DESIRE (Desirable Vitamin D Concentrations, n = 2010) and the LURIC (Ludwigshafen Risk and Cardiovascular Health, n = 2456) studies. A low vitamin D metabolite profile (vitamin D insufficiency) was defined by a 24,25(OH)2D concentration <1.2 ng/mL (<3 nmol/L) and a VMR <4%. Parathyroid hormone (PTH) and bone turnover markers were measured in both cohorts, whereas 10-year mortality data was recorded in LURIC only.

RESULTS

The median age in DESIRE and LURIC was 43.3 and 63.8 years, respectively. Median 25(OH)D concentrations were 27.2 ng/mL (68.0 nmol/L) and 15.5 ng/mL (38.8 nmol/L), respectively. Serum 25(OH)D deficiency, defined as <20.2 ng/mL (<50 nmol/L), was present in 483 (24.0%) and 1701 (69.3%) participants of DESIRE and LURIC, respectively. In contrast, only 77 (3.8%) and 521 (21.2%) participants had a low vitamin D metabolite profile. Regardless of the serum 25(OH)D concentration, a low vitamin D metabolite profile was associated with a significantly higher PTH, accelerated bone metabolism, and higher all-cause mortality than an unremarkable vitamin D metabolite profile.

CONCLUSIONS

The personalized assessment of vitamin D status using a functional approach better identifies patients with accelerated bone metabolism and increased mortality than the use of a fixed 25(OH)D cutoff of 20 ng/mL (50 nmol/L).

Vitamin D and Cardiovascular Diseases: An Update

Vitamin D is a vital nutrient that plays a significant part in several physiological processes within the human body, including calcium metabolism, bone health, immune function, and cell growth and differentiation. It is obtained mainly through exposure to sunlight but can be acquired from certain foods and supplements as well. Vitamin D deficiency (VDD) could be the risk factor for cardiovascular diseases (CVDs), such as heart disease and stroke. In blood vitamin D low levels have been linked with an enhanced risk of developing CVDs. However, it is unclear whether vitamin D levels are the leading cause or consequence of these conditions. While some studies highlight that taking vitamin D supplements could decrease the risk of CVD; however, more research is required to better understand the association between vitamin D and cardiovascular health. In this review, we aimed to summarize the currently available evidence supporting the association between vitamin D and CVDs and anesthesia considerations.

Phenotype of Idiopathic Infantile Hypercalcemia Associated with the Heterozygous Pathogenic Variant of SLC34A1 and CYP24A1

Idiopathic infantile hypercalcemia (IIH) is a rare genetic disease, also called hypersensitivity to vitamin D3. The molecular heterogeneity allows for the differentiation between the two forms; IIH type 1 caused by CYP24A1 genetic variants and IIH type 2 associated with SLC34A1 mutations. The affected individuals express a variety of symptoms: hypercalcemia, hypercalciuria, suppressed intact parathormone levels (PTH), nephrocalcinosis, elevated levels of serum 1,25 (OH)2-vitamin D3 or inappropriately normal levels, and kidney phosphate wasting. The present paper describes three cases of IIH with heterozygous mutations in SLC34A1 and CYP24A1 genes, respectively. The genetic diagnosis is of paramount importance for proper treatment and the prediction of long-term outcomes.

Successful treatment of hypercalcemia in a Chinese patient with a novel homozygous mutation in the CYP24A1 gene using zoledronic acid: a case report

OBJECTIVES

To emphasize the significance of genetic mutations in idiopathic infantile hypercalcemia and the potential therapeutic effectiveness of zoledronic acid in managing hypercalcemia attributed to gene mutations.

CASE PRESENTATION

A 1-year-old female infant was referred to our hospital. The patient developed hypercalcemia despite no vitamin D prophylaxis or intake. In the acute phase, conventional calcium-lowering treatments showed limited efficacy, while the administration of zoledronic acid demonstrated effectiveness in controlling hypercalcemia. Subsequently the patient maintained normal calcium levels via a low-calcium diet and avoiding vitamin D intake. Genetic testing confirmed a homozygous mutation (c.476G>C) in the CYP24A1 gene.

CONCLUSIONS

Family screening and genetic counseling are crucial for early detection and prevention of hypercalcemia. This case emphasizes the importance of genetic mutations in disease development and the potential therapeutic efficacy of zoledronic acid in managing hypercalcemia attributed to gene mutations.

Hypervitaminosis D Secondary to a CYP24A1 Loss-of-Function Mutation: An Unusual Cause of Hypercalcemia in Two Siblings

Hypervitaminosis D as a cause of hypercalcemia may be due to vitamin D intoxication, granulomatous diseases, or abnormalities of vitamin D metabolism. The CYP24A1 gene encodes for the 24-hydroxylase enzyme, which is responsible for the catabolism of 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D). Mutations in CYP24A1 can result in elevated 1,25(OH)2D causing parathyroid hormone (PTH)-independent hypercalcemia, hypercalciuria, nephrolithiasis, and nephrocalcinosis. We present the cases of two siblings exhibiting hypercalcemia secondary to a CYP24A1 loss-of-function mutation. Case 1 presented initially with PTH-dependent hypercalcemia, with localization of a left upper parathyroid adenoma on parathyroid technetium sestamibi (99mTc-MIBI) uptake study. Despite parathyroidectomy (180 mg adenoma), hypercalcemia, hypercalciuria, and low normal PTH levels persisted. A repeat parathyroid 99mTc-MIBI uptake study localized a second adenoma and a right inferior parathyroidectomy was performed (170 mg adenoma). PTH subsequently became undetectable, however hypercalcemia and hypercalciuria persisted. A new presentation of PTH-independent hypercalcemia found to be secondary to a CYP24A1 loss-of-function mutation in his sibling, Case 2, signaled the underlying cause. Cascade testing confirmed both siblings were homozygous for the pathogenic variant c.1186C>T, p.Arg396Trp (R396W) of CYP24A1 (NM_000782.5). In clinical practice CYP24A1 loss-of-function mutations should be considered in patients presenting with PTH-independent hypercalcemia, hypercalciuria, and 1,25(OH)2D levels in the upper normal or elevated range. Although in our case assays of 24,25(OH)2D were not available, calculation of the 25(OH)D:24,25(OH)2D ratio can assist in the diagnostic process. Possible treatments to manage the risk of hypercalcemia in patients with a CYP24A1 loss-of-function mutation include avoidance of vitamin D oversupplementation and excessive sun exposure. Hydration and bisphosphonate therapy can be useful in managing the hypercalcemia. Although not utilized in our cases, treatment with ketoconazole, fluconazole, and rifampicin have been described as potential therapeutic options. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Analytical performance specifications for the measurement uncertainty of 24,25-dihydroxyvitamin D examinations

OBJECTIVES

The exploration of the metabolites in the degradation pathways of vitamin D (VTD) has gained importance in recent years and simultaneous quantitation of twenty-five-hydroxy vitamin D (25(OH)D) mass concentration together with 24,25-dihydroxyvitamin D (24,25(OH)2D) has been proposed as a newer approach to define VTD deficiency. Yet, no data are available on 24,25(OH)2D biological variation (BV). In this study, we evaluated 24,25(OH)2D's BV on the European Biological Variation Study (EuBIVAS) cohort samples to determine if analytical performance specifications (APS) for 24,25(OH)2D could be generated.

METHODS

Six European laboratories recruited 91 healthy participants. 25(OH)D and 24,25(OH)2D concentrations in K3-EDTA plasma were examined weekly for up to 10 weeks in duplicate with a validated LC-MS/MS method. The Vitamin D Metabolite Ratio (24,25(OH)2D divided by 25(OH)D × 100) was also calculated at each time point.

RESULTS

Linear regression of the mean 24,25(OH)2D concentrations at each blood collection showed participants were not in steady state. Variations of 24,25(OH)2D over time were significantly positively associated with the slopes of 25(OH)D concentrations over time and the concentration of 25(OH)D of the participant at inclusion, and negatively associated with body mass index (BMI), but not with age, gender, or location of the participant. The variation of the 24,25(OH)2D concentration in participants over a 10 weeks period was 34.6%. Methods that would detect a significant change linked to the natural production of 24,25(OH)2D over this period at p<0.05 would need a relative measurement uncertainty (u%)<14.9% while at p<0.01, relative measurement uncertainty should be <10.5%.

CONCLUSIONS

We have defined for the first time APS for 24,25(OH)2D examinations. According to the growing interest in this metabolite, several laboratories and manufacturers might aim to develop specific methods for its determination. The results presented in this paper are thus necessary prerequisites for the validation of such methods.

25(OH)D Concentration in Neonates, Infants, Toddlers, Older Children and Teenagers from Poland-Evaluation of Trends during Years 2014-2019

INTRODUCTION

Local and international guidelines have provided schedules for the vitamin D supplementation of general populations of different ages, including children. Our study aimed to assess 25(OH)D concentration and its potential change during a growth and maturation period, adding parameters that reflect the risk of hypercalcemia.

MATERIALS AND METHODS

The available 25(OH)D concentration values (n = 17,636; 7.8 ± 6.0 years), calcium (n = 2673; 16.3 ± 6.1 years) and phosphate (n = 2830; 3.8 ± 5.2 years) metabolism markers were analyzed in a studied group of patients (0-18 years).

RESULTS

In the studied group the mean 25(OH)D concentration was 29.4 ± 11.7 ng/mL. Concentrations of 25(OH)D < 10 ng/mL were observed in 1.7% of patients (n = 292), 10-20 ng/mL in 17.2% (n = 3039), 20-30 ng/mL in 39.5% (n = 6960) and 30-50 ng/mL in 37.2% (n = 6567). In patients with a 25(OH)D concentration <10 ng/mL, normal calcemia (2.25-2.65 mmol/L) was observed in 29.5% of cases (n = 86). Three patients had 25(OH)D concentrations above 100 ng/mL with co-existing hypercalcemia; the mean was Ca = 3.40 mmol/L. Hypocalcemia (Ca < 2.25 mmol/L) was observed in 10,4% of patients (n = 2797). Furthermore, 5.0% of patients showed an increased calcium concentration >2.65 mmol/L (n = 1327). The highest mean 25(OH)D concentration of 32.1 ng/mL ± 12.9 was noted in the years 2018-2019 (n = 3931) and the lowest in the year 2015 (27.2 ng/mL ± 11.0; n = 2822).

CONCLUSIONS

Vitamin D deficiency (<20 ng/mL) was noted in 18,9% of subjects in the years 2014-2019. An effective prevention of vitamin D deficiency was observed in children aged 3 years and younger. A relationship between the concentrations of calcium and 25(OH)D was not observed.

Liquid chromatography-tandem mass spectrometry in fat-soluble vitamin deficiency

Fat-soluble vitamins, including vitamins A, D, E, and K, are essential for maintaining normal body function and metabolism. Fat-soluble vitamin deficiency may lead to bone diseases, anemia, bleeding, xerophthalmia, etc. Early detection and timely interventions are significant for preventing vitamin deficiency-related diseases. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is developing into a potent instrument for the precise detection of fat-soluble vitamins due to its high sensitivity, high specificity, and high resolution.

Advances in the Administration of Vitamin D Analogues to Support Bone Health and Treat Chronic Diseases

Vitamin D (VD) exerts a wide variety of biological actions in addition to its well-known roles in calcium homeostasis. Nutritional VD deficiency induces rachitic abnormalities in growing children and osteomalacia in adults, and it has been proposed to underlie the onset and development of multiple non-communicable chronic diseases. Therefore, the administration of VD or synthetic VD analogues represents a promising therapeutic strategy; indeed, VD and a VD agonist have shown clinical promise in mitigating osteoporosis and symptoms of insufficient calcium intake. However, even though high doses of VD analogues have shown pre-clinical efficacy against several diseases, including cancers, they have not yet had wide-spread clinical success. This difference may be due to limitation of clinical doses in light of the inherent calcemic action of VD. An approach to overcome this problem involves the development of VD analogues with lower calcemic activity, which could be administered in high doses to attenuate the onset and progress of disease. In a similar strategy, selective estrogen receptor modulators have had success as anti-osteoporosis drugs, and they have shown benefit for other estrogen target organs by serving as partial antagonists or agonists of estrogen receptor α. It is thus conceivable to generate synthetic partial antagonists or agonists for the VD receptor (VDR) that would exert beneficial effects on bone and other VD target organs. In this review, we discuss the molecular basis of the development of such synthetic VDR ligands from the viewpoint of roles of VDR in gene regulation.

A Case of Delayed Diagnosis of Idiopathic Infantile Hypercalcemia Due to CYP24A1 Mutation: A 10-Year Journey

The parathyroid gland is responsible for the synthesis and secretion of parathyroid hormone, which is synthesized and released at an inverse relationship to the level of ionized calcium in the blood. Primary hyperparathyroidism affects women more than men. There are various causes for hyperparathyroidism-induced hypercalcemia and the most common cause is parathyroid adenoma. A less common cause of vitamin D-mediated parathyroid hormone-independent hypercalcemia is the loss of function mutation of the CYP24A1 gene. The CYP24A1 gene encodes the vitamin D 24-hydroxylase enzyme, responsible for hydroxylating the active form of vitamin D into an inactive form, and mutations in the CY24A1 gene can lead to elevated active vitamin D metabolite levels. It can result in hypercalcemia and hypercalciuria-related complications. We present a case of a 72-year-old male patient referred to the endocrine clinic, who had repeated treatments for hypercalcemia and recurrent renal calculi. He underwent ultrasound, computerized tomography, and sestamibi scans, all reported as normal. Following this, the patient underwent a positron emission tomography (PET) scan, which was also normal. He then finally underwent genetic testing and tested positive for the CYP24A1 gene. He was started on fluconazole 50mg once a day and cinacalcet 30mg twice with normalization of calcium level. Three of his family members also tested positive for the condition.

USP11-mediated LSH deubiquitination inhibits ferroptosis in colorectal cancer through epigenetic activation of CYP24A1

Ferroptosis is an iron-dependent form of regulated cell death characterized by lipid peroxidation. Colorectal cancer (CRC) cells evade ferroptosis despite their requirement of substantial iron and reactive oxygen species (ROS) to sustain active metabolism and extensive proliferation. However, the underlying mechanism is unclear. Herein, we report the role of lymphoid-specific helicase (LSH), a chromatin-remodeling protein, in suppressing erastin-induced ferroptosis in CRC cells. We demonstrate that erastin treatment leads to dose- and time-dependent downregulation of LSH in CRC cells, and depletion of LSH increases cell sensitivity to ferroptosis. Mechanistically, LSH interacts with and is stabilized by ubiquitin-specific protease 11 (USP11) via deubiquitination; this interaction was disrupted by erastin treatment, resulting in increased ubiquitination and LSH degradation. Moreover, we identified cytochrome P450 family 24 subfamily A member 1 (CYP24A1) as a transcriptional target of LSH. LSH binds to the CYP24A1 promoter, promoting nucleosome eviction and reducing H3K27me3 occupancy, thus leading to transcription of CYP24A1. This cascade inhibits excessive intracellular Ca2+ influx, thereby reducing lipid peroxidation and ultimately conferring resistance to ferroptosis. Importantly, aberrant expression of USP11, LSH, and CYP24A1 is observed in CRC tissues and correlates with poor patient prognosis. Taken together, our study demonstrates the crucial role of the USP11/LSH/CYP24A1 signaling axis in inhibiting ferroptosis in CRC, highlighting its potential as a therapeutic target in CRC treatment.

Rifampin monotherapy for children with idiopathic infantile hypercalcemia

Idiopathic Infantile Hypercalcemia (IIH) is characterized by hypercalcemia and hypercalciuria owing to PTH-independent increases in circulating concentrations of 1,25(OH)2D. At least 3 forms of IHH can be distinguished genetically and mechanistically: infantile hypercalcemia-1 (Hypercalcemia, Infantile, 1; HCINF1) due to CYP24A1 mutations results in decreased inactivation of 1,25(OH)2D; HCINF2 due to SLC34A1 mutations results in excessive 1,25(OH)2D production; and HCINF3 in which a variety of gene variants of uncertain significance (VUS) have been identified and where the mechanism for increased 1,25 (OH)2D is unclear. Conventional management with dietary calcium and vitamin D restriction has only limited success. Induction of the P450 enzyme CYP3A4 by rifampin can provide an alternate pathway for inactivation of 1,25(OH)2D that is useful in HCINF1 and may be effective in other forms of IIH. We sought to assess the efficacy of rifampin to decrease levels of serum 1,25(OH)2D and calcium, and urinary calcium concentrations in subjects with HCINF3, and to compare the response to a control subject with HCINF1. Four subjects with HCINF3 and the control subject with HCINF1 completed the study using rifampin 5 mg/kg/day and 10 mg/kg/day each for 2 months separated by a 2-month washout period. Patients had age-appropriate intake of dietary calcium plus 200 IU vitamin D/day. Primary outcome was efficacy of rifampin to lower serum concentrations of 1,25(OH)2D. The secondary outcomes included the reduction of serum calcium, urinary calcium excretion (as random urine calcium: creatinine (ca:cr) ratio) and serum 1,25(OH)2D/PTH ratio. Rifampin was well tolerated and induced CYP3A4 at both doses in all subjects. The control subject with HCINF1 showed significant response to both rifampin doses with decreases in the serum concentration of 1,25(OH)2D and the 1,25(OH)2D/PTH ratio while the serum and urine ca:cr levels were unchanged. The four patients with HCINF3 showed reductions in 1,25(OH)2D and urinary ca:cr after 10 mg/kg/d, but hypercalcemia did not improve and there were variable responses in 1,25(OH)2D/PTH ratios. These results support further longer-term studies to clarify the usefulness of rifampin as a medical therapy for IIH.

Severe Hypercalcemia Due to Primary Hyperparathyroidism and Heterozygous Pathogenic Variant of CYP24A1

Pathogenic variants of CYP24A1 are associated with hypercalcemia due to disruptions in the ability of 24-hydroxylase to break down 1,25-dihydroxyvitamin D (1,25-DHVD). A case involving a heterozygous pathogenic variant of CYP24A1 and primary hyperparathyroidism leading to severe hypercalcemia has not been previously reported. A 23-year-old woman presented with fatigue and was found to be hypercalcemic at 13.8 mg/dL [reference range, 8.4-10.2 pg/mL]. Her parathyroid hormone (PTH) was 62 pg/mL [reference range, 19-88 pg/mL] and 1,25-DHVD was elevated to 242.7 pg/mL [reference range, 18-72 pg/mL]. Other laboratory workup was unrevealing. She had a bone scan, whole body CT scan, and thyroid ultrasound that were normal. Her 25-hydroxy-vitamin D to 24,25-dihydroxy-vitamin D ratio was elevated at 25.18 (normal, < 25). Because of concern for primary hyperparathyroidism, she was referred to an endocrine surgeon and underwent a parathyroidectomy with the removal of a 3.5-gram adenoma. Pathology showed a parafibromin-deficient parathyroid neoplasm. Genetic testing demonstrated a heterozygous pathogenic variant in CYP24A1. Three weeks after surgery, PTH was 14 pg/mL (1.48 pmol/L), calcium and 1,25-DHVD normalized. In summary, we report a case where a patient with severe symptomatic hypercalcemia was found to have primary hyperparathyroidism exacerbated by an underlying heterozygous pathogenic variant in CYP24A1.

Involucrin Modulates Vitamin D Receptor Activity in the Epidermis

Terminally differentiated keratinocytes are critical for epidermal function and are surrounded by involucrin (IVL). Increased IVL expression is associated with a near-selective sweep in European populations compared with those in Africa. This positive selection for increased IVL in the epidermis identifies human adaptation outside of Africa. The functional significance is unclear. We hypothesize that IVL modulates the environmentally sensitive vitamin D receptor (VDR) in the epidermis. We investigated VDR activity in Ivl‒/‒ and wild-type mice using vitamin D agonist (MC903) treatment and comprehensively determined the inflammatory response using single-cell RNA sequencing and associated skin microbiome changes using 16S bacterial phylotyping. VDR activity and target gene expression were reduced in Ivl‒/‒ mouse skin, with decreased MC903-mediated skin inflammation and significant reductions in CD4+ T cells, basophils, macrophages, monocytes, and type II basal keratinocytes and an increase in suprabasal keratinocytes. Coinciding with the dampened MC903-mediated inflammation, the skin microbiota of Ivl‒/‒ mice was more stable than that of the wild-type mice, which exhibited an MC903-responsive increase in Bacteroidetes and a decrease in Firmicutes. Together, our studies in Ivl‒/‒ mice identify a functional role for IVL to positively impact VDR activity and suggest an emerging IVL/VDR paradigm for adaptation in the human epidermis.

Role of Coactivator Associated Arginine Methyltransferase 1 (CARM1) in the Regulation of the Biological Function of 1,25-Dihydroxyvitamin D3

1,25-Dihydroxyvitamin D3 (1,25(OH)₂D₃), the hormonally active form of vitamin D, activates the nuclear vitamin D receptor (VDR) to mediate the transcription of target genes involved in calcium homeostasis as well as in non-classical 1,25(OH)₂D₃ actions. In this study, CARM1, an arginine methyltransferase, was found to mediate coactivator synergy in the presence of GRIP1 (a primary coactivator) and to cooperate with G9a, a lysine methyltransferase, in 1,25(OH)₂D₃ induced transcription of Cyp24a1 (the gene involved in the metabolic inactivation of 1,25(OH)₂D₃). In mouse proximal renal tubule (MPCT) cells and in mouse kidney, chromatin immunoprecipitation analysis demonstrated that dimethylation of histone H3 at arginine 17, which is mediated by CARM1, occurs at Cyp24a1 vitamin D response elements in a 1,25(OH)₂D₃ dependent manner. Treatment with TBBD, an inhibitor of CARM1, repressed 1,25(OH)₂D₃ induced Cyp24a1 expression in MPCT cells, further suggesting that CARM1 is a significant coactivator of 1,25(OH)₂D₃ induction of renal Cyp24a1 expression. CARM1 was found to act as a repressor of second messenger-mediated induction of the transcription of CYP27B1 (involved in the synthesis of 1,25(OH)₂D₃), supporting the role of CARM1 as a dual function coregulator. Our findings indicate a key role for CARM1 in the regulation of the biological function of 1,25(OH)₂D₃.

Iron Deficiency and Iron Deficiency Anemia: Potential Risk Factors in Bone Loss

Iron is one of the essential mineral elements for the human body and this nutrient deficiency is a worldwide public health problem. Iron is essential in oxygen transport, participates in many enzyme systems in the body, and is an important trace element in maintaining basic cellular life activities. Iron also plays an important role in collagen synthesis and vitamin D metabolism. Therefore, decrease in intracellular iron can lead to disturbance in the activity and function of osteoblasts and osteoclasts, resulting in imbalance in bone homeostasis and ultimately bone loss. Indeed, iron deficiency, with or without anemia, leads to osteopenia or osteoporosis, which has been revealed by numerous clinical observations and animal studies. This review presents current knowledge on iron metabolism under iron deficiency states and the diagnosis and prevention of iron deficiency and iron deficiency anemia (IDA). With emphasis, studies related to iron deficiency and bone loss are discussed, and the potential mechanisms of iron deficiency leading to bone loss are analyzed. Finally, several measures to promote complete recovery and prevention of iron deficiency are listed to improve quality of life, including bone health.

Idiopathic infantile hypercalcemia in children with chronic kidney disease due to kidney hypodysplasia

BACKGROUND

Idiopathic infantile hypercalcemia (IIH) etiologies include pathogenic variants in CYP24A1, leading to increased 1,25(OH)₂ D, hypercalciuria and suppressed parathyroid hormone (PTH), and in SLC34A1 and SLC34A3, leading to the same metabolic profile via increased phosphaturia. IIH has not been previously described in CKD due to kidney hypodysplasia (KHD).

METHODS

Retrospective study of children with bilateral KHD and simultaneously tested PTH and 1,25(OH)₂D, followed in a tertiary care center between 2015 and 2021.

RESULTS

Of 295 screened patients, 139 had KHD, of them 16 (11.5%) had IIH (study group), 26 with normal PTH and any 1,25(OH)₂D were controls. There were no differences between groups' gender, obstructive uropathy rate and baseline eGFR. Study patients were younger [median (IQR) age: 5.2 (3.2-11.3) vs. 61 (13.9-158.3) months, p < 0.001], had higher 1,25(OH)₂D (259.1 ± 91.7 vs. 156.5 ± 46.4 pmol/l, p < 0.001), total calcium (11.1 ± 0.4 vs. 10.7 ± 0.3 mg/dl, p < 0.001), and lower phosphate standard deviation score (P-SDS) [median (IQR): - 1.4 (- 1.9, - 0.4) vs. - 0.3 (- 0.8, - 0.1), p = 0.03]. During 12 months of follow-up, PTH increased among the study group (8.8 ± 2.8 to 22.7 ± 12.4 pg/ml, p < 0.001), calcium decreased (11 ± 0.5 to 10.3 ± 0.6 mg/dl, p = 0.004), 1,25(OH)₂D decreased (259.5 ± 91.7 to 188.2 ± 42.6 pmol/l, p = 0.1), P-SDS increased [median (IQR): - 1.4 (- 1.9, - 0.4) vs. - 0.3 (- 0.9, 0.4), p = 0.04], while eGFR increased. Five of 9 study group patients with available urine calcium had hypercalciuria. Five patients had nephrocalcinosis/lithiasis. Genetic analysis for pathogenic variants in CYP24A1, SLC34A1 and SLC34A3 had not been performed.

CONCLUSIONS

Transient IIH was observed in infants with KHD, in association with hypophosphatemia, resembling SLC34A1 and SLC34A3 pathogenic variants' metabolic profile. A higher resolution version of the Graphical abstract is available as Supplementary information.

Vitamin D: marker, measurand & measurement

The measurement of vitamin D metabolites aids in assessing vitamin D status and in diagnosing disorders of calcium homeostasis. Most laboratories measure total 25-hydroxyvitamin D (25(OH)D), while others have taken the extra effort to measure 25(OH)D2 and 25(OH)D3 separately and additional metabolites such as 1,25-dihydroxyvitamin D and 24,25-dihydroxyvitamin D. The aim of this review is to provide an updated overview of the main markers of vitamin D metabolism, define the intended measurands, and discuss the advantages and disadvantages of the two most widely used assays, automated assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Whether using the easy and fast automated assays or the more complex LC-MS/MS, one should know the pitfalls of the used technique in order to interpret the measurements. In conclusion, automated assays are unable to accurately measure 25(OH)D in all patient groups, including persons using D2. In these cases, an LC-MS/MS method, when appropriately developed and standardized, produces a more reliable measurement.

Vitamin D and Calcium Supplementation and Urolithiasis: A Controversial and Multifaceted Relationship

Patients with urolithiasis, and particularly those with hypercalciuria, frequently have a marked reduction of bone mineral content up to the levels of osteoporosis, with a significant increase in bone fracture risk. For these reasons, the indication to prescribe vitamin D and/or calcium supplementations is very frequent in such patients. On the other hand, both calcium supplementation, and even more vitamin D therapy, can worsen the risk of developing urolithiasis by increasing calcium, phosphate, and oxalate urinary excretion. Despite the clinical and practical relevance of this issue, the evidence on this topic is scarce and contradictory. Therefore, some concerns exist about how and whether to prescribe such supplements to a patient with a history of kidney stones. In this narrative review, we resume some pivotal pathophysiological concepts strictly related to the dealt topic, and we draw some considerations and personal opinions on the pros and cons of such prescriptions. Finally, we share with the reader our pragmatic algorithm for handling the urolithiasis risk in patients who have strong indications to be prescribed vitamin D and calcium supplementations.

3' Untranslated Region Structural Elements in CYP24A1 Are Associated With Infantile Hypercalcemia Type 1

Loss-of-function mutations in the CYP24A1 protein-coding region causing reduced 25 hydroxyvitamin D (25OHD) and 1,25 dihydroxyvitamin D (1,25(OH)₂ D) catabolism have been observed in some cases of infantile hypercalcemia type 1 (HCINF1), which can manifest as nephrocalcinosis, hypercalcemia and adult-onset hypercalciuria, and renal stone formation. Some cases present with apparent CYP24A1 phenotypes but do not exhibit pathogenic mutations. Here, we assessed the molecular mechanisms driving apparent HCINF1 where there was a lack of CYP24A1 mutation. We obtained blood samples from 47 patients with either a single abnormality of no obvious cause or a combination of hypercalcemia, hypercalciuria, and nephrolithiasis as part of our metabolic and stone clinics. We used liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine serum vitamin D metabolites and direct sequencing to confirm CYP24A1 genotype. Six patients presented with profiles characteristic of altered CYP24A1 function but lacked protein-coding mutations in CYP24A1. Analysis upstream and downstream of the coding sequence showed single nucleotide variants (SNVs) in the CYP24A1 3' untranslated region (UTR). Bioinformatics approaches revealed that these 3' UTR abnormalities did not result in microRNA silencing but altered the CYP24A1 messenger RNA (mRNA) secondary structure, which negatively impacted translation. Our experiments showed that mRNA misfolding driven by these 3' UTR sequence-dependent structural elements was associated with normal 25OHD but abnormal 1,25(OH)₂ D catabolism. Using CRISPR-Cas9 gene editing, we developed an in vitro mutant model for future CYP24A1 studies. Our results form a basis for future studies investigating structure-function relationships and novel CYP24A1 mutations producing a semifunctional protein. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Vitamin D Metabolites: Analytical Challenges and Clinical Relevance

Recent research activities have provided new insights in vitamin D metabolism in various conditions. Furthermore, substantial progress has been made in the analysis of vitamin D metabolites and related biomarkers, such as vitamin D binding protein. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methods are capable of accurately measuring multiple vitamin D metabolites in parallel. Nevertheless, only 25(OH)D and the biologically active form 1,25(OH)2D are routinely measured in clinical practice. While 25(OH)D remains the analyte of choice for the diagnosis of vitamin D deficiency, 1,25(OH)2D is only recommended in a few conditions with a dysregulated D metabolism. 24,25(OH)2D, free and bioavailable 25(OH)D, and the vitamin D metabolite ratio (VMR) have shown promising results, but technical pitfalls in their quantification, limited clinical data and the lack of reference values, impede their use in clinical practice. LC-MS/MS is the preferred method for the measurement of all vitamin D related analytes as it offers high sensitivity and specificity. In particular, 25(OH)D and 24,25(OH)2D can accurately be measured with this technology. When interpreted together, they seem to provide a functional measure of vitamin D metabolism beyond the analysis of 25(OH)D alone. The determination of VDBP, free and bioavailable 25(OH)D is compromised by unresolved analytical issues, lacking reference intervals and insufficient clinical data. Therefore, future research activities should focus on analytical standardization and exploration of their clinical value. This review provides an overview on established and new vitamin D related biomarkers including their pathophysiological role, preanalytical and analytical aspects, expected values, indications and influencing conditions.

Association of CYP24A1 Gene rs6127099 (A > T) Polymorphism with Lower Risk to COVID-19 Infection in Kazakhstan

In December 2019, SARS-CoV-2 was identified in Wuhan, China. Infection by SARS-CoV-2 causes coronavirus disease 2019 (COVID-19), which is characterized by fever, cough, dyspnea, anosmia, and myalgia in many cases. There are discussions about the association of vitamin D levels with COVID-19 severity. However, views are conflicting. The aim of the study was to examine associations of vitamin D metabolism pathway gene polymorphisms with symptomless COVID-19 susceptibility in Kazakhstan. The case-control study examined the association between asymptomatic COVID-19 and vitamin D metabolism pathway gene polymorphisms in 185 participants, who previously reported not having COVID-19, were PCR negative at the moment of data collection, and were not vaccinated. A dominant mutation in rs6127099 (CYP24A1) was found to be protective of asymptomatic COVID-19. Additionally, the G allele of rs731236 TaqI (VDR), dominant mutation in rs10877012 (CYP27B1), recessive rs1544410 BsmI (VDR), and rs7041 (GC) are worth consideration since they were statistically significant in bivariate analysis, although their independent effect was not found in the adjusted multivariate logistic regression model.

Assessing vitamin D metabolism - four decades of experience

One hundred years ago, the role of vitamin D for bone mineralization and the prevention of rickets was discovered. Vitamin D comprises a group of over 50 metabolites with multiple functions that go far beyond calcium homeostasis and bone mineralization. Approximately 50 years ago, first methods for the measurement of 25-hydroxyvitamin D (25(OH)D) in human blood were developed. Over the years, different analytical principals were employed including competitive protein binding assays, high-performance liquid chromatography, various immunoassay and mass spectrometric formats. Until the recent standardization of serum 25(OH)D measurement, agreement between methods was unsatisfactory. Since then, comparability has improved, but substantial variability between methods remains. With the advent of liquid chromatography tandem mass spectrometry (LC-MS/MS), the accurate determination of 25(OH)D and other metabolites, such as 24,25(OH)2D, becomes increasingly accessible for clinical laboratories. Easy access to 25(OH)D testing has triggered extensive clinical research showing that large parts of the population are vitamin D deficient. The variable response of vitamin D deficient individuals to supplementation indicates that assessing patients' vitamin D stores by measuring 25(OH)D provides limited insight into the metabolic situation. Meanwhile, first evidence has emerged suggesting that the simultaneous measurement of 25(OH)D, 24,25(OH)2D and other metabolites allows a dynamic evaluation of patients' vitamin D status on metabolic principals. This may help to identify patients with functional vitamin D deficiency from those without. It can be expected that research into the assessment vitamin D status will continue for another 50 years and that this will help rationalizing our approach in clinical practice.

Research Trends of Vitamin D Metabolism Gene Polymorphisms Based on a Bibliometric Investigation

Vitamin D requires activation to show its pharmacological effect. While most studies investigate the association between vitamin D and disease, only a few focus on the impact of vitamin D metabolism gene polymorphisms (vitDMGPs). This bibliometric study aims to provide an overview of current publications on vitDMGPs (CYP27B1, CYP24A1, CYP2R1, CYP27A1, CYP2R1, DHCR7/NADSYN1), compare them across countries, affiliations, and journals, and inspect keywords, co-citations, and citation bursts to identify trends in this research field. CiteSpace© (version 6.1.R3, Chaomei Chen), Bibliometrix© (R version 4.1.3 library, K-Synth Srl, University of Naples Federico II, Naples, Italy), VOSviewer© (version 1.6.1, Nees Jan van Eck and Ludo Waltman, Leiden University, Leiden, Netherlands) and Microsoft® Excel 365 (Microsoft, Redmond, Washington, USA) classified and summarized Web of Science articles from 1998 to November 2022. We analyzed 2496 articles and built a timeline of co-citations and a bibliometric keywords co-occurrence map. The annual growth rate of vitDMGPs publications was 18.68%, and their relative research interest and published papers were increasing. The United States of America leads vitDMGPs research. The University of California System attained the highest quality of vitDMGPs research, followed by the American National Institutes of Health and Harvard University. The three productive journals on vitDMGPs papers are J. Steroid. Biochem. Mol. Biol., PLOS ONE, and J. Clin. Endocrinol. Metab. We highlighted that the vitDMGPs domain is relatively new, and many novel research opportunities are available, especially those related to studying single nucleotide polymorphisms or markers in a specific gene in the vitamin D metabolism cycle and their association with disease. Genome-wide association studies, genetic variants of vitDMGPs, and vitamin D and its role in cancer risk were the most popular studies. CYP24A1 and CYB27A1 were the most-studied genes in vitDMGPs. Insulin was the longest-trending studied hormone associated with vitDMGPs. Trending topics in this field relate to bile acid metabolism, transcriptome and gene expression, biomarkers, single nucleotide polymorphism, and fibroblast growth factor 23. We also expect an increase in original research papers investigating the association between vitDMGPs and coronavirus disease 2019, hypercalcemia, Smith-Lemli-Opitz syndrome, 27-hydroxycholesterol, and mendelian randomization. These findings will provide the foundations for innovations in the diagnosis and treatment of a vast spectrum of conditions.

Case report: Two heterozygous pathogenic variants of CYP24A1: A novel cause of hypercalcemia and nephrocalcinosis in adulthood

Background and aims

Vitamin D 24-hydroxylase is an enzyme encoded by the CYP24A1 gene, which inhibits the activation of vitamin D to form inactive metabolites. More than 20 currently described pathogenic variants (usually biallelic) of this gene are responsible for idiopathic infantile hypercalcemia manifested typically in childhood (often in newborns) with hypercalcemia, hypercalciuria, and nephrocalcinosis. However, a few patients (mostly with monoallelic heterozygous pathogenic variants) can develop mild symptoms in adulthood.

Case description

We present the case of a 43-year-old male patient with hypertension and heterozygous Leiden mutation, with mural thrombi in the common iliac artery, who was sent by a nephrologist to endocrinological examination due to hypoparathyroidism, progressive hypercalcemia, hypercalciuria, and CKDG2A1. Complete laboratory and imaging methods (including PET-CT) excluded PTH-related peptide-mediated hypercalcemia and granulomatosis. Finally, the genetic analysis of the CYP24A1 gene revealed the presence of a novel combination of two heterozygous pathogenic variants: CYP24A1: c. 443T>C p.(Leu148Pro) and c.1186C>T p.(Arg396Trp).

Conclusion

Differential diagnosis of patients with hypercalciuria, nephrocalcinosis, and hypercalcemia related to vitamin D exposure should include the CYP24A1 gene mutation. To the best of our knowledge, this is the first case of the novel combination of two heterozygous pathogenic variants of CYP24A1.