Evaluation of diagnostic potential of CD38 in rickets.

BACKGROUND: Rickets occurs in infants and children (aged 2 months to 3 years), compromising their skeletal development and damaging nervous, hematopoietic, immune, and other system functions. This study aimed to explore the significance of CD38 in rickets. METHODS: The microarray dataset GSE22523 was analyzed to obtain differentially expressed genes in rickets patients. A total of 36 rickets patients and healthy controls were recruited for the study, and their blood samples were collected, followed by detecting mRNA levels of CD38 using quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, the significance of CD38 in rickets patients was analyzed by receiver operating characteristic (ROC) analysis, while the correlation between CD38 and 25-hydroxy-vitamin D (25OHD)/parathyroid hormone (PTH) was analyzed with Pearson's correlation. RESULTS: Results showed that CD38 mRNA levels and PTH contents were significantly increased in the rickets patients while 25OHD contents were decreased. Correlation analysis indicated that CD38 was positively correlated with PTH and negatively correlated with 25OHD in both serum and plasma samples of rickets patients. Moreover, ROC analysis showed that serum CD38 was 0.9005 (95 % CI: 0.8313-0.9696), and the AUCs of plasma CD38 was 0.7215 (95 % CI: 0.6031-0.8398) in differentiating rickets patients from healthy persons, advocating serum CD38 had better diagnostic value. CONCLUSION: CD38 mRNA levels were upregulated in rickets patients and closely correlated with PTH and 25OHD contents, indicating CD38 might be a diagnostic marker of rickets patients. Further research on the diagnostic utility of CD38 is necessary for the diagnosis and treatment of ricketsin rickets in the future.

Characterization of Rickets Type II Model Rats to Reveal Functions of Vitamin D and Vitamin D Receptor.

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.

Feline precision medicine using whole-exome sequencing identifies a novel frameshift mutation for vitamin D-dependent rickets type 2.

OBJECTIVES: A 14-week-old female domestic longhair kitten presented with shifting lameness and disproportionately smaller size compared with a co-housed littermate. METHODS: Hematology and serum biochemical testing were conducted to investigate causes for delayed growth, and radiographs of the appendicular skeleton were obtained. RESULTS: The afflicted kitten had marked hypocalcemia, mild hypophosphatemia and substantial elevations in alkaline phosphatase activity, as well as pathognomonic radiographic findings consistent with rickets. Skeletal changes and hypocalcemia prompted testing of concentrations of parathyroid hormone (PTH) and vitamin D metabolites. Endocrine testing demonstrated significant increases in serum concentrations of PTH and 1,25-dihydroxycholecalciferol (calcitriol), supporting a diagnosis of vitamin D-dependent rickets type 2. Provision of analgesia, supraphysiologic doses of calcitriol and calcium carbonate supplementation achieved normalization of the serum calcium concentration and restoration of normal growth, although some skeletal abnormalities persisted. Once skeletally mature, ongoing calcitriol supplementation was not required. Whole-exome sequencing (WES) was conducted to identify the underlying DNA variant. A cytosine deletion at cat chromosome position B4:76777621 in VDR (ENSFCAT00000029466:c.106delC) was identified and predicted to cause a stop codon in exon 2 (p.Arg36Glufs*18), disrupting >90% of the receptor. The variant was unique and homozygous in this patient and absent in the sibling and approximately 400 other cats for which whole-genome and whole-exome data were available. CONCLUSIONS AND RELEVANCE: A unique, heritable form of rickets was diagnosed in a domestic longhair cat. WES identified a novel frameshift mutation affecting the gene coding for the vitamin D3 receptor, determining the likely causal genetic variant. Precision medicine techniques, including whole-exome and whole-genome sequencing, can be a standard of care in cats to identify disease etiologies, and to target therapeutics and personalize treatment.

Rickets manifestations in a child with metaphyseal anadysplasia, report of a spontaneously resolving case.

INTRODUCTION: Rickets is not an unusual diagnosis for pediatricians even currently in developed countries. Children typically present with leg bowing, enlargement of wrists, rachitic rosary (swelling of costochondral junctions) and/or waddling gait. But not every child with growth delay and enlarged metaphyses is diagnosed with rickets. Metaphyseal anadysplasia (MAD) is a disorder of variable severity with metaphyseal flaring and irregularities, without vertebral abnormalities. MAD is characterized by an early onset and a regressive course in late childhood without treatment, despite persistent short stature. Autosomal dominant or recessive variants in the matrix metalloproteinase 13 gene (MMP13) are responsible for these transient metaphyseal changes. CASE PRESENTATION: We report a new pathogenic heterozygous variant in MMP13 (NM_002427.4: c.216G>C, p.Gln72His) in a toddler, initially thought to have rickets, and his father, with MAD phenotypes. Additionally, we review the seven reported MMP13 variants. CONCLUSION: One should keep a wide differential diagnosis in cases of suspected rickets, including skeletal dysplasias which might have a regressive course.

Vitamin D and Cardiovascular Disease: An Updated Narrative Review.

During the last two decades, the potential impact of vitamin D on the risk of cardiovascular disease (CVD) has been rigorously studied. Data regarding the effect of vitamin D on CVD risk are puzzling: observational data indicate an inverse nonlinear association between vitamin D status and CVD events, with the highest CVD risk at severe vitamin D deficiency; however, preclinical data and randomized controlled trials (RCTs) show several beneficial effects of vitamin D on the surrogate parameters of vascular and cardiac function. By contrast, Mendelian randomization studies and large RCTs in the general population and in patients with chronic kidney disease, a high-risk group for CVD events, largely report no significant beneficial effect of vitamin D treatment on CVD events. In patients with rickets and osteomalacia, cardiovascular complications are infrequently reported, except for an increased risk of heart failure. In conclusion, there is no strong evidence for beneficial vitamin D effects on CVD risk, either in the general population or in high-risk groups. Whether some subgroups such as individuals with severe vitamin D deficiency or a combination of low vitamin D status with specific gene variants and/or certain nutrition/lifestyle factors would benefit from vitamin D (metabolite) administration, remains to be studied.

Soluble Klotho causes hypomineralization in Klotho-deficient mice.

The type I transmembrane protein αKlotho (Klotho) serves as a coreceptor for the phosphaturic hormone fibroblast growth factor 23 (FGF23) in kidney, while a truncated form of Klotho (soluble Klotho, sKL) is thought to exhibit multiple activities, including acting as a hormone, but whose mode(s) of action in different organ systems remains to be fully elucidated. FGF23 is expressed primarily in osteoblasts/osteocytes and aberrantly high levels in the circulation acting via signaling through an FGF receptor (FGFR)-Klotho coreceptor complex cause renal phosphate wasting and osteomalacia. We assessed the effects of exogenously added sKL on osteoblasts and bone using Klotho-deficient (kl/kl) mice and cell and organ cultures. sKL induced FGF23 signaling in bone and exacerbated the hypomineralization without exacerbating the hyperphosphatemia, hypercalcemia and hypervitaminosis D in kl/kl mice. The same effects were seen in rodent bone models in vitro, in which we also detected formation of a sKL complex with FGF23-FGFR and decreased Phex (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression. Further, sKL-FGF23-dependent hypomineralization in vitro was rescued by soluble PHEX. These data suggest that exogenously added sKL directly participates in FGF23 signaling in bone and that PHEX is a downstream effector of the sKL-FGF23-FGFR axis in bone.

Genetic disorders of Vitamin D biosynthesis and degradation.

Vitamin D, an inactive secosteroid pro-hormone, is produced by the action of ultraviolet light on 7-dehydrocholesterol in the skin. The active hormone, 1,25(OH)2D is produced by sequential 25-hydroxylation in the liver, principally by CYP2R1, and 1α-hydroxylation in the kidney by CYP27B1. Mutations in CYP27B1 cause 1α-hydroxylase deficiency, also known as vitamin D dependent rickets type I or hereditary pseudo-vitamin D deficient rickets; very rare mutations in CYP2R1 can cause 25-hydroxylase deficiency. Both deficiencies cause hypocalcemia, secondary hyperparathyroidism, severe rickets in infancy, and low serum concentrations of 1,25(OH)2D; both disorders respond to hormonal replacement therapy with calcitriol. The inactivation of vitamin D is principally initiated by its 23- and 24-hydroxylation by CYP24A1. Mutations in CYP24A1 can cause both severe neonatal hypercalcemia and a less severe adult hypercalcemic syndrome. Other pathways of vitamin D metabolism are under investigation, notably its 20-hydroxylation by the cholesterol side-chain cleavage enzyme, CYP11A1.

A case of corneal cystinosis in a patient with rickets and chronic renal failure.

A 22-year-old man diagnosed with nephropathic cystinosis at the age of 4 years was found to have progressive bilateral corneal crystal deposition. He presented with severe photophobia and decreased visual acuity. Ocular cystinosis was diagnosed on observing the typical crystals. Optical coherence tomography showed multiple areas of stromal hyperreflectivity due to crystal deposits within the corneal stroma. Ex vivo transmission electron microscopy of the cornea showed pathognomonic crystal deposits in corneal stromal keratocytes. Using polymerase chain reaction sequencing of the entire coding region, we identified five gene mutations, including two unreported mutations.

What Can We Learn About the Neural Functions of TNAP from Studies on Other Organs and Tissues?

To-date, the function of tissue-nonspecific alkaline phosphatase (TNAP) has largely been defined through studies in patients and mice affected by hypophosphatasia (HPP), a rare inborn-error-of-metabolism caused by mutation(s) in the TNAP gene (ALPL). The skeletal disease in HPP can be explained by alterations in the Pi/PPi ratio, with accumulation in the concentration of the mineralization inhibitor PPi as the culprit in preventing propagation of mineralization onto the collagenous extracellular matrix in bones and teeth. Accumulation of phosphorylated osteopontin increases the severity of HPP, at least in mice. Disruption in the metabolism of vitamin B6 leads to intracellular deficiency of pyridoxal, and this causes vitamin B6-responsive seizures in patients with the severe forms of the disease. Recent findings also implicate TNAP in the metabolism of ATP, in the production of adenosine and in the dephosphorylation of the bacterial toxin lipopolysaccharide, all molecules known to be involved in inflammation. The role of TNAP in establishing the ATP/adenosine ratio is important for purinergic signaling, and these mechanisms could be significant in determining axonal growth in the brain. Finally, the potential involvement of TNAP in dephosphorylating tau protein and its role in the pathogenesis of Alzheimer's disease is intriguing.

Genetic rescue of glycosylation-deficient Fgf23 in the Galnt3 knockout mouse.

Fibroblast growth factor 23 (FGF23) is a hormone that inhibits renal phosphate reabsorption and 1,25-dihydroxyvitamin D biosynthesis. The FGF23 subtilisin-like proprotein convertase recognition sequence ((176)RHTR(179)↓) is protected by O-glycosylation through ppGalNAc-T3 (GALNT3) activity. Thus, inactivating GALNT3 mutations render FGF23 susceptible to proteolysis, thereby reducing circulating intact hormone levels and leading to hyperphosphatemic familial tumoral calcinosis. To further delineate the role of glycosylation in the Fgf23 function, we generated an inducible FGF23 transgenic mouse expressing human mutant FGF23 (R176Q and R179Q) found in patients with autosomal dominant hypophosphatemic rickets (ADHR) and bred this animal to Galnt3 knockout mice, a model of familial tumoral calcinosis. Due to the low intact Fgf23 level, Galnt3 knockout mice with wild-type Fgf23 alleles were hyperphosphatemic. In contrast, carriers of the mutant FGF23 transgene, regardless of Galnt3 mutation status, had significantly higher serum intact FGF23, resulting in severe hypophosphatemia. Importantly, serum phosphorus and FGF23 were comparable between transgenic mice with or without normal Galnt3 alleles. To determine whether the presence of the ADHR mutation could improve biochemical and skeletal abnormalities in Galnt3-null mice, these mice were also mated to Fgf23 knock-in mice, carrying heterozygous or homozygous R176Q ADHR Fgf23 mutations. The knock-in mice with functional Galnt3 had normal Fgf23 but were slightly hypophosphatemic. The stabilized Fgf23 ADHR allele reversed the Galnt3-null phenotype and normalized total Fgf23, serum phosphorus, and bone Fgf23 mRNA. However, the skeletal phenotype was unaffected. In summary, these data demonstrate that O-glycosylation by ppGaINAc-T3 is only necessary for proper secretion of intact Fgf23 and, once secreted, does not affect Fgf23 function. Furthermore, the more stable Fgf23 ADHR mutant protein could normalize serum phosphorus in Galnt3 knockout mice.

Malignant infantile osteopetrosis: case report with review of literature.

Malignant Infantile Osteopetrosis (MIOP) is a rare genetic disorder due to osteoclast abnormal activity. We report a thirteen month-old male patient, diagnosed as MIOP while investigating the cause of hepatosplenomegaly associated with hydrocephalus. His medical history revealed non consanguineous parents and one brother's death at the same age of unknown etiology (similar symptoms). Systemic examination showed hepatosplenomegaly, growth failure, developmental milestones delay, and rickets features. Ophthalmic exam yielded bilateral optic atrophy. Skeleton radiographs detected generalized dense bone and rickets. Cerebral CT scan revealed hydrocephalus. Histological examination showed hypoplastic bone marrow and extra-medullary hematopoeisis. Diagnosis was confirmed by genetic testing that showed two heterozygote mutations within the TCIRG1 gene. The patient received supportive treatment. He died from an acute respiratory distress. MIOP should be kept in mind as a rare cause of hepatosplenomegaly. Early diagnosis and timely Hematopoietic stem cell transplantation are the only curative approach for an otherwise fatal disease.

Coupling fibroblast growth factor 23 production and cleavage: iron deficiency, rickets, and kidney disease.

PURPOSE OF REVIEW: High levels of fibroblast growth factor 23 (FGF23) cause the rare disorders of hypophosphatemic rickets and are a risk factor for cardiovascular disease and death in patients with chronic kidney disease (CKD). Despite major advances in understanding FGF23 biology, fundamental aspects of FGF23 regulation in health and in CKD remain mostly unknown. RECENT FINDINGS: Autosomal dominant hypophosphatemic rickets (ADHR) is caused by gain-of-function mutations in FGF23 that prevent its proteolytic cleavage, but affected individuals experience a waxing and waning course of phosphate wasting. This led to the discovery that iron deficiency is an environmental trigger that stimulates FGF23 expression and hypophosphatemia in ADHR. Unlike osteocytes in ADHR, normal osteocytes couple increased FGF23 production with commensurately increased FGF23 cleavage to ensure that normal phosphate homeostasis is maintained in the event of iron deficiency. Simultaneous measurement of FGF23 by intact and C-terminal assays supported these breakthroughs by providing minimally invasive insight into FGF23 production and cleavage in bone. These findings also suggest a novel mechanism of FGF23 elevation in patients with CKD, who are often iron deficient and demonstrate increased FGF23 production and decreased FGF23 cleavage, consistent with an acquired state that mimics the molecular pathophysiology of ADHR. SUMMARY: Iron deficiency stimulates FGF23 production, but normal osteocytes couple increased FGF23 production with increased cleavage to maintain normal circulating levels of biologically active hormone. These findings uncover a second level of FGF23 regulation within osteocytes, failure of which culminates in elevated levels of biologically active FGF23 in ADHR and perhaps CKD.

Relationship between polymorphisms in vitamin D metabolism-related genes and the risk of rickets in Han Chinese children.

BACKGROUND: Vitamin D deficiency rickets is common in China. Genetic factors may play an important role in the susceptibility to rickets. Our study aimed to identify the relationship between three vitamin D-related genes (group specific component [GC], cytochrome P450, family 2, subfamily R, polypeptide 1 (CYP2R1), and 7-dehydrocholesterol reductase/nicotinamide-adenine dinucleotide synthetase 1 (DHCR7/NADSYN1) and rickets in Han Chinese children from northeastern China. METHODS: A total of 506 Han children from northeastern China were enrolled in the current study. Twelve SNPs in three candidate genes were genotyped using the SNaPshot assay. Linear regression was used to examine the effect of 12 single-nucleotide polymorphisms (SNPs) on the risk of rickets. RESULTS: In our case-control cohort, six alleles of the 12 SNPs conferred a significantly increased risk of rickets in GC (rs4588 C, P = 0.003, OR: 0.583, 95% CI: 0.412-0.836; rs222020 C, P = 0.009, OR: 1.526, 95% CI: 1.117-2.0985; rs2282679 A, P = 0.010, OR: 0.636, 95% CI: 0.449-0.900; and rs2298849 C, P = 0.001, OR: 1.709, 95% CI: 1.250-2.338) and in CYP2R1 (rs10741657 G, P = 0.019, OR: 1.467, 95% CI: 1.070-2.011; and rs2060793 G, P = 0.023, OR: 0.689, 95% CI: 0.502-0.944). The results remained significant after adjustment for sex and body mass index. We further analyzed the effect of genotypes under three different genetic models. After using Bonferroni's method for multiple corrections, rs4588, rs2282679, and rs2298849 of the GC gene were significantly associated with rickets under the dominant (P =0.003 for rs4588, P =0.024 for rs2282679, and P =0.005 for rs2298849) and additive models (P = 0.006 for rs4588, P = 0.024 for rs2282679, and P = 0.005 for rs2298849). Haplotype analysis showed that the CAT haplotype of the GC gene (P = 0.005) and the GAA haplotype of the CYP2R1 gene (P = 0.026) were associated with susceptibility to rickets. CONCLUSIONS: This case-control study confirmed the strong effect of GC and CYP2R1 loci on rickets in Han children from northeastern China.

[Updates on rickets and osteomalacia: vitamin D dependency].

Vitamin D dependency was first termed for patients resembling vitamin D-deficiency but require high doses of vitamin D administration. Now this disease is known to be caused by defective conversion of 25OHD to 1,25 (OH) 2D, which is termed vitamin D-dependent rickets type 1 or 1α-hydroxylase deficiency, or by end-organ unresponsiveness to 1,25 (OH) 2D, which is called vitamin D-dependent rickets type 2 or hereditary vitamin D-resistant rickets. Recent advance in the molecular analysis of these diseases revealed variety in the presentation and in the inheritance patterns. Molecular diagnosis would be preferable for some atypical cases for adequate therapy.

[Updates on rickets and osteomalacia: the role of NaPi-2c/SLC34A3 and hypophosphataemic rickets].

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) , an autosomal recessive disorder first identified in a large Bedouin tribe, is characterized by hypophosphatemia secondary to renal inorganic phosphate (Pi) wasting, resulting in increased serum1,25-dihydroxyvitamin D3 concentrations with associated intestinal calcium hyperabsorption, hypercalciuria, rickets, and osteomalacia. Recent studies identified several mutations in the NaPi-2c/NPT2c transporter gene (SLC34A3) as the cause of HHRH. The fact that HHRH is caused by NaPi-2c loss-of-function mutations is compatible with the HHRH phenotype and the prevailing view of renal Pi regulation. The NaPi-2c mutants in HHRH show defective processing and stability.

[Updates on rickets and osteomalacia: biological function of osteocyte and FGF23/klotho system].

Osteocytes are known to synthesize FGF23 which would bind to FGFR1c/klotho complex in proximal renal tubules in kidney, thereby, reducing serum concentration of Pi and the activity of 1α-hydroxylase. Meanwhile, recent studies suggest the possibility that osteocytes might induce osteolysis of lacuna walls. Compact, cortical bone develops well-organized distribution of osteocyte-lacunar canalicular system (OLCS) , which appears to be efficient for osteocytic function. There seems some relation between the geometrical regularity of OLCS and osteocytic regulation of systemic and local mineral balance.

[Updates on rickets and osteomalacia: various roles of Klotho and FGF23 in vivo ].

Recent understandings of phosphate regulation have, at least in part, depended upon the findings of fibroblast growth factor (FGF) 23, the hormone specific for phosphate regulation. Moreover, FGF23 would be the most important marker for prognosis in chronic kidney disease (CKD) . On the other hand, Klotho was firstly developed as a responsible gene for senescence. Although the role of Klotho has been so far established as a co-receptor for FGF23 in mineral metabolism, Klotho would play rather various roles than FGF23 signaling. Thus Klotho is not necessarily equivalent to FGF23. Further studies for both Klotho and FGF23 will elucidate to understand mineral homeostasis.