Clinical and genetic findings in a Chinese family with VDR-associated hereditary vitamin D-resistant rickets

Hereditary vitamin D-resistant rickets （HVDRR） is a rare autosomal recessive disorder characterized by severe rickets, hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, and elevated alkaline phosphatase. This disorder is caused by homogeneous or heterogeneous mutations affecting the function of the vitamin D receptor （VDR）, which lead to complete or partial target organ resistance to the action of 1,25- dihydroxy vitamin D~ A non-consanguineous family of Chinese Han origin with one affected individual demonstrating HVDRR was recruited, with the proband evaluated clinically, biochemically and radiographically. To identify the presence of mutations in the VDR gene, all the exons and exon-intron junctions of the VDR gene from all family members were amplified using PCR and sequenced. The proband showed rickets, progressive alopecia, hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, and elevated alkaline phosphatase. She also suffered from epilepsy, which is rarely seen in patients with HVDRR. Direct sequencing analysis revealed a homozygous missense mutation c.122G 〉 A （p.C41Y） in the VDR gene of the proband, which is located in the first zinc finger of the DNA-binding domain. Both parents had a normal phenotype and were found to be heterozygous for this mutation. We report a Chinese Han family with one individual affected with HVDRR. A homozygous missense mutation c.122G 〉 A （p.C41Y） in the VDR gene was found to be responsible for the patient＇s syndrome. In contrast to the results of treatment of HVDRR in other patients, our patient responded well to a supplement of oral calcium and a low dose of calcitriol.

Atypical skeletal manifestations of rickets in a familial hypocalciuric hypercalcemia patient

Familial hypocalciuric hypercalcemia （FHH） is caused by inactivating mutations in the calcium-sensing receptor （CaSR） gene. The loss of function of CaSR presents with rickets as the predominant skeletal abnormality in mice, but is rarely reported in humans. Here we report a case of a 16-year-old boy with FHH who presented with skeletal manifestations of rickets. To identify the possible pathogenic mutation, the patient was evaluated clinically, biochemically, and radiographicaUy. The patient and his family members were screened for genetic mutations. Physical examination revealed a pigeon breast deformity and X-ray examinations showed epiphyseal broadening, both of which indicate rickets. Biochemical tests also showed increased parathyroid hormone （PTH）, 1,25-dihydroxyvitamin D, and elevated ionized calcium. Based on these results, a diagnosis of FHH was suspected. Sequence analysis of the patient＇s CaSR gene revealed a new missense mutation （c.2279T 〉 A） in exon 7, leading to the damaging amino change （p.I760N） in the mature CaSR protein, confirming the diagnosis of ~H. Moreover, the skeletal abnormities may be related to but not limited to vitamin D abnormity. Elevated ~H levels and a rapid skeletal growth period in adolescence may have also contributed. Our study revealed that rickets-like features have a tendency to present atypically in FHH patients who have a mild vitamin D deficiency, and that CaSR mutations may have a partial role in the pathogenesis of skeletal deformities.

Four Cases of X-Linked Hypophosphatemic Rickets, Clinical Description and Genetic Testing

One of the major causes of congenital hypophosphatemic rickets is the X-linked hypophosphatemic rickets (XHR), due to a defect on PHEX gene. The XHR increases the renal elimination of phosphate, that condition leads a defective mineralization of bones and also affects the growth in children. Clinical diagnosis should be suspected in children with signs of rickets and hypophosphatemia with normal calcium levels. We describe clinical characteristics and genetic results of four patients diagnosed and treated in our Nephrology Section. All patients have a “de novo” XHR as none familiars are affected. Early diagnosis should be suspected before the bone deformities have been submitted and the growth would have been impaired.

Levels and dynamic changes of serum fibroblast growth factor 23 in hypophosphatemic rickets/osteomalacia

Background Hypophosphatemic rickets/osteomalacia is a group of diseases characterised by defective mineralization of bone due to hypophosphatemia and low 1,25-dihydroxy vitamin D. To explore the role of fibroblast growth factor 23 （FGF-23） in the regulation of phosphate homeostasis, we measured the circulating concentrations of this growth factor in healthy individuals and in patients with hypophosphatemic rickets/osteomalacia. Methods Nineteen patients with hypophosphatemic rickets/osteomalacia were included in hypophosphatemic group （HP, 12 female and 7 male, mean age was 30 years）, and 19 healthy age-matched individuals served as the control group. Full length FGF-23 fragments were measured by two-site enzyme-linked immunosorbent assay.Results Mean FGF-23 concentrations were significantly higher in the HP group （（87.4±43.6） pg/ml） compared with the control group （（19.2±6.16） pg/ml; P 〈0.001）. In 1 patient with tumour-induced osteomalacia, serum FGF-23 concentrations were 84.1 pg/ml; these concentrations were normalized 2 hours after a hemangiopericytoma resection （7.8 pg/ml）. Subsequently, serum 1,25（OH）2 vitamin D3 concentrations significantly increased from 21.3 pg/ml to 89.3 pg/ml, and serum phosphorus levels were normalized. Conclusions Serum FGF-23 concentrations were markedly elevated in patients with hypophosphatemic rickets. FGF-23 plays an important role in the pathogenesis of hypophosphatemic rickets/osteomalacia.

Oral findings of hypophosphatemic vitamin D-resistant rickets:report of two cases

Hypophosphatemic vitamin D-resistant rickets or X-linked hypophosphatemia （XLH） is a rare hereditary metabolic disease manifesting marked hypophosphatemia, short stature and rickets. Its prevalence is approximately 1 in 20 000. Except early exfoliation of the teeth, there are a few oral findings of XLH described in China. Here we present two cases in one family.

FGF23 and Phosphate Wasting Disorders

A decade ago, only two hormones, parathyroid hormone and 1,25（OH）2D, were widely recognized to direct-ly affect phosphate homeostasis. Since the discovery of fibroblast growth factor 23 （FGF23） in 2000 （1）, our understanding of the mechanisms of phosphate homeostasis and of bone mineralization has grown exponentially. FGF23 is the link between intestine, bone, and kidney together in phosphate regulation. However, we still do not know the complex mechanism of phosphate homeostasis and bone mineralization. The physiological role of FGF23 is to regulate serum phosphate. Secreted mainly by osteocytes and osteo- blasts in the skeleton （2-3）, it modulates kidney handling of phosphate reabsorption and calcitriol produc-tion. Genetic and acquired abnormalities in FGF23 structure and metabolism cause conditions of either hyper-FGF23 or hypo-FGF23. Hyper-FGF23 is related to hypophosphatemia, while hypo-FGF23 is related to hyperphosphatemia. Both hyper-FGF23 and hypo-FGF23 are detrimentalto humans. In this review, we will discuss the vathovhvsiology of FGF23 and hvver-FGF23 related renal vhosvhate wasting disorders （4）.

Nucleus-targeted Dmp1 transgene fails to rescue dental defects in Dmp1 null mice

Dentin matrix protein 1（DMP1） is essential to odontogenesis. Its mutations in human subjects lead to dental problems such as dental deformities, hypomineralization and periodontal impairment. Primarily, DMP1 is considered as an extracellular matrix protein that promotes hydroxyapatite formation and activates intracellular signaling pathway via interacting with avb3 integrin. Recent in vitro studies suggested that DMP1 might also act as a transcription factor. In this study, we examined whether full-length DMP1 could function as a transcription factor in the nucleus and regulate odontogenesis in vivo. We first demonstrated that a patient with the DMP1M1 V mutation, which presumably causes a loss of the secretory DMP1 but does not affect the nuclear translocation of DMP1, shows a typical rachitic tooth defect. Furthermore, we generated transgenic mice expressingNLSDMP1, in which the endoplasmic reticulum（ER） entry signal sequence of DMP1 was replaced by a nuclear localization signal（NLS） sequence, under the control of a 3.6 kb rat type I collagen promoter plus a 1.6 kb intron 1. We then crossbred theNLSDMP1 transgenic mice with Dmp1 null mice to express the NLSDMP1 in Dmp1-deficient genetic background. Although immunohistochemistry demonstrated thatNLSDMP1 was localized in the nuclei of the preodontoblasts and odontoblasts, the histological, morphological and biochemical analyses showed that it failed to rescue the dental and periodontal defects as well as the delayed tooth eruption in Dmp1 null mice. These data suggest that the full-length DMP1 plays no apparent role in the nucleus during odontogenesis.

Amorphous Calcium Salt Composition Bioavailability Evaluation in Chickens

Despite the market saturation with a wide range of calcium preparations in dietary supplements as well as in pharmaceuticals, calcium product safety and efficacy remain an item for further optimization. Bones and teeth mainly consist of calcium phosphate, but tablets and capsules are predominantly produced from calcium carbonate. On the other hand, in human food Ca2+ is bound with a lot of anions—carbonates, sulphates, chlorides, phosphates, citrates, oxalates etc. It seems that traditional calcium formulations due its low bioavailability cannot provide all spectra of biological calcium-dependant effects and dietary calcium might be safer and more effective than traditional calcium supplements and medicines. To increase calcium salt efficacy a new formulation of calcium salts has been developed. It is a mixture (water suspension) of amorphous calcium carbonate, citrate, hydrocarbonate, as well as magnesium hydrocarbonate and hydrocitrate as stabilizers. The capacity of a cockerel’s duodenal mucosa to absorb Ca2+ after peroral ingestion of the mentioned composition in vivo was as much as 126% higher in comparison with CaCO3 suspension intake. Vitamin D3 enhanced the amorphous antirachitic activity of calcium salts. The aim of the study was to compare original amorphous calcium salt composition bioavailability with Ca salts most often in food and medicines, as well as to evaluate the antirachitic activity of the mentioned composition in combination with vitamin D3 in chickens.

Vitamin D Status among Infants Attending a Reproductive and Child Health Clinic in Arusha, Tanzania: A Cross-Sectional Study

Background: Globally there is a high burden of low serum vitamin D deficiency (VDD) with children being acknowledged at risk due to low vitamin D content in both breastmilk and available foods and inadequate cutaneous synthesis of vitamin D. Even in countries with abundant sunshine, vitamin D deficiency (VDD) remains a problem. There is little characterization of the status of vitamin D among infants in East Africa. This study aimed to determine the prevalence and factors associated with vitamin D deficiency among infants attending the Reproductive and Child Health (RCH) Clinic in Arusha, Tanzania. Methods: A cross-sectional study of 304 infants aged 6 weeks to 12 months was conducted at Arusha Lutheran Medical Centre (ALMC). Infants were enrolled during the warm season between November 2018 and January 2019. A pre-coded questionnaire was used to collect data on sociodemographic characteristics of the infant with consent from their caretakers. Physical examination was done for anthropometric measures and signs of rickets. Blood was drawn for assessment of serum 25-hydroxyvitamin D 25(OH)D, calcium, phosphorus and alkaline phosphate. Vitamin D deficiency was defined as 25(OH)D level below 20 ng/ml (<50 nmol/L) and Vitamin D insufficiency defined as a 25(OH)D level 20 - 30 ng/ml (50 - 75 nmol/L). Statistical analysis was performed using STATA 14 version and factors associated with VDD explored with multivariate analysis. Results: The mean serum 25(OH)D among infants was 34.51 ng/ml (±15.53). Vitamin D deficiency was found in 67/304 (22%) infants and Vitamin D insufficiency in 50 (16.5%) infants. Hypocalcemia was observed in 33 (10.9%) infants and clinical findings of rickets were found in 11 infants (3.6%). Factors independently associated with VDD included age < 6 months (Adjusted Odds Ratio (AOR) 1.56, 95% CI 1.19 - 4.0, p value < 0.026), serum signs of rickets and serum hypocalcemia (p-value < 0.001 and <0.002, respectively). Conclusion and Recommendation: A high prevalence of Vitamin D deficiency (22%) and insufficiency (16.5%) was observed among infants attending RCH Clinic in Arusha, Tanzania. Age < 6 months, a single serum measurement of hypocalcemia and the presence of the clinical sign of rickets were independently associated with VDD. Clinicians should actively assess for VDD and supplement with vitamin D as indicated, especially among infants < 6 months.

Glucose metabolic abnormality is associated with defective mineral homeostasis in skeletal disorder mouse model

Bone was reported as a crucial organ for regulating glucose homeostasis. In this study, we found that Phex mutant mice(PUG), a model of human X-linked hypophosphatemic rickets(XLH), displayed metabolic abnormality in addition to abnormal phosphate homeostasis, skeletal deformity and growth retardation. Glucose tolerance was elevated with enhanced insulin sensitivity in PUG, though circulating insulin level decreased. Interestingly, bone mineral density defects and glucose metabolic abnormality were both rescued by adding phosphorus- and calcium-enriched supplements in daily diet. Serum insulin level, glucose tolerance and insulin sensitivity showed no differences between PUG and wild-type mice with rescued osteocalcin(OCN) following treatment. Our study suggested that OCN is a potential mediator between mineral homeostasis and glucose metabolism. This investigation brings a new perspective on glucose metabolism regulation through skeleton triggered mineral homeostasis and provides new clues in clinical therapeutics of potential metabolic disorders in XLH patients.