Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q00604 (X-linked)
 16,883 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two animal models of the human disorder hypophosphatemic vitamin D-resistant rickets exist, the Hyp and Gy mice. Affected mice and humans both manifest an X-linked phenotype, and show decreased Na+/Pi transport activity in the renal proximal tubules, which is characterized by a decreased maximal velocity (Vmax). The defect in Hyp mice is most likely due to a decreased transcription rate of the renal Na+/Pi transporter gene. The current studies were designed to define the molecular defect in the Gy mice. Sodium-dependent uptake of phosphate (Pi) in renal BBMV showed uptake levels of 170.58 +/- 25 and 66.00 +/- 11 pmol x mg protein-1 x 6 s-1 in normal and Gy mice, respectively (n=3, P=0.0102). Glucose uptake levels in the BBMV were 1.94 +/- 0.87 and 1.91 +/- 0.35 pmol x mg protein-1 x 6 s-1 in normal and Gy mice, respectively (n=3). Northern blot analysis of kidney cortex in both mice revealed nearly equivalent message levels (normal/Gy=1.01 +/- 0.12, n=3). In situ hybridization localized the mRNA to the renal cortex in both mice and confirmed equal message levels. Western blot analysis of renal BBM proteins, using a polyclonal antiserum, showed one predominant band at 87 kDa in both mouse samples, with intensities being decreased in the Gy mice (normal/Gy=4.129 +/- 0.70, n=4, P< 0.04). Immunohistochemical analysis localized the protein to the apical membrane of proximal tubules in both mice. These results suggest that the molecular defect in the Gy mice is distinct from that in the Hyp mice, and furthermore, that the manifestation of the diseased phenotype in Gy mice is related to a different defect in the renal Na+/Pi transporter expression pathway. The molecular mechanism of the defect likely relates to protein processing, metabolic turnover rate, or translocation to the brush-border membrane. These results further suggest that two distinct X-linked factors modulate different steps in the expression pathway of the Na+/Pi transporter gene.
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PMID:The molecular defect in the renal sodium-phosphate transporter expression pathway of Gyro (Gy) mice is distinct from that of hypophosphatemic (Hyp) mice. 863 92

X-linked hypophosphataemic vitamin D-resistant rickets is a rare cause of spinal canal stenosis. Two brothers with this condition presented in adulthood with thoracic myelopathy due to spinal canal stenosis. Both were treated by laminectomy using diamond-tipped burrs, with symptomatic improvement.
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PMID:Thoracic spinal stenosis in two brothers due to vitamin D-resistant rickets. 872 93

Using a mouse model (Hyp) of human hypophosphatemic vitamin D-resistant rickets [X-linked hypophosphatemia (XLH)], we compared the effects of 22-oxa-1,25-dihydroxyvitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on restoring defects in mineral and skeletal metabolism. Hyp/Y mice received OCT or 1,25(OH)2D3 at doses of 0.05-0.25 micron.kg-1.day-1 for 4 wk. OCT normalized serum calcium levels, whereas 1,25(OH)2D3 produced hypercalcemia in Hyp/Y. OCT and 1,25(OH)2D3 also normalized serum phosphate levels and increased urinary calcium levels. Additionally, OCT and 1,25(OH)2D3 reduced elevated urinary pyridinoline levels and suppressed urinary adenosine 3',5'-cyclic monophosphate levels to normal. Bone ash content was low in Hyp/Y, and OCT was more effective than 1,25(OH)2D3 in reversing this defect. Histomorphometric analysis of bone turnover, mineralization rate, and osteoid content demonstrated comparable responses with OCT and 1,25(OH)2D3, although the highest dose of 1,25(OH)2D3 resulted in increased osteoid content and delayed mineralization. OCT appears to be more effective and definitely less toxic than 1,25(OH)2D3 in reversing skeletal lesions in Hyp/Y mice and may prove to be the drug of choice in the treatment of childhood XLH.
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PMID:Comparison of 22-oxacalcitriol and 1,25(OH)2D3 on bone metabolism in young X-linked hypophosphatemic male mice. 877 86

Hypophosphatemic rickets is commonly an X-linked dominant disorder (XLH or HYP) associated with a renal tubular defect in phosphate transport and bone deformities. The XLH gene, referred to as PHEX, or formerly as PEX (phosphate regulating gene with homologies to endopeptidases on the X-chromosome), encodes a 749-amino acid protein that putatively consists of an intracellular, transmembrane, and extracellular domain. PHEX mutations have been observed in XLH patients, and we have undertaken studies to characterize such mutations in 46 unrelated XLH kindreds and 22 unrelated patients with nonfamilial XLH by single stranded conformational polymorphism and DNA sequence analysis. We identified 31 mutations (7 nonsense, 6 deletions, 2 deletional insertions, 1 duplication, 2 insertions, 4 splice site, 8 missense, and 1 within the 5' untranslated region), of which 30 were scattered throughout the putative extracellular domain, together with 6 polymorphisms that had heterozygosity frequencies ranging from less than 1% to 43%. Single stranded conformational polymorphism was found to detect more than 60% of these mutations. Over 20% of the mutations were observed in nonfamilial XLH patients, who represented de novo occurrences of PHEX mutations. The unique point mutation (a-->g) of the 5'untranslated region together with the other mutations indicates that the dominant XLH phenotype is unlikely to be explained by haplo-insufficiency or a dominant negative effect.
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PMID:Mutational analysis of PHEX gene in X-linked hypophosphatemia. 976 74

The genes responsible for X-linked hypophosphatemic (XLH) vitamin D-resistant rickets and the murine homolog, hypophosphatemic mice (Hyp), were identified as PHEX and Phex (phosphate-regulating gene with homology to endopeptidases on the X chromosome), respectively. However, the mechanism by which inactivating mutations of PHEX cause XLH remains unknown. We investigated the mechanisms by syngeneic bone marrow transplantation (BMT) from wild mice to Hyp mice. The expression of the Phex gene was detected in mouse BM cells. BMT introduced a chimerism in recipient Hyp mice and a significant increase in the serum phosphorus level. The renal sodium phosphate cotransporter gene expression was significantly increased. The effect of BMT on the serum phosphorus level depended on engraftment efficiencies, which represent the dosage of normal gene. Similarly, the serum alkaline phosphatase (ALP) activity was decreased and bone mineral density was increased. Furthermore, the renal expression of 25-hydroxyvitamin D3 24-hydroxylase, which is a key enzyme in the catabolic pathway and is increased in XLH/Hyp, was improved. From these results, we conclude that transplantation of normal BM cells improved abnormal bone mineral metabolism and deranged vitamin D metabolism in Hyp by replacing defective gene product(s) with normal gene product(s). This result may provide strong evidence for clinical application of BMT in metabolic bone disorders.
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PMID:The effects of bone marrow transplantation on X-linked hypophosphatemic mice. 1093 43

A case of familial hypophosphatemic vitamin D-resistant rickets or X-linked hypophosphatemia (XLH) accompanied by specific systemic and dental findings is reported. A 15-year-old boy with XLH visited our facility complaining of a toothache in the left lower canine region. Two other family members of the patient, his younger sister and their mother, also had XLH, whereas the other 2 members, his younger brother and father, are healthy. Those with XLH show systemic signs of the disease, such as growth retardation, limb deformity, and spinal curvature disorders; however, these symptoms are more severe in the patient than in the others. The patient had multiple periodontal abscesses, but no evidence of dental caries, trauma, or periodontal disease on the corresponding teeth at the time of his oral examination. A radiographic examination showed root dysplasia and enlarged pulp chambers.A histologic examination of an extracted third molar showed marked globular dentin and an increased predentin width. The abscess was thought to be caused by pulpal infection, which came from bacterial invasion through enamel cracks and dentinal microcleavage of the teeth. The treatments provided in this case are discussed.
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PMID:Familial hypophosphatemic vitamin D-resistant rickets: dental findings and histologic study of teeth. 1098 52

The identification of FGF23 as a factor involved in several disorders of phosphate regulation and of PHEX as the gene mutated in X-linked Hypophosphatemic Rickets indicates that both these genes may be involved in phosphate homeostasis, although their physiological roles are unclear. In this study, FGF23 mRNA expression was analyzed by real-time RT-PCR and found to be higher in normal human bone than in kidney, liver, thyroid, or parathyroid tissue, while expression in oncogenic osteomalacia tumor tissue was several hundred-fold higher than in bone. Expression of FGF23 mRNA in human osteoblast-like bone cells, quantitated by real-time RT-PCR, increased with increasing extracellular phosphate and was 2-fold higher in cells treated with 2 mM extracellular phosphate compared to 0 mM phosphate treatment. PHEX mRNA expression increased 1.3-fold after treatment with 2 mM phosphate. FGF23 expression in the bone cells increased with increased mineralization over a 20-day treatment period under mineralizing conditions with beta-glycerophosphate, while PHEX expression decreased. The results indicate that FGF23 mRNA expression in bone cells is regulated by extracellular phosphate and by mineralization. These results support proposals that bone may be a source of circulating FGF23 and suggest that FGF23 expression by bone is regulated.
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PMID:Bone as a source of FGF23: regulation by phosphate? 1554 45

Three metabolic bone diseases display similar characteristics such as hypophosphatemia due to chronically elevated renal phosphate clearance, inappropriately low 1,25 (OH)2 vitamin D serum levels, and variable bone disease (rickets and osteomalacia). X-linked dominant hypophosphatemic rickets (XLH), also called vitamin D-resistant rickets and autosomal dominant hypophosphatemic rickets (ADHR) represent two inherited diseases, whereas oncogenic hypophosphatemia (OHO), also known as tumor induced osteomalacia (TIO), is an acquired paraneoplastic syndrome that, in certain aspects, has much in common with XLH and ADHR. Although the primary causes for these disorders are distinct and well established, their similar features suggest a unifying pathophysiological basis. This review summarizes what is known about the mechanisms that underlie these diseases and includes most up-to-date information about recently introduced factors that might be involved in the regulation of phosphate homeostasis and skeletal mineralization.
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PMID:Renal phosphate loss in hereditary and acquired disorders of bone mineralization. 1558 4

Vitamin D-resistant rickets is a group of rare disease characterized by lack of reaction to vitamin D administered in doses sufficient to manage patients with rickets caused by vitamin D deficiency. These disorders result from disturbed metabolism and activity of vitamin D and/or disturbed phosphate metabolism. The most common vitamin D-resistant form of rickets is X-linked hypophosphatemic vitamin D-resistant rickets. Other forms are as the following: oncogenic hypophosphatemic osteomalacia, autosomal dominant hypophosphatemic rickets, hereditary hypophosphatemic rickets with hypercalciuria and pseudo-vitamin D deficient rickets type I and II.
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PMID:[Vitamin D-resistant rickets]. 1586 46

Renal proximal tubular reabsorption of phosphate and intestinal absorption both regulate phosphate homeostasis. Brush-border membrane Npt2a cotransporter is the key element in proximal tubular P (i) reabsorption. Inactivating mutations of Npt2a cause bone demineralisation and urolithiasis. An excess of a phosphaturic factor, called "Phosphatonin", could modulate phosphate reabsorption by inhibition on Npt2a. Inactivating mutation of PHEX, an endopeptidase-membrane coding gene, is responsible for X-linked Hypophosphatemia (XLH), because of an impaired degradation of phosphatonine by PHEX product. Autosomic Dominant Hypophosphatemic Rickets (ADHR) is explained by a mutation preventing FGF23 (one of the best identified phosphatonines) from cleavage. According recent data, FGF23, MEPE (Matrix Extracellular Phosphoglycoprotein) et FRP4 (frizzled related protein-4) are 3 putative "phosphatonines".
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PMID:[Genetic hypophosphatemia: recent advances in physiopathogenic concept]. 1595 11


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