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)

Therapy for X-linked hypophosphatemia (XLH) only partially corrects skeletal lesions and is often complicated by hyperparathyroidism. 24,25(OH)2 D3 improves skeletal lesions in a murine model of XLH and suppresses PTH secretion in animals. Therefore, we undertook a placebo-controlled trial of 24,25(OH)2 D3 supplementation to standard treatment in patients with XLH to improve bone disease and reduce hyperparathyroid complications. Fifteen subjects with XLH receiving standard treatment [1,25(OH)2 D3 or dihydrotachysterol plus phosphate] were evaluated, supplemented with placebo, and reevaluated one yr later. 24,25(OH)2 D3 supplementation was then begun and studies repeated after another year. Each patient underwent a detailed evaluation of calcium homeostasis over a 24-h period. Rachitic abnormalities were assessed radiographically in children. Adults underwent bone biopsies. 24,25(OH)2 D3 normalized PTH values in nine subjects (peak PTH was 46.5 +/- 6.6 pmol/L at entry, 42.3 +/- 5.9 pmol/L after placebo, and 23.3 +/- 5.4 pmol/L after 24,25(OH)2 D3). Nephrogenous cAMP decreased at night, coincident with the decrease in PTH, and serum phosphorus was slightly greater with 24,25(OH)2 D3. Radiographic features of rickets improved during 24,25(OH)2 D3 supplementation in children, and osteoid surface decreased in adults. 24,25(OH)2 D3 is a useful adjunct to standard therapy in XLH by effecting correction of hyperparathyroidism and improvement of rickets and osteomalacia.
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PMID:24,25 Dihydroxyvitamin D supplementation corrects hyperparathyroidism and improves skeletal abnormalities in X-linked hypophosphatemic rickets--a clinical research center study. 896 81

A sensitive method for very-long-chain fatty acid analysis was developed by gas chromatography-nitrogen-phosphorus detection by using cyanomethyl derivatization. Bromoacetonitrile as alkylating reagent was used to improve nitrogen phosphorus detection detectability of compounds containing non-nitrogen. The carboxyl group of very-long-chain fatty acid was alkylated to cyanomethyl esters. Reaction conditions were 40 min at 60 degrees C under potassium carbonate base. Heptacosanoic acid was used as an internal standard and hexane was used as a solvent of extraction. The extraction yield was 82.8% or more, relative standard deviation of the precision test was 8.3% or more and the result of linearity test showed a good correlation coefficient of r2=0.999 in the range of 0.1-50 microg/ml. The quantification limits were 10 ng/ml when 0.5 ml of serum was used. The present method proved simple, rapid, inexpensive and resistant to contaminants. When it was applied to serum samples taken from patients with X-linked adrenoleukodystrophy which is a hereditary X-linked disorder characterized by progressive demyelination and adrenal insufficiency during childhood, relative increase of the concentration of hexacosanoic acid and the concentration ratios of hexacosanoic, lignoceric to behenic acid was observed in comparison with control samples.
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PMID:Determination of very-long-chain fatty acids in serum by gas chromatography-nitrogen-phosphorus detection following cyanomethylation. 1002 31

We describe a familial syndrome in two brothers who were investigated after the casual discovery of tubular proteinuria in their 1st month of life. During a follow-up of 20 and 11 years, respectively, the two children grew well and were asymptomatic, but developed the same biochemical abnormalities, i.e., tubular proteinuria and hyperphosphaturia, progressive decrease in serum phosphorus below the normal values for age, and an increase in serum 1,25-dihydroxyvitamin D levels over normal values. Moreover, hyperabsorptive hypercalciuria and systemic osteopenia developed and progressively worsened. In both children, at a different age, medullary nephrocalcinosis appeared. The oldest boy suffered a progressive decrease in urinary concentration ability and in glomerular filtration rate. Oral phosphate supplementation led to reversal of all biochemical abnormalities, with the exception of decreased phosphate tubular reabsorption and tubular proteinuria. With long-term phosphate supplementation, a normal bone mass was reached, while progression of nephrocalcinosis was arrested and impairment of renal function was slowed down. In a family study (siblings and parents), the only detectable abnormality was microglobinuria in the mother, thus suggesting a X-linked inheritance of this disorder. In the two probands a mutation within the renal chloride channel gene (CLCN5) was discovered.
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PMID:A familial syndrome due to Arg648Stop mutation in the X-linked renal chloride channel gene. 1078 36

PHEX gene and hypophosphatemia. X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO) are diseases that have in common abnormal proximal renal tubular function resulting in increased renal clearance of inorganic phosphorus and hypophosphatemia. The recent discovery of the PHEX gene has provided new insights to these disorders. In this regard, identification of the PHEX gene product as a membrane-bound endopeptidase suggests that the pathophysiologic cascade underlying XLH likely involves inactivation mutations of the gene causing a failure to clear an active hormone, phosphatonin, from the circulation. The presence of this hormone through unknown mechanisms decreases the sodium-dependent phosphate cotransporter in the kidney, resulting in impaired phosphate transport. In contrast, TIO likely evolves secondary to tumor overproduction of the putative phosphatonin, which exerts physiologic function despite efforts to counteract the resultant hypophosphatemia with overproduction of PHEX transcripts that are insufficient to accommodate the enhanced substrate load. These potential pathophysiologic mechanisms for XLH and TIO provide valuable inroads to understanding phosphate homeostasis, as well as vitamin D metabolism, bone mineralization, and calcium metabolism.
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PMID:PHEX gene and hypophosphatemia. 1062 Jan 82

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

Dietary phosphorus deprivation causes hypophosphatemia and an increase in serum 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] concentrations. To determine the molecular mechanisms of this regulation, the effects of dietary phosphorus deprivation and hypophysectomy on 25-hydroxyvitamin D(3) 1alpha-hydroxylase (1alpha-hydroxylase) protein and messenger RNA (mRNA) expression were examined in rats. A low phosphorus diet (LPD) for 4 days resulted in hypophosphatemia and an increase in serum 1,25-(OH)(2)D(3) levels. This increase was caused by the induction of 1alpha-hydroxylase protein and mRNA expression (4- and 10-fold increases, respectively). Administration of the LPD or normal phosphorus diet to hypophysectomized (HPX) rats resulted in hypophosphatemia and suppression of 1alpha-hydroxylase gene expression, indicating that hypophosphatemia itself is not sufficient to induce 1alpha-hydroxylase mRNA expression. Administration of GH to HPX rats fed LPD could partially restore 1alpha-hydroxylase mRNA expression, whereas supplementation with insulin-like growth factor I, T(3), estrogen, or corticosterone had no effect. We also examined Phex gene expression in the bone, because the clinical features of X-linked hypophosphatemia resemble those of HPX rats. Phex mRNA expression, however, was not altered in HPX rats. In conclusion, we demonstrated that the increase in serum 1,25-(OH)(2)D(3) levels caused by dietary phosphorus deprivation is due to the induction of 1alpha-hydroxylase mRNA expression, and this increase is mediated in part by a GH-dependent mechanism.
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PMID:Dietary phosphorus deprivation induces 25-hydroxyvitamin D(3) 1alpha-hydroxylase gene expression. 1131 34

An enzyme with FAD-AMP lyase (cyclizing) activity, splitting FAD to AMP and riboflavin 4',5'-phosphate (cFMN), was recently identified [Fraiz, F., et al. (1998) Biochem. J. 330, 881-888]. Now, it has been purified to apparent homogeneity from a rat liver supernatant, by a procedure that includes affinity for ADP-agarose (adsorption required the activating cation Mn2+ and desorption required its removal), to a final activity of 2.2 units/mg after a 240-fold purification with a 15% yield. By SDS-PAGE, only one protein band was observed (Mr = 59 000). The correspondence between protein and enzyme activity was demonstrated by renaturation after SDS-PAGE, by gradient ultracentrifugation followed by analytical SDS-PAGE, and by native PAGE with visualization of enzyme activity by fluorescence. A native Mr of 100 000 (ultracentrifugation) or 140 000 (gel filtration) indicated that FAD-AMP lyase could be a dimer. The enzyme required millimolar concentrations of Mn2+ or Co2+, exhibited different optimum pH values with these cations (pH 8.5 or 7.3, respectively), and was strongly inhibited by ADP or ATP, but not by dADP, dATP, or the reaction products AMP and cFMN. A specificity study was conducted with 35 compounds related to FAD, mostly nucleoside diphosphate-X (NDP-X) derivatives. Besides FAD, the enzyme split 11 of these compounds with the pattern NDP-X --> NMP + P=X. Structure-activity correlations of substrates, nonsubstrates, and inhibitors, and the comparison of the enzymic reactivities of NDP-X compounds with their susceptibilities to metal-dependent chemical degradation, pinpointed the following specificity pattern. FAD-AMP lyase splits ribonucleoside diphosphate-X compounds in which X is an acyclic or cyclic monosaccharide or derivative bearing an X-OH group that is able to attack internally the proximal phosphorus with the geometry necessary to form a P=X product, either a five-atom monocyclic phosphodiester or a cis-bicyclic phosphodiester-pyranose fusion. For instance, NDP-glucose and GDP-alpha-L-fucose were substrates, but dTDP-glucose, NDP-mannose, and GDP-beta-L-fucose were not. Judging from kcat/Km ratios, we found the best substrate to be FAD, followed closely by ADP-glucose (kcat/Km only 2-fold lower, but not a physiological compound in mammals), whereas other substrates exhibited 50-500-fold lower kcat/Km values. However, there was no evidence for specific flavin recognition. Instead, what seems to be recognized is the NDP moiety of NDP-X, with a strong preference for ADP-X. Splitting would then depend on the presence of an adequate X-OH group. The possibility that, besides FAD, there could be in mammals other ADP-X substrates of FAD-AMP lyase is discussed, with emphasis placed on some ADP-ribose derivatives.
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PMID:Purification, characterization, and substrate and inhibitor structure-activity studies of rat liver FAD-AMP lyase (cyclizing): preference for FAD and specificity for splitting ribonucleoside diphosphate-X into ribonucleotide and a five-atom cyclic phosphodiester of X, either a monocyclic compound or a cis-bicyclic phosphodiester-pyranose fusion. 1169 20

X-linked hypophosphatemic (Hyp) mice exhibit hypophosphatemia, impaired renal phosphate reabsorption, defective skeletal mineralization, and disordered regulation of vitamin D metabolism: In Hyp mice, restriction of dietary phosphorus induces a decrease in serum concentration of 1,25-dihydroxyvitamin D and renal activity of 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase), and induces an increase in renal activity of 25-hydroxyvitamin D-24-hydroxylase (24-hydroxylase). In contrast, in wild-type mice, phosphorus restriction stimulates renal 1alpha-hydroxylase gene expression and suppresses that of 24-hydroxylase. To determine the molecular basis for the disordered regulation of vitamin D metabolism in Hyp mice, we determined renal mitochondrial 1alpha-hydroxylase activity and the renal abundance of p450c1alpha and p450c24 mRNA in wild-type and Hyp mice fed either control, low-, or high-phosphorus diets for 5 d. In wild-type mice, phosphorus restriction increased 1alpha-hydroxylase activity and p450c1alpha mRNA expression by 6-fold and 3-fold, respectively, whereas in the Hyp strain the same diet induced changes of similar magnitude but opposite in direction. Phosphorus supplementation was without effect in wild-type mice, whereas in Hyp mice the same diet induced 3-fold and 2-fold increases, respectively, in enzyme activity and p450c1alpha mRNA abundance. In wild-type mice, both renal 1alpha-hydroxylase activity and p450c1alpha mRNA abundance varied inversely and significantly with serum phosphorus concentrations, whereas in Hyp mice the relationship between both renal parameters and serum phosphorus concentration was direct. In Hyp mice, phosphorus restriction induced a significant increase in renal p450c24 mRNA abundance, in contrast to the lack of effect observed in wild-type mice. The present findings demonstrate that regulation of both the p450c1alpha and p45024 genes by phosphorus is disordered in Hyp mice at the level of renal 1alpha-hydroxylase activity and renal p450c1alpha and p450c24 mRNA expression.
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PMID:Disordered regulation of renal 25-hydroxyvitamin D-1alpha-hydroxylase gene expression by phosphorus in X-linked hypophosphatemic (hyp) mice. 1286 26

Young adult heterozygous (carrier) female dogs with X-linked hereditary nephropathy (XLHN) have glomerular proteinuria but are otherwise healthy. Because data regarding dietary influences on the magnitude of proteinuria in dogs with spontaneous glomerular disease are not available, 12 such dogs were studied in a double crossover experiment intended to determine effects of altering dietary protein intake for up to 6 weeks. Dogs were blocked by urine protein : creatinine ratio (UPC) and randomly assigned to receive 2 diets: high protein (34.6% dry matter [DM], HP) or low protein (14.1% DM, LP) fed in HP-LP-HP or LP-HP-LP sequence. Food intake was measured daily, body weight (BW) was measured twice weekly, and UPC, plasma creatinine, blood urea nitrogen, phosphorus, albumin, and protein concentrations were measured at 2-week intervals. Nutrient digestibility was measured during the third treatment period. Diet had a significant effect (P < .0001) on all measured variables except plasma phosphorus (P > .5), but unintended differences in digestibility of protein and energy (P < or = .01) prevented assignment of the diet effect exclusively to protein. Proteinuria was greater (UPC 4.7 +/- 2.2 versus 1.8 +/- 1.1, P < .0001) when the HP diet was fed, but the LP diet did not maintain starting BW or plasma albumin concentration within the normal reference range. Diet greatly affects the magnitude of proteinuria in XLHN carrier females. Dietary protein restriction can reduce proteinuria in dogs with glomerular disease, but BW and blood protein concentrations may not be maintained if the restriction is too severe.
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PMID:Diet modulates proteinuria in heterozygous female dogs with X-linked hereditary nephropathy. 1505 67

The Identification and characterization of FGF-23 has provided an opportunity to gain new insight into phosphorus metabolism. Circulating FGF-23 promotes renal excretion of phosphorus, and FGF-23 is measurable in the serum of normal subjects. Serum levels of FGF-23 are elevated in patients with renal phosphate wasting disorders such as tumor induced osteomalacia, X-linked hypophosphatemia and fibrous dysplasia. However, the factors that alter its serum concentration are not known. The study of serum FGF-23 is confounded by the fact that high serum calcium, PTH, and any other putative phosphotonins, have similar effects on serum and urine phosphorus. To circumvent the confounding effect of serum PTH and calcium, we studied serum FGF-23 and phosphate levels in patients with chronic hypoparathyroidism and hyperphosphatemia. Serum was collected in the morning after an overnight fast from three groups: 1) 9 patients with chronic hypoparathyroidism on stable treatment with calcium and calcitriol, 2) 9 patients with primary hyperparathyroidism, and 3) 77 normal controls. Patients with hypoparathyroidism had predictably higher levels of serum phosphorus than patients with hyperparathyroidism or normal controls (5.6 +/- 1.1, 3.1 +/- 0.6, and 3.1 +/- 0.5 mg/dL, mean +/- 1 SD, respectively (p < 0.01 for hypoparathyroid vs. either group)). They also had higher levels of FGF-23 (150 +/- 120 vs. 70 +/- 60, or 55 +/- 20 RIU/ml, respectively (p < 0.05 vs. either group)). In conclusion, serum FGF-23 levels are elevated in patients with hyperphosphatemia and chronic hypoparathyroidism, suggesting a feedback system in which serum FGF-23 responds to serum phosphorus and regulates it. However, in the setting of chronic hypoparathyroidism, the degree of elevation of FGF-23 is insufficient to normalize serum phosphorus.
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PMID:FGF-23 is elevated by chronic hyperphosphatemia. 1535 53


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