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Abstract
PURPOSE OF REVIEW The search for hormones which specifically regulate phosphate metabolism has fuelled recent tantalizing studies. These studies have been motivated by diseases involving renal phosphate wasting, including tumor-induced osteomalacia, X-linked hypophosphatemic rickets, and autosomal dominant hypophosphatemia. This review focuses on likely candidate 'phosphatonins' and their possible physiological significance. RECENT FINDINGS Candidate phosphatonins include fibroblast growth factor 23, matrix extracellular phosphoglycoprotein, stanniocalcin, and Frizzled-related protein 4. Fibroblast growth factor 23 has emerged as the prime candidate explaining pathophysiology of these diseases. FGF-23 is expressed in most tumors in tumor-induced osteomalacia. Serum fibroblast growth factor 23 is increased in most patients with X-linked hypophosphatemic rickets and tumor-induced osteomalacia. Injection of recombinant fibroblast growth factor 23 induces phosphaturia, hypophosphatemia, and suppression of 1,25-dihydroxyvitamin D in animals. Many unanswered questions remain, including the relationship between PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) mutations and elevated fibroblast growth factor 23. It is also not clear whether these candidate phosphatonins play a role in phosphate or vitamin D metabolism in healthy humans, or that this role is endocrine. The most compelling evidence derives from the fibroblast growth factor 23-knockout mouse which shows hyperphosphatemia and increased serum 1,25-dihydroxyvitamin D. A physiologically relevant phosphatonin should explain renal adaptation to variable dietary phosphate intake. The tissue source and determinants of serum fibroblast growth factor 23 are unknown. SUMMARY Pathophysiological and animal studies serve as a logical foundation on which to base further questions of human physiology. The definition of what is or is not a phosphatonin may need to be refined. There is a need to return to 'old-fashioned' human physiology studies to place recent findings in perspective.
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Baroncelli GI, Bertelloni S, Sodini F, Galli L, Vanacore T, Fiore L, Saggese G. Genetic advances, biochemical and clinical features and critical approach to treatment of patients with X-linked hypophosphatemic rickets. PEDIATRIC ENDOCRINOLOGY REVIEWS : PER 2004; 1:361-79. [PMID: 16437029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
X-linked hypophosphatemic rickets (XLH) is an hereditary form of rickets due to isolated renal tubular phosphate wasting and impaired production of 1,25-dihydroxyvitamin D [1,25(OH)2D]. XLH is caused by mutations in the PHEX (phosphate regulating gene with homology to endopeptidases) gene, which is located on Xp22.1. The pathogenetic mechanisms by which mutations in the PHEX gene cause XLH are not completely known. Hypophosphatemia associated with disproportionate short stature and bone deformities of the lower limbs are the main findings in XLH patients. Some studies have shown that conventional treatment with vitamin D metabolites, such as 1,25(OH)2D3 or 1 alpha-hydroxyvitamin D3, combined with inorganic phosphate salts is able to improve serum phosphate concentrations and linear growth, as well as healing rickets. However, some patients may have poor beneficial effects by this therapy. On the other hand, some important treatment complications, such as hypervitaminosis D, nephrocalcinosis and secondary/tertiary hyperparathyroidism may occur during the current therapy. Despite conventional treatment, some patients may require surgical correction of bone deformities. In the light of the recent genetic advances the mechanisms that could be involved in the pathogenesis of XLH are discussed. Furthermore, the article reviews the effects of the medical treatment providing current recommendations for the management of XLH patients.
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Miao D, Bai X, Panda DK, Karaplis AC, Goltzman D, McKee MD. Cartilage abnormalities are associated with abnormal Phex expression and with altered matrix protein and MMP-9 localization in Hyp mice. Bone 2004; 34:638-47. [PMID: 15050894 DOI: 10.1016/j.bone.2003.12.015] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2003] [Revised: 12/05/2003] [Accepted: 12/11/2003] [Indexed: 11/16/2022]
Abstract
X-linked hypophosphatemic rickets (HYP) in humans is caused by mutations in the PHEX gene. This gene mutation is also found in Hyp mice, the murine homologue of the human disease. At present, it is unknown why loss of Phex function leads to cartilage abnormalities in Hyp mice. In the present study, we compared in wild-type and Hyp mice Phex protein localization in cartilage of developing long bone as well as localization of skeletal matrix proteins and matrix metalloproteinase-9 (MMP-9). Also compared were chondrocyte apoptosis in the growth plate, mineralization and cartilage remnant retention in the metaphysis, and chondroclast/osteoclast characteristics in the primary spongiosa. Phex protein was detected in proliferating and hypertrophic chondrocytes in growth plate cartilage of wild-type mice, but not in Hyp mice. Hyp mice exhibited a widened and irregular hypertrophic zone in growth plate cartilage showing hypomineralization, increased cartilage remnants from the growth plate in both metaphyseal trabecular and cortical bone, and fewer and smaller chondroclasts/osteoclasts in the primary spongiosa. Increased link protein and C-propeptide of type II procollagen of Hyp mice reflected the increase in chondrocytes and matrix in the cartilaginous growth plate and in bone. In addition, growth plate osteocalcin and bone sialoprotein levels were decreased, while osteonectin was increased, in hypertrophic chondrocytes and cartilage matrix in Hyp mice. MMP-9 in hypertrophic chondrocytes was also reduced in Hyp mice and fewer apoptotic hypertrophic chondrocytes were detected. These findings suggest that Phex may control mineralization and removal of hypertrophic chondrocytes and cartilage matrix in growth plate by regulating the synthesis and deposition of certain bone matrix proteins and proteases such as MMP-9.
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Sochett E, Doria AS, Henriques F, Kooh SW, Daneman A, Mäkitie O. Growth and metabolic control during puberty in girls with X-linked hypophosphataemic rickets. HORMONE RESEARCH 2004; 61:252-6. [PMID: 15031616 DOI: 10.1159/000077401] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2003] [Accepted: 02/10/2004] [Indexed: 11/19/2022]
Abstract
OBJECTIVE X-linked hypophosphataemic rickets (XLH) results in defective bone mineralization and impaired growth. Treatment with oral phosphate (Pi) and calcitriol improves but does not normalize growth. This study assessed whether pubertal growth and metabolic control contribute to the height deficit. METHODS Study included patients with XLH who were treated with Pi-calcitriol from diagnosis to adult height; their hospital records, biochemistry and radiographs were reviewed. RESULTS Six females with XLH were included. Their mean peak height velocity and total height gain during puberty were nearly normal despite deteriorating metabolic control. CONCLUSIONS In treated girls with XLH, the pubertal growth is nearly normal despite suboptimal metabolic control. The major height loss occurs prior to puberty and is not recovered during the pubertal growth spurt.
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Qiu ZQ, Travers R, Rauch F, Glorieux FH, Scriver CR, Tenenhouse HS. Effect of gene dose and parental origin on bone histomorphometry in X-linked Hyp mice. Bone 2004; 34:134-9. [PMID: 14751570 DOI: 10.1016/j.bone.2003.09.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
X-linked hypophosphatemia (XLH) is characterized by rickets and osteomalacia and arises from mutations in the Phex and PHEX genes in mice (Hyp) and humans, respectively. The present study was undertaken to examine the effect of gene dose on the skeletal phenotype using a histomorphometric approach. Metrical traits (vertebral length, growth plate thickness, cancellous osteoid volume per bone volume, and cancellous, endocortical, and periosteal osteoid thickness) were compared in caudal vertebrae of mutant female (Hyp/+, Hyp/Hyp) and male (Hyp/Y) mice and their normal female (+/+) and male (+/Y) littermates. Mutant animals had trait values that differed significantly from those of normal animals. However, with the exception of vertebral length and cancellous osteoid thickness, values were not significantly different between the three mutant genotypes. We also examined the effect of gamete-of-origin on histomorphometric parameters in obligate Hyp/+ females derived from male or female transmitting parents. The metrical trait values in both groups of Hyp/+ mice were similar, with the exception of vertebral length and cancellous osteoid volume per bone volume. In summary, we demonstrate that the amount of osteoid per bone volume is similar in the three mutant genotypes and conclude that the extent and magnitude of the mineralization defect is fully dominant and likely not affected by gene dose. The differences in vertebral length in the mutants suggest that rickets and osteomalacia are not the only causes of decreased vertebral growth in Hyp mice and that Phex protein may influence bone growth and mineralization by distinct pathways.
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Ritz E, Haxsen V, Zeier M. Disorders of phosphate metabolism--pathomechanisms and management of hypophosphataemic disorders. Best Pract Res Clin Endocrinol Metab 2003; 17:547-58. [PMID: 14687588 DOI: 10.1016/s1521-690x(03)00055-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hypophosphataemia does not necessarily indicate phosphate (Pi) depletion. In acute emergencies such as septicaemia, alkalosis or re-feeding, hypophosphataemia may result from redistribution of Pi from the extracellular to the intracellular space. Hypophosphataemia from true Pi depletion gives rise to skeletal (osteomalacia) and extraskeletal (myopathy, cardiomyopathy) disorders. It is practically never the result of diminished nutritional intake. The most severe syndromes of Pi depletion result from diminished tubular Pi re-absorption and renal Pi wasting. In the differential diagnosis mainly four conditions have to be considered: (i) tumour-associated osteomalacia, (ii) X-linked hypophosphataemia (XLH), (iii) autosomal dominant hypophosphataemia, and (iv) hypercalcaemic renal phosphate wasting. Recent molecular insight has put fibroblast growth factor (FGF-23) into the centre of pathophysiological considerations because of (i) overproduction (tumour-associated osteomalacia) or (ii) hypothetically, accumulation resulting from mutations causing resistance to processing or degradation (autosomal dominant hypophosphataemia) or (iii) loss-of-function of a protease (PHEX) interfering with FGF-23 breakdown (XLH). In oncogenic osteomalacia the treatment of choice is resection of the tumour. Recently, pharmacological treatment has also become possible, i.e. administration of octreotide. XLH and autosomal dominant hypophosphataemia must be managed by oral administration of phosphate and calcitriol. In patients with gastrointestinal intolerance to phosphate or with severely symptomatic bone disease, prolonged intravenous administration of Pi is necessary.
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Negri AL. [Fibroblast growth factor 23 (FGF 23): a new fosfaturic hormone?]. Nefrologia 2003; 23:478-81. [PMID: 15002780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023] Open
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Mäkitie O, Doria A, Kooh SW, Cole WG, Daneman A, Sochett E. Early treatment improves growth and biochemical and radiographic outcome in X-linked hypophosphatemic rickets. J Clin Endocrinol Metab 2003; 88:3591-7. [PMID: 12915641 DOI: 10.1210/jc.2003-030036] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
X-Linked hypophosphatemic rickets (XLH) is characterized by hypophosphatemia, rickets, and impaired growth. Despite oral phosphate and 1,25-dihydroxyvitamin D(3) treatment, many patients have suboptimal growth and bone healing. The aim of this study was to assess whether age at treatment onset impacts the outcome. Growth data, biochemistry, and radiographs of 19 well-controlled patients with XLH were analyzed retrospectively. Patients were divided into two groups based on the age at treatment onset (group 1, <1.0 yr; group 2, >or=1.0 yr). The median height z-score was higher in group 1 (n = 8) than in group 2 (n = 11) at treatment onset [-0.4 SD score (SDS) vs. -1.7 SDS; P = 0.001], at the end of the first treatment year (-0.7 SDS vs. -1.8 SDS; P = 0.009), throughout childhood (P > 0.05) and until predicted adult height (-0.2 SDS vs. -1.2 SDS; P = 0.06). The degree of hypophosphatemia was similar in both groups, but serum alkaline phosphatase remained higher in group 2 throughout childhood. Radiographic signs of rickets were more marked in group 2, but even patients with early treatment developed significant skeletal changes of rickets. These data suggest that treatment commenced in early infancy results in improved outcome in patients with XLH, but does not completely normalize skeletal development.
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Kittaka A, Kurihara M, Peleg S, Suhara Y, Takayama H. 2 alpha-(3-hydroxypropyl)- and 2 alpha-(3-hydroxypropoxy)-1 alpha,25-dihydroxyvitamin D3 accessible to vitamin D receptor mutant related to hereditary vitamin D-resistant rickets. Chem Pharm Bull (Tokyo) 2003; 51:357-8. [PMID: 12612432 DOI: 10.1248/cpb.51.357] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hereditary vitamin D-resistant rickets (HVDRR) is a genetic disorder caused by mutations in the vitamin D receptor, which lead to resistance to 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)]. We found that the A ring-modified analogues, 2alpha-(3-hydroxypropyl)- and 2alpha-(3-hydroxypropoxy)-1alpha,25(OH)(2)D(3), (O1C3 and O2C3) can bind better than the natural hormone to the mutant VDR (R274A), which similar to the HVDRR mutant, R274L, had lost the hydrogen bond to the 1alpha-hydroxyl group of 1alpha,25(OH)(2)D(3).
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Mäkitie O, Kooh SW, Sochett E. Prolonged high-dose phosphate treatment: a risk factor for tertiary hyperparathyroidism in X-linked hypophosphatemic rickets. Clin Endocrinol (Oxf) 2003; 58:163-8. [PMID: 12580931 DOI: 10.1046/j.1365-2265.2003.01685.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE X-linked hypophosphatemic rickets is characterized by renal phosphate wasting, hypophosphatemia and defective bone mineralization. Treatment with oral phosphate (Pi) and calcitriol improves skeletal changes but associates with secondary hyperparathyroidism and nephrocalcinosis. Tertiary hyperparathyroidism is a rare complication of the treatment. The aim of the present study was to identify treatment-related factors that might be associated with the transition of secondary hyperparathyroidism to tertiary hyperparathyroidism in patients with X-linked hypophosphatemic rickets. DESIGN Thirteen patients with X-linked hypophosphatemic rickets and secondary or tertiary hyperparathyroidism were included in the study. Their hospital records were reviewed and compared for onset, duration and dosage of treatment, and for age of diagnosis and degree of secondary hyperparathyroidism. RESULTS Two patients developed tertiary hyperparathyroidism and 11 patients secondary hyperparathyroidism during the treatment. Patients with tertiary hyperparathyroidism had, on average, earlier onset and longer duration of treatment, higher dose of Pi and longer duration of treatment with very high Pi doses (> 100 mg/kg/day) compared to the 11 patients with secondary hyperparathyroidism. However, variation of all parameters was great with considerable overlap. Very high S-PTH levels > or = 42 pmol/l were observed in those who later developed tertiary hyperparathyroidism. CONCLUSIONS Prolonged very high dose oral Pi treatment is a major risk factor for the development of tertiary hyperparathyroidism in X-linked hypophosphatemic rickets.
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Malloy PJ, Zhu W, Bouillon R, Feldman D. A novel nonsense mutation in the ligand binding domain of the vitamin D receptor causes hereditary 1,25-dihydroxyvitamin D-resistant rickets. Mol Genet Metab 2002; 77:314-8. [PMID: 12468277 DOI: 10.1016/s1096-7192(02)00173-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hereditary 1,25-dihydroxyvitamin D resistant rickets (HVDRR) is a genetic disorder most often caused by mutations in the vitamin D receptor (VDR). In this report, we present our findings on a young girl who exhibited the typical clinical features of HVDRR with early onset rickets, hypocalcemia, secondary hyperparathyroidism, and elevated serum concentrations of alkaline phosphatase and 1,25-dihydroxyvitamin D [1,25(OH)(2)D(3)]. The patient also had total body alopecia. Fibroblasts from the patient were cultured for analysis of the VDR structure and function. In [3H]1,25(OH)(2)D(3) binding assays, no significant specific binding to the VDR was observed in cytosols from the patient's fibroblasts. The patient's fibroblast were also totally resistant to high doses of 1,25(OH)(2)D(3) as demonstrated by their failure to induce expression of the 24-hydroxylase gene, a marker of 1,25(OH)(2)D(3) activity. DNA sequence analysis of the VDR gene uncovered a unique C to T mutation in exon 8. The mutation changed the codon for glutamine to a premature stop codon at amino acid 317 (Q317X). Restriction enzyme analysis showed that the patient was homozygous for the mutation. Both parents were heterozygous for the mutant allele. In conclusion, we have identified a novel mutation in the VDR, Q317X, as the molecular defect in a patient with HVDRR. The Q317X mutation deletes 110 amino acids of the ligand-binding domain of the VDR and results in the loss of [3H]1,25(OH)(2)D(3) binding and target gene transactivation.
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Abstract
Bone accretion is a two-stage process, with the osteoblasts laying down osteoid, which is then mineralized. Mineralization of osteoid requires vitamin D to be available in its active form (1,25(OH) 2 D); in addition, mineralization also requires normal levels of serum calcium, phosphorus, and alkaline phosphate. Deficiencies of any of these will result in defective mineralization of bone, in which the mineral-osteoid ratio is reduced (a qualitative abnormality). In the juvenile skeleton deficiencies particularly affect enchondral ossification at the growth plates, giving the characteristic clinical and radiological features of rickets. The bone may be soft, leading to deformity. In this article the causes of rickets in childhood are reviewed, together with the clinical and radiological features and strategies for prevention and treatment.
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Strewler GJ. FGF23, hypophosphatemia, and rickets: Has phosphatonin been found? Proc Natl Acad Sci U S A 2001; 98:5945-6. [PMID: 11371627 PMCID: PMC33399 DOI: 10.1073/pnas.111154898] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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Velan GJ, Currier BL, Clarke BL, Yaszemski MJ. Ossification of the posterior longitudinal ligament in vitamin D-resistant rickets: case report and review of the literature. Spine (Phila Pa 1976) 2001; 26:590-3. [PMID: 11242392 DOI: 10.1097/00007632-200103010-00029] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN A case report of cervical myelopathy caused by ossification of the posterior longitudinal ligament in a patient with vitamin D-resistant rickets is presented together with a review of literature. OBJECTIVE To report the diagnosis of ossification of the posterior longitudinal ligament in a white woman with vitamin D-resistant rickets. SUMMARY OF BACKGROUND DATA The association between ossification of the posterior longitudinal ligament and untreated vitamin D-resistant rickets has been reported in Japan, but infrequently in white populations. In whites, ossification of the posterior longitudinal ligament is closely associated with diffuse idiopathic skeletal hyperostosis. A clear association between ossification of the posterior longitudinal ligament and vitamin D-resistant rickets in white populations has not yet been established. METHODS The medical record and imaging studies of a patient treated at the authors' institution for cervical myelopathy caused by ossification of the posterior longitudinal ligament in the setting of treated vitamin D-resistant rickets were reviewed. A Medline search of the medical literature between 1966-1999 was performed to identify pertinent studies and similar case reports. RESULTS The occurrence of spinal stenosis in untreated adults with vitamin D-resistant rickets has been reported in all regions of the spine in Japanese patients. The association between ossification of the posterior longitudinal ligament and untreated vitamin D-resistant rickets was first reported in Japan, where ossification of the posterior longitudinal ligament is endemic. This association may be incidental, because reports on ossification of the posterior longitudinal ligament in whites are not as frequent as in Japanese, reflecting the higher prevalence of this condition in Japan. CONCLUSION Ossification of the posterior longitudinal ligament and ossification of the posterior longitudinal ligament associated with deranged calcium or phosphate metabolism may be different pathologic entities sharing a common outcome. Adequate treatment of vitamin D-resistant rickets may not always prevent or reverse ossification of the posterior longitudinal ligament.
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Jones AO, Tzenova J, Frappier D, Crumley MJ, Roslin NM, Kos CH, Tieder M, Langman CB, Proesmans W, Carpenter TO, Rice A, Anderson D, Morgan K, Fujiwara TM, Tenenhouse HS. Hereditary hypophosphatemic rickets with hypercalciuria is not caused by mutations in the Na/Pi cotransporter NPT2 gene. J Am Soc Nephrol 2001; 12:507-514. [PMID: 11181798 DOI: 10.1681/asn.v123507] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a renal phosphate (Pi) wasting disease first described in an extended Bedouin kindred, is characterized by hypophosphatemia, elevated serum 1,25-dihydroxyvitamin D levels, hypercalciuria, rickets, and osteomalacia. Correction of all abnormalities, except for renal Pi wasting, can be achieved by oral Pi supplementation. These findings and the demonstration that mice that are homozygous for the disrupted Na/Pi cotransporter gene Npt2 exhibit many of the biochemical features of HHRH suggested that mutations in the human orthologue NPT2 might be responsible for HHRH. The NPT2 gene in affected individuals from the Bedouin kindred and four small families was screened for mutations to test this hypothesis. No putative disease-causing mutation was found. Two single nucleotide polymorphisms (SNP), a silent substitution in exon 7 and a nucleotide substitution in intron 4, were identified, and neither consistently segregated with HHRH in the Bedouin kindred. Linkage analysis indicated that the two NPT2 intragenic SNP as well as five microsatellite markers in the NPT2 gene region were not linked to HHRH in the Bedouin kindred. Therefore, this is evidence to exclude NPT2 as a candidate gene for HHRH in the families that were studied.
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Morimoto T, Chiba A, Kondo Y, Takahashi S, Igarashi T, Inoue CN, Iinuma K. A new approach to mRNA in proximal tubule cells of patients with CLCN5 channelopathy. Pediatr Nephrol 2001; 16:110-2. [PMID: 11261675 DOI: 10.1007/s004670000533] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
ClC-5 is a chloride channel whose gene mutations have been reported to be associated with X-linked nephrolithiasis (XRN), X-linked recessive hypophosphatemic rickets (XLRH), Dent disease, and idiopathic low-molecular-weight proteinuria (ILMWP) in Japanese children. To establish more efficient screening for CLCN5 abnormalities, we developed a new diagnostic method using reverse transcription and polymerase chain reaction (RT-PCR) of cultured renal tubular cells from the urine of patients. Using this new method, we successfully detected microdeletion of ClC-5 mRNA in a patient and splicing abnormality of the CLCN5 Cl channel.
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Baroncelli GI, Bertelloni S, Saggese G. Good metabolic control prevents post-surgical imbalance of mineral metabolism in patients with X-linked hypophosphatemic rickets. J Pediatr Endocrinol Metab 2001; 14:223-4. [PMID: 11305803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
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Miao D, Bai X, Panda D, McKee M, Karaplis A, Goltzman D. Osteomalacia in hyp mice is associated with abnormal phex expression and with altered bone matrix protein expression and deposition. Endocrinology 2001; 142:926-39. [PMID: 11159866 DOI: 10.1210/endo.142.2.7976] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
To explore how the loss of Phex function contributes to the pathogenesis of osteomalacia, we examined the abnormalities of mineralization, Phex, and bone matrix protein expression occurring in Hyp mice in vivo and in ex vivo bone marrow cell cultures. The results in vivo show that mineralization was decreased significantly in Hyp mouse bone. Phex protein was identifiable in osteoblasts and osteocytes in wild-type mice, but not in Hyp mice. In Hyp mice, osteocalcin, bone sialoprotein, and vitronectin expression were down-regulated, whereas biglycan and fibrillin-1 expression were up-regulated in osteocytes and bone matrix relative to those in their wild-type counterparts. Parallel studies ex vivo demonstrated that cells derived from 18-day Hyp mouse bone marrow cell cultures had a 3'-Phex deletion, no Phex protein expression, decreased alkaline phosphatase activity, collagen deposition, and calcium accumulation, and reduced osteocalcin, bone sialoprotein, and vitronectin at both the protein and messenger RNA levels. Furthermore conditioned medium from Hyp mouse bone marrow cultures could induce analogous defects in bone marrow cell cultures of wild-type cells. These novel findings indicate that there is an intrinsic osteogenic cell differentiation defect in addition to the known hypomineralization of bone in Hyp mice, which may be inducible by an autocrine/paracrine secreted factor. These results suggest that alterations in the Phex gene may control bone matrix mineralization indirectly by regulating the synthesis and deposition of bone matrix proteins.
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van den Heuvel L, Op de Koul K, Knots E, Knoers N, Monnens L. Autosomal recessive hypophosphataemic rickets with hypercalciuria is not caused by mutations in the type II renal sodium/phosphate cotransporter gene. Nephrol Dial Transplant 2001; 16:48-51. [PMID: 11208993 DOI: 10.1093/ndt/16.1.48] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND At present the genetic defect for autosomal recessive and autosomal dominant hypophosphataemic rickets with hypercalciuria (HHRH) is unknown. Type II sodium/phosphate cotransporter (NPT2) gene is a serious candidate for being the causative gene in either or both autosomal recessive and autosomal dominant HHRH. In the present study we tested this hypothesis in one autosomal recessive family. METHODS The gene structure of human NPT2 is known. We tested the complete open reading frame in the affected siblings by polymerase chain reaction in combination with automatic DNA sequencing for the presence of mutations. RESULTS We did not observe disease-causing mutations in the NPT2 gene of the affected siblings. A T855C polymorphism resulting in a histidine to arginine transition was present in the open reading frame of NPT2. The polymorphism was present in both affected as well as unaffected family members. CONCLUSION The hypothesis that a defect in the NPT2 gene could be an underlying cause for autosomal recessive HHRH could not be sustained in our study.
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Yamamoto T, Miyamoto KI, Ozono K, Taketani Y, Katai K, Miyauchi A, Shima M, Yoshikawa H, Yoh K, Takeda E, Okada S. Hypophosphatemic rickets accompanying McCune-Albright syndrome: evidence that a humoral factor causes hypophosphatemia. J Bone Miner Metab 2001; 19:287-95. [PMID: 11498730 DOI: 10.1007/s007740170012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2000] [Accepted: 03/16/2001] [Indexed: 11/29/2022]
Abstract
McCune-Albright syndrome (MAS) is sometimes complicated by hypophosphatemia. However, it remains unclear whether a humoral factor is associated with the cause of hypophosphatemia. We isolated cells with mutations of the Gsalpha gene from fibrous bone dysplasia tissues of two MAS patients (MAS cells). Severe combined immunodeficiency (SCID) mice were subjected to experiments using from one of these cells patients. Effects of conditioned media (CM) isolated from MAS cells (MAS-CM) on phosphate transport were investigated by using rat renal slices, the renal cell line OK-B, rat intestinal rings and the human intestinal cell line Caco-2. In addition, the effects of MAS-CM on human sodium-dependent phosphate transporter (NPT2) gene promoter activity expression were investigated in the renal cell line OK-B2400 and were compared with the effects of CM isolated from a patient with oncogenic hypophosphatemic osteomalacia (OHO). MAS cells caused significant hypophosphatemia (P < 0.05) and elevated serum alkaline phosphatase activity (P < 0.05) in SCID mice. The MAS-CM significantly inhibited phosphate uptake in everted intestinal rings (P < 0.01), whereas it had no effect on glucose uptake. The MAS-CM had no effect on either phosphate uptake in the kidney or NPT2 gene promoter activity. In contrast, the CM of the OHO patient significantly inhibited phosphate uptake and NPT2 gene promoter activity. These results indicate that the humoral factor derived from fibrous dysplasia cells of the MAS patient is different to that from OHO patients, because the humoral factor from the MAS patient inhibited phosphate transport not in the kidney but in the intestine.
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MESH Headings
- Adolescent
- Adult
- Animals
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Cells, Cultured
- Culture Media, Conditioned/pharmacology
- Female
- Fibrous Dysplasia, Polyostotic/complications
- Fibrous Dysplasia, Polyostotic/metabolism
- GTP-Binding Protein alpha Subunits, Gs/genetics
- Hot Temperature
- Humans
- Hypophosphatemia/etiology
- Hypophosphatemia/metabolism
- Hypophosphatemia, Familial/etiology
- Hypophosphatemia, Familial/metabolism
- In Vitro Techniques
- Jejunum/drug effects
- Jejunum/metabolism
- Kidney/cytology
- Kidney/drug effects
- Kidney/metabolism
- Membrane Transport Proteins/genetics
- Membrane Transport Proteins/metabolism
- Mice
- Mice, SCID
- Phosphates/metabolism
- Promoter Regions, Genetic
- Rats
- Rats, Wistar
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47
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Nordahl J, Hollberg K, Mengarelli-Widholm S, Andersson G, Reinholt FP. Morphological and functional features of clasts in low phosphate, vitamin D-deficiency rickets. Calcif Tissue Int 2000; 67:400-7. [PMID: 11136539 DOI: 10.1007/s002230001151] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Focusing on resorption processes, we have extended our previous studies on chondroclasts and osteoclasts in normally developing tissues, using a model of nutritionally induced vitamin D-deficiency rickets. To analyze the resorption process, we investigated the matrix-resorbing cells in this modified and poorly mineralized tissue regarding morphological features and expression of tartrate-resistant acid phosphatase (TRAP) at the subcellular level. Our goal was to test the hypotheses that initiation of resorption is impaired with unmineralized matrix, and that such alterations involve changes in the subcellullar distribution of TRAP, implicating a role for this enzyme in the resorption process. Our results reveal distinctly different morphological appearances of clast-like cells in rickets compared with normal osteoclasts and chondroclasts. Ordinary resorption structures of osteoclasts and chondroclasts at the cell-matrix border, i.e., ruffled borders and clear zones, are profoundly altered in favor of a less well-defined intermediate zone. TRAP distribution at the subcellullar level is also clearly different from that in osteoclasts and chondroclasts from normal rodents, with impaired secretion; consequently, the enzyme is unable to function in the matrix outside the ruffled border. Our ultrastructural observations demonstrate that in rickets, the clasts are incapable of degrading the poorly mineralized cartilage and bone efficiently. Rachitic clasts seem to be recruited to the matrix surface and interaction between cell and matrix is also initiated, but definitive resorption structures at the cell-matrix border are not normally developed. Whether resorption is inhibited by the mere lack of mineral or mineral-associated proteins, or by other mechanisms remains to be settled.
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48
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Abstract
X-Linked hypophosphataemic rickets (XLH) is frequently associated with short stature even when conventional treatment (1, 25-dihydroxyvitamin D(3) or 1alpha-hydroxyvitamin D(3) plus inorganic phosphate salts) is administered for a long time. The pathogenesis of growth retardation is probably multifactorial. Affected patients usually show normal growth hormone (GH) secretion. In some poorly growing XLH patients, long-term GH treatment associated with conventional therapy improves linear growth. GH treatment also increases phosphate retention but this effect is transient.
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49
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Abstract
Tumor-induced osteomalacia (TIO) is a rare and unique syndrome characterized by hypophosphatemia, excessive urinary phosphate excretion, reduced 1,25-dihydroxyvitamin D concentrations, and osteomalacia. Removal of the tumor is associated with a cure of the lesion. Several laboratories have now shown that conditioned medium derived from cultures of such tumors contain a small, heat-sensitive substance ("phosphatonin") of <25,000 daltons that specifically inhibits sodium-dependent phosphate transport in cultured renal proximal tubular epithelia. This substance does not increase cyclic adenosine monophosphate (cAMP) formation in tubular epithelial cells and does not increase cAMP excretion in urine. A substance with similar properties is present in the circulation of patients on hemodialysis. A syndrome with a remarkably similar biochemical phenotype, namely, X-linked hypophosphatemic rickets (XLH), also has a circulating factor with properties similar, if not identical, to those of the tumor-derived factor, "phosphatonin." The molecular defect in XLH has been shown to be due to a mutant endopeptidase, PHEX, whose substrate might be "phosphatonin." Hypophosphatemia and other biochemical abnormalities in TIO are due to excessive production of "phosphatonin" with normal PHEX function, whereas the biochemical abnormalities in XLH are caused by a mutant PHEX enzyme that fails to process "phosphatonin."
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50
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Cortet B, Bernière L, Solau-Gervais E, Hacène A, Cotten A, Delcambre B. Axial osteomalacia with sacroiliitis and moderate phosphate diabetes: report of a case. Clin Exp Rheumatol 2000; 18:625-8. [PMID: 11072608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
We report a new case of axial osteomalacia diagnosed in a 51-year-old white Caucasian male, made particular by its association with sacroiliitis, positive HLA-B27 antigen, and also moderate phosphate diabetes responsible for a decreased appendicular bone mass. The diagnosis was suspected when X-ray evaluation showed increased density and coarse trabeculation mainly involving the pelvis and spine. Dual energy X-ray absorptiometry confirmed the elevated bone density at the lumbar spine (T score: +1.92) contrasting with a decreased bone mass at the femoral neck (T score: -2.33). The diagnosis was confirmed by histomorphometry of the iliac crest showing marked thickening of the cortices (2190 microns +/- 0.574, N = 780 +/- 40) and an increased trabecular bone volume (33.24%, N = 14 +/- 3). Osteoid parameters were also markedly increased with an osteoid volume of 2.1% (N = 1.2 +/- 0.5) and a mean osteoid thickness of 28.7 microns (N = 13 +/- 2.5), with a normal bone fluoride content (0.082%, N < 0.10). Bone resorption as assessed on bone biopsy and by the measurement of markers of bone remodeling (serum procollagen type I C-terminal telopeptide and 24 hr urinary cross-laps to creatinine ratio) was increased. This latter finding was not necessarily due to axial osteomalacia and could be the consequence of moderate phosphate diabetes. The patient was treated with calcitriol which was promptly discontinued due to gastrointestinal symptoms and replaced by calcidiol without any significant effect on the low back pain.
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