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Phosphaturic mesenchymal tumor with symptoms related to osteomalacia that appeared one year after tumorectomy.

A 45-year-old man was admitted to our hospital because of bone pain and hypophosphatemia. He had undergone surgery 2 years previously for a "benign unclassified mesenchymal tumor" in the skull, but there were no clinical symptoms related to osteomalacia. His laboratory examination revealed low serum phosphate, high alkaline phosphatase, and normal calcium levels. The diagnosis of tumor-induced osteomalacia due to phosphaturic mesenchymal tumor mixed connective tissue variant (PMTMCT) was made by re-examining the pathologic specimens. Oral supplementation with phosphate and 1-25-dihydroxyvitamin D relieved his clinical symptoms and laboratory values returned to normal. However, subcutaneous administration of octreotide had no clinical effect. Clinicians and pathologists should be aware of the existence of PMTMCT especially nonphosphaturic or asymptomatic variants of this disorder.

Cranial Fossa, Posterior↗

Vitamin D resistant hypophosphatemic osteomalacia associated with osteosarcoma of the mandible: report of a case.

A case of vitamin D resistant hypophosphatemic osteomalacia associated with osteosarcoma of the mandible is presented. The patient complained of lumbar, knee and foot pain and muscle weakness of two years' duration. Serum phosphorous was 1.0-1.6 mg/dl, tubular reabsorption of phosphorus was 47 to 58%, TmPO4/GFR was o.7-1.2 mg/dl. Aminoaciduria was noted. Bone biopsy confirmed the diagnosis of osteomalacia. He partially responded to the treatment with 1 alpha()H) D3 and sodium phosphate. After removal of sarcoma of the mandible, symptoms remitted and pertinent laboratory data became normal except serum alkaline phosphatase for more than one year without treatment. It is suggested that an impaired response of the tubule and bone to active vitamin D3, caused in some way by the osteosarcoma might be one of the causes of osteomalacia in this case.

Adult↗

Erythrocytosis in hypophosphatemic rickets: irreversible complication due to nephrocalcinosis after vitamin D and phosphate therapy.

A patient with hypophosphatemic vitamin D-resistant rickets developed secondary erythrocytosis during treatment with large doses of vitamin D2 and phosphate. Erythrocytosis was accompanied by a fall in circulating plasma volume and appeared to have developed as a consequence of nephrocalcinosis because it occurred after the appearance of nephrocalcinosis following several episodes of hypercalcemia and hyperphosphatemia. Nephrocalcinosis and erythrocytosis did not disappear even after recovery of renal function. Thus, the present observations point to the importance of preventing these irreversible complications that could cause renal failure, erythrocytosis, and thrombotic events during the management of hypophosphatemic vitamin D-resistant rickets.

Adult↗

Electrocochleographic changes in the hearing loss associated with X-linked hypophosphataemic osteomalacia.

Transtympanic electrocochleography was carried out on 13 patients (21 ears) suffering from X-linked hypophosphataemic osteomalacia, and known to have cochlear hearing loss. The majority of ears exhibited a cochlear pattern of cochleogram with a recruiting input/output function and a markedly biphasic action potential. In addition 14 ears yielded a greatly enhanced negative summating potential, suggesting the presence of endolymphatic hydrops. It is proposed that the hearing loss so frequently associated with this condition is in part due to endolymphatic hydrops.

Acoustic Stimulation↗

Hypophosphatemic rickets with sacroiliitis-like presentation in an adolescent.

Rickets can manifest with a wide variety of rheumatic symptoms. In this paper, a fifteen year old female patient with hypophosphatemic rickets presenting with symptoms suggesting sacroiliitis at disease onset is reported. The sacroiliac joint involvement in this case was attributed to the subchondral bone fractures due to the secondary hyperparathyroidism. Her symptoms resolved completely after treatment with calcitriol and phosphate solution for hypophosphatemic rickets.

Adolescent↗

Inherited renal disease and genetic counseling.

Inherited renal abnormalities and diseases are less common than acquired disorders. However, they are of great interest because their study results in increased understanding of the embryogenesis and physiology of the kidney, the pathogenesis of acquired disease, improved therapeutic approaches and accuracy of genetic counseling. Inherited defects of the kidney may be structural, functional or part of genetically transmitted systemic diseases that have major effects on renal structure and/or functions. Most structural defects of the kidney, with the exception of varying forms of cystic disease and the hereditary nephritides, are congenital and only rarely inherited in a Mendelian sense. The majority of genetically transmitted abnormalities of proximal and distal tubular function are caused by inborn metabolic errors or enzyme defects and deficiencies. Amniocentesis, ultrasonography and enzymatic assays have made the prenatal diagnosis of many inherited renal diseases possible so that more accurate counseling early therapeutic intervention may be provided.

Adolescent↗

Genetic defects of the 1,25-dihydroxyvitamin D3 receptor.

Target organ resistance to steroid hormone action is known to produce clinical disorders ranging from testicular feminization in the case of androgen resistance to hypocalcemic vitamin D-resistant ricets (HVDRR) in the case of 1,25-dihydroxyvitamin D3. The etiologic basis of these disorders is thought to be genetic mutations in the gene encoding receptors for these hormones. We investigated this possibility by analyzing the vitamin D receptor (VDR) protein, mRNA, and DNA from patients with HVDRR. This autosomal recessive disease of children is characterized by early onset rickets, hypocalcemia, hyperparathyroidism, and elevated levels of 1,25-(OH)2D3. Cells from patients fall into three general classes of molecular defects: (i) decreased or absent hormone binding; (ii) decreased affinity of VDR for DNA, or; (iii) defective nuclear translocation or retention. Analysis of the DNA and/or mRNA from these cells has identified missense mutations in the DNA binding (zinc finger) domain and a nonsense mutation in the steroid binding domain of VDR. The mutations were individually recreated in wild type VDR and the expressed mutant protein behaved biochemically identically to the patient receptor. Further studies have shown that the receptor is unable to interact with the specific hormone response element (HRE) of the osteocalcin gene and activate appropriate transcription. Rapid diagnostic genotyping of these mutations is possible with either restriction digestion or allele-specific oligonucleotide hybridization. Analysis of these naturally occurring, disease producing mutations of a gene regulatory protein should provide insight into the key amino acid residues of the protein and the mechanism by which steroids modulate gene transcription.

Amino Acid Sequence↗

Craniosynostosis in vitamin D-resistant rickets. A mouse model.

Craniosynostosis and associated craniofacial deformities, such as frontal bossing, often occur as symptoms of vitamin D-resistant rickets in children. Similar skull deformities develop in mice with X-linked dominant hypophosphatemia, the most common form of vitamin D-resistant rickets. These mice have a short, wide, high neurocranium, which suggested an inhibition of coronal suture growth. To study this question, we compared histologically the postnatal development of the coronal sutures in normal and hypophosphatemic mice between 1 and 13 weeks of age. Premature fusion of the coronal suture occurred in hypophosphatemic mice by 4 weeks of age. The proportion of the suture obliterated by bone varied among individual animals, but craniosynostosis was present in all animals studied at 4 weeks and older. Fusion of the coronal suture did not occur through 13 weeks of age in any of the normal mice studied. The x-linked hypophosphatemic mouse is an animal model that can be used to study the role of vitamin D-resistant rickets in the development of craniosynostosis, to relate craniosynostosis to the development of associated skull deformities, and to test new treatment procedures.

Animals↗

Transport of phosphate by plasma membranes of the jejunum and kidney of the mouse model of hypophosphatemic vitamin D-resistant rickets.

The hypophosphatemic mouse is a useful model for the study of hypophosphatemic vitamin D-resistant rickets in humans. Hypophosphatemia and hyperphosphaturia are the main biochemical findings in the patients and in mice with the disorder. The exact membrane localization of the site of the defect in phosphate transport in humans is not known. We utilized a well-validated technique of brush border and basolateral membrane vesicles to investigate phosphate transport across the enterocyte and the renal tubule cells of the hypophosphatemic (Hyp) mice model. Phosphate uptake by brush border membranes of jejunal enterocytes revealed similar initial rates (slopes were 0.007 and 0.006 for Hyp and control mice, respectively). Kinetics of jejunal Na(+)-dependent phosphate uptake showed a Vmax of 0.21 +/- 0.03 and 0.19 +/- 0.02 nmol/mg protein/15 sec, and Km of 0.12 +/- 0.07 and 0.09 +/- 0.02 mM in the Hyp and control mice, respectively. Kinetics of basolateral uptake of phosphate were also similar (Vmax of 0.05 +/- 0.01 and 0.06 +/- 0.02 nmol/mg protein/10 sec and Km of 0.013 +/- 0.004 and 0.028 +/- 0.022 mM, respectively). On the other hand, kinetics of Na(+)-dependent phosphate uptake by renal brush border membrane vesicles (BBMV) were markedly decreased (Vmax of 0.42 +/- 0.03 and 1.09 +/- 0.06 nmol/mg protein/15 sec, P < 0.01, and Km of 0.01 +/- 0.003 and 0.05 +/- 0.02 mM, P < 0.02, in the Hyp and control mice, respectively). Kinetics of Na(+)-dependent phosphate uptake by renal basolateral membrane were not decreased (Vmax of 0.19 +/- 0.02 and 0.21 +/- 0.02 nmol/mg protein/10 sec and Km of 0.012 +/- 0.003 and 0.012 +/- 0.004 mM for Hyp and control mice, respectively). To determine whether the decrease in renal BBMV is secondary to alteration in the Na(+)-dependent phosphate transporter or due to changes in the Na+ gradient, two studies were conducted: first, a tracer exchange study in renal BBMV which showed a decrease in phosphate uptake in Hyp BBMV compared with controls, confirming the kinetic studies; and second, an Na+ permeability study in renal BBMV of Hyp and control mice which showed no differences in Na+ permeability across the renal BBMV. These findings suggest that the defect in the hypophosphatemic mice is localized only to the brush border membranes of the kidney and is not due to alteration in the driving forces across the membranes.

Animals↗