Phosphaturic mesenchymal tumor and related wound problem.

INTRODUCTION: Phosphaturic mesenchymal tumor mixed connective tissue type (PMT/MCT) is the most common type (up to 90%) of phosphaturic mesenchymal tumor (PMT), a rare clinicopathologic entity. Besides overproduction of fibroblast growth factor 23 (FGF23), there is a big variation of immunohistochemical characteristic across types of PMT, which makes it difficult to obtain an early diagnosis of PMT/MCT. As a benign tumor, PMT/MCT usually happens in subcutaneous tissues and leads to nonhealing of wound. A complete excision of PMT/MCT facilitates wound healing. CONCLUSIONS: Review of the existing evidence indicates that early diagnosis of PMT/MCT is critically important when treating PMT/MCT wound. Hence standardization of early diagnosis for PMT/MCT is mandated.

Tumor(s) induced osteomalacia--a curious case of double trouble.

CONTEXT: We report a case of tumor-induced osteomalacia with evidence of synchronous multifocal fibroblast growth factor 23 (FGF23) production. OBJECTIVE: The aim is to present a case of tumor-induced osteomalacia and to highlight the fact that incomplete removal of multifocal FGF23-producing tumors, which are not entirely picked up by functional imaging, could be the cause of treatment failure. SETTING: The patient was treated in the Department of Endocrinology of a tertiary care center in India. PATIENT: We report the case of a 42-year-old male with tumor-induced osteomalacia. INTERVENTION: We treated the tumor-induced osteomalacia with staged surgery of the two tumors. The 18F-fluorodeoxyglucose (FDG)-avid lesion (considered the sole culprit lesion after functional imaging) was resected first, followed by the non-FDG-avid lesion. The sequential removal of both tumors resulted in complete cure. RESULTS: The patient had hypophosphatemia and hyperphosphaturia. C-Terminal FGF23 level was elevated. Positron emission tomography-computed tomography showed two lesions-an FDG-avid lesion in the right leg, and a non-avid lesion in the left thigh. After removal of the FDG-avid lesion, the hypophosphatemia persisted, and the FGF23 level showed only modest reduction. The patient had complete clinical and biochemical resolution only after removal of the second non-FDG-avid tumor. CONCLUSIONS: We present the case of a tumor-induced osteomalacia whose biochemical parameters did not improve after removal of the FDG-avid tumor initially. The possibility of multifocal FGF23 production was considered, and the second, non-FDG-avid lesion was resected, which resulted in complete cure. Thorough clinical examination and meticulous follow-up with documentation of the biochemical resolution are necessary for management of all patients with this rare disorder.

Selective venous catheterization for the localization of phosphaturic mesenchymal tumors.

Tumor-induced osteomalacia (TIO) is characterized by renal phosphate wasting, hypophosphatemia, and aberrant vitamin D(3) metabolism and is caused by fibroblast growth factor 23 (FGF-23)-producing mesenchymal tumors, which are often difficult to locate. We investigated the utility of selective venous sampling in tumor localization. The primary endpoint was identification of the FGF-23 concentration ratio between the venous drainage of the tumor bed and the general circulation that was diagnostic of the location of an FGF-23-secreting tumor. Fourteen subjects underwent 15 sampling procedures after functional and anatomic imaging studies. Subjects fit into three imaging categories: no suspicious site, multiple sites, and single site (positive controls). FGF-23 levels were measured by ELISA. Suspicious tumors were resected for diagnosis, confirmation, and cure. In subjects with a positive venous sampling study and subsequent cure, a minimum ratio of 1.6 was diagnostic. In 7 of 14 subjects there was suggestive imaging, a diagnostic ratio, and an associated TIO tumor (true positive). Four of these required complicated resection procedures. In 4 of 14 subjects with no suspicious site on imaging studies, an FGF-23 diagnostic ratio was not detected (true negative). Biopsy or resection of a single lesion in 2 of 14 subjects with a diagnostic ratio failed to identify a TIO tumor (false positive). A diagnostic FGF-23 ratio was absent in 1 of 14 subjects whose tumor was a single highly suspicious lesion on imaging studies (false negative). These data yield a sensitivity of 0.87 [95% confidence interval (CI) 0.47-0.99] and a specificity of 0.71 (95% CI 0.29-0.96). Selective venous sampling for FGF-23 was particularly useful in subjects with multiple suspicious sites or an anatomically challenging planned resection but not in the absence of a suspicious lesion on imaging studies.

Prenatal diagnosis of familial lethal hypophosphatasia using imaging, blood enzyme levels, chorionic villus sampling and archived fetal tissue.

Hypophosphatasia is an inheritable disorder characterized by defective bone mineralization and a deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) activity. Screening for mutations in the TNSALP gene allows genetic counseling and prenatal diagnosis of the disease in families with severe forms of hypophosphatasia. A 33-year-old, gravida 4, para 3 Japanese woman was referred to Nagoya City University Hospital for prenatal genetic counseling because of two previous occurrences of fetal bone anomalies. The molecular examination showed that the fetus was homozygous for the TNSALP gene mutation c.1559delT, each parent being heterozygous. Genetic counseling was offered and at the next pregnancy, chorionic villus sampling was performed, whereupon genetic analysis confirmed that the fetus did not carry the familial mutation c.1559delT. Postnatal molecular genetic analysis using the cord tissue can provide a diagnosis of lethal hypophosphatasia and prenatal genetic diagnosis of the TNSALP gene allows time for parental counseling and delivery planning.

Normal FGF23 levels in adult idiopathic phosphate diabetes.

Fibroblast growth factor 23 (FGF23), a recently discovered phosphaturic substance playing a key role in genetic and oncogenic phosphate diabetes, is involved in the physiological regulation of phosphate metabolism. Moderate idiopathic phosphate diabetes (IPD) leading to male osteoporosis and diffuse pain resembling fibromyalgia has been described. The aim of our study was to define the role of FGF23 in the mechanism of IPD. The study concerned 29 patients with IPD, mean age 53 +/- 11 years, of whom 72% were men. Fifteen subjects without bone disease and with normal serum phosphate and calcium levels were used as controls. Phosphate diabetes was confirmed by phosphate reabsorption level <85% and phosphate reabsorption threshold (TmPO4/GFR) <0.83. Known causes of phosphate diabetes were excluded. Fasting level of FGF23, serum phosphate, 1-25(OH)2D3, and parathyroid hormone were measured in patients and compared with FGF23 and serum phosphate in healthy controls. Spinal and hip bone mineral density (BMD) were measured by osteodensitometry. Sixteen of 29 patients had diffuse pain, 10 had osteoporosis according to the World Health Organization criteria, and 11 had osteopenia. Serum phosphate was significantly lower in patients than in controls, but FGF23 levels did not differ. Compared to patients with normal bone status, patients with osteopenia and osteoporosis had significantly decreased FGF23 levels, whereas serum phosphate was identical in the two groups. In all patients, serum phosphate and FGF23 were positively correlated and FGF23 and 1-25(OH)2D3 were negatively correlated. FGF23 seems not be a cause of IPD, and the FGF23/phosphate/1-25(OH)2D3 axis appeared to be functional.

Pathogenic role of Fgf23 in Hyp mice.

Inactivating mutations of the PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) endopeptidase, the disease-causing gene in X-linked hypophosphatemia (XLH), results in increased circulating levels of fibroblastic growth factor-23 (FGF23), a bone-derived phosphaturic factor. To determine the causal role of FGF23 in XLH, we generated a combined Fgf23-deficient enhanced green fluorescent protein (eGFP) reporter and Phex-deficient Hyp mouse model (Fgf23(+/-)/Hyp). eGFP expression was expressed in osteocytes embedded in bone that exhibited marked upregulation of eGFP in response to Phex deficiency and in CD31-positive cells in bone marrow venules that expressed low eGFP levels independently of Phex. In bone marrow stromal cells (BMSCs) derived from Fgf23(-/-)/Hyp mice, eGFP expression was also selectively increased in osteocyte-like cells within mineralization nodules and detected in low levels in CD31-positive cells. Surprisingly, eGFP expression was not increased in cell surface osteoblasts, indicating that Phex deficiency is necessary but not sufficient for increased Fgf23 expression in the osteoblast lineage. Additional factors, associated with either osteocyte differentiation and/or extracellular matrix, are necessary for Phex deficiency to stimulate Fgf23 gene transcription in bone. Regardless, the deletion of Fgf23 from Hyp mice reversed the hypophosphatemia, abnormal 1,25(OH)(2)D(3) levels, rickets, and osteomalacia associated with Phex deficiency. These results suggest that Fgf23 acts downstream of Phex to cause both the renal and bone phenotypes in Hyp mice.

Serum MEPE-ASARM-peptides are elevated in X-linked rickets (HYP): implications for phosphaturia and rickets.

MEPE (Matrix Extracellular PhosphoglycoprotEin) expression is markedly elevated in X-linked-hypophosphatemic-rickets (HYP) and tumor-induced osteomalacia (TIO). In normal individuals, circulating serum-levels of MEPE are tightly correlated with serum-phosphorus, parathyroid hormone (PTH) and bone mineral density (BMD). Also, MEPE derived, C-terminal ASARM-peptides are candidate minhibins and/or phosphatonins. Our aims were to determine: 1. whether MEPE-ASARM-peptide(s) are abnormally elevated in HYP/hyp serum, and, 2. whether the ASARM-peptide(s) accumulate in hyp mice kidney renal-tubules. Using a specific competitive ELISA we measured a five fold increase (P=0.007) of serum ASARM-peptide(s) in human HYP patients (normal subjects 3.25 microM n=9; S.E.M.=0.51 and HYP-patients 15.74 microM, n=9; S.E.M.=3.32). A 6.23 fold increase (P=0.008) was measured in hyp male mice compared with their normal male siblings (normal-siblings, 3.73 muM, S.E.M.=0.57, n=3; and hyp-mice 23.4 microM, n=3, S.E.M.=4.01). Renal immuno-histological screening also revealed a dramatic increase of ASARM-peptides in regions anatomically consistent with the proximal convoluted tubules. This study demonstrates for the first time that markedly elevated serum levels of protease-resistant ASARM-peptide(s) occur in HYP/hyp and they accumulate in murine hyp kidneys. These peptides are thus likely responsible for the phosphaturia and defective mineralization in HYP/hyp and TIO.

Transgenic mice overexpressing human fibroblast growth factor 23 (R176Q) delineate a putative role for parathyroid hormone in renal phosphate wasting disorders.

Fibroblast growth factor 23 (FGF23) is a recently characterized protein likely involved in the regulation of serum phosphate homeostasis. Increased circulating levels of FGF23 have been reported in patients with renal phosphate-wasting disorders, but it is unclear whether FGF23 is the direct mediator responsible for the decreased phosphate transport at the proximal renal tubules and the altered vitamin D metabolism associated with these states. To examine this question, we generated transgenic mice expressing and secreting from the liver human FGF23 (R176Q), a mutant form that fails to be degraded by furin proteases. At 1 and 2 months of age, mice carrying the transgene recapitulated the biochemical (decreased urinary phosphate reabsorption, hypophosphatemia, low serum 1,25-dihydroxyvitamin D(3)) and skeletal (rickets and osteomalacia) alterations associated with these disorders. Unexpectantly, marked changes in parameters of calcium homeostasis were also observed, consistent with secondary hyperparathyroidism. Moreover, in the kidney the anticipated alterations in the expression of hydroxylases associated with vitamin D metabolism were not observed despite the profound hypophosphatemia and increased circulating levels of PTH, both major physiological stimuli for 1,25-dihydroxyvitamin D(3) production. Our findings strongly support the novel concept that high circulating levels of FGF23 are associated with profound disturbances in the regulation of phosphate and vitamin D metabolism as well as calcium homeostasis and that elevated PTH levels likely also contribute to the renal phosphate wasting associated with these disorders.

Effect of gene dose and parental origin on bone histomorphometry in X-linked Hyp mice.

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.

Serum FGF23 levels in normal and disordered phosphorus homeostasis.

UNLABELLED: We investigated if the circulating levels of the phosphaturic factor FGF23 are elevated in subjects with XLH. Although we failed to find a statistically significant increase, FGF23 levels were significantly correlated with the degree of hypophosphatemia in XLH. In contrast, FGF23 levels were markedly increased in subjects with ESRD and correlated inversely with the degree of hyperphosphatemia. INTRODUCTION: Inactivating mutations of PHEX cause renal phosphate wasting in X-linked hypophosphatemic rickets (XLH) because of the accumulation of a phosphaturic hormone called phosphatonin. The recent discovery that FGF23 is the circulating phosphaturic factor in autosomal dominant hypophosphatemia raises the possibility that FGF23 is phosphatonin. METHODS: Fasting serum FGF23 levels and serum biochemical parameters were measured using a human FGF23 (C-terminal) ELISA assay in 11 subjects with XLH and 42 age-matched controls, 5 subjects with hypophosphatemia of unknown cause, and 14 hyperphosphatemic subjects with end stage renal disease (ESRD). Associations between variables were examined using the Spearman's correlation coefficient and linear regression analysis. RESULTS AND CONCLUSIONS: FGF23 (RU/ml) concentrations were not different (p = 0.11) between control and hypophosphatemic XLH subjects, but were significantly increased in hyperphosphatemic subjects with ESRD (p < 0.001). Western blot analysis found the presence of both full-length and C-terminal FGF23 fragments in serum from ESRD subjects. There was a strong inverse correlation between FGF23 and serum phosphorus (r = -0.60) and calcium and phosphorus (Ca x P) product (r = -0.65) in XLH, and a strong positive relationship between FGF23 and Pi (r = 0.50) and Ca x P product (r = 0.62) in ESRD. FGF23 levels were variably elevated in subjects with hypophosphatemia of unknown cause, one of which had tumor-induced osteomalacia (TIO). Removal of the tumor resulted in rapid reduction in serum FGF23 levels. These findings suggest that FGF23 has a possible role in mediating hypophosphatemia in XLH and TIO, but the overlapping levels of FGF23 in hypophosphatemic disorders and normal subjects indicate that serum phosphorus and FGF23 can also be independently regulated.

Fibroblast growth factor 23 in oncogenic osteomalacia and X-linked hypophosphatemia.

BACKGROUND: Mutations in fibroblast growth factor 23 (FGF-23) cause autosomal dominant hypophosphatemic rickets. Clinical and laboratory findings in this disorder are similar to those in oncogenic osteomalacia, in which tumors abundantly express FGF-23 messenger RNA, and to those in X-linked hypophosphatemia, which is caused by inactivating mutations in a phosphate-regulating endopeptidase called PHEX. Recombinant FGF-23 induces phosphaturia and hypophosphatemia in vivo, suggesting that it has a role in phosphate regulation. To determine whether FGF-23 circulates in healthy persons and whether it is elevated in those with oncogenic osteomalacia or X-linked hypophosphatemia, an immunometric assay was developed to measure it. METHODS: Using affinity-purified, polyclonal antibodies against [Tyr223]FGF-23(206-222)amide and [Tyr224]FGF-23(225-244)amide, we developed a two-site enzyme-linked immunosorbent assay that detects equivalently recombinant human FGF-23, the mutant form in which glutamine is substituted for arginine at position 179 (R179Q), and synthetic human FGF-23(207-244)amide. Plasma or serum samples from 147 healthy adults (mean [+/-SD] age, 48.4+/-19.6 years) and 26 healthy children (mean age, 10.9+/-5.5 years) and from 17 patients with oncogenic osteomalacia (mean age, 43.0+/-13.3 years) and 21 patients with X-linked hypophosphatemia (mean age, 34.9+/-17.2 years) were studied. RESULTS: Mean FGF-23 concentrations in the healthy adults and children were 55+/-50 and 69+/-36 reference units (RU) per milliliter, respectively. Four patients with oncogenic osteomalacia had concentrations ranging from 426 to 7970 RU per milliliter, which normalized after tumor resection. FGF-23 concentrations were 481+/-528 RU per milliliter in those with suspected oncogenic osteomalacia and 353+/-510 RU per milliliter (range, 31 to 2335) in those with X-linked hypophosphatemia. CONCLUSIONS: FGF-23 is readily detectable in the plasma or serum of healthy persons and can be markedly elevated in those with oncogenic osteomalacia or X-linked hypophosphatemia, suggesting that this growth factor has a role in phosphate homeostasis. FGF-23 measurements might improve the management of phosphate-wasting disorders.

Increased circulatory level of biologically active full-length FGF-23 in patients with hypophosphatemic rickets/osteomalacia.

Hypophosphatemic rickets/osteomalacia with inappropriately low serum 1,25-dihidroxyvitamin D level is commonly observed in X-linked hypophosphatemic rickets/osteomalacia, autosomal dominant hypophosphatemic rickets/osteomalacia and tumor-induced osteomalacia. Although the involvement of a newly identified factor, FGF-23, in the pathogenesis of ADHR and TIO has been suggested, clinical evidence indicating the role of FGF-23 has been lacking. We have previously shown that FGF-23 is cleaved between Arg(179) and Ser(180), and this processing abolished biological activity of FGF-23 to induce hypophosphatemia. Therefore, sandwich ELISA for biologically active intact human FGF-23 was developed using two kinds of monoclonal antibodies that requires the simultaneous presence of both the N-terminal and C-terminal portion of FGF-23. The serum levels of FGF-23 in healthy adults were measurable and ranged from 8.2 to 54.3 ng/L. In contrast, those in a patient with TIO were over 200 ng/L. After the resection of the responsible tumor, the elevated FGF-23 level returned to normal level within 1 h. The increase of serum concentrations of 1,25-dihidroxyvitamin D and phosphate, and the decrease of serum 24,25-dihydroxyvitamin D followed the change of FGF-23. In addition, the elevated serum FGF-23 levels were demonstrated in most patients with XLH. It is likely that increased serum levels of FGF-23 contributes to the development of hypophosphatemia not only in TIO but also in XLH.

Effect of dipyridamole on serum and urinary phosphate in X-linked hypophosphatemia.

X-linked hypophosphatemia (XLH) is characterized clinically by rickets, hypophosphatemia and hyperphosphaturia. Conventional treatment of XLH with oral phosphate and vitamin D is associated with hypercalcuria and nephrocalcinosis. Recently, intravenous and oral dipyridamole has been reported to decrease fractional excretion of phosphate in adults with idiopathic hyperphosphaturia. Our objective was to determine whether oral dipyridamole therapy reduces urinary phosphate excretion and increases serum phosphate concentration in children with XLH. A prospective study was performed in six children with XLH. The average age of the patients at the start of the study was 12.5+/-1.0 years. The effects of 12 weeks of oral dipyridamole therapy, at 4.4+/-0.4 mg/kg body weight per day, on serum phosphorous, parathyroid hormone (PTH), 1,25 (OH)2 vitamin D, osteocalcin, tubular maximum for phosphate reabsorption (TmP/GFR), urinary calcium excretion, and cyclic adenosine 3',5'-monophosphate (cAMP) excretion, were compared to baseline levels. Our results show that there was no change in serum phosphorous concentration or TmP/GFR after 12 weeks of dipyridamole therapy. Dipyridamole therapy also had no effect on serum PTH, serum 1,25 (OH)2 vitamin D, alkaline phosphatase, osteocalcin levels, urinary calcium or cAMP excretion. We therefore concluded that in children with XLH, a 12-week course of dipyridamole had no effect on serum phosphorous or its urinary excretion. Dipyridamole therapy is unlikely to improve the bone disease in children with XLH.

Renal Fanconi syndrome: first sign of partial respiratory chain complex IV deficiency.

A 2-year-old boy who developed hypophosphatemic rickets without signs of muscular weakness or neurological disturbances is presented. Biochemical findings included hypophosphatemia, metabolic acidosis, hypouricemia, hyperphosphaturia, severe glucosuria, generalized hyperaminoaciduria, hypercalciuria, proteinuria with elevated excretion of IgG, transferrin, albumin and high levels of alpha-1-microglobulin. Urine concentration capacity and creatinine clearance were normal. Lactaturia without elevated levels of plasma lactate and a high urinary excretion of beta-hydroxybutyrate were suggestive for mitochondriopathy. Partial deficiency of cytochrome c oxidase (complex IV of the respiratory chain) was found in skeletal muscle. A renal biopsy specimen demonstrated enlarged mitochondria with abnormal arborization and disorientation of the cristae in the proximal tubular cells. Reduced activity of mitochondrial cytochrome c oxidase in tubular cells could be demonstrated by ultracytochemistry. In conclusion, rickets due to the renal Fanconi syndrome can be the first clinical sign of mitochondrial cytopathies without extra-renal symptoms. Elevated excretion of lactate and ketone bodies in urine may serve as a diagnostic marker.

Brown tumour as a complication of secondary hyperparathyroidism in severe long-lasting vitamin D deficiency rickets.

UNLABELLED: Brown tumour is a localised form of fibrous-cystic osteitis associated with primary or secondary hyperparathyroidism. Despite the fact that secondary hyperparathyroidism occurs in vitamin D deficiency rickets, no cases of rickets with brown tumour have so far been described. We present a 2.9-year-old girl who had brown tumour of the mandible due to severe vitamin D deficiency rickets. Treatment with vitamin D3 corrected the hyperparathyroidism rapidly which was followed by gradual regression in tumour size. CONCLUSION: Brown tumour can develop in severe, long-standing vitamin D deficiency rickets and responds to vitamin D treatment.