Hyperphosphatemia associated with cortical hyperostosis and tumoral calcinosis

Familial Hyperphosphatemic Tumoral Calcinosis A Report From Saudi Arabia

The clinical details and radiologic and histopathologic findings of lesions from three male siblings and their female cousin with hyperphosphatemic tumoral calcinosis are presented. The three siblings were children of consanguineous parents. The patients were aged 5, 17, 19, and 20 years; however, they first presented when they were 3.5, 8, 4, and 5 years of age, respectively; resulting in a disease duration ranging from 1.5 to 15 years. All are alive with persistent disease. The eldest patient has an alpha-thalassemia trait. Sites of lesions included the periarticular soft tissues of gluteal region, the shoulder, elbow, interscapular area, axilla, and popliteal fossa. A calcified soft tissue mass was seen radiologically at all sites affected. Histologically, locules of calcified debris surrounded by multinucleated osteoclast-type giant cells and foamy histiocytes characterized all lesions. The cells showed cytoplasmic vacuoles that stained positively both with anti-alpha-1-antichymotrypsin and anti-alpha-1-antitrypsin. Ultrastructurally hydroxyapatite deposits were demonstrable in these cytoplasmic vacuoles. All patients had normocalcemia and hyperphosphatemia. A low normal blood level of 25-hydroxycholecalciferol was noted in the youngest patient. Surgical excision was unsuccessful as the lesions recurred and progressed. Medical therapy may only slow the progression of the disease process.

Dietary phosphate restriction normalizes biochemical and skeletal abnormalities in a murine model of tumoral calcinosis

Mutations in the GALNT3 gene cause tumoral calcinosis characterized by ectopic calcifications due to persistent hyperphosphatemia. We recently developed Galnt3 knockout mice in a mixed background, which had hyperphosphatemia with increased bone mineral density (BMD) and infertility in males. To test the effect of dietary phosphate intake on their phenotype, Galnt3 knockout mice were generated in the C57BL/6J strain and fed various phosphate diets: 0.1% (low), 0.3% (low normal), 0.6% (normal), and 1.65% (high). Sera were analyzed for calcium, phosphorus, alkaline phosphatase, creatinine, blood urine nitrogen, 1,25-dihydroxyvitamin D, osteocalcin, tartrate-resistant acid phosphatase 5b, and fibroblast growth factor 23 (Fgf23). Femurs were evaluated by dual-energy x-ray absorptiometry, dynamic histomorphometry, and/or microcomputed tomography. Galnt3 knockout mice in C57BL/6J had the same biochemical phenotype observed in our previous study: hyperphosphatemia, inappropriately normal 1,25-dihydroxyvitamin D level, decreased alkaline phosphatase activity, and low intact Fgf23 concentration but high Fgf23 fragments. Skeletal analyses of their femurs revealed significantly high BMD with increased cortical bone area and trabecular bone volume. On all four phosphate diets, Galnt3 knockout mice had consistently higher phosphorus levels and lower alkaline phosphatase and intact Fgf23 concentrations than littermate controls. The low-phosphate diet normalized serum phosphorus, alkaline phosphatase, and areal BMD but failed to correct male infertility in Galnt3 knockout mice. The high-phosphate diet did not increase serum phosphorus concentration in either mutant or control mice due to a compensatory increase in circulating intact Fgf23 levels. In conclusion, dietary phosphate restriction normalizes biochemical and skeletal phenotypes of Galnt3 knockout mice and, thus, can be an effective therapy for tumoral calcinosis.

Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations

The GALNT3 gene encodes GalNAc-T3, which prevents degradation of the phosphaturic hormone, fibroblast growth factor 23 (FGF23). Biallelic mutations in either GALNT3 or FGF23 result in hyperphosphatemic familial tumoral calcinosis or its variant, hyperostosis-hyperphosphatemia syndrome. Tumoral calcinosis is characterized by the presence of ectopic calcifications around major joints, whereas hyperostosis-hyperphosphatemia syndrome is characterized by recurrent long bone lesions with hyperostosis. Here we investigated four patients with hyperphosphatemia and clinical manifestations including tumoral calcinosis and/or hyperostosis-hyperphosphatemia syndrome to determine underlying genetic cause and delineate phenotypic heterogeneity of these disorders. Mutational analysis of FGF23 and GALNT3 in these patients revealed novel homozygous mutations in GALNT3. Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia. Three of the patients also had inappropriately normal 1,25-dihyroxyvitamin D [1,25(OH)(2)D] and confirmed low circulating intact FGF23 concentrations. The four novel GALNT3 mutations invariably resulted in hyperphosphatemia as a result of low intact FGF23, but other clinical manifestations were variable. Therefore, tumoral calcinosis and hyperostosis-hyperphosphatemia syndrome represent a continuous spectrum of the same disease caused by increased phosphate levels, rather than two distinct disorders.

Familial tumoral calcinosis and the role of O-glycosylation in the maintenance of phosphate homeostasis

Familial tumoral calcinosis refers to a group of disorders inherited in an autosomal recessive fashion. Hyperphosphatemic tumoral calcinosis is characterized by increased re-absorption of phosphate through the renal proximal tubule, resulting in elevated phosphate concentration and deposition of calcified deposits in cutaneous and subcutaneous tissues, as well as, occasionally, in visceral organs. The disease was found to result from mutations in at least 3 genes: GALNT3, encoding a glycosyltransferase termed ppGalNacT3, FGF23 encoding a potent phosphaturic protein, and KL encoding Klotho. Recent data showed that ppGalNacT3 mediates O-glycosylation of FGF23, thereby allowing for its secretion and possibly protecting it from proteolysis-mediated inactivation. Klotho was found to serve as a co-receptor for FGF23, thereby integrating the genetic data into a single physiological system. The elucidation of the molecular basis of HFTC shed new light upon the mechanisms regulating phosphate homeostasis, suggesting innovative therapeutic strategies for the management of hyperphosphatemia in common acquired conditions such as chronic renal failure.

Familial tumoral calcinosis: a forty-year follow-up on one family

BACKGROUND

Familial tumoral calcinosis is a rare autosomal recessive disorder that was first described well in a report on four patients from one family in 1969. The disease leads to periarticular ectopic calcifications. The original report described patients from black, healthy, unrelated parents with sixteen children, seven of whom had the disease.

METHODS

On the basis of retrospective chart reviews and interviews with surviving family members, we describe the long-term follow-up of this one family, encompassing as long as forty years. Of the sixteen siblings, seven had tumoral calcinosis.

RESULTS

All seven affected children had hyperphosphatemia. There were two subsequent generations comprising thirteen children and seven grandchildren with no instances of tumoral calcinosis. The seven affected patients were followed for as many as forty years and underwent an average of twenty-one operations (range, four to thirty-six operations) for the treatment of calcified lesions. The genetic defect has been identified as the GALNT3 gene, thus leading to the hyperphosphatemic form of the disease. Although two of the patients had died by the time of the present study, the remaining five provided accounts of the disease course, the response to surgery and to medical therapy, and the effect of therapy on their lives. Some members had relatively few lesions and surgical procedures (as few as four), whereas others had an unrelenting course of lesions, recurrences, and surgical procedures (as many as thirty-six, with numerous other procedures). Three patients had multiyear periods with few symptoms--one for seven years, one for twelve years, and one for fifteen years. No effective medical therapy was found to control the lesions, and operations were associated with a high recurrence rate.

CONCLUSIONS

Familial tumoral calcinosis has a varied natural history; some patients have an unrelenting course, while others may experience quiescent periods. The GALNT3 gene is responsible for the hyperphosphatemic form as seen in this family. Molecular testing may be of benefit to members of affected families, and future studies may help to explain the phenotypic variability among affected individuals. No medical or surgical treatment plan seemed to be effective for controlling the lesions in this family.

A novel missense mutation in GALNT3 causing hyperostosis-hyperphosphataemia syndrome

OBJECTIVE

Hyperostosis-hyperphosphataemia syndrome (HHS) is a rare hereditary disorder characterized by hyperphosphataemia, inappropriately normal or elevated 1,25-dihydroxyvitamin D(3) and localized painful cortical hyperostosis. HHS was shown to be caused by inactivating mutations in GALNT3, encoding UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase 3 (GalNAc-transferase; GALNT3). Herein, we sought to identify the genetic cause of hyperphosphataemia and tibial hyperostosis in a 19-year-old girl of Colombian origin.

METHODS

Genomic DNA was extracted and sequencing analysis of the GALNT3 and fibroblast growth factor 23 (FGF23) genes performed. Serum levels of intact and C-terminal FGF23 were measured using two different ELISA methods.

RESULTS

Mutational analysis identified a novel homozygous missense mutation in exon 6 of GALNT3 (1584 G>A), leading to an amino acid shift from Arg to His at residue 438 (R438H). The mutation was not found in over 200 control alleles or in any single nucleotide polymorphism databases. The R438 residue is highly conserved throughout species and in all known GalNAc-transferase family members. Modelling predicted the substitution deleterious for protein structure. Importantly, the phosphaturic factor FGF23 was differentially processed, as reflected by low intact (15 pg/ml) but high C-terminal (839 RU/ml) serum FGF23 levels.

CONCLUSIONS

We report on the first missense mutation in GALNT3 giving rise to HHS, since previous GALNT3 mutations in HHS caused aberrant splicing or premature truncation of the protein. The R438H substitution likely abrogates GALNT3 activity, in turn causing enhanced FGF23 degradation and subsequent hyperostosis/hyperphosphataemia.

Tumoral calcinosis: a case report

Tumoral Calcinosis is a distinct clinical and histological entity that is characterized by large periarticular deposits of calcium resembling a neoplasm and is found foremost in the region of hip, shoulder and elbow. We report a case of Tumoral Calcinosis in a 25-year-old male who presented to us with gradually increasing swelling of right axilla, and both hips of nearly two years duration. It was diagnostic enigma for the treating surgeons but with the help of an astute pathologist we diagnosed this rare condition and successfully treated it surgically.

Hyperostosis with hyperphosphatemia and tumoral calcinosis: a case report

The combination of hyperostosis and hyperphosphatemia is very rare. In this case report, we present a boy with a combination of diffuse hyperostosis and hyperphosphatemia. We evaluated most possible known causes of hyperphosphatemia and hyperostosis. He had normal renal function and serum parathormone level. Concerning some few similar cases, most of them from Middle Eastern countries, we present this combination (diffuse hyperostosis and hyperphosphatemia) as a new syndrome to be discussed in pediatric textbooks.

Novel GALNT3 mutations causing hyperostosis-hyperphosphatemia syndrome result in low intact fibroblast growth factor 23 concentrations

CONTEXT

Hyperostosis-hyperphosphatemia syndrome (HHS) is a rare metabolic disorder characterized by hyperphosphatemia and localized hyperostosis. HHS is caused by mutations in GALNT3, which encodes UDP-N-acetyl-alpha-D-galactosamine:polypeptide N- acetylgalactosaminyltransferase 3. Familial tumoral calcinosis (TC), characterized by ectopic calcifications and hyperphosphatemia, is caused by mutations in the GALNT3 or fibroblast growth factor 23 (FGF23) genes.

OBJECTIVE

Our objective was to identify mutations in FGF23 or GALNT3 and determine serum FGF23 levels in an HHS patient.

DESIGN

Mutation detection in FGF23 and GALNT3 was performed by DNA sequencing, and serum FGF23 concentrations were measured by ELISA.

PATIENTS OR OTHER PARTICIPANTS

A 5-year-old French boy with HHS and his family members participated.

RESULTS

The patient presented with painful cortical lesions in his leg. Radiographs of the affected bone showed diaphyseal hyperostosis. The lesional tissue comprised trabeculae of immature, woven bone surrounded by fibrous tissue. Biochemistry revealed elevated phosphate, tubular maximum rate for phosphate reabsorption per deciliter of glomerular filtrate, and 1,25-dihydroxyvitamin D levels. The patient was a compound heterozygote for two novel GALNT3 mutations. His parents and brother were heterozygous for one of the mutations and had no biochemical abnormalities. Intact FGF23 level in the patient was low normal, whereas C-terminal FGF23 was elevated, a pattern similar to TC.

CONCLUSION

The presence of GALNT3 mutations and elevated C-terminal, but low intact serum FGF23, levels in HHS resemble those seen in TC, suggesting that HHS and TC are different manifestations of the same disorder. The absence of biochemical abnormalities in the heterozygous individuals suggests that one normal allele is sufficient for secretion of intact FGF23.

Hyperostosis-hyperphosphatemia syndrome: a congenital disorder of O-glycosylation associated with augmented processing of fibroblast growth factor 23

Two hyperphosphatemic patients with mutations in GALNT3 showed low intact FGF23 levels with marked increase of processed C-terminal fragments. FGF23 protein has three O-linked glycans and FGF23 with incomplete glycosylation is susceptible to processing. Silencing GALNT3 resulted in enhanced processing of FGF23. Decreased function of FGF23 by enhanced processing is the cause of hyperphosphatemia in patients with GALNT3 mutation.

INTRODUCTION

Hyperostosis-hyperphosphatemia syndrome (HHS) is an autosomal recessive entity manifesting as severe hyperphosphatemia associated with episodic bone pain and radiological findings of cortical hyperostosis and periosteal reaction. Persistent hyperphosphatemia is not counterbalanced by PTH or 1,25-dihydroxyvitamin D, posing a mirror image of hypophosphatemic states attributed to increased fibroblast growth factor (FGF)23 activity.

MATERIALS AND METHODS

We describe two children with HHS who were found to be homozygous for a mutation in GALNT3 encoding a peptide involved in mucin-type O-glycosylation (ppGaNTase-T3). FGF23 levels were evaluated by two ELISAs and Western blotting. FGF23 protein was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Effect of silencing GALNT3 was evaluated using siRNA in cells transfected with expression vector for FGF23.

RESULTS

Both patients had low levels of the full-length FGF23 with markedly augmented amounts of the inactive fragments. Biologically active FGF23 has three O-linked glycans. FGF23 with only one or two O-linked glycans is processed into inactive fragments. Decreasing the expression of the GALNT3 gene by RNA interference resulted in enhanced processing of FGF23.

CONCLUSIONS

The primary defect in HHS is impairment of glycosylation of FGF23 resulting from mutations in GALNT3 and leading to augmented processing of FGF23. These changes in FGF23 abolish its phosphaturic effect and lead to severe persistent hyperphosphatemia. This study provides the pathogenetic mechanism of the first mucin-type O-glycosylation defect identified.

Hyperphosphatemia is prevalent among children with nephrotic syndrome and normal renal function

The aim of the study was to analyze systematically our observation that children with severe nephrotic syndrome (NS) have hyperphosphatemia despite normal kidney function. Forty-seven children with NS and normal glomerular filtration rate (GFR) were studied [26 with steroid-sensitive nephrotic syndrome (SSNS) and 21 with persistent NS]. The plasma phosphate level was expressed as the number of standard deviations (SDs) from the mean levels in age- and gender-matched controls. In SSNS plasma phosphate concentration was elevated (+3.7+/-2.0 SDs) during relapse and normalized (-0.7+/-1.7 SDs) in remission. In persistent NS the phosphate level was +4.0+/-2.1 SDs. Patients with marked hyperphosphatemia (>4 SDs) were younger (p<0.001), had lower plasma albumin (p<0.001), and had higher urinary protein levels (p<0.05). Hyperphosphatemia did not correlate with GFR, plasma calcium, or urinary sodium levels. Children with persistent NS had decreased serum 25(OH)D(3) and insulin-like growth factor 1 (IGF-1) concentrations. Hyperphosphatemia is prevalent among children with persistent nephrotic syndrome and normal renal function, correlates with its severity, and may result from increased urinary IGF-1 wasting.

Tumoral calcinosis: pearls, polemics, and alternative possibilities

Massive periarticular calcinosis of the soft tissues is a unique but not rare radiographic finding. On the contrary, tumoral calcinosis is a rare familial disease. Unfortunately, the term tumoral calcinosis has been liberally and imprecisely used to describe any massive collection of periarticular calcification, although this term actually refers to a hereditary condition associated with massive periarticular calcification. The inconsistent use of this term has created confusion throughout the literature. More important, if the radiologist is unfamiliar with tumoral calcinosis or disease processes that mimic this condition, then diagnosis could be impeded, treatment could be delayed, and undue alarm could be raised, possibly leading to unwarranted surgical procedures. The soft-tissue lesions of tumoral calcinosis are typically lobulated, well-demarcated calcifications that are most often distributed along the extensor surfaces of large joints. There are many conditions with similar appearances, including the calcinosis of chronic renal failure, calcinosis universalis, calcinosis circumscripta, calcific tendonitis, synovial osteochondromatosis, synovial sarcoma, osteosarcoma, myositis ossificans, tophaceous gout, and calcific myonecrosis. The radiologist plays a critical role in avoiding unnecessary invasive procedures and in guiding the selection of appropriate tests that can result in a conclusive diagnosis of tumoral calcinosis.

Tumoral calcinosis with hyperphosphatemia

Tumoral calcinosis is a rare disorder of mineral metabolism among adolescents and young adults characterized by deposition of calcific masses around large joints. It is less commonly reported in pediatric population and commonly mistaken for bone tumors. Typical lab parameters include hyperphosphatemia with normal levels of serum calcium, parathyroid hormone (PTH) and alkaline phosphatase. A ten-year-old boy with typical features of tumoral calcinosis is presented.

[Tumoral calcinosis of the plantar forefoot: a case report and review of the literature]

Tumoral calcinosis of the plantar forefoot is an uncommon benign condition resulting from deposits of hydroxyapatite crystals in periarticular soft tissue. The pathogenic mechanism remains to be clarified. This condition is generally observed in young subjects and a hereditary pattern is often discovered. We report the clinical, radiological, and biological findings in a case of right forefoot tumoral calcinosis observed in a sixteen-year-old girl and describe the surgical treatment and pathology results. Based on this case and a review of the literature, we discuss the different pathogenic hypotheses as well as the appropriate diagnostic and therapeutic approach.

Review of the literature: severe hyperphosphatemia

A patient with a markedly elevated serum phosphorus level (23.9 mg/dL) is described, followed by a brief review of severe hyperphosphatemia. Elevated serum phosphorus levels may be artifactual or true. True hyperphosphatemia is usefully subdivided according to (a) whether phosphorus is added to the extracellular fluid from a variety of exogenous or endogenous sources, or (b) whether the urinary excretion of phosphorus is reduced from either decreased glomerular filtration or increased tubular reabsorption. Severe hyperphosphatemia, defined herein as levels of 14 mg/dL or higher, is almost invariably multifactorial--usually resulting from addition of phosphorus to the extracellular fluid together with decreased phosphorus excretion. The hyperphosphatemia of the patient described herein appeared to result from a combination of dietary phosphorus supplementation, acute renal failure, acute pancreatitis, and ischemic bowel disease, complicated by lactic acidosis.