Skeletal mineralization is initiated in matrix vesicles (MVs), the small extracellular vesicles derived from osteoblasts and chondrocytes. Calcium and inorganic phosphate (Pi) taken up by MVs form hydroxyapatite crystals, which propagate on collagen fibrils to mineralize the extracellular matrix. Insufficient calcium or phosphate impairs skeletal mineralization. Because active vitamin D is necessary for intestinal calcium absorption, vitamin D deficiency is a significant cause of rickets/osteomalacia. Chronic hypophosphatemia also results in rickets/osteomalacia. Excessive action of fibroblast growth factor 23 (FGF23), a key regulator of Pi metabolism, leads to renal Pi wasting and impairs vitamin D activation. X-linked hypophosphatemic rickets (XLH) is the most common form of hereditary FGF23-related hypophosphatemia, and enhanced FGF receptor (FGFR) signaling in osteocytes may be involved in the pathogenesis of this disease. Increased extracellular Pi triggers signal transduction via FGFR to regulate gene expression, implying a close relationship between Pi metabolism and FGFR. An anti-FGF23 antibody, burosumab, has recently been developed as a new treatment for XLH. In addition to various forms of rickets/osteomalacia, hypophosphatasia (HPP) is characterized by impaired skeletal mineralization. HPP is caused by inactivating mutations in tissue-nonspecific alkaline phosphatase, an enzyme rich in MVs. The recent development of enzyme replacement therapy using bone-targeting recombinant alkaline phosphatase has improved the prognosis, motor function, and quality of life in patients with HPP. This links impaired skeletal mineralization with various conditions, and unraveling its pathogenesis will lead to more precise diagnoses and effective treatments.
Absorption ; Alkaline Phosphatase ; Calcium ; Chondrocytes ; Collagen ; Diagnosis ; Durapatite ; Enzyme Replacement Therapy ; Extracellular Matrix ; Extracellular Vesicles ; Familial Hypophosphatemic Rickets ; Fibroblast Growth Factors ; Gene Expression ; Humans ; Hypophosphatasia ; Hypophosphatemia ; Metabolism ; Miners ; Osteoblasts ; Osteocytes ; Prognosis ; Quality of Life ; Receptors, Fibroblast Growth Factor ; Rickets ; Signal Transduction ; Vitamin D ; Vitamin D Deficiency

Renal Fanconi syndrome (RFS) is caused by generalized proximal tubular dysfunction and can be divided into hereditary and acquired form. Adult-onset RFS is usually associated with drug toxicity or systemic disorders, and modern molecular genetics may explain the etiology of previous idiopathic cases of RFS. Here, we report the case of a 52-year-old woman with RFS whose etiology could not be identified. She presented with features of phosphaturia, renal glucosuria, aminoaciduria, tubular proteinuria, and proximal renal tubular acidosis. Her family history was unremarkable, and previous medications were nonspecific. Her bone mineral density was compatible with osteoporosis, serum intact parathyroid hormone level was mildly elevated, and 25(OH) vitamin D level was insufficient. Her blood urea nitrogen and serum creatinine levels were 8.4 and 1.19 mg/dL, respectively (estimated glomerular filtration rate, 53 mL/min/1.73 m²). Percutaneous renal biopsy was performed but revealed no specific renal pathology, including mitochondrial morphology. No mutation was detected in EHHADH gene. We propose the possibility of involvement of other genes or molecules in this case of adult RFS.
Acidosis, Renal Tubular ; Adult ; Biopsy ; Blood Urea Nitrogen ; Bone Density ; Creatinine ; Drug-Related Side Effects and Adverse Reactions ; Fanconi Syndrome ; Female ; Glomerular Filtration Rate ; Glycosuria, Renal ; Humans ; Hypophosphatemia, Familial ; Middle Aged ; Molecular Biology ; Osteoporosis ; Parathyroid Hormone ; Pathology ; Proteinuria ; Vitamin D

Fanconi syndrome is a dysfunction of the proximal renal tubules that results in impaired reabsorption and increased urinary loss of phosphate and other solutes. The pathophysiology of drug-induced Fanconi syndrome is unclear. Here we report the case of a 36-year-old woman who presented with pain in multiple bones and proteinuria. She had a 7-year history of taking adefovir at 10 mg/day for chronic hepatitis B. Three years previously she had received surgery for a nontraumatic right femur neck fracture, after which she continued to complain of pain in multiple bones, and proteinuria, glycosuria, and phosphaturia were noted. The findings of a light-microscope examination of a renal biopsy sample were normal, but mitochondrial damage of the proximal tubules was evident in electron microscopy. Western blot analysis revealed that the level of serum fibroblast growth factor 23 (FGF23) was lower than in normal controls. After 2 months of treatment, hypophosphatemia and proximal tubular dysfunction were reversed, and serum FGF23 had normalized. This case suggests that direct mitochondrial damage in proximal tubules can cause drug-induced Fanconi syndrome associated with osteomalacia.
Adult ; Biopsy ; Blotting, Western ; Fanconi Syndrome* ; Female ; Femoral Neck Fractures ; Fibroblast Growth Factors ; Glycosuria ; Hepatitis B, Chronic ; Humans ; Hypophosphatemia ; Hypophosphatemia, Familial ; Kidney Tubules, Proximal ; Microscopy, Electron ; Mitochondria ; Osteomalacia* ; Proteinuria

X-linked hypophosphatemia (XLH) is a hereditary metabolic disease caused by the loss of phosphate through the renal tubules into the urine, and an associated decrease in serum calcium and potassium phosphate. Its dental features include spontaneous dental abscesses that occur in the absence of trauma or dental caries. The aim of this case report was to describe the dental problems of XLH patients and to evaluate limitations in their treatment. A 14 year old male and a 38 year old female with XLH were referred to the Department of Conservative Dentistry for endodontic treatment. The dental findings were periapical abscesses without obvious trauma or caries. Conservative endodontic treatment was performed in teeth with pulp necrosis and abscess. In case 1, the treated teeth showed improvements in bone healing, without clinical symptoms. However, in case 2, the implants and the treated tooth showed hypermobility, and the final restoration was therefore postponed. Early diagnosis, periodic examinations, and communication with the patient's pediatrician are important in the dental management of patients with XLH.
Abscess ; Calcium ; Dental Caries ; Dental Pulp Necrosis ; Dentistry ; Early Diagnosis ; Familial Hypophosphatemic Rickets* ; Female ; Humans ; Hypophosphatemia ; Male ; Metabolic Diseases ; Periapical Abscess ; Potassium ; Tooth

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome, which is characterized by overproduction of FGF23 as a phosphaturic agent leading to chronic phosphaturia and hypophosphatemia, associated with inappropriately normal or low levels of vitamin D. We describe a rare case of a 57-year-old Indian female who presented with bone pains, muscle pains and lower limb weakness. On examination she was found to have hypophosphatemia. Our work up led to the identification of a FGF23 secreting parotid tumour. The tumour responsible for symptoms was a pleomorphic adenoma of the parotid gland. Its complete resection resulted in normalisation of patient's symptoms. Laboratory parameters and microsopic examination further revealed a mesenchymal tumour of mixed connective tissue type.

Human ; Female ; Middle Aged ; Adenoma, Pleomorphic ; Connective Tissue ; Hypophosphatemia ; Hypophosphatemia, Familial ; Lower Extremity ; Neoplasms, Connective Tissue ; Paraneoplastic Syndromes ; Parotid Gland ; Parotid Neoplasms ; Vitamin D ; Hypophosphatemia

Tubulointerstitial nephritis and uveitis (TINU) syndrome is a rare disease that comprises 4.7% of acute interstitial nephritis. With reno-ocular manifestations, TINU syndrome is accompanied by symptoms such as fever, fatigue, malaise, anorexia, vomiting, and arthralgia. TINU syndrome is reported mainly in children or adolescent girls, and it is rare in adults. Although TINU syndrome can present with multiple renal tubular defects, Fanconi syndrome characterized by generalized impairment of proximal tubular function, leading to renal glucosuria, hyperuricosuria, hyperphosphaturia, proximal renal tubular acidosis, and kaliuresis leading to hypokalemia, has rarely been described. We report a case of TINU syndrome with Fanconi syndrome in a 46-year-old HLA B27-positive Korean woman.
Acidosis, Renal Tubular ; Adolescent ; Adult ; Anorexia ; Arthralgia ; Child ; Fanconi Syndrome* ; Fatigue ; Female ; Fever ; Glycosuria, Renal ; Humans ; Hypokalemia ; Hypophosphatemia, Familial ; Middle Aged ; Nephritis, Interstitial* ; Rare Diseases ; Uveitis* ; Vomiting

Adefovir dipivoxil is used antiviral agent in the treatment of chronic hepatitis B virus infection. This drug is recommended for patients infected with lamivudine-refractory hepatitis B. Many studies of low-dose adefovir have shown little evidence of renal tubular dysfunction. However, hypophosphatemic osteomalacia has recently been reported in patients treated with adefovir. We report three cases of low dose adefovir-induced hypophosphatemic osteomalacia with fractures. All three patients had been receiving adefovir due to lamivudine-refractory hepatitis B, presented multiple bone pain. The laboratory tests revealed hypophosphatemia and phosphaturia. Bone scintigraphy showed increased uptake in multiple lesions. They were diagnosed as adefovir induced hypophophatemic osteomalacia. Changing the antiviral agent and administration of calcitriol and phosphates improved hypophosphatemia and clinical symptoms. Patients with hepatitis B virus treated with adefovir should be monitored with the serum phosphate levels and presenting symptoms of diffuse bone pain, clinicians need to suspect this infrequent complication.
Calcitriol ; Hepatitis B ; Hepatitis B virus ; Hepatitis B, Chronic ; Hepatitis, Chronic ; Humans ; Hypophosphatemia ; Hypophosphatemia, Familial ; Osteomalacia ; Phosphates ; Radionuclide Imaging

PURPOSE: Recent studies have suggested that renal phosphate leakage and the associated phosphaturia are significant underlying causes of calcium urolithiasis. The aims of this study were to assess whether phosphaturia relates to urinary metabolic abnormalities and recurrent stone formation. MATERIALS AND METHODS: A database of patient histories and urine chemistries was analyzed for 1,068 consecutive stone formers (SFs) and 106 normal controls. Urine values for phosphaturia that were higher than 95% of the normal control values were defined as indicating hyperphosphaturia, and the effect of phosphaturia on urinary metabolites and stone recurrence was determined. Of these patients, 247 patients (23.1%) who had been followed up for more than 36 months or had a recurrence of stones during follow-up (median, 46.0 months; range, 5-151) were included in the analyses for stone recurrence. RESULTS: Of the SFs, 19.9% (212/1,068) had increased urinary phosphate excretion. SFs with hyperphosphaturia had a greater urinary volume and higher levels of calcium, uric acid, oxalate, and citrate than did SFs with normophosphaturia. A multivariate Cox regression model, stratified by stone episodes, revealed that hyperphosphaturia was an independent predictor of recurrent stone formation in first-time SFs (hazard ratio [HR]: 2.122; 95% confidence interval [CI]: 1.100-4.097; p=0.025). No association was detected between hyperphosphaturia and recurrent stone formation in recurrent SFs. Kaplan-Meier curves showed identical results. CONCLUSIONS: This study demonstrates that hyperphosphaturia is closely associated with urinary metabolic abnormalities. Furthermore, hyperphosphaturia is a significant risk factor for stone recurrence in first-time SFs.
Calcium ; Citric Acid ; Follow-Up Studies ; Humans ; Hypophosphatemia, Familial ; Phosphates ; Recurrence ; Risk Factors ; Uric Acid ; Urolithiasis

Adult Fanconi syndrome is characterized by variable abnormalities caused by renal proximal transport defects, resulting in glycosuria, aminoaciduria, bicarbonaturia, uricosuria and phosphaturia. A 57-year-old man with kappa-light chain multiple myeloma, undergoing chemotherapy with prednisolone and melphalan for 17 month, was admitted with spontaneous femoral neck fracture and was consulted due to polyuria and refractory metabolic acidosis immediately after hemiarthroplasty. The laboratory values showed normal anion gap metabolic acidosis with normal urinary anion gap, hypokalemia, hypouricemia, hypophosphatemia at the time of consultation. After partial correction of acidemia, the fractional excretion of HCO3- was 11.9%, it was interpreted as proximal renal tubular acidosis. 24-hour urine collection showed increased level of excretion for most aminoacids. Diffuse osteopenia and multiple compression fractures on spine were detected on radiological examinations. Also, osteoporosis and osteomalacia was suggested during his clinical course. After the diagnosis of Fanconi syndrome was made, treatment was started with sodium bicarbonate, potassium citrate, calcitriol, calcium carbonate along with phosphate rich diet. Laboratory abnormalities were corrected and refractory multiple bone pain was ameliorated with these treatment.
Acid-Base Equilibrium ; Acidosis ; Acidosis, Renal Tubular ; Adult ; Bone Diseases, Metabolic ; Calcitriol ; Calcium Carbonate ; Diet ; Fanconi Syndrome ; Femoral Neck Fractures ; Fractures, Compression ; Glycosuria ; Hemiarthroplasty ; Humans ; Hypokalemia ; Hypophosphatemia ; Hypophosphatemia, Familial ; Melphalan ; Middle Aged ; Multiple Myeloma ; Osteomalacia ; Osteoporosis ; Polyuria ; Potassium Citrate ; Prednisolone ; Sodium Bicarbonate ; Spine ; Urine Specimen Collection

Adult ; Child, Preschool ; Chromosomes, Human, X ; Female ; Genetic Linkage ; Humans ; Hypophosphatemia, Familial ; genetics ; pathology ; Mouth ; pathology ; Rickets ; genetics ; pathology ; Vitamin D ; therapeutic use