Rare diseases of phosphate and calcium metabolism: Crossing glances between nephrology and endocrinology.

Rare diseases of phosphate/calcium metabolism correspond to a wide and heterogeneous spectrum of diseases. Recent knowledge in physiology and genetics has made it possible to better characterize them and to propose attractive therapeutic approaches based on the underlying pathophysiology. These diseases are often at the interface between nephrology and endocrinology. In this spirit of a multidisciplinary care, each specialty can bring its own critical point of view and its own specificities to improve patient care. The objective of this manuscript is to "read" with a nephrologist's point of view the main frameworks of diseases of phosphate/calcium metabolism, to illustrate the three crucial messages of nephro-protection sent to endocrinologists. First, calciuria must be interpreted both in absolute value (concentration hypercalciuria) and in ratio (flow hypercalciuria). Second, renal monitoring of therapies inducing hypercalciuria on kidneys with normal renal function (e.g. active vitamin D analogs or teriparatide) should be systematic. Last, hyperphosphatemia, often latent in hypoparathyroidism and pseudo-hypoparathyroidism, should be detected and at least benefit from dietary measures, in the context of Western diets rich in phosphate hidden in food additives.

Impacts of parathyroidectomy on calcium and phosphorus metabolism disorder, arterial calcification and arterial stiffness in haemodialysis patients.

BACKGROUND: Secondary hyperparathyroidism (SHPT) and calcium and phosphorus metabolism disorder are important complications in haemodialysis patients. Parathyroidectomy (PTX) may prevent or delay the progress of vascular calcification in haemodialysis patients. OBJECTIVE: To investigate the impacts of PTX on calcium and phosphorus metabolism, arterial calcification and arterial stiffness in haemodialysis patients with SHPT. METHODS: Twenty-one SHPT-haemodialysis patients were selected for PTX. The preoperative and postoperative 1-year scores of coronary artery calcification were measured via multislice spiral CT, along with the brachial-ankle pulse wave velocity (baPWV), and preoperative and postoperative 1-year indexes such as calcium, phosphorus, calcium-phosphorus product concentration and parathyroid hormone (PTH) level were compared. RESULTS: Compared with the preoperative score, the postoperative 1-year coronary artery calcification score was significantly reduced; the mean baPWVs of the bilateral limbs were reduced; and the levels of serum calcium, phosphorus, calcium-phosphorus product concentration and PTH were all reduced; all differences were statistically significant (P < 0.05). CONCLUSIONS: PTX can be used to correct calcium and phosphorus metabolism disorder, reduce arterial calcification, and improve arterial stiffness.

Phosphate salivary secretion in hemodialysis patients: implications for the treatment of hyperphosphatemia.

BACKGROUND/AIMS: Hyperphosphatemia is recognized as contributing to the increased risk of cardiac death in end-stage renal disease (ESRD) and hemodialysis (HD) patients. Currently available pharmacologic treatment for hyperphosphatemia is based on phosphate binders but, despite treatment, only half of the patients fall within the range for serum phosphorus of the K/DOQI guidelines. Therefore, there is a need to identify other therapeutic approaches in order to reduce serum phosphate. Salivary fluid contains phosphate which, if related to the daily salivary secretion (1,000-1,880 ml), may raise interest in order to identify further additive approaches to phosphorus removal in uremic patients, while data about salivary phosphate secretion in ESRD patients are controversial. METHODS: This study evaluates salivary phosphate secretion in 68 HD patients compared with 30 healthy subjects. Saxon's test confirmed normal salivary function in patients and controls. Salivary calcium and serum phosphate, calcium and PTH were also measured. RESULTS: HD patients had significantly higher salivary phosphorus levels compared with healthy controls: 30.35 (26.5-34.6) vs. 12.1 (10.58-14.73) mg/dl (p < 0.0001), and this significantly correlated (p < 0.0001) with serum phosphorus. Multiple regression analysis confirmed serum phosphorus as the only predictor (p < 0.0001) of salivary phosphorus. CONCLUSIONS: Given the functional secretive similarity between salivary glands and the kidneys, this increased salivary phosphate secretion might be interpreted as being compensatory in the presence of renal failure. Absorption of the increased salivary phosphate secretion, however, may worsen hyperphosphatemia; therefore, the binding of salivary phosphate might be considered as a further therapeutic approach to hyperphosphatemia in ESRD.

Reversal of uremic tumoral calcinosis by optimization of clinical treatment of bone and mineral metabolism disorder.

Tumoral calcinosis is an uncommon type of extraosseous calcification characterized by large rubbery or cystic masses containing calcium-phosphate deposits. The condition prevails in the periarticular tissue with preservation of osteoarticular structures. Elevated calcium-phosphorus products and severe secondary hyperparathyroidism are present in most patients with uremic tumoral calcionosis (UTC). Case report of an obese secondary to chronic glomerulonephritis, undergoing continuous ambulatory peritoneal dialysis (CAPD) reported the appearance of painless tumors in the medial surface of fifth finger and left arm. Tumoral calcinosis was confirmed by left biceps biopsy. Poor adherence to CAPD. The patient was transferred to the "tidal" modality of peritoneal dialysis and after was treated by hemodialysis, despite the persistence of severe hyperparathyroidism progressive reduction of UTC until near to its complete disappearance. Nowadays, one year after patient received deceased-donor kidney transplantation, he presents with an improvement in secondary hyperparathyroidism. UTC should be included in the elucidation of periarticular calcification of every patient on dialysis. Relevant laboratory findings such as secondary hyperparathyroidism and elevated calcium- phosphorus products in the presence of periarticular calcification should draw attention to the diagnosis of UTC.

A Quick Reference on Phosphorus.

Phosphorus, or phosphate, is the body's major intracellular anion involved in numerous biological processes. Most phosphate is intracellular, with the remaining amount contained within soft tissues and the extracellular space. Parathyroid hormone, calcitriol, calcitonin, and phosphatonins regulate normal phosphate homeostasis by adjusting renal and/or gastrointestinal absorption and/or excretion. Hypophosphatemia occurs secondary to decreased gastrointestinal absorption, transcellular shifts, increased renal excretion, or some combination of these general mechanisms. Hyperphosphatemia results from decreased renal excretion, increased intake or iatrogenic administration, transcellular shifts, or some combination of these.

Management of vascular calcification in CKD patients.

Vascular calcification is common in patients with chronic kidney disease (CKD) and it may affect almost every artery. It is associated with a significant increase in morbidity and mortality. Therefore, the detection, prevention and treatment of vascular calcification in CKD patients are critical for the overall approach for the management of these patients. Hyperphosphatemia, especially when the blood levels of serum phosphorus are above 5.5 mg/dl, plays a major role in the development of vascular calcification. Hyperphosphatemia induces vascular calcification by both passive and active processes. By increasing calcium-phosphate product, hyperphosphatemia results in direct deposition of calcium salts in the arteries and in cardiac valves. The active process involves the uptake of phosphate by the smooth muscle cells of the arteries by a Na-P co-transporter. This increase in cell phosphate then induces phenotypic changes of these cells, rendering them into osteoblasts which in turn, begin laying calcium salts in the arterial walls. Therefore, it is critical that the blood levels of serum phosphorus be maintained below 5.5 mg/dl in CKD patients. Inflammation and the production of C-reactive protein (CRP) and interleukin 6 are also risk factors for vascular injury and vascular calcification. In a study of 254 dialysis patients with elevated blood levels of CRP (>1.0 mg/l) and 258 patients with CRP levels equal to or less than 1.0 mg/l, it was found that higher levels of CRP are significantly associated with the presence of both atheromatous and medial calcification of the aorta and hand arteries. Also, it was reported that a significant association between CRP levels and cardiac valves calcification in patients undergoing continuous ambulatory peritoneal dialysis. The reasons for the elevation in CRP in dialysis patients are not clear, but certainly, is more evident in those with obvious inflammatory processes. Therefore, any inflammation that is detected should be treated appropriately.

Clinical and genetic analysis of two Chinese infants with Mabry syndrome.

OBJECTIVE: Hyperphosphatasia mental retardation syndrome (Mabry syndrome) is an autosomal recessive disorder. We aim to analyze two Chinese patients diagnosed as Mabry syndrome. METHODS: The clinical manifestations, diagnosis and treatment were observed in two patients. Genetic analysis including PIGV and PIGO was examined. RESULTS: Two patients were diagnosed as Mabry syndrome clinically and genetically. Developmental delay, hyperphosphatasia and seizures were presented in both of them. Typical facial dysmorphism and hypoplastic terminal phalanges were only found in one. Some novel presentations including congenital laryngeal cartilage softening, inguinal hernia, broken palmprint, optic atrophy and skeleton dysplasia such as carpal age delay and metaphysis anomalies were observed in two patients. Molecular genetic analysis revealed compound heterozygous mutations of PIGV or PIGO in our patients, including c.615C>G (p.Asn205Lys) and c.854A>G (p.Tyr285Cys) of PIGV in patient 1, and c.458T>C (p.Phe153Ser) and c.1355_1356del (p.Ala452Glyfs*52) of PIGO in patient 2. Additionally, a heterozygous c.2926G>A (Asp976Asn) of PCDH19 was identified in patient with PIGV mutations, the causative gene of Epilepsy and mental retardation limited to females (EFMR). CONCLUSION: To our best knowledge, this is the first time to report Chinese patients diagnosed as Mabry syndrome. For the PCDH19 mutation in our patient carrying PIGV mutations, due to lacking characteristics of EFMR and the ambiguity results in pathogenicity analysis, we were not sure how much pathogenic role PCDH19 mutation shared with PIGV mutations in this disease. The novel mutations of PIGV and PIGO, and novel clinical manifestations reported here might expand the genotype and phenotype spectrum of Mabry syndrome.

The clinical management of hyperphosphatemia.

As renal function declines in patients with end-stage renal disease (ESRD), excess dietary phosphorus accumulates in the bloodstream. Routine dialysis removes up to 70% of absorbed phosphorus; therefore, hyperphosphatemia is found in the majority of patients with ESRD. The consequences of this imbalance include secondary hyperparathyroidism and osteodystrophy. Recent studies have also documented that hyperphosphatemia can lead to soft-tissue and vascular calcification; the latter is strongly associated with cardiovascular disease and, thus, increased mortality and morbidity. The reduction of phosphorus levels is, therefore, an important therapeutic target in this patient group. Management of hyperphosphatemia using conventional phosphate binders is not always successful. However, emerging therapies aim to reduce the incidence of hyperparathyroidism, bone disease, and calcification in this patient population. In this article, the consequences of hyperphosphatemia are reviewed, and recent developments in the treatment of the condition are discussed.

[Changes of control of disorders of calcium and phosphorus metabolism in Lithuanian hemodialysis centers 1996-2003]. / Kalcio ir fosforo apykaitos sutrikimu kontroles pokyciai Lietuvos hemodializes centruose 1996-2003 m.

The aim of the study was to evaluate the changes of the rate of disorders of calcium and phosphorus metabolism and their control in patients on hemodialysis (HD) in Lithuania in 1996-2003. Every December during this period we visited all HD centers of Lithuania and collected data on calcium-phosphorus metabolism in HD patients. 51.8% of HD patients in 1999 and 44.6% in 2003 had hyperphosphatemia (>1.8 mmol/l) (p<0.05). The mean phosphate concentration was 1.82+/-0.56 mmol/l in 2003 (p<0.05, comparing with 1.95+/-0.72 mmol/l in 1999 and 1.9+/-0.72 mmol/l in 2001). 7.1% of HD patients had hypocalcemia in 2003 and 7.8% hypercalcemia. Serum parathyroid hormone level was investigated only in 27.3% of HD patients in 1999 and 84.8% in 2003 (p<0.05). Use of alfacalcidol significantly decreased from 77.5% in 1998 to 29.4% in 2003, when the evaluation of serum parathyroid hormone increased (r=-0.911, p=0.03). Serum parathyroid hormone level was not analyzed for 59.8% of patients who used alfacalcidol and 59.4% of them had hyperphosphatemia in 1999 (6.3% and 32.9% in 2003, respectively; p<0.05). 10.7% of these patients had hypercalcemia in 2003. In summary, the correction of disorders of calcium and phosphorus metabolism in HD patients was insufficient but ameliorative. Monitoring of serum parathyroid hormone increased significantly during 1997-2003. The percentage of the precarious use of alfacalcidol decreased significantly when the evaluation of serum parathyroid hormone level became regular.

Phosphate homeostasis and hypophosphatemia.

The clinical importance of an understanding of phosphate metabolism is derived from the crucial role of this anion in the regulation of many cellular functions. In recent years, a greater appreciation of disorders of phosphate metabolism has been recognized because of more frequent monitoring of serum phosphate concentration as well as the increased utilization of therapeutic interventions that profoundly affect overall phosphate balance. The present review focuses on the factors tha regulate phosphate homeostasis, explores the pathophysiology and manifestations of the phosphate depletion syndrome and provides a framework for the diagnosis and rational treatment of patients with abnormalities in phosphate metabolism.

Factors for increased morbidity and mortality in uremia: hyperphosphatemia.

Hyperphosphatemia is a metabolic abnormality present in the majority of patients treated by dialysis. Inorganic phosphorus (iP) can be categorized as a true uremic toxin given its known in vivo and in vitro effects and the ability to reduce these effects by normalizing iP levels. However, despite regular and adequate dialysis treatment, the goal of normalization of phosphorus levels rarely is achieved. This article briefly evaluates the significance of hyperphosphatemia in hemodialysis patients, current therapeutic approaches, and describes a new model for evaluating the dialysis prescription for iP balance.

A review of clinical and laboratory findings and treatment of tumor lysis syndrome.

Acute tumor lysis syndrome (TLS) has started to be considered a separate entity or condition associated with bulk tumor treatment. TLS is described as the biochemical disturbances associated with rapid destruction of tumor cells with subsequent synchronised massive release of cellular breakdown products sufficient to overwhelm excretory mechanisms and the body's normal reutilization capacity. The cardinal signs of TLS are: hyperkalemia, hyperphosphatemia, hypocalcemia and hyperuricemia. This review comprehensively discusses the differential diagnosis, pathophysiology and clinical features, possible causal indications for laboratory monitoring and treatment options of TLS.

Management of hyperphosphataemia in dialysis patients: role of phosphate binders in the elderly.

Phosphorus control remains a relevant clinical problem in dialysis patients. With age, however, serum phosphorus level decreases significantly because of a spontaneous decrease in protein intake. Older patients usually need lower doses of phosphorus binders. Nevertheless, hyperphosphataemia is observed in a quarter of patients aged >65 years. Phosphorus retention is related to an imbalance between phosphorus intake and removal by dialysis, and is usually aggravated when vitamin D analogues are employed. Hyperphosphataemia induces secondary hyperparathyroidism and the development of osteitis fibrosa. Recent publications describe an association between phosphorus retention and increased calcium and phosphorus product (Ca2+ x P), with significant progression of tissue calcification and higher mortality risk. Dietary intervention, phosphorus removal during dialysis and phosphorus binders are current methods for the management of hyperphosphataemia. However, the phosphorus removed by standard haemodialysis is insufficient to achieve a neutral phosphorus balance when protein intake is >50 g/day. Additional protein restriction may impose the risk of a negative protein balance. More frequent dialysis may help to control resistant hyperphosphataemia. Phosphorus binders constitute the mainstay of serum phosphorus level control in end-stage renal disease patients. Aluminium-based phosphorus binders, associated with toxic effects, have largely been substituted by calcium-based phosphorus binders. However, widespread use of calcium-based phosphorus binders has evidenced the frequent appearance of hypercalcaemia and long-term progressive cardiovascular calcification. Sevelamer, a relatively new phosphorus binder, has proved efficacious in lowering serum phosphorus and parathyroid hormone (PTH) levels without inducing hypercalcaemia. Furthermore, several investigators have reported that sevelamer may prevent progression of coronary calcification. However, its efficacy in severe cases of hyperphosphataemia remains to be confirmed in large series. There are no specific guidelines for phosphorus control in the elderly. Until more information is available, levels of mineral metabolites should be targeted in the same range as those recommended for the general population on dialysis (calcium 8.7-10.2 mg/dL, phosphorus 3.5-5.5 mg/dL and Ca2+ x P 50-55 mg2/dL2). PTH values over 120 ng/L help to avoid adynamic bone disease. Since elderly patients have a higher incidence of adynamic bone (which buffers less calcium) and vascular calcification, sevelamer should be the phosphorus binder of choice in this population; but sevelamer is costly and its long-term efficacy has not been definitively validated. Patients with low normal levels of calcium may receive calcium-based phosphorus binders with little risk. Patients with low values of PTH and high normal calcium should receive sevelamer. Tailored combinations of calcium-based phosphorus binders and sevelamer should be considered, and calcium dialysate concentration adjusted accordingly.

Severe hypophosphatemia in postoperative patients.

Severe hypophosphatemia may develop in postoperative patients for several reasons including alcohol withdrawal, diabetic ketoacidosis, nutritional recovery (refeeding) syndrome, and severe respiratory alkalosis. Severe hypophosphatemia may result in central nervous system abnormalities, muscle weakness, and renal, hepatic, cardiac, and respiratory dysfunction. Hypophosphatemia may be prevented by close monitoring of phosphorus concentrations in serum, especially in patients predisposed to developing this problem. Proper techniques for the maintenance and repletion of phosphate for both enteral and parenteral use are described.

[A comparison of phosphorus-chelating effect of calcium carbonate versus calcium acetate before dialysis]. / Comparación del efecto quelante del fósforo de carbonato vs acetato cálcico en prediálisis.

INTRODUCTION: The hyperphosphatemia, hypocalcemia and low calcitriol levels are pathogenic factors for secondary hyperparathyroidism in chronic renal failure. The phosphorus control is essential to prevent secondary hyperparathyroidism. There are not comparatives studies to test the efficacy of control of phosphorus binders in predialysis patients. AIM: To compare the efficacy of calcium carbonate vs calcium acetate as phosphate binder in predialysis patients. MATERIAL AND METHODS: The present study includes 28 patients with chronic renal failure (mean clearance of creatinine 21 ml/min). Patients were separated into two groups: Group 1: (n = 14) received calcium carbonate 2,500 mg/day (1,000 mg of calcium); Group 2: (n = 14) receives calcium acetate 1,000 mg (254 mg of calcium). Calcium and phosphorus were determined every 4 months; i-PTH, alkaline phosphatase and clearance of creatinine were determined every six months. RESULTS: Both groups were comparable regarding age, renal function, calcium, phosphorus, alkaline phosphatase and i-PTH on basal situation and the end of study were not different. The serum calcium increased, not significantly, in the calcium carbonate group (group 1) [from 9.2 to 9.8 mg/dl (p = 0.05)], however it was not modified in the calcium acetate group (group 2). The serum phosphorus decreased significantly (p < 0.05) in both groups, independently of the calcium levels. Alkaline phosphatase and i-PTH not was modified during the study period. CONCLUSIONS: 1) Both calcium carbonate and calcium acetate are similarly effective as phosphate binder. 2) The carbonate group required four fold greater doses of calcium that acetate group. 3) The calcium acetate has less hypercalcemic effect than calcium carbonate.

[Acute hyperphosphatemia secondary to phosphate administration for bowel preparation]. / Hiperfosforemia aguda tras preparación para colonoscopia.

We report a 75-years-old woman, stable on a three-weekly hemodialysis program over a period of 3 years, who develop acute hyperphosphatemia secondary to phosphate administration for bowel preparation. The quick clinical diagnosis and the treatment with intensive hemodialysis resulted in a correction of hyperphosphatemia, hypocalcemia, acidemia and other electrolyte abnormalities. The phosphate cathartics are contraindicated in patients with severe renal insufficient or in dialysis program. Our case shows the severe side effects secondary to injudicious use of sodium phosphate cathartics.

Calcium and phosphorus derangements.

Derangements in plasma calcium and phosphorus concentrations can precipitate serious and life-threatening complications in critically ill patients. An understanding of the function and homeostasis of these ions is essential to fully comprehend the causes, clinical manifestations, and treatment of calcium and phosphorus imbalances. This article will help the critical care nurse to identify patients at risk, to recognize derangements early (while they are still mild), and to seek and monitor appropriate treatment.

[Vitamin-resistant rickets cured by removal of a bone tumor. Review of the literature]. / Rachitisme vitamino-résistant guéri par l'éxérèse d'une tumeur osseuse. Revue de la littérature.

PURPOSE OF THE STUDY: Rickets secondary to bone or soft tissue tumors are rare in children. Majority of the reported cases occurred in adults older than thirty. This entity can be cured after tumor removal. The authors present a case in a ten year boy and literature review. MATERIAL: A ten year boy complained of diffuse bone and muscle weakness for two years. A diagnosis of arthritis was made but the patient continued to complain. Serum calcium level was normal (2.33 mmol/l), phosphorus was very low (0.43 mmol/l), serum alkaline phosphatase was high, parathyroid hormone and vitamin D level were normal. Urinalysis showed abnormal phosphate excretion. METHODS: The absence of malabsorption, no family history of rickets or hypophosphatermy presence of a marked excess of urinary phosphate, very low serum phosphate and normal serum calcium, vitamin D and parathyroid hormone levels led us to consider a diagnosis of tumor induced osteomalacia. Radiographs showed a large round radiolucent lesion in the left superior pubic ramus and generalized demineralisation. RESULTS: We performed a complete tumor resection and the space was filled with bone graft. On histopathologic examination it was a benign mesenchymal tumor. Rapid reversal of biochemical anomalies, radiographs anomalies and clinical manifestation were observed after complete tumor resection. DISCUSSION: The authors have described the tumor, the osteomalacia and the pathogenesis of tumor rickets. Histologically the most common causative tumors were vascular tumors, mesenchymal tumors and non ossifying tumors. The tumor were of bone or soft tissue origin. Clinical symptoms were muscular weakness, bone and muscle pain. Biochemically there is a very low phosphate level, a normal serum calcium level as well as a normal vitamin D and PTH level. There is a significant high level of urinal phosphate. The mechanism proposed to explain oncogenic osteomalacia includes tumor secretion of phosphaturic substance other than PTH and calcitonin. Another hypothesis is a substance interfering with normal vitamin D metabolism. The pathogenesis is not clearly defined. CONCLUSION: Regardless to the mechanism of osteomalacia, complete removal of the tumor will cure the patient. A diligent search for tumors should be done in patients with vitamin D resistant rickets.

[Disordered phosphorus metabolism and its correction in the acute period of severe craniocerebral trauma]. / Narushenie fosfornogo obmena i ego korrektsiia v ostrom periode tiazheloi cherepno-mozgovoi travmy.

Marked hypophosphatemia was discovered in 78 patients in the acute period of severe craniocerebral injury. It led to a decrease of the level of 2,3-diphosphoglycerate (2,3 DPG) and ATP in the red cells. The reduced ATP level in the red cells was one of the causes of reduced Ca2+ ATPase activity in their membranes. Intravenous infusion of 6.8% potassium dihydrophosphate solution prevented the development of hypophosphatemia and reduction of the content of 2,3 DPG and ATP in the red cells and Ca2+ ATPase activity in their membranes, which facilitated improvement in the course of acute posttraumatic period in patients with severe craniocerebral injury and decrease of mortality.