Evaluation of hypophosphatemia: lessons from patients with genetic disorders

X-Linked Familial Hypophosphatemia: A Case Report of 27-Year Old Male and Review of Literature

X-linked hypophosphatemia (XLH) associated with short stature during childhood are mostly referred to the hospital and diagnosed as vitamin D deficiency rickets and received vitamin D before adulthood. A case is presented with clinical features of hypophosphatemia from childhood who did not seek medical care for diagnosis and treatment, nor did his mother or two brothers, who have short statures, bone pain, and fractures. The patient was assessed for sociodemographic, hematological, and biochemical parameters together with a genetic assessment. A DEXA scan and X-ray were done to determine the abnormalities and deformities of joints and bones despite clinical examination by an expert physician. All imaging, laboratory parameters, and the genetic study confirmed the diagnosis of XLH. A detailed follow-up of his condition was performed after the use of phosphate tablets and other treatments. X-linked hypophosphatemia needs a good assessment, care, and follow up through a complementary medical team including several specialties. Phosphate tablets in adulthood significantly affects clinical and physical improvement and prevention of further skeletal abnormality and burden on daily activity. The patients should be maintained with an adequate dose of phosphate for better patient compliance. More awareness is needed in society and for health professionals when conducting medical checkups during the presence of stress fractures, frequent dental and gum problems, rickets, short stature, or abnormality in the skeleton or walking to think of secondary causes such as hypophosphatemia. Further investigations including a visit to a specialist is imperative to check for the primary cause of these disturbances.

Appropriateness of inpatient intravenous iron therapy in a Swiss tertiary care hospital

INTRODUCTION

Intravenous (IV) iron replacement is an established treatment for iron deficiency and is recommended in various medical guidelines, but cheaper oral iron formulations remain first-line therapy in several instances. Data on adherence to current prescription standards are lacking in Switzerland.

METHODS

Retrospective single center quality control study evaluating the appropriateness of IV iron replacement in 400 inpatients during 2019 and 2021 at a Swiss tertiary care hospital. Appropriateness of IV iron was assessed by expert chart review according to national and international guidelines.

RESULTS

IV iron prescriptions were assessed as inappropriate in 147 (37%) of cases (indication lacking in 13%, oral route preferred in 24%). Inappropriate prescribing was more common (p < .001) in surgical wards (66%) compared to medical units (48%) and the gynecologic ward (19%). Iron studies were lacking in 29% of inappropriate IV administrations. Insufficient replacement dosages were chosen in 38% of patients with appropriate prescription.

CONCLUSION

Based on current guidelines, inappropriate in-hospital prescription of IV iron was frequently observed. Considerable differences exist between hospital units, which are consistent with conflicting recommendations of professional societies. We recommend increased attention toward the prescription quality to avoid unnecessary, expensive, and potentially harmful use of IV iron.

An Expert Perspective on Phosphate Dysregulation With a Focus on Chronic Hypophosphatemia

Because of their rarity, diseases characterized by chronic hypophosphatemia can be underrecognized and suboptimally managed, resulting in poor clinical outcomes. Moreover, serum phosphate may not be measured routinely in primary care practice. Authors participated in several working sessions to advance the understanding of phosphate homeostasis and the causes, consequences, and clinical implications of chronic hypophosphatemia. Phosphate levels are regulated from birth to adulthood. Dysregulation of phosphate homeostasis can result in hypophosphatemia, which becomes chronic if phosphate levels cannot be normalized. Chronic hypophosphatemia may be underrecognized as serum phosphate measurement is not always part of routine analysis in the primary care setting and results might be misinterpreted, for instance, due to age-specific differences not being accounted for and circadian variations. Clinical consequences of chronic hypophosphatemia involve disordered endocrine regulation, affect multiple organ systems, and vary depending on patient age and the underlying disorder. Signs and symptoms of chronic hypophosphatemic diseases that manifest during childhood or adolescence persist into adulthood if the disease is inadequately managed, resulting in an accumulation of clinical deficits and a progressive, debilitating impact on quality of life. Early identification and diagnosis of patients with chronic hypophosphatemia is crucial, and clinical management should be started as soon as possible to maximize the likelihood of improving health outcomes. Furthermore, in the absence of a universally accepted description for "chronic hypophosphatemia," a definition is proposed here that aims to raise awareness of these diseases, facilitate diagnosis, and guide optimal phosphate management strategies by improving monitoring and assessment of patient response to treatment. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Phosphorus bioaccessibility measured in four amino acid-based formulas using in-vitro batch digestion translates well into phosphorus bioavailability in mice

OBJECTIVE

The aim of this study was to quantify the bioaccessibility of phosphorus from amino acid-based formulas (AAFs) under different digestive conditions.

METHODS

We developed in-vitro batch digestion models with stomach digestion at different pH mimicking the normal digestive condition and conditions representing use of acid-suppressive medication. To validate bioaccessibility findings, we devised a low phosphorus murine model to test phosphorus bioavailability under compromised digestive conditions using proton pump inhibitors (PPIs) to neutralize stomach pH.

RESULTS

In vitro phosphorus bioaccessibility of AAFs Neocate® Infant and Neocate Junior ranged between 57% and 65% under normal digestive conditions for infants (stomach pH 3.5) and between 38% and 46% under conditions that simulated bypass of stomach acidification, which is comparable to control diet and two EleCare® AAFs. In vivo bioavailability analysis showed that both Neocate formulas were able to normalize plasma phosphorus levels when administered to low phosphorus mice along with PPIs (control diet + PPI 8 ± 0.4; Neocate Infant 10.1 ± 0.9; Neocate Junior 9.2 ± 0.6; EleCare Infant 8.6 ± 0.4; EleCare Junior 8.7 ± 0.5; n = 8-10; P < 0.0001 versus baseline 3.4 ± 0.2 mg/dL). In comparison, plasma phosphorus levels remained lower on the low phosphorus diet (5.7 ± 0.2 mg/dL). Furthermore, urinary phosphorus/creatinine and intact fibroblast growth factor 23 were significantly lowered by low phosphorus diet. In contrast, intact parathyroid hormone and 1,25-dihydroxy vitamin D decreased and increased, respectively, and these parameters likewise normalized in mice administered AAFs.

CONCLUSION

The present findings indicated that phosphorus bioaccessibility in the in-vitro batch digestion model translates well into phosphorus bioavailability in mice even under compromised digestive conditions that bypass gastric acidification.

Beyond the Mind-Serum Trace Element Levels in Schizophrenic Patients: A Systematic Review

The alterations in serum trace element levels are common phenomena observed in patients with different psychiatric conditions such as schizophrenia, autism spectrum disorder, or major depressive disorder. The fluctuations in the trace element concentrations might act as potential diagnostic and prognostic biomarkers of many psychiatric and neurological disorders. This paper aimed to assess the alterations in serum trace element concentrations in patients with a diagnosed schizophrenia. The authors made a systematic review, extracting papers from the PubMed, Web of Science, and Scopus databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Among 5009 articles identified through database searching, 59 of them were assessed for eligibility. Ultimately, 33 articles were included in the qualitative synthesis. This review includes the analysis of serum levels of the following trace elements: iron, nickel, molybdenum, phosphorus, lead, chromium, antimony, uranium, magnesium, aluminum, zinc, copper, selenium, calcium, and manganese. Currently, there is no consistency regarding serum trace element levels in schizophrenic patients. Thus, it cannot be considered as a reliable prognostic or diagnostic marker of schizophrenia. However, it can be assumed that altered concentrations of those elements are crucial regarding the onset and exaggeration of either psychotic or negative symptoms or cognitive dysfunctions.

Hypophosphatemia Is Common After Intravenous Ferric Carboxymaltose Infusion Among Patients With Symptomatic Heart Failure With Reduced Ejection Fraction

Administration of intravenous ferric carboxymaltose (FCM) for iron-deficient patients suffering heart failure with reduced ejection fraction (HFrEF) has been associated with transient hypophosphatemia. We sought to investigate and model the effect of intravenous FCM on phosphate levels in iron-deficient patients with HFrEF. In this single-center retrospective study, serum phosphate levels, recorded for clinical reasons, were collected out to 60 days following intravenous FCM. Hypophosphatemia was defined as a nadir serum phosphate level <0.64 mmol/L. This was further categorized as severe (0.4 to <0.64 mmol/L) and extreme (<0.4 mmol/L). Factors associated with hypophosphatemia and change in serum phosphate over time were explored. Of 173 patients included, 47 (27%) experienced hypophosphatemia, 44 (25%) were classified as severe, and 3 (2%) extreme. Risk of hypophosphatemia was increased for patients with a creatinine clearance between 60 and <90 mL/min (odds ratio, 2.3; 95% confidence interval, 1.0-5.5), while <60 mL/min was protective. The median time to nadir in patients who experienced hypophosphatemia was 8 (interquartile range, 4-16) days, with a return to baseline levels at 6 weeks. Biochemically relevant hypophosphatemia is common following a single dose of intravenous FCM. The median time to nadir was 8 days, and creatinine clearance may influence phosphate levels following intravenous FCM. These observations support the need to increase awareness among clinicians administering intravenous FCM to iron-deficient patients with HFrEF.

More Bone with Less Minerals? The Effects of Dietary Phosphorus on the Post-Cranial Skeleton in Zebrafish

Dietary phosphorus (P) is essential for bone mineralisation in vertebrates. P deficiency can cause growth retardation, osteomalacia and bone deformities, both in teleosts and in mammals. Conversely, excess P supply can trigger soft tissue calcification and bone hypermineralisation. This study uses a wide range of complementary techniques (X-rays, histology, TEM, synchrotron X-ray tomographic microscopy, nanoindentation) to describe in detail the effects of dietary P on the zebrafish skeleton, after two months of administering three different diets: 0.5% (low P, LP), 1.0% (regular P, RP), and 1.5% (high P, HP) total P content. LP zebrafish display growth retardation and hypomineralised bones, albeit without deformities. LP zebrafish increase production of non-mineralised bone matrix, and osteoblasts have enlarged endoplasmic reticulum cisternae, indicative for increased collagen synthesis. The HP diet promotes growth, high mineralisation, and stiffness but causes vertebral centra fusions. Structure and arrangement of bone matrix collagen fibres are not influenced by dietary P in all three groups. In conclusion, low dietary P content stimulates the formation of non-mineralised bone without inducing malformations. This indicates that bone formation and mineralisation are uncoupled. In contrast, high dietary P content promotes mineralisation and vertebral body fusions. This new zebrafish model is a useful tool to understand the mechanisms underlying osteomalacia and abnormal mineralisation, due to underlying variations in dietary P levels.

Physiology of FGF23 and overview of genetic diseases associated with renal phosphate wasting

Phosphate is a cornerstone of several physiological pathways including skeletal development, bone mineralization, membrane composition, nucleotide structure, maintenance of plasma pH, and cellular signaling. The kidneys have a key role in phosphate homeostasis with three hormones having important functions in renal phosphate handling or intestinal absorption: parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and 1-25-dihydroxyvitamin D (1,25(OH)2D). FGF23 is mainly synthesized by osteocytes; it is a direct phosphaturic factor that also inhibits 1,25(OH)2D and PTH. In addition to crucial effects on phosphate and calcium metabolism, FGF23 also has 'off-target' effects notably on the cardiovascular, immune and central nervous systems. Genetic diseases may affect the FGF23 pathway, resulting in either increased FGF23 levels leading to hypophosphatemia (such as in X-linked hypophosphatemia) or defective secretion/action of intact FGF23 inducing hyperphosphatemia (such as in familial tumoral calcinosis). The aim of this review is to provide an overview of FGF23 physiology and pathophysiology in X-linked hypophosphatemia, with a focus on FGF23-associated genetic diseases.

Changes in serum phosphorus level in patients with severe burns: A prospective study

BACKGROUND

The second most abundant mineral in the body, phosphorus (P), is absorbed in the small intestine after ingestion enhanced by 1,25-dihydroxy vitamin D, and its excretion is exclusively regulated by the kidney. It is clinically significant, aside from its disturbance in burn ICU patient's P mechanism. The increasing rate of morbidity and mortality among the patients can be associated with severe hypophosphatemia. The current study aimed at investigating the changes in serum P levels in the early period after burns, the relationship between serum P level and TBSA (total body surface area) of burn, and the impact of hypophosphatemia on patients' clinical outcomes.

MATERIAL AND METHODS

The current prospective, observational study was conducted on 137 patients hospitalized in the burn intensive unit (BICU) of Velayat Sub-specialty Burn and Plastic Surgery Center from December 2015 to May 2017. According to the TBSA percentage, the patients were divided into three groups. The level of serum P was determined in the 1st, 3rd, 5th, 7th, and 9th days of hospital stay and before discharge. To evaluate the trend of P changes in the sixtime-points, the average changes along with 95% confidence intervals (CI) were used for multivariate analysis of variance with repeated measures (repeated measures ANOVA). A P-value of 0.05 or less was considered statistically significant. The analyses were performed using SPSS software, version 19 (SPSS Inc.).

RESULTS

Totally, 137 patients (70% male, mean age 32 ± 21years, and TBSA 32.6 ± 14%) were included in the study. The overall incidence of hypophosphatemia was 75.1%. Hypophosphatemia developed as early as 1.66 ± 0.136 (95%CI: 1.4-1.9) days after injury. The highest decrease in the serum P level was observed on the 3rd and 5th days after burn as 2.78 mg/dL and 2.85 mg/dL, respectively (P-value = 0.001). A correlation was observed between TBSA and serum P level. The mean serum P level decreased with increasing the percentage of burns. There was a correlation between serum P level and mortality; therefore, a decrease in serum P level increased the patient's mortality rate (P < 0.05).

CONCLUSION

The current study highlighted that hypophosphatemia is often observed in patients with burn injuries during their hospitalization. It is potentially beneficial to identify patients at risk of hypophosphatemia. Therefore, it is suggested that P level be assessed regularly in patients with burn injuries for the timely initiation of P replacement therapy.

Phosphate disorders and clinical management of hypophosphatemia and hyperphosphatemia

Serum phosphorus levels range from 2.5 and 4.5mg/dL (0.81-1.45 mmol/L) in adults, with higher levels in childhood, adolescence, and pregnancy. Intracellular phosphate is involved in intermediary metabolism and other essential cell functions, while extracellular phosphate is essential for bone matrix mineralization. Plasma phosphorus levels are maintained within a narrow range by regulation of intestinal absorption, redistribution, and renal tubular absorption of the mineral. Hypophosphatemia and hyperphosphatemia are common clinical situations, although changes are most often mild and oligosymptomatic. However, acute and severe conditions that require specific treatment may occur. In this document, members of the Mineral and Bone Metabolism Working Group of the Spanish Society of Endocrinology and Nutrition review phosphate disorders and provide algorithms for adequate clinical management of hypophosphatemia and hyperphosphatemia.

Proton-pump Inhibitor-induced Severe Hypomagnesemia and Hypocalcemia are Clinically Masked by Thiazide Diuretic

Hypomagnesemia, a side effect of proton-pump inhibitors (PPIs), can be asymptomatic. The presence of hypocalcemia or hypokalemia is indicative of hypomagnesemia; however, the concomitant use of PPIs and thiazide may mask hypocalcemia. A 79-year-old woman with a history of chronic heart failure and chronic kidney disease developed symptomatic hypocalcemia and hypomagnesemia. Five weeks earlier, she had developed thiazide-induced hyponatremia, so thiazide had been discontinued. Reviewing the patient's charts revealed that three discontinued thiazide administrations in the clinical course had unmasked hypocalcemia. Our case demonstrates that thiazide-induced hypercalcemia can be so prominent as to mask PPI-induced hypocalcemia and hypomagnesemia.

Hyperphosphatemic tumoral calcinosis caused by FGF23 compound heterozygous mutations: what are the therapeutic options for a better control of phosphatemia?

BACKGROUND

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disease caused by mutations in genes encoding FGF23 or its regulators, and leading to functional deficiency or resistance to fibroblast growth factor 23 (FGF23). Subsequent biochemical features include hyperphosphatemia due to increased renal phosphate reabsorption, and increased or inappropriately normal 1,25-dihydroxyvitamin D (1,25-D) levels.

CASE-DIAGNOSIS/TREATMENT

A 15-year-old girl was referred for a 1.2-kg-calcified mass of the thigh, with hyperphosphatemia (2.8 mmol/L); vascular impairment and soft tissue calcifications were already present. DNA sequencing identified compound heterozygous mutations in the FGF23 gene. Management with phosphate dietary restriction, phosphate binders (sevelamer, aluminum, nicotinamide), and acetazolamide moderately decreased serum phosphate levels; oral ketoconazole was secondary administered, leading to significantly decreased 1,25-D levels albeit only moderate additionally decreased phosphate levels. However, therapeutic compliance was questionable. Serum phosphate levels always remained far above the upper normal limit for age. The patient presented with two relapses of the thigh mass, requiring further surgery.

CONCLUSIONS

We suggest that control of phosphate metabolism is crucial to prevent recurrences and vascular complications in HFTC; however, the medical management remains challenging.

Hypophosphatemia-induced Cardiomyopathy

Relatively few studies have been conducted to evaluate the effect of hypophosphatemia on cardiac function. The goal of this review was to determine whether there is an association between hypophosphatemia and cardiac function and to increase awareness of hypophosphatemia-induced cardiomyopathy as a new clinical entity and a reversible cause of heart failure. We searched MEDLINE and PubMed from 1971 until March 2015 for primary studies, which reported the relationship between hypophosphatemia and cardiac function. A total of 837 articles were initially obtained. Of these articles, 826 publications were excluded according to the inclusion and exclusion criteria. In all, 11 articles were included in this review. These articles included 7 case series or case reports, 1 case-control study, 1 pretest versus posttest in a single group and 2 animal studies. In conclusion, the mechanisms of hypophosphatemia in cardiomyopathy have been reported to be a depletion of adenosine triphosphate in myocardial cells and decreased 2,3-diphosphoglycerate in erythrocytes. After correction of hypophosphatemia, left ventricular performance seems to improve in patients with severe hypophosphatemia, but not in those with mild-to-moderate hypophosphatemia. However, analyses of the relationship between cardiac function and hypophosphatemia using clinical end points have not been conducted.

Biphasic Effects of Vitamin D and FGF23 on Human Osteoclast Biology

Vitamin D and FGF23 play a major role in calcium/phosphate balance. Vitamin D may control bone resorption but the potential role of FGF23 has never been evaluated. The objective of this study was therefore to compare the effects of vitamin D and FGF23 on osteoclast differentiation and activity in human monocyte-derived osteoclasts. Human monocytes, purified from blood of healthy donors, were incubated with M-CSF and RANKL to obtain mature multinucleated osteoclasts (MNC). Experiments were carried out to assess the effects of FGF23 as compared to native vitamin D (25-D) and active vitamin D (1,25-D) on osteoclast differentiation and on bone-resorbing osteoclast activity. Additional experiments with the pan fibroblast growth factor receptor inhibitor (FGFR-i) were performed. Phosphorylation Akt and Erk pathways were analyzed by Western blot analyses. Both 1,25-D and FGF23, to a lesser extent, significantly inhibited osteoclastogenesis at early stages; when adding FGFR-i, osteoclast formation was restored. Biochemical experiments showed an activation of the Akt and Erk pathways under FGF23 treatment. In contrast, in terms of activity, 1,25-D had no effect on resorption, whereas FGF23 slightly but significantly increased bone resorption; 25-D had no effects on either differentiation or on activity. These data show that 1,25-D inhibits osteoclastogenesis without regulating osteoclast-mediated bone resorption activity; FGF23 has biphasic effects on osteoclast physiology, inhibiting osteoclast formation while stimulating slightly osteoclast activity. These results may be of importance and taken into account in chronic kidney disease when therapies modulating FGF23 are available.

Management of hyperphosphataemia in chronic kidney disease-challenges and solutions

Hyperphosphataemia is a clinical consequence of the advanced stages of chronic kidney disease (CKD). Considerable evidence points to a role of hyperphosphataemia in the pathogenesis of CKD-associated cardiovascular (CV) complications, including vascular calcification, and with increased all-cause and CV mortality. These observations place management of hyperphosphataemia at the centre of CKD treatment. Although our increased understanding of the physiological role of FGF-23 may provide a long-term alternative biomarker of phosphate load and underlying disease progression, regular determination of serum phosphate is currently the most frequently used parameter to evaluate phosphate load in clinical practice. This review considers the challenges physicians and patients face in trying to control hyperphosphataemia. Amongst these are the limitations of dietary phosphate restriction, giving rise to the need for phosphate binder therapy to maintain serum phosphate control. Once the decision to use phosphate binders has been made, considerations include the relative efficacy, different potential side effects and pill burden associated with various phosphate binders. Although a number of phosphate binders are available, adherence poses a major obstacle to effective treatment. This emphasizes that further improvements to phosphate binder therapy can be made. Evaluation of novel agents and their potential role in the clinic should continue.

Fibroblast growth factor 23 inhibits extrarenal synthesis of 1,25-dihydroxyvitamin D in human monocytes

Vitamin D is a potent stimulator of monocyte innate immunity, and this effect is mediated via intracrine conversion of 25-hydroxyvitamin D (25OHD) to 1,25-dihydroxyvitamin D (1,25(OH)(2) D). In the kidney, synthesis of 1,25(OH)(2) D is suppressed by fibroblast growth factor 23 (FGF23), via transcriptional suppression of the vitamin D-activating enzyme 1α-hydroxylase (CYP27B1). We hypothesized that FGF23 also suppresses CYP27B1 in monocytes, with concomitant effects on intracrine responses to 1,25(OH)(2) D. Healthy donor peripheral blood mononuclear cell monocytes (PBMCm) and peritoneal dialysate monocyte (PDm) effluent from kidney disease patients were assessed at baseline to confirm the presence of mRNA for FGF23 receptors (FGFRs), with Klotho and FGFR1 being more strongly expressed than FGFR2/3/4 in both cell types. Immunohistochemistry showed coexpression of Klotho and FGFR1 in PBMCm and PDm, with this effect being enhanced following treatment with FGF23 in PBMCm but not PDm. Treatment with FGF23 activated mitogen-activated protein kinase (MAPK) and protein kinase B (Akt) pathways in PBMCm, demonstrating functional FGFR signaling in these cells. FGF23 treatment of PBMCm and PDm decreased expression of mRNA for CYP27B1. In PBMCm this was associated with downregulation of 25OHD to 1,25(OH)(2) D metabolism, and concomitant suppression of intracrine induced 24-hydroxylase (CYP24A1) and antibacterial cathelicidin (LL37). FGF23 suppression of CYP27B1 was particularly pronounced in PBMCm treated with interleukin-15 to stimulate synthesis of 1,25(OH)(2) D. These data indicate that FGF23 can inhibit extra-renal expression of CYP27B1 and subsequent intracrine responses to 1,25(OH)(2) D in two different human monocyte models. Elevated expression of FGF23 may therefore play a crucial role in defining immune responses to vitamin D and this, in turn, may be a key determinant of infection in patients with chronic kidney disease (CKD).

Hypophosphatemic rickets

PURPOSE OF REVIEW

Description of the recent advances on the regulation of phosphate metabolism, gene mutations, and new approaches to treatment in patients with hypophosphatemic rickets.

RECENT FINDINGS

Fibroblast growth factor 23 (FGF23) overproduction may be a primary cause of hypophosphatemic rickets. Inactivating mutations of phosphate-regulating gene with homologies to endopeptidases on the X chromosome, dentin matrix acidic phosphoprotein 1, and ectonucleotide pyrophosphatase/phosphodiesterase 1 are associated with X-linked hypophosphatemic rickets, autosomal recessive hypophosphatemic rickets 1, and autosomal recessive hypophosphatemic rickets 2, respectively. Activating mutations of FGF23 gene is the cause of autosomal dominant hypophosphatemic rickets. Iron deficiency may affect autosomal dominant hypophosphatemic rickets phenotype by regulating FGF23 production.Current treatment with activated vitamin D metabolites and oral inorganic phosphate salts may partially correct skeletal lesions and linear growth in patients with hypophosphatemic rickets. However, some patients have poor improvement by the current treatment.

SUMMARY

Identification of the causative mutation in patients with hypophosphatemic rickets may be useful to confirm the diagnosis and probably for prognosis. Inhibition of FGF23 overproduction by anti-FGF23 neutralizing antibodies could be a future approach for treatment of patients with FGF23-dependent hypophosphatemic rickets.

Oncogenic osteomalacia illustrating the effect of fibroblast growth factor 23 on phosphate homeostasis

In oncogenic osteomalacia (OOM), fibroblast growth factor 23 (FGF23) induces renal phosphate wasting and inhibits the appropriate increase of calcitriol. A patient suffering from OOM is described. Serum calcium, phosphate, biointact parathyroid hormone and intact FGF23 as well as the calcitriol and 24,25-vitamin D levels were measured before and after tumour removal. The clinical approach to a patient with hypophosphataemia is discussed and the changes in mineral metabolism after removal of a FGF23-producing tumour are described.

Can features of phosphate toxicity appear in normophosphatemia?

Phosphate is an indispensable nutrient for the formation of nucleic acids and the cell membrane. Adequate phosphate balance is a prerequisite for basic cellular functions ranging from energy metabolism to cell signaling. More than 85% of body phosphate is present in the bones and teeth. The remaining phosphate is distributed in various soft tissues, including skeletal muscle. A tiny amount, around 1% of total body phosphate, is distributed both in the extracellular fluids and within the cells. Impaired phosphate balance can affect the functionality of almost all human systems, including muscular, skeletal, and vascular systems, leading to an increase in morbidity and mortality of the involved patients. Currently, measuring serum phosphate level is the gold standard to estimate the overall phosphate status of the body. Despite the biological and clinical significance of maintaining delicate phosphate balance, serum levels do not always reflect the amount of phosphate uptake and its distribution. This article briefly discusses the potential that some of the early consequences of phosphate toxicity might not be evident from serum phosphate levels.