Diminished linear growth during intermittent calcitriol therapy in children undergoing CCPD

Chromatin accessibility and epigenetic deoxyribose nucleic acid (DNA) modifications in chronic kidney disease (CKD) osteoblasts: a study of bone and osteoblasts from pediatric patients with CKD

Maturation defects are intrinsic features of osteoblast lineage cells in CKD patients. These defects persist ex vivo, suggesting that CKD induces epigenetic changes in bone cells. To gain insights into which signaling pathways contribute to CKD-mediated, epigenetically driven, impairments in osteoblast maturation, we characterized RNA expression and DNA methylation patterns by RNA-Seq and MethylationEpic in primary osteoblasts from nine adolescent and young adult dialysis patients with end-stage kidney disease and three healthy references. ATAC-Seq was also performed on a subset of osteoblasts. Bone matrix protein expression was extracted from the iliac crest and evaluated by proteomics. Gene set enrichment analysis was used to establish signaling pathways consistently altered in chromatin accessibility, DNA methylation, and RNA expression patterns. Single genes were suppressed in primary osteoblasts using shRNA and mineralization characterized in vitro. The effect of nuclear factor of activated T cells (NFAT) signaling suppression was also assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) incorporation. We found that signaling pathways critical for osteoblast differentiation were strongly downregulated in CKD osteoblasts. Gene set enrichment analysis identified highly significant methylation changes, differential chromatin accessibility, and altered RNA expression in NFAT signaling targets. NFAT inhibition reduced osteoblast proliferation. Combined analysis of osteoblast RNA expression and whole bone matrix composition identified 13 potential ligand-receptor pairs. In summary, epigenetic changes in CKD osteoblasts associate with altered expression of multiple osteoblast genes and signaling pathways. An increase in NFAT signaling may play a role in impaired CKD osteoblast maturation. Epigenetic changes also associate with an altered bone matrix, which may contribute to bone fragility. Further studies are necessary to elucidate the pathways affected by these genetic alterations since elucidating these pathways will be vital to correcting the underlying biology of bone disease in the CKD population.

Diagnosis and management of mineral and bone disorders in infants with CKD: clinical practice points from the ESPN CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce

BACKGROUND

Infants with chronic kidney disease (CKD) form a vulnerable population who are highly prone to mineral and bone disorders (MBD) including biochemical abnormalities, growth retardation, bone deformities, and fractures. We present a position paper on the diagnosis and management of CKD-MBD in infants based on available evidence and the opinion of experts from the European Society for Paediatric Nephrology (ESPN) CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce.

METHODS

PICO (Patient, Intervention, Comparator, Outcomes) questions were generated, and relevant literature searches performed covering a population of infants below 2 years of age with CKD stages 2-5 or on dialysis. Clinical practice points (CPPs) were developed and leveled using the American Academy of Pediatrics grading matrix. A Delphi consensus approach was followed.

RESULTS

We present 34 CPPs for diagnosis and management of CKD-MBD in infants, including dietary control of calcium and phosphate, and medications to prevent and treat CKD-MBD (native and active vitamin D, calcium supplementation, phosphate binders).

CONCLUSION

As there are few high-quality studies in this field, the strength of most statements is weak to moderate, and may need to be adapted to individual patient needs by the treating physician. Research recommendations to study key outcome measures in this unique population are suggested. A higher resolution version of the Graphical abstract is available as Supplementary information.

Bone marrow adiposity inversely correlates with bone turnover in pediatric renal osteodystrophy

Bone marrow adiposity is associated with bone disease in the general population. Although chronic kidney disease (CKD) is associated with increased bone fragility, the correlation between marrow adiposity and bone health in CKD is unknown. We evaluated the relationship between bone marrow adipocytes and bone histomorphometry in 32 pediatric patients. We also evaluated the effects of growth hormone and calcitriol (1,25(OH)₂D₃)—two therapies commonly prescribed for pediatric bone disease—on marrow adiposity and bone histomorphometry. Finally, the adipogenic potential of primary human osteoblasts from CKD patients was assessed in vitro, both alone and in the presence of 1,25(OH)₂D₃. In cross-sectional analysis, marrow adipocyte number per tissue area (Adi.N/T.Ar) correlated with bone formation rate/bone surface (BFR/BS) in patients with high bone turnover (r = −0.55, p = 0.01) but not in those with low/normal bone turnover. Changes in bone formation rate correlated with changes Adi.N/T.Ar on repeat bone biopsy(r = −0.48, p = 0.02). In vitro, CKD and control osteoblasts had a similar propensity to transition into an adipocyte-like phenotype; 1,25(OH)₂D₃ had very little effect on this propensity. In conclusion, marrow adiposity correlates inversely with bone turnover in pediatric patients with high turnover renal osteodystrophy. The range of adiposity observed in pediatric patients with low/normal bone turnover is not explained by intrinsic changes to precursor cells or by therapies but may reflect the effects of circulating factors on bone cell health in this population.

•

Marrow adipocyte numbers correlate with bone formation in high turnover renal osteodystrophy.

•

Marrow adipocyte numbers do not correlate with osteoid accumulation in CKD.

•

Circulating toxins may impair adipogenesis in low turnover osteodystrophy.

Serum Markers of Low-Turnover Bone Disease in Mexican Children with Chronic Kidney Disease Undergoing Dialysis

Background

The frequency of low-turnover bone disease (LTBD) in patients with chronic kidney disease (CKD) has increased in past years. This change is important because LTBD is associated with bone pain, growth delay, and higher risk for bone fractures and extraosseous calcifications. LTBD is a histological diagnosis. However, serum markers such as parathyroid hormone (PTH) and calcium levels offer a noninvasive alternative for diagnosing these patients.

Objective

To describe the prevalence of LTBD in pediatric patients with renal failure undergoing some form of renal replacement therapy, using serum calcium and intact PTH levels as serum markers.

Methods

In this cross-sectional study, 41 children with CKD undergoing dialysis treatment (31 on continuous ambulatory peritoneal dialysis and 10 on hemodialysis) were included. There were no inclusion restrictions with respect to gender, cause of CKD, or dialysis modality. The children were studied as outpatients. The demographic data, CKD course, time on dialysis, phosphate-binding agents, and calcitriol prescription were registered, as well as weight, height, Z-score for height, linear growth rate, and Z-score for body mass index. Serum calcium, phosphorus, aluminum, PTH, alkaline phosphatase, osteocalcin, glucose, creatinine, urea, cholesterol, and triglycerides were measured.

Results

There were 20 (48.8%) children with both PTH <150 pg/mL and corrected total calcium >10 mg/dL who were classified as having LTBD[(+)]; the remaining 21 (51.2%) children were classified as having no LTBD[(–)]. The LTBD(+) patients were younger (11.2 ± 2.7 vs 13.2 ± 2.4 years, p < 0.01) but they had no differences regarding Z-scores for height. Linear growth in 6 months was less than expected in both groups (-0.15 ± 0.23 cm/month), but the difference between expected and observed growth was higher in the LTBD(+) group (-0.24 ± 0.14 vs –0.07 ± 0.28 cm/mo, p < 0.03). LTBD(+) patients also had lower serum creatinine (8.69± 2.75 vs 11.19 ± 3.17 mg/dL, p < 0.01), higher serum aluminum levels [median (range) 38.4 (9 – 106) vs 28.1 (9 – 62) μg/L, p < 0.05], and lower systolic blood pressure (112.0 ± 10.3 vs 125.0 ±12.9 mmHg, p < 0.015) and diastolic blood pressure (76.0 ± 9.7 vs 84.5 ± 8.2 mmHg, p < 0.017). A significant correlation was found between PTH and alkaline phosphatase ( r = 0.68, p < 0.001), but not between PTH and aluminum.

Conclusion

The LTBD(+) biochemical profile was found in 48.8% of the children and was associated with impaired linear growth. Aluminum contamination, evidenced by higher serum aluminum levels, may have had a pathogenic role in these disorders. Higher systolic and diastolic blood pressure levels may be related to higher serum PTH levels.

Clinical practice recommendations for treatment with active vitamin D analogues in children with chronic kidney disease Stages 2-5 and on dialysis

In patients with chronic kidney disease (CKD), renal synthesis of active vitamin D [1,25-dihydroxyvitamin D (1,25(OH)2D)] declines and is associated with hypocalcaemia, secondary hyperparathyroidism and the spectrum of CKD-mineral and bone disorder (MBD). In advanced CKD, active vitamin D analogues, including alfacalcidol, calcitriol and paricalcitol, are routinely administered. There are few studies on the use of vitamin D analogues in children with CKD and on dialysis. It is difficult to define bone-specific outcomes that can guide treatment with active vitamin D analogues in children with CKD-MBD. A core working group (WG) of the European Society for Paediatric Nephrology (ESPN) CKD-MBD and Dialysis WGs has developed recommendations for the use of active vitamin D therapy in children with CKD and on dialysis. A second document in parallel with this one covers treatment recommendations for native vitamin D therapy. The WGs have performed an extensive literature review to include systematic reviews and randomized controlled trials in adults and children with CKD and prospective observational studies in children with CKD. The Grading of Recommendation, Assessment, Development and Evaluation (GRADE) system was used to develop and grade the recommendations. In the absence of applicable study data, the opinion of experts from the ESPN CKD-MBD and Dialysis WGs is provided, but clearly GRADE-ed as such and must be carefully considered by the treating physician and adapted to individual patient needs as appropriate.

Efficacy and safety of paricalcitol in children with stages 3 to 5 chronic kidney disease

BACKGROUND

Elevated intact parathyroid hormone (iPTH) levels can contribute to morbidity and mortality in children with chronic kidney disease (CKD). We evaluated the pharmacokinetics, efficacy, and safety of oral paricalcitol in reducing iPTH levels in children with stages 3-5 CKD.

METHODS

Children aged 10-16 years with stages 3-5 CKD were enrolled in two phase 3 studies. The stage 3/4 CKD study characterized paricalcitol pharmacokinetics and compared the efficacy and safety of paricalcitol with placebo followed by an open-label period. The stage 5 CKD study evaluated the efficacy and safety of paricalcitol (no comparator) in children with stage 5 CKD undergoing dialysis.

RESULTS

In the stage 3/4 CKD study, mean peak plasma concentration and area under the time curve from zero to infinity were 0.13 ng/mL and 2.87 ng•h/((or ng×h/))mL, respectively, for 12 children who received 3 μg paricalcitol. Thirty-six children were randomized to paricalcitol or placebo; 27.8% of the paricalcitol group achieved two consecutive iPTH reductions of ≥30% from baseline versus none of the placebo group (P = 0.045). Adverse events were higher in children who received placebo than in those administered paricalcitol during the double-blind treatment (88.9 vs. 38.9%; P = 0.005). In the stage 5 CKD study, eight children (61.5%) had two consecutive iPTH reductions of ≥30% from baseline, and five (38.5%) had two consecutive iPTH values of between 150 and 300 pg/mL. Clinically meaningful hypercalcemia occurred in 21% of children.

CONCLUSIONS

Oral paricalcitol in children aged 10-16 years with stages 3-5 CKD reduced iPTH levels and the treatment was well tolerated. Results support an initiating dose of 1 μg paricalcitol 3 times weekly in children aged 10-16 years.

Interventions for metabolic bone disease in children with chronic kidney disease

BACKGROUND

Bone disease is common in children with chronic kidney disease (CKD) and when untreated may result in bone deformities, bone pain, fractures and reduced growth rates. This is an update of a review first published in 2010.

OBJECTIVES

This review aimed to examine the benefits (improved growth rates, reduced risk of bone fractures and deformities, reduction in PTH levels) and harms (hypercalcaemia, blood vessel calcification, deterioration in kidney function) of interventions (including vitamin D preparations and phosphate binders) for the prevention and treatment of metabolic bone disease in children with CKD.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Specialised Register to 8 September 2015 through contact with the Trial's Search Co-ordinator using search terms relevant for this review.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing different interventions used to prevent or treat bone disease in children with CKD stages 2 to 5D.

DATA COLLECTION AND ANALYSIS

Data were assessed for study eligibility, risk of bias and extracted independently by two authors. Results were reported as risk ratios (RR) or risk differences (RD) with 95% confidence intervals (CI) for dichotomous outcomes. For continuous outcomes the mean difference (MD) or standardised mean difference (SMD) with 95% confidence intervals (CI) was used. Statistical analyses were performed using the random-effects model.

MAIN RESULTS

This review included 18 studies (576 children); three new studies were added for this update. Adequate sequence generation and allocation concealment were reported in 12 and 11 studies respectively. Only four studies reported blinding of children, investigators or outcome assessors. Nine studies were at low risk of attrition bias and 12 studies were at low risk of selective reporting bias.Eight different interventions were compared. Two studies compared intraperitoneal (IP) with oral calcitriol. PTH levels were significantly lower with IP compared with oral calcitriol (1 study: MD -501.00 pg/mL, 95% CI -721.54 to -280.46) but the number of children with abnormal bone histology did not differ between treatments. Three studies compared intermittent with daily oral calcitriol. The change in mean height SDS (1 study: MD 0.13, 95% CI -0.22 to 0.48) and the percentage fall in parathyroid hormone (PTH) levels at eight weeks (1 study: MD -5.50%, 95% CI -32.37 to 21.37) and 12 months (1 study: MD -6.00% 95% CI -25.27 to 13.27) did not differ between treatments.Four studies compared active vitamin D preparations (calcitriol, paricalcitol, 1α-hydroxyvitamin D) with placebo or no specific treatment. One study reported vitamin D preparations significantly reduced PTH levels (-55.00 pmol/L, 95% CI -83.03 to -26.97). There was no significant difference in hypercalcaemia risk with vitamin D preparations compared with placebo or no specific treatment (4 studies, 103 children: RD 0.08 mg/dL, 95% CI -0.08 to 0.24). However, there was heterogeneity (I(2) = 55%) with one study showing a significantly greater risk of hypercalcaemia with intravenous (IV) calcitriol administration. Two studies (97 children) compared calcitriol with other vitamin D preparations and both found no significant differences in growth between preparations.Two studies compared ergocalciferol in patients with CKD and vitamin D deficiency. Elevated PTH levels developed significantly later in ergocalciferol treated children (1 study: hazard ratio 0.30, 95% CI 0.09 to 0.93) though the number with elevated PTH levels did not differ between groups (1 study, 40 children: RR 0.33, 95% CI 0.11 to 1.05).Two studies compared calcium carbonate with aluminium hydroxide as phosphate binders. One study (17 children: MD -0.86 SDS, 95% CI -2.24 to 0.52) reported no significant difference in mean final height SDS between treatments. Three studies compared sevelamer with calcium-containing phosphate binders. There were no significant differences in the final calcium, phosphorus or PTH levels between binders. More episodes of hypercalcaemia occurred with calcium-containing binders. One study reported no significant differences between calcitriol and doxercalciferol in bone histology or biochemical parameters.

AUTHORS' CONCLUSIONS

Bone disease, assessed by changes in PTH levels, is improved by all vitamin D preparations. However, no consistent differences between routes of administration, frequencies of dosing or vitamin D preparations were demonstrated. Although fewer episodes of high calcium levels occurred with the non-calcium-containing phosphate binder, sevelamer, compared with calcium-containing binders, there were no differences in serum phosphorus and calcium overall and phosphorus values were reduced to similar extents. All studies were small with few data available on patient-centred outcomes (growth, bone deformities) and limited data on biochemical parameters or bone histology resulting in considerable imprecision of results thus limiting the applicability to the care of children with CKD.

Cardiac, Inflammatory and Metabolic Parameters: Hemodialysis versus Peritoneal Dialysis

INTRODUCTION

Mortality in dialysis patients is higher than in the general population, and cardiovascular disease represents the leading cause of death. Hypertension and volume overload are important risk factors for the development of left ventricular hypertrophy (LVH) in hemodialysis (HD) and peritoneal dialysis (PD) patients. Other factors are mainly represented by hyperparathyroidism, vascular calcification, arterial stiffness and inflammation. The aim of this study was to compare blood pressure (BP) and metabolic parameters with cardiovascular changes [cardiothoracic ratio (CTR), aortic arch calcification (AAC) and LV mass index (LVMI)] between PD and HD patients.

MATERIALS AND METHODS

45 patients (23 HD and 22 PD patients) were enrolled. BP measurements, echocardiography and chest X-ray were performed in each patient to determine the LVMI and to evaluate the CTR and AAC. Inflammatory indexes, intact parathyroid hormone (iPTH) and arterial blood gas analysis were also evaluated.

RESULTS

LVMI was higher in PD than HD patients (139 ŷ 19 vs. 104 ŷ 22; p = 0.04). In PD patients, a significant correlation between iPTH, C-reactive protein and the presence of LVH was observed (r = 0.70, p = 0.04; r = 0.70, p = 0.03, respectively). The CTR was increased in PD patients as compared to HD patients, while no significant differences in cardiac calcifications were determined.

CONCLUSIONS

Our data indicate that HD patients present more effective BP control than PD patients. Adequate fluid and metabolic control are necessary to assess the adequacy of BP, which is strongly correlated with the increase in LVMI and with the increased CTR in dialysis patients. PD is a home therapy and allows a better quality of life, but PD patients may present a further increased cardiovascular risk if not adequately monitored.

Effects of vitamin D on parathyroid hormone and clinical outcomes in peritoneal dialysis: a narrative review

Vitamin D deficiency is very prevalent in dialysis and peritoneal dialysis (PD) patients show lower levels of cholecalciferol (25(OH)D3) than hemodialysis patients. We conducted a systematic narrative review to assess the effects of vitamin D therapy on control of secondary hyperparathyroidism and clinical outcomes induced by vitamin D pleiotropic effects. Medline database was searched for cohort and intervention studies reporting data on vitamin D (all sterols including synthetic analogs) and peritoneal dialysis without language restriction. Two authors independently extracted data. Twenty-nine observational and eleven interventional studies were identified for inclusion (1,036 subjects). PTH levels decreased in twenty-nine studies, increased in one study and remained stable in ten studies. Thirty-three studies analyzed the oral route for vitamin D administration, ten the intraperitoneal, one the subcutaneous and one the intravenous. A significant decrease of peritonitis risk was observed in two studies. Proteinuria decreased in four studies and remained stable in one study. Peritoneal protein loss decreased in one study and was stable in two studies. Studies on the therapeutic effects of vitamin D in PD are limited and describe small population samples. Moreover, vitamin D compounds do not consistently reduce PTH levels. The administration of active vitamin D in PD may have interesting pleiotropic effects such as decreasing proteinuria and peritoneal protein loss. According to these effects, vitamin D could help to preserve residual renal function and ensure efficient peritoneal membrane dialysance.

[Online hemodiafiltration in children and hypoparathyroidism: a single-centre series of cases]

BACKGROUND

Due to technical requirements and cost, hemodiafiltration (HDF) is not widely used in pediatrics. We have been using online HDF (oHDF) since 2009 and we observed low parathyroid hormone (PTH) levels despite the accurate management of CKD-MBD.

METHODS

We reviewed the medical charts and parameters of mineral metabolism assessed on a before/after session basis in the 6 children undergoing chronic oHDF in our centre.

RESULTS

We observed low (<80pg/mL) PTH levels in all 6 patients and very low (<45pg/mL) PTH levels in 5, two of them presenting with pathological fractures. These low PTH levels were reversed after decreasing calcium concentration to 1.25 mmol/L in the dialysate, suggesting that high-efficiency oHDF may expose children to calcium during sessions in a too important amount when using 1.5 mmol/L dialysates. Last, C-terminal FGF23 levels before sessions were relatively low (<1600RU/mL), with a 32% clearance by oHDF.

CONCLUSION

PTH levels should be closely monitored in pediatric oHDF and solutions with a calcium concentration of 1.25 mmol/L should be used as first line in these patients.

Growth in children on renal replacement therapy: a shrinking problem?

Growth failure has been almost inextricably linked with chronic kidney disease (CKD) and end-stage renal disease (ESRD) since initial reports of renal dwarfism dating back to the turn of the twentieth century. Growth failure in CKD has been associated with both increased morbidity and mortality. Growth failure in the setting of kidney disease is multifactorial and is related to poor nutritional status as well as comorbidities, such as anemia, bone and mineral disorders, and alterations in hormonal responses, as well as to aspects of treatment such as steroid exposure. In this issue of Pediatric Nephrology, Franke et al. report on the gains made in growth and maturation in pediatric patients with ESRD in recent decades, particularly in Germany. Through advances in the care of CKD and ESRD over recent decades, the prevalence of growth failure appears to be decreasing. These findings, along with a recent report demonstrating decreases in mortality in childhood ESRD in the United States Renal Data System (USRDS), suggest overall improvements in the outcomes of care, perhaps reflecting improvements in the quality of care for children with kidney disease worldwide.

Chronic kidney disease: mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Early increases in bone and plasma fibroblast growth factor 23 (FGF23) are associated with early defects in skeletal mineralization. Later in the course of CKD, secondary hyperparathyroidism--caused by a combination of declining calcitriol values and phosphate retention--results in high-turnover renal osteodystrophy whereas increased levels of both phosphate and FGF23 contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves high-turnover bone disease but fails to correct defects in skeletal mineralization. Because overtreatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy therefore must be titrated carefully to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents and new treatment paradigms may suppress serum PTH levels effectively while limiting intestinal calcium absorption and skeletal FGF23 stimulation and may provide future therapeutic alternatives for children with CKD.

The osteocyte in CKD: new concepts regarding the role of FGF23 in mineral metabolism and systemic complications

The identification of elevated circulating levels of the osteocytic protein fibroblast growth factor 23 (FGF23) in patients with chronic kidney disease (CKD), along with recent data linking these values to the pathogenesis of secondary hyperparathyroidism and to systemic complications, has changed the approach to the pathophysiology and treatment of disordered bone and mineral metabolism in renal failure. It now appears that osteocyte biology is altered very early in the course of CKD and these changes have implications for bone biology, as well as for progressive cardiovascular and renal disease. Since circulating FGF23 values are influenced by therapies used to treat secondary hyperparathyroidism, the effects of different therapeutic paradigms on FGF23 have important implications for mineral metabolism as well as for morbidity and mortality. Further studies are critically needed to identify the initial trigger for abnormalities of skeletal mineralization and turnover as well as the potential effects that current therapeutic options may have on osteocyte biology.

The skeletal consequences of growth hormone therapy in dialyzed children: a randomized trial

BACKGROUND AND OBJECTIVE

The effects of recombinant human growth hormone on renal osteodystrophy are unknown; thus, the effects of growth hormone (GH) on bone histomorphometry were assessed in pediatric patients with ESRD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Thirty-three patients who underwent bone biopsy between July 1994 and May 1999 were randomly assigned to therapy with or without GH. Patients were stratified by bone formation rate; all patients with high bone turnover received intraperitoneal calcitriol. Serum biochemical values were obtained monthly, and bone biopsy was repeated after 8 months.

RESULTS

Median patient age was 11.7 years (interquartile range [IQR], 7.6, 14.1 years); 45% of patients were male, and 52% were prepubertal. Median dialysis duration was 0.4 (IQR, 0.3, 0.8) year. Bone formation rate per bone surface increased from 15.0 (9.6, 21.8) to 154.6 (23.7, 174.3) μm(2)/μm(3) per year (P=0.05) in patients with low bone turnover treated with GH, decreased from 103.3 (57.0, 173.4) to 60.3 (20.3, 13.7) μm(2)/μm(3) per year in patients with high bone turnover receiving standard therapy (P=0.03), and was unchanged in the other two groups. Bone formation rates were higher with GH, irrespective of underlying bone histologic features (P=0.05). Parathyroid hormone did not differ between groups. GH therapy resulted in greater increases in height SD scores (estimated mean difference in change ± SD, 0.324±0.076; P<0.001), irrespective of underlying bone histologic features.

CONCLUSIONS

GH therapy improves height in pediatric dialysis patients, irrespective of underlying bone histologic features. Bone formation rates are higher in GH recipients, and GH therapy alters the relationship between circulating parathyroid hormone values and bone turnover.

Phosphate binders, vitamin D and calcimimetics in the management of chronic kidney disease-mineral bone disorders (CKD-MBD) in children

In order to minimize complications on the skeleton and to prevent extraskeletal calcifications, the specific aims of the management of chronic kidney disease mineral and bone disorder (CKD-MBD) are to maintain blood levels of serum calcium and phosphorus as close to the normal range as possible, thereby maintaining serum parathyroid hormone (PTH) at levels appropriate for CKD stage, preventing hyperplasia of the parathyroid glands, avoiding the development of extra-skeletal calcifications, and preventing or reversing the accumulation of toxic substances such as aluminum and β2-microglobulin. In order to limit cardiovascular calcification, daily intake of elemental calcium, including from dietary sources and from phosphate binders, should not exceed twice the daily recommended intake for age and should not exceed 2.5 g/day. Calcium-free phosphate binders, such as sevelamer hydrochloride and sevelamer carbonate, are safe and effective alternatives to calcium-based binders, and their use widens the margin of safety for active vitamin D sterol therapy. Vitamin D deficiency is highly prevalent across the spectrum of CKD, and replacement therapy is recommended in vitamin D-deficient and insufficient individuals. Therapy with active vitamin D sterols is recommended after correction of the vitamin D deficiency state and should be titrated based on target PTH levels across the spectrum of CKD. Although the use of calcimimetic drugs has been proven to effectively control the biochemical features of secondary hyperparathyroidism, there is very limited experience with the use of such agents in pediatric patients and especially during the first years of life. Studies are needed to further define the role of such agents in the treatment of pediatric CKD-MBD.

Searching the optimal PTH target range in children undergoing peritoneal dialysis: new insights from international cohort studies

The treatment of the mineral and bone disorder associated with chronic kidney disease (CKD-MBD) remains a major challenge in pediatric patients. The principal aims of therapeutic measures are not only to prevent the debilitating skeletal complications and to achieve normal growth but also to preserve long-term cardiovascular health. Serum parathyroid hormone (PTH) levels are used as a surrogate parameter of bone turnover. Whereas it is generally accepted that serum calcium and phosphate levels should be kept within the range for age, current pediatric consensus guidelines differ markedly with respect to the optimal PTH target range and operate on a limited evidence base. Recently, the International Pediatric Dialysis Network (IPPN) established a global registry collecting detailed clinical and biochemical information, including data relevant to CKD-MBD in children on chronic peritoneal dialysis (PD). This review highlights the current evidence basis regarding the optimal PTH target range in pediatric CKD patients, and re-assesses the current guidelines in view of the outcome data collected by the IPPN registry. Based on a comprehensive evaluation of CKD-MBD outcome measures in this global patient cohort, a PTH target range of 1.7-3 times the upper limit of normal (i.e. 100-200 pg/ml) appears reasonable in children undergoing chronic PD.

Changes in bone matrix mineralization after growth hormone treatment in children and adolescents with chronic kidney failure treated by dialysis: a paired biopsy study

BACKGROUND

Patients with chronic kidney disease (CKD) develop renal osteodystrophy with alterations in bone turnover, mineralization, and volume (TMV). A specific skeletal complication in children is growth impairment, which currently is treated by recombinant human growth hormone (rhGH). The effects on bone material properties are poorly understood. This study assesses the effects of rhGH treatment on bone matrix mineralization.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

18 short children and adolescents (aged 3.6-16 years) with CKD on dialysis therapy.

PREDICTOR

rhGH treatment for 1 year.

OUTCOMES

Tetracycline-labeled bone biopsy classified according to the TMV system.

MEASUREMENTS

Bone mineralization density distribution (BMDD) was evaluated by quantitative backscattered electron imaging in trabecular and cortical compartments. Additional data for patients' height and biochemical bone serum parameters were obtained.

RESULTS

Prior to rhGH treatment, our cohort showed low bone turnover and high mineralization densities versus reference data: Ca(mean) (weighted mean calcium content) in cancellous bone, +3.3% (P = 0.04); Ca(mean) in cortical bone, +6.7% (P < 0.001); Ca(peak) (mode of the BMDD) in cancellous bone, +5.0% (P < 0.001); Ca(peak) in cortical bone, +8.2% (P < 0.001); Ca(width) (heterogeneity in mineralization), no significant difference for cancellous (P = 0.2) and cortical (P = 0.1) bone; Ca(high) (portion of fully mineralized bone) in cancellous bone, 5-fold greater (P < 0.001); Ca(high) in cortical bone, 14-fold greater (P < 0.001); Ca(low) (portion of low mineralized bone) in cancellous bone, +23.9% (P = 0.02); Ca(low) in cortical bone, -22.2% (P = 0.05). After rhGH treatment, height increased by 9.1 cm (P < 0.001) and bone turnover indices to normal values or beyond. Matrix mineralization was lesser and more heterogeneous compared to baseline: Ca(width) for cancellous bone, +15.3% (P < 0.001); Ca(width) for cortical bone, +34.1% (P < 0.001). Ca(mean), Ca(peak), and Ca(high) for cancellous bone and Ca(mean) and Ca(peak) for cortical bone were no longer significantly different from reference data. Ca(high) for cortical bone dramatically decreased after treatment but was still substantially greater than reference data.

LIMITATIONS

Low case number per TMV subgroup, no measurements of fibroblast growth factor 23.

CONCLUSIONS

Children and adolescents with CKD and growth deficiency are at risk of having low bone turnover. rhGH treatment improves height and concomitantly bone modeling/remodeling, which appears beneficial for bone matrix mineralization.

The consequences of chronic kidney disease on bone metabolism and growth in children

Growth retardation, decreased final height and renal osteodystrophy (ROD) are common complications of childhood chronic kidney disease (CKD), resulting from a combination of abnormalities in the growth hormone (GH) axis, vitamin D deficiency, hyperparathyroidism, hypogonadism, inadequate nutrition, cachexia and drug toxicity. The impact of CKD-associated bone and mineral disorders (CKD-MBD) may be immediate (serum phosphate/calcium disequilibrium) or delayed (poor growth, ROD, fractures, vascular calcifications, increased morbidity and mortality). In 2012, the clinical management of CKD-MBD in children needs to focus on three main objectives: (i) to provide an optimal growth in order to maximize the final height with an early management with recombinant GH therapy when required, (ii) to equilibrate calcium/phosphate metabolism so as to obtain acceptable bone quality and cardiovascular status and (iii) to correct all metabolic and clinical abnormalities that can worsen bone disease, growth and cardiovascular disease, i.e. metabolic acidosis, anaemia, malnutrition and 25(OH)vitamin D deficiency. The aim of this review is to provide an overview of the mineral, bone and vascular abnormalities associated with CKD in children in terms of pathophysiology, diagnosis and clinical management.

Mineral and bone disorders in children with chronic kidney disease

As children with chronic kidney disease (CKD) have a long lifespan, optimal control of bone and mineral homeostasis is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth but also for preserving long-term cardiovascular health. As the growing skeleton is highly dynamic and at particular risk of deterioration, close control of bone and mineral homeostasis is required in children with CKD. However, assessment of bone disease is hampered by the limited validity of biochemical parameters-major controversy exists on key issues such as parathyroid hormone target ranges and the lack of useful imaging techniques. The role of newly discovered factors in bone and mineral homeostasis, such as fibroblast growth factor 23, is not yet established. Even though scientific evidence is limited in children with CKD, ergocalciferol or cholecalciferol supplementation and the use of calcium-free phosphate binders is recommended. The new drug cinacalcet is highly promising; however, pediatric experience is still limited to observational data and the effect of cinacalcet on longitudinal growth and pubertal development is unknown. Randomized, controlled trials are underway, including studies of cinacalcet pharmacokinetics and pharmacodynamics in infants.

1,25(OH)2D3 alters growth plate maturation and bone architecture in young rats with normal renal function

Whereas detrimental effects of vitamin D deficiency are known over century, the effects of vitamin D receptor activation by 1,25(OH)₂D₃, the principal hormonal form of vitamin D, on the growing bone and its growth plate are less clear. Currently, 1,25(OH)₂D₃ is used in pediatric patients with chronic kidney disease and mineral and bone disorder (CKD-MBD) and is strongly associated with growth retardation. Here, we investigate the effect of 1,25(OH)₂D₃ treatment on bone development in normal young rats, unrelated to renal insufficiency. Young rats received daily i.p. injections of 1 µg/kg 1,25(OH)₂D₃ for one week, or intermittent 3 µg/kg 1,25(OH)₂D₃ for one month. Histological analysis revealed narrower tibial growth plates, predominantly in the hypertrophic zone of 1,25(OH)₂D₃-treated animals in both experimental protocols. This phenotype was supported by narrower distribution of aggrecan, collagens II and X mRNA, shown by in situ hybridization. Concomitant with altered chondrocyte maturation, 1,25(OH)₂D₃ increased chondrocyte proliferation and apoptosis in terminal hypertrophic cells. In vitro treatment of the chondrocytic cell line ATDC5 with 1,25(OH)₂D₃ lowered differentiation and increased proliferation dose and time-dependently. Micro-CT analysis of femurs from 1-week 1,25(OH)₂D₃-treated group revealed reduced cortical thickness, elevated cortical porosity, and higher trabecular number and thickness. 1-month administration resulted in a similar cortical phenotype but without effect on trabecular bone. Evaluation of fluorochrome binding with confocal microscopy revealed inhibiting effects of 1,25(OH)₂D₃ on intracortical bone formation. This study shows negative effects of 1,25(OH)₂D₃ on growth plate and bone which may contribute to the exacerbation of MBD in the CKD pediatric patients.

Parathyroid hormone and growth in chronic kidney disease

Growth failure is common in children with chronic kidney disease, and successful treatment is a major challenge in the management of these children. The aetiology is multi-factorial with "chronic kidney disease-metabolic bone disorder" being a key component that is particularly difficult to manage. Parathyroid hormone is at the centre of this mineral imbalance, consequent skeletal disease and, ultimately, growth failure. When other aetiologies are treated, good growth can be achieved throughout the course of the disease when parathyroid hormone (PTH) levels are in the normal range or slightly elevated. A direct correlation between PTH levels and growth has not been convincingly established, and the direct effect of PTH on growth has not been adequately described; furthermore, direct actions of PTH on the growth plate are unproven. The effects of PTH on growth stem from the pivotal role that PTH plays in the development of renal osteodystrophy. In severe secondary hyperparathyroidism, the growth plate is altered and growth is affected. At the other end of the spectrum, with an over-suppressed parathyroid gland, the rate of bone turnover and remodelling is markedly diminished, and some data suggest this is associated with poor growth. Most of the data available suggests that avoiding the development of significant bone disease through the strict control of PTH levels permits good growth. Absolute optimal ranges for PTH that maximise growth or minimise growth failure are not yet established.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

Value of the new bone classification system in pediatric renal osteodystrophy

BACKGROUND AND OBJECTIVES

Although lesions of renal osteodystrophy have traditionally been defined by bone turnover, alterations in skeletal mineralization and volume are also prevalent and may contribute to significant morbidity in patients with chronic kidney disease (CKD). The study presented here was undertaken to compare the traditional spectrum of renal osteodystrophy defined by bone turnover to a new classification system that includes T (turnover), M (mineralization), and V (volume) and to determine the value of biochemical parameters as predictors of specific TMV lesions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Pediatric patients (n = 161) treated with peritoneal dialysis were enrolled into the study.

RESULTS

Increased bone turnover and abnormal mineralization were prevalent (57% and 48%, respectively); bone volume was normal or increased in all subjects. Predictive algorithms for different skeletal diagnoses were established by Classification and regression tree analysis. Serum parathyroid hormone (PTH) less than 400 pg/ml in combination with alkaline phosphatase values less than 400 IU/L provided the highest correct prediction rate for patients with both normal bone turnover and normal mineralization. Levels of PTH were higher and serum calcium levels were lower in patients with defective mineralization, irrespective of bone turnover.

CONCLUSIONS

Although no single biochemical marker is able to provide a complete assessment of renal osteodystrophy, a combination of serum calcium, alkaline phosphatase, and PTH levels may lead to a more precise noninvasive assessment of turnover and mineralization abnormalities in this population.

Calcitriol and doxercalciferol are equivalent in controlling bone turnover, suppressing parathyroid hormone, and increasing fibroblast growth factor-23 in secondary hyperparathyroidism

We compared the effects of calcitriol and doxercalciferol, in combination with either calcium carbonate or sevelamer, on bone, mineral, and fibroblast growth factor-23 (FGF-23) metabolism in patients with secondary hyperparathyroidism. A total of 60 pediatric patients treated with peritoneal dialysis were randomized to 8 months of therapy with either oral calcitriol or doxercalciferol, combined with either calcium carbonate or sevelamer. Bone formation rates decreased during therapy and final values were within the normal range in 72% of patients. A greater improvement in eroded surface was found in patients treated with doxercalciferol than in those given calcitriol. On initial bone biopsy, a mineralization defect was identified in the majority of patients which did not normalize with therapy. Serum phosphate concentrations were controlled equally well by both binders, but serum calcium levels increased during treatment with calcium carbonate, and serum parathyroid hormone levels were decreased by 35% in all groups. Baseline plasma FGF-23 values were significantly elevated and rose over fourfold with calcitriol and doxercalciferol, irrespective of phosphate binder. Thus, doxercalciferol is as effective as calcitriol in controlling serum parathyroid hormone levels and suppressing the bone formation rate. Sevelamer allows the use of higher doses of vitamin D. Implications of these changes on bone and cardiovascular biology remain to be established.

The calcemic response to continuous parathyroid hormone (PTH)(1-34) infusion in end-stage kidney disease varies according to bone turnover: a potential role for PTH(7-84)

CONTEXT

Factors contributing to PTH resistance in dialysis patients remain elusive.

OBJECTIVES

The study assessed the skeletal and biochemical response to 46 h of PTH(1-34) infusion in dialysis patients.

DESIGN

The study was a prospective, controlled assessment of response to PTH(1-34).

SETTING

The study was performed at the University of California, Los Angeles, General Clinical Research Center.

PARTICIPANTS

Nineteen dialysis patients and 17 healthy volunteers were studied.

INTERVENTION

PTH(1-34) was infused at a rate of 8 pmol/kg x h for 46 h. Bone biopsy was performed in all dialysis patients.

MAIN OUTCOME MEASURES

Serum calcium, phosphorus, 1,25-dihydroxyvitamin D, PTH (four separate assays), and FGF-23 were determined at baseline and h 7, 23, 35, and 46 of the infusion.

RESULTS

Serum calcium levels rose in healthy volunteers (9.2 +/- 0.1 to 11.9 +/- 0.3 mg/dl; P < 0.01) and in dialysis patients with adynamic/normal bone turnover (9.0 +/- 0.3 to 10.7 +/- 0.7 mg/dl; P < 0.05) but did not change in dialysis patients with high bone turnover. Serum phosphorus levels declined in healthy volunteers (3.9 +/- 0.1 to 3.5 +/- 0.1 mg/dl; P < 0.05) but increased in all dialysis patients (6.7 +/- 0.4 to 8.0 +/- 0.3 mg/dl; P < 0.05). Full-length PTH(1-84) declined in all subjects; however, PTH(7-84) fragments declined only in healthy subjects and in dialysis patients with normal/adynamic bone but remained unchanged in dialysis patients with high bone turnover.

CONCLUSIONS

The skeleton of dialysis patients with high bone turnover is resistant to the calcemic actions of PTH. PTH(7-84) may contribute to this phenomenon.

Interventions for bone disease in children with chronic kidney disease

BACKGROUND

Bone disease is common in children with chronic kidney disease (CKD) and when untreated may result in bone deformities, bone pain, fractures and reduced growth rates.

OBJECTIVES

To investigate the benefits and harms of interventions for preventing and treating bone disease in children with CKD.

SEARCH STRATEGY

The Cochrane Renal Group's specialised register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, reference lists and abstracts were searched without language restriction.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing different interventions used to prevent or treat bone disease in children with CKD stages 2-5D compared with placebo, no treatment or other agents were included. Studies examining different routes or frequency of treatment were also included.

DATA COLLECTION AND ANALYSIS

Data were extracted by two authors. The random-effects model was used and results were reported as risk ratios or risk differences for dichotomous outcomes and mean differences for continuous outcomes with 95% confidence intervals.

MAIN RESULTS

Fifteen RCTs (369 children) were identified. Compared with oral calcitriol, intraperitoneal calcitriol significantly reduced the level of serum parathyroid hormone (PTH) but there were no significant differences in bone histology or other biochemical measures (2 RCTs). There were no significant differences detected in growth, PTH, serum calcium or phosphorus between daily versus intermittent calcitriol (3 RCTs). Vitamin D therapy significantly reduced PTH levels compared with placebo or no treatment. The number of children with hypercalcaemia did not differ significantly between groups (4 RCTs). No significant differences were detected in growth rates, bone histology or biochemical parameters between calcitriol and either dihydrotachysterol or ergocalciferol (2 RCTs). Though fewer episodes of hypercalcaemia were reported with sevelamer, no significant differences were detected in serum calcium, phosphorus and PTH levels between calcium-containing phosphate binders and either aluminium hydroxide or sevelamer (4 RCTs).

AUTHORS' CONCLUSIONS

Bone disease, assessed by changes in PTH levels, is improved by all vitamin D preparations. However no consistent differences between routes of administration, frequencies of dosing or vitamin D preparations have been demonstrated. Though fewer episodes of high calcium levels occurred with the non calcium-containing binder, sevelamer, compared with calcium-containing binders, there were no differences in serum phosphorus and calcium overall and phosphorus values were reduced to similar extents. All RCTs were small with few data available on patient-centred outcomes (growth, bone deformities) and limited data on biochemical parameters resulting in considerable imprecision of results thus limiting the applicability to care of children with CKD.

Middle-term use of Cinacalcet in paediatric dialysis patients

The effects of the calcimimetic drug Cinacalcet were assessed in six children with uncontrolled hyperparathyroidism secondary to stage 5 chronic kidney disease (CKD). Data were collected retrospectively regarding bone biochemistry and medications. Patients were between the ages of 11 months and 14 years on commencing Cinacalcet at initial doses of 0.4-1.4 mg/kg. Treatment, which was well tolerated in the majority and still on going in five patients, was for periods ranging between 3 months and 3 years. All six cases saw at least an 86% reduction in serum parathyroid hormone (PTH). Hypophosphataemia and/or hypocalcaemia were observed in three cases. Overall, achievement of UK Renal Association targets for corrected calcium (Ca), phosphate (P) and the calcium x phosphate product (Ca x P) were unaffected. We conclude that Cinacalcet is an effective treatment for correcting and sustaining correction of uncontrollable PTH levels seen in a difficult group of patients. Importantly, it has allowed the avoidance of parathyroidectomy for a significant time period in all cases. There remain questions about the effect of Cinacalcet on linear growth amongst paediatric dialysis patients, and future studies should aim to address this.

Current advances in chronic kidney disease in children: growth, cardiovascular, and neurocognitive risk factors

Linear growth and neurocognitive development are two of the most important differences between adults and children, in terms of clinical issues that must be addressed in patients with chronic kidney disease (CKD). Correction of metabolic acidosis, nutritional deficiency, and renal osteodystrophy improve linear growth, but many children require administration of growth hormone to achieve normal growth. A variety of neurocognitive deficits occur in children with CKD, although there has been an improvement in outcome via improved dialysis, correction of malnutrition, and decreased aluminum exposure. Although growth and neurocognitive development are delayed, cardiovascular complications are accelerated in children with CKD, and are reflected in a dramatic increase in cardiovascular mortality compared with healthy children. Other early cardiovascular complications in children with CKD include left ventricular hypertrophy, cardiac dysfunction, and vascular calcifications.

Cinacalcet for secondary hyperparathyroidism in children with end-stage renal disease

The efficacy and acceptability of cinacalcet for treatment of secondary hyperparathyroidism (SHPT) was assessed in seven pediatric patients suffering from end-stage renal disease (ESRD) presenting with inadequately controlled SHPT despite conventional management. Patients received daily treatment with cinacalcet (dosage 0.25 mg/kg body weight) for a total of 4 weeks. Within 4 h after application of the first dose, median levels of serum parathyroid hormone (PTH) had decreased from 932 pg/ml (range 511-1,938 pg/ml) to 584 pg/ml (88-937 pg/ml), and final pre-dose values after 4 weeks were 199 pg/ml (121-940 pg/ml; each P < 0.05 versus baseline). Median concentrations of serum calcium (Ca) decreased within 4 h of the first administration, from 2.56 mmol/l to 2.38 mmol/l, returning to 2.58 mmol/l at 24 h, and they remained slightly decreased compared to baseline values thereafter (each P < 0.05 versus baseline). Both the median levels of serum phosphorus (P) and the Ca x P ion product decreased significantly during the 4-week period. Cinacalcet was well tolerated and without drug-related adverse effects. Thus, even with approximately half of the dose usually given to adult dialysis patients, PTH and the Ca x P ion product were markedly reduced in pediatric ESRD patients presenting with inadequately controlled SHPT. Therefore, our results support the initiation of a randomized, controlled, long-term trial in children.

Bone histomorphometry in children prior to commencing renal replacement therapy

Renal osteodystrophy (ROD) develops early in the course of chronic kidney disease (CKD). With improving patient survival it's importance and relevance has increased. The last published bone biopsy data in children prior to renal replacement therapy (RRT) was in 1982, which demonstrated abnormal histology in all patients with a glomerular filtration rate (GFR) <20 ml/min per 1.73 m(2). Studies investigating the relationship between bone histology and parathyroid hormone levels (PTH) and/or growth in children with CKD are few (seven). These were mostly undertaken in patients already initiated on RRT-dialysis. We investigated the presence of ROD in children at the commencement of RRT and to investigate any relationship between histology, growth and PTH levels. Following double tetracycline labelling, bone biopsies were taken from patients at the time of RRT surgery. Histological classification was based on the newly proposed turnover/mineralisation/volume (TMV) system. Eleven patients underwent bone biopsy. Patients were followed for an average of 1.1 years (0.5-1.8) prior to biopsy over an average of eight clinic visits (3-14), when routine biochemical data were collected. Time-integrated median calcium, phosphate and PTH levels were calculated. PTH levels were within the normal range in two patients with low turnover, 1.1-1.4 times the upper limit of normal (ULN) in three with mixed osteodystrophy and >2.9 times the ULN in four patients with high bone turnover. There was no relationship between bone turnover and growth. The presence of ROD was universal in these children with severe CKD. Low bone turnover was associated with normal-range mean PTH levels, and high bone turnover occurred at lower PTH levels than current guidelines would suggest.

Mineral metabolism and bone abnormalities in children with chronic renal failure

Abnormalities in mineral metabolism and changes in skeletal histology may contribute to growth impairment in children with chronic renal failure. Hyperphosphatemia, hypocalcemia, metabolic acidosis, alterations in vitamin D and IGF synthesis and parathyroid gland dysfunction play significant roles in the development of secondary hyperparathyroidism and subsequently, bone disease in renal failure. The recent KDIGO conference has made recommendations to consider this as a systemic disorder (chronic kidney disease-mineral bone disorder) and to standardize bone histomorphometry to include bone turnover, mineralization and volume (TMV). The use of DXA to assess bone mass is controversial in children with chronic renal failure. Questions arise regarding the accuracy of bone measurements and difficulty in data interpretation especially in children with renal failure who are not only growth retarded but often have pubertal delay and osteosclerosis. The validity and feasibility of new modalities of skeletal imaging which can detect changes in both trabecular and cortical bone are currently being investigated in children. The management of mineral abnormalities and bone disease in chronic renal failure is multifactorial. To manage hyperphosphatemia, dietary phosphate restriction accompanied by intake of calcium-free and metal-free phosphate binding agents are widely utilized. Vitamin D analogs remain the primary therapy for secondary hyperparathyroidism, although the use of the less hypercalcemic agents is preferred due to concerns of calciphylaxis and vascular calcification. Future clinical studies are needed to evaluate the long-term effects of calcimimetic agents and bisphosphonate therapy in children with chronic renal failure.

Management of Renal Osteodystrophy: THe Heart and Bone of Pediatric Dialysis

Control of mineral homeostasis is a particularly challenging task in children and adolescents on dialysis. Treatment efforts must not only ensure patient survival and the absence of debilitating complications of bone disease, but in view of a potentially long lifespan, must also consider how to best promote long-term cardiovascular health and successful psychosocial transition into adult life. In that context, avoidance of cardiovascular calcifications and accomplishment of adequate statural growth and a normal final height are major objectives of uremic bone disease management in children. Unfortunately, current pediatric management guidelines operate on a small evidence base, and major controversy surrounds key issues such as optimal target ranges for serum parathyroid hormone, calcium, and phosphorus in the individual childhood phases, and individual risk–benefit ratios for the use of phosphate binders, vitamin D analogs, and calcimimetics in children. The present review summarizes the current state of knowledge and outlines future research requirements in bone disease associated with pediatric end-stage renal disease.

What parathyroid hormone levels should we aim for in children with stage 5 chronic kidney disease; what is the evidence?

The bone disease that occurs as a result of chronic kidney disease (CKD) is not only debilitating but also linked to poor growth and cardiovascular disease. It is suspected that abnormal bone turnover is the main culprit for these poor outcomes. Plasma parathyroid hormone (PTH) levels are used as a surrogate marker of bone turnover, and there is a small number of studies in children that have attempted to identify the range of PTH levels that correlates with normal bone histology. It is clear that high PTH levels are associated with high bone turnover, although the range is wide. However, the ability of PTH levels to distinguish between low and normal bone turnover is less clear. This is an important issue, because current guidelines for calcium and phosphate management are based upon there being an "optimum" range for PTH. This editorial takes a critical look at the evidence upon which these recommendations are based.

Chronic kidney disease mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Decreased activity of renal 1 alpha hydroxylase results in decreased intestinal calcium absorption, increased serum parathyroid hormone levels, and high-turnover renal osteodystrophy, with subsequent growth failure. Simultaneously, phosphorus retention exacerbates secondary hyperparathyroidism, and elevated levels contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves growth and high-turnover bone disease. However, target ranges for serum calcium, phosphorus, and parathyroid hormone (PTH) levels vary according to stage of CKD. Since over-treatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy must be carefully adjusted to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents, including calcium-free phosphate binding agents and new vitamin D analogues, effectively suppress serum PTH levels while limiting intestinal calcium absorption and may provide future therapeutic alternatives for children with CKD.

Intermittent or daily administration of 1-alpha calcidol for nephrectomised infants on peritoneal dialysis?

Secondary hyperparathyroidism and renal osteodystrophy are major problems in patients with end-stage renal failure and may result in poor growth in children on dialysis. Whether vitamin D sterols should be given intermittently or daily remains a controversial issue. We studied 16 bilaterally nephrectomised infants with congenital nephrosis of the Finnish type (median age 0.54 years), all on peritoneal dialysis. Nine of them were receiving intermittent 1-alpha calcidol therapy and seven daily 1-alpha calcidol therapy. The target serum parathyroid hormone (PTH) level was 2-3 times the upper limit of normal (ULN). There were no statistically significant differences in PTH values between the groups (1.7-times vs 0.5-times the ULN at 3 months and 3.1-times vs 3.4-times the ULN at 6 months, respectively). The required weekly doses of 1-alpha calcidol were low, and there were no significant differences between the intermittent and daily groups (0.06 microg/kg vs 0.04 microg/kg at 3 months and 0.09 microg/kg vs 0.05 microg/kg at 6 months, respectively). The infants on intermittent 1-alpha calcidol showed significant catch-up growth during dialysis after nephrectomy relative to the infants on daily 1-alpha calcidol (-1.6 SD to -0.7 SD vs -1.4 SD to -1.0 SD, respectively; P < 0.05). Our results indicate that either intermittent or daily vitamin D analogue therapy, if started early, will prevent secondary hyperparathyroidism equally well in children on peritoneal dialysis (PD), but intermittent therapy might be more favourable for growth.

A structural approach to the assessment of fracture risk in children and adolescents with chronic kidney disease

Children with chronic kidney disease (CKD) have multiple risk factors for impaired accretion of trabecular and cortical bone. CKD during childhood poses an immediate fracture risk and compromises adult bone mass, resulting in significantly greater skeletal fragility throughout life. High-turnover disease initially results in thickened trabeculae, with greater bone volume. As disease progresses, resorption cavities dissect trabeculae, connectivity degrades, and bone volume decreases. Increased bone turnover also results in increased cortical porosity and decreased cortical thickness. Dual-energy X-ray absorptiometry (DXA)-based measures of bone mineral density (BMD) are derived from the total bone mass within the projected bone area (g/cm(2)), concealing distinct disease effects in trabecular and cortical bone. In contrast, peripheral quantitative computed tomography (pQCT) estimates volumetric BMD (vBMD, g/cm(3)), distinguishes between cortical and trabecular bone, and provides accurate estimates of cortical dimensions. Recent data have confirmed that pQCT measures of cortical vBMD and thickness provide substantially greater fracture discrimination in adult dialysis patients compared with hip or spine DXA. The following review considers the structural effects of renal osteodystrophy as it relates to fracture risk and the potential advantages and disadvantages of DXA and alternative measures of bone density, geometry, and microarchitecture, such as pQCT, micro-CT (microCT), and micro magnetic resonance imaging (microMRI) for fracture risk assessment.

Bone mineral density and bone histomorphometry in children on long-term dialysis

Bone mineral density (BMD) at the lumbar vertebrae (L(1)-L(4)) was assessed by dual-energy X-ray absorptiometry (DXA) in 20 children with chronic kidney disease (CKD) on dialysis, and its results were compared with bone biopsy and biochemical parameters. Biopsy specimens provided evidence of hyperparathyroid bone disease in eight cases (40%), and low bone turnover in 12 (60%). For BMD, expressed as Z-scores relative to normal, median Z-scores were -1.05 (range -2.36 to 1.06) for hyperparathyroid patients and -1.05 (range -4.40 to -0.03) for low bone turnover patients, with no statistical differences between groups (P = 0.512). In relation to BMD, of the whole sample, five (25%) had a Z-score under -2.0. When it was corrected for height, BMD was in the normal range. Additionally, there were no significant differences in single samples of serum calcium, alkaline phosphatase, phosphorus and intact parathyroid hormone (PTH) between groups with high or low bone turnover. Assessment of nutritional status, through height/age, showed that ten patients had Z-scores below -2.0 (median -2.12, range -7.13 to 0.73). In conclusion, renal osteodystrophy (ROD) seems to have a high prevalence among CKD pediatric patients, although only approximately a quarter of them developed changes in BMD. In children with CKD, measurements of bone mineral density may not be used for classification of various forms of ROD.