Growth hormone and calcitriol as modifiers of bone formation in renal osteodystrophy

The consequences of pediatric renal transplantation on bone metabolism and growth

PURPOSE OF REVIEW

During childhood, growth retardation, decreased final height and renal osteodystrophy are common complications of chronic kidney disease (CKD). These problems remain present in patients undergoing renal transplantation, even though steroid-sparing strategies are more widely used. In this context, achieving normal height and growth in children after transplantation is a crucial issue for both quality of life and self-esteem. The aim of this review is to provide an overview of pathophysiology of CKD-mineral bone disorder (MBD) in children undergoing renal transplantation and to propose keypoints for its daily management.

RECENT FINDINGS

In adults, calcimimetics are effective for posttransplant hyperparathyroidism, but data are missing in the pediatric population. Fibroblast growth factor 23 levels are associated with increased risk of rejection, but the underlying mechanisms remain unclear. A recent meta-analysis also demonstrated the effectiveness of rhGH therapy in short transplanted children.

SUMMARY

In 2013, the daily clinical management of CKD-MBD in transplanted children should still focus on simple objectives: to optimize renal function, to develop and promote steroid-sparing strategies, to provide optimal nutritional support to maximize final height and avoid bone deformations, to equilibrate calcium/phosphate metabolism so as to provide acceptable bone quality and cardiovascular status, to correct all metabolic and clinical abnormalities that can worsen both bone and growth (mainly metabolic acidosis, anemia and malnutrition), promote good lifestyle habits (adequate calcium intake, regular physical activity, no sodas consumption, no tobacco exposure) and eventually to correct native vitamin D deficiency (target of 25-vitamin D >75 nmol/l).

Immune, metabolic and epidemiological aspects of vitamin D in chronic kidney disease and transplant patients

Chronic kidney disease strongly impacts on mineral and bone metabolism. Despite numerous medications, the biological targets recommended by international guidelines are often unmet. Among the treatment armamentarium, native or nutritional vitamin D (25OHD3) has been rediscovered in the early 2000s, and its general and specific actions further studied. Effects on bone, immunity, infection prevention, muscle function and phosphocalcic metabolism have been reviewed. Assessment of nutritional vitamin D status showed very low serum 25OHD3 levels and increase in nutritional vitamin D prescription led to improvement in these levels. However, about 45% of adult CKD patients still have insufficient serum 25OHD3 levels. Epidemiological studies should be enforced to describe further the mineral and bone disease management in CKD.

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.

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.

Differential effects of growth hormone and alpha calcidol on trabecular and cortical bones in hypophysectomized rats

Growth hormone (GH) deficiency in children causes severe growth retardation, vitamin D deficiency, and osteopenia. We investigated whether alfacalcidol (1OHD) alone or in combination with GH can improve bone formation. Forty hypophysectomized female rats (HX) at the age of 8 wk were divided into HX, HX + 1OHD (oral 0.25 microg/kg daily), HX+GH (0.666 mg/0.2 mL SC daily) and HX+GH + 1OHD groups for a 4-wk study. Results showed that GH increased body weight, bone area, bone mineral content (BMC), and bone mineral density (BMD), whereas 1OHD only increased BMC and BMD. In cortical bone, GH increased both periosteal and endocortical bone formation resulting in a significant increase in cortical size and area in percentage, whereas 1OHD suppressed endocortical erosion surface per bone surface (ES/BS) without a significant effect on bone formation rate per bone surface (BFR/BS). In trabecular bone, GH mitigated the bone loss by increasing BFR/BS, whereas the 1OHD effect was by suppression of trabecular bone turnover in the HX rats. The combination of GH and 1OHD had no additive effect on increasing trabecular bone mass. In conclusion, GH activates new bone formation and increases bone turnover whereas 1OHD suppresses bone turnover. The combination intervention does not seem to provide any additive benefit.

Role of parathyroid hormone and therapy with active vitamin D sterols in renal osteodystrophy

Renal osteodystrophy (ROD) represents a spectrum of bone lesions ranging from a high-turnover to a low-turnover state. The expression of the histologic bone lesions is modulated by parathyroid hormone (PTH), vitamin D, calcium, phosphorus, and aluminum that act as major regulators of osteoblastic activity and bone formation rate. The availability of immunometric PTH assays has allowed reasonable prediction of the subtypes of bone lesions in patients with chronic kidney disease (CKD). PTH levels as measured by these assays, however, may not reflect the true bone turnover state during treatment with intermittent active vitamin D. Early diagnosis and appropriate treatment of renal bone disease are essential in preventing the debilitating consequences of ROD on the growing skeleton. Calcitriol and calcium-containing phosphate binders have been the mainstay of treatment for secondary hyperparathyroidism. Complications such as hypercalcemia, vascular calcifications, and the development of adynamic bone may arise from aggressive treatment. New vitamin D analogs and calcium-free phosphate binders are promising in terms of limiting these complications. The management of ROD should be tailored to maintain normal rates of bone formation and turnover with age-appropriate serum calcium and phosphorus levels and with serum PTH levels that correspond to normal rates of skeletal remodeling. These treatment goals would maintain bone health, maximize growth potential, and prevent the development of soft tissue and vascular calcifications.

VITAMIN D IN HEALTH AND DISEASE: The Evolution of Assays for Parathyroid Hormone

Reliable measurements of the concentration of parathyroid hormone (PTH) in serum or plasma are crucial for the effective clinical management of patients with chronic kidney disease (CKD). New PTH assays that increase the specificity of such measurements are now available and are widely utilized. The current review summarizes key technical developments in the evolution of PTH assays. We also discuss the diagnostic value of various methods for measuring PTH in serum or plasma for the assessment of patients with renal bone disease.

The Consequences of Uncontrolled Secondary Hyperparathyroidism and Its Treatment in Chronic Kidney Disease

Secondary hyperparathyroidism (HPT) is a common complication of chronic kidney disease (CKD) and a frequent cause of clinically significant bone disease. Soft-tissue and vascular calcification, cardiovascular disease, and calcific uremic arteriolopathy (CUA) are additional serious consequences of the disorder that may contribute directly to cardiovascular morbidity and mortality in patients with CKD. Less widely appreciated manifestations include neurological disturbances, hematological abnormalities, and endocrine dysfunction. Secondary HPT arises from alterations in calcium, phosphorus, and vitamin D metabolism that develop early in the course of CKD and become more pronounced as kidney function declines. Treatment is often delayed, however, until the disease is well established. Current therapeutic strategies rely largely on the use of vitamin D sterols to diminish excess parathyroid hormone (PTH) synthesis and to lower serum or plasma PTH levels, but their use is often confounded by increases in serum calcium and phosphorus concentrations, changes that can aggravate soft-tissue and vascular calcification. As such, there is a need for new therapeutic interventions that can effectively lower serum or plasma PTH levels without producing untoward side effects. The current review summarizes the diverse manifestations of secondary HPT in patients with CKD. The consequences of inadequately controlled secondary HPT and the adverse effects of selected therapeutic interventions for the disorder on vascular calcification and cardiovascular disease in those with CKD are discussed.

Special aspects of renal osteodystrophy in children

Renal osteodystrophy represents a spectrum of skeletal lesions that range from high-turnover to low-turnover bone disease. Similar factors are involved in the pathogenesis of renal osteodystrophy in adult and pediatric patients with chronic kidney disease (CKD). However, growth retardation and the development of bone deformities are specific complications that occurred in pediatric patients with CKD. Metabolic acidosis, renal osteodystrophy, malnutrition, and disturbances in the insulin growth factor (IGF)/growth hormone (GH) are among the main factors involved and they are discussed briefly in this article. In addition to disturbances in bone remodeling, longitudinal bone growth occurs at the growth plate cartilage by endochondral ossification. Although young rats with experimental CKD have growth retardation, the characteristics of the growth plate are markedly different between animals with severe secondary hyperparathyroidism and those with calcium-induced adynamic osteodystrophy. These disturbances may suggest potential molecular mechanisms by which endochondral bone formation may be altered in renal failure, consequently leading to growth retardation.

New assays for parathyroid hormone (PTH) and the relevance of PTH fragments in renal failure

BACKGROUND

Immunometric assays for parathyroid hormone (PTH) are used extensively to assess bone and mineral metabolism in patients with end-stage renal disease (ESRD) who are treated with dialysis. Results generally correspond to bone histology as documented by bone biopsy, and they are useful in monitoring disease progression. Recent work has shown, however, that older, first-generation immunometric PTH assays detect not only full-length PTH(1-84), but also other amino-terminally-truncated PTH fragments (ntPTH) that may have inhibitory effects on bone cell metabolism and/or contribute to the development of adynamic renal osteodystrophy. New second-generation immunometric PTH assays, by contrast, detect PTH(1-84) exclusively. The diagnostic value of plasma PTH determinations using second-generation immunometric PTH assays and the utility of estimates of the concentration of ntPTH in plasma in patients with ESRD has been assessed only recently.

METHODS

Results were reviewed from three published studies that examined the relationship between bone histology and plasma PTH levels as measured both by first- and by second-generation immunometric PTH assays in patients with ESRD. In all three studies, the concentration of ntPTH was estimated from the numerical difference between the results obtained with each assay and a ratio of PTH(1-84)/ntPTH was calculated.

RESULTS

In one report, all patients with adynamic renal osteodystrophy had PTH(1-84)/ntPTH ratio values <1.0, although some patients with high-turnover skeletal lesions also had values <1.0. Estimates of the ratio of PTH(1-84)/ntPTH were found to be a better predictor of adynamic bone than PTH values measured by either assay. By contrast, two other studies failed to confirm these observations. One made use of the same second-generation immunometric PTH assay employed in the original report, whereas the other used a different assay with similar specificity for PTH(1-84). Plasma PTH levels obtained by first- and second-generation assays were highly correlated in these two independent reports.

CONCLUSION

Plasma PTH levels, as determined by first-generation and second-generation immunometric assays, are highly correlated and have similar diagnostic value for the non-invasive assessment of renal osteodystrophy. The contention that ntPTH estimates and values for the PTH(1-84)/ntPTH ratio are useful in the diagnostic assessment of renal osteodystrophy has yet to be confirmed.

Parathyroid hormone (PTH), PTH-derived peptides, and new PTH assays in renal osteodystrophy

Parathyroid hormone (PTH), PTH-derived peptides, and new PTH assays in renal osteodystrophy. Reliable measurements of parathyroid hormone (PTH) concentrations in serum or plasma are critical for the appropriate diagnosis and management of patients with renal osteodystrophy. With the introduction of second generation immunometric assays for PTH, it is now possible to measure exclusively full-length, biologically active PTH(1-84). In contrast, first generation immunometric assays that have been used widely for many years detect not only PTH(1-84), but also other large amino-terminally-truncated, PTH-derived peptides. This development will require a careful re-evaluation of PTH measurements, as determined by either first or second generation immunometric assays, and their relationship to bone histology and bone remodeling rates in patients with end-stage renal disease (ESRD). Such information is essential for proper clinical management, but only limited bone biopsy data are available to guide the interpretation of PTH results using second generation PTH assays. The different performance characteristics of first and second generation immunometric PTH assays also makes it possible to quantify the plasma levels of amino-terminally-truncated, PTH-derived peptides, which may accumulate disproportionately in patients with ESRD. Recent experimental evidence indicates that one or more of these peptides can modify bone cell activity and skeletal remodeling, possibly by interacting with a PTH receptor distinct from the type I PTH receptor that binds to the amino-terminal portion of PTH and mediates the classical biological actions of the hormone. The putative C-PTH receptor interacts with mid- and/or carboxyterminal regions of PTH and other amino-terminally-truncated PTH-derived peptides; signaling through it may contribute to the skeletal resistance to PTH that characterizes ESRD. The current review discusses certain aspects of the molecular structure of PTH and its interaction with various receptors, briefly comments about selected components of PTH secretion, highlights recent technical advances in PTH assays, and summarizes the effects of various PTH-derived peptides on bone cells and on skeletal metabolism.

Osteoporosis in childhood: bone density of children in health and disease

Bone mineral density in later life largely depends on the peak bone mass achieved in adolescence or young adulthood. A reduced bone density is associated with increased fracture risk in adults as well as in children. Pediatricians should therefore play an important role in the early recognition and treatment of childhood osteoporosis. Juvenile idiopathic osteoporosis and osteogenesis imperfecta are examples of primary osteoporosis in childhood. However, osteoporosis is more frequently a complication of a chronic disease or its treatment. This paper provides an overview of bone and bone metabolism in healthy children and the use of diagnostic tools, such as biochemical markers of bone turnover and several bone densitometry techniques. Furthermore, a number of diseases associated with osteoporosis in childhood and possible treatment strategies are discussed.

A calcimimetic agent lowers plasma parathyroid hormone levels in patients with secondary hyperparathyroidism

BACKGROUND

The calcimimetic agent R-568 lowers plasma parathyroid hormone (PTH) levels in hemodialysis patients with mild secondary hyperparathyroidism, but its efficacy in those with more severe secondary hyperparathyroidism has not been studied.

METHODS

Twenty-one patients undergoing hemodialysis three times per week with plasma PTH levels between 300 and 1200 pg/mL were randomly assigned to 15 days of treatment with either 100 mg of R-568 (N = 16) or placebo (N = 5). Plasma PTH and blood ionized calcium levels were measured at intervals of up to 24 hours after oral doses on days 1, 2, 3, 5, 8, 11, 12, and 15.

RESULTS

Pretreatment PTH levels were 599 +/- 105 (mean +/- SE) and 600 +/- 90 pg/mL in subjects given R-568 or placebo, respectively, and values on the first day of treatment did not change in those given placebo. In contrast, PTH levels fell by 66 +/- 5%, 78 +/- 3%, and 70 +/- 3% at one, two, and four hours, respectively, after initial doses of R-568, remaining below pretreatment values for 24 hours. Blood ionized calcium levels also decreased after the first dose of R-568 but did not change in patients given placebo. Despite lower ionized calcium concentrations on both the second and third days of treatment, predose PTH levels were 422 +/- 70 and 443 +/- 105 pg/mL, respectively, in patients given R-568, and values fell each day by more than 50% two hours after drug administration. Predose PTH levels declined progressively over the first nine days of treatment with R-568 and remained below pretreatment levels for the duration of study. Serum total and blood ionized calcium concentrations decreased from pretreatment levels in patients given R-568, whereas values were unchanged in those given placebo. Blood ionized calcium levels fell below 1.0 mmol/L in 7 of 16 patients receiving R-568; five patients withdrew from study after developing symptoms of hypocalcemia, whereas three completed treatment after the dose of R-568 was reduced.

CONCLUSIONS

The calcimimetic R-568 rapidly and markedly lowers plasma PTH levels in patients with secondary hyperparathyroidism caused by end-stage renal disease.

Impaired growth, delayed ossification, and reduced osteoclastic activity in the growth plate of calcium-supplemented rats with renal failure

Linear growth is reduced in prepubertal children with adynamic renal osteodystrophy, suggesting that the proliferation and/or differentiation of epiphyseal growth plate chondrocytes is abnormal in this disorder. To examine this issue, in situ hybridization and histochemistry were used to measure selected markers of endochondral bone formation and bone resorption in the proximal tibia of subtotally nephrectomized rats fed a high calcium diet to induce biochemical changes consistent with adynamic osteodystrophy. Blood ionized calcium concentrations were higher and serum PTH levels were lower in nephrectomized, calcium-supplemented rats than in either intact or nephrectomized control animals. Linear growth and tibial length were reduced, but messenger RNA levels for type II collagen, type X collagen, and the PTH/PTHrP receptor did not differ from control values in nephrectomized rats given supplemental calcium. In contrast, both the width of epiphyseal cartilage and the height of the zone of hypertrophic chondrocytes were greater in calcium-supplemented nephrectomized rats. These morphological changes were associated with decreases in histochemical staining for tartrate-resistant acid phosphatase and lower levels of messenger RNA expression for the matrix metalloproteinase MMP-9/gelatinase B immediately adjacent to the epiphyseal growth plate. Diminished chondroclastic/osteoclastic activity alters growth plate morphology and adversely affects linear bone growth in calcium-supplemented, nephrectomized rats.

Daily intermittent decreases in serum levels of parathyroid hormone have an anabolic-like action on the bones of uremic rats with low-turnover bone and osteomalacia

The calcium receptor agonist (calcimimetic) compound NPS R-568 causes rapid decreases in circulating levels of parathyroid hormone (PTH) in rats and humans. We hypothesized that daily intermittent decreases in serum PTH levels may have different effects on bone than do chronically sustained decreases. To test this hypothesis, we compared two NPS R-568 dosing regimens in rats with chronic renal insufficiency induced by two intravenous injections of adriamycin. Fourteen weeks after the second adriamycin injection, creatinine clearance was reduced by 52%, PTH levels were elevated approximately 2.5-fold, and serum 25(OH)D3 and 1,25(OH)2D3 levels were reduced substantially. Treatment by daily per os gavage, which decreased PTH levels intermittently, or continuous subcutaneous infusion, which resulted in a sustained suppression of serum PTH levels, then began for 8 weeks. Despite the hyperparathyroidism, the adriamycin-injected rats developed a low-turnover bone lesion with osteomalacia (fourfold increase in osteoid volume in the proximal tibial metaphysis) and osteopenia (67% decrease in cancellous bone volume and an 18% reduction in bone mineral density at the distal femur). Daily administered (but not infused) NPS R-568 significantly increased cancellous bone volume solely by normalizing trabecular thickness, and increased femoral bone mineral density by 14%. These results indicate that daily intermittent, but not sustained, decreases in PTH levels have an "anabolic-like" effect on bones with a low-turnover lesion in this animal model of chronic renal insufficiency.

Growth retardation in children with chronic renal failure

Growth retardation is a major obstacle to full rehabilitation of children with chronic renal failure (CRF). Several factors have been identified as contributors to impaired linear growth and they include protein and calorie malnutrition, metabolic acidosis, growth hormone resistance, anemia, and renal osteodystrophy. Although therapeutic interventions such as the use of recombinant human growth hormone, recombinant human erythropoietin, and calcitriol have made substantial contributions, the optimal therapeutic strategy remains to be defined. Indeed, growth failure persists in a substantial proportion of children with renal failure and those treated with maintenance dialysis. In addition, the increasing prevalence of adynamic lesions of renal osteodystrophy and its effect on growth have raised concern about the continued generalized use of calcitriol in children with CRF. Recent studies have shown the critical roles of parathyroid hormone-related protein (PTHrP) and the PTH/PTHrP receptor in the regulation of endochondral bone formation. The PTH/PTHrP receptor mRNA expression has been shown to be down-regulated in kidney and growth plate cartilage of animals with renal failure. Differences in the severity of secondary hyperparathyroidism influence not only growth plate morphology but also the expression of selected markers of chondrocyte proliferation and differentiation in these animals. Such findings suggest potential molecular mechanisms by which cartilage and bone development may be disrupted in children with CRF, thereby contributing to diminished linear growth.

Bone mineral density, bone metabolism and body composition of children with chronic renal failure, with and without growth hormone treatment

OBJECTIVE

Osteopenia has been reported in adult patients with chronic renal failure (CRF). Only a few studies have been performed in children. The objective of this study was to evaluate bone mineral density (BMD), bone turnover, body composition in children with CRF and to study the effect of GH on these variables.

DESIGN

Two groups were identified: patients with growth retardation who received GH (GH-group) and patients most of whom were not growth retarded who did not receive GH (no-GH-group). After an observation period of 6 months, the patients in the GH-group started GH treatment. Patients were studied every 6 months during 18 months.

PATIENTS

Thirty-six prepubertal patients (27 boys and 9 girls), mean age 7.9 years, with CRF participated in the study. The GH-group consisted of 17 patients of whom 14 completed one year treatment. The no-GH-group consisted of 19 patients, of whom 16 were followed for 6 months, 14 for 12 months and 13 for 18 months.

MEASUREMENTS

Lumbar spine BMD, total body BMD and body composition were assessed by dual energy X-ray absorptiometry, compared to age-and sex-matched reference values of the same population and expressed as standard deviation scores (SDS). BMD of appendicular bone was measured by quantitative microdensitometry (QMD). Blood samples were obtained to assess bone metabolism and growth factors.

RESULTS

Baseline mean lumbar spine and total body BMD SDS of all patients were not significantly different from normal. Mean lumbar spine and total body BMD SDS did not change significantly in the GH-group during GH treatment. The change of QMD at the midshaft during the first 6 months of GH treatment was significantly smaller than during the observation period (P < 0.01). Height SDS and biochemical markers of both bone formation and bone resorption increased significantly during GH treatment; 1,25-dihydroxyvitamin D remained stable. Lean tissue mass increased (P < 0.001) and percentage body fat decreased (P < 0.01) during GH treatment. BMD, the biochemical markers of bone turnover which are independent of renal function, and body composition remained stable in the no-GH-group.

CONCLUSIONS

Mean lumbar spine and total body BMD of children with chronic renal failure did not differ from healthy controls. The lack of a GH-induced increase in 1,25-dihydroxyvitamin D levels, probably due to treatment with alpha-calcidol, might be linked to the absence of a response in BMD during GH treatment in children with chronic renal failure.

Renal osteodystrophy in dialysis patients: diagnosis and treatment

This article reviews the clinical, biological, radiological, and pathological procedures and their respective indications for the practical diagnosis of the following various histological patterns of renal osteodystrophy: osteitis fibrosa due to parathyroid hormone (PTH) hypersecretion: osteomalacia or rickets due to native vitamin D deficiency and/or aluminum overload; and adynamic bone disease (ABD) due to aluminum overload and/or PTH secretion oversuppression. Our advice regarding bone biopsy is to restrict it to patients with symptoms and hypercalcemia, especially those who have been previously exposed to aluminum. In other cases, we propose relying merely on the determination of the plasma concentrations of calcium, protide, phosphate, bicarbonate, intact PTH, aluminum, 25(OH)D3, and alkaline phosphatase (total and bony if hepatic disease is associated) to choose the appropriate treatment. Because of the danger of the desferrioxamine treatment necessary to chelate and remove aluminum, the suspicion of aluminic bone disease (osteomalacia or ABD) will always be confirmed by a bone biopsy. In the case of nonaluminic osteomalacia, correction of the vitamin D deficiency by native vitamin D or 25(OH)D3, and of the calcium deficiency and acidosis by alkaline salts of calcium and if necessary sodium bicarbonate are sufficient to cure the disease. In the case of nonaluminic ABD, the stimulation of PTH secretion by the discontinuation of 1alpha hydroxylated vitamin D and the induction of a negative calcium balance during dialysis by decreasing the calcium concentration in the dialysate will allow an increase of the CaCO3 dose to correct for hyperphosphatemia without inducing hypercalcemia. For hyperparathyroidism, i.e., plasma intact PTH levels greater than two- or four-fold the upper limit of normal levels (according to the absence or presence of previous aluminum exposure), the treatment will consist in increasing the CaCO3 dose to correct for hyperphosphatemia together with a decrease of the calcium concentration in the dialysate if the dose of CaCO3 is so high that it induces hypercalcemia. When the hyperphosphatemia has been corrected and there is still a low or normal corrected plasma calcium level, 1alpha(OH)D3 in an oral bolus 2 or 3 times a week should be given at the minimal dose of 1 microg. When the PTH level stays above 400 pg while hypercalcemia occurs and hyperphosphatemia persists, surgical subtotal parathyroidectomy is recommended or the injection of calcitriol into the big nodular hyperplastic parathyroid glands under sonography control in high surgical risk patients. Special recommendations are given for children.

Bone disease in children and adolescents undergoing successful renal transplantation

Little is known about the extent and severity of bone disease in children undergoing successful renal transplantation. To address this issue, 47 patients with stable renal function 3.2 +/- 1.7 years after transplantation (Tx) underwent iliac crest bone biopsy. The mean age of patients was 12 +/- 2.0 years; 36 had received cadaveric renal grafts, whereas 11 had undergone living-related Tx. Immunosuppressive drugs included cyclosporine 0.17 +/- 0.4 mg/kg/day, prednisone 7.5 +/- 2.1 mg/kg/day, and either azathioprine 1.6 +/- 0.9 mg/kg/day or mycophenolate mofetil 30 +/- 3 mg/kg/day. In addition to quantitative bone histomorphometry, the bone mineral content (BMC) of the lumbar spine was measured by dual energy X-ray absorptiometry (DXA) in 24/47 patients. Thirty-one transplant recipients had normal bone formation (N-Bfr), 11 had mild hyperparathyroidism (HPT) and 5 had adynamic skeletal lesions (AD). The interval since Tx, duration of dialysis before Tx and cumulative prednisone dose did not differ among groups. Trabecular bone area was highest in subjects with HPT. Unexpectedly, eroded bone perimeter exceeded normal reference values both in patients with AD and in those with N-Bfr; the osteoid area and osteoid perimeter were also elevated in these two groups. Hyperparathyroidism improved or resolved after Tx in all 14 subjects with this skeletal lesion prior to Tx, but one patient developed AD after Tx. Bone histology did not change after Tx in those with N-Bfr during regular dialysis, but bone formation increased after Tx in two of three patients with AD during regular dialysis. Z-scores for height in pre-pubertal patients after Tx were below age-appropriate values in each histologic subgroup, but values did not differ among groups. Z-scores for bone mineral content at the lumbar spine were also less than age-predicted values, -0.67 +/- 1.2. After adjusting for the degree of growth retardation, height-adjusted z-scores for lumbar spine BMC after Tx were above normal in all three histologic groups (0.68 +/- 1.0). The results suggest that reductions in bone mass and post-transplant osteoporosis are not prominent findings in pediatric renal transplant recipients when the influence of growth retardation on bone mass measurements by DXA is carefully considered.

Bone mineral density and body composition before and during treatment with gonadotropin-releasing hormone agonist in children with central precocious and early puberty

Major changes in bone mineral density (BMD) and body composition occur during puberty. In the present longitudinal study, we evaluated BMD and calculated volumetric BMD [bone mineral apparent density (BMAD)], bone metabolism, and body composition of children (32 girls and 2 boys) with central precocious and early puberty before and during treatment with GnRH agonist (GnRH). Patients were studied at baseline and during treatment for 6 months (n = 34), 1 yr (n = 33), and 2 yr (n = 16). Lumbar spine and total body BMD and body composition were measured with dual-energy x-ray absorptiometry. The variables were compared with age- and sex-matched reference values of the same population and expressed as SD score (SDS). Bone age was assessed. Serum calcium, phosphate, alkaline phosphatase, osteocalcin, the carboxyterminal propeptide of type I collagen (PICP), cross-linked telopeptide of collagen I (ICTP), 1,25 dihydroxyvitamin D and urinary hydroxyproline/creatinine, and calcium/ creatinine ratios were measured. Mean lumbar spine BMD SDS was significantly higher than zero at baseline (P < 0.02) and did not differ from normal, after 2 yr of treatment. Mean spinal BMAD SDS and total body BMD SDS were not significantly different from zero at baseline and had not changed significantly after 2 yr of treatment. During therapy, fat mass and percentage body fat SDS increased, whereas lean tissue mass SDS decreased. Mean lumbar spine BMD and BMAD and total body BMD SDS, calculated for bone age, were all lower than zero at baseline (BMD P < 0.001 and BMAD P < 0.05) and also after 2 yr treatment (respectively, P < 0.001, P < 0.05, and P < 0.01). Biochemical bone parameters were significantly higher than prepubertal values at baseline, and they decreased during treatment. In conclusion, patients with central precocious and early puberty had normal BMD for chronological age but low BMD for bone age, after 2 yr of treatment with GnRH. Bone turnover decreased during treatment. Changes in body composition resembled those seen in patients with GH deficiency.

The renal bone diseases in children treated with dialysis

Renal osteodystrophy represents a spectrum from high- to low-turnover bone lesions. The specific pattern, however, may change during selected therapeutic interventions. As in the past, osteitis fibrosa remains the most frequent histologic lesion in pediatric patients on dialysis, although recently the prevalence of low-turnover bone lesions without aluminum toxicity has been increasing in the pediatric population. This may be a consequence of aggressive calcitriol and calcium therapy. The different factors involved in the development of secondary hyperparathyroidism include hyperphosphatemia, hypocalcemia, altered vitamin D synthesis, impairments in parathyroid hormone (PTH) secretion and metabolism, and, recently, possible downregulation of renal PTH/PTH-rP messenger RNA receptor. New developments in molecular biology have demonstrated the relationship between vitamin D and PTH. The use of high-dose pulse intravenous, intraperitoneal, and oral calcitriol therapy has significantly decreased serum PTH levels and retarded the progression of osteitis fibrosa. These therapeutic interventions, however, may have led to the development of adynamic bone lesions. The impact of adynamic bone lesions in the young and growing skeleton remains to be determined.

Bone and mineral metabolism in childhood end-stage renal disease

Renal osteodystrophy represents a spectrum from high to low turn-over lesions of bone, and the specific pattern may change during the evolution of chronic renal failure and as a consequence of specific therapeutic interventions. Although secondary hyperparathyroidism remains the predominant histologic lesion in patients undergoing maintenance dialysis, recent evidence indicates higher frequency of adynamic lesion not associated with aluminum intoxication. The different factors involved in the development of each of the histologic subtypes have been described together with the clinical manifestations of renal bone disease in childhood. Avoidance of aluminum-containing medications and the intermittent administration of calcitriol are effective approaches for the management of the renal bone diseases. The long-term consequences of the adynamic lesion remain to be determined.