Bone mineral density in children with primary hyperoxaluria type I

Bone health in children with primary hyperoxaluria type 1 following liver and kidney transplantation

Background

Primary hyperoxaluria type 1 is characterized by hepatic oxalate overproduction, leading to nephrocalcinosis, kidney stones, kidney failure and systemic oxalosis, including oxalate osteopathy. Combined liver-kidney transplantation (CLKT) and kidney after liver transplantation (KALT) were established therapeutic options to stop the devastating consequences of oxalate bone disease.

Methods

We describe a retrospective cohort of 10 children with PH1who were referred to our hospital from different countries for combined transplantation. Demographic and clinical data were collected and symptoms of bone disease, conventional radiological examinations, plasma oxalate levels and other determinants of calcium-phosphate metabolism were compared pre and post transplantation.

Results

Ten patients (7 male, median age 5.8 years, median follow-up time 8.1 years) were included in this study. Seven patients were diagnosed with infantile oxalosis and 9 patients received an intensified dialysis regime prior to transplantation. In one patient the transplanted kidney never achieved primary function and the boy remained on HD. All other patients remained without graft failure and retained stable kidney and liver function. Prior to transplantation, seven patients suffered from severe skeletal pain and three children presented with 1-3 series of pathological fractures. Pathological fractures did no longer occur in children who underwent successful CLKT or KALT. Plasma oxalate levels dropped within 6 months following Tx. Determinants of calcium-phosphorus metabolism did not differ significantly in comparison to other HD children. Seven of ten children showed a restricted growth at the time of transplantation and presented a moderate catch-up-growth at the time of last follow-up.

Conclusions

Patients with PH1 suffer from severe consequences of a disturbed bone metabolism. However, bone health and growth can partially improve following CLKT/KALT.

Three Tesla magnetic resonance imaging detects oxalate osteopathy in patients with primary hyperoxaluria type I

BACKGROUND

With declining kidney function and therefore increasing plasma oxalate, patients with primary hyperoxaluria type I (PHI) are at risk to systemically deposit calcium-oxalate crystals. This systemic oxalosis may occur even at early stages of chronic kidney failure (CKD) but is difficult to detect with non-invasive imaging procedures.

METHODS

We tested if magnetic resonance imaging (MRI) is sensitive to detect oxalate deposition in bone. A 3 Tesla MRI of the left knee/tibial metaphysis was performed in 46 patients with PHI and in 12 healthy controls. In addition to the investigator's interpretation, signal intensities (SI) within a region of interest (ROI, transverse images below the level of the physis in the proximal tibial metaphysis) were measured pixelwise, and statistical parameters of their distribution were calculated. In addition, 52 parameters of texture analysis were evaluated. Plasma oxalate and CKD status were correlated to MRI findings. MRI was then implemented in routine practice.

RESULTS

Independent interpretation by investigators was consistent in most cases and clearly differentiated patients from controls. Statistically significant differences were seen between patients and controls (p < 0.05). No correlation/relation between the MRI parameters and CKD stages or Pox levels was found. However, MR imaging of oxalate osteopathy revealed changes attributed to clinical status which differed clearly to that in secondary hyperparathyroidism.

CONCLUSIONS

MRI is able to visually detect (early) oxalate osteopathy in PHI. It can be used for its monitoring and is distinguished from renal osteodystrophy. In the future, machine learning algorithms may aid in the objective assessment of oxalate deposition in bone. Graphical Abstract A higher resolution version of the Graphical abstract is available as Supplementary information.

Meta-analyses of the quantitative computed tomography data in dialysis patients show differential impacts of renal failure on the trabecular and cortical bones

Dialysis patients have compromised bone health that increases their fracture risk due to low bone mass and deterioration in bone microarchitecture. Through meta-analyses of published studies, we conclude that dialysis patients suffer from impaired compartmental bone parameters compared with healthy controls.

INTRODUCTION

We performed meta-analyses to determine the effect of chronic kidney disease (CKD) patients under dialysis on the trabecular and cortical parameters of radius and tibia.

METHODS

This is a meta-analysis of cross-sectional and prospective clinical studies. PubMed, Web of Science, Google Scholar, and Scopus were searched using various permutation combinations. Dialysis patients were compared with non-CKD healthy controls using quantitative computed tomography. High-resolution peripheral quantitative computed tomography (HR-pQCT) and pQCT data of dialysis patients were dissected from eligible studies for pooled analysis of each parameter.

RESULTS

Ten studies met the inclusion criteria that included data from 457 dialysis patients and 2134 controls. Pooled analysis showed a significant decrease (a) in total vBMD at distal radius [standard deviation of the mean (SDM) = -0.842, p = 0.000] and tibia (SMD = -0.705, p = 0.000) and (b) in cortical vBMD (SDM = -1.037, p = 0.000) at radius of dialysis patients compared with control. There were strong correlations between total vBMD and microarchitecture parameters at tibia in dialysis patients.

CONCLUSIONS

At radius and tibia, bone mass, microarchitecture, and geometry at trabecular and cortical envelopes displayed impairments in dialysis patients compared with control. Tibial vBMD may have diagnostic value in dialysis. HR-pQCT and pQCT may be used to further understand the compartmental bones response to CKD-induced loss at different stages of CKD.

A stone in the bone

Primary hyperoxaluria (PH) is a group of diseases due to mutations in genes coding for enzymes involved in oxalate metabolism. Three types of PH are identified depending on the gene mutated. Type 1 is the most frequent with 80% of the cases, while PH2 and PH3 are rarer. The severity of renal involvement varies between the three types. Indeed, between 60% and 80% of PH1 but only 20% of PH2 patients will reach end-stage kidney disease. In PH3 patients, dialysis is uncommon. Because oxalate clearance is impaired in CKD patients, oxalate can precipitate in various organs leading to systemic oxalosis. We report an uncommon presentation of bone oxalosis associated with hypercalcemia in a dialyzed patient. This report emphasizes the difficulties to diagnose primary hyperoxaluria and the challenge of treating dialyzed patients.

ENDOCRINE MANIFESTATIONS OF PRIMARY HYPEROXALURIA

OBJECTIVE

Primary hyperoxaluria type 1 (PH1) is a rare metabolic disorder of oxalate overproduction. It is associated with urolithiasis and nephrocalcinosis, which progress to end-stage renal disease and systemic oxalosis. As oxalate deposits in tissues, non-parathyroid hormone (nonPTH)-mediated hypercalcemia, oxalate osteopathy, primary hypothyroidism, and primary hypogonadism develop. In this review, we will present a case of PH1 and provide an overview of this clinical entity and its endocrine manifestations.

METHODS

We conducted a PubMed search for articles related to PH1. The terms "primary hyperoxaluria," "nonPTH mediated hypercalcemia," "hypothyroidism," and "hypogonadism" were used to identify pertinent literature.

RESULTS

Given the rarity of PH1, there is scant literature regarding the incidence and clinical significance of endocrine manifestations of this disorder. There are rare reports of hypercalcemia secondary to osteoclast-stimulating activity of macrophages in bone granulomas, which occur in response to oxalate deposits. We report that hypercalcemia may also be mediated by 1,25-dihydroxyvitamin D and PTH-related protein (PTHrP). Primary hypothyroidism and primary hypogonadism are thought to be due partly to calcium oxalate deposition in thyroid and testicular tissue. The presented case is the first to report PTHrP-mediated hypercalcemia and primary hypogonadism in a patient with PH1.

CONCLUSION

PH1 is a metabolic disease with significant morbidity and mortality. Owing to its rarity, it is not widely recognized in the field of endocrinology, despite presenting with several endocrinopathies. Recognition of endocrine disturbances can result in early and successful treatment, limiting morbidity and improving quality of life in these challenging patients.

ABBREVIATIONS

1,25(OH)₂D= 1,25-dihydoxyvitamin D AGT = alanine:glyoxylate aminotransferase ESRD = end-stage renal disease GRHPR = glyoxylate reductase-hydroxypyruvate reductase nonPTH = non-parathyroid hormone PH = primary hyperoxaluria pQCT = peripheral quantitative computed tomography PTH = parathyroid hormone PTHrP = parathyroid hormone-related protein T4 = thyroxine TSH = thyroid-stimulating hormone.

Type 1 primary hyperoxaluria: A case report and focus on bone impairment of systemic oxalosis

Primary hyperoxaluria is a rare genetic disorder characterized by oxalate overproduction, leading to kidney failure due to nephrocalcinosis, and is eventually responsible for systemic oxalosis. Bone impairment, secondary to oxalate deposits, is one of the many complications that may occur. Skeletal involvement can be difficult to diagnose because of lack of clinical symptoms and therefore needs to be confirmed by invasive testing, such as transiliac bone biopsy. If confirmed, bone oxalosis is the proof of disease severity and that combined liver-kidney transplantation should be performed.

The primary hyperoxalurias: A practical approach to diagnosis and treatment

Although the primary hyperoxalurias (PH) are rare disorders, they are of considerable clinical importance in relation to calcium oxalate urolithiasis and as a cause of renal failure worldwide. Three distinct disorders have been described at the molecular level. The investigation of any child or adult presenting with urinary tract stones or nephrocalcinosis, must exclude PH as an underlying cause. This paper provides a practical approach to the investigation and diagnosis of PH, indicating the importance of distinguishing between the PH types for the purposes of targeting appropriate therapy. Conservative management is explored and the various transplant options are discussed.

Bone impairment in primary hyperoxaluria: a review

Deposition of calcium oxalate crystals in the kidney and bone is a hallmark of primary hyperoxaluria (PH). Since the bone compartment can store massive amounts of oxalate, patients present with recurrent low-trauma fractures, bone deformations, severe bone pains, and specific oxalate osteopathy on X-ray. Bone biopsy from the iliac crest displays specific features such as oxalate crystals surrounded by a granulomatous reaction corresponding to an invasion of bone surface by macrophages. The objective of this manuscript is therefore to provide an overview of bone impairment in PH, by reviewing the current literature on bone and dental symptoms as well as imaging techniques used for assessing bone disease.

Update on oxalate crystal disease

Oxalate arthropathy is a rare cause of arthritis characterized by deposition of calcium oxalate crystals within synovial fluid. This condition typically occurs in patients with underlying primary or secondary hyperoxaluria. Primary hyperoxaluria constitutes a group of genetic disorders resulting in endogenous overproduction of oxalate, whereas secondary hyperoxaluria results from gastrointestinal disorders associated with fat malabsorption and increased absorption of dietary oxalate. In both conditions, oxalate crystals can deposit in the kidney leading to renal failure. Since oxalate is primarily renally eliminated, it accumulates throughout the body in renal failure, a state termed oxalosis. Affected organs can include bones, joints, heart, eyes, and skin. Since patients can present with renal failure and oxalosis before the underlying diagnosis of hyperoxaluria has been made, it is important to consider hyperoxaluria in patients who present with unexplained soft tissue crystal deposition. The best treatment of oxalosis is prevention. If patients present with advanced disease, treatment of oxalate arthritis consists of symptom management and control of the underlying disease process.

Changes in bone structure and the muscle-bone unit in children with chronic kidney disease

The impact of pediatric chronic kidney disease (CKD) on acquisition of volumetric bone mineral density (BMD) and cortical dimensions is lacking. To address this issue, we obtained tibia quantitative computed tomography scans from 103 patients aged 5-21 years with CKD (26 on dialysis) at baseline and 12 months later. Gender, ethnicity, tibia length, and/or age-specific Z-scores were generated for trabecular and cortical BMD, cortical area, periosteal and endosteal circumference, and muscle area based on over 700 reference subjects. Muscle area, cortical area, and periosteal and endosteal Z-scores were significantly lower at baseline compared with the reference cohort. Cortical BMD, cortical area, and periosteal Z-scores all exhibited a significant further decrease over 12 months. Higher parathyroid hormone levels were associated with significantly greater increases in trabecular BMD and decreases in cortical BMD in the younger patients (significant interaction terms for trabecular BMD and cortical BMD). The estimated glomerular filtration rate was not associated with changes in BMD Z-scores independent of parathyroid hormone. Changes in muscle and cortical area were significantly and positively associated in control subjects but not in CKD patients. Thus, children and adolescents with CKD have progressive cortical bone deficits related to secondary hyperparathyroidism and potential impairment of the functional muscle-bone unit. Interventions are needed to enhance bone accrual in childhood-onset CKD.

Assessment of dual-energy X-ray absorptiometry measures of bone health in pediatric chronic kidney disease

BACKGROUND

Dual-energy X-ray absorptiometry (DXA) techniques are limited in childhood chronic kidney disease (CKD) by the confounding effect of short stature and opposing parathyroid hormone effects on trabecular and cortical bone. Peripheral quantitative computed tomography (pQCT) is not subject to these limitations.

METHODS

Lumbar spine (LS) and whole-body (WB) DXA and tibia pQCT scans were obtained in 88 stage 4-5 CKD and >650 healthy participants, ages 5-21 years. Sex- and race-specific Z-scores were generated for bone mineral density (BMD) and bone mineral content (BMC) by DXA, relative to age and adjusted for height Z-score (LS-BMD-Z and WB-BMC-Z), and compared to pQCT Z-scores for trabecular BMD (TrabBMD-Z) for age and cortical BMC (CortBMC-Z) for age and tibia length.

RESULTS

LS-BMD-Z [0.50 (95% C.I. 0.28, 0.73), p<0.0001] and TrabBMD-Z [0.53 (0.27, 0.79), p<0.0001] were greater in CKD, and WB-BMC-Z [-0.36 (-0.53, -0.19), p<0.0001] and CortBMC-Z [-0.48 (-0.70, -0.27), p<0.0001] were lower, compared to reference participants. Z-scores were correlated at trabecular (LS-BMD-Z and TrabBMD-Z: R=0.36) and cortical (WB-BMC-Z and CortBMC-Z: R=0.64) sites in CKD; similar to correlations in reference participants.

CONCLUSIONS

Lumbar spine and whole-body DXA suggested greater trabecular BMD and lower cortical BMC in CKD, consistent with pQCT results; however, correlations were modest. Studies are needed to identify methods that predict fracture in childhood CKD.

Volumetric bone mineral density and bone structure in childhood chronic kidney disease

Chronic kidney disease (CKD) is associated with increased fracture risk and skeletal deformities. The impact of CKD on volumetric bone mineral density (vBMD) and cortical dimensions during growth is unknown. Tibia quantitative computed tomographic scans were obtained in 156 children with CKD [69 stages 2 to 3, 51 stages 4 to 5, and 36 stage 5D (dialysis)] and 831 healthy participants aged 5 to 21 years. Sex-, race-, and age- or tibia length-specific Z-scores were generated for trabecular BMD (TrabBMD), cortical BMD (CortBMD), cortical area (CortArea) and endosteal circumference (EndoC). Greater CKD severity was associated with a higher TrabBMD Z-score in younger participants (p < .001) compared with healthy children; this association was attenuated in older participants (interaction p < .001). Mean CortArea Z-score was lower (p < .01) in CKD 4-5 [-0.49, 95% confidence interval (CI) -0.80, -0.18)] and CKD 5D (-0.49, 95% CI -0.83, -0.15) compared with healthy children. Among CKD participants, parathyroid hormone (PTH) levels were positively associated with TrabBMD Z-score (p < .01), and this association was significantly attenuated in older participants (interaction p < .05). Higher levels of PTH and biomarkers of bone formation (bone-specific alkaline phosphatase) and resorption (serum C-terminal telopeptide of type 1 collagen) were associated with lower CortBMD and CortArea Z-scores and greater EndoC Z-score (r = 0.18-0.36, all p ≤ .02). CortBMD Z-score was significantly lower in CKD participants with PTH levels above versus below the upper limit of the Kidney Disease Outcome Quality Initiative (KDOQI) CKD stage-specific target range: -0.46 ± 1.29 versus 0.12 ± 1.14 (p < .01). In summary, childhood CKD and secondary hyperparathyroidism were associated with significant reductions in cortical area and CortBMD and greater TrabBMD in younger children. Future studies are needed to establish the fracture implications of these alterations and to determine if cortical and trabecular abnormalities are reversible.

Primary hyperoxaluria

Primary hyperoxalurias (PH) are inborn errors in the metabolism of glyoxylate and oxalate. PH type 1, the most common form, is an autosomal recessive disorder caused by a deficiency of the liver-specific enzyme alanine, glyoxylate aminotransferase (AGT) resulting in overproduction and excessive urinary excretion of oxalate. Recurrent urolithiasis and nephrocalcinosis are the hallmarks of the disease. As glomerular filtration rate decreases due to progressive renal damage, oxalate accumulates leading to systemic oxalosis. Diagnosis is often delayed and is based on clinical and sonographic findings, urinary oxalate assessment, DNA analysis, and, if necessary, direct AGT activity measurement in liver biopsy tissue. Early initiation of conservative treatment, including high fluid intake, inhibitors of calcium oxalate crystallization, and pyridoxine in responsive cases, can help to maintain renal function in compliant subjects. In end-stage renal disease patients, the best outcomes have been achieved with combined liver-kidney transplantation which corrects the enzyme defect.

[Primary hyperoxaluria]

Primary hyperoxalurias are rare recessive inherited inborn errors of glyoxylate metabolism. They are responsible for progressive renal involvement, which further lead to systemic oxalate deposition, which can even occur in infants. Primary hyperoxaluria type 1 is the most common form in Europe and is due to alanine-glyoxylate aminostransferase deficiency, a hepatic peroxisomal pyridoxin-dependent enzyme. Therefore primary hyperoxaluria type 1 is responsible for hyperoxaluria leading to aggressive stone formation and nephrocalcinosis. As glomerular filtration rate decreases, systemic oxalate storage occurs throughout all the body, and mainly in the skeleton. The diagnosis is first based on urine oxalate measurement, then on genotyping, which may also allow prenatal diagnosis to be proposed. Conservative measures - including hydration, crystallization inhibitors and pyridoxine - are safe and may allow long lasting renal survival, provided it is given as soon as the diagnosis has been even suspected. No dialysis procedure can remove enough oxalate to compensate oxalate overproduction from the sick liver, therefore a combined liver and kidney transplantation should be planned before advanced renal disease has occurred, in order to limit/avoid systemic oxalate deposition. In the future, primary hyperoxaluria type 1 may benefit from hepatocyte transplantation, chaperone molecules, etc.

Bone assessment in children with chronic kidney disease: data from two new bone imaging techniques in a single-center pilot study

Bone damage in children with chronic kidney disease (CKD) is a challenge for pediatric nephrologists. Areal measurements of bone mineral density (BMD) by dual x-ray absorptiometry (DXA) have been routinely performed to assess bone mass but recent international guidelines have concluded that DXA was of less value in CKD. The aim of this study is to evaluate bone quality in CKD children using new bone imaging techniques in a pilot cross-sectional single-center study. We performed bone imaging (high-resolution peripheral quantitative computed tomography, HR-pQCT, XtremeCT, Scanco Medical AG, Switzerland), to assess compartmental volumetric BMD and trabecular microarchitecture in 22 CKD children and 19 controls. In seven younger patients (i.e., under 10 years of age), we performed bone texture analysis (BMA, D3A Medical Systems, France) in comparison to 15 healthy prepubertal controls. Among older children, CKD patients had significantly lower height and body weight without significant impairment of BMD and microarchitecture than healthy controls. In univariate analysis, there were significant correlations between cortical BMD and glomerular filtration rate (r= -0.46), age (r=0.60) and body mass index (r=0.67). In younger children, bone texture parameters were not different between patients and controls. Our results did not show significant differences between healthy controls and CKD children for compartmental bone densities and microarchitecture, but the small sample size and the heterogeneity of the CKD group require caution in the interpretation. Novel bone imaging techniques seem feasible in children, and further longitudinal studies are required to thoroughly explore long-term cardiovascular and bone consequences of phosphate-calcium metabolism deregulation during CKD.

Bone metabolism in oxalosis: a single-center study using new imaging techniques and biomarkers

The deposition of calcium oxalate crystals in the kidney and bone is a hallmark of primary hyperoxaluria type 1 (PH1). We report here an evaluation of the bone status of 12 PH1 children based on bone biomarkers [parathyroid hormone, vitamin D, fibroblast growth factor 23 (FGF23)] and radiological assessments (skeletal age, three-dimensional high-resolution peripheral quantitative computed tomography, HR-pQCT) carried out within the framework of a cross-sectional single-center study. The controls consisted of healthy and children with chronic kidney disease already enrolled in local bone and mineral metabolism studies. The mean age (+ or - standard deviation) age of the patients was 99 (+ or - 63) months. Six children suffered from fracture. Bone maturation was accelerated in five patients, four of whom were <5 years. The combination of new imaging techniques and biomarkers highlighted new and unexplained features of PH1: advanced skeletal age in young PH1 patients, increased FGF23 levels and decreased total volumetric bone mineral density with bone microarchitecture alteration.

Primary hyperoxaluria type 1: still challenging!

Primary hyperoxaluria type 1, the most common form of primary hyperoxaluria, is an autosomal recessive disorder caused by a deficiency of the liver-specific enzyme alanine: glyoxylate aminotransferase (AGT). This results in increased synthesis and subsequent urinary excretion of the metabolic end product oxalate and the deposition of insoluble calcium oxalate in the kidney and urinary tract. As glomerular filtration rate (GFR) decreases due to progressive renal involvement, oxalate accumulates and results in systemic oxalosis. Diagnosis is still often delayed. It may be established on the basis of clinical and sonographic findings, urinary oxalate +/- glycolate assessment, DNA analysis and, sometimes, direct AGT activity measurement in liver biopsy tissue. The initiation of conservative measures, based on hydration, citrate and/or phosphate, and pyridoxine, in responsive cases at an early stage to minimize oxalate crystal formation will help to maintain renal function in compliant subjects. Patients with established urolithiasis may benefit from extracorporeal shock-wave lithotripsy and/or JJ stent insertion. Correction of the enzyme defect by liver transplantation should be planned, before systemic oxalosis develops, to optimize outcomes and may be either sequential (biochemical benefit) or simultaneous (immunological benefit) liver-kidney transplantation, depending on facilities and access to cadaveric or living donors. Aggressive dialysis therapies are required to avoid progressive oxalate deposition in established end-stage renal disease (ESRD), and minimization of the time on dialysis will improve both the patient's quality of life and survival.