Assessment of mineral and bone biomarkers highlights a high frequency of hypercalciuria in asymptomatic healthy teenagers

Genotype-phenotype Description of Vitamin D-dependent Rickets 1A: CYP27B1 p.(Ala129Thr) Variant Induces a Milder Disease

INTRODUCTION

Vitamin D-dependent rickets type 1A (VDDR1A) is a rare genetic disease associated with loss-of-function variations in the gene encoding the vitamin D-activating enzyme 1α-hydroxylase (CYP27B1). Phenotype-genotype correlation is unclear. Long-term outcome data are lacking. The objective of this study was to describe characteristics and outcomes to search for a phenotype-genotype correlation.

METHODS

We retrospectively collected clinical data, genetic features, and outcomes from 24 genetically confirmed cases from 10 French centers; results are presented as median (min-max).

RESULTS

Clinical symptoms at diagnosis (age, 1.5 [0.5-8.7] years) were mainly bone and neurological abnormalities, and laboratory data showed hypocalcemia (1.97 [1.40-2.40] mmol/L), hypophosphatemia (-3.4 [-13.4 to (-)0.2] SD score for age), low 25OHD and low 1,25(OH)2D3, secondary hyperparathyroidism with PTH at 6.6 (1.3-13.7) times the upper limit for normal (ULN; PTH expressed as ULN to homogenize data presentation), and increased alkaline phosphatase (1968 [521-7000] IU/L). Bone radiographs were abnormal in 83% of patients. We identified 17 variations (11 missense, 3 frameshift, 2 truncating, and 1 acceptor splice site variations) in 19 families (homozygous state in 58% [11/19]). The partial loss-of-function variation p.(Ala129Thr) was associated with a milder phenotype: older age at diagnosis, higher serum calcium (2.26 vs 1.85 mmol/L), lower PTH (4.7 vs 7.5 ULN), and lower alkaline phosphatase (759 vs 2082 IU/L). Patients were treated with alfacalcidol. Clinical (skeletal, neurological), biochemical, and radiological outcomes were satisfactory, and complications occurred if there was bad adherence.

CONCLUSION

Overall, our findings highlight good outcomes under substitutive treatment and the need of a closer follow-up of eyes, teeth, kidneys, and blood pressure in VDDR1A.

X-linked hypophosphatemia, obesity and arterial hypertension: data from the XLH21 study

BACKGROUND

The underlying mechanisms of obesity in X-linked hypophosphatemia (XLH) are not known. We aimed to evaluate whether FGF21, an endocrine FGF involved in the regulation of carbohydrate-lipid metabolism, could be involved.

METHODS

We performed a prospective multicenter cross-sectional study comparing FGF23, Klotho, and FGF21 levels in teenagers with XLH compared to healthy controls (VITADOS cohort) after matching for age, gender, and puberty. Non-parametric tests were performed (results presented as median (min-max)).

RESULTS

A total of 40 XLH teenagers (n = 20 Standard Of Care, SOC, n = 20 burosumab) were included. While patients receiving burosumab displayed increased BMI as compared to patients receiving SOC, systolic blood pressure expressed as percentile was progressively and significantly lower when comparing the three groups: 77 (4-99) in SOC, 47 (9-98) in burosumab, and 28 (1-94) in controls (p = 0.007). When compared to patients receiving SOC, patients receiving burosumab displayed significantly increased phosphate and 1,25(OH)2D levels. We found increased Klotho levels in patients receiving burosumab. No differences were found for either carbohydrate-lipid biomarkers or FGF21 between the three groups. A total of 21 XLH patients (53%) had insulin resistance (HOMA > 2.4, N = 10 SOC, N = 11 burosumab).

CONCLUSION

FGF21 does not explain obesity/overweight in XLH. Of note, this study was performed in France in 2018-2019, early after the approval authorizing burosumab only in case of severe XLH despite SOC. As such, the data on systolic blood pressure highlighting a possible impact of burosumab to decrease blood pressure as well as increase Klotho levels deserve further studies given their potential effect on long-term cardiovascular risk. A higher resolution version of the Graphical abstract is available as Supplementary information.

Circulating autotaxin levels in healthy teenagers: Data from the Vitados cohort

Autotaxin (ATX) is a secreted enzyme with a lysophospholipase D activity, mainly secreted by adipocytes and widely expressed. Its major function is to convert lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA), an essential bioactive lipid involved in multiple cell processes. The ATX-LPA axis is increasingly studied because of its involvement in numerous pathological conditions, more specifically in inflammatory or neoplastic diseases, and in obesity. Circulating ATX levels gradually increase with the stage of some pathologies, such as liver fibrosis, thus making them a potentially interesting non-invasive marker for fibrosis estimation. Normal circulating levels of ATX have been established in healthy adults, but no data exist at the pediatric age. The aim of our study is to describe the physiological concentrations of circulating ATX levels in healthy teenagers through a secondary analysis of the VITADOS cohort. Our study included 38 teenagers of Caucasian origin (12 males, 26 females). Their median age was 13 years for males and 14 years for females, ranging from Tanner 1 to 5. BMI was at the 25th percentile for males and 54th percentile for females, and median blood pressure was normal. ATX median levels were 1,049 (450-2201) ng/ml. There was no difference in ATX levels between sexes in teenagers, which was in contrast to the male and female differences described in the adult population. ATX levels significantly decreased with age and pubertal status, reaching adult levels at the end of puberty. Our study also suggested positive correlations between ATX levels and blood pressure (BP), lipid metabolism, and bone biomarkers. However, except for LDL cholesterol, these factors were also significantly correlated with age, which might be a confounding factor. Still, a correlation between ATX and diastolic BP was described in obese adult patients. No correlation was found between ATX levels and inflammatory marker C-reactive protein (CRP), Body Mass Index (BMI), and biomarkers of phosphate/calcium metabolism. In conclusion, our study is the first to describe the decline in ATX levels with puberty and the physiological concentrations of ATX levels in healthy teenagers. It will be of utmost importance when performing clinical studies in children with chronic diseases to keep these kinetics in mind, as circulating ATX might become a non-invasive prognostic biomarker in pediatric chronic diseases.

X-Linked Hypophosphatemia, Not Only a Skeletal Disease But Also a Chronic Inflammatory State

CONTEXT

X-linked hypophosphatemia (XLH) is a rare genetic disease caused by a primary excess of fibroblast growth factor 23 (FGF23). FGF23 has been associated with inflammation and impaired osteoclastogenesis, but these pathways have not been investigated in XLH.

OBJECTIVE

This work aimed to evaluate whether XLH patients display peculiar inflammatory profile and increased osteoclastic activity.

METHODS

We performed a prospective, multicenter, cross-sectional study analyzing transcript expression of 8 inflammatory markers (Il6, Il8, Il1β, CXCL1, CCL2, CXCR3, Il1R, Il6R) by real-time quantitative polymerase chain reaction on peripheral blood mononuclear cells (PBMCs) purified from total blood samples extracted from patients and healthy control individuals. The effect of native/active vitamin D on osteoclast formation was also assessed in vitro from XLH patients' PBMCs.

RESULTS

In total, 28 XLH patients (17 children, among them 6 undergoing standard of care [SOC] and 11 burosumab therapy) and 19 controls were enrolled. Expression of most inflammatory markers was significantly increased in PBMCs from XLH patients compared to controls. No differences were observed between the burosumab and SOC subgroups. Osteoclast formation was significantly impaired in XLH patients. XLH mature osteoclasts displayed higher levels of inflammatory markers, being however lower in cells derived from the burosumab subgroup (as opposed to SOC).

CONCLUSION

We describe for the first time a peculiar inflammatory profile in XLH. Since XLH patients have a propensity to develop arterial hypertension, obesity, and enthesopathies, and because inflammation can worsen these clinical outcomes, we hypothesize that inflammation may play a critical role in these extraskeletal complications of XLH.

Klinefelter Bone Microarchitecture Evolution with Testosterone Replacement Therapy

Klinefelter Syndrome (KS) patients, defined by a 47 XXY karyotype, have increased risk of fragility fractures. We have assessed bone microarchitecture by high resolution peripheral quantitative CT (HR-pQCT) at the radius and tibia in young KS patients, naïve from testosterone replacement therapy (TRT). Areal bone mineral density (BMD) and body composition were assessed by dual X-ray absorptiometry (DXA). Total testosterone (tT) was measured at baseline. Bone measurements have been repeated after 30 months of TRT. We enrolled 24 KS patients and 72 age-matched controls. KS patients were (mean ± SD) 23.7 ± 7.8 year-old. KS patients had significantly lower relative appendicular lean mass index (RALM) and lower aBMD at spine and hip than controls. Ten patients (42%) had low tT level (≤ 10.4 nmol/L). At baseline, we observed at radius a marked cortical (Ct) impairment reflected by lower Ct.area, Ct.perimeter, and Ct.vBMD than controls. At tibia, in addition to cortical fragility, we also found significant alterations of trabecular (Tb) compartment with lower trabecular bone volume (BV/TV) and Tb.vBMD as compared to controls. After 30 months of TRT, 18 (75%) KS patients were reassessed. Spine aBMD and RALM significantly increased. At radius, both cortical (Ct.Pm, Ct.Ar, Ct.vBMD, Ct.Th) and trabecular (Tb.vBMD) parameters significantly improved. At tibia, the improvement was found only in the cortical compartment. Young TRT naïve KS patients have inadequate bone microarchitecture at both the radius and tibia, which can improve on TRT.

Copper Isotope Evidence of Oxidative Stress-Induced Hepatic Breakdown and the Transition to Hepatocellular Carcinoma

Background and Aims

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide, and finding a single reliable biomarker to follow liver degradation is a challenging task. To document the relationship between liver failure, hypoxia, and HCC, copper isotope variations (δ65Cu) were evaluated in the serum of HCC-negative and HCC-positive patients as a biomarker of hepatic failure.

Methods

We analyzed Cu isotope variations in serum samples from 293 patients with potentially degraded liver functions presenting hepatitis B virus, hepatitis C virus, nonalcoholic steatohepatitis, and alcohol uptake (OH) etiologies and 105 controls. Ninety-five of the patients were diagnosed with HCC.

Results

On average, the δ65Cu values of the serum of patients with F3-F4 fibrosis score or HCC-positive are low. The Cu isotope data are strikingly bimodal with well-defined δ65Cu modes which imperfectly reflect etiology. The population with normal values (ca -0.3‰) is progressively replaced by a population with atypical δ65Cu values (ca -0.8‰), which reflects the progressive degradation of hepatic functions.

Conclusion

The clear bimodality does not correspond to a progressive shift of the δ65Cu values but to a replacement of one population by another. This bimodality sheds light on the persisting difficulties epitomized by α-fetoprotein in finding high-sensitivity and high-specificity HCC biomarkers. It is interpreted as a switch in the resistance of hepatic tissues to the oxidative stress that eventually leads to HCC oncogenesis.

TmP/GFR reference values from childhood to adulthood in the era of IDMS-standardized creatinine values

BACKGROUND

The assessment of phosphate homeostasis in clinical practice relies on circulating phosphate levels but also on phosphate tubular reabsorption, ideally assessed using the Tubular maximum Phosphate Reabsorption per Glomerular Filtration Rate (TmP/GFR). TmP/GFR reference values were established before the onset of IDMS-standardized creatinine assays, and thus need to be updated. Our objective is to provide reference values for TmP/GFR from childhood to adulthood, using the gold-standard of GFR assessment and IDMS-standardized creatinine values.

METHODS

We retrospectively analyzed all the inulin and iohexol clearances (mGFR) performed in children and in adults screened for a living-donation in our unit since the beginning of IDMS-creatinine assays. TmP/GFR was calculated on a fasting sample, using the conventional formula without correction for TRP in subjects below 19 years of age.

RESULTS

A total of 2051 subjects (1711 children, 340 adults), aged from 1.9 to 73.4 years with normal GFR, normal phosphate and normal calcium levels, was included for TmP/GFR analysis. As expected, there was a progressive decrease along puberty in both genders of plasma phosphate and TmP/GFR, the decrease occurring earlier in girls. After the age of 19, there was a stabilization of plasma phosphate and TmP/GFR levels until the age of 55, phosphate levels and TmP/GFR being slightly lower in men than in women.

CONCLUSION

We present the largest cohort describing TmP/GFR reference values in the era of IDMS-standardized creatinine assays. We believe that these data will help physicians to better diagnose and manage patients with abnormal phosphate metabolism in daily clinical routine.

A prospective case-control pilot study to evaluate bone microarchitecture in children and teenagers on long-term parenteral nutrition using HR-pQCT

Long-term parenteral nutrition (PN) may induce bone complications. Tridimensional bone imaging techniques such as high-resolution peripheral quantitative computed tomography (HR-pQCT) allow the assessment of both compartmental volumetric densities and microarchitecture. Our aim was to evaluate these parameters in children and teenagers receiving long-term PN. This cross-sectional, case–control study included children older than 9 years undergoing PN for at least 2 years. They were age-, gender- and puberty-matched with healthy controls (1:2). Evaluation included biological assessment of bone metabolism (serum calcium, phosphate, and albumin; urinary calcium and creatinine; 25-OH vitamin D, osteocalcin and PTH), dual X-ray absorptiometry (DXA) and HR-pQCT at the ultradistal tibia and radius. Results are presented as median [range]. Eleven patients (3 girls) with a median age of 16 [9–19] years were included. Bone parameters assessed by HR-pQCT at the ultradistal radius and tibia were similar in patients and controls. Parathyroid hormone (PTH) levels were higher (14 [7–115] vs 16 [12–27]) and osteocalcin levels were lower (44 [15–65] vs 65 [38–142]) in patients than in controls, although within the normal range. Conclusions: there were no differences for compartmental bone densities and microarchitecture in patients undergoing chronic PN. Further longitudinal studies are required to confirm these quite reassuring preliminary results.

Intermittent Bi-Daily Sub-cutaneous Teriparatide Administration in Children With Hypoparathyroidism: A Single-Center Experience

Introduction: The use of teriparatide has been reported in children with hypoparathyroidism as an investigational physiologic replacement therapy. Methods: We aimed to retrospectively report our pediatric experience of bi-daily sub-cutaneous teriparatide. Results are presented as median (25th-75th quartile). As part of the routine follow-up of these patients with hypoparathyroidism, total calcium at H0 (i.e., just before injection) and H4 (i.e., 4 h after teriparatide injection) and other biomarker parameters were regularly assessed. Results: At a median age of 10.7 (8.1-12.6) years, an estimated glomerular filtration rate (eGFR) of 110 (95-118) mL/min/1.73 m², calcium levels of 1.87 (1.81-1.96) mmol/L and an age-standardized phosphate of 3.8 (2.5-4.9) SDS, teriparatide therapy was introduced in 10 patients at the dose of 1.1 (0.7-1.5) μg/kg/day (20 μg twice daily), with further adjustment depending on calcium levels. Six patients already displayed nephrocalcinosis. Severe side effects were reported in one child: two episodes of symptomatic hypocalcemia and one of iatrogenic hypercalcemia; one teenager displayed dysgueusia. Calcium levels at H0 did not significantly increase whilst calcium at H4 and phosphate levels significantly increased and decreased, respectively. After 12 months, eGFR, calcium and age-standardized phosphate levels were 108 (90-122) mL/min/1.73 m², 2.36 (2.23-2.48) mmol/L, 0.5 (-0.1 to 1.5), and 68 (63-74) nmol/L, respectively, with a significant decrease in phosphate levels (p = 0.01). Urinary calcium and calcium/creatinine ratio remained stable; no nephrolithiasis was observed but two moderate nephrocalcinosis appeared. Conclusion: Intermittent teriparatide therapy significantly improves calcium and phosphate control, without increasing calciuria. It appears to be safe and well-tolerated in children.

The interest of oral calcium loads test in the diagnosis and management of pediatric nephrolithiasis with hypercalciuria: Experience from a tertiary pediatric centre

INTRODUCTION

The use of calcium load has been forgotten in pediatrics until recently whereas it is of utmost importance to have a practical approach to guide management of hypercalciuric nephrolithiasis.

OBJECTIVE

The purpose of this study was to evaluate the practical interest of oral calcium loads to improve the overall management of nephrolithiasis in children.

METHODS

We retrospectively studied all pediatric patients having undergone an oral calcium load in our pediatric nephrology unit between September 2015 and April 2017.

RESULTS

A total of 16 patients were included, at a median age of 12.0 (5.5-17.5) years. The indications of oral calcium load were: presence of an active urolithiasis without any obvious explanation after ruling out the "classical" biological abnormalities, or presence of hypercalciuria with stones composed of weddellite or carbapatite crystals. Among the 16 patients, 6 (38%) patients displayed absorptive hypercalciuria, 2 (12%) renal leak, 3 (19%) "unclassified" inadapted PTH, and 5 (31%) a normal calcium load test. The result of oral calcium load modified the clinical management in 14 (88%) patients, mainly based on the type of hypercalciuria. It allowed us to individualize nutritional advice: in patients with absorptive hypercalciuria, we proposed calcium intake within the lower normal range for age with dairy products not enriched with vitamin D, with the advice to avoid salt and calcium loads during evenings. Conversely, in patients with resorptive hypercalciuria, we proposed normal calcium intake for age. Showing the results of the calcium load is meaningful to patients and parents, and can be considered as an "educational" tool.

DISCUSSION

To the best of our knowledge, this study is the first to evaluate the interest of calcium load in children with nephrolithiasis in an era of routine PTH and 1-25-D assessment. Here, we demonstrate the feasibility and safety of oral calcium load in children, its interest to understand the underlying mechanisms of hypercalciuria, and its major interest as an "educational tool" for patients to explain them the underlying mechanisms and thus guide the therapeutic management using an individualized dietary approach. This study did not include many patients, but to the best of our knowledge, this is the first study evaluating and validating the feasibility of a safe and non-expensive diagnosis tool in pediatric hypercalciuria.

CONCLUSION

Oral calcium load is helpful to guide therapeutic adaptation in pediatrics using an individualized dietary approach.

Compositional and mechanical properties of growing cortical bone tissue: a study of the human fibula

Human cortical bone contains two types of tissue: osteonal and interstitial tissue. Growing bone is not well-known in terms of its intrinsic material properties. To date, distinctions between the mechanical properties of osteonal and interstitial regions have not been investigated in juvenile bone and compared to adult bone in a combined dataset. In this work, cortical bone samples obtained from fibulae of 13 juveniles patients (4 to 18 years old) during corrective surgery and from 17 adult donors (50 to 95 years old) were analyzed. Microindentation was used to assess the mechanical properties of the extracellular matrix, quantitative microradiography was used to measure the degree of bone mineralization (DMB), and Fourier transform infrared microspectroscopy was used to evaluate the physicochemical modifications of bone composition (organic versus mineral matrix). Juvenile and adult osteonal and interstitial regions were analyzed for DMB, crystallinity, mineral to organic matrix ratio, mineral maturity, collagen maturity, carbonation, indentation modulus, indicators of yield strain and tissue ductility using a mixed model. We found that the intrinsic properties of the juvenile bone were not all inferior to those of the adult bone. Mechanical properties were also differently explained in juvenile and adult groups. The study shows that different intrinsic properties should be used in case of juvenile bone investigation.