European cystic fibrosis bone mineralisation guidelines.

Patients with cystic fibrosis (CF) are at risk of developing low bone mineral density (BMD) and fragility fractures. This paper presents consensus statements that summarise current knowledge of the epidemiology and pathophysiology of CF-related skeletal deficits and provides guidance on its assessment, prevention and treatment. The statements were validated using a modified Delphi methodology.

Abnormal presence of the matrix extracellular phosphoglycoprotein-derived acidic serine- and aspartate-rich motif peptide in human hypophosphatemic dentin.

Severe dental troubles are associated with X-linked hypophosphatemic rickets and are mainly related to impaired dentin mineralization. In dentin matrix, matrix extracellular phosphoglycoprotein (MEPE) may be protected from proteolysis by a specific interaction with PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome). The objective of our work was to determine whether PHEX impairment induces MEPE cleavage in dentin and the subsequent release of the C-terminal acidic serine- and aspartate-rich motif (ASARM) peptide, which is known to inhibit mineralization. By Western blot analysis, we explored dentin extracts from seven hypophosphatemic patients with mutations of the PHEX gene. A proteomic approach combining immunoprecipitation, surface-enhanced laser desorption/ionization-time of flight-mass spectrometry and matrix-assisted laser desorption ionization-time of flight analysis of the samples completed this exploration. This study shows a 4.1-kDa peptide containing the MEPE-derived ASARM peptide in hypophosphatemic samples. The presence of ASARM was less marked in patients treated with 1-hydroxylated vitamin D and phosphate during growth. Moreover, recombinant ASARM implanted in a rat pulp injury model disturbed the formation of the reparative dentin bridge. These results suggest that abnormal MEPE cleavage occurs when PHEX activity is deficient in humans, the ASARM peptide may be involved in the mineralization defects and the PHEX-MEPE interaction may be indirect, as ensuring a better phosphate and vitamin D environment to the mineralizing dentin prevents MEPE cleavage.

Regulation of phosphate homeostasis in infants, children, and adolescents, and the role of phosphatonins in this process.

PURPOSE OF REVIEW: Unlike calcium metabolism, the control of phosphate homeostasis has long been poorly understood. The identification of 'phosphatonins' in the serum of hypophosphatemic patients, the unveiling of the genetic causes of hypo and hyperphosphatemic diseases in patients, and the creation of finely adapted animal models have revolutionized our understanding of phosphate homeostasis. RECENT FINDINGS: Original reports published in 2006/2007 bring valuable pieces of information that enable better understanding of the physiological regulation of phosphate homeostasis by more precisely defining the interplay between PHEX, vitamin D, and phosphatonins; identification of new genes causing hypophosphatemic rickets, aside from PHEX and fgf23, namely the genes encoding for a renal sodium-phosphate cotransporter, NaPiIIc, and for a bone matrix protein, DmpI; and improved diagnosis of tumor-induced osteomalacia with more precise imaging techniques for tumor localization and more precise fibroblast growth factor 23 assays. SUMMARY: From a clinical point of view, these findings offer new tools for the diagnosis of hypophosphatemic rickets (biologic, genetic, imaging techniques) and open the way to new treatment strategies.

Vitamin D-resistant rickets and type 1 diabetes in a child with compound heterozygous mutations of the vitamin D receptor (L263R and R391S): dissociated responses of the CYP-24 and rel-B promoters to 1,25-dihydroxyvitamin D3.

UNLABELLED: We report here the first association between vitamin D-resistant rickets, alopecia, and type 1 diabetes in a child with compound heterozygous mutations in the VDR gene. Transfection studies suggest dissociated effects of VDR gene mutations on the regulation of genes involved in vitamin D metabolism and dendritic cell maturation. INTRODUCTION: Whereas vitamin D may play a role in the immune tolerance process, no patient has been reported to associate hereditary vitamin D-resistant rickets (HVDRR) and an autoimmune disease, and no attempt has been made to delineate the outcome of mutations of the vitamin D receptor (VDR) on the transcription of genes controlling immune tolerance. MATERIALS AND METHODS: The VDR gene was analyzed in a child with vitamin D-resistant rickets, total alopecia, and early childhood-onset type 1 diabetes. Patient's fibroblasts and COS-7 cells transfected with wildtype or mutant VDRs were studied for ligand-binding capacity, transactivation activity using two gene promoters [CYP-24, a classical 1,25(OH)2D3-responsive gene, and relB, a critical NF-kappaB component for regulation of dendritic cell differentiation], VDR-RXR heterodimers association to CYP 24 VDREs by gel mobility shift assays, and co-activator binding by Glutathione-S-transferase pull-down assays. RESULTS: Two novel compound heterozygous mutations (L263R and R391S) were identified in the VDR ligand-binding domain in this child. Both mutations significantly impaired VDR ligand-binding capacity but had dissociated effects on CYP-24 and RelB promoter responses to vitamin D. CYP 24 response binding to SRC-1 and RXR-heterodimer binding to CYP24 VDREs were abolished in L263R mutants but normal or partially altered in R391S mutants. In the opposite, RelB responses to vitamin D were close to normal in L263R mutants but abolished in R391S mutants. CONCLUSIONS: We report the first clinical association between HVDRR, total alopecia, and early childhood-onset type 1 diabetes. Mutations in the VDR ligand-binding domain may hamper the 1,25(OH)2D3-mediated relB responses, an effect that depends on the site of the VDR mutation and cannot be anticipated from VDR ligand-binding ability or CYP-24 response. Based on these results, we propose to survey the immune function in patients with HVDRR, including those with moderate features of rickets.

Possible involvement of pregnane X receptor-enhanced CYP24 expression in drug-induced osteomalacia.

Vitamin D controls calcium homeostasis and the development and maintenance of bones through vitamin D receptor activation. Prolonged therapy with rifampicin or phenobarbital has been shown to cause vitamin D deficiency or osteomalacia, particularly in patients with marginal vitamin D stores. However, the molecular mechanism of this process is unknown. Here we show that these drugs lead to the upregulation of 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24) gene expression through the activation of the nuclear receptor pregnane X receptor (PXR; NR1I2). CYP24 is a mitochondrial enzyme responsible for inactivating vitamin D metabolites. CYP24 mRNA is upregulated in vivo in mice by pregnenolone 16alpha-carbonitrile and dexamethasone, 2 murine PXR agonists, and in vitro in human hepatocytes by rifampicin and hyperforin, 2 human PXR agonists. Moreover, rifampicin increased 24-hydroxylase activity in these cells, while, in vivo in mice, pregnenolone 16alpha-carbonitrile increased the plasma concentration of 24,25-dihydroxyvitamin D(3). Transfection of PXR in human embryonic kidney cells resulted in rifampicin-mediated induction of CYP24 mRNA. Analysis of the human CYP24 promoter showed that PXR transactivates the sequence between -326 and -142. We demonstrated that PXR binds to and transactivates the 2 proximal vitamin D-responsive elements of the human CYP24 promoter. These data suggest that xenobiotics and drugs can modulate CYP24 gene expression and alter vitamin D(3) hormonal activity and calcium homeostasis through the activation of PXR.

Dental abnormalities in patients with familial hypophosphatemic vitamin D-resistant rickets: prevention by early treatment with 1-hydroxyvitamin D.

OBJECTIVE: To evaluate the dental effects of 1-hydroxylated vitamin D3 treatment in patients with familial hypophosphatemic vitamin D-resistant rickets. Study design Forty-eight children and adult patients were included in the study; 16 had received no treatment or phosphate supplements with vitamin D/25-(OH) D3 before puberty. The 32 younger ones had received phosphate supplements with 1alpha-(OH)D3 from infancy. All patients were clinically examined, and panoramic and periapical radiographs were made. Evaluations of decayed, missing, or filled teeth and decayed or filled teeth indexes and of pulp ratios allowed comparison with healthy age-matched control patients. RESULTS: Poor dental health and characteristic dental anomalies were found in the 16 older patients. In contrast, the 32 younger patients had a normal dental status as regards reference ranges in healthy age-matched populations, although they still showed prominent pulp horns on deciduous teeth and increased pulp area/tooth area ratios. CONCLUSIONS: This investigation shows the beneficial effects of 1alpha-(OH)D3 treatment on the dental status of vitamin D-resistant rickets patients and emphasizes the necessity of early treatment. Remaining defects may result from early exposure of odontoblasts and surrounding osteoblasts to hypophosphatemia, before the commencement of treatment, and/or from intrinsic cell disturbances linked to the genetic alteration(s).

PASSCLAIM - Bone health and osteoporosis.

BACKGROUND: The EC Concerted Action PASSCLAIM aims to produce a generic tool for assessing the scientific support for health-related claims for foods and food components. AIM: The task of the ITGB Working Group was to critically evaluate the categories of scientific evidence needed to support claims in relation to bone health and osteoporosis. METHODS: A framework was developed to describe the chain of evidence that is required to link the consumption of a food or food component to bone health outcomes. Techniques available for interrogating each link in the chain were identified and their strengths and weaknesses considered. This framework was used to determine intermediate markers of health outcome with respect to osteoporosis and to debate the level of evidence that would be required to substantiate claims of enhanced function or reduced disease risk. RESULTS: Use of this framework with osteoporotic fracture as the health endpoint resulted in the following judgements based on current knowledge: 1) bone mineral density (BMD) is an intermediate marker of bone health which, for people of any age and sex, can provide evidence of enhanced function; 2) for people over 50 years living in populations with a high incidence of fracture, BMD is an intermediate marker of osteoporotic fracture risk which can provide evidence of an increased probability of reduced disease risk; 3) because osteoporosis is defined as a state of increased fracture risk due to low bone mass and deterioration in bone microarchitecture, a claim of a definite reduction in osteoporosis or fracture risk requires similar substantiation to claims that fractures are prevented or treated, including clinical trials and animal studies; 4) data from lower in the chain of evidence, such as bone turnover and calcium bioavailability, are not, by themselves, sufficiently strongly related to bone health endpoints to provide evidence of enhanced function or reduced disease risk but can provide supporting information. CONCLUSIONS: In the light of existing scientific knowledge, a framework has been developed as a tool for considering the scientific support for claims relating to bone health and osteoporosis. To provide a working example, the framework has been used to assess the current position with osteoporotic fracture as the health endpoint. This experience will contribute to the formulation under PASSCLAIM of a generic tool for assessing the scientific support of health claims on foods.

GNAS1 lesions in pseudohypoparathyroidism Ia and Ic: genotype phenotype relationship and evidence of the maternal transmission of the hormonal resistance.

We conducted clinical and biological studies including screening for mutations in the gene encoding the alpha subunit of G(s) (GNAS1) in 30 subjects (21 unrelated families) with Albright's hereditary osteodystrophy (AHO), pseudohypoparathyroidism (PHP); and decreased erythrocyte G(s) activity (PHP-Ia; n = 19); AHO and decreased erythrocyte G(s) activity (isolated AHO; n = 10); or AHO, hormonal resistance, and normal erythrocyte G(s) activity (PHP-Ic; n = 1). A heterozygous GNAS1 gene lesion was found in 14 of 17 PHP-Ia index cases (82%), including 11 new mutations and a mutational hot-spot involving codons 189-190 (21%). These lesions lead to a truncated protein in all but three cases with missense mutations R280K, V159M, and D156N. In the patient diagnosed with PHP-Ic, G(s)alpha protein was shortened by just four amino acids, a finding consistent with the conservation of G(s) activity in erythrocytes and the loss of receptor contact. No GNAS1 lesions were found in individuals with isolated AHO that were not relatives to PHP-Ia patients (n = 5). Intrafamilial segregation analyses of the mutated GNAS1 allele in nine PHP-Ia patients established that the mutation had either occurred de novo on the maternal allele (n = 4) or had been transmitted by a mother with a mild phenotype (n = 5). This finding is consistent with an imprinting of GNAS1 playing a role in the clinical phenotype of loss of function mutations and with a functional maternal GNAS1 allele having a predominant role in preventing the hormonal resistance of PHP-Ia.

Lower circulating insulin-like growth factor I and 1,25-dihydroxyvitamin D levels in preeclampsia

Objetivo. Evaluar si las concentraciones e la somatomedina C )IGF-I) en el suero de mujeres preeclámticas son menores que las encontradas en mujeres embarazadas normotensasm y si las concentraciones en el suero del IGF-I se correlacionan con las de la 1,25-dihidroxivitamina D (1,25-(OH)2D). Diseño del estudio. El estudio fue transversal y se realizó entre las semanas 26.7 y 39.7 del embarazo. Los resultados obtenidos en mujeres preeclámpticas se compararon con los obtenidos en mujeres embarazadas normotensas de la misma edad gestacional (grupo testigo). Lugar. Todas las voluntarias eran pacientes del Hospital General de México, México, D.F., y todos los análisis de laboratorio se realizaron en el Instituto Nacional de la Nutrición Salvador Zubirán, México, D.F. Sujetos. En el estudio participaron 26 mujeres preeclámpticas y 26 mujeres embarazadas normotensas. Todas participaron informada y libremente. Procedimiento. Se realizaron las siguientes medicaciones: concentraciones en el suero del IGF-I, de la 1,25-(OH)2D, de la hormona paratiroidea intacta (PTH), del fósforo inorgánico, de la creatinina y del calcio y magnesio totales y iónicos. Además, se midieron la excreción urinaria del calcio y la depuración renal de la creatinina y se obtuvieron datos antropométricos y sobre la dieta habitual. Todos los análisis de laboratorio se realizaron en forma ciega. La comparación entre grupos se realizó mediante la prueba U de Mann-Whitney y las asociaciones entre variables se analizaron mediante las pruebas de correlación de rangos de Sperman y regresión por pasos. Resultados. Las concentraciones del IGF-I en el suero fueron 26.1 ñ 10.2 nmol/L (promedio ñ DE) en el grupo de mujeres preeclámticas y 49.9 ñ 14.3 nmol/L en el grupo testigo (p= 0.0003). Las concentraciones de la 1,25-(OH)2d en el suero fueron 43.6 ñ 8.2 pg/mL en el grupo de mujeres preeclámpticas y 52.1 ñ 10.2 pg/mL en el grupo testigo (p= 0.005). Las concentraciones de PTH intacta en el suero fueron similares en el grupo de mujeres preeclámpticas y en el grupo testigo. Las concentraciones en el suero del IGF-I, de la 1,25-(OH)2D y de la PTH intacta se correlacionaron significativamente entre sí en el grupo testigo. En las mujeres preeclámpticas sólo se correlacionaron los valores del IGF-I y de la 1,25-(OH)2D. Conclusiones. Del presente estudio se derivan dos observaciones originales: primero, que las concentraciones del IGF-I en el suero de las mujeres preeclámpticas fueron significativamente menores que las observadas en las embarazadas testigo; y segundo, la existencia de una correlación significativa entre las concentraciones séricas de IGF-I y de 1,25-(OH)2D tanto en el grupo testigo como en las mujeres preclámpticas