Vitamin D receptor genotype in hypophosphatemic rickets as a predictor of growth and response to treatment.

CONTEXT: Treatment of X-linked hypophosphatemic rickets improves bone mineralization and bone deformities, but its effect on skeletal growth is highly variable. OBJECTIVE: Genetic variants in the promoter region of the vitamin D receptor (VDR) gene may explain the response to treatment because this receptor mediates vitamin D action. DESIGN: We studied the VDR promoter haplotype structure in a large cohort of 91 patients with hypophosphatemic rickets including 62 patients receiving 1alpha-hydroxyvitamin D3 derivatives and phosphates from early childhood on. RESULTS: Treatment improved bone deformities and final height, but 39% of treated patients still had short stature at the end of growth (-2 sd score or below). Height was closely associated with VDR promoter Hap1 genotype. Hap1(-) patients (35% of the cohort) had severe growth defects. This disadvantageous association of Hap1(-) status with height was visible before treatment, under treatment, and on to adulthood. Gender and age at initiation of treatment could not account for the Hap1 effect. No association with growth was found with a polymorphism of the PTH receptor gene otherwise found to be associated with adult height. Compared with Hap1(+) patients, those who were Hap1(-) had a higher urinary calcium response to 1alpha-hydroxyvitamin D3 and had significantly lower circulating FGF23 levels (C-terminal assay), taking into account their phosphate and 1alpha-hydroxyvitamin D3 intakes. CONCLUSIONS: The present work identifies the VDR promoter genotype as a key predictor of growth under treatment with 1alpha-hydroxyvitamin D3 derivatives in patients with hypophosphatemic rickets, including those with established PHEX alterations. The VDR promoter genotype appears to provide valuable information for adjusting treatment and for deciding upon the utility of early GH therapy.

A maternal epimutation of GNAS leads to Albright osteodystrophy and parathyroid hormone resistance.

CONTEXT: Pseudohypoparathyroidism (PHP) type Ia is a rare maternally transmitted disease due to maternal loss-of-function mutations of GNAS, the gene encoding Galphas, the alpha-stimulatory subunit of the G protein. Affected individuals display hormonal resistance (mainly PTH and TSH resistance) and Albright hereditary osteodystrophy. PHP type Ib (PHP-Ib), usually defined by isolated renal resistance to PTH and sometimes mild TSH resistance, is due to a maternal loss of GNAS exon A/B methylation, leading to decreased Galphas expression in specific tissues. OBJECTIVE AND RESULTS: We report a girl with obvious Albright osteodystrophy features, PTH resistance, normal Galphas bioactivity in red blood cells, yet no loss-of-function mutation in the GNAS coding sequence (exons 1-13). The methylation analysis of the four GNAS differentially methylated regions, i.e. NESP, AS, XL, and A/B, revealed broad methylation changes at all differentially methylated regions, including GNAS exon A/B, leading to a paternal epigenotype on both alleles. CONCLUSIONS: This observation suggests that: 1) the decreased expression of Galphas due to GNAS epimutations is not restricted to the renal tubule but may affect nonimprinted tissues like bone; 2) PHP-Ib is a heterogeneous disorder that should lead to studying GNAS epigenotype in patients with PHP and no mutation in GNAS exons 1-13, regardless of their physical features.

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.

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).

Making the unit of insulin: standards, clinical work, and industry, 1920-1925.

The standardization of insulin is generally considered by historians to have been a process conducted by physiologists under the direction of Henry Dale. This article shows that it actually involved many actors and began with the earliest administration to patients in Canada and the United States. During this first phase, the drug company Eli Lilly also contributed actively to the standardization, under the scientific direction of George Clowes. This is not to undermine the role of Dale, whose political leadership was paramount for the international phase of the standardization. His scientific contribution, however, was a continuation of previous work led by physiologists, clinicians, and pharmacists. The production and packaging of insulin in standardized units thus appears to be the result of the impressive working of a transdisciplinary and transnational network. It also highlights how new modes of drug regulation were elaborated by state bodies in the early 1920s and paved the way for more extensive reforms.