Sir Leonard Parsons of Birmingham (1879-1950) and antenatal paediatrics.
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Born and educated in the Midlands, Sir Leonard Parsons made major contributions to the field of paediatrics in that area and played a leading role in the regional organisation of this specialty throughout the United Kingdom in the later years of his life. He was a founder member and later President of the British Paediatric Association, and later became Vice-President of the International Pediatric Congress and the President of the paediatric section of the Royal Society of Medicine. (+info)
Tissue-nonspecific alkaline phosphatase and plasma cell membrane glycoprotein-1 are central antagonistic regulators of bone mineralization.
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Osteoblasts mineralize bone matrix by promoting hydroxyapatite crystal formation and growth in the interior of membrane-limited matrix vesicles (MVs) and by propagating the crystals onto the collagenous extracellular matrix. Two osteoblast proteins, tissue-nonspecific alkaline phosphatase (TNAP) and plasma cell membrane glycoprotein-1 (PC-1) are involved in this process. Mutations in the TNAP gene result in the inborn error of metabolism known as hypophosphatasia, characterized by poorly mineralized bones, spontaneous fractures, and elevated extracellular concentrations of inorganic pyrophosphate (PP(i)). PP(i) suppresses the formation and growth of hydroxyapatite crystals. PP(i) is produced by the nucleoside triphosphate pyrophosphohydrolase activity of a family of isozymes, with PC-1 being the only member present in MVs. Mice with spontaneous mutations in the PC-1 gene have hypermineralization abnormalities that include osteoarthritis and ossification of the posterior longitudinal ligament of the spine. Here, we show the respective correction of bone mineralization abnormalities in knockout mice null for both the TNAP (Akp2) and PC-1 (Enpp1) genes. Each allele of Akp2 and Enpp1 has a measurable influence on mineralization status in vivo. Ex vivo experiments using cultured double-knockout osteoblasts and their MVs demonstrate normalization of PP(i) content and mineral deposition. Our data provide evidence that TNAP and PC-1 are key regulators of the extracellular PP(i) concentrations required for controlled bone mineralization. Our results suggest that inhibiting PC-1 function may be a viable therapeutic strategy for hypophosphatasia. Conversely, interfering with TNAP activity may correct pathological hyperossification because of PP(i) insufficiency. (+info)
Progressive intrahepatic cholestasis (Byler's disease): case report.
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This paper reports the case of a child in which the clinical and laboratory data indicate a progressive intrahepatic cholestasis of the type described as Byler's disease. The histological and histochemical findings suggest an intrahepatic cholestasis. Electron microscopy reveals interruptions of the bile canalicular membrane, which have been described as characteristic of this disease. A striking feature in the present case is the remarkable increase of microfilamentous structures in the pericanalicular ectoplasm and in the hepatocytic cytoplasm. The findings suggest a primary disturbance in bile acid secretion as the casue of cholestasis, entailing a hypertrophy of pericanalicular microfilaments which supposedly play a role in the final step of biliary secretion. (+info)
Modulation of renal Ca2+ transport protein genes by dietary Ca2+ and 1,25-dihydroxyvitamin D3 in 25-hydroxyvitamin D3-1alpha-hydroxylase knockout mice.
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Pseudovitamin D-deficiency rickets (PDDR) is an autosomal disease characterized by hyperparathyroidism, rickets, and undetectable levels of 1,25-dihydroxyvitaminD3 (1,25(OH)2D3). Mice in which the 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) gene was inactivated presented the same clinical phenotype as patients with PDDR and were used to study renal expression of the epithelial Ca2+ channel (ECaC1), the calbindins, Na+/Ca2+ exchanger (NCX1), and Ca2+-ATPase (PMCA1b). Serum Ca2+ (1.20+/-0.05 mM) and mRNA/protein expression of ECaC1 (41+/-3%), calbindin-D28K (31+/-2%), calbindin-D9K (58+/-7%), NCX1 (10+/-2%), PMCA1b (96+/-4%) were decreased in 1alpha-OHase-/- mice compared with 1alpha-OHase+/- littermates. Feeding these mice a Ca2+-enriched diet normalized serum Ca2+ levels and expression of Ca2+ proteins except for calbindin-D9K expression. 1,25(OH)2D3 repletion resulted in increased expression of Ca2+ transport proteins and normalization of serum Ca2+ levels. Localization of Ca2+ transport proteins was clearly polarized in which ECaC1 was localized along the apical membrane, calbindin-D28K in the cytoplasm, and calbindin-D9K along the apical and basolateral membranes, resulting in a comprehensive mechanism facilitating renal transcellular Ca2+ transport. This study demonstrated that high dietary Ca2+ intake is an important regulator of the renal Ca2+ transport proteins in 1,25(OH)2D3-deficient status and thus contributes to the normalization of blood Ca2+ levels. (+info)
An ethyl-nitrosourea-induced point mutation in phex causes exon skipping, x-linked hypophosphatemia, and rickets.
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We describe the clinical, genetic, biochemical, and molecular characterization of a mouse that arose in the first generation (G(1)) of a random mutagenesis screen with the chemical mutagen ethyl-nitrosourea. The mouse was observed to have skeletal abnormalities inherited with an X-linked dominant pattern of inheritance. The causative mutation, named Skeletal abnormality 1 (Ska1), was shown to be a single base pair mutation in a splice donor site immediately following exon 8 of the Phex (phosphate-regulating gene with homologies to endopeptidases located on the X-chromosome) gene. This point mutation caused skipping of exon 8 from Phex mRNA, hypophosphatemia, and features of rickets. This experimentally induced phenotype mirrors the human condition X-linked hypophosphatemia; directly confirms the role of Phex in phosphate homeostasis, normal skeletal development, and rickets; and illustrates the power of mutagenesis in exploring animal models of human disease. (+info)
Primary care pediatrician knowledge of nutritional rickets.
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OBJECTIVE: The purpose of this study is to determine primary care pediatricians' level of awareness in the diagnosis and management of rickets. The information will be useful in assessing the need for provider education related to appropriate advice regarding vitamin D supplementation for infants. STUDY DESIGN: A one-page questionnaire was sent to a sample of 510 pediatricians in states surrounding the Great Lakes. These physicians were chosen depending based on practice listings from local telephone directories. Results were analyzed using the Chi-squared (chi2) test. RESULTS: Of the 248 respondents, 43% (n = 105) had encountered at least one actual or suspected case of rickets in the past five years. Sixty-nine percent of respondents chose vitamin D deficiency rickets-specific diagnostic tests, 24% chose rickets-specific tests, and 7% chose tests that are not specific to diagnosing rickets. Ninety-four percent of respondents chose treatments specific to vitamin D deficiency rickets, while 6% chose treatments not specific to rickets. CONCLUSION: Most primary care pediatricians from major metropolitan areas in the Great Lakes region are aware of the appropriate methods to diagnose and treat vitamin D-deficiency rickets. However, educational interventions are still necessary for both physicians and parents to promote widespread use of vitamin D supplementation in all breastfed infants. (+info)
The autosomal dominant hypophosphatemic rickets R176Q mutation in fibroblast growth factor 23 resists proteolytic cleavage and enhances in vivo biological potency.
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Missense mutations in fibroblast growth factor 23 (FGF23) are the cause of autosomal dominant hypophosphatemic rickets (ADHR). The mutations (R176Q, R179W, and R179Q) replace Arg residues within a subtilisin-like proprotein convertase (SPC) cleavage site (RXXR motif), leading to protease resistance of FGF23. The goals of this study were to examine in vivo the biological potency of the R176Q mutant FGF23 form and to characterize alterations in homeostatic mechanisms that give rise to the phenotypic presentation of this disorder. For this, wild type and R176Q mutant FGF23 were overexpressed in the intact animals using a tumor-bearing nude mouse system. At comparable circulating levels, the mutant form was more potent in inducing hypophosphatemia, in decreasing circulating concentrations of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and in causing rickets and osteomalacia in these animals compared with wild type FGF23. Parameters of calcium homeostasis were also altered, leading to secondary hyperparathyroidism and parathyroid gland hyperplasia. However, the raised circulating levels of parathyroid hormone were ineffective in normalizing the reduced 1,25(OH)(2)D(3) levels by increasing renal expression of 25(OH)D(3)-1alpha-hydroxylase (Cyp40) to promote its synthesis and by decreasing that of 25(OH)D(3)-24-hydroxylase (Cyp24) to prevent its catabolism. The findings provide direct in vivo evidence that missense mutations from ADHR kindreds are gain-of-function mutations that retain and increase the protein's biological potency. Moreover, for the first time, they define a potential role for FGF23 in dissociating parathyroid hormone actions on mineral fluxes and on vitamin D metabolism at the level of the kidney. (+info)
Genetic aspects of nutritional rickets.
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Amino acid excretion was investigated in 21 rachitic infants and in 22 of their parents. There was (a) increased alpha-amino acid excretion in one-third of the infants a long time after the rickets had healed, (b) an abnormally high excretion of alpha-amino nitrogen and of phosphorus in many of the parents (c) an abnormal pattern of amino acid excretion in all 9 infants tested, and (d) a good correlation between the excretion of individual amino acids by an infant and by its parents. Our findings suggest that in at least some cases of nutritional rickets there is a genetic element which may manifest itself only under adverse environmental conditions. (+info)