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Jan J M De Vijlder - One of the best experts on this subject based on the ideXlab platform.
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The Journal of Clinical Endocrinology & Metabolism Printed in U.S.A. Copyright © 2000 by The Endocrine Society Two Decades of Screening for Congenital Hypothyroidism in the Netherlands: TPO Gene Mutations in Total Iodide Organification Defects (an Update)
2013Co-Authors: Bert Bakker, Thomas Vulsma, Hennie Bikker, Janine S E De Randamie, Brenda M Wiedijk, Jan J M De VijlderAbstract:Presented is a cohort study to assess the nature and frequency of thyroid peroxidase (TPO) mutations in 45 patients (35 families) with congenital hypothyroidism due to a total iodide Organification defect; incidence is 1:66,000 in The Netherlands. The presentation is consistently similar with a severe form of congenital hypothyroidism and also characterized by a complete and immediate release of accumulated radioiodide from the thyroid after sodium perchlorate administration. Sixteen different mutations were found, including eight novel mutations; the majority occurs in exons 8, 9, or 10. The GGCC insertion in exon 8 at nucleotide 1277, leading to an early termination signa
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inactivating mutations in the gene for thyroid oxidase 2 thox2 and congenital hypothyroidism
The New England Journal of Medicine, 2002Co-Authors: Jose C Moreno, Jan J M De Vijlder, Thomas Vulsma, Hennie Bikker, Frank Baas, Marlies Kempers, A Paul S Van Trotsenburg, Carrie RisstalpersAbstract:Background Several genetic defects are associated with permanent congenital hypothyroidism. Immunologic, environmental, and iatrogenic (but not genetic) factors are known to induce transient congenital hypothyroidism, which spontaneously resolves within the first months of life. We hypothesized that molecular defects in the thyroid oxidase system, which is composed of at least two proteins, might be involved in the pathogenesis of permanent or transient congenital hypothyroidism in babies with defects in iodide Organification, for which the oxidase system is required. Methods Nine patients were recruited who had idiopathic congenital hypothyroidism (one with permanent and eight with transient hypothyroidism) and an iodide-Organification defect and who had been identified by the screening program for congenital hypothyroidism. The DNA of the patients and their relatives was analyzed for mutations in the genes for thyroid oxidase 1 (THOX1 ) and 2 (THOX2 ). Results The one patient with permanent and severe t...
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maternal isodisomy for chromosome 2p causing severe congenital hypothyroidism
The Journal of Clinical Endocrinology and Metabolism, 2001Co-Authors: Bert H Bakker, Ed J P Lommen, Mariette G J Schipper, Thomas Vulsma, Raoul C M Hennekam, Hennie Bikker, Jan J M De VijlderAbstract:Severe congenital hypothyroidism (CH) due to a total iodide Organification defect (TIOD) is usually due to mutations in the thyroid peroxidase (TPO) gene located at chromosome 2p25. A homozygous deletion[Δ T2512 (codon 808)] in exon 14 was identified in a patient with classical TIOD. The transmission pattern of the TPO gene in this family was anomalous; the mother was heterozygous for the deletion; and the mutation was absent in the father. Polymorphic short tandem repeat (STR) markers confirmed paternity and demonstrated on chromosome 2 that the propositus was homozygous for most markers on chromosome 2p and that these were identical to one of the maternal 2p homologs. A normal karyotype was found in the propositus, his parents and sister. We conclude that the homozygosity in the patient is due to partial maternal isodisomy of the short arm of chromosome 2, carrying a defective TPO gene. The patient, born small for gestational age, develops and grows well and appears healthy (while being treated with thy...
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two decades of screening for congenital hypothyroidism in the netherlands tpo gene mutations in total iodide Organification defects an update
The Journal of Clinical Endocrinology and Metabolism, 2000Co-Authors: Bert N Bakker, Thomas Vulsma, Hennie Bikker, Janine S E De Randamie, Brenda M Wiedijk, Jan J M De VijlderAbstract:Presented is a cohort study to assess the nature and frequency of thyroid peroxidase (TPO) mutations in 45 patients (35 families) with congenital hypothyroidism due to a total iodide Organification defect; incidence is 1:66,000 in The Netherlands. The presentation is consistently similar with a severe form of congenital hypothyroidism and also characterized by a complete and immediate release of accumulated radioiodide from the thyroid after sodium perchlorate administration. Sixteen different mutations were found, including eight novel mutations; the majority occurs in exons 8, 9, or 10. The GGCC insertion in exon 8 at nucleotide 1277, leading to an early termination signal in exon 9, is the most frequently occurring mutation. These mutations were detected in 29 families in both TPO alleles (13 homozygous and 16 compound heterozygous). In one family, partial maternal isodisomy of 2p was detected, in four families only one mutated TPO allele could be detected, and in one family no inactivating TPO mutation could be found. Because all patients clearly had the clinicopathologic features of a total iodide Organification defect, we conclude that in these five families the mutations in the (other) alleles could be either located in the intronic sequences or in the promoter region. Mutations in the TPO gene result in total iodide Organification defects.
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molecular analysis of mutated thyroid peroxidase detected in patients with total iodide Organification defects
The Journal of Clinical Endocrinology and Metabolism, 1997Co-Authors: Hennie Bikker, Frank Baas, Jan J M De VijlderAbstract:Wild-type and mutant thyroid peroxidase (TPO) was expressed in a Semliki Forest Virus (SFV)-based transient expression system in Chinese hamster ovary-K1 cells. Twenty four hours after transfection proteins immunoreactive with TPO antibodies could be detected on a Western blot. Peroxidase activity was assayed using both the guaiacol and the I3- assay. Addition of hematin was necessary to obtain enzymatic active TPO. Thyroid peroxidase complementary DNA constructs containing mutations originally found in patients with hereditary congenital hypothyroidism caused by total iodide Organification defects were analyzed using these techniques. In all cases TPO was expressed as shown by Western blotting and immunostaining. Enzymatic activity (measured by guaiacol and iodide oxidation assay) was below the detection level in four out of five mutants. The only mutant yielding TPO with enzymatic activity was G 1858 A (Gly 590 Ser). However, the mutation could affect splicing of TPO messenger RNA, leading to inactive TPO, because it is located at the exon 10/intron 10 border.
Aiqin Wang - One of the best experts on this subject based on the ideXlab platform.
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efficient adsorption of methylene blue on an alginate based nanocomposite hydrogel enhanced by organo illite smectite clay
Chemical Engineering Journal, 2013Co-Authors: Yizhe Wang, Wenbo Wang, Aiqin WangAbstract:The mixed-layer illite/smectite clay (IS) was organified and compounded with the sodium alginate-g-poly(sodium acrylate-co-styrene) (NaAlg-g-p(AA-co-St)) matrix to prepare a NaAlg-g-p(AA-co-St)/org-ano-I/S nanocomposite for adsorbing methylene blue (MB). Fourier transform infrared spectroscopy, Xray diffraction and scanning electron microscope analyses confirmed the Organification of I/S and the formation of the nanocomposite. The adsorption properties of the nanocomposite for MB was systematically investigated by optimizing the influence parameters, such as the Organification degree of I/S, the pH of MB solution, contact time, initial concentration of MB and temperature. It was found that the nanocomposite can rapidly adsorb MB with a higher adsorption capacity (1843.46 mg/g), and the adsorption isotherm and kinetics were described well by Langmuir isotherm model and Ho's pseudo-second-order model, respectively. The moderate Organification (0.25 E) of I/S contributes to enhance the adsorption capacity of the nanocomposite for MB, which renders the nanocomposite promising for the efficient removal of cationic dyes.
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efficient adsorption of methylene blue on an alginate based nanocomposite hydrogel enhanced by organo illite smectite clay
Chemical Engineering Journal, 2013Co-Authors: Yizhe Wang, Wenbo Wang, Aiqin WangAbstract:Abstract The mixed-layer illite/smectite clay (I/S) was organified and compounded with the sodium alginate-g-poly(sodium acrylate-co-styrene) (NaAlg-g-p(AA-co-St)) matrix to prepare a NaAlg-g-p(AA-co-St)/organo-I/S nanocomposite for adsorbing methylene blue (MB). Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope analyses confirmed the Organification of I/S and the formation of the nanocomposite. The adsorption properties of the nanocomposite for MB was systematically investigated by optimizing the influence parameters, such as the Organification degree of I/S, the pH of MB solution, contact time, initial concentration of MB and temperature. It was found that the nanocomposite can rapidly adsorb MB with a higher adsorption capacity (1843.46 mg/g), and the adsorption isotherm and kinetics were described well by Langmuir isotherm model and Ho’s pseudo-second-order model, respectively. The moderate Organification (0.25 E) of I/S contributes to enhance the adsorption capacity of the nanocomposite for MB, which renders the nanocomposite promising for the efficient removal of cationic dyes.
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effects of modified vermiculite on the synthesis and swelling behaviors of hydroxyethyl cellulose g poly acrylic acid vermiculite superabsorbent nanocomposites
Journal of Polymer Research, 2011Co-Authors: Jinlei Wang, Wenbo Wang, Yian Zheng, Aiqin WangAbstract:A series of hydroxyethyl cellulose-g-poly(acrylic acid)/vermiculite (HEC-g-PAA/VMT) superabsorbent nanocomposites were prepared by radical solution polymerization among hydroxyethyl cellulose (HEC), partially neutralized acrylic acid (AA), raw vermiculite (RVMT), acidified vermiculite (AVMT) and organo-vermiculite (OVMT) in the presence of initiator ammonium persulfate (APS) and crosslinker N,N’-methylenebisacrylamide (MBA). FTIR results revealed that AA was grafted onto HEC backbone and VMT participated in polymerization. VMT was exfoliated during polymerization reaction and a nanocomposite structure was formed as shown by XRD and TEM analysis. Effects of VMT content, concentration of HCl solution and Organification degree of OVMT on water absorbency were investigated and the swelling kinetics of the developed nanocomposites was also evaluated. Results showed that incorporation of VMT greatly enhanced the water absorbency, and the modified VMT by acidification and Organification can improve the water absorbency more remarkably than raw one. OVMT can improve the swelling capabilities and swelling rate to the highest degree in contrast to RVMT and AVMT.
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preparation characterization and properties of superabsorbent nanocomposites based on natural guar gum and modified rectorite
Carbohydrate Polymers, 2009Co-Authors: Wenbo Wang, Aiqin WangAbstract:Novel guar gum-g-poly(sodium acrylate)/rectorite (GG-g-PNaA/REC) superabsorbent nanocomposites were prepared in aqueous solution using guar gum (GG), partially neutralized acrylic acid (NaA), acidified rectorite (H + -REC) and organified rectorite (CTA + -REC) by cetyltrimethylammonium bromide (CTAB) as raw materials, ammonium persulfate (APS) as initiator and N,N 0 -methylenebisacrylamide (MBA) as crosslinker. FTIR spectra confirmed that NaA had been grafted onto GG chains and the AOH groups of REC participated in polymerization reaction. Exfoliated nanocomposite was obtained for H + -REC and intercalated structure was formed for CTA + -REC as shown by XRD results. SEM observations show REC has been uniformly dispersed in polymeric matrix. Effects of HCl concentration, Organification degree of CTA + -REC and content of REC on swelling capabilities were investigated and the swelling kinetics of nanocomposites was evaluated. Results indicate that modifying REC by acidification and Organification can improve swelling properties of the resultant nanocomposites, and GG-g-PNaA/CTA + -REC exhibited higher swelling capability and swelling rate contrast to GG-g-PNaA/H + -REC.
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study on superabsorbent composites xxi synthesis characterization and swelling behaviors of chitosan g poly acrylic acid organo rectorite nanocomposite superabsorbents
Journal of Applied Polymer Science, 2008Co-Authors: Jianghua Liu, Aiqin WangAbstract:A novel chitosan-g-poly(acrylic acid)/organo-rectorite (CTS-g-PAA/OREC) nanocomposite superabsorbent was synthesized by aqueous polymerization using N, N′-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. Rectorite was organified with four different degree of hexadecyltrimethyl ammonium bromide, and the Organification of rectorite was proved by FTIR and XRD. The effect of Organification degree of rectorite on water absorbency of CTS-g-PAA/OREC with different organo-rectorite content was investigated. The swelling behaviors in distilled water and various pH solutions were also studied. The results from IR spectroscopy and XRD data show that acrylic acid had been grafted polymerization with chitosan and organo-rectorite and formed nanocomposite. Introducing organo-rectorite into the CTS-g-PAA polymeric network can improved water absorbency and swelling rate of CTS-g-PAA/OREC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Hennie Bikker - One of the best experts on this subject based on the ideXlab platform.
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The Journal of Clinical Endocrinology & Metabolism Printed in U.S.A. Copyright © 2000 by The Endocrine Society Two Decades of Screening for Congenital Hypothyroidism in the Netherlands: TPO Gene Mutations in Total Iodide Organification Defects (an Update)
2013Co-Authors: Bert Bakker, Thomas Vulsma, Hennie Bikker, Janine S E De Randamie, Brenda M Wiedijk, Jan J M De VijlderAbstract:Presented is a cohort study to assess the nature and frequency of thyroid peroxidase (TPO) mutations in 45 patients (35 families) with congenital hypothyroidism due to a total iodide Organification defect; incidence is 1:66,000 in The Netherlands. The presentation is consistently similar with a severe form of congenital hypothyroidism and also characterized by a complete and immediate release of accumulated radioiodide from the thyroid after sodium perchlorate administration. Sixteen different mutations were found, including eight novel mutations; the majority occurs in exons 8, 9, or 10. The GGCC insertion in exon 8 at nucleotide 1277, leading to an early termination signa
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genetics and phenomics of hypothyroidism and goiter due to tpo mutations
Molecular and Cellular Endocrinology, 2010Co-Authors: Carrie Risstalpers, Hennie BikkerAbstract:Abstract Thyroid peroxidase (TPO) is a heme binding protein localized on the apical membrane of the thyrocyte. TPO enzymatic activity is essential for thyroid hormonogenesis. Inactivating mutations form the molecular basis for a specific subtype of congenital hypothyroidism: thyroid dyshormonogenesis due to an iodide Organification defect. The most common phenotype of this autosomal recessive disease is a total iodide Organification defect, with severe and permanent hypothyroidism as a consequence. Currently 61 properly annotated mutations in the TPO gene have been reported, of which the majority are missense mutations. Functional data of most missense mutations is not available, making it necessary to revert to in silico methods for functional interpretation of mutations. We hypothesize that iodine status is the main phenomic modifier of TPO function.
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inactivating mutations in the gene for thyroid oxidase 2 thox2 and congenital hypothyroidism
The New England Journal of Medicine, 2002Co-Authors: Jose C Moreno, Jan J M De Vijlder, Thomas Vulsma, Hennie Bikker, Frank Baas, Marlies Kempers, A Paul S Van Trotsenburg, Carrie RisstalpersAbstract:Background Several genetic defects are associated with permanent congenital hypothyroidism. Immunologic, environmental, and iatrogenic (but not genetic) factors are known to induce transient congenital hypothyroidism, which spontaneously resolves within the first months of life. We hypothesized that molecular defects in the thyroid oxidase system, which is composed of at least two proteins, might be involved in the pathogenesis of permanent or transient congenital hypothyroidism in babies with defects in iodide Organification, for which the oxidase system is required. Methods Nine patients were recruited who had idiopathic congenital hypothyroidism (one with permanent and eight with transient hypothyroidism) and an iodide-Organification defect and who had been identified by the screening program for congenital hypothyroidism. The DNA of the patients and their relatives was analyzed for mutations in the genes for thyroid oxidase 1 (THOX1 ) and 2 (THOX2 ). Results The one patient with permanent and severe t...
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maternal isodisomy for chromosome 2p causing severe congenital hypothyroidism
The Journal of Clinical Endocrinology and Metabolism, 2001Co-Authors: Bert H Bakker, Ed J P Lommen, Mariette G J Schipper, Thomas Vulsma, Raoul C M Hennekam, Hennie Bikker, Jan J M De VijlderAbstract:Severe congenital hypothyroidism (CH) due to a total iodide Organification defect (TIOD) is usually due to mutations in the thyroid peroxidase (TPO) gene located at chromosome 2p25. A homozygous deletion[Δ T2512 (codon 808)] in exon 14 was identified in a patient with classical TIOD. The transmission pattern of the TPO gene in this family was anomalous; the mother was heterozygous for the deletion; and the mutation was absent in the father. Polymorphic short tandem repeat (STR) markers confirmed paternity and demonstrated on chromosome 2 that the propositus was homozygous for most markers on chromosome 2p and that these were identical to one of the maternal 2p homologs. A normal karyotype was found in the propositus, his parents and sister. We conclude that the homozygosity in the patient is due to partial maternal isodisomy of the short arm of chromosome 2, carrying a defective TPO gene. The patient, born small for gestational age, develops and grows well and appears healthy (while being treated with thy...
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two decades of screening for congenital hypothyroidism in the netherlands tpo gene mutations in total iodide Organification defects an update
The Journal of Clinical Endocrinology and Metabolism, 2000Co-Authors: Bert N Bakker, Thomas Vulsma, Hennie Bikker, Janine S E De Randamie, Brenda M Wiedijk, Jan J M De VijlderAbstract:Presented is a cohort study to assess the nature and frequency of thyroid peroxidase (TPO) mutations in 45 patients (35 families) with congenital hypothyroidism due to a total iodide Organification defect; incidence is 1:66,000 in The Netherlands. The presentation is consistently similar with a severe form of congenital hypothyroidism and also characterized by a complete and immediate release of accumulated radioiodide from the thyroid after sodium perchlorate administration. Sixteen different mutations were found, including eight novel mutations; the majority occurs in exons 8, 9, or 10. The GGCC insertion in exon 8 at nucleotide 1277, leading to an early termination signal in exon 9, is the most frequently occurring mutation. These mutations were detected in 29 families in both TPO alleles (13 homozygous and 16 compound heterozygous). In one family, partial maternal isodisomy of 2p was detected, in four families only one mutated TPO allele could be detected, and in one family no inactivating TPO mutation could be found. Because all patients clearly had the clinicopathologic features of a total iodide Organification defect, we conclude that in these five families the mutations in the (other) alleles could be either located in the intronic sequences or in the promoter region. Mutations in the TPO gene result in total iodide Organification defects.
Lewis E Braverman - One of the best experts on this subject based on the ideXlab platform.
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EXPERIMENTAL STUDY Regulation of the sodium iodide symporter by iodide in FRTL-5 cells
2014Co-Authors: Peter H K Eng, Guemalli R Cardona, Michael C Previti, William W Chin, Lewis E BravermanAbstract:Objective: The acute decrease in iodide Organification in the thyroid in response to excess iodide is termed the acute Wolff–Chaikoff effect and normal Organification resumes in spite of continued high plasma iodide concentrations (escape from the acute Wolff–Chaikoff effect). We have recently reported that large doses of iodide given to rats chronically decrease the sodium/iodide symporter (NIS) mRNA and protein, suggesting that escape is due to a decrease in NIS and subsequent iodide transport. We have now studied the effect of excess iodide on NIS in FRTL-5 cells to further explore the mechanisms whereby excess iodide decreases NIS. Design: FRTL-5 cells were employed and were incubated in the presence or absence of various concentrations of iodide. NIS mRNA and protein and the turnover of NIS were assessed. Methods: NIS mRNA was measured by Northern analysis, NIS protein by Western analysis and NIS turnover by pulse–chase labeling experiments. Results: Iodide (1023 mol/l) had no effect on NIS mRNA in FRTL-5 cells at 24 and 48 h compared with cells cultured in the absence of iodide. However, excess iodide decreased NIS protein by 50 % of control values at 24 h and by 70 % at 48 h. This effect of iodide was dose dependent. Pulse–chas
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Printed in U.S.A. Copyright © 1999 by The Endocrine Society Escape from the Acute Wolff-Chaikoff Effect Is Associated with a Decrease in Thyroid Sodium/Iodide Symporter Messenger Ribonucleic Acid and Protein*
2013Co-Authors: Peter H K Eng, Guemalli R Cardona, William W Chin, Shihlieh Fang, Michael Previti, Sharon Alex, Nancy Carrasco, Lewis E BravermanAbstract:In 1948, Wolff and Chaikoff reported that organic binding of iodide in the thyroid was decreased when plasma iodide levels were elevated (acute Wolff-Chaikoff effect), and that adaptation or escape from the acute effect occurred in approximately 2 days, in the presence of continued high plasma iodide concentrations. We later demonstrated that the escape is attributable to a decrease in iodide transport into the thyroid, lowering the intrathyroidal iodine content below a critical inhibitory threshold and allowing Organification of iodide to resume. We have now measured the rat thyroid sodium/iodide symporter (NIS) messenger RNA (mRNA) and protein levels, in response to both chronic and acute iodide excess, in an attempt to determine the mechanism responsible for the decreased iodide transport. Rats were given 0.05 % NaI in their drinking water for 1 and 6 days in the chronic experiments, and a single 2000-�g dose of NaI ip in the acute experiments
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escape from the acute wolff chaikoff effect is associated with a decrease in thyroid sodium iodide symporter messenger ribonucleic acid and protein
Endocrinology, 1999Co-Authors: Peter H K Eng, Guemalli R Cardona, William W Chin, Shihlieh Fang, Michael Previti, Sharon Alex, Nancy Carrasco, Lewis E BravermanAbstract:In 1948, Wolff and Chaikoff reported that organic binding of iodide in the thyroid was decreased when plasma iodide levels were elevated (acute Wolff-Chaikoff effect), and that adaptation or escape from the acute effect occurred in approximately 2 days, in the presence of continued high plasma iodide concentrations. We later demonstrated that the escape is attributable to a decrease in iodide transport into the thyroid, lowering the intrathyroidal iodine content below a critical inhibitory threshold and allowing Organification of iodide to resume. We have now measured the rat thyroid sodium/iodide symporter (NIS) messenger RNA (mRNA) and protein levels, in response to both chronic and acute iodide excess, in an attempt to determine the mechanism responsible for the decreased iodide transport. Rats were given 0.05% NaI in their drinking water for 1 and 6 days in the chronic experiments, and a single 2000-μg dose of NaI ip in the acute experiments. Serum was collected for iodine and hormone measurements, an...
Samuel Refetoff - One of the best experts on this subject based on the ideXlab platform.
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mice deficient in dual oxidase maturation factors are severely hypothyroid
Molecular Endocrinology, 2012Co-Authors: Helmut Grasberger, Xavier De Deken, Olga Barca Mayo, Houssam Raad, Mia Weiss, Xiao Hui Liao, Samuel RefetoffAbstract:Dual oxidases (DUOX1 and DUOX2) are evolutionary conserved reduced nicotinamide adenine dinucleotide phosphate oxidases responsible for regulated hydrogen peroxide (H(2)O(2)) release of epithelial cells. Specific maturation factors (DUOXA1 and DUOXA2) are required for targeting of functional DUOX enzymes to the cell surface. Mutations in the single-copy Duox and Duoxa genes of invertebrates cause developmental defects with reduced survival, whereas knockdown in later life impairs intestinal epithelial immune homeostasis. In humans, mutations in both DUOX2 and DUOXA2 can cause congenital hypothyroidism with partial iodide Organification defects compatible with a role of DUOX2-generated H(2)O(2) in driving thyroid peroxidase activity. The DUOX1/DUOXA1 system may account for residual iodide Organification in patients with loss of DUOX2, but its physiological function is less clear. To provide a murine model recapitulating complete DUOX deficiency, we simultaneously targeted both Duoxa genes by homologous recombination. Knockout of Duoxa genes (Duoxa(-/-) mice) led to a maturation defect of DUOX proteins lacking Golgi processing of N-glycans and to loss of H(2)O(2) release from thyroid tissue. Postnatally, Duoxa(-/-) mice developed severe goitreous congenital hypothyroidism with undetectable serum T4 and maximally disinhibited TSH levels. Heterozygous mice had normal thyroid function parameters. (125)I uptake and discharge studies and probing of iodinated TG epitopes corroborated the iodide Organification defect in Duoxa(-/-) mice. Duoxa(-/-) mice on continuous T4 replacement from P6 showed normal growth without an overt phenotype. Our results confirm in vivo the requirement of DUOXA for functional expression of DUOX-based reduced nicotinamide adenine dinucleotide phosphate oxidases and the role of DUOX isoenzymes as sole source of hormonogenic H(2)O(2).
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biallelic inactivation of the dual oxidase maturation factor 2 duoxa2 gene as a novel cause of congenital hypothyroidism
The Journal of Clinical Endocrinology and Metabolism, 2008Co-Authors: I Zamproni, Helmut Grasberger, Francesca Cortinovis, Maria Cristina Vigone, G Chiumello, Stefano Mora, Kazumichi Onigata, Laura Fugazzola, Samuel Refetoff, Luca PersaniAbstract:Context: Dual oxidase 2 (DUOX2) is the catalytic core of the H2O2 generator crucial for the iodination of thyroglobulin in thyroid hormone synthesis. DUOX2 deficiency produces congenital hypothyroidism (CH) in humans and mice. We recently cloned a novel gene, the product of which (dual oxidase maturation factor 2; DUOXA2) is required to express DUOX2 enzymatic activity. Objective: Our objective was to identify DUOXA2 mutations as a novel cause of CH due to dyshormonogenesis. Patients: Subjects included 11 CH patients with partial iodine Organification defect but negative for other known genetic causes of partial iodine Organification defect. Results: One Chinese patient born to nonconsanguineous parents was homozygous for a nonsense mutation (p.Y246X), producing a truncated DUOXA2 protein lacking transmembrane helix 5 and the C-terminal cytoplasmic domain. The mutant protein was inactive in reconstituting DUOX2 in vitro. Pedigree analysis demonstrated recessive inheritance, because heterozygous carriers h...
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Biallelic inactivation of the dual oxidase maturation factor 2 (DUOXA2) gene as a novel cause of congenital hypothyroidism
'The Endocrine Society', 2008Co-Authors: I Zamproni, Helmut Grasberger, Francesca Cortinovis, Maria Cristina Vigone, G Chiumello, Stefano Mora, Kazumichi Onigata, Laura Fugazzola, Samuel Refetoff, Luca PersaniAbstract:Context: Dual oxidase 2 (DUOX2) is the catalytic core of the H 2O2 generator crucial for the iodination of thyroglobulin in thyroid hormone synthesis. DUOX2 deficiency produces congenital hypothyroidism (CH) in humans and mice. We recently cloned a novel gene, the product of which (dual oxidase maturation factor 2; DUOXA2) is required to express DUOX2 enzymatic activity. Objective: Our objective was to identify DUOXA2 mutations as a novel cause of CH due to dyshormonogenesis. Patients: Subjects included 11 CH patients with partial iodine Organification defect but negative for other known genetic causes of partial iodine Organification defect. Results: One Chinese patient born to nonconsanguineous parents was homozygous for a nonsense mutation (p.Y246X), producing a truncated DUOXA2 protein lacking transmembrane helix 5 and the C-terminal cytoplasmic domain. The mutant protein was inactive in reconstituting DUOX2 in vitro. Pedigree analysis demonstrated recessive inheritance, because heterozygous carriers had normal thyroid function including negative results in neonatal TSH screening. One heterozygous carrier of Y246X was identified in unrelated Chinese controls (n = 92) but not in Caucasian or Japanese controls, indicating that homozygosity for Y246X could be a frequent cause of CH in Chinese. Functional studies suggest that the DUOXA2 paralog (DUOXA1) can partially compensate DUOXA2 deficiency, consistent with the proband having a milder CH phenotype than patients with biallelic DUOX2 nonsense mutations. Conclusions: We report the first mutation in DUOXA2, identified in a patient with CH and dyshormonogenic goiter. Results of our studies provide evidence for the critical role of DUOXA2 in thyroid hormonogenesis. Biallelic DUOXA2 mutations are a novel genetic event in permanent CH. Copyrigh
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a familial thyrotropin tsh receptor mutation provides in vivo evidence that the inositol phosphates ca2 cascade mediates tsh action on thyroid hormone synthesis
The Journal of Clinical Endocrinology and Metabolism, 2007Co-Authors: Helmut Grasberger, Yardena Tenenbaumrakover, Jacqueline Van Sande, Ahmad Hagdahood Mahameed, Samuel RefetoffAbstract:Context: In the human thyroid gland, TSH activates both the cAMP and inositol phosphates (IP) signaling cascades via binding to the TSH receptor (TSHR). Biallelic TSHR loss-of-function mutations cause resistance to TSH, clinically characterized by hyperthyrotropinemia, and normal or reduced thyroid gland volume, thyroid hormone output, and iodine uptake. Objective: We report and study a novel familial TSHR mutation (L653V). Results: Homozygous individuals expressing L653V had euthyroid hyperthyrotropinemia. Paradoxically, patients had significantly higher 2-h radioiodide uptake and 2- to 24-h radioiodide uptake ratios compared with heterozygous, unaffected family members, suggesting an imbalance between iodide trapping and Organification. In transfected COS-7 cells, the mutant TSHR had normal surface expression, basal activity, and TSH-binding affinity, equally (2.2-fold) increased EC50 values for TSH-induced cAMP and IP accumulation, and normal maximum cAMP generation. In contrast, the efficacy of TSH fo...
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two different mutations in the thyroid peroxidase gene of a large inbred amish kindred power and limits of homozygosity mapping
The Journal of Clinical Endocrinology and Metabolism, 1999Co-Authors: Silvana Pannain, Roy E Weiss, Charles E Jackson, Donald Dian, John S Beck, Val C Sheffield, Nancy J Cox, Samuel RefetoffAbstract:Approximately 10% of newborns with congenital hypothyroidism are unable to convert iodide into organic iodine. This iodide Organification defect has a prevalence of 1 in 40,000 newborns and may be caused by defects in the thyroid peroxidase enzyme (TPO), the hydrogen peroxide-generating system, the TPO substrate thyroglobulin, or inhibitors of TPO. We identified a high incidence of severe hypothyroidism due to a complete iodide Organification defect in the youngest generation of five nuclear families belonging to an inbred Amish kindred. Genealogical records permitted us to trace their origin to an ancestral couple 7-8 generations back and to identify an autosomal recessive pattern of inheritance. Initial studies of homozygosity by descent using two polymorphic markers within the TPO gene showed no linkage to the phenotype. In fact, 4 of 15 affected siblings from 2 of the nuclear families were heterozygous, resulting in homozygosity values of 73% and 53% in affected and unaffected family members, respectively. A genome-wide homozygosity screen using DNA pools from affected and unaffected family members localized the defect to a locus close to the TPO gene. Linkage analysis using 4 additional polymorphic markers within the TPO gene reduced the number of homozygous unaffected siblings to zero without altering the percent homozygosity initially found in the affected. Sequencing of the TPO gene revealed 2 missense mutations, E799K and R648Q. TPO 779K was found in both alleles of the 11 affected homozygotes, both mutations were present in each of the 3 affected compound heterozygotes, and there were no TPO mutations in 1 subject with hypothyroidism of different etiology. These results demonstrate the power of the DNA pooling strategy in the localization of a defective gene and the pitfalls of linkage analysis when 2 relatively rare mutations coexist in an inbred population.