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Tamao Endo - One of the best experts on this subject based on the ideXlab platform.
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Molecular Characterization of Protein O-linked Mannose β-1,2-N-acetylglucosaminyltransferase 1 in Zebrafish
Journal of Glycomics & Lipidomics, 2014Co-Authors: Yutaka Tamaru, Tamao Endo, Hiroshi Manya, Eriko Avarban Ban, Shinichi AkiyamaAbstract:Muscular dystrophies are genetic diseases characterized by progressive muscle degeneration and muscular weakening. Defects in glycosylation of α-dystroglycan are responsible for certain congenital muscular dystrophies to be called α-dystroglycanopathies. The structure of glycans in α-dystroglycan is Siaα2-3Galβ1-4GlcNAcβ1- 2Manα1-Ser/Thr and required for binding basal lamina proteins. The first step of O-mannosyl glycan synthesis on α-dystroglycan is catalyzed by protein O-mannosyltransferases (POMT1 and POMT2), and detect in POMT1 or POMT2 result in Walker-Warburg syndrome one of the α-dystroglycanopathies. Next step is catalyzed by O-mannose β-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) and it is responsible for muscle-eye-brain disease. We have previously reported that protein O-mannosylation is necessary for normal embryonic development in zebrafish and revealed that zebrafish is a useful model for α-dystroglycanopathies. In this study, we focused on zebrafish POMGnT1. Zebrafish POMGnT1 revealed high level of expression in ovary and ubiquitously throughout early developmental stage as well as zebrafish POMT1 and POMT2. Morpholino experiments of zebrafish POMGnT1 in juvenile zebrafish showed several phenotypes of bended body, small eyes and edematous pericardium. More importantly, morpholino-injected zebrafish had reduction of the reactivity to the monoclonal antibody IIH6 that recognizes a glycosylated α-dystroglycan. Furthermore, phenotypes observed by knockdown of zebrafish POMGnT1 were similar to zebrafish POMT2 rather than zebrafish POMT1. Finally, in order to measure POMGnT1 activity, we cloned and expressed zebrafish POMGnT1 in human embryonic kidney 293T cells. As a result, zebrafish POMGnT1 had the enzymatic activity to transfer GlcNAc from UDP-GlcNAc to O-mannosyl peptide, indicating that O-mannosylation pathway of α-dystroglycan is conserved in zebrafish.
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Different roles of the two components of human protein O-mannosyltransferase, POMT1 and POMT2
Biochemical and biophysical research communications, 2011Co-Authors: Keiko Akasaka-manya, Hiroshi Manya, Masami Hayashi, Tamao EndoAbstract:Protein O-mannosyltransferase 1 (POMT1) and its homolog, POMT2, are responsible for the catalysis of the first step in O-mannosyl glycan synthesis. Mutations in their genes are associated with a type of congenital muscular dystrophy called Walker-Warburg syndrome. Arg(64), Glu(78) and Arg(138) in the N-terminus region of ScPmt1p, a POMT homolog in Saccharomyces cerevisiae, are important for transferase activity. Arg(138) is also essential for complex formation with ScPmt2p. Here we examined the effects of replacing the corresponding residues in human POMT1 and POMT2 with Ala on complex formation and enzymatic activity. The human POMT1 mutants lost almost all transferase activity while the POMT2 mutants retained enzymatic activity. Neither mutant lost its ability to form complexes with the native counter component. These results indicate that ScPmtps and human POMTs have different mechanisms of complex formation. They also suggest that human POMT1 and POMT2 have discrete functions since the effect of amino acid substitutions on enzymatic activity are different.
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POMGnT1, POMT1, and POMT2 Mutations in Congenital Muscular Dystrophies
Methods in enzymology, 2010Co-Authors: Tamao Endo, Hiroshi Manya, Nathalie Seta, Pascale GuicheneyAbstract:Abstract α-Dystroglycanopathies are a group of rare inherited neuromuscular disorders characterized by reduced glycosylation of α-dystroglycan (α-DG). Mutations in six genes (POMT1, POMT2, POMGNT1, FKTN, FKRP, and LARGE) have been identified in patients with α-dystroglycanopathies. Due to an extremely broad clinical spectrum and relatively poor phenotype–genotype correlation, diagnosis of α-dystroglycanopathies is difficult and requires searching for mutations gene by gene. At present, of the six proteins involved on α-dystroglycanopathies, the function of the gene products is only known for POMT1, POMT2, and POMGnT1, all responsible for the O-mannosylglycan biosynthesis. This chapter describes the assay protocols to diagnose patients with α-dystroglycanopathy by measuring glycosyltransferase activity.
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Role of N-glycans in maintaining the activity of protein O-mannosyltransferases POMT1 and POMT2
Journal of biochemistry, 2009Co-Authors: Hiroshi Manya, Keiko Akasaka-manya, Ai Nakajima, Masao Kawakita, Tamao EndoAbstract:The complex of protein O-mannosyltransferase 1 (POMT1) and POMT2 catalyzes the initial step of O-mannosyl glycan biosynthesis. The mutations in either POMT1 or POMT2 can lead to Walker-Warburg syndrome, a congenital muscular dystrophy with abnormal neuronal migration. Here, we used three algorithms for predicting transmembrane helices to construct the secondary structural models of human POMT1 and POMT2. In these models, POMT1 and POMT2 have seven- and nine-transmembrane helices and contain four and five potential N-glycosylation sites, respectively. To determine whether these sites are actually glycosylated, we prepared mutant proteins that were defective in each site by site-directed mutagenesis. Three of the POMT1 sites and all of the POMT2 sites were found to be N-glycosylated, suggesting that these sites face the luminal side of the endoplasmic reticulum. Mutation of any single site did not significantly affect POMT activity, but mutations of all N-glycosylation sites of either POMT1 or POMT2 caused a loss of POMT activity. The loss of activity appeared to be due to the decreased hydrophilicity. These results suggest that the N-glycosylation of POMT1 and POMT2 is required for maintaining the conformation as well as the activity of the POMT1-POMT2 complex.
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POMT2 intragenic deletions and splicing abnormalities causing congenital muscular dystrophy with mental retardation.
European Journal of Medical Genetics, 2009Co-Authors: Akiko Yanagisawa, Sandrine Vuillaumier-barrot, Céline Bouchet, Norma Romero, Susana Quijano-roy, Nigel Clarke, Sylvie Odent, Diana Rodriguez, Makiko Osawa, Tamao EndoAbstract:BACKGROUND: Alpha-dystroglycanopathies are a group of congenital muscular dystrophies (CMDs) with autosomal recessive inheritance characterized by abnormal glycosylation of alpha-dystroglycan. Although six genetic causes have been identified (FKTN, POMGNT1, POMT1, POMT2, FKRP, and LARGE) many alpha-dystroglycanopathy patients remain without a genetic diagnosis after standard exon sequencing. To date POMT2 mutations have been identified in CMD cases with a wide range of clinical severities from Walker-Warburg syndrome to limb girdle muscular dystrophy without structural brain or ocular involvement. METHODS: We analyzed POMT2 in six CMD patients, who had severe diffuse muscle weakness, generalized joint contractures, microcephaly, severe mental retardation and elevated CK levels. Eye involvement was absent or limited to myopia or strabismus. We sequenced the coding regions of POMT2 using genomic DNA and cDNA generated from blood lymphocytes or B lymphoblastoid cell lines. Quantitative PCR analysis of genomic DNA was used to identify and determine the breakpoints of large deletions. RESULTS: We report five novel mutations in POMT2, four of which were outside of coding exons, two large genomic deletions and two intronic single base substitutions that induced aberrant mRNA splicing. CONCLUSIONS: Large scale DNA rearrangements (such as large deletions) and cryptic splice mutations, that can be missed on standard sequencing of genomic DNA, may be relatively common in POMT2. Additional techniques, such as sequencing of cDNA are needed to identify all mutations. These results also confirm that POMT2 mutations are an important cause of the less severe alpha-dystroglycanopathy phenotypes.
Tobias Willer - One of the best experts on this subject based on the ideXlab platform.
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a novel missense mutation in POMT1 modulates the severe congenital muscular dystrophy phenotype associated with POMT1 nonsense mutations
Neuromuscular Disorders, 2014Co-Authors: Tobias Willer, Thomas L. Winder, S E Wallace, Jessie H Conta, Jamie M Eskuri, Richard H Haas, Kathleen Patterson, Kevin P. CampbellAbstract:Abstract Mutations in POMT1 lead to a group of neuromuscular conditions ranging in severity from Walker–Warburg syndrome to limb girdle muscular dystrophy. We report two male siblings, ages 19 and 14, and an unrelated 6-year old female with early onset muscular dystrophy and intellectual disability with minimal structural brain anomalies and no ocular abnormalities. Compound heterozygous mutations in POMT1 were identified including a previously reported nonsense mutation (c.2167dupG; p.Asp723Glyfs*8) associated with Walker–Warburg syndrome and a novel missense mutation in a highly conserved region of the protein O-mannosyltransferase 1 protein (c.1958C>T; p.Pro653Leu). This novel variant reduces the phenotypic severity compared to patients with homozygous c.2167dupG mutations or compound heterozygous patients with a c.2167dupG mutation and a wide range of other mutant POMT1 alleles.
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Correlation of enzyme activity and clinical phenotype in POMT1-associated dystroglycanopathies
Neurology, 2010Co-Authors: Mark Lommel, Tobias Willer, Gökhan Uyanik, Sebahattin Cirak, R. Hermann, J.h.l.m. Van Bokhoven, C. Korner, T. Voit, Ivo Barić, Ute HehrAbstract:Background: Mutations in protein O-mannosyltransferases ( POMTs ) cause a heterogeneous group of muscular dystrophies with abnormal glycosylation of α-dystroglycan (dystroglycanopathies). The wide spectrum of clinical severities ranges from Walker-Warburg syndrome (WWS), associated with brain and eye abnormalities, to mild forms of limb girdle muscular dystrophy (LGMD). Objective: The aim of this study was to elucidate the impact of mutations in POMT1 on the clinical phenotype. Methods: We examined 2 patients with POMT1 -associated α-dystroglycanopathy, 1 displaying a LGMD2K and 1 with a WWS phenotype. Using dermal fibroblasts, we analyzed the influence of the POMT1 mutations on the glycosylation status of α-dystroglycan, protein O-mannosyltransferase activity, and the stability of the mutant POMT1 protein. Results: We report on novel compound heterozygous mutations in POMT1 (p.L171A and p.A589VfsX38) that result in LGMD2K. We further demonstrate that a homozygous splice site mutation of a recently identified WWS patient results in POMT1 p.del77-93. Using dermal fibroblasts, we show that mannosyltransferase activity is reduced in the patients and that stability of POMT1 mutant proteins p.A589VfsX38 and p.del77-93 is significantly decreased. Conclusions: Our results suggest that dermal fibroblasts can be applied to facilitate the diagnostic analysis of dystroglycanopathy patients as well as to study the pathogenic mechanism of POMT mutations. Characterization of the POMT1 substrate protein α-dystroglycan and POMT in vitro mannosyltransferase activity shows that the severity of the clinical phenotype of the patients analyzed is inversely correlated with POMT activity.
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POMT1 is essential for protein O-mannosylation in mammals.
Methods in enzymology, 2010Co-Authors: Mark Lommel, Tobias Willer, Jesús Cruces, Sabine StrahlAbstract:Abstract Over the past decade it has emerged that O -mannosyl glycans are not restricted to yeast and fungi but are also present in higher eukaryotes up to humans. In mammals, the protein O -mannosyltransferases POMT1 and POMT2 act as a heteromeric complex to initiate O -mannosylation in the endoplasmic reticulum. In humans, mutations in POMT1 and POMT2 result in hypoglycosylation of α-dystroglycan (α-DG) thereby abolishing its binding to extracellular matrix ligands such as laminin. As a consequence, POMT mutations cause a heterogeneous group of severe recessive congenital muscular dystrophies in humans. However, little is known about the function of O -mannosyl glycans in mammals apart from its crucial role for the ligand binding abilities of α-DG. In this chapter we discuss the methods used to analyze the expression of POMT1 in adult mouse organs and during embryo development. Further, we describe the generation and immunohistochemical analysis of POMT1 knockout mice.
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Brain and Eye Malformations Resembling Walker–Warburg Syndrome Are Recapitulated in Mice by Dystroglycan Deletion in the Epiblast
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2008Co-Authors: Jakob S. Satz, Tobias Willer, Rita Barresi, Madeleine Durbeej, Amy Turner, Steven A. Moore, Kevin P. CampbellAbstract:Walker–Warburg syndrome (WWS) is a severe congenital disease that is characterized by brain and eye malformations and lethality during the first year of life. Genetic mutations have been identified in a subset of WWS patients, but a majority of clinical cases have unknown etiologies. POMT1 and POMT2, two of the causative genes, form an active enzyme complex in the posttranslational biosynthetic pathway of dystroglycan. Deletion of either POMT1 or the dystroglycan gene causes early embryonic lethality in mice. Here we report that mice with epiblast-specific loss of dystroglycan develop brain and eye defects that broadly resemble the clinical spectrum of the human disease, including aberrant neuron migration, hydrocephalus, and malformations of the anterior and posterior chambers of the eye. Breaches of basement membranes coincide with the pathology, revealing an important function for dystroglycan in the morphogenesis of the brain and eye. These findings demonstrate the central role of dystroglycan in WWS and suggest that novel defects in posttranslational processing or mutations of the dystroglycan gene itself may underlie cases in which no causative mutation has been found.
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pomt2 a key enzyme in walker warburg syndrome somatic spomt2 but not testis specific tpomt2 is crucial for mannosyltransferase activity in vivo
Glycobiology, 2008Co-Authors: Mark Lommel, Tobias Willer, Sabine StrahlAbstract:O-Mannosylation represents an evolutionarily conserved, essential protein modification. In mammals the protein O-mannosyltransferases POMT1 and POMT2 act as a heteromeric complex to initiate O-mannosylation in the endoplasmic reticulum. Mutations in human POMT1 and POMT2 cause a group of congenital muscular dystrophies due to reduced O-glycosylation of α-dystroglycan. The most severe of these autosomal recessive conditions is Walker-Warburg syndrome (WWS) with severe brain and ocular involvement. We previously showed in the murine model that POMT1 is expressed in WWS-related tissues both during embryogenesis and in adults. Whereas there is only a single POMT1 transcript in adult mice, we demonstrated that there are two Pomt2 transcripts, somatic sPomt2 and testis-specific tPomt2. In this study we demonstrate that sPomt2, but not tPomt2, is prominently expressed in mouse embryos in the tissues that are most severely affected in WWS (developing muscle, eye, and brain). Correlation of POMT transcripts and protein isoforms with POMT mannosyltransferase enzyme activity demonstrates that sPOMT2-POMT1 complexes catalyze mannosyltransfer in adult somatic tissues and testis. It is suggested that the gonadal defects described in some WWS cases are associated with defects in O-mannosylation. Our data further show that whereas sPOMT2 is widely expressed, tPOMT2 is restricted to the acrosome of male germ cells and is not involved in the biosynthesis of O-mannosyl glycans in vivo. We prove that tPOMT2 is highly conserved among mammals, including humans, suggesting a crucial function that is distinct from sPOMT2.
Hiroshi Manya - One of the best experts on this subject based on the ideXlab platform.
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Analysis of phenotype, enzyme activity and genotype of Chinese patients with POMT1 mutation.
Journal of human genetics, 2016Co-Authors: Haipo Yang, Hiroshi Manya, Kazuhiro Kobayashi, Hui Jiao, Jiangxi Xiao, Jingmin Wang, Yuwu Jiang, Tatsushi TodaAbstract:Protein O-mannosyltransferase 1 (POMT1) is a glycosyltransferase involved in α-dystroglycan glycosylation. POMT1 mutations cause a wide spectrum of clinical conditions from Walker-Warburg syndrome (WWS), which involves muscle, eye and brain abnormalities, to mild forms of limb-girdle muscular dystrophy with mental retardation. We aimed to elucidate the impact of different POMT1 mutations on the clinical phenotype. We report five Chinese patients with POMT1 mutations: one had a typical clinical manifestation of WWS, and the other four were diagnosed with congenital muscular dystrophy with mental retardation of varying severity. We analyzed the influence of the POMT1 mutations on POMT activity by assaying the patients' muscles and cultured skin fibroblasts. We demonstrated different levels of decreased POMT activity that correlated highly with decreased α-dystroglycan glycosylation. Our results suggest that POMT activity is inversely proportional to clinical severity, and demonstrate that skin fibroblasts can be used for differential diagnosis of patients with α-dystroglycanopathies. We have provided clinical, histological, enzymatic and genetic evidence of POMT1 involvement in five unrelated Chinese patients.
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Molecular Characterization of Protein O-linked Mannose β-1,2-N-acetylglucosaminyltransferase 1 in Zebrafish
Journal of Glycomics & Lipidomics, 2014Co-Authors: Yutaka Tamaru, Tamao Endo, Hiroshi Manya, Eriko Avarban Ban, Shinichi AkiyamaAbstract:Muscular dystrophies are genetic diseases characterized by progressive muscle degeneration and muscular weakening. Defects in glycosylation of α-dystroglycan are responsible for certain congenital muscular dystrophies to be called α-dystroglycanopathies. The structure of glycans in α-dystroglycan is Siaα2-3Galβ1-4GlcNAcβ1- 2Manα1-Ser/Thr and required for binding basal lamina proteins. The first step of O-mannosyl glycan synthesis on α-dystroglycan is catalyzed by protein O-mannosyltransferases (POMT1 and POMT2), and detect in POMT1 or POMT2 result in Walker-Warburg syndrome one of the α-dystroglycanopathies. Next step is catalyzed by O-mannose β-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) and it is responsible for muscle-eye-brain disease. We have previously reported that protein O-mannosylation is necessary for normal embryonic development in zebrafish and revealed that zebrafish is a useful model for α-dystroglycanopathies. In this study, we focused on zebrafish POMGnT1. Zebrafish POMGnT1 revealed high level of expression in ovary and ubiquitously throughout early developmental stage as well as zebrafish POMT1 and POMT2. Morpholino experiments of zebrafish POMGnT1 in juvenile zebrafish showed several phenotypes of bended body, small eyes and edematous pericardium. More importantly, morpholino-injected zebrafish had reduction of the reactivity to the monoclonal antibody IIH6 that recognizes a glycosylated α-dystroglycan. Furthermore, phenotypes observed by knockdown of zebrafish POMGnT1 were similar to zebrafish POMT2 rather than zebrafish POMT1. Finally, in order to measure POMGnT1 activity, we cloned and expressed zebrafish POMGnT1 in human embryonic kidney 293T cells. As a result, zebrafish POMGnT1 had the enzymatic activity to transfer GlcNAc from UDP-GlcNAc to O-mannosyl peptide, indicating that O-mannosylation pathway of α-dystroglycan is conserved in zebrafish.
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Different roles of the two components of human protein O-mannosyltransferase, POMT1 and POMT2
Biochemical and biophysical research communications, 2011Co-Authors: Keiko Akasaka-manya, Hiroshi Manya, Masami Hayashi, Tamao EndoAbstract:Protein O-mannosyltransferase 1 (POMT1) and its homolog, POMT2, are responsible for the catalysis of the first step in O-mannosyl glycan synthesis. Mutations in their genes are associated with a type of congenital muscular dystrophy called Walker-Warburg syndrome. Arg(64), Glu(78) and Arg(138) in the N-terminus region of ScPmt1p, a POMT homolog in Saccharomyces cerevisiae, are important for transferase activity. Arg(138) is also essential for complex formation with ScPmt2p. Here we examined the effects of replacing the corresponding residues in human POMT1 and POMT2 with Ala on complex formation and enzymatic activity. The human POMT1 mutants lost almost all transferase activity while the POMT2 mutants retained enzymatic activity. Neither mutant lost its ability to form complexes with the native counter component. These results indicate that ScPmtps and human POMTs have different mechanisms of complex formation. They also suggest that human POMT1 and POMT2 have discrete functions since the effect of amino acid substitutions on enzymatic activity are different.
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POMGnT1, POMT1, and POMT2 Mutations in Congenital Muscular Dystrophies
Methods in enzymology, 2010Co-Authors: Tamao Endo, Hiroshi Manya, Nathalie Seta, Pascale GuicheneyAbstract:Abstract α-Dystroglycanopathies are a group of rare inherited neuromuscular disorders characterized by reduced glycosylation of α-dystroglycan (α-DG). Mutations in six genes (POMT1, POMT2, POMGNT1, FKTN, FKRP, and LARGE) have been identified in patients with α-dystroglycanopathies. Due to an extremely broad clinical spectrum and relatively poor phenotype–genotype correlation, diagnosis of α-dystroglycanopathies is difficult and requires searching for mutations gene by gene. At present, of the six proteins involved on α-dystroglycanopathies, the function of the gene products is only known for POMT1, POMT2, and POMGnT1, all responsible for the O-mannosylglycan biosynthesis. This chapter describes the assay protocols to diagnose patients with α-dystroglycanopathy by measuring glycosyltransferase activity.
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Role of N-glycans in maintaining the activity of protein O-mannosyltransferases POMT1 and POMT2
Journal of biochemistry, 2009Co-Authors: Hiroshi Manya, Keiko Akasaka-manya, Ai Nakajima, Masao Kawakita, Tamao EndoAbstract:The complex of protein O-mannosyltransferase 1 (POMT1) and POMT2 catalyzes the initial step of O-mannosyl glycan biosynthesis. The mutations in either POMT1 or POMT2 can lead to Walker-Warburg syndrome, a congenital muscular dystrophy with abnormal neuronal migration. Here, we used three algorithms for predicting transmembrane helices to construct the secondary structural models of human POMT1 and POMT2. In these models, POMT1 and POMT2 have seven- and nine-transmembrane helices and contain four and five potential N-glycosylation sites, respectively. To determine whether these sites are actually glycosylated, we prepared mutant proteins that were defective in each site by site-directed mutagenesis. Three of the POMT1 sites and all of the POMT2 sites were found to be N-glycosylated, suggesting that these sites face the luminal side of the endoplasmic reticulum. Mutation of any single site did not significantly affect POMT activity, but mutations of all N-glycosylation sites of either POMT1 or POMT2 caused a loss of POMT activity. The loss of activity appeared to be due to the decreased hydrophilicity. These results suggest that the N-glycosylation of POMT1 and POMT2 is required for maintaining the conformation as well as the activity of the POMT1-POMT2 complex.
Jürgen Winkler - One of the best experts on this subject based on the ideXlab platform.
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an autosomal recessive limb girdle muscular dystrophy lgmd2 with mild mental retardation is allelic to walker warburg syndrome wws caused by a mutation in the POMT1 gene
Neuromuscular Disorders, 2005Co-Authors: Burcu Balci, Tobias Willer, Ute Hehr, Beril Talim, C. Gross, Pervin Dinçer, Goknur Haliloglu, Gülsev Kale, G Uyanik, Jürgen WinklerAbstract:Abstract Mutations of the protein O-mannosyltransferase ( POMT1 ) gene affect glycosylation of α-dystroglycan, leading to Walker–Warburg syndrome, a lethal disorder in early life with severe congenital muscular dystrophy, and brain and eye malformations. Recently, we described a novel form of recessive limb girdle muscular dystrophy with mild mental retardation, associated with an abnormal α-dystroglycan pattern in the muscle, suggesting a glycosylation defect. Here, we present evidence that this distinct phenotype results from a common mutation (A200P) in the POMT1 gene. Our findings further expand the phenotype of glycosylation disorders linked to POMT1 mutations. Furthermore, the A200P mutation is part of a conserved core haplotype, indicating an ancestral founder mutation.
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An autosomal recessive limb girdle muscular dystrophy (LGMD2) with mild mental retardation is allelic to Walker–Warburg syndrome (WWS) caused by a mutation in the POMT1 gene
Neuromuscular disorders : NMD, 2005Co-Authors: Burcu Balci, Tobias Willer, Gökhan Uyanik, Ute Hehr, Beril Talim, C. Gross, Pervin Dinçer, Goknur Haliloglu, Gülsev Kale, Jürgen WinklerAbstract:Abstract Mutations of the protein O-mannosyltransferase ( POMT1 ) gene affect glycosylation of α-dystroglycan, leading to Walker–Warburg syndrome, a lethal disorder in early life with severe congenital muscular dystrophy, and brain and eye malformations. Recently, we described a novel form of recessive limb girdle muscular dystrophy with mild mental retardation, associated with an abnormal α-dystroglycan pattern in the muscle, suggesting a glycosylation defect. Here, we present evidence that this distinct phenotype results from a common mutation (A200P) in the POMT1 gene. Our findings further expand the phenotype of glycosylation disorders linked to POMT1 mutations. Furthermore, the A200P mutation is part of a conserved core haplotype, indicating an ancestral founder mutation.
Ute Hehr - One of the best experts on this subject based on the ideXlab platform.
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Broad Phenotypic Spectrum of A-Dystroglycanopathies due to POMT1 Mutations in 16 Families
Neuropediatrics, 2014Co-Authors: Tobias Geis, Haluk Topaloglu, Wolfgang Müller-felber, S. Schirmer, Ute HehrAbstract:Introduction: Congenital muscular dystrophies with defective O-glycosylation of α-dystroglycan (α-dystroglycanopathies) are a heterogeneous group of autosomal recessive inherited disorders explained by mutations in an increasing number of related genes. Among those, POMT1 was initially associated with Walker-Warburg syndrome (WWS) at the most severe end of the disease spectrum. Subsequently, milder POMT1-associated phenotypes such as congenital muscular dystrophy (CMD) or limb girdle muscular dystrophy (LGMD) have been described. In an ongoing study, we aim to further characterize the genotype-phenotype correlation and genotype-dependent long-term course of patients with genetically confirmed forms of those dystroglycanopathies and here present the wide clinical spectrum of POMT1-associated phenotypes. Methods: Evaluation of the patients’ medical reports and MRI as available were done. Linkage analysis for suitable families, Sanger sequencing, and more recently targeted or exome next generation sequencing were evaluated. Results: POMT1 mutations were identified in 22 patients from 16 families including 12 patients or fetal samples from 7 families with suspected WWS, 9 patients from 8 families with suspected LGMD2K, and 1 patient clinically classified as CMD. Interestingly, among WWS patients exclusively homozygous or compound heterozygous truncating mutations were observed. Three WWS families had two or more affected offspring showing a uniformly fatal prenatal presentation with severe hydrocephalus. In three WWS families, prenatal diagnosis was requested in subsequent pregnancies. Two patients with LGMD2K and the CMD patient were compound heterozygous for one missense mutation and one truncating POMT1 mutation. A rather uniform LGMD2K phenotype with proximal muscle weakness and cognitive impairment was observed in patients from six families homozygous for the POMT1 mutation p.Ala200Pro. The CMD patient had a neonatal disease onset with muscular hypotonia and subsequently delayed motor development and substantial cognitive impairment without brain MRI abnormalities. During the first decade of life, his phenotype was suggestive of Duchenne muscular dystrophy with creatine kinase values above 5,000 U/L. However, he had an unusually slow progression of his proximally pronounced CMD and a preserved ability to walk into his early thirties. His genetic diagnosis was finally confirmed at the age of 32 years. Conclusion: Our data suggest a genotype-phenotype correlation for POMT1 with homozygous or compound heterozygous truncating mutations resulting in WWS while the presence of at least one missense mutation is associated with a milder phenotype. Mutations in POMT1 and other related genes should also be considered in adult LGMD and CMD patients, in particular, in those with associated cognitive and psychomotor delay with or without structural brain abnormalities.
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160 kb deletion in ISPD unmasking a recessive mutation in a patient with Walker-Warburg syndrome.
European journal of medical genetics, 2013Co-Authors: Johanna Christina Czeschik, Ute Hehr, Britta Hartmann, Hermann-josef Lüdecke, Thorsten Rosenbaum, Bernd Schweiger, Dagmar WieczorekAbstract:Abstract Walker–Warburg syndrome (WWS) is a severe muscular dystrophy with eye and brain malformations. On a molecular level, WWS is a disorder of the O-linked glycosylation of α-dystroglycan and therefore referred to as one of the dystroglycanopathies. The disease family of muscular dystrophy–dystroglycanopathy (MDDG) contains a spectrum of severe to mild disorders, designated as MDDG type A to C. WWS, as the most severe manifestation, corresponds to MDDG type A. Defects in the genes POMT1 , POMT2 , POMGNT1 , FKTN , FKRP , LARGE , GTDC2 , G3GALNT2 , GMPPB , B3GNT1 , TMEM5 and COL4A1 and ISPD have been described as causal for several types of MDDG including WWS, but can only be confirmed in about 60–70% of the clinically diagnosed individuals. The proteins encoded by these genes are involved in the posttranslational modification of α-dystroglycan. Mutations in POMT1 , POMT2 , POMGNT1 , FKTN , FKRP , LARGE , GMPPB , TMEM5 and COL4A1 and ISPD lead to a wide spectrum of phenotypes of congenital muscular dystrophies with or without eye and brain abnormalities. Patients with WWS frequently demonstrate a complete lack of psychomotor development, severe eye malformations, cobblestone lissencephaly and a hypoplastic cerebellum and brainstem, seizures, hydrocephalus and poor prognosis. Here, we present a boy with WWS who showed compound heterozygous changes in ISPD and discuss the clinical and radiological phenotype and the molecular genetic findings, including a novel pathogenic mutation in ISPD .
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Correlation of enzyme activity and clinical phenotype in POMT1-associated dystroglycanopathies
Neurology, 2010Co-Authors: Mark Lommel, Tobias Willer, Gökhan Uyanik, Sebahattin Cirak, R. Hermann, J.h.l.m. Van Bokhoven, C. Korner, T. Voit, Ivo Barić, Ute HehrAbstract:Background: Mutations in protein O-mannosyltransferases ( POMTs ) cause a heterogeneous group of muscular dystrophies with abnormal glycosylation of α-dystroglycan (dystroglycanopathies). The wide spectrum of clinical severities ranges from Walker-Warburg syndrome (WWS), associated with brain and eye abnormalities, to mild forms of limb girdle muscular dystrophy (LGMD). Objective: The aim of this study was to elucidate the impact of mutations in POMT1 on the clinical phenotype. Methods: We examined 2 patients with POMT1 -associated α-dystroglycanopathy, 1 displaying a LGMD2K and 1 with a WWS phenotype. Using dermal fibroblasts, we analyzed the influence of the POMT1 mutations on the glycosylation status of α-dystroglycan, protein O-mannosyltransferase activity, and the stability of the mutant POMT1 protein. Results: We report on novel compound heterozygous mutations in POMT1 (p.L171A and p.A589VfsX38) that result in LGMD2K. We further demonstrate that a homozygous splice site mutation of a recently identified WWS patient results in POMT1 p.del77-93. Using dermal fibroblasts, we show that mannosyltransferase activity is reduced in the patients and that stability of POMT1 mutant proteins p.A589VfsX38 and p.del77-93 is significantly decreased. Conclusions: Our results suggest that dermal fibroblasts can be applied to facilitate the diagnostic analysis of dystroglycanopathy patients as well as to study the pathogenic mechanism of POMT mutations. Characterization of the POMT1 substrate protein α-dystroglycan and POMT in vitro mannosyltransferase activity shows that the severity of the clinical phenotype of the patients analyzed is inversely correlated with POMT activity.
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A case of Walker-Warburg syndrome resulting from a homozygous POMT1 mutation.
European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society, 2006Co-Authors: Uluç Yiş, Gökhan Uyanik, Eray Dirik, Semra Hiz Kurul, Erdener Özer, C. Gross, Ute HehrAbstract:Walker––Warburg syndrome (WWS), the most severe α-dystroglycanopathy, is characterized by brain and eye anomalies, and congenital muscular dystrophy (CMD). So far at least four genes (POMT1, POMT2, Fukutin, and FKRP gene) have been implicated in WWS, accounting for about 30% of all cases. We report a male patient with WWS resulting from a homozygous nonsense mutation (R514X) in the POMT1 gene. The patient had congenital hydrocephalus which was detected at 29 weeks of gestation. A brain MRI obtained after birth revealed type II lissencephaly, hydrocephalus, and pontocerebellar hypoplasia. The case also exhibited severe ocular malformations and muscular hypotonia due to CMD.
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an autosomal recessive limb girdle muscular dystrophy lgmd2 with mild mental retardation is allelic to walker warburg syndrome wws caused by a mutation in the POMT1 gene
Neuromuscular Disorders, 2005Co-Authors: Burcu Balci, Tobias Willer, Ute Hehr, Beril Talim, C. Gross, Pervin Dinçer, Goknur Haliloglu, Gülsev Kale, G Uyanik, Jürgen WinklerAbstract:Abstract Mutations of the protein O-mannosyltransferase ( POMT1 ) gene affect glycosylation of α-dystroglycan, leading to Walker–Warburg syndrome, a lethal disorder in early life with severe congenital muscular dystrophy, and brain and eye malformations. Recently, we described a novel form of recessive limb girdle muscular dystrophy with mild mental retardation, associated with an abnormal α-dystroglycan pattern in the muscle, suggesting a glycosylation defect. Here, we present evidence that this distinct phenotype results from a common mutation (A200P) in the POMT1 gene. Our findings further expand the phenotype of glycosylation disorders linked to POMT1 mutations. Furthermore, the A200P mutation is part of a conserved core haplotype, indicating an ancestral founder mutation.