Deficiency of Dol-P-Man Synthase Subunit DPM3 Bridges the Congenital Disorders of Glycosylation with the Dystroglycanopathies

Laboratory of Pediatrics & Neurology, Institute for Genetic and Metabolic Disease, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands.
The American Journal of Human Genetics (Impact Factor: 10.93). 08/2009; 85(1):76-86. DOI: 10.1016/j.ajhg.2009.06.006
Source: PubMed


Alpha-dystroglycanopathies such as Walker Warburg syndrome represent an important subgroup of the muscular dystrophies that have been related to defective O-mannosylation of alpha-dystroglycan. In many patients, the underlying genetic etiology remains unsolved. Isolated muscular dystrophy has not been described in the congenital disorders of glycosylation (CDG) caused by N-linked protein glycosylation defects. Here, we present a genetic N-glycosylation disorder with muscular dystrophy in the group of CDG type I. Extensive biochemical investigations revealed a strongly reduced dolichol-phosphate-mannose (Dol-P-Man) synthase activity. Sequencing of the three DPM subunits and complementation of DPM3-deficient CHO2.38 cells showed a pathogenic p.L85S missense mutation in the strongly conserved coiled-coil domain of DPM3 that tethers catalytic DPM1 to the ER membrane. Cotransfection experiments in CHO cells showed a reduced binding capacity of DPM3(L85S) for DPM1. Investigation of the four Dol-P-Man-dependent glycosylation pathways in the ER revealed strongly reduced O-mannosylation of alpha-dystroglycan in a muscle biopsy, thereby explaining the clinical phenotype of muscular dystrophy. This mild Dol-P-Man biosynthesis defect due to DPM3 mutations is a cause for alpha-dystroglycanopathy, thereby bridging the congenital disorders of glycosylation with the dystroglycanopathies.

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Available from: Daniel Hess
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    • "Enzyme defects in these steps lead to alpha dystroglycanopathies; however, the availability of activated mannose is also essential to make the proper O-linked mannosylated glycan. DPM-complex-related defects lead to different alpha dystroglycanopathies, which are syndromes of variable severity imitating muscle-eye-brain disease (Mercuri and Muntoni 2012, Lefeber et al. 2009, Barone et al. 2012). Upon the initial definition of DPM1-CDG as a severe neurologic disease with developmental delay and muscle weakness with CK elevations (MIM 608799), and DPM3-CDG as a mild limb-girdle-type muscle dystrophy with cardiomyopathy, Barone et al. defined the DPM2-related CDG that leads to alpha dystroglycanopathy, elevated CK levels, abnormal muscle histology , and associations with microcephaly and severe seizure disorder (Barone et al. 2012). "
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    ABSTRACT: Almost 50 inborn errors of metabolism have been described due to congenital defects in N-linked glycosylation. These phenotypically diverse disorders typically present as clinical syndromes, affecting multiple systems including the central nervous system, muscle function, transport, regulation, immunity, endocrine system, and coagulation. An increasing number of disorders have been discovered using novel techniques that combine glycobiology with next-generation sequencing or use tandem mass spectrometry in combination with molecular gene-hunting techniques. The number of “classic” congenital disorders of glycosylation (CDGs) due to N-linked glycosylation defects is still rising. Eight novel CDGs affecting N-linked glycans were discovered in 2013 alone. Newly discovered genes teach us about the significance of glycosylation in cell–cell interaction, signaling, organ development, cell survival, and mosaicism, in addition to the consequences of abnormal glycosylation for muscle function. We have learned how important glycosylation is in posttranslational modification and how glycosylation defects can imitate recognizable, previously described phenotypes. In many CDG subtypes, patients unexpectedly presented with long-term survival, whereas some others presented with nonsyndromic intellectual disability. In this review, recently discovered N-linked CDGs are described, with a focus on clinical presentations and therapeutic ideas. A diagnostic approach in unsolved N-linked CDG cases with abnormal transferrin screening results is also suggested.
    Full-text · Article · May 2014 · Journal of Inherited Metabolic Disease
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    • "Alpha-dystroglycanopathies are a clinically and genetically distinct group of muscular dystrophies characterized by the reduced or absent glycosylation of the extracellular scaffolding protein alpha-dystroglycan (Buysse et al., 2013; Lefeber et al., 2009; Manzini et al., 2012; Muntoni et al., 2002; Riisager et al., 2013). The clinical manifestations of alphadystroglycanopathies are extremely variable, leading to a broad spectrum of phenotypes with limb-girdle muscular dystrophy (LGMD) without mental retardation delineating the milder end, and Walker–Warburg syndrome (WWS), muscle–eye–brain disease (MEB) and Fukuyama type congenital muscular dystrophy (FCMD) the severe end of the spectrum (Muntoni and Voit, 2004; Muntoni et al., 2011; Willer et al., 2012). "
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    ABSTRACT: Fukuyama-type congenital muscular dystrophy (FCMD, MIM#253800) is an autosomal recessive disorder characterized by severe muscular dystrophy associated with brain malformations. FCMD is the second most common form of muscular dystrophy after Duchenne muscular dystrophy and one of the most common autosomal recessive diseases among the Japanese population, and yet few patients outside of Japan had been reported with this disorder. We report the first known Egyptian patient with FCMD, established by clinical features of generalized weakness, pseudohypertrophy of calf muscles, progressive joint contractures, severe scoliosis, elevated serum creatine kinase level, myopathic electrodiagnostic changes, brain MRI with cobblestone complex, and mutation in the fukutin gene. In addition, our patient displayed primary microcephaly, not previously reported associated with fukutin mutations. Our results expand the geographic and clinical spectrum of fukutin mutations.
    Full-text · Article · Feb 2014 · Gene
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    • "The dystroglycanopathies are a subgroup of the CMDs characterised by aberrant α-dystroglycan (α-DG) glycosylation. They are caused by mutations in several genes involved in the glycosylation of α-DG; Protein O-mannosyltransferase [1] (POMT1; MIM 607423), Protein O-mannosyltransferase 2 [2] (POMT2; MIM 607439), Protein O-mannose ß-1,2-N-acetylglucosaminyltransferase [3] (POMGNT1; MIM 606822), Fukutin [4] (FKTN; MIM 607440), Fukutin-related protein [5] (FKRP; MIM 606596), like-acetylglucosaminyltransferase [6] (LARGE; MIM 603590), Dolichyl-phosphate mannosyltransferase 2 [7] (DPM2: MIM 603564), Dolichyl-phosphate mannosyltransferase 3 [8] (DPM3; MIM 605951), Dolichol Kinase [9] (DOLK; MIM 610746), Isoprenoid Synthase Domain Containing [10], [11], [12] (ISPD; MIM 614631), Glycosyltransferase-like domain containing 2 [13] (GTDC2; MIM 147730), β-1,3-N-acetylgalactosaminyltransferase 2 [14] (B3GALNT2; MIM 610194), Transmembrane protein 5 (TMEM5; MIM 605862) [15], β-1,3-N-acetylglucosaminyltransferase 1 (B3GNT1; MIM 605517) [16], GDP-mannose pyrophosphorylase B (GMPPB) [17], and protein kinase-like protein SgK196 (SGK196) [18]. "
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    ABSTRACT: α-dystroglycan (α-DG) is a peripheral membrane protein that is an integral component of the dystrophin-glycoprotein complex. In an inherited subset of muscular dystrophies known as dystroglycanopathies, α-DG has reduced glycosylation which results in lower affinity binding to several extracellular matrix proteins including laminins. The glycosylation status of α-DG is normally assessed by the binding of the α-DG antibody IIH6 to a specific glycan epitope on α-DG involved in laminin binding. Immunocytochemistry and immunoblotting are two of the most widely used methods to detect the amount of α-DG glycosylation in muscle. While the interpretation of the presence or absence of the epitope on muscle using these techniques is straightforward, the assessment of a mild defect can be challenging. In this study, flow cytometry was used to compare the amount of IIH6-reactive glycans in fibroblasts from dystroglycanopathy patients with defects in genes known to cause α-DG hypoglycosylation to the amount in fibroblasts from healthy and pathological control subjects. A total of twenty one dystroglycanopathy patient fibroblasts were assessed, as well as fibroblasts from three healthy controls and seven pathological controls. Control fibroblasts have clearly detectable amounts of IIH6-reactive glycans, and there is a significant difference in the amount of this glycosylation, as measured by the mean fluorescence intensity of an antibody recognising the epitope and the percentage of cells positive for the epitope, between these controls and dystroglycanopathy patient fibroblasts (p<0.0001 for both). Our results indicate that the amount of α-DG glycosylation in patient fibroblasts is comparable to that in patient skeletal muscle. This method could complement existing immunohistochemical assays in skeletal muscle as it is quantitative and simple to perform, and could be used when a muscle biopsy is not available. This test could also be used to assess the pathogenicity of variants of unknown significance in genes involved in dystroglycanopathies.
    Full-text · Article · Jul 2013 · PLoS ONE
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