Congenital disorders of glycosylation type Ia and IIa are associated with different primary haemostatic complications

In vitro treatment with liposome-encapsulated Mannose-1-phosphate restores N-glycosylation in PMM2-CDG patient-derived fibroblasts

PMM2-CDG is the most common congenital disorder of glycosylation (CDG). Patients with this disease often carry compound heterozygous mutations of the gene encoding the phosphomannomutase 2 (PMM2) enzyme. PMM2 converts mannose-6-phosphate (M6P) to mannose-1-phosphate (M1P), which is a critical upstream metabolite for proper protein N-glycosylation. Therapeutic options for PMM2-CDG patients are limited to management of the disease symptoms, as no drug is currently approved to treat this disease. GLM101 is a M1P-loaded liposomal formulation being developed as a candidate drug to treat PMM2-CDG. This report describes the effect of GLM101 treatment on protein N-glycosylation of PMM2-CDG patient-derived fibroblasts. This treatment normalized intracellular GDP-mannose, increased the relative glycoprotein mannosylation content and TNFα-induced ICAM-1 expression. Moreover, glycomics profiling revealed that GLM101 treatment of PMM2-CDG fibroblasts resulted in normalization of most high mannose glycans and partial correction of multiple complex and hybrid glycans. In vivo characterization of GLM101 revealed its favorable pharmacokinetics, liver-targeted biodistribution, and tolerability profile with achieved systemic concentrations significantly greater than its effective in vitro potency. Taken as a whole, the results described in this report support further exploration of GLM101's safety, tolerability, and efficacy in PMM2-CDG patients.

Association between acute complications in PMM2-CDG patients and haemostasis anomalies: Data from a multicentric study and suggestions for acute management

OBJECTIVES

Patients with PMM2-CDG develop acute events (stroke-like episodes (SLEs), thromboses, haemorrhages, seizures, migraines) associated with both clotting factors (factor XI) and coagulation inhibitors (antithrombin, protein C and protein S) deficiencies. The aim of the study was to correlate acute events to haemostasis and propose practical guidelines.

METHODS

In this multicentric retrospective study, we evaluated clinical, radiological, haemostasis and electroencephalography data for PMM2-CDG patients hospitalized for acute events. Cerebral events were classified as thrombosis, haemorrhage, SLE, or "stroke mimic" (SM: normal brain imaging or evoking a migraine).

RESULTS

Thirteen patients had a total of 31 acute episodes: 27 cerebral events with 7 SLEs, 4 venous thromboses, 4 haemorrhages (3 associated with thrombosis), 15 SMs at a mean age of 7.7 years; 4 non-cerebral thromboses, one of which included bleeding. A trigger was frequently involved (infection, head trauma). Although sometimes normal at baseline state, factor XI, antithrombin and protein C levels decreased during these episodes. No correlation between haemostasis anomalies and type of acute event was found.

DISCUSSION

Acute events in PMM2-CDG are not negligible and are associated with haemostasis anomalies. An emergency protocol is proposed for their prevention and treatment (https://www.filiere-g2m.fr/urgences). For cerebral events, brain Magnetic Resonance Imaging with perfusion weight imaging and diffusion sequences, electroencephalogram and haemostasis protein levels guide the treatment: anticoagulation, antithrombin or fresh frozen plasma supplementation, antiepileptic therapy. Preventing bleeding and thrombosis is required in cases of surgery, prolonged immobilization, hormone replacement therapy.

CONCLUSION

Acute events in PMM2-CDG are associated with abnormal haemostasis, requiring practical guidance.

Immune dysfunction in MGAT2-CDG: A clinical report and review of the literature

Glycosylation is a critical post/peri-translational modification required for the appropriate development and function of the immune system. As an example, abnormalities in glycosylation can cause antibody deficiency and reduced lymphocyte signaling, although the phenotype can be complex given the diverse roles of glycosylation. Human MGAT2 encodes N-acetylglucosaminyltransferase II, which is a critical enzyme in the processing of oligomannose to complex N-glycans. Complex N-glycans are essential for immune system functionality, but only one individual with MGAT2-CDG has been described to have an abnormal immunologic evaluation. MGAT2-CDG (CDG-IIa) is a congenital disorder of glycosylation (CDG) associated with profound global developmental disability, hypotonia, early onset epilepsy, and other multisystem manifestations. Here, we report a 4-year old female with MGAT2-CDG due to a novel homozygous pathogenic variant in MGAT2, a 4-base pair deletion, c.1006_1009delGACA. In addition to clinical features previously described in MGAT2-CDG, she experienced episodic asystole, persistent hypogammaglobulinemia, and defective ex vivo mitogen and antigen proliferative responses, but intact specific vaccine antibody titers. Her infection history has been mild despite the testing abnormalities. We compare this patient to the 15 previously reported patients in the literature, thus expanding both the genotypic and phenotypic spectrum for MGAT2-CDG.

Characterization of Bombyx mori N-acetylglucosaminyltransferase II splicing variants

N-Acetylglucosaminyltransferase II (GNTII), which catalyzes the transfer of N-acetylglucosamine to N-glycans, plays an essential role in the biosynthesis of branched and complex-type N-glycans. Some characteristics of the GNTIIs from various species have been identified, but not all features have been revealed because some insects have GNTII redundancies due to the possession of splicing variants. In this study, we focused on four splicing variants of silkworm Bombyx mori GNTII (BmGNTII) that differ only in the absence or presence of Exon 2, Exon 9 or both, and we characterized the spatiotemporal transcript levels and enzymatic properties of each. Two of the splicing variants, BmGNTII-B and BmGNTII-D, lack Exon 9, and were expressed more highly in silk glands than any other organs. With respect to the enzymatic properties, optimal temperature and pH were similar among the recombinant BmGNTIIs, but the specific activities and temperature stabilities differed according to the presence or absence of Exon 9 in the splicing variants. These results demonstrate that the B. mori genome encodes splicing variants of GNTII with different enzymatic properties.

Platelets and Defective N-Glycosylation

N-glycans are covalently linked to an asparagine residue in a simple acceptor sequence of proteins, called a sequon. This modification is important for protein folding, enhancing thermodynamic stability, and decreasing abnormal protein aggregation within the endoplasmic reticulum (ER), for the lifetime and for the subcellular localization of proteins besides other functions. Hypoglycosylation is the hallmark of a group of rare genetic diseases called congenital disorders of glycosylation (CDG). These diseases are due to defects in glycan synthesis, processing, and attachment to proteins and lipids, thereby modifying signaling functions and metabolic pathways. Defects in N-glycosylation and O-glycosylation constitute the largest CDG groups. Clotting and anticlotting factor defects as well as a tendency to thrombosis or bleeding have been described in CDG patients. However, N-glycosylation of platelet proteins has been poorly investigated in CDG. In this review, we highlight normal and deficient N-glycosylation of platelet-derived molecules and discuss the involvement of platelets in the congenital disorders of N-glycosylation.

Consensus guideline for the diagnosis and management of mannose phosphate isomerase-congenital disorder of glycosylation

Mannose phosphate isomerase-congenital disorder of glycosylation (MPI-CDG) deficiency is a rare subtype of congenital disorders of protein N-glycosylation. It is characterised by deficiency of MPI caused by pathogenic variants in MPI gene. The manifestation of MPI-CDG is different from other CDGs as the patients suffer dominantly from gastrointestinal and hepatic involvement whereas they usually do not present intellectual disability or neurological impairment. It is also one of the few treatable subtypes of CDGs with proven effect of oral mannose. This article covers a complex review of the literature and recommendations for the management of MPI-CDG with an emphasis on the clinical aspect of the disease. A team of international experts elaborated summaries and recommendations for diagnostics, differential diagnosis, management, and treatment of each system/organ involvement based on evidence-based data and experts' opinions. Those guidelines also reveal more questions about MPI-CDG which need to be further studied.

Elevated thrombin generation in patients with congenital disorder of glycosylation and combined coagulation factor deficiencies

BACKGROUND

Congenital disorders of glycosylation are rare inherited diseases affecting many different proteins. The lack of glycosylation notably affects the hemostatic system and leads to deficiencies of both procoagulant and anticoagulant factors.

OBJECTIVE

To assess the hemostatic balance in patients with multiple coagulation disorders by using a thrombin generation assay.

METHOD

We performed conventional coagulation assays and a thrombin generation assay on samples from patients with congenital disorder of glycosylation. The thrombin generation assay was performed before and after activation of the protein C system by the addition of soluble thrombomodulin.

RESULTS

A total of 35 patients were included: 71% and 57% had low antithrombin and factor XI levels, respectively. Protein C and protein S levels were abnormally low in 29% and 26% of the patients, respectively, whereas only 11% displayed low factor IX levels. Under baseline conditions, the thrombin generation assay revealed a significantly higher endogenous thrombin potential and thrombin peak in patients, relative to controls. After spiking with thrombomodulin, we observed impaired involvement of the protein C system. Hence, 54% of patients displayed a hypercoagulant phenotype in vitro. All the patients with a history of stroke-like episodes or thrombosis displayed this hypercoagulant phenotype.

CONCLUSION

A thrombin generation assay revealed a hypercoagulant in vitro phenotype under baseline condition; this was accentuated by impaired involvement of the protein C system. This procoagulant phenotype may thus reflect the risk of severe vascular complications. Further research will have to determine whether the thrombin generation assay is predictive of vascular events.

Unusual Presentation of PMM2-Congenital Disorder of Glycosylation With Isolated Strokelike Episodes in a Young Girl

Congenital disorders of glycosylation (CDG) are multisystemic inherited metabolic disorders with marked phenotypic variability. The most frequent described type is PMM2-CDG (earlier known as CDG Type Ia) which presents either with pure neurologic features or with combined neurologic and systemic features. The classical presentation is characterized by varied combinations of developmental delay, hypotonia, ataxia, dysmorphism, inverted nipples, and abnormal fat distribution. Strokelike episodes and seizures are known acute complications that usually occur on a background of developmental delay, ataxia, or dysmorphism. We report here a developmentally normal young girl who presented with isolated strokelike episodes and was diagnosed to have CDG Type Ia. This condition should be kept in the differentials of unexplained strokelike episodes in children. The diagnosis has important therapeutic and prognostic implications.

International clinical guidelines for the management of phosphomannomutase 2-congenital disorders of glycosylation: Diagnosis, treatment and follow up

Phosphomannomutase 2 (PMM2-CDG) is the most common congenital disorder of N-glycosylation and is caused by a deficient PMM2 activity. The clinical presentation and the onset of PMM2-CDG vary among affected individuals ranging from a severe antenatal presentation with multisystem involvement to mild adulthood presentation limited to minor neurological involvement. Management of affected patients requires a multidisciplinary approach. In this article, a systematic review of the literature on PMM2-CDG was conducted by a group of international experts in different aspects of CDG. Our managment guidelines were initiated based on the available evidence-based data and experts' opinions. This guideline mainly addresses the clinical evaluation of each system/organ involved in PMM2-CDG, and the recommended management approach. It is the first systematic review of current practices in PMM2-CDG and the first guidelines aiming at establishing a practical approach to the recognition, diagnosis and management of PMM2-CDG patients.

PIGO deficiency: palmoplantar keratoderma and novel mutations

Background

Several genetic defects have been identified in the glycosylphosphatidylinositol (GPI) anchor synthesis, including mutations in PIGO encoding phosphatidylinositol glycan anchor biosynthesis class O protein. These defects constitute a subgroup of the congenital disorders of glycosylation (CDG). Seven patients from five families have been reported carrying variants in PIGO that cause an autosomal recessive syndrome characterised by dysmorphism, psychomotor disability, epilepsy and hyperphosphatasemia.

Methods

Whole exome sequencing was performed in a boy with dysmorphism, psychomotor disability, epilepsy, palmoplantar keratoderma, hyperphosphatasemia and platelet dysfunction without a clinical bleeding phenotype.

Results

Two novel variants in PIGO were detected. The missense variant encoding p. His871Pro was inherited from the boy’s father while the frameshift variant encoding p. Arg604ProfsTer40 was maternally inherited.

Conclusion

A boy with two novel PIGO variants is reported. The skin phenotype and platelet dysfunction in this patient have not been described in previously reported patients with PIGO deficiency but it is of course uncertain whether these are caused by this disorder. The literature on PIGO deficiency is reviewed.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0654-9) contains supplementary material, which is available to authorized users.

A Population-Based Study on Congenital Disorders of Protein N- and Combined with O-Glycosylation Experience in Clinical and Genetic Diagnosis

OBJECTIVE

To describe the clinical, biochemical, and genetic features of patients with congenital disorders of glycosylation (CDG) identified in Spain during the last 20 years.

STUDY DESIGN

Patients were selected among those presenting with multisystem disease of unknown etiology. The isoforms of transferrin and of ApoC3 and dolichols were analyzed in serum; phosphomannomutase and mannosephosphate isomerase activities were measured in fibroblasts. Conventional or massive parallel sequencing (customized panel or Illumina Clinical-Exome Sequencing TruSight One Gene Panel) was used to identify genes and mutations.

RESULTS

Ninety-seven patients were diagnosed with 18 different CDG. Eighty-nine patients had a type 1 transferrin profile; 8 patients had a type 2 transferrin profile, with 6 of them showing an alteration in the ApoC3 isoform profile. A total of 75% of the patients had PMM2-CDG presenting with a heterogeneous mutational spectrum. The remaining patients showed mutations in any of the following genes: MPI, PGM1, GFPT1, SRD5A3, DOLK, DPGAT1, ALG1, ALG6, RFT1, SSR4, B4GALT1, DPM1, COG6, COG7, COG8, ATP6V0A2, and CCDC115.

CONCLUSION

Based on literature and on this population-based study of CDG, a comprehensive scheme including reported clinical signs of CDG is offered, which will hopefully reduce the timeframe from clinical suspicion to genetic confirmation. The different defects of CDG identified in Spain have contributed to expand the knowledge of CDG worldwide. A predominance of PMM2 deficiency was detected, with 5 novel PMM2 mutations being described.

Initial diagnosis of the congenital disorder of glycosylation PMM2-CDG (CDG1a) in a 4-year-old girl after neurosurgical intervention for cerebral hemorrhage

The congenital disorder of glycosylation characterized by a deficiency of phosphomannomutase 2 (PMM2-CDG) is the most common variant of congenital disorders of glycosylation. Besides typical clinical features, such as dysmorphism and abnormal body fat distribution, coagulation abnormities often lead to thromboembolic and hemorrhagic events in these patients. However, only 2 cases of intracerebral bleeding in patients with PMM2-CDG have been described so far. A 4-year-old girl who initially presented with symptoms resulting from raised intracranial pressure underwent acute neurosurgical intervention for intracranial hemorrhage. The differential diagnoses after MRI included arteriovenous malformation and intraparenchymal brain tumor. However, clinical investigations promoted the diagnosis of PMM2-CDG, which was supported further by neuropathological findings and finally confirmed by isoelectric focusing and mutational analysis. No major complications or neurological deficits were evident after surgery, and the patient was able to attend an integrated kindergarten. Unexplained intracranial hemorrhage should raise suspicion of a metabolic disorder and should be discussed with specialists to rule out an orphan disease such as PMM2-CDG.

GPI-anchor and GPI-anchored protein expression in PMM2-CDG patients

BACKGROUND

Mutations in PMM2 impair phosphomannomutase-2 activity and cause the most frequent congenital disorder of glycosylation, PMM2-CDG. Mannose-1-phosphate, that is deficient in this disorder, is also implicated in the biosynthesis of glycosylphosphatidyl inositol (GPI) anchors.

OBJECTIVE

To evaluate whether GPI-anchor and GPI-anchored proteins are defective in PMM2-CDG patients.

METHODS

The expression of GPI-anchor and seven GPI-anchored proteins was evaluated by flow cytometry in different cell types from twelve PMM2-CDG patients. Additionally, neutrophil CD16 and plasma hepatic proteins were studied by Western blot. Transferrin glycoforms were evaluated by HPLC.

RESULTS

Patients and controls had similar surface expression of GPI-anchor and most GPI-anchored proteins. Nevertheless, patients displayed a significantly diminished binding of two anti-CD16 antibodies (3G8 and KD1) to neutrophils and also of anti-CD14 (61D3) to monocytes. Interestingly, CD16 immunostaining and asialotransferrin levels significantly correlated with patients' age. Analysis by flow cytometry of CD14 with MΦP9, and CD16 expression in neutrophils by Western blot using H-80 ruled out deficiencies of these antigens.

CONCLUSIONS

PMM2 mutations do not impair GPI-anchor or GPI-anchored protein expression. However, the glycosylation anomalies caused by PMM2 mutations might affect the immunoreactivity of monoclonal antibodies and lead to incorrect conclusions about the expression of different proteins, including GPI-anchored proteins. Neutrophils and monocytes are sensitive to PMM2 mutations, leading to abnormal glycosylation in immune receptors, which might potentially affect their affinity to their ligands, and contribute to infection. This study also confirms less severe hypoglycosylation defects in older PMM2-CDG patients.

Elucidating the role of carbohydrate determinants in regulating hemostasis: insights and opportunities

Recent improvement in modern analytical technologies has stimulated an explosive growth in the study of glycobiology. In turn, this has lead to a richer understanding of the crucial role of N- and O-linked carbohydrates in dictating the properties of the proteins to which they are attached and, in particular, their centrality in the control of protein synthesis, longevity, and activity. Given their importance, it is unsurprising that both gross and subtle defects in glycosylation often contribute to human disease pathology. In this review, we discuss the accumulating evidence for the significance of glycosylation in mediating the functions of the plasma glycoproteins involved in hemostasis and thrombosis. In particular, the role of naturally occurring coagulation protein glycoforms and inherited defects in carbohydrate attachment in modulating coagulation is considered. Finally, we describe the therapeutic opportunities presented by new insights into the role of attached carbohydrates in shaping coagulation protein function and the promise of carbohydrate modification in the delivery of novel therapeutic biologics with enhanced functional properties for the treatment of hemostatic disorders.

Identification of intercellular cell adhesion molecule 1 (ICAM-1) as a hypoglycosylation marker in congenital disorders of glycosylation cells

Many human inherited disorders cause protein N-glycosylation defects, but there are few cellular markers to test gene complementation for such defects. Plasma membrane glycoproteins are potential biomarkers because they may be reduced or even absent in plasma membranes of glycosylation-deficient cells. We combined stable isotope labeling by amino acids in cell culture (SILAC) with linear ion trap mass spectrometry (LTQ Orbitrap(TM)) to identify and quantify membrane proteins from wild-type CHO and glycosylation-deficient CHO (Lec9) cells. We identified 165 underrepresented proteins from 1447 unique quantified proteins, including 18 N-glycosylated plasma membrane proteins. Using various methods, we found that intercellular cell adhesion molecule 1 (ICAM-1) was reduced in Lec9 cells and in fibroblasts from 31 congenital disorder of glycosylation (CDG) patients compared with normal controls. Mannose supplementation of phosphomannose isomerase-deficient CDG-Ib (MPI-CDG) cells and complementation with PMM2 in PMM2-deficient CDG-Ia (PMM2-CDG) cells partially corrected hypoglycosylation based on increased ICAM-1 presence on the plasma membrane. These data indicate that ICAM-1 could be a useful hypoglycosylation biomarker to assess gene complementation of CDG-I patient cells and to monitor improved glycosylation in response to therapeutic drugs.

Glycobiology of immune responses

Unlike their protein "roommates" and their nucleic acid "cousins," carbohydrates remain an enigmatic arm of biology. The central reason for the difficulty in fully understanding how carbohydrate structure and biological function are tied is the nontemplate nature of their synthesis and the resulting heterogeneity. The goal of this collection of expert reviews is to highlight what is known about how carbohydrates and their binding partners-the microbial (non-self), tumor (altered-self), and host (self)-cooperate within the immune system, while also identifying areas of opportunity to those willing to take up the challenge of understanding more about how carbohydrates influence immune responses. In the end, these reviews will serve as specific examples of how carbohydrates are as integral to biology as are proteins, nucleic acids, and lipids. Here, we attempt to summarize general concepts on glycans and glycan-binding proteins (mainly C-type lectins, siglecs, and galectins) and their contributions to the biology of immune responses in physiologic and pathologic settings.

Congenital protein hypoglycosylation diseases

Glycosylation is an essential process by which sugars are attached to proteins and lipids. Complete lack of glycosylation is not compatible with life. Because of the widespread function of glycosylation, inherited disorders of glycosylation are multisystemic. Since the identification of the first defect on N-linked glycosylation in the 1980s, there are over 40 different congenital protein hypoglycosylation diseases. This review will include defects of N-linked glycosylation, O-linked glycosylation and disorders of combined N- and O-linked glycosylation.

Dystroglycanopathies: coming into focus

A common group of muscular dystrophies is associated with the aberrant glycosylation of α-dystroglycan. These clinically heterogeneous disorders, collectively termed dystroglycanopathies, are often associated with central nervous system and more rarely eye pathology. Defects in a total of eight putative and demonstrated glycosyltransferases or accessory proteins of glycosyltransferases have been shown to cause a dystroglycanopathy phenotype. In recent years the systematic analysis of large patient cohorts has uncovered a complex relationship between the underlying genetic defect and the resulting clinical phenotype. These studies have also drawn attention to the high proportion of patients that remain without a genetic diagnosis implicating novel genes in the pathogenesis of dystroglycanopathies. Recent glycomic analyses of α-dystroglycan have reported complex patterns of glycan composition and have uncovered novel glycan modifications. The exact glycan synthesis and modification pathways involved, as well as their role in ligand binding, remain only partially characterised. This review will focus on recent studies that have extended our knowledge of the mechanisms underlying dystroglycanopathies and have further characterised this patient population.

Deficiency of Dol-P-Man synthase subunit DPM3 bridges the congenital disorders of glycosylation with the dystroglycanopathies

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.

Different neuroradiological findings during two stroke-like episodes in a patient with a congenital disorder of glycosylation type Ia

Congenital disorders of glycosylation type Ia (CDG-Ia) are the most common type of CDG and are characterized by liver dysfunction, coagulation disorders, mental retardation, hypotonia, cerebellar dysfunction, polyneuropathy, seizures, and stroke-like episodes. Stroke-like episodes occur in 40-55% of cases, but their etiology is not fully understood. Although it has been stated that an epileptic process may cause the stroke-like episodes, there is no clear evidence of ischemic stroke. Here, we describe two stroke-like episodes in a patient with CDG. We performed radiological studies during each episode and obtained two distinct magnetic resonance imaging (MRI) findings: one revealed an ischemic stroke, and the other demonstrated marked edema followed by focal necrosis. This is the first direct evidence of ischemic stroke, and we report that another process may affect the etiology in the same patient.

The clinical spectrum of phosphomannomutase 2 deficiency (CDG-Ia)

Congenital disorders of glycosylation are a clinically and genetically heterogeneous group of disorders resulting from abnormal glycosylation of various glycoconjugates. The first description of congenital disorders of glycosylation was published in the early 80s and once screening tests for glycosylation disorders (CDGs) became readily available, CDG-Ia became the most frequently diagnosed CDG subtype. CDG-Ia is pan-ethnic and the spectrum of the clinical manifestations is still evolving: it spans from severe hydrops fetalis and fetal loss to a (nearly) normal phenotype. However, the most common presentation in infancy is of a multisystem disorder with central nervous system involvement.

Recurrent thrombo-embolism in a child with a congenital disorder of glycosylation (CDG) type Ib and treatment with mannose

Thrombosis is a multifactorial disorder. Congenital disorders of glycosylation (CDG) are one of the known risk factors for its occurrence. These disorders result in glycosylation defects of glycoproteins, including those of the (anti-)coagulation system. CDG-Ib can specifically be treated with mannose, as illustrated by the case of a 4-year-old girl in whom deep venous thrombosis was the presenting symptom after a common viral infection. The diagnosis was made after recurrent episodes of thrombo-embolism and consumptive coagulopathy. After treatment with mannose no such episodes recurred. The pathophysiology of CDG as a risk factor for thrombotic disease is discussed.

Screening and diagnosis of congenital disorders of glycosylation

The aim of this paper is to review the diagnostics of congenital disorders of glycosylation (CDG), an ever expanding group of diseases. Development delay, neurological, and other clinical abnormalities as well as various non-specific laboratory changes can lead to the first suspicion of the disease. Still common screening test for most CDG types, including CDG Ia, is isoelectric focusing/polyacrylamide gel electrophoresis (IEF). IEF demonstrates the hypoglycosylation of various glycoproteins, usually serum transferrin. Other methods, such as agarose electrophoresis, capillary electrophoresis, high-performance liquid chromatography, micro-column separation combined with turbidimetry, enzyme-(EIA) and radioimmunoassay (RIA) have also been used for screening. However, these methods do not recognize all CDG defects, so other approaches including analysis of membrane-linked markers and urine oligosaccharides should be taken. Confirmation of diagnosis and detailed CDG subtyping starts with thorough structure analysis of the affected lipid-linked oligosaccharide or protein-(peptide)-linked-glycan using metabolic labeling and various (possibly mass-spectrometry combined) techniques. Decreased enzyme activity in peripheral leukocytes/cultured fibroblasts or analysis of affected transporters and other functional proteins combined with identification of specific gene mutations confirm the diagnosis. Prenatal diagnosis, based on enzyme assay or mutation analysis, is also available. Peri-/post-mortem investigations of fatal cases are important for genetic counseling. Evaluation of various analytical approaches and proposed algorithms for investigation complete the review.

Radiologic and neurophysiologic aspects of stroke-like episodes in children with congenital disorder of glycosylation type Ia

In an effort to shed light on the mechanism of hemiparetic stroke-like events experienced by patients with congenital disorder of glycosylation type Ia, we evaluated 3 children with this disorder by brain imaging studies and continuous electroencephalogram monitoring during such events. No evidence of ischemia or infarction was revealed on imaging studies and electrographic seizures or intermittent epileptiform activity was demonstrated on electrographic recordings. All 3 patients showed clinical and electrographic improvement after administration of antiepileptic medication. Epileptic phenomena can complicate the stroke-like events of patients with congenital disorder of glycosylation type Ia, and the cause of the hemiparesis may indeed be an active epileptic inhibitory process. As such, electroencephalogram monitoring is warranted, and treatment with anticonvulsant agents is indicated.

Congenital disorders of N-glycosylation including diseases associated with O- as well as N-glycosylation defects

The congenital disorders of N-glycosylation (CDG), a steadily increasing group of multi-systemic disorders, have severe clinical implications in infancy and early childhood. The various inborn errors responsible adversely affect N-glycosylation of lysosomal proteins because of either failing assembly of lipid-linked (LL) oligosaccharides (OS) in the endoplasmic reticulum, CDG Type I, or faulty processing of the asparagines (N)-linked OS in the ER and in the Golgi, CDG Type II. The overlap of phenotypes precludes specific clinical delineation. Isoelectric focusing (IEF) of plasma transferrin remains a valuable, albeit imperfect, screening tool. IEF of plasma ApoC-III protein, introduced O-glycosylation defects that delineated some new CDGs due to mutations of both N- and O-glycosylation. Only CDG-Ib is amenable to treatment with free mannose supplementation. Hence, early specific diagnosis of any one entity is crucial for genetic counseling and elective preventive measures.

Intracranial hemorrhage as the initial manifestation of a congenital disorder of glycosylation

Intracranial hemorrhage in a term neonate is a rare event in the absence of an identifiable precipitating factor such as severe thrombocytopenia, mechanical trauma, asphyxia, infections, or congenital vascular malformations. Congenital disorders of glycosylation are a genetically and clinically heterogeneous group of multisystem disorders characterized by the abnormal glycosylation of a number of glycoproteins. Although bleeding caused by abnormal glycosylation of various coagulation factors is a well-known clinical complication of several types of congenital disorders of glycosylation, intracranial hemorrhage has not been reported as an initial manifestation of this entity. Here we report the detailed history of a family with 2 consecutive male infants, both born at term with intracranial hemorrhage diagnosed within the first 24 hours of life. The diagnosis of a congenital disorder of glycosylation was established in the second infant by an abnormal glycosylation of serum transferrin detected by electrospray-ionization mass spectrometry. Both infants showed significant neurologic deterioration during the first month of life, and both died at 5 months of age. Intracranial hemorrhage in a term neonate without a potential precipitating factor represents yet another clinical feature that should raise the suspicion for a congenital disorder of glycosylation.

The congenital disorders of glycosylation: a multifaceted group of syndromes

The congenital disorders of glycosylation (CDG) are a rapidly expanding group of metabolic syndromes with a wide symptomatology and severity. They all stem from deficient N-glycosylation of proteins. To date the group contains 18 different subtypes: 12 of Type I (disrupted synthesis of the lipid-linked oligosaccharide precursor) and 6 of Type II (malfunctioning trimming/processing of the protein-bound oligosaccharide). Main features of CDG involve psychomotor retardation; ataxia; seizures; retinopathy; liver fibrosis; coagulopathies; failure to thrive; dysmorphic features, including inverted nipples and subcutaneous fat pads; and strabismus. No treatment currently is available for the vast majority of these syndromes (CDG-Ib and CDG-IIc are exceptions), even though attempts to synthesize drugs for the most common subtype, CDG-Ia, have been made. In this review we will discuss the individual syndromes, with focus on their neuronal involvement, available and possible treatments, and future directions.

Cutaneous findings in congenital disorders of glycosylation: the hanging fat sign

The congenital disorders of glycosylation are a group of rare metabolic disorders with predominantly neurologic findings. Some variants of this disorder also exhibit cutaneous manifestations. We report a patient with a congenital disorder of glycosylation type Ia, the most common form, with emphasis on the cutaneous findings of this type, and summarize the cutaneous findings in the other forms of the disorder.

Defectos congénitos de la glucosilación: últimos avances y experiencia española

Congenital disorders of glycosylation (CDG) are a group of inherited disorders caused by defects in the synthesis and processing of the linked glycans of glycoproteins and other molecules. The first patients with CDG were described in 1980. Fifteen years later, phosphomannomutase was found to be the basis of the most frequent type: CDG-Ia. Over the last years, several novel types have been identified related to the N-glycosylation pathway, affecting enzymes or transporters of the cytosol, endoplasmic reticulum or the Golgi compartment. CDGs are multisystemic disorders, mainly affecting the central nervous system. Yet CDG-Ib and Ih are mainly hepato-intestinal diseases. Recently, several defects involving the O-glycosylation pathways have been described, indicating that some congenital muscular dystrophies and neuronal migration disorders are caused by congenital disorders of glycosylation.

Congenital disorders of glycosylation (CDG): update and new developments

After a brief overview on CDG, this workshop concentrated on the experience with (mostly) known CDG in a European country (the Czech Republic) and on the Australasian experience, on recent developments regarding congenital muscular dystrophies due to O-mannoslyglycan assembly defects, and on new presentations of CDG. It was concluded that we are still at the beginning of 'explosive' research on CDG and that we need to apply new and known technologies to the diagnosis, understanding of pathophysiology, and treatment of CDG.

Komrower Lecture. Congenital disorders of glycosylation (CDG): it's all in it!

Congenital disorders of glycosylation (CDGs) are due to defects in the synthesis of the glycan moiety of glycoproteins or other glycoconjugates. This review is devoted mainly to the clinical aspects of protein glycosylation defects. There are two main types of protein glycosylation: N-glycosylation and O-glycosylation. N-glycosylation generally consists of an assembly pathway (in cytosol and endoplasmic reticulum) and a processing pathway (in endoplasmic reticulum and Golgi). O-glycosylation lacks a processing pathway but is otherwise more complex. Sixteen disease-causing defects are known in protein glycosylation: 12 in N-glycosylation and four in O-glycosylation. The N-glycosylation defects comprise eight assembly defects (CDG-I) designated CDG-Ia to CDG-Ih, and four processing defects (CDG-II) designated CDG-IIa to CDG-IId. By far the most frequent is CDG-Ia (phosphomannomutase-2 deficiency). It affects the nervous system and many other organs. Its clinical expression varies from extremely severe to very mild (and thus probably underdiagnosed). The most interesting disease in this group is CDG-Ib (phosphomannose isomerase deficiency) because it is so far the only efficiently treatable CDG (mannose treatment). It has a hepatic-intestinal presentation. The O-glycosylation defects comprise two O-xylosylglycan defects (a progeroid variant of Ehlers-Danlos syndrome and the multiple exostoses syndrome) and two O-mannosylglycan defects (Walker-Warburg syndrome and muscle-eye-brain disease). All known CDGs have a recessive inheritance except for multiple exostoses syndrome, which is dominantly inherited. There is a rapidly growing group of putative CDGs with a large spectrum of clinical presentations (CDG-x). Serum transferrin iso-electrofocusing remains the cornerstone of the screening for N-glycosylation defects associated with sialic acid deficiency. Abnormal patterns can be grouped in to type 1 and type 2. However, a normal pattern does not exclude these defects. Screening for the other CDGs is much more difficult, particularly when the defect is organ- or system-restricted. The latter group promises to become an important new chapter in CDG. It is concluded that CDGs will eventually cover the whole clinical spectrum of paediatric and adult disease manifestations.

Congenital disorders of glycosylation: the rapidly growing tip of the iceberg

In addition to many other organs, the brain is affected in 10 of the 11 known congenital disorders of N-linked glycosylation, mostly to a severe degree. Because a large number of enzymes, transporters and other proteins are involved in glycosylation (both N-linked and O-linked), it is expected that the great majority of congenital disorders of glycosylation (CDG) are yet to be identified. Many neurological patients with a CDG escape diagnosis for that reason, but also because existing screening methods fail to detect all patients with a known CDG. These disorders should be looked for in any patient, regardless of age, with an unexplained neurological disorder.