Congenital disorder of glycosylation type Ia presenting with hydrops fetalis

Revisiting the immunopathology of congenital disorders of glycosylation: an updated review

Glycosylation is a critical post-translational modification that plays a pivotal role in several biological processes, such as the immune response. Alterations in glycosylation can modulate the course of various pathologies, such as the case of congenital disorders of glycosylation (CDG), a group of more than 160 rare and complex genetic diseases. Although the link between glycosylation and immune dysfunction has already been recognized, the immune involvement in most CDG remains largely unexplored and poorly understood. In this study, we provide an update on the immune dysfunction and clinical manifestations of the 12 CDG with major immune involvement, organized into 6 categories of inborn errors of immunity according to the International Union of Immunological Societies (IUIS). The immune involvement in phosphomannomutase 2 (PMM2)-CDG - the most frequent CDG - was comprehensively reviewed, highlighting a higher prevalence of immune issues during infancy and childhood and in R141H-bearing genotypes. Finally, using PMM2-CDG as a model, we point to links between abnormal glycosylation patterns in host cells and possibly favored interactions with microorganisms that may explain the higher susceptibility to infection. Further characterizing immunopathology and unusual host-pathogen adhesion in CDG can not only improve immunological standards of care but also pave the way for innovative preventive measures and targeted glycan-based therapies that may improve quality of life for people living with CDG.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Clinical and biochemical footprints of inherited metabolic diseases. XII. Immunological defects

Immunological problems are increasingly acknowledged manifestations in many inherited metabolic diseases (IMDs), ranging from exaggerated inflammation, autoimmunity and abnormal cell counts to recurrent microbial infections. A subgroup of IMDs, the congenital disorders of glycosylation (CDG), includes CDG types that are even classified as primary immunodeficiencies. Here, we reviewed the list of metabolic disorders reported to be associated with various immunological defects and identified 171 IMDs accompanied by immunological manifestations. Most IMDs are accompanied by immune dysfunctions of which immunodeficiency and infections, innate immune defects, and autoimmunity are the most common abnormalities reported in 144/171 (84%), 44/171 (26%) and 33/171 (19%) of IMDs with immune system involvement, respectively, followed by autoinflammation 17/171 (10%). This article belongs to a series aiming at creating and maintaining a comprehensive list of clinical and metabolic differential diagnoses according to organ system involvement.

Perinatal manifestations of congenital disorders of glycosylation-A clue to early diagnosis

N-glycosylation defects-isolated or mixed with other glycosylation defects-are the most frequent congenital disorders of glycosylation and present mostly in childhood, with a specific combination of non-specific phenotypic features. The diagnosis, however, is often delayed. The aim of this study is to describe the perinatal phenotype of congenital disorders of N-glycosylation. We present an analysis of perinatal symptoms in a group of 24 one-center Polish patients with N-glycosylation defects-isolated or mixed. The paper expands the perinatal phenotype of CDGs and shows that some distinctive combinations of symptoms present in the perinatal period should raise a suspicion of CDGs in a differential diagnosis.

Evaluation of Cell Models to Study Monocyte Functions in PMM2 Congenital Disorders of Glycosylation

Congenital disorders of glycosylation (CDG) are inherited metabolic diseases characterized by mutations in enzymes involved in different steps of protein glycosylation, leading to aberrant synthesis, attachment or processing of glycans. Recently, immunological dysfunctions in several CDG types have been increasingly documented. Despite these observations, detailed studies on immune cell dysfunction in PMM2-CDG and other CDG types are still scarce. Studying PMM2-CDG patient immune cells is challenging due to limited availability of patient material, which is a result of the low incidence of the disease and the often young age of the subjects. Dedicated immune cell models, mimicking PMM2-CDG, could circumvent many of these problems and facilitate research into the mechanisms of immune dysfunction. Here we provide initial observations about the immunophenotype and the phagocytic function of primary PMM2-CDG monocytes. Furthermore, we assessed the suitability of two different glycosylation-impaired human monocyte models: tunicamycin-treated THP-1 monocytes and PMM2 knockdown THP-1 monocytes induced by shRNAs. We found no significant differences in primary monocyte subpopulations of PMM2-CDG patients as compared to healthy individuals but we did observe anomalous surface glycosylation patterns in PMM2-CDG patient monocytes as determined using fluorescent lectin binding. We also looked at the capacity of monocytes to bind and internalize fungal particles and found a slightly increased uptake of C. albicans by PMM2-CDG monocytes as compared to healthy monocytes. Tunicamycin-treated THP-1 monocytes showed a highly decreased uptake of fungal particles, accompanied by a strong decrease in glycosylation levels and a high induction of ER stress. In contrast and despite a drastic reduction of the PMM2 enzyme activity, PMM2 knockdown THP-1 monocytes showed no changes in global surface glycosylation levels, levels of fungal particle uptake similar to control monocytes, and no ER stress induction. Collectively, these initial observations suggest that the absence of ER stress in PMM2 knockdown THP-1 cells make this model superior over tunicamycin-treated THP-1 cells and more comparable to primary PMM2-CDG monocytes. Further development and exploitation of CDG monocyte models will be essential for future in-depth studies to ultimately unravel the mechanisms of immune dysfunction in CDG.

Precision genetic cellular models identify therapies protective against ER stress

Rare monogenic disorders often share molecular etiologies involved in the pathogenesis of common diseases. Congenital disorders of glycosylation (CDG) and deglycosylation (CDDG) are rare pediatric disorders with symptoms that range from mild to life threatening. A biological mechanism shared among CDG and CDDG as well as more common neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis, is endoplasmic reticulum (ER) stress. We developed isogenic human cellular models of two types of CDG and the only known CDDG to discover drugs that can alleviate ER stress. Systematic phenotyping confirmed ER stress and identified elevated autophagy among other phenotypes in each model. We screened 1049 compounds and scored their ability to correct aberrant morphology in each model using an agnostic cell-painting assay based on >300 cellular features. This primary screen identified multiple compounds able to correct morphological phenotypes. Independent validation shows they also correct cellular phenotypes and alleviate each of the ER stress markers identified in each model. Many of the active compounds are associated with microtubule dynamics, which points to new therapeutic opportunities for both rare and more common disorders presenting with ER stress, such as Alzheimer's disease and amyotrophic lateral sclerosis.

Importance of evaluating protein glycosylation in pluripotent stem cell-derived cardiomyocytes for research and clinical applications

Proper protein glycosylation is critical to normal cardiomyocyte physiology. Aberrant glycosylation can alter protein localization, structure, drug interactions, and cellular function. The in vitro differentiation of human pluripotent stem cells into cardiomyocytes (hPSC-CM) has become increasingly important to the study of protein function and to the fields of cardiac disease modeling, drug testing, drug discovery, and regenerative medicine. Here, we offer our perspective on the importance of protein glycosylation in hPSC-CM. Protein glycosylation is dynamic in hPSC-CM, but the timing and extent of glycosylation are still poorly defined. We provide new data highlighting how observed changes in hPSC-CM glycosylation may be caused by underlying differences in the protein or transcript abundance of enzymes involved in building and trimming the glycan structures or glycoprotein gene products. We also provide evidence that alternative splicing results in altered sites of glycosylation within the protein sequence. Our findings suggest the need to precisely define protein glycosylation events that may have a critical impact on the function and maturation state of hPSC-CM. Finally, we provide an overview of analytical strategies available for studying protein glycosylation and identify opportunities for the development of new bioinformatic approaches to integrate diverse protein glycosylation data types. We predict that these tools will promote the accurate assessment of protein glycosylation in future studies of hPSC-CM that will ultimately be of significant experimental and clinical benefit.

Vascular ring anomaly in a patient with phosphomannomutase 2 deficiency: A case report and review of the literature

BACKGROUND

Congenital disorders of glycosylation (CDG) are a group of metabolic disorders well known to be associated with developmental delay and central nervous system anomalies. The most common CDG is caused by pathogenic variants in the phosphomannomutase 2 gene (PMM2), which impairs one of the first steps of N-glycosylation and affects multiple organ systems. Cardiac involvement can include pericardial effusion, cardiomyopathy, and arrhythmia, while an association with cardiovascular congenital anomalies is not well studied.

CASE SUMMARY

We report a 6-year-old individual who initially presented with inverted nipples, developmental delay, and failure to thrive at 3 months of age. At 4 months, due to feeding problems, swallowing exam and echocardiography were performed which revealed a vascular ring anomaly based on a right aortic arch and aberrant left subclavian artery. Subsequent whole exome gene sequencing revealed two pathogenic PMM2-CDG variants (E139K/R141H) and no known pathogenic mutations related to congenital heart defect (CHD).

DISCUSSION

This is the first report of vascular ring anomaly in a patient with PMM2-CDG. We conducted a literature review of PMM2-CDG patients with reported CHD. Of the 14 patients with PMM2-CDG and cardiac malformation, the most common CHD's were tetralogy of Fallot, patent ductus arteriosus, and truncus arteriosus. The potential important link between CDG and CHD is stressed and discussed. Furthermore, the importance of multidisciplinary care for CDG patients including early referral to pediatric cardiologists is highlighted.

Factor XII in PMM2-CDG patients: role of N-glycosylation in the secretion and function of the first element of the contact pathway

Background

Congenital disorders of glycosylation (CDG) are rare diseases with impaired glycosylation and multiorgan disfunction, including hemostatic and inflammatory disorders. Factor XII (FXII), the first element of the contact phase, has an emerging role in hemostasia and inflammation. FXII deficiency protects against thrombosis and the p.Thr309Lys variant is involved in hereditary angioedema through the hyperreactivity caused by the associated defective O-glycosylation. We studied FXII in CDG aiming to supply further information of the glycosylation of this molecule, and its functional and clinical effects. Plasma FXII from 46 PMM2-CDG patients was evaluated by coagulometric and by Western Blot in basal conditions, treated with N-glycosydase F or activated by silica or dextran sulfate. A recombinant FXII expression model was used to validate the secretion and glycosylation of wild-type and variants targeting the two described FXII N-glycosylation sites (p.Asn230Lys; p.Asn414Lys) as well as the p.Thr309Lys variant.

Results

PMM2-CDG patients had normal FXII levels (117%) but high proportions of a form lacking N-glycosylation at Asn414. Recombinant FXII p.Asn230Lys, and p.Asn230Lys&p.Asn414Lys had impaired secretion and increased intracellular retention compared to wild-type, p.Thr309Lys and p.Asn414Lys variants. The hypoglycosylated form of PMM2-CDG activated similarly than FXII fully glycosylated. Accordingly, no PMM2-CDG had angioedema. FXII levels did not associate to vascular events, but hypoglycosylated FXII, like hypoglycosylated transferrin, antithrombin and FXI levels did it.

Conclusions

N-glycosylation at Asn230 is essential for FXII secretion. PMM2-CDG have high levels of FXII lacking N-glycosylation at Asn414, but this glycoform displays similar activation than fully glycosylated, explaining the absence of angioedema in CDG.

In Vitro Fertilisation (IVF) Associated with Preimplantation Genetic Testing for Monogenic Diseases (PGT-M) in a Romanian Carrier Couple for Congenital Disorder of Glycosylation Type Ia (CDG-Ia): A Case Report

Background: Congenital disorder of glycosylation (CDG) is a severe morphogenic and metabolic disorder that affects all of the systems of organs and is caused by a mutation of the gene PMM2, having a mortality rate of 20% during the first months of life. Results: Here we report the outcome of an in vitro fertilisation (IVF) cycle associated with preimplantation genetic testing for monogenic diseases (PGT-M) in a Romanian carrier couple for CDG type Ia with distinct mutations of the PMM2 gene. The embryonic biopsy was performed on day five of the blastocyst stage for six embryos. The amplification of the whole genome had been realized by using the PicoPLEX WGA kit. Using the Array Comparative Genomic Hybridisation technique, we detected both euploid and aneuploid embryos. The identification of the PMM2 mutation on exon 5 and exon 6 was performed for the euploid embryos through Sanger Sequencing with specific primers on ABI 3500. Of the six embryos tested, only three were euploid. One had compound heterozygosity and the remaining two were simple heterozygotes. Conclusion: PGT-M should be strongly considered for optimising embryo selection in partners with single-gene mutations in order to prevent transmission to the offspring.

Lysosomal storage disease spectrum in nonimmune hydrops fetalis: a retrospective case control study

OBJECTIVES

Nonimmune hydrops fetalis (NIHF) accounts for 90% of hydrops fetalis cases. About 15% to 29% of unexplained NIHF cases are caused by lysosomal storage diseases (LSD). We review the spectrum of LSD and associated clinical findings in NIHF in a cohort of patients referred to our institution.

METHODS

We present a retrospective case-control study of cases with NIHF referred for LSD biochemical testing at a single center. Cases diagnosed with LSD were matched to controls with NIHF and negative LSD testing and analyzed according to the STROBE criteria to the extent the retrospective nature of this study allowed.

RESULTS

Between January 2006 and December 2018, 28 patients with NIHF were diagnosed with a LSD. Eight types of LSD were diagnosed: galactosialidosis 8/28 (28.6%), sialic acid storage disease (SASD) 5/28 (17.9%), mucopolysaccharidosis VII 5/28 (17.9%), Gaucher 4/28 (14.3%), sialidosis 2/28 (7.1%), GM1 gangliosidosis 2/28 (7.1%), Niemann-Pick disease type C 1/28 (3.6%), and mucolipidosis II/III 1/28 (3.6%). Associated clinical features were hepatomegaly 16/21 (76.2%) vs 22/65 (33.8%), P < .05, splenomegaly 12/20 (60.0%) vs 14/58 (24.1%), P < .05, and hepatosplenomegaly 10/20 (50.0%) vs 13/58 (22.4%) P < .05.

CONCLUSION

The most common LSD in NIHF were galactosialidosis, SASD, mucopolysaccharidosis VII, and Gaucher disease. LSD should be considered in unexplained NIHF cases, particularly if hepatomegaly, splenomegaly, or hepatosplenomegaly is visualized on prenatal ultrasound.

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.

Recognizable phenotypes in CDG

Pattern recognition, using a group of characteristic, or discriminating features, is a powerful tool in metabolic diagnostic. A classic example of this approach is used in biochemical analysis of urine organic acid analysis, where the reporting depends more on the correlation of pertinent positive and negative findings, rather than on the absolute values of specific markers. Similar uses of pattern recognition in the field of biochemical genetics include the interpretation of data obtained by metabolomics, like glycomics, where a recognizable pattern or the presence of a specific glycan sub-fraction can lead to the direct diagnosis of certain types of congenital disorders of glycosylation. Another indispensable tool is the use of clinical pattern recognition-or syndromology-relying on careful phenotyping. While genomics might uncover variants not essential in the final clinical expression of disease, and metabolomics could point to a mixture of primary but also secondary changes in biochemical pathways, phenomics describes the clinically relevant manifestations and the full expression of the disease. In the current review we apply phenomics to the field of congenital disorders of glycosylation, focusing on recognizable differentiating findings in glycosylation disorders, characteristic dysmorphic features and malformations in PMM2-CDG, and overlapping patterns among the currently known glycosylation disorders based on their pathophysiological basis.

Renal involvement in PMM2-CDG, a mini-review

Phosphomannomutase 2 deficiency (PMM2-CDG) is the most common N-linked glycosylation disorder. The majority of patients present with a multisystem phenotype, including central nervous system involvement, hepatopathy, gastrointestinal and cardiac symptoms, endocrine dysfunction and abnormal coagulation. Renal abnormalities including congenital malformations and altered renal function are part of the multisystem manifestations of congenital disorders of glycosylation. We reviewed the literature on 933 patients with molecularly and/or enzymatically confirmed PMM2 deficiency to evaluate the incidence of renal involvement in PMM2-CDG. Renal abnormalities were reported in 56 patients. Congenital abnormalities were present in 41 out of these 55. Cystic kidney and mild proteinuria were the most common findings. One of the most severe renal manifestations, congenital nephrotic syndrome, was detected in 6 children. Renal manifestations were not associated with the presence of specific PMM2 alleles. This review summarizes the reported renal abnormalities in PMM2-CDG and draws attention to the pathophysiological impact of abnormal glycosylation on kidney structure and function.

Metabolic causes of nonimmune hydrops fetalis: A next-generation sequencing panel as a first-line investigation

PURPOSES

Hydrops fetalis is a life-threatening fetal condition, and 85% of all cases are classified as nonimmune hydrops fetalis (NIHF). Up to 15% of NIHF cases may be due to inborn errors of metabolism (IEM), but a large proportion of cases linked to metabolic disorders remains undiagnosed. This lack of diagnosis may be related to the limitations of conventional biological procedures, which involve sequential investigations and require multiple samples and steps. In addition, this approach is time consuming. We have developed a next-generation sequencing (NGS) panel to investigate metabolic causes of NIHF, ascites, and polyhydramnios associated to another fetal abnormality.

METHODS

The hydrops fetalis (HydFet) panel was designed to cover the coding regions and flanking intronic sequences of 41 genes. A retrospective study of amniotic fluid samples from 40 subjects was conducted. A prospective study was subsequently initiated, and six samples were analyzed using the NGS panel.

RESULTS

Five IEM diagnoses were made using the HydFet panel (Niemann-Pick type C (NPC), Barth syndrome, HNF1Β deficiency, GM1 gangliosidosis, and Gaucher disease). This analysis also allowed the identification of 8p sequence triplication in an additional case.

CONCLUSION

NGS combined with robust bioinformatics analyses is a useful tool for identifying the causative variants of NIHF. Subsequent functional characterization of the protein encoded by the altered gene and morphological studies may confirm the diagnosis. This paradigm shift allows a significant improvement of IEM diagnosis in NIHF.

Cardiac complications of congenital disorders of glycosylation (CDG): a systematic review of the literature

Congenital disorders of glycosylation (CDG) are inborn errors of metabolism due to protein and lipid hypoglycosylation. This rapidly growing family of genetic diseases comprises 103 CDG types, with a broad phenotypic diversity ranging from mild to severe poly-organ -system dysfunction. This literature review summarizes cardiac involvement, reported in 20% of CDG. CDG with cardiac involvement were divided according to the associated type of glycosylation: N-glycosylation, O-glycosylation, dolichol synthesis, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, COG complex, V-ATPase complex, and other glycosylation pathways. The aim of this review was to document and interpret the incidence of heart disease in CDG patients. Heart disorders were grouped into cardiomyopathies, structural defects, and arrhythmogenic disorders. This work may contribute to improved early management of cardiac complications in CDG.

Immunological aspects of congenital disorders of glycosylation (CDG): a review

Congenital disorders of glycosylation (CDG) are a rapidly growing family of genetic diseases comprising more than 85 known distinct disorders. They show a great phenotypic variability ranging from multi-organ/system to mono-organ/system involvement with very mild to extremely severe expression. Immunological dysfunction has a significant impact on the phenotype in a minority of CDG. CDG with major immunological involvement are ALG12-CDG, MAGT1-CDG, MOGS-CDG, SLC35C1-CDG and PGM3-CDG. This review discusses the variety of immunological abnormalities reported in human CDG. Understanding the immunological aspects of CDG may contribute to a better management/treatment of these pathologies and possibly of more common diseases, such as inflammatory diseases.

Further Delineation of the ALG9-CDG Phenotype

ALG9-CDG is one of the less frequently reported types of CDG. Here, we summarize the features of six patients with ALG9-CDG reported in the literature and report the features of four additional patients. The patients presented with drug-resistant infantile epilepsy, hypotonia, dysmorphic features, failure to thrive, global developmental disability, and skeletal dysplasia. One patient presented with nonimmune hydrops fetalis. A brain MRI revealed global atrophy with delayed myelination. Exome sequencing identified a novel homozygous mutation c.1075G>A, p.E359K of the ALG9 gene. The results of our analysis of these patients expand the knowledge of ALG9-CDG phenotype.

TMEM165 Deficiency: Postnatal Changes in Glycosylation

Congenital disorders of glycosylation form a rapidly growing group of inherited metabolic diseases. As glycosylation affects proteins all over the organism, a mutation in a single gene leads to a multisystemic disorder. We describe a patient with TMEM165-CDG with facial dysmorphism, nephrotic syndrome, cardiac defects, enlarged cerebral ventricles, feeding problems, and neurological involvement. Having confirmed the diagnosis via prenatal diagnostics, we were able to observe the glycosylation right from birth, finding a pathological pattern already on the first day of life. Within the next few weeks, hypoglycosylation progressed to less sialylated and then also to hypogalactosylated isoforms. On the whole, there has not been much published evidence concerning postnatal glycosylation and its adaptational process. This is the first paper reporting changes in glycosylation patterns over the first postnatal weeks in TMEM165-CDG.

Statistical Metamodeling and Sequential Design of Computer Experiments to Model Glyco-Altered Gating of Sodium Channels in Cardiac Myocytes

Glycan structures account for up to 35% of the mass of cardiac sodium ( Nav ) channels. To question whether and how reduced sialylation affects Nav activity and cardiac electrical signaling, we conducted a series of in vitro experiments on ventricular apex myocytes under two different glycosylation conditions, reduced protein sialylation (ST3Gal4(-/-)) and full glycosylation (control). Although aberrant electrical signaling is observed in reduced sialylation, realizing a better understanding of mechanistic details of pathological variations in INa and AP is difficult without performing in silico studies. However, computer model of Nav channels and cardiac myocytes involves greater levels of complexity, e.g., high-dimensional parameter space, nonlinear and nonconvex equations. Traditional linear and nonlinear optimization methods have encountered many difficulties for model calibration. This paper presents a new statistical metamodeling approach for efficient computer experiments and optimization of Nav models. First, we utilize a fractional factorial design to identify control variables from the large set of model parameters, thereby reducing the dimensionality of parametric space. Further, we develop the Gaussian process model as a surrogate of expensive and time-consuming computer models and then identify the next best design point that yields the maximal probability of improvement. This process iterates until convergence, and the performance is evaluated and validated with real-world experimental data. Experimental results show the proposed algorithm achieves superior performance in modeling the kinetics of Nav channels under a variety of glycosylation conditions. As a result, in silico models provide a better understanding of glyco-altered mechanistic details in state transitions and distributions of Nav channels. Notably, ST3Gal4(-/-) myocytes are shown to have higher probabilities accumulated in intermediate inactivation during the repolarization and yield a shorter refractory period than WTs. The proposed statistical design of computer experiments is generally extensible to many other disciplines that involve large-scale and computationally expensive models.

Thrombotic complications in patients with PMM2-CDG

Many proteins regulating coagulation, including factor IX, factor XI, Antithrombin-III, Protein C and Protein S are deficient or decreased in activity in congenital disorders of glycosylation (CDG). Because of the imbalance of coagulation and anticoagulation factors, some patients develop acute vascular events, such as thrombosis. Identifying patients with increased risk for thrombotic events could prevent serious complications and even mortality. We performed a systematic review on patients diagnosed with the most common CDG form; PMM2-CDG, reported between 1990 and 2012 in medical literature. We also evaluated our PMM2-CDG patient-cohort of 15 patients. In total, based on the availability of comprehensive clinical descriptions, 100 patients were included in the study. Patients with and without thrombotic events were compared based on the alterations of the following glycosylated coagulation and anticoagulation factors: Antithrombin-III, Protein C, Protein S, factors IX and XI. We also assessed the global hemostasis, family history and provoking events. In the group of 100 PMM2-CDG patients 14 had suffered a venous or arterial thrombotic event. Low activity of several anticoagulation factors correlated with thrombotic events. Relatively high factor IX and XI activities were not associated with thrombosis. Prolonged PT and aPTT did not seem to protect against thrombosis in patients. Surgical procedures were frequently associated with thrombotic events. Based on the association of thrombosis and surgery in PMM2-CDG we advise to avoid elective surgical procedures in PMM2-CDG patients. Easily preventable risk factors like immobility should be treated with regular physiotherapy. We suggest a yearly follow-up for Antithrombin-III and Protein C levels and parent education for early thrombotic signs in CDG.

Perinatal and early infantile symptoms in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) are a rapidly growing family of inborn errors. Screening for CDG in suspected cases is usually performed in the first year of life by serum transferrin isoelectric focusing or mass spectrometry. Based on the transferrin analysis patients can be biochemically diagnosed with a type 1 or type 2 transferrin pattern, and labeled as CDG-I, or CDG-II. The diagnosis of CDG is frequently delayed due to the highly variable phenotype, some cases showing single organ involvement and others mimicking syndromes, like skeletal dysplasia, cutis laxa syndrome, or congenital muscle dystrophy. The aim of our study was to evaluate perinatal abnormalities and early discriminative symptoms in 58 patients consecutively diagnosed with diverse CDG-subtypes. Neonatal findings and clinical features in the first months of life were studied in 36 children with CDG-I and 22 with CDG-II. Maternal complications were found in five, small for gestational age in nine patients. Five children had abnormal neonatal screening results for hypothyroidism. Congenital microcephaly and neonatal seizures were common in CDG-II. Inverted nipples were uncommon with 5 out of 58 children. Dysmorphic features were mostly nonspecific, except for cutis laxa. Early complications included feeding problems, cardiomyopathy, thrombosis, and bleeding. Cases presenting in the neonatal period had the highest mortality rate. Survival in CDG patients is highly dependent on early intervention therapy. We recommend low threshold screening for glycosylation disorders in infants with neurologic symptoms, even in the absence of abnormal fat distribution. Growth retardation and neonatal bleeding increase suspicion for CDG.

Lysosomal storage disorder in non-immunological hydrops fetalis (NIHF): more common than assumed? Report of four cases with transient NIHF and a review of the literature

Background

Lysosomal storage disorders (LSD) are a rare cause of non immunological hydrops fetalis (NIHF) and congenital ascites. The reported incidence is about 1%. The incidence of idiopathic NIHF is estimated to be about 18%.

Patients and methods

We report four cases with transient hydrops fetalis resulting from LSD and performed a literature review on LSD with NIHF and congenital ascites in combination.

Results

At present, 12 different LSDs are described to be associated with NIHF or congenital ascites. Most patients had a family history of NIHF, where the preceding sibling had not been examined. A diagnostic approach to the fetus with NIHF due to suspected LSD either in utero or postnatal is suggested. Transient forms of NIHF and/or ascites in association with MPS IVA, MPS VII and NPC are described for the first time in this publication.

Conclusions

LSD should be considered in transient hydrops. Enzymatic studies in chorionic villous sample or amniotic cultured cells, once the most common conditions associated with fetal ascites or hydrops have been ruled out, are important. This paper emphasizes the fact that LSD is significantly higher than the estimated 1% in previous studies, which is important for genetic counseling as there is a high risk of recurrence and the availability of enzyme replacement therapy for an increasing number of LSD.

Thyroid function in PMM2-CDG: diagnostic approach and proposed management

Glycoproteins are essential in the production, transport, storage and regulation of thyroid hormones. Altered glycosylation has a potential impact on thyroid function. Abnormal thyroid function tests have been described in patients with congenital disorders of glycosylation. We evaluated the reliability of biochemical markers and investigated thyroid function in 18 PMM2-CDG patients. We propose an expectative therapeutic approach for neonates with thyroid abnormalities in CDG.

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.

Autosomal recessive dilated cardiomyopathy due to DOLK mutations results from abnormal dystroglycan O-mannosylation

Genetic causes for autosomal recessive forms of dilated cardiomyopathy (DCM) are only rarely identified, although they are thought to contribute considerably to sudden cardiac death and heart failure, especially in young children. Here, we describe 11 young patients (5-13 years) with a predominant presentation of dilated cardiomyopathy (DCM). Metabolic investigations showed deficient protein N-glycosylation, leading to a diagnosis of Congenital Disorders of Glycosylation (CDG). Homozygosity mapping in the consanguineous families showed a locus with two known genes in the N-glycosylation pathway. In all individuals, pathogenic mutations were identified in DOLK, encoding the dolichol kinase responsible for formation of dolichol-phosphate. Enzyme analysis in patients' fibroblasts confirmed a dolichol kinase deficiency in all families. In comparison with the generally multisystem presentation in CDG, the nonsyndromic DCM in several individuals was remarkable. Investigation of other dolichol-phosphate dependent glycosylation pathways in biopsied heart tissue indicated reduced O-mannosylation of alpha-dystroglycan with concomitant functional loss of its laminin-binding capacity, which has been linked to DCM. We thus identified a combined deficiency of protein N-glycosylation and alpha-dystroglycan O-mannosylation in patients with nonsyndromic DCM due to autosomal recessive DOLK mutations.

Classification, diagnosis and potential mechanisms in pontocerebellar hypoplasia

Pontocerebellar Hypoplasia (PCH) is group of very rare, inherited progressive neurodegenerative disorders with prenatal onset. Up to now seven different subtypes have been reported (PCH1-7). The incidence of each subtype is unknown. All subtypes share common characteristics, including hypoplasia/atrophy of cerebellum and pons, progressive microcephaly, and variable cerebral involvement. Patients have severe cognitive and motor handicaps and seizures are often reported. Treatment is only symptomatic and prognosis is poor, as most patients die during infancy or childhood. The genetic basis of different subtypes has been elucidated, which makes prenatal testing possible in families with mutations. Mutations in three tRNA splicing endonuclease subunit genes were found to be responsible for PCH2, PCH4 and PCH5. Mutations in the nuclear encoded mitochondrial arginyl- tRNA synthetase gene underlie PCH6. The tRNA splicing endonuclease, the mitochondrial arginyl- tRNA synthetase and the vaccinia related kinase1 are mutated in the minority of PCH1 cases. These genes are involved in essential processes in protein synthesis in general and tRNA processing in particular. In this review we describe the neuroradiological, neuropathological, clinical and genetic features of the different PCH subtypes and we report on in vitro and in vivo studies on the tRNA splicing endonuclease and mitochondrial arginyl-tRNA synthetase and discuss their relation to pontocerebellar hypoplasia.

Clinical, neuroradiological and genetic findings in pontocerebellar hypoplasia

Pontocerebellar hypoplasia is a group of autosomal recessive neurodegenerative disorders with prenatal onset. The common characteristics are cerebellar hypoplasia with variable atrophy of the cerebellum and the ventral pons. Supratentorial involvement is reflected by variable neocortical atrophy, ventriculomegaly and microcephaly. Mutations in the transfer RNA splicing endonuclease subunit genes (TSEN54, TSEN2, TSEN34) were found to be associated with pontocerebellar hypoplasia types 2 and 4. Mutations in the mitochondrial transfer RNA arginyl synthetase gene (RARS2) were associated with pontocerebellar hypoplasia type 6. We studied a cohort of 169 patients from 141 families for mutations in these genes, of whom 106 patients tested positive for mutations in one of the TSEN genes or the RARS2 gene. In order to delineate the neuroradiological and clinical phenotype of patients with mutations in these genes, we compared this group with 63 patients suspected of pontocerebellar hypoplasia who were negative on mutation analysis. We found a strong correlation (P < 0.0005) between TSEN54 mutations and a dragonfly-like cerebellar pattern on magnetic resonance imaging, in which the cerebellar hemispheres are flat and severely reduced in size and the vermis is relatively spared. Mutations in TSEN54 are clinically associated with dyskinesia and/or dystonia and variable degrees of spasticity, in some cases with pure generalized spasticity. Nonsense or splice site mutations in TSEN54 are associated with a more severe phenotype of more perinatal symptoms, ventilator dependency and early death. In addition, we present ten new mutations in TSEN54, TSEN2 and RARS2. Furthermore, we show that pontocerebellar hypoplasia type 1 together with elevated cerebrospinal fluid lactate may be caused by RARS2 mutations.

Should PMM2-deficiency (CDG Ia) be searched in every case of unexplained hydrops fetalis?

Hydrops fetalis (HF) is characterized by an accumulation of fluid in the extracellular compartments and in body cavities. Non-immune HF (NIHF) is caused by a wide variety of disorders and overall, 20-25% of NIHF remain unexplained. Inborn errors of metabolism, mostly lysosomal storage diseases have been estimated to account for 1-2% of cases, leading to HF by anemia or liver failure. Very few cases of NIHF and Congenital Disorder of Glycosylation (CDG) have been reported. We present here a case of recurrence of HF in a non-related couple in which the diagnosis of CDG type I was suspected at fetal pathological examination then confirmed at the enzymatic and molecular levels, as well as on a characteristic CDG I serum transferrin profile at 30weeks of gestation. We also provide a systematic review of reported cases with CDG type I and NIHF reported thus far. When NIHF remains unexplained despite exhaustive obstetrical screening, analysis of PMM activity in the parents' leucocytes is possible and might be performed easily during pregnancy. The accurate diagnosis is important in terms of counseling during pregnancy or later, in order to allow an early molecular prenatal diagnosis for the following pregnancies.

Comprehensive description of the phenotype of the first case of congenital disorder of glycosylation due to RFT1 deficiency (CDG In)

Very recently, Haeuptle and colleagues described a new glycosylation defect due to RFT1 deficiency (CDG In). Accumulation of intracellular DolPP-GlcNAc(2)Man(5) with absence of cytosolic GlcNAc(2)Man(5) resembled the profile of a yeast mutant deficient in RFT1, a protein that is thought to have a role as a flippase. This is the first detailed description of the clinical phenotype of this patient. It was a severe disorder affecting intrauterine development and movement, and leading to intrauterine growth retardation. The child was born with several musculoskeletal abnormalities including arthrogryposis. Postnatally, severe reflux and irregular bowl movements contributed to failure to thrive. The patient showed very little development and no vision and suffered from drug-resistant epilepsy. Abnormal coagulation resulted in thrombosis and the patient died at the age of 4 years from a pulmonary embolus.

Long-term evolution of eight Spanish patients with CDG type Ia: typical and atypical manifestations

Congenital disorder of glycosylation Ia (CDG-Ia) is a metabolic disease with a broad spectrum of clinical signs, including recently described mild phenotypes. Our aim was to describe the clinical presentation and follow-up of eight CDG-Ia patients highlighting atypical features and aspects of evolution of the disease. CDG diagnosis was confirmed by enzymatic analysis of phosphomannomutase (PMM2) and molecular studies of the PMM2 gene. Four neonates presented with cerebral haemorrhage (1), failure to thrive (2) and non-immune hydrops (1) and a fatal course to death (2); pathological examination of the brain in one case revealed olivopontocerebellar atrophy of prenatal origin. During infancy failure to thrive, coagulopathy and hepatopathy were the most significant causes of morbidity, but these disappeared after the first years of life in most patients. Three patients are currently in their 20s; they present mental retardation and severe motor impairment but no acute decompensations were noticed after the first decade of life. They do not present spinal or thoracic deformities otherwise observed in patients from northern countries. A 10-year-old patient who manifested gastrointestinal dysfunction in early childhood showed normal neurodevelopment. Mutation analysis of the PMM2 gene showed great variability, with all patients being compound heterozygous for two different mutations. Long-term evolution in our patients indicates that CDG-Ia is a stable systemic and neurological condition after the first decade of life. The diverse phenotypes and atypical manifestations in our series may be due to their genetic heterogeneity.

Primary disorders of metabolism and disturbed fetal brain development

There exists a link between the in utero metabolic environment and the development of the fetal nervous system. Prenatal neurosonography offers a unique, noninvasive tool in the detection of developmental brain malformations and the ability to monitor changes over time. This article explores the association of malformations of cerebral development reported in association with inborn errors of metabolism, and speculates on potential mechanisms by which such malformations arise. The detection of cerebral malformations prenatally should lead to a search for both genetic etiologies and inborn errors of metabolism in the fetus. Improving the changes of an early diagnosis provides for timely therapeutic interventions and it is hoped a brighter future for affected children and their families.

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.

Pericardial and abdominal fluid accumulation in congenital disorder of glycosylation type Ia

The association of fetal hydrops with Congenital Disorders of Glycosylation (CDG) has been reported previously. Pericardial fluid accumulation and ascites were also observed in a few young patients with CDG type Ia. Here we describe the clinical and biochemical features in three children developing life-threatening extravascular fluid accumulation. All patients carried severe PMM2 mutations comparable to the earlier reported patients with fetal hydrops. One patient was successfully treated with a pericardial-pleural shunt placement. Pericardial fluid accumulation and generalized oedema resolved temporarily in the other two children on regular albumin infusions and the use of diuretics. Sequential abdominal punctures were unsuccessful in the treatment of the extensive ascites production. The use of non-steroid anti-inflammatory agents and the application of high dose steroids had no clinical effect. Severe extravascular fluid accumulation progressed to decompensation and death. Biochemical investigations of the abdominal fluid and pericardial fluid demonstrated a high extracellular protein concentration, increased cytokine concentrations and an abnormal transferrin isoelectric focusing pattern characteristic of CDG type I. Our results are consistent with a local activation of the cytokine pathways and subsequent protein transport through the endothelial surface to the extravascular space. Normal glycosylation of cell surface proteins is essential for the normal fluid balance and protein transport through the pericardial and peritoneal membrane. Future therapeutic efforts should be directed to inhibit the abnormal immune response and excessive protein transport in this life-threatening complication of CDG syndrome.

Genetic syndromes and prenatally detected renal anomalies

Renal anomalies are frequently detected on the routine second trimester scan offered to all pregnant women in the UK. These anomalies may be isolated but can also be associated with other congenital anomalies. Many combinations of ultrasound scan findings constitute recognised genetic entities. Knowledge of these conditions is essential for adequate management of the pregnancy and subsequent balanced parental counselling. This short review discusses the common genetic syndromes associated with the renal abnormalities identified on the antenatal ultrasound scan, and also provides an overview of renal symptoms in chromosome imbalances and after teratogenic influences.

Cerebellar ataxia and congenital disorder of glycosylation Ia (CDG-Ia) with normal routine CDG screening

Cerebellar ataxia can have many genetic causes among which are the congenital disorders of glycosylation type I (CDG-I). In this group of disorders, a multisystem phenotype is generally observed including the involvement of many organs, the endocrine, hematologic and central nervous systems. A few cases of CDG-Ia have been reported with a milder presentation, namely cerebellar hypoplasia as an isolated abnormality. To identify patients with a glycosylation disorder, isofocusing of plasma transferrin is routinely performed. Here, we describe two CDG-Ia patients,who presented with mainly ataxia and cerebellar hypoplasia and with a normal or only slightly abnormal transferrin isofocusing result. Surprisingly, the activity of the corresponding enzyme phosphomannomutase was clearly deficient in both leucocytes and fibroblasts. Therefore, in patients presenting with apparently recessive inherited ataxia caused by cerebellar hypoplasia and an unknown genetic aetiology after proper diagnostic work-up, we recommend the measurement of phosphomannomutase activity when transferrin isofocusing is normal or inconclusive.