Congenital disorders of glycosylation

Case report: Novel genotype of ALG2-CDG and confirmation of the heptasaccharide glycan (NeuAc-Gal-GlcNAc-Man2-GlcNAc2) as a specific diagnostic biomarker

This report outlines the case of a child affected by a type of congenital disorder of glycosylation (CDG) known as ALG2-CDG (OMIM 607906), presenting as a congenital myasthenic syndrome (CMS) caused by variants identified in ALG2, which encodes an α1,3-mannosyltransferase (EC 2.4.1.132) involved in the early steps of N-glycosylation. To date, fourteen cases of ALG2-CDG have been documented worldwide. From birth, the child experienced perinatal asphyxia, muscular weakness, feeding difficulties linked to an absence of the sucking reflex, congenital hip dislocation, and hypotonia. Over time, additional complications emerged, such as inspiratory stridor, gastroesophageal reflux, low intake, recurrent seizures, respiratory infections, an inability to maintain the head upright, and a global developmental delay. Whole genome sequencing (WGS) revealed the presence of two ALG2 variants in compound heterozygosity: a novel variant c.1055_1056delinsTGA p.(Ser352Leufs*3) and a variant of uncertain significance (VUS) c.964C>A p.(Pro322Thr). Additional studies, including determination of carbohydrate-deficient transferrin (CDT) revealed a mild type I CDG pattern and the presence of an abnormal transferrin glycoform containing a linear heptasaccharide consisting of one sialic acid, one galactose, one N-acetyl-glucosamine, two mannoses and two N-acetylglucosamines (NeuAc-Gal-GlcNAc-Man2-GlcNAc2), ALG2-CDG diagnostic biomarker, confirming the pathogenicity of these variants.

Lectin-Based Immunophenotyping and Whole Proteomic Profiling of CT-26 Colon Carcinoma Murine Model

A murine colorectal carcinoma (CRC) model was established. CT26 colon carcinoma cells were injected into BALB/c mice's spleen to study the primary tumor and the mechanisms of cell spread of colon cancer to the liver. The CRC was verified by the immunohistochemistry of Pan Cytokeratin and Vimentin expression. Immunophenotyping of leukocytes isolated from CRC-bearing BALB/c mice or healthy controls, such as CD19+ B cells, CD11+ myeloid cells, and CD3+ T cells, was carried out using fluorochrome-labeled lectins. The binding of six lectins to white blood cells, such as galectin-1 (Gal1), siglec-1 (Sig1), Sambucus nigra lectin (SNA), Aleuria aurantia lectin (AAL), Phytolacca americana lectin (PWM), and galectin-3 (Gal3), was assayed. Flow cytometric analysis of the splenocytes revealed the increased binding of SNA, and AAL to CD3 + T cells and CD11b myeloid cells; and increased siglec-1 and AAL binding to CD19 B cells of the tumor-bearing mice. The whole proteomic analysis of the established CRC-bearing liver and spleen versus healthy tissues identified differentially expressed proteins, characteristic of the primary or secondary CRC tissues. KEGG Gene Ontology bioinformatic analysis delineated the established murine CRC characteristic protein interaction networks, biological pathways, and cellular processes involved in CRC. Galectin-1 and S100A4 were identified as upregulated proteins in the primary and secondary CT26 tumor tissues, and these were previously reported to contribute to the poor prognosis of CRC patients. Modelling the development of liver colonization of CRC by the injection of CT26 cells into the spleen may facilitate the understanding of carcinogenesis in human CRC and contribute to the development of novel therapeutic strategies.

PIGN c.776T>C (p.Phe259Ser) variant present in trans with a pathogenic variant for PIGN-congenital disorder of glycosylation: Bella-Noah syndrome

Glycosylation is the most common protein and lipid post-translational modification in humans. Congenital disorders of glycosylation (CDG) are characterized by both genetic and clinical heterogeneity, presenting multisystemic manifestations, and in most cases are autosomal recessive in inheritance. The PIGN gene is responsible for the addition of phosphoethanolamine to the first mannose in the glycosylphosphatidylinositol (GPI)-anchor biosynthesis pathway, a highly conserved process that enables proteins to bind to the cell surface membrane. Here, we report a family with two siblings pediatric cases with the exact same compound heterozygous variants in PIGN. The (c.776T > C) variant of uncertain significance (VUS) together with a known pathogenic variant (c.932T > G), resulting in clinical features compatible with PIGN-related conditions, more specific the CDG. This is the first time that PIGN variant c.776T > C is reported in literature in individuals with PIGN-congenital disorder of glycosylation (PIGN-CDG), and the current submission in ClinVar by Invitae® is specifically of our case. Detailed clinical information and molecular analyses are presented. Here, we show for the first time two affected siblings with one pathogenic variant (c.932T > G) and the c.776T > C VUS in trans. In honor of the family, we propose the name Bella-Noah Syndrome for disorder.

Resilience in patients and family caregivers living with congenital disorders of glycosylation (CDG): a quantitative study using the brief resilience coping scale (BRCS)

BACKGROUND

Patients and family caregivers living with Congenital Disorders of Glycosylation (CDG) experience a heavy burden, which can impact their resiliency and quality of life. The study's purpose was to measure the resilience levels of patients and family caregivers living with CDG using the brief resilience coping scale.

METHODS

We conducted an observational, cross-sectional study with 23 patients and 151 family caregivers living with CDG. Descriptive analyses were performed to characterize patients with CDG and family caregivers' samples. Additionally, we assessed correlations between resilience and specific variables (e.g., age, academic degree, time until diagnosis) and examined resilience differences between groups (e.g., sex, marital status, occupation, professional and social support).

RESULTS

GNE myopathy was the most prevalent CDG among patients, while in family caregivers was PMM2-CDG. Both samples showed medium levels of resilience coping scores. Individuals with GNE myopathy had significantly higher scores of resilience compared to patients with other CDG. Resilience was positively correlated with educational degree in patients with CDG. Family caregivers had marginally significant higher scores of resilience coping if they received any kind of professional support or had contact with other families or people with the same or similar disease, compared with unsupported individuals.

CONCLUSIONS

Despite the inherited difficulties of living with a life-threatening disease like CDG, patients and family caregivers showed medium resilient coping levels. Resilience scores changed significantly considering the CDG genotype, individual's academic degree and professional and social support. These exploratory findings can empower the healthcare system and private institutions by promoting the development of targeted interventions to enhance individuals` coping skills and improve the overall well-being and mental health of the CDG community.

A rare case report of type 1 congenital disorders of glycosylation with acute decompensated heart failure and the incidental discovery of congenital disorders of glycosylation associated dilated cardiomyopathy and acute myocarditis

Background

Congenital disorders of glycosylation (CDG) are rare genetically inherited defects leading to enzyme deficiency or malfunction in the glycosylation pathway. Normal glycosylation is essential to the development of normal cardiac anatomy and function. Congenital disorders of glycosylation-related cardiomyopathy are often the first manifestation detected in early life and may lead to sudden cardiac death. Approximately one-fifth of CDG types are related to cardiac diseases that include cardiomyopathy, rhythm disturbances, pericardial effusions, and structural heart disease.

Case summary

We report a rare case of a 26-year-old lady with CDG-1 who presented with acute-onset dyspnoea. She had respiratory tract symptoms for the past 2 weeks. With the relevant clinical and biochemical findings, including supportive findings on echocardiogram and cardiac magnetic resonance imaging, we have managed to arrive at a diagnosis of severe pneumonia leading to acute decompensated heart failure, as well as the discovery of an underlying CDG-associated dilated cardiomyopathy (DCM) and acute myocarditis. Anti-failure medications and i.v. methylprednisolone were commenced, and she showed gradual clinical improvement with an increase of her left ventricular function. She was discharged home well with anti-failure therapy, prednisolone, and a follow-up echocardiogram with further review in the heart failure clinic.

Discussion

In conclusion, this case report highlights the need for accurate diagnosis and prompt management of CDG-associated DCM, leading to a successful recovery and discharge from hospital care. With this, we hope to add to the increasing number of reported cases of CDG-related cardiac disease in the medical literature to emphasize the importance of screening and follow-up for any underlying cardiac diseases in patients with CDG.

Splice-Modulating Antisense Oligonucleotides as Therapeutics for Inherited Metabolic Diseases

The last decade (2013-2023) has seen unprecedented successes in the clinical translation of therapeutic antisense oligonucleotides (ASOs). Eight such molecules have been granted marketing approval by the United States Food and Drug Administration (US FDA) during the decade, after the first ASO drug, fomivirsen, was approved much earlier, in 1998. Splice-modulating ASOs have also been developed for the therapy of inborn errors of metabolism (IEMs), due to their ability to redirect aberrant splicing caused by mutations, thus recovering the expression of normal transcripts, and correcting the deficiency of functional proteins. The feasibility of treating IEM patients with splice-switching ASOs has been supported by FDA permission (2018) of the first "N-of-1" study of milasen, an investigational ASO drug for Batten disease. Although for IEM, owing to the rarity of individual disease and/or pathogenic mutation, only a low number of patients may be treated by ASOs that specifically suppress the aberrant splicing pattern of mutant precursor mRNA (pre-mRNA), splice-switching ASOs represent superior individualized molecular therapeutics for IEM. In this work, we first summarize the ASO technology with respect to its mechanisms of action, chemical modifications of nucleotides, and rational design of modified oligonucleotides; following that, we precisely provide a review of the current understanding of developing splice-modulating ASO-based therapeutics for IEM. In the concluding section, we suggest potential ways to improve and/or optimize the development of ASOs targeting IEM.

Glycan Modifications as Regulators of Stem Cell Fate

Glycosylation is a process where proteins or lipids are modified with glycans. The presence of glycans determines the structure, stability, and localization of glycoproteins, thereby impacting various biological processes, including embryogenesis, intercellular communication, and disease progression. Glycans can influence stem cell behavior by modulating signaling molecules that govern the critical aspects of self-renewal and differentiation. Furthermore, being located at the cell surface, glycans are utilized as markers for stem cell pluripotency and differentiation state determination. This review aims to provide a comprehensive overview of the current literature, focusing on the effect of glycans on stem cells with a reflection on the application of synthetic glycans in directing stem cell differentiation. Additionally, this review will serve as a primer for researchers seeking a deeper understanding of how synthetic glycans can be used to control stem cell differentiation, which may help establish new approaches to guide stem cell differentiation into specific lineages. Ultimately, this knowledge can facilitate the identification of efficient strategies for advancing stem cell-based therapeutic interventions.

Hypomorphic variants of SEL1L-HRD1 ER-associated degradation are associated with neurodevelopmental disorders

Recent studies using cell type-specific knockout mouse models have improved our understanding of the pathophysiological relevance of suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) endoplasmic reticulum-associated (ER-associated) degradation (ERAD); however, its importance in humans remains unclear, as no disease variant has been identified. Here, we report the identification of 3 biallelic missense variants of SEL1L and HRD1 (or SYVN1) in 6 children from 3 independent families presenting with developmental delay, intellectual disability, microcephaly, facial dysmorphisms, hypotonia, and/or ataxia. These SEL1L (p.Gly585Asp, p.Met528Arg) and HRD1 (p.Pro398Leu) variants were hypomorphic and impaired ERAD function at distinct steps of ERAD, including substrate recruitment (SEL1L p.Gly585Asp), SEL1L-HRD1 complex formation (SEL1L p.Met528Arg), and HRD1 activity (HRD1 p.Pro398Leu). Our study not only provides insights into the structure-function relationship of SEL1L-HRD1 ERAD, but also establishes the importance of SEL1L-HRD1 ERAD in humans.

Compound heterozygous variants in MAN2B2 identified in a Chinese child with congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) is a group inherited disorders. It is characterized by multi-organ dysfunction with significant morbidity and mortality. MAN2B2-CDG caused by pathogenic variants in the MAN2B2 gene was a rare CDG. To date, only one case of MAN2B2-CDG was reported. The representative clinical features were immune deficiency, dysmorphic facial features, coagulopathy, and severe developmental delay. More cases are needed to support the pathogenesis of MAN2B2 variation and elucidate its clinical heterogeneity. In this study, we described the clinical presentations of a CDG proband with compound heterozygous variants in MAN2B2. Serum N-glycan profiling was measured by MALDI coupled to time-of-flight mass spectrometry (MALDI-TOF MS). MALDI-TOF MS analysis of patient serum showed disorders of N-linked glycosylation, including increased N-glycans and elevated Man5/Man6 and Man5/Man9 value. Our proband presented severe developmental delay, dysmorphic facial features as in the previous case. But our case presented new features, including cleft palate and hypospadias with no immune deficiency. Our data expands both the molecular and clinical phenotypes of MAN2B2-CDG and highlights the importance of the role of MAN2B2 gene in CDG.

Biliary atresia is associated with polygenic susceptibility in ciliogenesis and planar polarity effector genes

BACKGROUND & AIMS

Biliary atresia (BA) is poorly understood and leads to liver transplantation (LT), with the requirement for and associated risks of lifelong immunosuppression, in most children. We performed a genome-wide association study (GWAS) to determine the genetic basis of BA.

METHODS

We performed a GWAS in 811 European BA cases treated with LT in US, Canadian and UK centers, and 4,654 genetically matched controls. Whole-genome sequencing of 100 cases evaluated synthetic association with rare variants. Functional studies included whole liver transcriptome analysis of 64 BA cases and perturbations in experimental models.

RESULTS

A GWAS of common single nucleotide polymorphisms (SNPs), i.e. allele frequencies >1%, identified intronic SNPs rs6446628 in AFAP1 with genome-wide significance (p = 3.93E-8) and rs34599046 in TUSC3 at sub-threshold genome-wide significance (p = 1.34E-7), both supported by credible peaks of neighboring SNPs. Like other previously reported BA-associated genes, AFAP1 and TUSC3 are ciliogenesis and planar polarity effectors (CPLANE). In gene-set-based GWAS, BA was associated with 6,005 SNPs in 102 CPLANE genes (p = 5.84E-15). Compared with non-CPLANE genes, more CPLANE genes harbored rare variants (allele frequency <1%) that were assigned Human Phenotype Ontology terms related to hepatobiliary anomalies by predictive algorithms, 87% vs. 40%, p <0.0001. Rare variants were present in multiple genes distinct from those with BA-associated common variants in most BA cases. AFAP1 and TUSC3 knockdown blocked ciliogenesis in mouse tracheal cells. Inhibition of ciliogenesis caused biliary dysgenesis in zebrafish. AFAP1 and TUSC3 were expressed in fetal liver organoids, as well as fetal and BA livers, but not in normal or disease-control livers. Integrative analysis of BA-associated variants and liver transcripts revealed abnormal vasculogenesis and epithelial tube formation, explaining portal vein anomalies that co-exist with BA.

CONCLUSIONS

BA is associated with polygenic susceptibility in CPLANE genes. Rare variants contribute to polygenic risk in vulnerable pathways via unique genes.

IMPACT AND IMPLICATIONS

Liver transplantation is needed to cure most children born with biliary atresia, a poorly understood rare disease. Transplant immunosuppression increases the likelihood of life-threatening infections and cancers. To improve care by preventing this disease and its progression to transplantation, we examined its genetic basis. We find that this disease is associated with both common and rare mutations in highly specialized genes which maintain normal communication and movement of cells, and their organization into bile ducts and blood vessels during early development of the human embryo. Because defects in these genes also cause other birth defects, our findings could lead to preventive strategies to lower the incidence of biliary atresia and potentially other birth defects.

Congenital disorders of glycosylation (CDG): state of the art in 2022

Congenital disorders of glycosylation (CDG) are a complex and heterogeneous family of rare metabolic diseases. With a clinical history that dates back over 40 years, it was the recent multi-omics advances that mainly contributed to the fast-paced and encouraging developments in the field. However, much remains to be understood, with targeted therapies' discovery and approval being the most urgent unmet need. In this paper, we present the 2022 state of the art of CDG, including glycosylation pathways, phenotypes, genotypes, inheritance patterns, biomarkers, disease models, and treatments. In light of our current knowledge, it is not always clear whether a specific disease should be classified as a CDG. This can create ambiguity among professionals leading to confusion and misguidance, consequently affecting the patients and their families. This review aims to provide the CDG community with a comprehensive overview of the recent progress made in this field.

Functional classification of DDOST variants of uncertain clinical significance in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) are rare genetic disorders with a spectrum of clinical manifestations caused by abnormal N-glycosylation of secreted and cell surface proteins. Over 130 genes are implicated and next generation sequencing further identifies potential disease drivers in affected individuals. However, functional testing of these variants is challenging, making it difficult to distinguish pathogenic from non-pathogenic events. Using proximity labelling, we identified OST48 as a protein that transiently interacts with lysyl oxidase (LOX), a secreted enzyme that cross-links the fibrous extracellular matrix. OST48 is a non-catalytic component of the oligosaccharyltransferase (OST) complex, which transfers glycans to substrate proteins. OST48 is encoded by DDOST, and 43 variants of DDOST are described in CDG patients, of which 34 are classified as variants of uncertain clinical significance (VUS). We developed an assay based on LOX N-glycosylation that confirmed two previously characterised DDOST variants as pathogenic. Notably, 39 of the 41 remaining variants did not have impaired activity, but we demonstrated that p.S243F and p.E286del were functionally impaired, consistent with a role in driving CDG in those patients. Thus, we describe a rapid assay for functional testing of clinically relevant CDG variants to complement genome sequencing and support clinical diagnosis of affected individuals.

Intracellular traffic and polarity in brain development

Neurons forming the human brain are generated during embryonic development by neural stem and progenitor cells via a process called neurogenesis. A crucial feature contributing to neural stem cell morphological and functional heterogeneity is cell polarity, defined as asymmetric distribution of cellular components. Cell polarity is built and maintained thanks to the interplay between polarity proteins and polarity-generating organelles, such as the endoplasmic reticulum (ER) and the Golgi apparatus (GA). ER and GA affect the distribution of membrane components and work as a hub where glycans are added to nascent proteins and lipids. In the last decades our knowledge on the role of polarity in neural stem and progenitor cells have increased tremendously. However, the role of traffic and associated glycosylation in neural stem and progenitor cells is still relatively underexplored. In this review, we discuss the link between cell polarity, architecture, identity and intracellular traffic, and highlight how studies on neurons have shaped our knowledge and conceptual framework on traffic and polarity. We will then conclude by discussing how a group of rare diseases, called congenital disorders of glycosylation (CDG) offers the unique opportunity to study the contribution of traffic and glycosylation in the context of neurodevelopment.

IgG glycans in health and disease: Prediction, intervention, prognosis, and therapy

Immunoglobulin (IgG) glycosylation is a complex enzymatically controlled process, essential for the structure and function of IgG. IgG glycome is relatively stable in the state of homeostasis, yet its alterations have been associated with aging, pollution and toxic exposure, as well as various diseases, including autoimmune and inflammatory diseases, cardiometabolic diseases, infectious diseases and cancer. IgG is also an effector molecule directly involved in the inflammation processes included in the pathogenesis of many diseases. Numerous recently published studies support the idea that IgG N-glycosylation fine-tunes the immune response and plays a significant role in chronic inflammation. This makes it a promising novel biomarker of biological age, and a prognostic, diagnostic and treatment evaluation tool. Here we provide an overview of the current state of knowledge regarding the IgG glycosylation in health and disease, and its potential applications in pro-active prevention and monitoring of various health interventions.

Large-Scale and Site-Specific Mapping of the Murine Brain O-Glycoproteome with IMPa

Altered protein glycosylation is typically associated with cognitive defects and other phenotypes, but there is a lack of knowledge about the brain glycoproteome. Here, we used the newly available O-glycoprotease IMPa from Pseudomonas aeruginosa for comprehensive O-glycoproteomic analyses of the mouse brain. In this approach, total tryptic glycopeptides were prepared, extracted, purified, and conjugated to a solid support before an enzymatic cleavage by IMPa. O-glycopeptides were analyzed by electron-transfer/higher-energy collision dissociation (EThcD), which permits site-specific and global analysis of all types of O-glycans. We developed two complementary approaches for the analysis of the total O-glycoproteome using HEK293 cells and derivatives. The results demonstrated that IMPa and EThcD facilitate the confident localization of O-glycans on glycopeptides. We then applied these approaches to characterize the O-glycoproteome of the mouse brain, which revealed the high frequency of various sialylated O-glycans along with the unusual presence of the Tn antigen. Unexpectedly, the results demonstrated that glycoproteins in the brain O-glycoproteome only partly overlap with those reported for the brain N-glycoproteome. These approaches will aid in identifying the novel O-glycoproteomes of different cells and tissues and foster clinical and translational insights into the functions of protein O-glycosylation in the brain and other organs.

A Case of Congenital Disorder of Glycosylation Type 1b Presenting as Hyperinsulinemic Hypoglycemia and Failure to Thrive

We describe initial manifestations, approach to diagnosis, and treatment of a patient with congenital disorder of glycosylation type 1b (CDG 1b), previously managed as acetylcarnitine deficiency. A 9-year-old girl initially diagnosed with and treated for acetylcarnitine deficiency at an outside hospital presented with recurrent hypoglycemia, failure to thrive, poor weight gain, and short stature. She had discontinued levocarnitine therapy because of lack of response, and testing with us demonstrated a normal carnitine and acyl carnitine panel and hyperinsulinemic hypoglycemia during a diagnostic fast. Oral diazoxide and hydrochlorothiazide were initiated with resolution of hypoglycemia. She had iron deficiency anemia, but an upper gastrointestinal evaluation was normal. Genetic testing confirmed a diagnosis of CDG 1b caused by deficiency of mannose phosphate isomerase. Oral mannose was started with gradual reduction in and eventual discontinuation of the diazoxide dose. Hypoglycemia in the pediatric age group needs a systematic approach. It is important to raise awareness of CDG 1b, which can present as persistent hyperinsulinemic hypoglycemia. Mannose supplementation can ameliorate clinical symptoms and biochemical abnormalities.

Metabolic adaptation of human skin fibroblasts to ER stress caused by glycosylation defect in PMM2-CDG

PMM2-CDG is the most prevalent type of congenital disorders of glycosylation (CDG). It is caused by pathogenic variants in the gene encoding phosphomannomutase 2 (PMM2), which converts mannose-6-phosphate to mannose-1-phosphate and thus activates this saccharide for further glycosylation processes. Defective glycosylation can lead to an abnormal accumulation of unfolded proteins in endoplasmic reticulum (ER) and cause its stress. The ER is a key compartment for glycosylation, and its connection and communication with mitochondria has been described extensively in literature. Their crosstalk is important for cell proliferation, calcium homeostasis, apoptosis, mitochondrial fission regulation, bioenergetics, autophagy, lipid metabolism, inflammasome formation and unfolded protein response. Therefore, in the present study we posed a question, whether defective glycosylation leads to bioenergetic disruption. Our data reveal possible chronic stress in ER and activated unfolded protein response via PERK pathway in PMM2-CDG fibroblasts. Presumably, it leads to bioenergetic reorganization and increased assembly of respiratory chain complexes into supercomplexes together with suppressed glycolysis in PMM2-CDG patient cells. These changes cause alterations in Krebs cycle, which is tightly connected to electron transport system in mitochondria. In summary, we present data showing metabolic adaptation of cells to glycosylation defect caused by various pathogenic variants in PMM2.

A Novel Homozygous GPAA1 Variant in a Patient with a Glycosylphosphatidylinositol Biosynthesis Defect

Glycosylphosphatidylinositol biosynthesis defect 15 is a rare autosomal recessive disorder due to biallelic loss of function of GPAA1. At the moment, less than twenty patients have been reported, usually compound heterozygous for GPAA1 variants. The main clinical features are intellectual disability, hypotonia, seizures, and cerebellar atrophy. We describe a 4-year-old male with a novel, homozygous variant. The patient presents with typical features, such as developmental delay, hypotonia, seizures, and atypical features, such as macrocephaly, preauricular, and cheek appendages. When he was 15 months, the cerebellum was normal. When he was 33 months old, after the molecular diagnosis, magnetic resonance imaging was repeated, showing cerebellar atrophy. This case extends the clinical spectrum of the GPAA1-related disorder and helps to delineate phenotypic differences with defects of other subunits of the transamidase complex.

Golgi Apparatus Target Proteins in Gastroenterological Cancers: A Comprehensive Review of GOLPH3 and GOLGA Proteins

The Golgi apparatus plays a central role in protein sorting, modification and trafficking within cells; its dysregulation has been implicated in various cancers including those affecting the GI tract. This review highlights two Golgi target proteins, namely GOLPH3 and GOLGA proteins, from this apparatus as they relate to gastroenterological cancers. GOLPH3-a highly conserved protein of the trans-Golgi network-has become a key player in cancer biology. Abnormal expression of GOLPH3 has been detected in various gastrointestinal cancers including gastric, colorectal and pancreatic cancers. GOLPH3 promotes tumor cell proliferation, survival, migration and invasion via various mechanisms including activating the PI3K/Akt/mTOR signaling pathway as well as altering Golgi morphology and vesicular trafficking. GOLGA family proteins such as GOLGA1 (golgin-97) and GOLGA7 (golgin-84) have also been implicated in gastroenterological cancers. GOLGA1 plays an essential role in protein trafficking within the Golgi apparatus and has been associated with poor patient survival rates and increased invasiveness; GOLGA7 maintains Golgi structure while having been shown to affect protein glycosylation processes. GOLPH3 and GOLGA proteins play a pivotal role in gastroenterological cancer, helping researchers unlock molecular mechanisms and identify therapeutic targets. Their dysregulation affects various cellular processes including signal transduction, vesicular trafficking and protein glycosylation, all contributing to tumor aggressiveness and progression.

PMM2 -CDG T237M Mutation in a Patient with Cerebral Palsy-Like Phenotypes Reported from South India

Congenital disorder of glycosylation (CDG) is an autosomal recessively inherited disorder. Hypotonia, stroke-like episodes, and peripheral neuropathy are also associated with the condition that typically develops during infancy. The patient, a 12-year-old girl born to healthy consanguineous parents, was diagnosed with cerebral palsy as a child. The affected patient has hypotonia, inadequate speech, strabismus, and developmental delay with mild mental retardation, which are key symptoms of CDG. Whole-exome sequencing (WES) identified the known missense pathogenic variant PMM2 c.710 C > T, p.T237M in the patient coding for the phosphomannomutase 2 (PMM2) confirming molecular testing of CDG. The patient's parents carried heterozygous PMM2 c.710 C > T variants. This study highlights the importance of WES in patients with a developmental disability or other neurological conditions, which is also useful in screening risk factors in couples with infertility or miscarriage issues.

Rare inherited coagulation and fibrinolytic defects that challenge diagnostic laboratories

BACKGROUND

Coagulation factors, anticoagulants, and fibrinolytic proteins are important for hemostasis, and mutations affecting these proteins causes some rare inherited bleeding disorders that are particularly challenging to diagnose.

AIMS

This review provides current information on rare inherited bleeding disorders that are difficult to diagnose.

MATERIAL & METHODS

A review of the literature was conducted for up to date information on rare and difficult to diagnose bleeding disorders.

RESULTS

Some rare bleeding disorders cause an inherited deficiency of multiple coagulation factors (F), such as combined FV and FVIII deficiency and familial vitamin K-dependent clotting factor deficiency. Additionally, congenital disorders of glycosylation can affect a variety of procoagulant and anticoagulant proteins and also platelets. Some bleeding disorders reflect mutations with unique impairments in the procoagulant/anticoagulant balance, including those caused by F5 mutations that secondarily increase the plasma levels of tissue factor pathway inhibitor as well as THBD mutations that increase functional thrombomodulin in plasma or cause a consumptive coagulopathy due to thrombomodulin deficiency. Some bleeding disorders accelerate fibrinolysis due to loss-of-function mutations in SERPINE1 and SERPINF2 or in the case of Quebec platelet disorder, a duplication mutation that rewires PLAU and selectively increases expression in megakaryocytes, resulting in a unique platelet-dependent gain-of-function defect in fibrinolysis.

DISCUSSION

Current information on rare and difficult to diagnose bleeding disorders indicates they have unique clinical and laboratory features, and pathogenic characteristics to consider for diagnostic evaluation.

CONCLUSION

Laboratories and clinicians should consider rare inherited disorders, and difficult to diagnose conditions, in their strategy for diagnosing bleeding disorders.

The trap of genetic tag: The importance of pathogenicity prediction tools in the correct interpretation of variants of uncertain significance in the era of high-throughput genome sequencing

Although recent advancements in DNA sequencing technologies and their widely used, the interpretation of variants of uncertain significance from these large datasets is not clear-cut. Here, we present the case of a family referred to our metabolic disease department, in which three males' individuals were affected by a suspected a genetic inherited disease, resulting from next-generation sequencing results. A correct assessment of the clinical significance of the genetic variant found in our cases, with a review of the literature, the evaluation of population database and the use of computational predictive program changed the initial suspect. Despite NGS technologies have increased diagnostic sensitivity, most of these variants remains of uncertain clinical significance. An efficient systematic approach is fundamental to determine the pathogenicity of a variant, avoiding incorrect interpretation in a clinical setting.

Loss of hepatic manganese transporter ZIP8 disrupts serum transferrin glycosylation and the glutamate-glutamine cycle

BACKGROUND

ZIP8, encoded by SLC39A8, is a membrane transporter that facilitates the cellular uptake of divalent biometals including zinc (Zn), manganese (Mn), and iron (Fe). The hepatic system has long been accepted as the central modulator for whole-body biometal distribution. Earlier investigations suggest the propensity of ZIP8 to prioritize Mn influx, as opposed to Fe or Zn, in hepatocytes. Hepatic ZIP8 Mn transport is crucial for maintaining homeostasis of various Mn-dependent metalloenzymes and their associated pathways. Herein, we hypothesize that a drastic decrease in systemic Mn, via the loss of hepatic ZIP8, disrupts two unique cellular pathways, post-translational glycosylation and the glutamate-glutamine cycle.

METHODS

ZIP8 liver-specific knockout (LSKO) mice were chosen in an attempt to substantially decrease whole-body Mn levels. To further elucidate the role of Mn in serum glycosylation, a Mn-deficient diet was adopted in conjunction with the LSKO mice to model a near-complete loss of systemic Mn. After the treatment course, transferrin sialylation profiles were determined using imaged capillary isoelectric focusing (icIEF). We also investigated the role of Mn in the glutamate-glutamine cycle; the conversion of glutamate to glutamine in F/F and LSKO mice was assessed by the glutamine/glutamate ratio in cerebrospinal fluid (CSF) via HPLC-MS. An open-field study was ultimately conducted to check if these mice displayed atypical behavior.

RESULTS

Two major biological pathways were found to be significantly altered due to the loss of hepatic ZIP8. We identified a disparity between F/F and LSKO transferrin sialylation profiles that were exacerbated under a Mn-deficient diet. Additionally, we discovered a neurotransmitter imbalance between the levels of glutamine and glutamate, exclusive to LSKO mice. This was characterized by the decreased glutamine/glutamate ratio in CSF. Secondary to the neurotransmitter alteration, LSKO mice exhibited an increase in locomotor activity in an open-field.

CONCLUSION

Our model successfully established a connection between the loss of hepatic ZIP8 and two Mn-dependent cellular pathways, namely, protein glycosylation and the glutamate-glutamine cycle.

Identifying Novel Risk Conferring Genes Involved in Glycosylation Processes with Familial Schizophrenia in an Indian Cohort: Prediction of ADAMTS9 gene Variant for Structural Stability

Schizophrenia is a complex neuropsychiatric disorder and heritability is as high as 80% making it the most heritable mental disorder. Although GWAS has identified numerous variants, the pathophysiology is still elusive. Here, an attempt was made to identify genetic risk factors in familial cases of schizophrenia that are associated with a common causative pathway. To achieve this objective, exome sequencing was done in 4 familial cases and identified six unique coding variants in five genes. Among these genes, PIGQ gene has two pathogenic variants, one nonsense and in-frame deletion. One missense variant in GALNT16 and one in GALNT5 have variable damaging score, however, the other variants, in ADAMTS9 and in LTBP4 have the highest damaging score. Further analysis showed that the variant of LTBP4 was not present in the functional domain. The other missense variant in the ADAMTS9 gene was found to be significant and was present in the thrombospondin repeat motif, one of the important motifs. Detailed molecular dynamics simulation study on this variant showed a damaging effect on structural stability. Since, all these genes culminated into the glycosylation process, it was evident that an aberrant glycosylation process may be one of the risk factors. Although, extracellular matrix formation through glycosylation have been shown to be associated, the involvement of ADAMTS9 and PIGQ gene mediated glycosylation has not been reported. In this paper, a novel link between ADAMTS9 and PIGQ gene with schizophrenia have been reported. Therefore, this novel observation has contributed immensely to the existing knowledge on risk factor of Schizophrenia.

GlycoMME, a Markov modeling platform for studying N-glycosylation biosynthesis from glycomics data

Variations in N-glycosylation, which is crucial to glycoprotein functions, impact many diseases and the safety and efficacy of biotherapeutic drugs. Here, we present a protocol for using GlycoMME (Glycosylation Markov Model Evaluator) to study N-glycosylation biosynthesis from glycomics data. We describe steps for annotating glycomics data and quantifying perturbations to N-glycan biosynthesis with interpretable models. We then detail procedures to predict the impact of mutations in disease or potential glycoengineering strategies in drug development. For complete details on the use and execution of this protocol, please refer to Liang et al. (2020).¹.

Congenital disorders of glycosylation and infantile epilepsy

Congenital disorders of glycosylation (CDG) are a group of rare inherited metabolic disorders caused by defects in various defects of protein or lipid glycosylation pathways. The symptoms and signs of CDG usually develop in infancy. Epilepsy is commonly observed in CDG individuals and is often a presenting symptom. These epilepsies can present across the lifespan, share features of refractoriness to antiseizure medications, and are often associated with comorbid developmental delay, psychomotor regression, intellectual disability, and behavioral problems. In this review, we discuss CDG and infantile epilepsy, focusing on an overview of clinical manifestations and electroencephalographic features. Finally, we propose a tiered approach that will permit a clinician to systematically investigate and identify CDG earlier, and furthermore, to provide genetic counseling for the family.

Clinical Presentation of a Patient with a Congenital Disorder of Glycosylation, Type IIs (ATP6AP1), and Liver Transplantation

The congenital disorder of glycosylation type IIs (ATP6AP1-CDG; OMIM# 300972) is a rare X-linked recessive complex syndrome characterized by liver dysfunction, recurrent bacterial infections, hypogammaglobulinemia, and defective glycosylation of serum proteins. Here, we examine the case of a 1-year-old male patient of Buryat origin, who presented with liver dysfunction. At the age of 3 months, he was hospitalized with jaundice and hepatosplenomegaly. Whole-exome sequencing identified the ATP6AP1 gene missense variant NM_001183.6:c.938A>G (p.Tyr313Cys) in the hemizygous state, which was previously reported in a patient with immunodeficiency type 47. At the age of 10 months, the patient successfully underwent orthotopic liver transplantation. After the transplantation, the use of Tacrolimus entailed severe adverse effect (colitis with perforation). Replacing Tacrolimus with Everolimus led to improvement. Previously reported patients demonstrated abnormal N- and O-glycosylation, but these data were collected without any specific treatment. In contrast, in our patient, isoelectric focusing (IEF) of serum transferrin was performed only after the liver transplant and showed a normal IEF pattern. Thus, liver transplantation could be a curative option for patients with ATP6AP1-CDG.

The Hexosamine Biosynthesis Pathway: Regulation and Function

The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate-N-acetyl glucosamine, UDP-GlcNAc, which is a key metabolite that is used for N- or O-linked glycosylation, a co- or post-translational modification, respectively, that modulates protein activity and expression. The production of hexosamines can occur via de novo or salvage mechanisms that are catalyzed by metabolic enzymes. Nutrients including glutamine, glucose, acetyl-CoA, and UTP are utilized by the HBP. Together with availability of these nutrients, signaling molecules that respond to environmental signals, such as mTOR, AMPK, and stress-regulated transcription factors, modulate the HBP. This review discusses the regulation of GFAT, the key enzyme of the de novo HBP, as well as other metabolic enzymes that catalyze the reactions to produce UDP-GlcNAc. We also examine the contribution of the salvage mechanisms in the HBP and how dietary supplementation of the salvage metabolites glucosamine and N-acetylglucosamine could reprogram metabolism and have therapeutic potential. We elaborate on how UDP-GlcNAc is utilized for N-glycosylation of membrane and secretory proteins and how the HBP is reprogrammed during nutrient fluctuations to maintain proteostasis. We also consider how O-GlcNAcylation is coupled to nutrient availability and how this modification modulates cell signaling. We summarize how deregulation of protein N-glycosylation and O-GlcNAcylation can lead to diseases including cancer, diabetes, immunodeficiencies, and congenital disorders of glycosylation. We review the current pharmacological strategies to inhibit GFAT and other enzymes involved in the HBP or glycosylation and how engineered prodrugs could have better therapeutic efficacy for the treatment of diseases related to HBP deregulation.

Glycoproteomics meets thermodynamics: A calorimetric study of the effect of sialylation and synergistic anion on the binding of iron to human serum transferrin

The thermodynamic parameters for the binding of ferric ions to human serum transferrin (hTf) as the major mediator of iron transport in blood plasma were determined by isothermal titration calorimetry in the presence of carbonate and oxalate as synergistic anions at pH 7.4. The results indicate that the binding of ferric ions to the two binding sites of hTf is driven both enthalpically and entropically in a lobe-dependent manner: binding to the C-site is mainly enthalpically driven, whereas binding to the N-site is mainly entropically driven. Lower sialic acid content of hTf leads to more exothermic apparent binding enthalpies for both lobes, while the increased apparent binding constants for both sites were found in the presence of carbonate. Sialylation also unequally affected the heat change rates for both sites only in the presence of carbonate, but not in the presence of oxalate. Overall, the results suggest that the desialylated hTf has a higher iron sequestering ability, which may have implications for iron metabolism.

Thrombosis risk with estrogen use for puberty induction in congenital disorders of glycosylation

Congenital disorders of glycosylation are a group of rare related disorders causing multisystem dysfunction, including ovarian failure in females that requires early estrogen replacement. Glycosylation defects also disrupt normal synthesis of several coagulation factors, increasing thrombotic risks and complicating hormone replacement. This series describes four females with different types of CDG who developed venous thromboses while on transdermal estrogen replacement. The authors highlight the knowledge gaps around anticoagulation for this population and propose further investigations.

Vaccination strategies for people living with inborn errors of metabolism in Brazil

OBJECTIVE

Through a literature review, make recommendations regarding immunizations in people living with Inborn Error of Metabolism (IEM) in Brazil, assess the possible impact on metabolic decompensations after immunization, and if this specific population may have an impaired immune response to vaccines.

SOURCE OF DATA

The MeSH Terms vaccination OR vaccine OR immunization associated with the term inborn error of metabolism AND recommendation were used in combination with search databases. Only articles published after 1990, in the languages English, Spanish, French or Portuguese, human-related were included.

SYNTHESIS OF DATA

A total of 44 articles were included to make the following recommendations. Individuals with IEMs need to be up to date with their immunizations. Regarding which vaccines should be offered, children and adults should follow the routine immunization schedules locally available, including the COVID-19 vaccines. The only exception is the rotavirus vaccine for hereditary fructose intolerance. The benefit of immunization outweighs the very low risk of metabolic decompensation. Since not all patients will have an adequate immune response, measuring antibody conversion and titers is recommended CONCLUSIONS: All patients should receive age-appropriate immunizations in their respective schedules without delays. The only situation when vaccination may be contraindicated is with oral rotavirus vaccine in hereditary fructose intolerance. Monitoring the levels of antibodies should be done to detect any immune dysfunction or the necessity for boosters. A personalized immunization schedule is ideal for patients with IEMs. The reference organizations could improve their recommendations to address all IEMs, not only some of them.

Elevated oxysterol and N-palmitoyl-O-phosphocholineserine levels in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) and Niemann-Pick type C (NPC) disease are inborn errors of metabolism that can both present with infantile-onset severe liver disease and other multisystemic manifestations. Plasma bile acid and N-palmitoyl-O-phosphocholineserine (PPCS) are screening biomarkers with proposed improved sensitivity and specificity for NPC. We report an infant with ATP6AP1-CDG who presented with cholestatic liver failure and elevated plasma oxysterols and bile acid, mimicking NPC clinically and biochemically. On further investigation, PPCS, but not the bile acid derivative N-(3β,5α,6β-trihydroxy-cholan-24-oyl) glycine (TCG), were elevated in plasma samples from individuals with ATP6AP1-, ALG1-, ALG8-, and PMM2-CDG. These findings highlight the importance of keeping CDG within the diagnostic differential when evaluating children with early onset severe liver disease and elevated bile acid or PPCS to prevent delayed diagnosis and treatment.

N-Glycoprofiling of SLC35A2-CDG: Patient with a Novel Hemizygous Variant

Congenital disorders of glycosylation (CDG) are a group of rare inherited metabolic disorders caused by a defect in the process of protein glycosylation. In this work, we present a comprehensive glycoprofile analysis of a male patient with a novel missense variant in the SLC35A2 gene, coding a galactose transporter that translocates UDP-galactose from the cytosol to the lumen of the endoplasmic reticulum and Golgi apparatus. Isoelectric focusing of serum transferrin, which resulted in a CDG type II pattern, was followed by structural analysis of transferrin and serum N-glycans, as well as the analysis of apolipoprotein CIII O-glycans by mass spectrometry. An abnormal serum N-glycoprofile with significantly increased levels of agalactosylated (Hex3HexNAc4-5 and Hex3HexNAc5Fuc1) and monogalactosylated (Hex4HexNAc4 ± NeuAc1) N-glycans was observed. Additionally, whole exome sequencing and Sanger sequencing revealed de novo hemizygous c.461T > C (p.Leu154Pro) mutation in the SLC35A2 gene. Based on the combination of biochemical, analytical, and genomic approaches, the set of distinctive N-glycan biomarkers was characterized. Potentially, the set of identified aberrant N-glycans can be specific for other variants causing SLC35A2-CDG and can distinguish this disorder from the other CDGs or other defects in the galactose metabolism.

[Advances in the diagnosis and treatment of phosphomannomutase 2 deficiency]

Phosphomannomutase 2 deficiency is the most common form of N-glycosylation disorders and is also known as phosphomannomutase 2-congenital disorder of glycosylation (PMM2-CDG). It is an autosomal recessive disease with multi-system involvements and is caused by mutations in the PMM2 gene (OMIM: 601785), with varying severities in individuals. At present, there is still no specific therapy for PMM2-CDG, and early identification, early diagnosis, and early treatment can effectively prolong the life span of pediatric patients. This article reviews the advances in the diagnosis and treatment of PMM2-CDG.

Novel variants in GALE cause syndromic macrothrombocytopenia by disrupting glycosylation and thrombopoiesis

Glycosylation is recognized as a key process for proper megakaryopoiesis and platelet formation. The enzyme uridine diphosphate (UDP)-galactose-4-epimerase, encoded by GALE, is involved in galactose metabolism and protein glycosylation. Here, we studied 3 patients from 2 unrelated families who showed lifelong severe thrombocytopenia, bleeding diathesis, mental retardation, mitral valve prolapse, and jaundice. Whole-exome sequencing revealed 4 variants that affect GALE, 3 of those previously unreported (Pedigree A, p.Lys78ValfsX32 and p.Thr150Met; Pedigree B, p.Val128Met; and p.Leu223Pro). Platelet phenotype analysis showed giant and/or grey platelets, impaired platelet aggregation, and severely reduced alpha and dense granule secretion. Enzymatic activity of the UDP-galactose-4-epimerase enzyme was severely decreased in all patients. Immunoblotting of platelet lysates revealed reduced GALE protein levels, a significant decrease in N-acetyl-lactosamine (LacNAc), showing a hypoglycosylation pattern, reduced surface expression of gylcoprotein Ibα-IX-V (GPIbα-IX-V) complex and mature β1 integrin, and increased apoptosis. In vitro studies performed with patients-derived megakaryocytes showed normal ploidy and maturation but decreased proplatelet formation because of the impaired glycosylation of the GPIbα and β1 integrin, and reduced externalization to megakaryocyte and platelet membranes. Altered distribution of filamin A and actin and delocalization of the von Willebrand factor were also shown. Overall, this study expands our knowledge of GALE-related thrombocytopenia and emphasizes the critical role of GALE in the physiological glycosylation of key proteins involved in platelet production and function.

Neurological Consequences of Congenital Disorders of Glycosylation

The chapter is devoted to neurological aspects of congenital disorders of glycosylation (CDG). At the beginning, the various types of CDG with neurological presentation of symptoms are summarized. Then, the occurrence of various neurological constellation of abnormalities (for example: epilepsy, brain anomalies on neuroimaging, ataxia, stroke-like episodes, autistic features) in different CDG types are discussed followed by data on possible biomarkers and limited treatment options.

Novel insights into the phenotype and long-term D-gal treatment in PGM1-CDG: a case series

Phosphoglucomutase-1-congenital disorder of glycosylation (PGM1-CDG) (OMIM: 614921) is a rare autosomal recessive inherited metabolic disease caused by the deficiency of the PGM1 enzyme. Like other CDGs, PGM1-CDG has a multisystemic presentation. The most common clinical findings include liver involvement, rhabdomyolysis, hypoglycemia, and cardiac involvement. Phenotypic severity can vary, though cardiac presentation is usually part of the most severe phenotype, often resulting in early death. Unlike the majority of CDGs, PGM1-CDG has a treatment: oral D-galactose (D-gal) supplementation, which significantly improves many aspects of the disorder. Here, we describe five PGM1-CDG patients treated with D-gal and report both on novel clinical symptoms in PGM1-CDG as well as the effects of the D-gal treatment. D-gal resulted in notable clinical improvement in four patients, though the efficacy of treatment varied between the patients. Furthermore, there was a significant improvement or normalization in transferrin glycosylation, liver transaminases and coagulation factors in three patients, creatine kinase (CK) levels in two, while hypoglycemia resolved in two patients. One patient discontinued the treatment due to urinary frequency and lack of clinical improvement. Furthermore, one patient experienced recurrent episodes of rhabdomyolysis and tachycardia even on higher doses of therapy. D-gal also failed to improve the cardiac function, which was initially abnormal in three patients, and remains the biggest challenge in treating PGM1-CDG. Together, our findings expand the phenotype of PGM1-CDG and underline the importance of developing novel therapies that would specifically treat the cardiac phenotype in PGM1-CDG.

Setting the stage for universal pharmacological targeting of the glycocalyx

All cells in the human body are covered by a complex meshwork of sugars as well as proteins and lipids to which these sugars are attached, collectively termed the glycocalyx. Over the past few decades, the glycocalyx has been implicated in a range of vital cellular processes in health and disease. Therefore, it has attracted considerable interest as a therapeutic target. Considering its omnipresence and its relevance for various areas of cell biology, the glycocalyx should be a versatile platform for therapeutic intervention, however, the full potential of the glycocalyx as therapeutic target is yet to unfold. This might be attributable to the fact that glycocalyx alterations are currently discussed mainly in the context of specific diseases. In this perspective review, we shift the attention away from a disease-centered view of the glycocalyx, focusing on changes in glycocalyx state. Furthermore, we survey important glycocalyx-targeted drugs currently available and finally discuss future steps. We hope that this approach will inspire a unified, holistic view of the glycocalyx in disease, helping to stimulate novel glycocalyx-targeted therapy strategies.

N-glycoproteomics reveals distinct glycosylation alterations in NGLY1-deficient patient-derived dermal fibroblasts

Congenital disorders of glycosylation are genetic disorders that occur due to defects in protein and lipid glycosylation pathways. A deficiency of N-glycanase 1, encoded by the NGLY1 gene, results in a congenital disorder of deglycosylation. The NGLY1 enzyme is mainly involved in cleaving N-glycans from misfolded, retro-translocated glycoproteins in the cytosol from the endoplasmic reticulum before their proteasomal degradation or activation. Despite the essential role of NGLY1 in deglycosylation pathways, the exact consequences of NGLY1 deficiency on global cellular protein glycosylation have not yet been investigated. We undertook a multiplexed tandem mass tags-labeling-based quantitative glycoproteomics and proteomics analysis of fibroblasts from NGLY1-deficient individuals carrying different biallelic pathogenic variants in NGLY1. This quantitative mass spectrometric analysis detected 8041 proteins and defined a proteomic signature of differential expression across affected individuals and controls. Proteins that showed significant differential expression included phospholipid phosphatase 3, stromal cell-derived factor 1, collagen alpha-1 (IV) chain, hyaluronan and proteoglycan link protein 1, and thrombospondin-1. We further detected a total of 3255 N-glycopeptides derived from 550 glycosylation sites of 407 glycoproteins by multiplexed N-glycoproteomics. Several extracellular matrix glycoproteins and adhesion molecules showed altered abundance of N-glycopeptides. Overall, we observed distinct alterations in specific glycoproteins, but our data revealed no global accumulation of glycopeptides in the patient-derived fibroblasts, despite the genetic defect in NGLY1. Our findings highlight new molecular and system-level insights for understanding NGLY1-CDDG.

Whole exome sequencing reveals several novel variants in congenital disorders of glycosylation and glycogen storage diseases in seven patients from Iran

BACKGROUND

Congenital disorder of glycosylation (CDG) and Glycogen storage diseases (GSDs) are inborn metabolic disorders caused by defects in some metabolic pathways. These disorders are a heterogeneous group of diseases caused by impaired O- as well as N-glycosylation pathways. CDG patients show a broad spectrum of clinical presentations; many GSD types (PGM1-CDG) have muscle involvement and hypoglycemia.

METHODS

We applied WES for all seven patients presenting GSD and CDG symptoms. Then we analyzed the data using various tools to predict pathogenic variants in genes related to the patients' diseases.

RESULTS

In the present study, we identified pathogenic variants in Iranian patients suffering from GSD and CDG, which can be helpful for patient management, and family counseling. We detected seven pathogenic variants using whole exome sequencing (WES) in known AGL (c.1998A>G, c.3635T>C, c.3682C>T), PGM1 (c.779G>A), DPM1 (c.742T>C), RFT1 (c.127A>G), and GAA (c.1314C>A) genes.

CONCLUSION

The suspected clinical diagnosis of CDG and GSD patients was confirmed by identifying missense and or nonsense mutations in PGM1, DPM1, RFT1, GAA, and AGL genes by WES of all 7 cases. This study helps us understand the scenario of the disorder causes and consider the variants for quick disease diagnosis.

Ataxia in Neurometabolic Disorders

Ataxia is a movement disorder that manifests during the execution of purposeful movements. It results from damage to the structures of the cerebellum and its connections or the posterior cords of the spinal cord. It should be noted that, in addition to occurring as part of many diseases, pediatric ataxia is a common symptom in neurometabolic diseases. To date, there are more than 150 inherited metabolic disorders that can manifest as ataxia in children. Neuroimaging studies (magnetic resonance imaging of the head and spinal cord) are essential in the diagnosis of ataxia, and genetic studies are performed when metabolic diseases are suspected. It is important to remember that most of these disorders are progressive if left untreated. Therefore, it is crucial to include neurometabolic disorders in the differential diagnosis of ataxia, so that an early diagnosis can be made. Initiating prompt treatment influences positive neurodevelopmental outcomes.

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.

A case of ALG11-congenital disorders of glycosylation diagnosed by post-mortem whole exome sequencing

INTRODUCTION

Congenital disorders of glycosylation (CDG) are inherited inborn errors of metabolism due to abnormal protein and lipid glycosylation that present with multi-systemic manifestations. The heterogeneity of CDG poses a serious diagnostic challenge; therefore, whole-exome sequencing (WES), which plays an increasingly important role in the molecular diagnosis of CDG, is used for examining patients with CDG.

CASE REPORT

We report the case of a two-month-old male patient who developed developmental and epileptic encephalopathy (DEE) with intractable seizures and microcephaly. EEG demonstrated a suppression-burst (S-B) pattern, and MRI showed delayed myelination and progressive atrophic changes. Although CDG was clinically suspected, serum transferrin isoelectric focusing analysis appeared to be normal. The patient died by six years of age. Postmortem WES performed approximately 20 years after the patient's death revealed homozygous variants in ALG11 (NM_001004127.3: c.935A > C, p.Glu312Ala), and the patient was diagnosed with ALG11-CDG.

CONCLUSION

We present a case of the patient with ALG11-CDG diagnosed using post-mortem WES. The EEG revealed a S-B pattern that indicated severely drug-resistant DEE, which was associated with poor prognosis. If a CDG is suspected, WES should be considered.

Glycan quality control in and out of the endoplasmic reticulum of mammalian cells

The endoplasmic reticulum (ER) is equipped with multiple quality control systems (QCS) that are necessary for shaping the glycoproteome of eukaryotic cells. These systems facilitate the productive folding of glycoproteins, eliminate defective products, and function as effectors to evoke cellular signaling in response to various cellular stresses. These ER functions largely depend on glycans, which contain sugar-based codes that, when needed, function to recruit carbohydrate-binding proteins that determine the fate of glycoproteins. To ensure their functionality, the biosynthesis of such glycans is therefore strictly monitored by a system that selectively degrades structurally defective glycans before adding them to proteins. This system, which is referred to as the glycan QCS, serves as a mechanism to reduce the risk of abnormal glycosylation under conditions where glycan biosynthesis is genetically or metabolically stalled. On the other hand, glycan QCS increases the risk of global hypoglycosylation by limiting glycan availability, which can lead to protein misfolding and the activation of unfolded protein response to maintaining cell viability or to initiate cell death programs. This review summarizes the current state of our knowledge of the mechanisms underlying glycan QCS in mammals and its physiological and pathological roles in embryogenesis, tumor progression, and congenital disorders associated with abnormal glycosylation.

Patient reported outcomes for phosphomannomutase 2 congenital disorder of glycosylation (PMM2-CDG): listening to what matters for the patients and health professionals

Background

Congenital disorders of glycosylation (CDG) are a growing group of rare genetic disorders. The most common CDG is phosphomannomutase 2 (PMM2)-CDG which often has a severe clinical presentation and life-limiting consequences. There are no approved therapies for this condition. Also, there are no validated disease-specific quality of life (QoL) scales to assess the heterogeneous clinical burden of PMM2-CDG which presents a challenge for the assessment of the disease severity and the impact of a certain treatment on the course of the disease.

Aim and methods

This study aimed to identify the most impactful clinical signs and symptoms of PMM2-CDG, and specific patient and observer reported outcome measures (PROMs and ObsROMs, respectively) that can adequately measure such impact on patients’ QoL. The most burdensome signs and symptoms were identified through input from the CDG community using a survey targeting PMM2-CDG families and experts, followed by family interviews to understand the real burden of these symptoms in daily life. The list of signs and symptoms was then verified and refined by patient representatives and medical experts in the field. Finally, a literature search for PROMs and ObsROMs used in other rare or common diseases with similar signs and symptoms to those of PMM2-CDG was performed.

Results

Twenty-four signs/symptoms were identified as the most impactful throughout PMM2-CDG patients’ lifetime. We found 239 articles that included tools to measure those community-selected PMM2-CDG symptoms. Among them, we identified 80 QoL scales that address those signs and symptoms and, subsequently, their psychometric quality was analysed. These scales could be applied directly to the PMM2-CDG population or adapted to create the first PMM2-CDG-specific QoL questionnaire.

Conclusion

Identifying the impactful clinical manifestations of PMM2-CDG, along with the collection of PROMs/ObsROMs assessing QoL using a creative and community-centric methodology are the first step towards the development of a new, tailored, and specific PMM2-CDG QoL questionnaire. These findings can be used to fill a gap in PMM2-CDG clinical development. Importantly, this methodology is transferable to other CDG and rare diseases with multiple signs and symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02551-y.

A Dpagt1 Missense Variant Causes Degenerative Retinopathy without Myasthenic Syndrome in Mice

Congenital disorders of glycosylation (CDG) are a heterogenous group of primarily autosomal recessive mendelian diseases caused by disruptions in the synthesis of lipid-linked oligosaccharides and their transfer to proteins. CDGs usually affect multiple organ systems and vary in presentation, even within families. There is currently no cure, and treatment is aimed at ameliorating symptoms and improving quality of life. Here, we describe a chemically induced mouse mutant, tvrm76, with early-onset photoreceptor degeneration. The recessive mutation was mapped to Chromosome 9 and associated with a missense mutation in the Dpagt1 gene encoding UDP-N-acetyl-D-glucosamine:dolichyl-phosphate N-acetyl-D-glucosaminephosphotransferase (EC 2.7.8.15). The mutation is predicted to cause a substitution of aspartic acid with glycine at residue 166 of DPAGT1. This represents the first viable animal model of a Dpagt1 mutation and a novel phenotype for a CDG. The increased expression of Ddit3, and elevated levels of HSPA5 (BiP) suggest the presence of early-onset endoplasmic reticulum (ER) stress. These changes were associated with the induction of photoreceptor apoptosis in tvrm76 retinas. Mutations in human DPAGT1 cause myasthenic syndrome-13 and severe forms of a congenital disorder of glycosylation Type Ij. In contrast, Dpagt1tvrm76 homozygous mice present with congenital photoreceptor degeneration without overt muscle or muscular junction involvement. Our results suggest the possibility of DPAGT1 mutations in human patients that present primarily with retinitis pigmentosa, with little or no muscle disease. Variants in DPAGT1 should be considered when evaluating cases of non-syndromic retinal degeneration.

Hypogonadism in Males With Genetic Neurodevelopmental Syndromes

Genetic syndromes that affect the nervous system may also disrupt testicular function, and the mechanisms for these effects may be interrelated. Most often neurological signs and symptoms predominate and hypogonadism remains undetected and untreated, while in other cases, a thorough evaluation of a hypogonadal male reveals previously unrecognized ataxia, movement disorder, muscle weakness, tremor, or seizures, leading to a syndromic diagnosis. Androgen deficiency in patients with neurological diseases may aggravate muscle weakness and fatigue and predispose patients to osteoporosis and obesity. The purpose of this mini review is to provide a current understanding of the clinical, biochemical, histologic, and genetic features of syndromes in which male hypogonadism and neurological dysfunction may coexist and may be encountered by the clinical endocrinologist.

Analysis of Lipid-linked Oligosaccharides Synthesized in vivo in Schizosaccharomyces pombe

Dolichol diphosphate-linked oligosaccharides (LLO) are the sugar donors in N -glycosylation, a fundamental protein post-translational modification of the eukaryotic secretory pathway. Defects in LLO biosynthesis produce human Congenital Disorders of Glycosylation Type I. The synthesis of LLOs and the transfer reactions to their protein acceptors is highly conserved among animal, plant, and fungi kingdoms, making the fission yeast Schizosaccharomyces pombe a suitable model to study these processes. Here, we present a protocol to determine the LLO patterns produced in vivo by S. pombe cells that may be easily adapted to other cell types. First, exponentially growing cultures are labeled with a pulse of [ ¹⁴ C]-glucose. LLOs are then purified by successive extractions with organic solvents, and glycans are separated from the lipid moieties in mild acid hydrolysis and a new solvent extraction. The purified glycans are then run on paper chromatography. We use a deconvolution process to adjust the profile obtained to the minimal number of Gaussian functions needed to fit the data and determine the proportion of each species with respect to total glycan species present in the cell. The method we provide here might be used without any expensive or specialized equipment. The deconvolution process described here might also be useful to analyze species in non-completely resolved chromatograms. Graphical abstract: Workflow for the labeling, extraction, separation, and identification of LLO species in S. pombe . (A) Radioactive pulse of S. pombe cells with [ ¹⁴ C]-glucose for 15 min at 28 °C. (B) Organic extraction of LLOs from labeled yeasts sequentially using methanol, chloroform, H ₂ O, chloroform:methanol:H ₂ O (1:1:0.3), 0.02 M HCl (to separate glycans from dolichol), and chloroform:methanol:H ₂ O (1:16:16). (C) Preparation of the sample for chromatography on paper: drying by airflow and radioactivity check. (D) Loading of samples in chromatographic paper and descendent chromatography in a glass chamber. The obtained plots (CPM versus running distance) need to be analyzed to identify single glycan species.

Acetazolamide treatment in late onset CDG type 1 due to biallelic pathogenic DHDDS variants

Pathogenic variants in DHDDS have been associated with either autosomal recessive retinitis pigmentosa or DHDDS-CDG. Heterozygous variants in DHDDS have been described in patients with a progressive neurodegenerative disease. Here we report on an individual presenting with a multisystem CDG phenotype who was diagnosed with known homozygous pathogenic DHDDS variants, previously associated with isolated retinitis pigmentosa.

An adult Ashkenazi Jewish female developed multiple symptoms of late onset type 1 CDG including seizures, ataxia, protein losing enteropathy, tremor, and titubation in association with elevated mono-oligo/di-oligo transferrin ratio in blood, and classic retinitis pigmentosa. She was diagnosed by whole exome sequencing with the common Ashkenazi Jewish, homozygous p.K42E variants in DHDDS. She was started on Acetazolamide and responded well to the treatment which improved her titubation, tremor, and generalized edema.

Reviewing the literature, families with DHDDS variants and multisystem presentation were different from our patient's presentation in terms of clinical manifestations, severity, genetic defect, and mode of inheritance. In previously reported patients with neurologic symptoms including seizures, movement abnormalities, and global development delay, the phenotype was caused by heterozygous pathogenic variants in DHDDS. The infant who was reported with a multisystem phenotype and fatal type 1 CDG had compound heterozygosity for a nonsense and a splice site variant in DHDDS, resulting in DHDDS-CDG.

The discovery of the novel phenotype associated with the common p.K42E pathogenic variant in DHDDS expands the spectrum of CDG and further enhances our understanding on the role of DHDDS in glycosylation beyond the retina.

•

We report on the first individual carrying homozygous p.K42E variants in DHDDS associated with protein losing enteropathy, seizures, and ataxia.

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We observed familial variability in association with p.K42E and progressive ataxia in siblings with in DHDDS-CDG.

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The novel DHDDS-CDG patient phenotype broadens the current spectrum of CDG.

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Acetazolamide was successful in treating titubation and recurrent edema in our DHDDS-CDG patient of Ashkenazi Jewish descent.

Clinical and Diagnostic Significance of Sialic Acids Determination in Biological Material

Sialic acids (SA) are neuraminic acid derivatives, located at the terminal position in the chains of monosaccharide residues of various glycoconjugates. SA play a dual role: they either mask recognition sites, or, on the contrary, represent biological targets that can be recognized by receptor proteins and serve as ligands. The desialylation/sialylation processes can be considered as a dynamic modification regulated by sialyltransferases and sialidases in response to external or internal stimuli. This review describes the structural and functional diversity and the potential use of SA fractions as biomarkers for various pathological conditions. Almost any extreme impact on the body and inflammatory processes are accompanied by an increase in the level of both total and free SA in the blood and tissues. Possible reasons for the increase of sialoglycoconjugate metabolism indicators in biological material include: (i) activation of the hepatocyte synthesis and secretion of various acute-phase proteins, many of which are sialoglycoproteins, (ii) impaired membrane integrity and destruction of body cells, (iii) high activity of sialidases (neurominidases) and sialyltransferases. Most acute and chronic liver diseases are characterized by the decrease in the total level of SA in the blood serum (because many plasma proteins are synthesized and glycosylated in hepatocytes). Aberrant sialylation results in changes of sialoglycoconjugate structure, its ability to perform biological functions and sialoglycoconjugate half-life. Glycosylation is the most common post-translational modification of proteins in the virus, which not only promotes the formation of specific conformation of viral proteins, but also modulates their interaction with receptors and affects host cell recognition, viral replication and infectivity. Serum total SA concentration increases in some benign and inflammatory conditions, which indicates a lack of specificity and limits their use for early detection and screening of neoplastic diseases. Clinical and diagnostic value of determining the sialoglycoconjugate metabolic indicators, including changes in the content of both SA fractions and specific proteins in various biological fluids and tissues, consists in establishing the causes and mechanisms of biochemical changes in the body in certain diseases. In combination with the measurement of existing markers, they can be used to improve diagnosis, staging and monitoring of therapeutic response in some pathological conditions where the need for specificity is less than for specific diagnostics.