Treatment Options in Congenital Disorders of Glycosylation

Computational profiling of molecular biomarkers in congenital disorders of glycosylation Type-I and binding analysis of Ginkgolide A with P4HB

AIMS

Congenital disorders of glycosylation (CDG) comprise a diverse group of genetic diseases characterized by aberrant glycosylation that leads to severe multi-systematic effects. Despite advancements in understanding the underlying molecular mechanisms, curative options remain limited. This study employed computational methods to identify key molecular biomarkers for CDG-I and examine the pharmacological effects of Ginkgolide A (GA), a potent bioactive natural compound.

METHODS

We analyzed the GSE8440 microarray dataset to discover differentially expressed genes (DEGs) in patients compared to healthy individuals with CDG-I utilizing GEO2R. Functional enrichments, including gene ontologies (GO) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analyses, were conducted to contextualize the biological mechanisms and molecular signatures involved in CDG-I (Congenital Disorders of Glycosylation Type-1). The protein-protein interaction (PPI) network for DEGs was constructed using the STRING database, and the central hub genes within the PPI network were identified using Cytohubba. Furthermore, the 3D structure of the top hub gene (P4HB) was predicted by using the Robetta server. The CASTp was employed to evaluate the active sites. Molecular docking of P4HB with GA was carried out to investigate the binding affinity using the PyRx tool, and the stability of the docked complex was validated through MD simulation. The pharmacokinetics, toxicity, and bioactivity score of GA were comprehensively assessed using SwissADME, ProTox-II, and Molinspiration.

RESULTS

Our findings indicated 247 significant DEGs, including 146 up-regulated and 101 down-regulated genes. GO and KEGG pathway analyses confirmed that the up-regulated and hub genes were strongly associated with protein folding, glycoprotein processing in the endoplasmic reticulum, and endoplasmic reticulum stress (ER) pathways. P4HB emerged as the top hub gene in CDG-I, playing a significant role in protein folding and ER stress. The 3D structure of P4HB was refined and validated, achieving 95.8 % residues in the most favored region of the Ramachandran plot, with an overall quality of 92.97 %. The CASTp server predicted the largest active site with an area of 2243.660 Å2 and a volume of 3236.584 Å3. Molecular docking revealed that GA has a strong binding affinity with P4HB (-8.9 kcal/mol). The ADME (Absorption, Distribution, Metabolism, Excretion) and toxicity assessments confirmed promising drug-like characteristics, excellent bioavailability, and minimal toxicity risk.

CONCLUSION

This study emphasizes GA as a potential treatment possibility option to alleviated CDG-I pathology by targeting protein misfolding and ER stress, which are fundamental aspects of the disease. Additionally, our findings indicate that P4HB is a critical molecular target in CDG-I. These results pave the way for future preclinical and clinical investigations aimed at advancing the targeted and tailored treatments for CDG.

The long way to diagnosis: attention disorder, alcohol addiction or congenital disorder of glycosylation? A case report

Attention deficit hyperactivity disorder (ADHD) is a relatively common disorder in clinical psychiatry. Patients often suffer from symptoms long before the diagnosis due to an overlap with other psychiatric differential diagnosis. Importantly, alcohol addiction and other illicit drug dependence and withdrawal symptoms mimicking ADHD symptoms should be ruled out. Here we present a rare case of a young female patient with symptoms of ADHD and an extremely high carbohydrate-deficient transferrin (CDT) of 19,6% (< 1,3%) indicating the presence of a congenital disorder of glycosylation (CDG). A thorough diagnostic workup excluded alcohol addiction as a cause of the constantly high CDT levels. The CDT test was positive due a transferrin mutation affecting the glycosylation site. Nevertheless, psychiatric symptoms can be due to metabolic disorders which should be considered. Further, substance-use disorders (SUD) are a critical and potentially complicated differential diagnosis concerning diagnostic procedures and treatment in ADHD.

Swift Universal Glycan Acquisition (SUGA) Enables Quantitative Glycan Profiling across Diverse Sample Types

The ability to rapidly analyze complex mixtures of glycans derived from glycoproteins is important, but techniques are often laborious and require multiple glycan derivatization steps. Here, we describe an approach termed Swift Universal Glycan Acquisition (SUGA) in which the total released, nonreduced N-glycan samples are analyzed following direct injection and electrospray ionization in a mass spectrometer with a rapid 3 min run time for each sample. As electrospray ionization (ESI) can generate multiple charge states and adducts for the same glycan composition (MS1), deconvolution is performed to yield the relative intensity profile for each detected glycan composition; each annotated composition is supported by an annotated MS2 spectrum. This combination of MS1 and MS2 data enables confident glycan identification. The data obtained by SUGA are comparable to those obtained using permethylated N-glycans analyzed by matrix-assisted laser desorption/ionization (MALDI)-MS. The SUGA approach was applied to the analyses of several purified glycoproteins and N-glycans derived from cells and compared to spectra obtained following permethylation and analysis by MALDI-MS. This new approach will facilitate the rapid and high-throughput analysis of N-glycans from diverse biological samples.

Therapeutic development approaches to treat haploinsufficiency diseases: restoring protein levels

Rare diseases affect one in ten people but only a small fraction of these diseases have an FDA-approved treatment. Haploinsufficiency, caused by a dominant loss-of-function mutation, is a unique rare disease group because patients have one normal allele of the affected gene. This makes rare haploinsufficiency diseases promising candidates for drug development by increasing expression of the normal gene allele, decreasing the target protein degradation and enhancing the target protein function. This review summarizes recent progresses and approaches used in the translational research of therapeutics to treat haploinsufficiency diseases including gene therapy, nucleotide-based therapeutics and small-molecule drug development. We hope that these drug development strategies will accelerate therapeutic development to treat haploinsufficiency diseases.

Genetic counseling for congenital disorders of glycosylation (CDG)

Congenital disorders of glycosylation (CDGs) are a genetically and clinically diverse group of disorders that arise as a result of defects within glycosylation synthetic pathways. CDGs are caused by pathogenic variants in many different genes in the glycosylation network. With over 160 different CDG types currently identified and a vast range of severity and presentations existing within and across those types, the road to a CDG diagnosis is often lengthy and complicated. The perils of this arduous CDG diagnostic odyssey are fraught with various genetic counseling uncertainties: (1) confusion about family planning, (2) queries about inheritance, (3) managing treatment, and (4) dealing with the uncertainty of rare diseases. Thus, the role of the genetic counselor is paramount in helping affected individuals and their families navigate these genetic counseling complexities. Case examples of common genetic counseling difficulties for CDGs are outlined, providing clinical applications of what CDG presentations, diagnostic processes, and common difficulties look like. Information on the nomenclature, incidence, prevalence, diagnostic testing, treatment, and management of CDGs are also discussed to provide a comprehensive summary of CDGs for genetic counselors, and subsequently to affected individuals and their families.

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

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

Treatment of congenital disorders of glycosylation: An overview

While the identification and diagnosis of congenital disorders of glycosylation (CDG) have rapidly progressed, the available treatment options are still quite limited. Mostly, we are only able to manage the disease symptoms rather than to address the underlying cause. However, recent years have brought about remarkable advances in treatment approaches for some CDG. Innovative therapies, targeting both the root cause and resulting manifestations, have transitioned from the research stage to practical application. The present paper aims to provide a detailed overview of these exciting developments and the rising concepts that are used to treat these ultra-rare diseases.

Altered expression of Sialyl Lewis X in experimental models of Parkinson's disease

The mechanisms underlying neurodegeneration in Parkinson's disease (PD) are still not fully understood. Glycosylation is an important post-translational modification that affects protein function, cell-cell contacts and inflammation and can be modified in pathologic conditions. Although the involvement of aberrant glycosylation has been proposed for PD, the knowledge of the diversity of glycans and their role in PD is still minimal. Sialyl Lewis X (sLeX) is a sialylated and fucosylated tetrasaccharide with essential roles in cell-to-cell recognition processes. Pathological conditions and pro-inflammatory mediators can up-regulate sLeX expression on cell surfaces, which has important consequences in intracellular signalling and immune function. Here, we investigated the expression of this glycan using in vivo and in vitro models of PD. We show the activation of deleterious glycation-related pathways in mouse striatum upon treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin-based model of PD. Importantly, our results show that MPTP triggers the presentation of more proteins decorated with sLeX in mouse cortex and striatum in a time-dependent manner, as well as increased mRNA expression of its rate-limiting enzyme fucosyltransferase 7. sLeX is expressed in neurons, including dopaminergic neurons, and microglia. Although the underlying mechanism that drives increased sLeX epitopes, the nature of the protein scaffolds and their functional importance in PD remain unknown, our data suggest for the first time that sLeX in the brain may have a role in neuronal signalling and immunomodulation in pathological conditions. KEY MESSAGES: MPTP triggers the presentation of proteins decorated with sLeX in mouse brain. MPTP triggers the expression of sLeX rate-limiting enzyme FUT 7 in striatum. sLeX is expressed in neurons, including dopaminergic neurons, and microglia. sLeX in the brain may have a role in neuronal signalling and immunomodulation.

Neurological manifestations in PMM2-congenital disorders of glycosylation (PMM2-CDG): Insights into clinico-radiological characteristics, recommendations for follow-up, and future directions

PURPOSE

In the absence of prospective data on neurological symptoms, disease outcome, or guidelines for system specific management in phosphomannomutase 2-congenital disorders of glycosylation (PMM2-CDG), we aimed to collect and review natural history data.

METHODS

Fifty-one molecularly confirmed individuals with PMM2-CDG enrolled in the Frontiers of Congenital Disorders of Glycosylation natural history study were reviewed. In addition, we prospectively reviewed a smaller cohort of these individuals with PMM2-CDG on off-label acetazolamide treatment.

RESULTS

Mean age at diagnosis was 28.04 months. Developmental delay is a constant phenotype. Neurological manifestation included ataxia (90.2%), myopathy (82.4%), seizures (56.9%), neuropathy (52.9%), microcephaly (19.1%), extrapyramidal symptoms (27.5%), stroke-like episodes (SLE) (15.7%), and spasticity (13.7%). Progressive cerebellar atrophy is the characteristic neuroimaging finding. Additionally, supratentorial white matter changes were noted in adult age. No correlation was observed between the seizure severity and SLE risk, although all patients with SLE have had seizures in the past. "Off-label" acetazolamide therapy in a smaller sub-cohort resulted in improvement in speech fluency but did not show statistically significant improvement in objective ataxia scores.

CONCLUSION

Clinical and radiological findings suggest both neurodevelopmental and neurodegenerative pathophysiology. Seizures may manifest at any age and are responsive to levetiracetam monotherapy in most cases. Febrile seizure is the most common trigger for SLEs. Acetazolamide is well tolerated.

Glycosylation: A new signaling paradigm for the neurovascular diseases

A wide range of life-threatening conditions with complicated pathogenesis involves neurovascular disorders encompassing Neurovascular unit (NVU) damage. The pathophysiology of NVU is characterized by several features including tissue hypoxia, stimulation of inflammatory and angiogenic processes, and the initiation of intricate molecular interactions, collectively leading to an elevation in blood-brain barrier permeability, atherosclerosis and ultimately, neurovascular diseases. The presence of compelling data about the significant involvement of the glycosylation in the development of diseases has sparked a discussion on whether the abnormal glycosylation may serve as a causal factor for neurovascular disorders, rather than being just recruited as a secondary player in regulating the critical events during the development processes like embryo growth and angiogenesis. An essential tool for both developing new anti-ischemic therapies and understanding the processes of ischemic brain damage is undertaking pre-clinical studies of neurovascular disorders. Together with the post-translational modification of proteins, the modulation of glycosylation and its enzymes implicates itself in several abnormal activities which are known to accelerate neuronal vasculopathy. Despite the failure of the majority of glycosylation-based preclinical and clinical studies over the past years, there is a significant probability to provide neuroprotection utilizing modern and advanced approaches to target abnormal glycosylation activity at embryonic stages as well. This article focuses on a variety of experimental evidence to postulate the interconnection between glycosylation and vascular disorders along with possible treatment options.

Oral sialic acid supplementation in NANS-CDG: Results of a single center, open-label, observational pilot study

NANS-CDG is a congenital disorder of glycosylation (CDG) caused by biallelic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. It presents with intellectual developmental disorder (IDD), skeletal dysplasia, neurologic impairment, and gastrointestinal dysfunction. Some patients suffer progressive intellectual neurologic deterioration (PIND), emphasizing the need for a therapy. In a previous study, sialic acid supplementation in knockout nansa zebrafish partially rescued skeletal abnormalities. Here, we performed the first in-human pre- and postnatal sialic-acid study in NANS-CDG. In this open-label observational study, 5 patients with NANS-CDG (range 0-28 years) were treated with oral sialic acid for 15 months. The primary outcome was safety. Secondary outcomes were psychomotor/cognitive testing, height and weight, seizure control, bone health, gastrointestinal symptoms, and biochemical and hematological parameters. Sialic acid was well tolerated. In postnatally treated patients, there was no significant improvement. For the prenatally treated patient, psychomotor and neurologic development was better than two other genotypically identical patients (one treated postnatally, one untreated). The effect of sialic acid treatment may depend on the timing, with prenatal treatment potentially benefiting neurodevelopmental outcomes. Evidence is limited, however, and longer-term follow-up in a larger number of prenatally treated patients is required.

DPAGT1-CDG: Recurrent fetal death

BACKGROUND

Congenital disorders of glycosylation (CDG) are a series of relatively uncommon genetic disorders, and variants in the dolichyl-phosphate N-acetylglucosamine-1-phosphotransferase (DPAGT1) gene can cause DPAGT1-CDG, which is characterized by multisystem abnormalities: failure to thrive, psychomotor retardation, seizures, etc. PATIENTS: Two fetuses in a nonconsanguineous family recurrently presented with irregular skull morphology, micrognathia, adduction and supination by prenatal ultrasound. They were finally found dead in utero. Pedigree whole exome sequencing revealed novel compound heterozygous variants in the DPAGT1 gene. We also reviewed 11 previous reports associated with DPAGT1-CDG.

CONCLUSIONS

We report novel variants in the DPAGT1 gene in two fetuses from the same family with intrauterine death.

Treatment of neurometabolic epilepsies: Overview and recent advances

The rarity and heterogeneity of neurometabolic diseases make it challenging to reach evidence-based principles for their specific treatments. Indeed, current treatments for many of these diseases remain symptomatic and supportive. However, an ongoing scientific and medical revolution has led to dramatic breakthroughs in molecular sciences and genetics, revealing precise pathophysiologic mechanisms. Accordingly, this has led to significant progress in the development of novel therapeutic approaches aimed at treating epilepsy resulting from these conditions, as well as their other manifestations. We overview recent notable treatment advancements, from vitamins, trace minerals, and diets to unique medications targeting the elemental pathophysiology at a molecular or cellular level, including enzyme replacement therapy, enzyme enhancing therapy, antisense oligonucleotide therapy, stem cell transplantation, and gene therapy.

[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.

Mannose phosphate isomerase gene mutation leads to a congenital disorder of glycosylation: A rare case report and literature review

We report the case of a 2-year-old girl who was diagnosed with Mannose-6-phosphate isomerase-congenital disorder of glycosylation (MPI-CDG) and provide a review of the relevant literature. The young girl presented with recurrent unexplained diarrhea, vomiting, hypoproteinemia, and elevated liver transaminases. Whole-exome sequencing revealed that the patient had compound heterozygous mutations in the MPI gene (NM_0024). An exon 4 (c.455G > T, p.R152l) mutation was inherited from the mother and an exon 7 (c.884G > A, p.R295H) mutation from the father. One week after the start of mannose treatment, the vomiting and diarrhea symptoms disappeared completely and did not show any side effects. We also provide a brief review of the relevant literature. Including the present case, a total of 52 patients from hospitals across 17 countries were diagnosed with MPI-CDG. Age at disease onset ranged from birth to 15 years, with an onset under 2 years in most patients (43/50). Overall, patients presented with at least one or more of the following symptoms: chronic diarrhea (41/46), vomiting (23/27), hepatomegaly (39/44), hepatic fibrosis (20/37), protein-losing enteropathy (30/36), elevated serum transaminases (24/34), hyperinsulinemic-hypoglycemia (24/34), hypoalbuminemia (33/38), prolonged coagulation (26/30), splenomegaly (13/21), non-pitting edema (14/20), failure to thrive (13/36), portal hypertension (4/9), epilepsy (2/17), thrombosis (12/14), and abnormally elevated leukocytes (5). None of the patients was reported to have an intellectual disability (0/28). The majority of patients (26/30) showed clinical symptoms, and laboratory results improved after oral mannose administration. Our findings suggest that MPI-CDG should be considered in children with unexplained recurrent digestive and endocrine systems involvement, and gene examination should be performed immediately to obtain a definite diagnosis in order to begin treatment in a timely manner.

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.

Systematic Review: Drug Repositioning for Congenital Disorders of Glycosylation (CDG)

Advances in research have boosted therapy development for congenital disorders of glycosylation (CDG), a group of rare genetic disorders affecting protein and lipid glycosylation and glycosylphosphatidylinositol anchor biosynthesis. The (re)use of known drugs for novel medical purposes, known as drug repositioning, is growing for both common and rare disorders. The latest innovation concerns the rational search for repositioned molecules which also benefits from artificial intelligence (AI). Compared to traditional methods, drug repositioning accelerates the overall drug discovery process while saving costs. This is particularly valuable for rare diseases. AI tools have proven their worth in diagnosis, in disease classification and characterization, and ultimately in therapy discovery in rare diseases. The availability of biomarkers and reliable disease models is critical for research and development of new drugs, especially for rare and heterogeneous diseases such as CDG. This work reviews the literature related to repositioned drugs for CDG, discovered by serendipity or through a systemic approach. Recent advances in biomarkers and disease models are also outlined as well as stakeholders' views on AI for therapy discovery in CDG.

Stakeholders' views on drug development: the congenital disorders of glycosylation community perspective

BACKGROUND

Congenital disorders of glycosylation (CDG) are a large family of rare genetic diseases for which therapies are virtually nonexistent. However, CDG therapeutic research has been expanding, thanks to the continuous efforts of the CDG medical/scientific and patient communities. Hence, CDG drug development is a popular research topic. The main aim of this study was to understand current and steer future CDG drug development and approval by collecting and analysing the views and experiences of the CDG community, encompassing professionals and families. An electronic (e-)survey was developed and distributed to achieve this goal.

RESULTS

A total of 128 respondents (46 CDG professionals and 82 family members), mainly from Europe and the USA, participated in this study. Most professionals (95.0%) were relatively familiar with drug development and approval processes, while CDG families revealed low familiarity levels, with 8.5% admitting to never having heard about drug development. However, both stakeholder groups agreed that patients and families make significant contributions to drug development and approval. Regarding their perceptions of and experiences with specific drug development and approval tools, namely biobanks, disease models, patient registries, natural history studies (NHS) and clinical trials (CT), the CDG community stakeholders described low use and participation, as well as variable familiarity. Additionally, CDG professionals and families shared conflicting views about CT patient engagement and related information sharing. Families reported lower levels of involvement in CT design (25.0% declared ever being involved) and information (60.0% stated having been informed) compared to professionals (60.0% and 85.7%, respectively). These contrasting perceptions were further extended to their insights and experiences with patient-centric research. Finally, the CDG community (67.4% of professionals and 54.0% of families) reported a positive vision of artificial intelligence (AI) as a drug development tool. Nevertheless, despite the high AI awareness among CDG families (76.8%), professionals described limited AI use in their research (23.9%).

CONCLUSIONS

This community-centric study sheds new light on CDG drug development and approval. It identifies educational, communication and research gaps and opportunities for CDG professionals and families that could improve and accelerate CDG therapy development.

Nutrition interventions in congenital disorders of glycosylation

Congenital disorders of glycosylation (CDG) are a group of more than 160 inborn errors of metabolism affecting multiple pathways of protein and lipid glycosylation. Patients present with a wide range of symptoms and therapies are only available for very few subtypes. Specific nutritional treatment options for certain CDG types include oral supplementation of monosaccharide sugars, manganese, uridine, or pyridoxine. Additional management includes specific diets (i.e., complex carbohydrate or ketogenic diet), iron supplementation, and albumin infusions. We review the dietary management in CDG with a focus on two subgroups: N-linked glycosylation defects and GPI-anchor disorders.