GM1 Gangliosidosis: Mechanisms and Management

Creation of an in vitro model of GM1 gangliosidosis by CRISPR/Cas9 knocking-out the GLB1 gene in SH-SY5Y human neuronal cell line

GM1 gangliosidosis is one type of hereditary error of metabolism that occurs due to the absence or reduction of β-galactosidase enzyme content in the lysosome of cells, including neurons. In vitro, the use of neural cell lines could facilitate the study of this disease. By creating a cell model of GM1 gangliosidosis on the SH-SY5Y human nerve cell line, it is possible to understand the main role of this enzyme in breaking down lipid substrate and other pathophysiologic phenomena this disease. To knock-out the human GLB1 gene, guides targeting exons 14 and 16 of the GLB1 gene were designed using the CRISPOR and CHOP-CHOP websites, and high-efficiency guides were selected for cloning in the PX458 vector. After confirming the cloning, the vectors were transformed into DH5α bacteria and then the target vector was extracted and transfected into human nerve cells (SH-SY5Y cell line) by electroporation. After 48 h, GFP+ cells were sorted using the FACS technique and homozygous (compound heterozygous) single cells were isolated using the serial dilution method and sequencing was done to confirm them. Finally, gap PCR tests, X-gal and Periodic acid-Schiff (PAS) staining, and qPCR were used to confirm the knock-out of the human GLB1 gene. Additionally, RNA sequencing data analysis from existing data of the Gene Expression Omnibus (GEO) was used to find the correlation of GLB1 with other genes, and then the top correlated genes were tested for further evaluation of knock-out effects. The nonviral introduction of two guides targeting exons 14 and 16 of the GLB1 gene into SH-SY5Y cells led to the deletion of a large fragment with a size of 4.62 kb. In contrast to the non-transfected cell, X-gal staining resulted in no blue color in GLB1 gene knock-out cells indicating the absence of β-galactosidase enzyme activity in these cells. Real-time PCR (qPCR) results confirmed the RNA-Seq analysis outcomes on the GEO data set and following the GLB1 gene knock-out, the expression of its downstream genes, NEU1 and CTSA, has been decreased. It has been also shown that the downregulation of GLB1-NEU1-CTSA complex gene was involved in suppressed proliferation and invasion ability of knock-out cells. This study proved that using dual guide RNA can be used as a simple and efficient tool for targeting the GLB1 gene in nerve cells and the knockout SH-SY5Y cells can be used as a model investigation of basic and therapeutic surveys for GM1 gangliosidosis disease.

GM1 Ameliorates Neuronal Injury in Rats after Cerebral Ischemia and Reperfusion: Potential Contribution of Effects on SPTBN1-mediated Signaling

Monosialoganglioside GM1 (GM1) has long been used as a therapeutic agent for neurological diseases in the clinical treatment of ischemic stroke. However, the mechanism underlying the neuroprotective function of GM1 is still obscure until now. In this study, we investigated the effects of GM1 in ischemia and reperfusion (I/R) brain injury models. Middle cerebral artery occlusion and reperfusion (MCAO/R) rats were treated with GM1 (60 mg·kg-1·d-1, tail vein injection) for 2 weeks. The results showed that GM1 substantially attenuated the MCAO/R-induced neurological dysfunction and inhibited the inflammatory responses and cell apoptosis in ischemic parietal cortex. We further revealed that GM1 inhibited the activation of NFκB/MAPK signaling pathway induced by MCAO/R injury. To explore its underlying mechanism of the neuroprotective effect, transcriptome sequencing was introduced to screen the differentially expressed genes (DEGs). By function enrichment and PPI network analyses, Sptbn1 was identified as a node gene in the network regulated by GM1 treatment. In the MCAO/R model of rats and oxygen-glucose deprivation and reperfusion (OGD/R) model of primary culture of rat cortical neurons, we first found that SPTBN1 was involved in the attenuation of I/R induced neuronal injury after GM1 administration. In SPTBN1-knockdown SH-SY5Y cells, the treatment with GM1 (20 μM) significantly increased SPTBN1 level. Moreover, OGD/R decreased SPTBN1 level in SPTBN1-overexpressed SH-SY5Y cells. These results indicated that GM1 might achieve its potent neuroprotective effects by regulating inflammatory response, cell apoptosis, and cytomembrane and cytoskeleton signals through SPTBN1. Therefore, SPTBN1 may be a potential target for the treatment of ischemic stroke.

Altered GM1 catabolism affects NMDAR-mediated Ca2+ signaling at ER-PM junctions and increases synaptic spine formation in a GM1-gangliosidosis model

Endoplasmic reticulum-plasma membrane (ER-PM) junctions mediate Ca2+ flux across neuronal membranes. The properties of these membrane contact sites are defined by their lipid content, but little attention has been given to glycosphingolipids (GSLs). Here, we show that GM1-ganglioside, an abundant GSL in neuronal membranes, is integral to ER-PM junctions; it interacts with synaptic proteins/receptors and regulates Ca2+ signaling. In a model of the neurodegenerative lysosomal storage disease, GM1-gangliosidosis, pathogenic accumulation of GM1 at ER-PM junctions due to β-galactosidase deficiency drastically alters neuronal Ca2+ homeostasis. Mechanistically, we show that GM1 interacts with the phosphorylated N-methyl D-aspartate receptor (NMDAR) Ca2+ channel, thereby increasing Ca2+ flux, activating extracellular signal-regulated kinase (ERK) signaling, and increasing the number of synaptic spines without increasing synaptic connectivity. Thus, GM1 clustering at ER-PM junctions alters synaptic plasticity and worsens the generalized neuronal cell death characteristic of GM1-gangliosidosis.

Therapeutic developments for neurodegenerative GM1 gangliosidosis

GM1 gangliosidosis (GM1) is a rare but fatal neurodegenerative disease caused by dysfunction or lack of production of lysosomal enzyme, β-galactosidase, leading to accumulation of substrates. The most promising treatments for GM1, include enzyme replacement therapy (ERT), substrate reduction therapy (SRT), stem cell therapy and gene editing. However, effectiveness is limited for neuropathic GM1 due to the restrictive nature of the blood-brain barrier (BBB). ERT and SRT alleviate substrate accumulation through exogenous supplementation over the patient's lifetime, while gene editing could be curative, fixing the causative gene, GLB1, to enable endogenous enzyme activity. Stem cell therapy can be a combination of both, with ex vivo gene editing of cells to cause the production of enzymes. These approaches require special considerations for brain delivery, which has led to novel formulations. A few therapeutic interventions have progressed to early-phase clinical trials, presenting a bright outlook for improved clinical management for GM1.

Ganglioside GM1 Drives Hemin and Protoporphyrin Adsorption in Phospholipid Membranes: A Structural Study

Monosialoganglioside (GM1), a ubiquitous component of lipid rafts, and hemin, an integral part of heme proteins such as hemoglobin, are essential to the cell membranes of brain neurons and erythrocyte red blood cells for regulating cellular communication and oxygen transport. Protoporphyrin IX (PPIX) and its derivative hemin, on the contrary, show significant cytotoxic effects when in excess causing hematological diseases, such as thalassemia, anemia, malaria, and neurodegeneration. However, the in-depth molecular etiology of their interactions with the cell membrane has so far been poorly understood. Herein, the structure of the polymer cushion-supported lipid bilayer (SLB) of the binary mixture of phospholipid and GM1 in the presence of PPIX and its derivative hemin has been investigated to predict the molecular interactions in model phospholipid membranes. A high-resolution synchrotron-based X-ray scattering technique has been employed to explore the out-of-plane structure of the assembly at different compositions and concentrations. The structural changes have been complemented with the isobaric changes in the mean molecular area obtained from the Langmuir monolayer isotherm to predict the additive-induced membrane condensation and fluidization. PPIX-induced fluidization of phospholipid SLB without GM1 was witnessed, which was reversed to condensation with 2-fold higher structural changes in the presence of GM1. A hemin concentration-dependent linear condensing effect was observed in the pristine SLB. The effect was significantly reduced, and the linearity was observed to be lost in the mixed SLB containing GM1. Our study shows that GM1 alters the interaction of hemin and PPIX with the membrane, which could be explained with the aid of hydrophobic and electrostatic interactions. Our study indicates favorable and unfavorable interactions of GM1 with PPIX and hemin, respectively, in the membrane. The observed structural changes in both SLB and the underlying polymer cushion layer lead to the proposal of a molecule-specific interaction model that can benefit the pharmaceutical industries specialized for drug designing. Our study potentially enriches our fundamental biophysical understanding of neurodegenerative diseases and drug-membrane interactions.

Case report: Preimplantation genetic testing for infantile GM1 gangliosidosis

Ganglioside-monosialic acid (GM1) gangliosidosis (ICD-10: E75.1; OMIM: 230500, 230600, 230650) is a rare autosomal recessive hereditary disease, lysosomal storage disorder caused by mutations in the GLB1 gene that lead to the absence or insufficiency of β-galactosidase. In this study, we report a case of a Russian family with a history of GM1 gangliosidosis. The family had a child who, from the age of 6 months, experienced a gradual loss of developmental skills, marked by muscle flaccidity, psychomotor retardation, hepatosplenomegaly, and the onset of tonic seizures by the age of 8 months. Funduscopic examination revealed a «cherry red spot» in the macula, which is crucial for the diagnosis of lipid storage disorders. To find the pathogenic variants responsible for these clinical symptoms, the next-generation sequencing approach was used. The analysis revealed two variants in the heterozygous state: a frameshift variant c.699delG (rs1452318343, ClinVar ID 928700) in exon 6 and a missense variant c.809A>C (rs371546950, ClinVar ID 198727) in exon 8 of the GLB1 gene. The spouses were advised to plan the pregnancy with assisted reproductive technology (ART), followed by preimplantation genetic testing for monogenic disorder (PGT-M) on the embryos. Trophectoderm biopsy was performed on 8 out of 10 resulting embryos at the blastocyst stage. To perform PGT-M, we developed a novel testing system, allowing for direct analysis of disease-causing mutations, as well as haplotype analysis based on the study of polymorphic markers-short tandem repeats (STR), located upstream and downstream of the GLB1 gene. The results showed that four embryos were heterozygous carriers of pathogenic variants in the GLB1 gene (#1, 2, 5, 8). Two embryos had a compound heterozygous genotype (#3, 4), while the embryos #7 and 9 did not carry disease-causing alleles of the GLB1 gene. The embryo #7 without pathogenic variants was transferred after consideration of its morphology and growth rate. Prenatal diagnosis in the first trimester showed the absence of the variants analyzed in the GLB1 gene in the fetus. The pregnancy resulted in the delivery of a female infant who did not inherit the disease-causing variants in the GLB1 gene.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

Gene therapy approaches for GM1 gangliosidosis: Focus on animal and cellular studies

One of the most important inherited metabolic disorders is GM1 gangliosidosis, which is a progressive neurological disorder. The main cause of this disease is a genetic defect in the enzyme β-galactosidase due to a mutation in the glb1 gene. Lack of this enzyme in cells (especially neurons) leads to the accumulation of ganglioside substrate in nerve tissues, followed by three clinical forms of GM1 disease (neonatal, juvenile, and adult variants). Genetically, many mutations occur in the exons of the glb1 gene, such as exons 2, 6, 15, and 16, so the most common ones reported in scientific studies include missense/nonsense mutations. Therefore, many studies have examined the genotype-phenotype relationships of this disease and subsequently using gene therapy techniques have been able to reduce the complications of the disease and alleviate the signs and symptoms of the disease. In this regard, the present article reviews the general features of GM1 gangliosidosis and its mutations, as well as gene therapy studies and animal and human models of the disease.

Glycosphingolipids within membrane contact sites influence their function as signaling hubs in neurodegenerative diseases

Intracellular organelles carry out many of their functions by engaging in extensive interorganellar communication through specialized membrane contact sites (MCSs) formed where two organelles tether to each other or to the plasma membrane (PM) without fusing. In recent years, these ubiquitous membrane structures have emerged as central signaling hubs that control a multitude of cellular pathways, ranging from lipid metabolism/transport to the exchange of metabolites and ions (i.e., Ca2+ ), and general organellar biogenesis. The functional crosstalk between juxtaposed membranes at MCSs relies on a defined composite of proteins and lipids that populate these microdomains in a dynamic fashion. This is particularly important in the nervous system, where alterations in the composition of MCSs have been shown to affect their functions and have been implicated in the pathogenesis of neurodegenerative diseases. In this review, we focus on the MCSs that are formed by the tethering of the endoplasmic reticulum (ER) to the mitochondria, the ER to the endo-lysosomes and the mitochondria to the lysosomes. We highlight how glycosphingolipids that are aberrantly processed/degraded and accumulate ectopically in intracellular membranes and the PM change the topology of MCSs, disrupting signaling pathways that lead to neuronal demise and neurodegeneration. In particular, we focus on neurodegenerative lysosomal storage diseases linked to altered glycosphingolipid catabolism.

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

Altered GM1 catabolism affects NMDAR-mediated Ca 2+ signaling at ER-PM junctions and increases synaptic spine formation

Endoplasmic reticulum-plasma membrane (ER-PM) junctions mediate Ca 2+ flux across neuronal membranes. The properties of these membrane contact sites are defined by their lipid content, but little attention has been given to glycosphingolipids (GSLs). Here, we show that GM1-ganglioside, an abundant GSL in neuronal membranes, is integral to ER-PM junctions; it interacts with synaptic proteins/receptors and regulates Ca 2+ signaling. In a model of the neurodegenerative lysosomal storage disease, GM1-gangliosidosis, pathogenic accumulation of GM1 at ER-PM junctions due to β-galactosidase deficiency drastically alters neuronal Ca 2+ homeostasis. Mechanistically, we show that GM1 interacts with the phosphorylated NMDAR Ca 2+ channel, thereby increasing Ca 2+ flux, activating ERK signaling, and increasing the number of synaptic spines without increasing synaptic connectivity. Thus, GM1 clustering at ER-PM junctions alters synaptic plasticity and exacerbates the generalized neuronal cell death characteristic of GM1-gangliosidosis.

A pentasaccharide for monitoring pharmacodynamic response to gene therapy in GM1 gangliosidosis

BACKGROUND

GM1 gangliosidosis is a rare, fatal, neurodegenerative disease caused by mutations in the GLB1 gene and deficiency in β-galactosidase. Delay of symptom onset and increase in lifespan in a GM1 gangliosidosis cat model after adeno-associated viral (AAV) gene therapy treatment provide the basis for AAV gene therapy trials. The availability of validated biomarkers would greatly improve assessment of therapeutic efficacy.

METHODS

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to screen oligosaccharides as potential biomarkers for GM1 gangliosidosis. The structures of pentasaccharide biomarkers were determined with mass spectrometry, as well as chemical and enzymatic degradations. Comparison of LC-MS/MS data of endogenous and synthetic compounds confirmed the identification. The study samples were analyzed with fully validated LC-MS/MS methods.

FINDINGS

We identified two pentasaccharide biomarkers, H3N2a and H3N2b, that were elevated more than 18-fold in patient plasma, cerebrospinal fluid (CSF), and urine. Only H3N2b was detectable in the cat model, and it was negatively correlated with β-galactosidase activity. Following intravenous (IV) AAV9 gene therapy treatment, reduction of H3N2b was observed in central nervous system, urine, plasma, and CSF samples from the cat model and in urine, plasma, and CSF samples from a patient. Reduction of H3N2b accurately reflected normalization of neuropathology in the cat model and improvement of clinical outcomes in the patient.

INTERPRETATIONS

These results demonstrate that H3N2b is a useful pharmacodynamic biomarker to evaluate the efficacy of gene therapy for GM1 gangliosidosis. H3N2b will facilitate the translation of gene therapy from animal models to patients.

FUNDING

This work was supported by grants U01NS114156, R01HD060576, ZIAHG200409, and P30 DK020579 from the National Institutes of Health (NIH) and a grant from National Tay-Sachs and Allied Diseases Association Inc.

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

GM1 gangliosidosis: patients with different phenotypic features and novel mutations

OBJECTIVES

GM1-gangliosidosis is an autosomal recessive lysosomal storage disorder caused by beta-galactosidase deficiency encoded by GLB1. It is mainly characterized by progressive neurodegeneration due to accumulation of glycosphingolipids in central nervous system and classified into 3 forms according to the age of onset and severity of symptoms.

CASE PRESENTATIONS

In this study, we described the demographic, clinical, molecular, biochemical characteristics of 4 patients from 3 unrelated families diagnosed with GM1-gangliosidosis. The ages of the patients included in the study were between 5 months and 10 years old and all were male. All families had third degree consanguinity. Two of the patients were diagnosed as infantile type and the other two siblings were diagnosed as juvenile type. Infantile type patients had coarse facial appearance, developmental delay and early neurodegeneration. Juvenile type patients had mild motor and cognitive developmental delays at the beginning, but they did not have coarse facial features. Cherry-red macula and cardiac involvement were detected in only one infantile patient, while hepatomegaly was present in both infantile type patients. Beta galactosidase enzyme levels were extremely low in all patients and two novel variants were identified in GLB1.

CONCLUSIONS

In this study, we identified four patients with different phenotypic features and two new mutations. GM1 gangliosidosis shows clinical heterogeneity according to age of onset. In some patients, developmental delay can be seen before the loss of gained functions. Therefore, this disorder should be kept in mind in patients with developmental delay who have not yet started neurodegeneration. There is no curative treatment for the disease yet, but ongoing gene therapy studies are promising for curing the disease in the future.

A Mouse Systems Genetics Approach Reveals Common and Uncommon Genetic Modifiers of Hepatic Lysosomal Enzyme Activities and Glycosphingolipids

Identification of genetic modulators of lysosomal enzyme activities and glycosphingolipids (GSLs) may facilitate the development of therapeutics for diseases in which they participate, including Lysosomal Storage Disorders (LSDs). To this end, we used a systems genetics approach: we measured 11 hepatic lysosomal enzymes and many of their natural substrates (GSLs), followed by modifier gene mapping by GWAS and transcriptomics associations in a panel of inbred strains. Unexpectedly, most GSLs showed no association between their levels and the enzyme activity that catabolizes them. Genomic mapping identified 30 shared predicted modifier genes between the enzymes and GSLs, which are clustered in three pathways and are associated with other diseases. Surprisingly, they are regulated by ten common transcription factors, and their majority by miRNA-340p. In conclusion, we have identified novel regulators of GSL metabolism, which may serve as therapeutic targets for LSDs and may suggest the involvement of GSL metabolism in other pathologies.

Zebra-Sphinx: Modeling Sphingolipidoses in Zebrafish

Sphingolipidoses are inborn errors of metabolism due to the pathogenic mutation of genes that encode for lysosomal enzymes, transporters, or enzyme cofactors that participate in the sphingolipid catabolism. They represent a subgroup of lysosomal storage diseases characterized by the gradual lysosomal accumulation of the substrate(s) of the defective proteins. The clinical presentation of patients affected by sphingolipid storage disorders ranges from a mild progression for some juvenile- or adult-onset forms to severe/fatal infantile forms. Despite significant therapeutic achievements, novel strategies are required at basic, clinical, and translational levels to improve patient outcomes. On these bases, the development of in vivo models is crucial for a better understanding of the pathogenesis of sphingolipidoses and for the development of efficacious therapeutic strategies. The teleost zebrafish (Danio rerio) has emerged as a useful platform to model several human genetic diseases owing to the high grade of genome conservation between human and zebrafish, combined with precise genome editing and the ease of manipulation. In addition, lipidomic studies have allowed the identification in zebrafish of all of the main classes of lipids present in mammals, supporting the possibility to model diseases of the lipidic metabolism in this animal species with the advantage of using mammalian lipid databases for data processing. This review highlights the use of zebrafish as an innovative model system to gain novel insights into the pathogenesis of sphingolipidoses, with possible implications for the identification of more efficacious therapeutic approaches.

Gene Therapy of Sphingolipid Metabolic Disorders

Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.

GM1-gangliosidosis: The caregivers' assessments of symptom impact and most important symptoms to treat

GM1-gangliosidosis (GM1) is a rare neurodegenerative disorder leading to early mortality and causing progressive decline of physical skills and cerebral functioning. No approved treatment for GM1 exists. In this study-the first to explore priorities of parents of subjects with pediatric onset forms of GM1-we address a crucial gap by characterizing symptoms most critical to caregivers of children with GM1 to treat. Our two-part, mixed-methods approach began with focus groups, followed by interviews with a distinct set of parents. Interviews included a prioritization activity that used best-worst scaling. Quantitative data were analyzed descriptively. Qualitative data were analyzed using thematic analysis and rapid analysis process. Parents prioritized the symptoms they believed would increase their child's lifespan and improve their perceived quality of life (QoL); these symptoms focused on communicating wants/needs, preventing pain/discomfort, getting around and moving one's body, and enhancing eating/feeding. Although lifespan was highly valued, almost all parents would not desire a longer lifespan without acceptable child QoL. Parents indicated high caregiver burden and progressive reduction in QoL for children with GM1. This novel study of caregiver priorities identified important symptoms for endpoints' selection in patient-focused drug development in the context of high disease impact and unmet treatment needs.

The landscape of CRISPR/Cas9 for inborn errors of metabolism

Since its discovery as a genome editing tool, the clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR/Cas9) system has opened new horizons in the diagnosis, research, and treatment of genetic diseases. CRISPR/Cas9 can rewrite the genome at any region with outstanding precision to modify it and further instructions for gene expression. Inborn Errors of Metabolism (IEM) are a group of more than 1500 diseases produced by mutations in genes encoding for proteins that participate in metabolic pathways. IEM involves small molecules, energetic deficits, or complex molecules diseases, which may be susceptible to be treated with this novel tool. In recent years, potential therapeutic approaches have been attempted, and new models have been developed using CRISPR/Cas9. In this review, we summarize the most relevant findings in the scientific literature about the implementation of CRISPR/Cas9 in IEM and discuss the future use of CRISPR/Cas9 to modify epigenetic markers, which seem to play a critical role in the context of IEM. The current delivery strategies of CRISPR/Cas9 are also discussed.

Models to study basic and applied aspects of lysosomal storage disorders

The lack of available treatments and fatal outcome in most lysosomal storage disorders (LSDs) have spurred research on pathological mechanisms and novel therapies in recent years. In this effort, experimental methodology in cellular and animal models have been developed, with aims to address major challenges in many LSDs such as patient-to-patient variability and brain condition. These techniques and models have advanced knowledge not only of LSDs but also for other lysosomal disorders and have provided fundamental insights into the biological roles of lysosomes. They can also serve to assess the efficacy of classical therapies and modern drug delivery systems. Here, we summarize the techniques and models used in LSD research, which include both established and recently developed in vitro methods, with general utility or specifically addressing lysosomal features. We also review animal models of LSDs together with cutting-edge technology that may reduce the need for animals in the study of these devastating diseases.

Lysosomal positioning diseases: beyond substrate storage

Lysosomal storage diseases (LSDs) comprise a group of inherited monogenic disorders characterized by lysosomal dysfunctions due to undegraded substrate accumulation. They are caused by a deficiency in specific lysosomal hydrolases involved in cellular catabolism, or non-enzymatic proteins essential for normal lysosomal functions. In LSDs, the lack of degradation of the accumulated substrate and its lysosomal storage impairs lysosome functions resulting in the perturbation of cellular homeostasis and, in turn, the damage of multiple organ systems. A substantial number of studies on the pathogenesis of LSDs has highlighted how the accumulation of lysosomal substrates is only the first event of a cascade of processes including the accumulation of secondary metabolites and the impairment of cellular trafficking, cell signalling, autophagic flux, mitochondria functionality and calcium homeostasis, that significantly contribute to the onset and progression of these diseases. Emerging studies on lysosomal biology have described the fundamental roles of these organelles in a variety of physiological functions and pathological conditions beyond their canonical activity in cellular waste clearance. Here, we discuss recent advances in the knowledge of cellular and molecular mechanisms linking lysosomal positioning and trafficking to LSDs.

Preclinical Enzyme Replacement Therapy with a Recombinant β-Galactosidase-Lectin Fusion for CNS Delivery and Treatment of GM1-Gangliosidosis

GM1-gangliosidosis is a catastrophic, neurodegenerative lysosomal storage disease caused by a deficiency of lysosomal β-galactosidase (β-Gal). The primary substrate of the enzyme is GM1-ganglioside (GM1), a sialylated glycosphingolipid abundant in nervous tissue. Patients with GM1-gangliosidosis present with massive and progressive accumulation of GM1 in the central nervous system (CNS), which leads to mental and motor decline, progressive neurodegeneration, and early death. No therapy is currently available for this lysosomal storage disease. Here, we describe a proof-of-concept preclinical study toward the development of enzyme replacement therapy (ERT) for GM1-gangliosidosis using a recombinant murine β-Gal fused to the plant lectin subunit B of ricin (mβ-Gal:RTB). We show that long-term, bi-weekly systemic injection of mβ-Gal:RTB in the β-Gal-/- mouse model resulted in widespread internalization of the enzyme by cells of visceral organs, with consequent restoration of enzyme activity. Most importantly, β-Gal activity was detected in several brain regions. This was accompanied by a reduction of accumulated GM1, reversal of neuroinflammation, and decrease in the apoptotic marker caspase 3. These results indicate that the RTB lectin delivery module enhances both the CNS-biodistribution pattern and the therapeutic efficacy of the β-Gal ERT, with the potential to translate to a clinical setting for the treatment of GM1-gangliosidosis.

Fluorescent In Situ Staining and Flow Cytometric Procedures as New Pre-Diagnostic Tests for Sialidosis, GM1 Gangliosidosis and Niemann–Pick Type C

Background: Early diagnosis is essential in the field of lysosomal storage disorders for the proper management of patients and for starting therapies before irreversible damage occurs, particularly in neurodegenerative conditions. Currently, specific biomarkers for the diagnosis of lysosomal storage disorders are lacking in routine laboratory practice, except for enzymatic tests, which are available only in specialized metabolic centers. Recently, we established a method for measuring and verifying changes in GM1 ganglioside levels in peripheral blood lymphocytes in patients with GM1 gangliosidosis. However, fresh blood is not always available, and using frozen/thawed lymphocytes can lead to inaccurate results. Methods: We used frozen/thawed fibroblasts obtained from stored biopsies to explore the feasibility of fluorescent imaging and flow-cytometric methods to track changes in storage materials in fibroblasts from patients with three lysosomal neurodegenerative conditions: GM1 gangliosidosis, Sialidosis, and Niemann–Pick type C. We used specific markers for each pathology. Results and Conclusions: We demonstrated that with our methods, it is possible to clearly distinguish the levels of accumulated metabolites in fibroblasts from affected and unaffected patients for all the three pathologies considered. Our methods proved to be rapid, sensitive, unbiased, and potentially applicable to other LSDs.

Carrier Rate and Mutant Allele Frequency of GM1 Gangliosidosis in Miniature Shiba Inus (Mame Shiba): Population Screening of Breeding Dogs in Japan

GM1 gangliosidosis is a progressive, recessive, autosomal, neurodegenerative, lysosomal storage disorder that affects the brain and multiple systemic organs due to an acid β-galactosidase deficiency encoded by the GLB1 gene. This disease occurs in the Shiba Inu breed, which is one of the most popular traditional breeds in Japan, due to the GLB1:c.1649delC (p.P550Rfs*50) mutation. Previous surveys performed of the Shiba Inu population in Japan found a carrier rate of 1.02–2.94%. Currently, a miniature type of the Shiba Inu called “Mame Shiba”, bred via artificial selection to yield smaller individuals, is becoming more popular than the standard Shiba Inu and it is now one of the most popular breeds in Japan and China. The GM1 gangliosidosis mutation has yet to be surveyed in the Mame Shiba population. This study aimed to determine the frequency of the mutant allele and carrier rate of GM1 gangliosidosis in the Mame Shiba breed. Blood samples were collected from 1832 clinically healthy adult Mame Shiba Inus used for breeding across 143 Japanese kennels. The genotyping was performed using a real-time PCR assay. The survey found nine carriers among the Mame Shibas, indicating that the carrier rate and mutant allele frequency were 0.49% and 0.00246, respectively. This study demonstrated that the mutant allele has already been inherited by the Mame Shiba population. There is a risk of GM1 gangliosidosis occurrence in the Mame Shiba breed if breeders use carriers for mating. Further genotyping surveys are necessary for breeding Mame Shibas to prevent the inheritance of this disease.

GM1 Gangliosidosis-A Mini-Review

GM1 gangliosidosis is a progressive, neurosomatic, lysosomal storage disorder caused by mutations in the GLB1 gene encoding the enzyme β-galactosidase. Absent or reduced β-galactosidase activity leads to the accumulation of β-linked galactose-containing glycoconjugates including the glycosphingolipid (GSL) GM1-ganglioside in neuronal tissue. GM1-gangliosidosis is classified into three forms [Type I (infantile), Type II (late-infantile and juvenile), and Type III (adult)], based on the age of onset of clinical symptoms, although the disorder is really a continuum that correlates only partially with the levels of residual enzyme activity. Severe neurocognitive decline is a feature of Type I and II disease and is associated with premature mortality. Most of the disease-causing β-galactosidase mutations reported in the literature are clustered in exons 2, 6, 15, and 16 of the GLB1 gene. So far 261 pathogenic variants have been described, missense/nonsense mutations being the most prevalent. There are five mouse models of GM1-gangliosidosis reported in the literature generated using different targeting strategies of the Glb1 murine locus. Individual models differ in terms of age of onset of the clinical, biochemical, and pathological signs and symptoms, and overall lifespan. However, they do share the major abnormalities and neurological symptoms that are characteristic of the most severe forms of GM1-gangliosidosis. These mouse models have been used to study pathogenic mechanisms, to identify biomarkers, and to evaluate therapeutic strategies. Three GLB1 gene therapy trials are currently recruiting Type I and Type II patients (NCT04273269, NCT03952637, and NCT04713475) and Type II and Type III patients are being recruited for a trial utilizing the glucosylceramide synthase inhibitor, venglustat (NCT04221451).

White Matter Pathology as a Barrier to Gangliosidosis Gene Therapy

The gangliosidoses are a family of neurodegenerative lysosomal storage diseases that have recently seen promising advances in gene therapy. White matter deficits are well established components of gangliosidosis pathology that are now receiving more attention because they are partially refractory to correction by gene therapy. After a brief synopsis of normal myelinogenesis, this review outlines current viewpoints on the origin of white matter deficits in the gangliosidoses and potential obstacles to treating them effectively by gene therapy. Dysmyelinogenesis (failure of myelin sheaths to form properly) is proposed as the predominant contributor to white matter pathology, but precise mechanistic details are not well understood. The involvement of neuronal storage deficits may extend beyond secondary demyelination (destruction of myelin due to axonal loss) and contribute to dysmyelinogenesis. Preclinical studies in animal models of the gangliosidoses have substantially improved lifespan and quality of life, leading to the initiation of several clinical trials. However, improvement of white matter pathology has lagged behind other metrics and few evidence-based explanations have been proposed to date. Research groups in the field are encouraged to include myelin-specific investigations in future gene therapy work to address this gap in knowledge.