Therapeutic Strategies For Tay-Sachs Disease

Evaluation of the PP6D5 Polymer as a Novel Non-Viral Vector in the Development of a CRISPR/nCas9-Based Gene Therapy for Tay-Sachs Disease

Background/Objectives: Tay-Sachs disease (TSD) is a neurodegenerative disorder caused by a deficiency in β-hexosaminidase A (HexA), which accumulates GM2 gangliosides, primarily in neurons. Currently, therapeutic options are limited, highlighting the need for new strategies such as gene therapy. Despite their effectiveness, viral vectors can elicit adverse immune responses; consequently, non-viral vectors are being explored as an alternative. We have previously investigated the use of CRISPR/Cas9 nickase (nCas9) as a potential tool for treating TSD. Here, we expanded our study by evaluating the PP6D5 polymer as a novel non-viral vector for delivering the CRISPR/nCas9 system to restore HexA activity. Methods: First, we evaluated the PP6D5-mediated CRISPR/nCas9 system's transfection efficiency in NIH-3T3 fibroblasts, U87MG astrocytoma, SHSY5Y neuroblastoma, and TSD fibroblasts. We then evaluated the potential of PP6D5 to correct the gene defect in TSD fibroblasts. Results: The results showed that PP6D5 exhibited significantly higher transfection efficiency compared to lipofectamine 3000 in all tested cell models. In TSD fibroblasts, transfection with both HEXA and HEXB cDNAs increased the HexA activity levels by up to 7.4-fold, compared to a 3.2-fold increase in cells transfected only with HEXA cDNA after 15 days post-transfection. These levels were up to 4.5-fold higher than those observed in lipofectamine-mediated transfection. Additionally, PP6D5-mediated CRISPR/nCas9-based genome editing led to a significant reduction in the lysosomal mass of TSD fibroblasts. Conclusions: This study provides promising evidence for the use of the PP6D5 polymer as a non-viral vector for delivering CRISPR/nCas9-based gene therapy in TSD. The use of the PP6D5 polymer may offer some advantages that viral vectors cannot, such as a reduction in cytotoxicity and higher TE in difficult-to-transfect cell lines. Furthermore, this type of polymeric vector has not been extensively explored for gene therapy, making this study an important contribution to the development of non-viral delivery systems for the treatment of neurodegenerative diseases.

A systematic review of hereditary neurological disorders diagnosed by whole exome sequencing in Pakistani population: updates from 2014 to November 2024

Hereditary neurological disorders (HNDs) are a group of heterogeneous disorders characterized by significant genetic and clinical variability. HNDs are caused by dysfunction of the central or peripheral nervous system due to aberrant electrical impulses. More than 600 types of HNDs have been documented, and overall, these are the second leading cause of death worldwide. This systematic review is based on a retrospective analysis of research articles reporting HNDs diagnosed using whole exome sequencing in Pakistani families from 2014 to November 2024. Original research articles were retrieved through online surveys, notably Google Scholar, PubMed, and the Web of Science. Based on stringent selection criteria, 89 research articles and 188 variants published around 10 years were considered. Variants and research articles were cross-checked and further validated in different online databases/resources to confirm their genomic nomenclature and pathogenicity according to the ACMG guidelines. A total of 188 variants in 143 distinct genes in Pakistani families identified through whole exome sequencing have been reported to date that caused genetic and clinically heterogeneous HNDs. Consanguineous parentage was found in around 90% of cases, and approximately 91% of causative alleles were reported in homozygous state showing a predominant burden of HNDs because of blood-related marriages. The most frequent type of pathogenic variants were single nucleotide substitutions (92 missense and 39 nonsense). Among 188 variants, 76 variants were reported in 2024 and 44 variants were observed in 2023. Pakistan is the fifth most populous country in the world having an extreme prevalence of consanguinity resulting in the expression of pathogenic variants due to homozygosity. Therefore, there is a prevalence of genetic disorders particularly rare monogenic or Mendelian disorders. Next-generation sequencing approach is strongly recommended for diagnosis, early therapeutic intervention and genetic counselling.

Differential gene expression patterns in Niemann-Pick Type C and Tay-Sachs diseases: Implications for neurodegenerative mechanisms

Lysosomal storage disorders (LSDs) are a group of rare genetic conditions characterized by the impaired function of enzymes responsible for lipid digestion. Among these LSDs, Tay-Sachs disease (TSD) and Niemann-Pick type C (NPC) may share a common gene expression profile. In this study, we conducted a bioinformatics analysis to explore the gene expression profile overlap between TSD and NPC. Analyses were performed on RNA-seq datasets for both TSD and NPC from the Gene Expression Omnibus (GEO) database. Datasets were subjected to differential gene expression analysis utilizing the DESeq2 package in the R programming language. A total of 147 differentially expressed genes (DEG) were found to be shared between the TSD and NPC datasets. Enrichment analysis was then performed on the DEGs. We found that the common DEGs are predominantly associated with processes such as cell adhesion mediated by integrin, cell-substrate adhesion, and urogenital system development. Furthermore, construction of protein-protein interaction (PPI) networks using the Cytoscape software led to the identification of four hub genes: APOE, CD44, SNCA, and ITGB5. Those hub genes not only can unravel the pathogenesis of related neurologic diseases with common impaired pathways, but also may pave the way towards targeted gene therapy of LSDs.In addition, they serve as the potential biomarkers for related neurodegenerative diseases warranting further investigations.

Precise template-free correction restores gene function in Tay-Sachs disease while reframing is ineffective

Tay-Sachs disease is a fatal neurodegenerative disorder caused by HEXA mutations inactivating the metabolic enzyme HexA. The most common mutation is c.1278insTATC, a tandem 4-bp duplication disrupting HEXA expression by frameshift. In an engineered cell model, we explore the use of CRISPR-Cas9 for therapeutic editing of c.1278insTATC. Within genomic microduplications, the microhomology-mediated end joining (MMEJ) pathway is favored to repair double-stranded breaks with collateral deletion of one repeat. Protospacer adjacent motif (PAM) constraints on Cas9 endonuclease activity prevented cleavage at the duplication center, the optimal position for MMEJ initiation. Rather, cleavage 1 bp from the c.1278insTATC duplication center spontaneously reconstructed the wild-type sequence at ∼14.7% frequency, with concomitant restoration of normal cellular HexA activity. As an alternative to perfect correction, short insertions or deletions were serially introduced to restore an open reading frame across a 19-bp sequence encompassing c.1278insTATC. Frame-restored variants did not recover significant HexA function, presumably due to structural incompatibility of incurred amino acid insertions. Hence, precise correction of c.1278insTATC is the only therapeutically relevant outcome achieved in this study, with MMEJ highlighted as a potential template-free CRISPR-Cas9 modality to that end.

Diagnosing Late-Onset Tay-Sachs Through Next Generation Sequencing and Functional Enzyme Testing: From Genes to Enzymes

Tay-Sachs disease is a neurodegenerative disorder characterized by progressive neurologic impairment due to pathogenic variants in the HEXA gene that codes for the alpha subunit of β-hexosaminidase. We report 2 cases of adult-onset progressive weakness, ataxia, and neuropsychiatric symptoms in a 30-year-old man and 37-year-old woman. Both patients had compound heterozygosity in the HEXA gene with 4 distinct variants. The first patient had subsequent confirmatory functional enzyme testing displaying reduced hexosaminidase concentration, and the second patient had functional enzyme testing before genetic testing, exemplifying alternative avenues for the diagnosis of late-onset Tay-Sachs (LOTS) disease.

Simultaneous surgery for gastrostomy and laryngotracheal separation in a patient with Tay‒Sachs disease

Genetic testing identified novel compound heterozygous missense variants in the HEXA gene (NM_00520.6: c.775A>C and NM_000520.6: c.508C>T) in a 16-month-old girl diagnosed with Tay‒Sachs disease. The patient gradually became unable to consume food orally. She suffered severe aspiration pneumonia and underwent gastrostomy and laryngotracheal separation at 2 years and 4 months of age. Despite an initially good prognosis, she died at 3 years of age.

Unleashing the potential of mRNA therapeutics for inherited neurological diseases

Neurological monogenic loss-of-function diseases are hereditary disorders resulting from gene mutations that decrease or abolish the normal function of the encoded protein. These conditions pose significant therapeutic challenges, which may be resolved through the development of innovative therapeutic strategies. RNA-based technologies, such as mRNA replacement therapy, have emerged as promising and increasingly viable treatments. Notably, mRNA therapy exhibits significant potential as a mutation-agnostic approach that can address virtually any monogenic loss-of-function disease. Therapeutic mRNA carries the information for a healthy copy of the defective protein, bypassing the problem of targeting specific genetic variants. Moreover, unlike conventional gene therapy, mRNA-based drugs are delivered through a simplified process that requires only transfer to the cytoplasm, thereby reducing the mutagenic risks related to DNA integration. Additionally, mRNA therapy exerts a transient effect on target cells, minimizing the risk of long-term unintended consequences. The remarkable success of mRNA technology for developing coronavirus disease 2019 vaccines has rekindled interest in mRNA as a cost-effective method for delivering therapeutic proteins. However, further optimization is required to enhance mRNA delivery, particularly to the CNS, while minimizing adverse drug reactions and toxicity. In this comprehensive review, we delve into past, present and ongoing applications of mRNA therapy for neurological monogenic loss-of-function diseases. We also discuss the promises and potential challenges presented by mRNA therapeutics in this rapidly advancing field. Ultimately, we underscore the full potential of mRNA therapy as a game-changing therapeutic approach for neurological disorders.

Current approaches in CRISPR-Cas systems for hereditary diseases

CRISPR-Cas technologies have drastically revolutionized genetic engineering and also dramatically changed the potential for treating inherited disorders. The potential to correct genetic mutations responsible for numerous hereditary disorders from single-gene disorders to complex polygenic diseases through precise DNA editing is feasible. The tactic now employed in CRISPR-Cas systems for treating inherited disorders is the usage of particular guide RNAs to target and edit disease-causing mutations in the patient's genome. Several methods such as CRISPR-Cas9, CRISPR-Cas12, and CRISPR-Cas13 are being thoroughly researched and optimized to increase effectiveness, accuracy, and safety in gene editing. Additionally, it is predicted that CRISPR-based therapies will be able to treat complex genetic illnesses such as cancer predisposition syndromes, neurological disorders, and cardiovascular conditions in addition to single-gene disorders. The available editing tools and creation of base editing technology facilitate the simultaneous correction of many mutations or accurate nucleotide changes leading to further advances in the development of multiplex editing tools and base editing technology fiction. When combined with other paradigms such as gene therapy using stem cell treatment, CRISPR-Cas promises improved efficacy. Patient treatment and lowering side effects significantly in individual genetic profiles will guide CRISPR-based treatments. These procedures will undoubtedly lead to therapies that are both efficient and curative of a wide range of genetic diseases, ushering in a new era of precision medicine. This chapter discusses about CRISPR Cas9 mechanism and its significance in the treatment of Hereditary disorders.

Evidence of Lysosomal β-Hexosaminidase Enzymatic Activity Associated with Extracellular Vesicles: Potential Applications for the Correction of Sandhoff Disease

Extracellular vesicles (EVs) can be isolated from biological fluids and cell culture medium. Their nanometric dimension, relative stability, and biocompatibility have raised considerable interest for their therapeutic use as delivery vehicles of macromolecules, namely nucleic acids and proteins. Deficiency in lysosomal enzymes and associated proteins is at the basis of a group of genetic diseases known as lysosomal storage disorders (LSDs), characterized by the accumulation of undigested substrates into lysosomes. Among them, GM2 gangliosidoses are due to a deficiency in the activity of lysosomal enzyme β-hexosaminidase, leading to the accumulation of the GM2 ganglioside and severe neurological symptoms. Current therapeutic approaches, including enzyme replacement therapy (ERT), have proven unable to significantly treat these conditions. Here, we provide evidence that the lysosomal β-hexosaminidase enzyme is associated with EVs released by HEK cells and that the EV-associated activity can be increased by overexpressing the α-subunit of β-hexosaminidase. The delivery of EVs to β-hexosaminidase-deficient fibroblasts results in a partial cross-correction of the enzymatic defect. Overall findings indicate that EVs could be a source of β-hexosaminidase that is potentially exploitable for developing therapeutic approaches for currently untreatable LSDs.

Who has a meaningful life? A care ethics analysis of selective trait abortion

Trait Selective Abortions (TSA) have come under critique as a medical practice that presents potential disabled infants as burdens and lacking the potential for meaningful lives. This paper, using the author's background as a disabled person, contends that the philosophy underpinning TSAs reflects liberal society's lack of a theory of needs. The author argues for a care ethics based approach informed by disability analyses to engage with TSAs.

Founder mutations and rare disease in the Arab world

Founder mutations are disease-causing variants that occur frequently in geographically or culturally isolated groups whose shared ancestor(s) carried the pathogenic variant. While some disease alleles may vanish from the genetic pool due to natural selection, variants with weaker effects may survive for a long time, thereby enhancing the prevalence of some rare diseases. These are predominantly autosomal recessive diseases but can also be autosomal dominant traits with late-onset or mild phenotypes. Cultural practices, such as endogamy and consanguinity, in these isolated groups lead to higher prevalence of such rare diseases compared to the rest of the population and worldwide. In this Perspective, we define population isolates and the underlying genetic mechanisms for accumulating founder mutations. We also discuss the current and potential scientific, clinical and public-health implications of studying founder mutations in population isolates around the world, with a particular focus on the Arab population.

Cinnamic acid, a natural plant compound, exhibits neuroprotection in a mouse model of Sandhoff disease via PPARα

Tay-Sachs disease (TSD) and its severe form Sandhoff disease (SD) are autosomal recessive lysosomal storage metabolic disorders, which often result into excessive GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Although patients with these diseases appear normal at birth, the progressive accumulation of undegraded GM2 gangliosides in neurons leads to early death accompanied by manifestation of motor difficulties and gradual loss of behavioral skills. Unfortunately, there is still no effective treatment available for TSD/SD. The present study highlights the importance of cinnamic acid (CA), a naturally occurring aromatic fatty acid present in a number of plants, in inhibiting the disease process in a transgenic mouse model of SD. Oral administration of CA significantly attenuated glial activation and inflammation and reduced the accumulation of GM2 gangliosides/glycoconjugates in the cerebral cortex of Sandhoff mice. Besides, oral CA also improved behavioral performance and increased the survival of Sandhoff mice. While assessing the mechanism, we found that oral administration of CA increased the level of peroxisome proliferator-activated receptor α (PPARα) in the brain of Sandhoff mice and that oral CA remained unable to reduce glycoconjugates, improve behavior and increase survival in Sandhoff mice lacking PPARα. Our results indicate a beneficial function of CA that utilizes a PPARα-dependent mechanism to halt the progression of SD and thereby increase the longevity of Sandhoff mice.

Clinical, Imaging, Genetic, and Disease Course Characteristics in Patients With GM2 Gangliosidosis: Beyond Age of Onset

BACKGROUND AND OBJECTIVES

GM2 gangliosidoses, a group of autosomal-recessive neurodegenerative lysosomal storage disorders, result from β-hexosaminidase (HEX) deficiency with GM2 ganglioside as its main substrate. Historically, GM2 gangliosidoses have been classified into infantile, juvenile, and late-onset forms. With disease-modifying treatment trials now on the horizon, a more fine-grained understanding of the disease course is needed.

METHODS

We aimed to map and stratify the clinical course of GM2 gangliosidoses in a multicenter cohort of pediatric and adult patients. Patients were stratified according to age at onset and age at diagnosis. The 2 resulting GM2 disease clusters were characterized in-depth for respective disease features (detailed standardized clinical, laboratory, and MRI assessments) and disease evolution.

RESULTS

In 21 patients with GM2 gangliosidosis (17 Tay-Sachs, 2 GM2 activator deficiency, 2 Sandhoff disease), 2 disease clusters were discriminated: an early-onset and early diagnosis cluster (type I; n = 8, including activator deficiency and Sandhoff disease) and a cluster with very variable onset and long interval until diagnosis (type II; n = 13 patients). In type I, rapid onset of developmental stagnation and regression, spasticity, and seizures dominated the clinical picture. Cherry red spot, startle reactions, and elevated AST were only seen in this cluster. In type II, problems with balance or gait, muscle weakness, dysarthria, and psychiatric symptoms were specific and frequent symptoms. Ocular signs were common, including supranuclear vertical gaze palsy in 30%. MRI involvement of basal ganglia and peritrigonal hyperintensity was seen only in type I, whereas predominant infratentorial atrophy (or normal MRI) was characteristic in type II. These types were, at least in part, associated with certain genetic variants.

DISCUSSION

Age at onset alone seems not sufficient to adequately predict different disease courses in GM2 gangliosidosis, as required for upcoming trial planning. We propose an alternative classification based on age at disease onset and dynamics, predicted by clinical features and biomarkers, into type I-an early-onset, rapid progression cluster-and type II-a variable onset, slow progression cluster. Specific diagnostic workup, including GM2 gangliosidosis, should be performed in patients with combined ataxia plus lower motor neuron weakness to identify type II patients.

Possibilities and limitations of antisense oligonucleotide therapies for the treatment of monogenic disorders

Antisense oligonucleotides (ASOs) are incredibly versatile molecules that can be designed to specifically target and modify RNA transcripts to slow down or halt rare genetic disease progression. They offer the potential to target groups of patients or can be tailored for individual cases. Nonetheless, not all genetic variants and disorders are amenable to ASO-based treatments, and hence, it is important to consider several factors before embarking on the drug development journey. Here, we discuss which genetic disorders have the potential to benefit from a specific type of ASO approach, based on the pathophysiology of the disease and pathogenic variant type, as well as those disorders that might not be suitable for ASO therapies. We further explore additional aspects, such as the target tissues, intervention time points, and potential clinical benefits, which need to be considered before developing a compound. Overall, we provide an overview of the current potentials and limitations of ASO-based therapeutics for the treatment of monogenic disorders.

Infantile Monosialoganglioside2 (GM2) Gangliosidosis With Concurrent Bronchopneumonia: An Extraordinary Case of Tay-Sachs Disease

Tay-Sachs disease (TSD) is a rare, fatal neurodegenerative disorder characterized by the deficiency of the enzyme hexosaminidase-A (Hex A), which results in the accumulation of monosialoganglioside2 (GM2) ganglioside within nerve cells, predominantly affecting individuals of Ashkenazi Jewish descent. We report a remarkable case of a three-year-old South Asian male with infantile GM2 gangliosidosis, compounded by bronchopneumonia, a rarely documented complication in Tay-Sachs patients. The patient presented with recurrent seizures, fever, cough, and developmental delay. Confirmation of the diagnosis was obtained through reduced Hex A enzyme activity, corroborated by imaging and blood and urine analyses. Family history was significant for consanguinity and similar sibling fatalities. Despite the progressive nature of the disease, symptomatic management, including antiepileptic drugs, antibiotic therapy, and supportive care, led to an improvement in clinical condition, though ongoing monitoring remains essential. In this case, the coexistence of bronchopneumonia with Tay-Sachs disease is unusual, reflecting the necessity for this case report. The patient's response highlights the potential for symptomatic management, the importance of genetic counseling, and the imperative for research into gene and enzyme replacement therapies. The uniqueness of this case provides novel insights into the disease's spectrum, enhancing awareness, encouraging early diagnosis, and refining care strategies for Tay-Sachs disease, aligning with the broader goals of improving patient outcomes and advancing medical research.

Targeting GM2 Ganglioside Accumulation in Dementia: Current Therapeutic Approaches and Future Directions

Dementia in neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and dementia with Lewy bodies (DLB) is a progressive neurological condition affecting millions worldwide. The amphiphilic molecule GM2 gangliosides are abundant in the human brain and play important roles in neuronal development, intercellular recognition, myelin stabilization, and signal transduction. GM2 ganglioside's degradation requires hexosaminidase A (HexA), a heterodimer composed of an α subunit encoded by HEXA and a β subunit encoded by HEXB. The hydrolysis of GM2 also requires a non-enzymatic protein, the GM2 activator protein (GM2-AP), encoded by GM2A. Pathogenic mutations of HEXA, HEXB, and GM2A are responsible for autosomal recessive diseases known as GM2 gangliosidosis, caused by the excessive intralysosomal accumulation of GM2 gangliosides. In AD, PD and DLB, GM2 ganglioside accumulation is reported to facilitate Aβ and α-synuclein aggregation into toxic oligomers and plaques through activation of downstream signaling pathways, such as protein kinase C (PKC) and oxidative stress factors. This review explored the potential role of GM2 ganglioside alteration in toxic protein aggregations and its related signaling pathways leading to neurodegenerative diseases. Further review explored potential therapeutic approaches, which include synthetic and phytomolecules targeting GM2 ganglioside accumulation in the brain, holding a promise for providing new and effective management for dementia.

Gene and Cellular Therapies for Leukodystrophies

Leukodystrophies are a heterogenous group of inherited, degenerative encephalopathies, that if left untreated, are often lethal at an early age. Although some of the leukodystrophies can be treated with allogeneic hematopoietic stem cell transplantation, not all patients have suitable donors, and new treatment strategies, such as gene therapy, are rapidly being developed. Recent developments in the field of gene therapy for severe combined immune deficiencies, Leber's amaurosis, epidermolysis bullosa, Duchenne's muscular dystrophy and spinal muscular atrophy, have paved the way for the treatment of leukodystrophies, revealing some of the pitfalls, but overall showing promising results. Gene therapy offers the possibility for overexpression of secretable enzymes that can be released and through uptake, allow cross-correction of affected cells. Here, we discuss some of the leukodystrophies that have demonstrated strong potential for gene therapy interventions, such as X-linked adrenoleukodystrophy (X-ALD), and metachromatic leukodystrophy (MLD), which have reached clinical application. We further discuss the advantages and disadvantages of ex vivo lentiviral hematopoietic stem cell gene therapy, an approach for targeting microglia-like cells or rendering cross-correction. In addition, we summarize ongoing developments in the field of in vivo administration of recombinant adeno-associated viral (rAAV) vectors, which can be used for direct targeting of affected cells, and other recently developed molecular technologies that may be applicable to treating leukodystrophies in the future.

Use of metabolic glycoengineering and pharmacological inhibitors to assess lipid and protein sialylation on cells

Metabolic glycoengineering (MGE) has been developed to visualize carbohydrates on live cells. The method allows the fluorescent labeling of sialic acid (Sia) sugar residues on neuronal plasma membranes. For instance, the efficiency of glycosylation along neurite membranes has been characterized as cell health measure in neurotoxicology. Using human dopaminergic neurons as model system, we asked here, whether it was possible to separately label diverse classes of biomolecules and to visualize them selectively on cells. Several approaches suggest that a large proportion of Sia rather incorporated in non-protein components of cell membranes than into glycoproteins. We made use here of deoxymannojirimycin (dMM), a non-toxic inhibitor of protein glycosylation, and of N-butyl-deoxynojirimycin (NBdNM) a well-tolerated inhibitor of lipid glycosylation, to develop a method of differential labeling of sialylated membrane lipids (lipid-Sia) or sialylated N-glycosylated proteins (protein-Sia) on live neurons. The time resolution at which Sia modification of lipids/proteins was observable was in the range of few hours. The approach was then extended to several other cell types. Using this technique of target-specific MGE, we found that in dopaminergic or sensory neurons >60% of Sia is lipid bound, and thus polysialic acid-neural cell adhesion molecule (PSA-NCAM) cannot be considered the major sialylated membrane component. Different from neurons, most Sia was bound to protein in HepG2 hepatoma cells or in neural crest cells. Thus, our method allows visualization of cell-specific sialylation processes for separate classes of membrane constituents.