Gene Therapy for Neurological Disorders: Navigating Challenges and Seizing Opportunities

Neurological disorders encompass a wide spectrum of conditions affecting the central and peripheral nervous systems, including neurodegenerative diseases (e.g., Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis), neuromuscular syndromes (e.g., muscular dystrophies, spinal muscular atrophy), demyelinating conditions (e.g., multiple sclerosis), epilepsies, and neurodevelopmental syndromes such as Rett syndrome and autism spectrum disorder [1,2]. Collectively, they represent the leading cause of disability worldwide, with the Global Burden of Disease Study 2021 reporting that over 3.4 billion people were affected, contributing to more than 443 million disability-adjusted life years (DALYs) lost [3]. Dementia alone impacts more than 55 million individuals globally, with projections exceeding 150 million by 2050 [4]. These conditions disproportionately affect low- and middle-income countries, reflecting inequities in diagnosis and care [5,6].

Despite advances in symptomatic treatments (e.g., cholinesterase inhibitors for AD, dopamine replacement in PD), most neurological disorders remain intractable and progressive [7]. Conventional pharmacological approaches target downstream pathways but rarely address the underlying genetic or molecular causes.

In recent decades, molecular therapeutics—including antisense oligonucleotides (ASOs), RNA interference (RNAi), and viral vector-based gene supplementation—have provided proof of principle that genetic modulation can alter disease trajectories in neurological disorders [8]. The approval of onasemnogene abeparvovec (Zolgensma) for SMA illustrates the transformative potential of genetic therapies [9]. Yet, these strategies often modulate rather than correct disease-causing genes, require repeated administration, or carry risks of systemic toxicity [10].

Gene editing technologies have emerged as powerful tools capable of addressing these limitations. ZFNs and TALENs introduced the first programmable nucleases for site-specific DNA cleavage, but their complexity restricted broad application [11]. By contrast, the RNA-guided CRISPR–Cas9 system revolutionised genome engineering through its simplicity, efficiency, and adaptability [12]. More recently, precision editors including base editors (enabling single-nucleotide substitutions without double-strand breaks) [13], prime editors (allowing versatile “search-and-replace” genome editing) [14], and RNA-targeting CRISPR enzymes (e.g., Cas13) [15]—have expanded therapeutic possibilities beyond conventional gene disruption. Collectively, these platforms offer opportunities to not only inactivate pathogenic alleles but also repair, silence, or modulate gene expression in disease-relevant neural populations [16,17].

Figure 1 Prime Editing

Figure 2 Delivery Particle Genome

Figure 3 TALENs

This review provides a critical evaluation of the applications of gene editing in neurological disorders, highlighting advances in disease-specific models, innovations in delivery across the blood–brain barrier, and the evolving landscape of preclinical and early clinical trials. Special attention is given to both the promise (long-lasting, one-time curative potential) and the challenges (off-target effects, immunogenicity, ethical constraints) that define the translational path of these therapies.

2. Gene Editing Tools and Neurological Disorders Overview

2.1 Evolution of Genome Editing Technologies

The last three decades have witnessed remarkable advances in genome engineering. Early programmable nucleases—ZFNs and TALENs—enabled targeted double-strand breaks (DSBs) in DNA but required labor-intensive protein engineering [11]. The development of CRISPR–Cas9 in 2012 marked a turning point, allowing RNA-guided targeting with unprecedented simplicity and efficiency [12]. Beyond conventional CRISPR–Cas9, next-generation editors now provide finer control:

• Base editors (BEs) introduce targeted nucleotide substitutions without DSBs [13].
• Prime editors (PEs) enable versatile insertions, deletions, and substitutions [14].
• RNA-targeting CRISPR systems (Cas13, CasRx) permit reversible knockdown of transcripts [15].
• Epigenome editors modulate chromatin states without altering DNA [16].

These platforms collectively extend therapeutic potential for neurological disorders [17].

2.2 Neurological Disorders: Scope and Burden

Neurological disorders—including AD, PD, HD, ALS, SMA, and Rett syndrome—affect billions globally [1–4]. The global burden continues to rise due to population aging, lifestyle factors, and improved diagnostics. By 2050, dementia cases alone may exceed 150 million [4]. The unmet need for disease-modifying treatments highlights the urgency of developing durable genome-based interventions [5–7].

2.3 Why Gene Editing is Transformative for Neurology

Several factors position gene editing as uniquely suited for neurological disorders:

1. Genetic Basis: Many conditions—including HD, SMA, Rett syndrome, and subsets of ALS and PD—are monogenic, making them direct targets for corrective editing [8,9].
2. Durability: Edited neurons, being largely post-mitotic, are less likely to dilute edits through cell division, allowing for one-time interventions with potentially lifelong effects [11,12].
3. Cell-Type Specificity: Advances in promoters and regulatory elements allow selective targeting of disease-relevant neurons (e.g., dopaminergic neurons in PD, motor neurons in ALS) [16].
4. Multimodal Potential: Beyond correction, editing can be applied to reduce toxic protein aggregates (e.g., mutant huntingtin), silence risk alleles (e.g., APOE ε4 in AD), or modulate synaptic plasticity genes for cognitive resilience [13–15].
5. Complementarity with Other Therapies: Editing strategies can be combined with gene supplementation (e.g., in SMA), RNA-targeting drugs (ASOs), or pharmacological approaches to provide synergistic effects [8,9,17].

2.4 Current Limitations and the Path Forward

Despite transformative potential, challenges remain significant:

• Delivery to the CNS: The blood–brain barrier (BBB) limits access of nucleases and vectors, necessitating intrathecal, intraparenchymal, or systemic delivery with specialized vectors such as AAV9 [18].
• Safety: Risks include off-target mutagenesis, unintended immune activation, and long-term consequences of permanent edits [19].
• Heterogeneity: Complex disorders (e.g., AD, PD) involve multiple genetic and environmental factors, complicating therapeutic design [20].
• Ethical considerations: Brain-targeted editing raises concerns regarding consent, reversibility, and unintended modification of cognition or behavior [21].

Nevertheless, the accelerating pace of preclinical advances and the emergence of first-in-human gene-editing trials for neurological disorders underscore the field’s rapid transition from proof-of-concept to clinical reality [22].

3. Applications of Gene Editing in Neurological Disorders

3.1 Huntington’s Disease (HD)

Huntington’s disease (HD) is a progressive autosomal dominant neurodegenerative disorder caused by an abnormal expansion of CAG trinucleotide repeats in the HTT gene, which encodes mutant huntingtin protein [23]. This expansion leads to toxic protein aggregation, selective striatal neuronal loss, and clinical features including motor dysfunction, cognitive decline, and psychiatric symptoms. The monogenic etiology makes HD an attractive target for gene editing–based interventions [24].

Gene Editing Strategies

Several gene editing approaches are under investigation for HD:

• CRISPR–Cas9–mediated disruption of the expanded HTT allele has been shown to selectively reduce mutant protein while preserving wild-type function [25].
• Base editing enables targeted contraction of the expanded CAG repeats without inducing double-strand breaks [26].
• Prime editing has demonstrated precise correction of HTT expansions in mouse brains with minimal off-target effects [27].
• RNA-targeting systems (Cas13/CasRx) allow transient and reversible silencing of mutant HTT transcripts, avoiding permanent genomic alterations [28].

Delivery Approaches

Efficient delivery to the central nervous system (CNS) remains a major challenge. Strategies include:

• AAV vectors, including AAV9 and engineered capsids, which can cross the blood–brain barrier and target striatal neurons [29].
• Dual-AAV systems, used for large gene editors such as prime editors [27].
• Non-viral nanoparticles, enabling allele-selective targeting and reduced immunogenicity [30].

Preclinical and Translational Advances

• Monteys et al. [25] demonstrated allele-selective CRISPR–Cas9 editing in HD mouse models, leading to reduced mutant HTT protein, improved motor function, and decreased aggregation.
• Li et al. [26] reported the use of base editors in patient-derived iPSCs and mouse models, achieving up to 50% efficiency in contracting expanded repeats.
• Anzalone et al. [27] achieved therapeutically relevant prime editing efficiency (~20–30%) in neural tissue with significant behavioral recovery.
• CasRx-based RNA editing produced reversible silencing of mutant transcripts in preclinical models with motor and cognitive improvements [28].
• The uniQure AMT-130 trial (NCT04120493) is the first-in-human study investigating an AAV5-delivered gene therapy targeting HTT. Although it uses a gene-silencing approach rather than CRISPR, it paves the translational pathway for editing-based therapies [31].

Figure 4 Huntington's Disease

Figure 5 Gene Editing Tools

Critical Perspective

HD has emerged as a flagship candidate for CRISPR-based therapeutics due to its monogenic nature and well-characterized pathology. Preclinical results are promising, with clear demonstration of both gene correction and functional recovery. However, key challenges remain:

• Achieving allele-selectivity to avoid editing wild-type HTT.
• Ensuring safe and efficient CNS delivery at therapeutic scales.
• Addressing long-term safety, including off-target edits and immune responses.
• Transitioning from preclinical models (mice, iPSCs) to human trials, which will require rigorous safety validation and scalable manufacturing.

Despite these hurdles, ongoing technological progress in base and prime editing, alongside non-viral delivery innovations, makes HD one of the most promising neurological targets for first-in-human CRISPR therapies.

3.2 Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the progressive degeneration of upper and lower motor neurons, leading to muscle weakness, paralysis, and death typically within 2–5 years of onset [32]. While most ALS cases are sporadic, ~10% are familial, frequently associated with mutations in SOD1, C9orf72, TARDBP, and FUS genes [33]. These mutations drive toxic protein aggregation, RNA foci, and neuroinflammation, making ALS a strong candidate for genetic intervention.

Gene Editing Strategies

Multiple gene editing approaches have been developed to address ALS pathogenesis:

• CRISPR–Cas9–mediated disruption of mutant SOD1, which reduces toxic protein accumulation and rescues motor neuron survival [34].
• Base and prime editing strategies allow correction of SOD1 point mutations and other causative variants [35].
• Cas13 RNA-targeting systems have been used to degrade pathogenic C9orf72 repeat-containing transcripts, mitigating RNA foci and dipeptide repeat protein toxicity [36].
• Dual approaches combining CRISPR and RNAi enhance therapeutic efficacy, targeting multiple disease pathways simultaneously [37].

Delivery Approaches

The blood–brain barrier poses a significant barrier to therapeutic access. Strategies include:

• AAV9 vectors, capable of broad CNS transduction, used extensively in ALS mouse models [34].
• Lipid nanoparticles (LNPs), enabling non-viral delivery with reduced immunogenicity and potential repeat dosing [38].
• Dual-AAV delivery, necessary for large editing cargos such as prime editors [35].

Preclinical and Translational Advances

• Gaj et al. demonstrated CRISPR–Cas9-mediated SOD1 disruption in mouse models, leading to improved motor function and extended survival [34].
• A high-fidelity Cas13 variant selectively targeted C9orf72 repeat RNA in patient-derived iPSCs and mice, reducing RNA foci and toxic peptides while minimizing collateral RNA cleavage [36].
• Base editing corrected SOD1 point mutations in preclinical models, extending survival and reducing neuroinflammation [35].
• Proof-of-concept CRISPR deletion of C9orf72 hexanucleotide repeats in human cells halted pathological progression [39].
• Early-phase ASO and RNAi therapies targeting SOD1 (e.g., tofersen) have already reached clinical trials (NCT02623699), paving the way for CRISPR-based interventions [40].

Figure 6 ALS

Critical Perspective

Gene editing offers a promising avenue for ALS therapy, particularly in familial cases with known mutations. CRISPR-mediated SOD1 knockdown has shown consistent efficacy in preclinical models, while Cas13 RNA-targeting approaches may offer a safer, reversible alternative. Base and prime editors introduce precision correction capabilities, though delivery and efficiency remain key barriers.

Clinical translation is advancing rapidly: while ASOs have reached human trials, CRISPR-based ALS therapies remain preclinical, with first-in-human studies expected in the coming years [40]. Challenges include the heterogeneity of ALS genetics, the rapid progression of disease, and the need for early intervention before significant neuronal loss occurs. Nonetheless, ALS represents one of the most active and promising frontiers in neurological gene editing.

3.3 Alzheimer’s Disease (AD)

Alzheimer’s disease (AD) is the most common cause of dementia, affecting more than 55 million people worldwide and projected to surpass 150 million cases by 2050 [41]. Pathologically, AD is characterized by extracellular amyloid-β (Aβ) plaques, intracellular neurofibrillary tangles of hyperphosphorylated tau, synaptic dysfunction, and progressive neuronal loss [42]. Genetic risk factors play a significant role: early-onset familial AD is linked to mutations in APP, PSEN1, and PSEN2, while the APOE ε4 allele is the strongest genetic risk factor for sporadic late-onset AD [43]. These insights position gene editing as a promising approach for both monogenic and multifactorial forms of the disease.

Gene Editing Strategies

• CRISPR–Cas9 disruption of APP cleavage sites to reduce amyloidogenic processing and Aβ accumulation [44].
• Base editing to convert pathogenic mutations in PSEN1 and APP to benign variants [45].
• CRISPR interference (CRISPRi) and epigenome editing to downregulate expression of risk alleles, such as APOE ε4 [46].
• RNA-targeting CRISPR (Cas13) to degrade tau transcripts, preventing tangle formation [47].
• Prime editing for precision correction of familial AD mutations, though still at proof-of-concept stage [48].

Delivery Approaches

• AAV9 and AAV-PHP.B vectors for widespread brain transduction [49].
• Focused ultrasound with microbubbles, transiently opening the blood–brain barrier to enhance delivery [50].
• Lipid nanoparticles (LNPs) designed for non-viral CNS delivery, currently in preclinical testing [51].

Preclinical and Translational Advances

• CRISPR–Cas9 disruption of BACE1 in AD mouse models significantly reduced Aβ levels and improved cognitive performance [44].
• Base editing corrected familial AD mutations in PSEN1 in patient-derived iPSCs, normalising γ-secretase activity and reducing Aβ42/40 ratios [45].
• Epigenome editing suppressed APOE ε4 expression in human astrocytes, shifting lipid metabolism toward a neuroprotective phenotype [46].
• Cas13-mediated tau mRNA silencing reduced tangle pathology and improved cognition in transgenic mice [47].
• Prime editing strategies have corrected APP mutations in preclinical neuronal models, though in vivo efficiency remains limited [48].

Figure 7 Pathophysiology Of Alzheimer's Disease

Critical Perspective

AD presents a unique challenge compared to monogenic diseases like HD or SMA, given its multifactorial etiology and late-onset progression. Nonetheless, gene editing offers several promising avenues:

• Familial AD mutations (APP, PSEN1/2) are tractable targets for correction with base and prime editors.
• Risk allele modulation (APOE ε4) may enable preventive strategies in high-risk carriers.
• Pathway-targeting approaches (BACE1, tau) could yield symptomatic and disease-modifying benefits.

Major barriers include the need for broad brain delivery, early intervention before extensive neurodegeneration, and balancing safety with irreversible edits. However, the combination of next-generation editors with emerging CNS delivery technologies positions AD as a leading candidate for translational genome editing research.

3.4 Parkinson’s Disease (PD)

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, characterized by progressive loss of dopaminergic neurons in the substantia nigra, accumulation of α-synuclein aggregates (Lewy bodies), and motor symptoms including tremor, rigidity, and bradykinesia [52]. Genetic contributors include mutations in SNCA (α-synuclein), LRRK2, PARK7, PINK1, and GBA, making PD partially amenable to gene editing interventions [53].

Gene Editing Strategies

• CRISPR–Cas9 knockout of SNCA reduces α-synuclein accumulation [54].
• Base editing and prime editing correct pathogenic mutations in LRRK2 and PINK1 [55].
• CRISPRa/ CRISPRi modulation of dopaminergic neuron survival pathways (e.g., GDNF) to promote neuroprotection [56].
• Cas13-based RNA targeting to reduce SNCA mRNA levels without genomic alterations [57].

Preclinical Advances

• CRISPR-mediated SNCA disruption decreased Lewy body pathology and rescued motor deficits in rodent models [54].
• Base editing corrected LRRK2 G2019S mutation in iPSC-derived neurons, restoring mitochondrial function [55].
• Epigenome editing enhanced GDNF expression, improving dopaminergic survival [56].
• Cas13 RNA silencing reduced α-synuclein expression and improved locomotor activity in PD mice [57].

Critical Perspective

Gene editing in PD offers both disease-modifying (mutation correction) and symptomatic (neuroprotective) strategies. However, heterogeneity of sporadic PD limits broad application. Promisingly, SNCA silencing and LRRK2 correction are advancing toward translational relevance.

3.5 Spinal Muscular Atrophy (SMA)

SMA is a neuromuscular disorder caused by loss-of-function mutations in SMN1, leading to reduced survival motor neuron (SMN) protein and motor neuron degeneration [58]. SMA is a monogenic disease, making it highly suitable for gene therapy and editing.

Gene Editing Strategies

• CRISPR correction of SMN1 mutations, restoring SMN protein [59].
• Exon-skipping and splicing modulation using CRISPRa/ CRISPRi on the paralog SMN2 to increase SMN production [60].
• Base editing for precise SMN1 correction in iPSCs [61].

Preclinical Advances

• CRISPR editing restored SMN expression in SMA mice, significantly improving motor function and survival [59].
• CRISPRa upregulated SMN2 expression in patient-derived neurons, correcting phenotype [60].
• Base editing in SMA iPSCs corrected causative mutations and normalized motor neuron differentiation [61].

Figure 8 SMA

Figure 9 Pathophysiology Of SMA

Rett syndrome is an X-linked neurodevelopmental disorder caused primarily by mutations in MECP2, leading to impaired synaptic function, intellectual disability, and autistic features [62].

Gene Editing Strategies

• CRISPR–Cas9 correction of MECP2 mutations in iPSCs [63].
• Base editors for precise correction of nonsense mutations [64].
• RNA-targeting Cas13 for reversible transcript correction [65].
• Epigenome editing to restore MECP2 transcriptional regulation [66].

Preclinical Advances

• CRISPR correction of MECP2 mutations rescued neuronal morphology in patient-derived neurons [63].
• Base editors restored protein function in Rett mouse models [64].
• Cas13 enabled temporary rescue of MECP2 expression [65].

Figure 10 Rett Syndrome