Gene therapy offers the potential for durable, potentially curative treatment of neurodegenerative diseases by delivering genetic material into target cells to modify disease processes at their source. Using vectors—primarily adeno-associated viruses (AAV)—to deliver therapeutic genes, this approach can replace deficient proteins, overexpress neurotrophic factors, or silence disease-causing genes. While still in early-stage clinical development for most neurodegenerative conditions, the technology has achieved remarkable successes in related neurological disorders, including spinal muscular atrophy and inherited retinal diseases.
Gene therapy approaches for neurodegeneration include:
- Deliver functional copies of mutated genes
- Particularly relevant for monogenic forms of disease
- Examples: GBA for Gaucher disease-associated Parkinson's
- Deliver genes encoding neurotrophic factors
- Enhance cellular resilience and function
- Examples: GDNF, BDNF, NRTN (Neurturin)
- RNA interference (shRNA) to reduce toxic protein expression
- CRISPR-based approaches for permanent editing
- Examples: Huntingtin-lowering for Huntington's disease
- Modulate gene expression patterns
- Convert glial cells to neuronal-like cells
- Enhance cellular regeneration capacity
¶ Approved and Late-Stage Programs
| Program |
Company |
Target |
Indication |
Status |
| Zolgensma |
Novartis |
SMN1 |
Spinal Muscular Atrophy |
Approved |
| Luxturna |
Spark Therapeutics |
RPE65 |
Leber Congenital Amaurosis |
Approved |
| VY-AADC |
Voyager Therapeutics |
AADC |
Parkinson's Disease |
Phase 1/2 |
| AAV-GRN |
Biogen/Yumanity |
GRN |
FTD |
Phase 1/2 |
| AAV-hGBA1 |
Eli Lilly |
GBA1 |
GBA-PD |
Phase 1/2 |
Parkinson's Disease:
- VY-AADC (Voyager Therapeutics): Delivers aromatic L-amino acid decarboxylase gene to convert levodopa to dopamine in the brain. Phase 1b trial showed sustained improvements in motor function and reduced levodopa requirements.
- AAV-GBA1: Gene therapy for Parkinson's associated with GBA mutations, delivering functional glucocerebrosidase enzyme.
- Cere-120 (NTN): AAV-neurturin (NRTN) to provide trophic support to dopaminergic neurons.
- CDNF (Herantis Pharma): Cerebral Dopamine Neurotrophic Factor delivered via intraparenchymal infusion. Phase 1-2 trial (NCT01362994) completed, demonstrating safety and tolerability with no serious adverse events related to treatment. 12-month treatment period completed; patients now in 1-year follow-up study.
Alzheimer's Disease:
- AAV-BACE1: Delivering BACE1 antisense to reduce amyloid production.
- AAV-APOE4: Delivering APOE2 to carriers of risk alleles.
- AAV-trehalase: Modulating tau pathology.
Other Neurodegenerative Conditions:
- AAV-GRN (Biogen): For frontotemporal dementia with GRN mutations.
- AAV-ARS (Sangamo): For Amyotrophic Lateral Sclerosis with SOD1 mutations.
- AAV-ATXN2 (UniQure): For Spinocerebellar Ataxia type 2.
Corticobasal syndrome (CBS) and Progressive Supranuclear Palsy (PSP) represent Tauopathies where gene therapy approaches are being explored:
MAPT-Targeting Approaches:
- AAV-antisense to MAPT: Reducing tau protein expression to address tau pathology which is central to both CBS and PSP
- CRISPR-based MAPT regulation: Using CRISPRi to allele-specifically reduce mutant MAPT expression
- Tau phosphorylation modulators: Gene therapy delivering kinases or phosphatases to modify tau phosphorylation state
GRN-Related Therapy:
- AAV-GRN (Biogen): Progranulin replacement therapy for CBS/PSP cases with GRN mutations. Progranulin deficiency leads to increased tau pathology, making GRN restoration a rational approach.
Neurotrophin-Based Approaches:
- CDNF/CERF: Cerebral Dopamine Neurotrophic Factor may provide neuroprotection for subcortical structures affected in PSP (basal ganglia, brainstem)
- AAV-BDNF: Brain-derived neurotrophic factor for protecting corticospinal tract neurons affected in CBS
Current Status:
- No CBS/PSP-specific gene therapy has entered clinical trials yet
- Preclinical work is focused on AAV delivery to subcortical structures and allele-specific silencing of pathogenic MAPT mutations
- The close relationship between FTD (with GRN mutations) and CBS provides a translational pathway
- Single administration may provide years of benefit
- Avoids repeated invasive procedures
- May reduce lifetime treatment burden
- Addresses underlying genetic causes
- Particularly valuable for monogenic forms
- May prevent disease onset in at-risk individuals
- Can deliver any gene sequence
- Engineered for specific expression patterns
- Tissue-specific promoters enable precision
- Unlike symptomatic treatments, may alter disease course
- Potential for prevention in pre-symptomatic individuals
- Blood-brain barrier restricts systemic delivery
- Requires direct brain injection or specialized vectors
- Limited distribution within the brain after injection
- Pre-existing antibodies to AAV vectors common in humans
- Immune response limits repeat dosing
- Neutralizing antibodies reduce efficacy
- AAV can only deliver ~4.7 kb of DNA
- Limits complexity of genetic programs
- Larger genes require split-intein approaches
- Integration into host genome (rare with AAV but possible)
- Off-target effects with CRISPR approaches
- Insertional mutagenesis risk
- Immune reactions to expressed proteins
¶ Manufacturing and Cost
- Complex, expensive to manufacture
- High development costs
- Limited scalable production methods
Different AAV serotypes show tropism for different cell types:
- AAV2: Neuronal tropism, well-characterized
- AAV9: Crosses blood-brain barrier more efficiently, widely used in clinical trials
- AAVrh.10: Non-human primate serotype with good CNS delivery
- AAV-PHP.B: Enhanced CNS delivery in mice (limited human translation)
- AAV-PHP.eB: Further improved CNS delivery
- AAV-TT: Novel engineered serotype with enhanced neuronal transduction
- MyrTag68: Engineered capsid for improved brain penetration via systemic delivery
Recent advances in AAV engineering include:
- Capsid engineering: Directing evolution of AAV for enhanced CNS tropism
- Logic-gated vectors: Cell-type-specific targeting through engineered receptors
- Self-complementary AAV: Faster onset of expression (bypasses second-strand synthesis)
- Mini-AAV: Truncated capsids for improved tissue penetration
- Lentiviruses: Larger cargo capacity, integrates into genome
- Adenoviruses: High expression, immunogenic
- Non-viral delivery: Lipid nanoparticles, electroporation
- Engineered AAV variants with enhanced CNS delivery
- Brain-specific promoters for neuron-specific expression
- Self-inactivating vectors for improved safety
- Base editing for precise genetic modifications
- Prime editing for scarless gene insertion
- In vivo CRISPR delivery to CNS
- Gene therapy + cell therapy
- Gene therapy + antibody
- Multiple gene delivery for polygenic diseases