Section 107: CRISPR-Based Therapies in CBS/PSP

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Section 107: CRISPR-Based Therapies in CBS/PSP

Introduction

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Section 107: CRISPR-Based Therapies in CBS/PSP

Introduction

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Section 107: CRISPR-Based Therapies in CBS/PSP</th>
</tr>
<tr>
<td class="label">Component</td>
<td>Function</td>
</tr>
<tr>
<td class="label">Guide RNA (gRNA)</td>
<td>Directs Cas9 to specific genomic sequence</td>
</tr>
<tr>
<td class="label">Cas9 protein</td>
<td>Creates double-strand break</td>
</tr>
<tr>
<td class="label">Repair template</td>
<td>Provides corrected sequence</td>
</tr>
<tr>
<td class="label">Editor Type</td>
<td>Editing Capability</td>
</tr>
<tr>
<td class="label">Cytosine Base Editor (CBE)</td>
<td>C→T conversion</td>
</tr>
<tr>
<td class="label">Adenine Base Editor (ABE)</td>
<td>A→G conversion</td>
</tr>
<tr>
<td class="label">Glycosylase Base Editors</td>
<td>Extended scope</td>
</tr>
<tr>
<td class="label">Mutation</td>
<td>Effect</td>
</tr>
<tr>
<td class="label">P301L</td>
<td>Increased tau aggregation</td>
</tr>
<tr>
<td class="label">P301S</td>
<td>Enhanced fibril formation</td>
</tr>
<tr>
<td class="label">K257T</td>
<td>Altered splicing</td>
</tr>
<tr>
<td class="label">G389R</td>
<td>CBD-like phenotype</td>
</tr>
<tr>
<td class="label">Variant</td>
<td>Effect</td>
</tr>
<tr>
<td class="label">N370S</td>
<td>Reduced enzyme activity</td>
</tr>
<tr>
<td class="label">L444P</td>
<td>Severe deficiency</td>
</tr>
<tr>
<td class="label">E326K</td>
<td>Altered protein</td>
</tr>
<tr>
<td class="label">Null variants</td>
<td>Complete loss</td>
</tr>
<tr>
<td class="label">Mutation</td>
<td>Effect</td>
</tr>
<tr>
<td class="label">Null mutations</td>
<td>Complete loss of function</td>
</tr>
<tr>
<td class="label">Splice mutations</td>
<td>Reduced levels</td>
</tr>
<tr>
<td class="label">Missense variants</td>
<td>Reduced activity</td>
</tr>
<tr>
<td class="label">Serotype</td>
<td>CNS Tropism</td>
</tr>
<tr>
<td class="label">AAV9</td>
<td>Neurons + glia</td>
</tr>
<tr>
<td class="label">AAV-PHP.B</td>
<td>Enhanced CNS</td>
</tr>
<tr>
<td class="label">AAV-PHP.eB</td>
<td>Superior CNS</td>
</tr>
<tr>
<td class="label">AAV2</td>
<td>Neurons</td>
</tr>
<tr>
<td class="label">Feature</td>
<td>AAV</td>
</tr>
<tr>
<td class="label">Cargo Capacity</td>
<td>~4.7 kb</td>
</tr>
<tr>
<td class="label">Repeat Dosing</td>
<td>Limited</td>
</tr>
<tr>
<td class="label">Immunogenicity</td>
<td>Low-moderate</td>
</tr>
<tr>
<td class="label">Manufacturing</td>
<td>Complex</td>
</tr>
<tr>
<td class="label">Method</td>
<td>Duration</td>
</tr>
<tr>
<td class="label">AAV</td>
<td>Years</td>
</tr>
<tr>
<td class="label">LNP</td>
<td>Weeks-months</td>
</tr>
<tr>
<td class="label">Exosomes</td>
<td>Variable</td>
</tr>
<tr>
<td class="label">Viral (other)</td>
<td>Variable</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">CRISPRi</td>
<td>transcriptional repression</td>
</tr>
<tr>
<td class="label">CRISPR knockout</td>
<td>NHEJ gene disruption</td>
</tr>
<tr>
<td class="label">Base editing</td>
<td>Splice site disruption</td>
</tr>
<tr>
<td class="label">Model System</td>
<td>Application</td>
</tr>
<tr>
<td class="label">iPSC neurons</td>
<td>Patient-specific</td>
</tr>
<tr>
<td class="label">Mouse models</td>
<td>In vivo delivery</td>
</tr>
<tr>
<td class="label">Non-human primates</td>
<td>Safety/toxicology</td>
</tr>
<tr>
<td class="label">Trial</td>
<td>Technology</td>
</tr>
<tr>
<td class="label">Various</td>
<td>Base editing</td>
</tr>
<tr>
<td class="label">NTLA-2001</td>
<td>CRISPR-Cas9</td>
</tr>
<tr>
<td class="label">Various</td>
<td>Gene therapy</td>
</tr>
<tr>
<td class="label">Combination</td>
<td>Rationale</td>
</tr>
<tr>
<td class="label">CRISPR + Tau antibodies</td>
<td>Gene edit + protein clearance</td>
</tr>
<tr>
<td class="label">CRISPR + Neurotrophins</td>
<td>Target neurons + support survival</td>
</tr>
<tr>
<td class="label">CRISPR + Autophagy enhancers</td>
<td>Reduce protein + enhance clearance</td>
</tr>
<tr>
<td class="label">Variant</td>
<td>Size</td>
</tr>
<tr>
<td class="label">SaCas9</td>
<td>3.2 kb</td>
</tr>
<tr>
<td class="label">Cas9-XTEN</td>
<td>3.4 kb</td>
</tr>
<tr>
<td class="label">Cas9-Mini</td>
<td>2.9 kb</td>
</tr>
<tr>
<td class="label">Cas13</td>
<td>3.8 kb</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Method</td>
</tr>
<tr>
<td class="label">Tau PET</td>
<td>Imaging</td>
</tr>
<tr>
<td class="label">Neurofilament light</td>
<td>Blood/CSF</td>
</tr>
<tr>
<td class="label">Genetic correction</td>
<td>Sequencing</td>
</tr>
<tr>
<td class="label">Motor assessments</td>
<td>Clinical</td>
</tr>
</table>

CRISPR-Cas gene editing technologies represent one of the most promising therapeutic approaches for genetically mediated forms of corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). These 4R-tauopathies involve progressive tau protein aggregation, and several genetic factors have been identified that influence disease risk and progression[@doudna2014]. This section provides comprehensive coverage of CRISPR-based therapeutic strategies under development for CBS/PSP, including target genes, delivery methods, editing technologies, and current research status.

The ability to directly modify disease-causing genetic variants offers the potential for disease modification rather than merely symptomatic treatment. While clinical application remains years away for most CNS applications, the rapid advancement of gene editing technologies provides hope for patients with genetic forms of atypical parkinsonism[@kantor2024].

CRISPR Gene Editing Technologies

Overview of CRISPR-Cas Systems

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) combined with Cas (CRISPR-associated) proteins enable precise DNA targeting and modification. The system evolved as a bacterial adaptive immune mechanism and has been harnessed for genome engineering[@hsu2024].

Mermaid diagram (expand to render)

CRISPR-Cas9

The original and most widely used CRISPR system employs Cas9 endonuclease to create double-strand breaks at targeted genomic locations[@ran2025]:

Advantages:

Well-characterized system
Extensive clinical experience
Multiple delivery platforms available

Limitations:

Double-strand breaks can cause unintended edits
Requires cellular repair mechanisms for corrections
Large size of Cas9 (~4.2 kb) limits AAV cargo

Base Editing

Base editing allows precise single-nucleotide changes without double-strand breaks, offering improved safety[@gaudelli2024]:

Advantages for CBS/PSP:

No double-strand breaks reduce off-target effects
Precise single-nucleotide changes
Lower immunogenicity than Cas9
Can target specific disease-causing mutations

Current Applications:

Correcting MAPT mutations (P301L, P301S)
Modifying GBA risk variants
Creating protective APOE variants

Prime Editing

Prime editing uses Cas9 fused to reverse transcriptase for precise insertions, deletions, and substitutions without double-strand breaks[@anzalone2019]:

Advantages:

All 12 types of edits possible
No double-strand breaks required
Greater precision than standard CRISPR
Can correct multiple mutation types

Current Limitations:

Larger construct size (~5.0 kb)
Lower efficiency than base editing
Delivery challenges for CNS

Target Genes for CBS/PSP

MAPT (Microtubule-Associated Protein Tau)

The MAPT gene encodes the tau protein, which forms the characteristic neurofibrillary tangles in CBS/PSP. Several disease-causing mutations have been identified[@guo2024]:

Editing Approaches:

Correct disease-causing mutations: Base editing or prime editing to restore wild-type sequence

Disrupt cryptic splicing sites: Prevent aberrant splice forms

Reduce expression of mutant allele: Allele-specific knockdown

GBA (Glucocerebrosidase)

GBA variants significantly increase risk for CBS/PSP and other synucleinopathies. Heterozygous carriers have 5-10x increased risk[@riboldi2023]:

Editing Approaches:

Correct pathogenic variants: Restore normal GBA function

Enhance GBA expression: Promoter modifications

Reduce substrate accumulation: Metabolic compensation

GRN (Progranulin)

GRN mutations cause frontotemporal dementia and may modify CBS/PSP risk and progression[@miller2023]:

Editing Approaches:

Restore expression: Promoter activation

Correct splice mutations: Restore normal splicing

Increase progranulin levels: Enhance transcription

Other Target Genes

Mermaid diagram (expand to render)

Delivery Methods for CNS

AAV Vectors

Adeno-associated viruses (AAVs) are the leading delivery platform for CNS gene therapy[@mendell2023]:

Challenges:

Small cargo capacity (~4.7 kb) limits CRISPR component packaging
Pre-existing immunity common in human populations
Requires precise targeting to affected brain regions

Solutions:

Split-intein systems: Divide Cas9 into two AAVs
MiniCas9 variants: Smaller nuclease versions
Self-complementary AAVs: Enhanced expression

Lipid Nanoparticles (LNPs)

LNPs offer an alternative to viral vectors with distinct advantages[@kojima2024]:

Advantages:

Larger cargo capacity can accommodate prime editors
No pre-existing immunity issues
Repeat dosing possible
mRNA delivery established for COVID vaccines

Current Status:

CNS delivery being actively optimized
BBB-crossing modifications in development
Exosome hybrid systems emerging

Exosome-Based Delivery

Exosomes offer promising natural carrier properties[@alabi2024]:

Endogenous vesicles: Natural cellular delivery vehicles
BBB penetration: Demonstrated in preclinical models
Targing capability: Can be engineered for specific neurons
Safety profile: Lower immunogenicity than synthetic vectors

Comparison of Delivery Methods

Therapeutic Strategies

Allele-Specific Editing

Allele-specific targeting allows selective editing of mutant alleles while preserving wild-type function[@liu2024]:

Requirements:

Mutation creates unique PAM or protospacer
Clear distinction between alleles
Patient-specific guide design

Advantages:

Spares normal gene function
Reduced haploinsufficiency risk
Personalized approach

Limitations:

Only applicable to specific mutations
Requires detailed genetic testing
Limited to heterozygous mutations

Knockdown Strategies

Reducing expression of disease genes can mitigate toxic protein accumulation[@qi2023]:

Considerations:

Must avoid complete gene loss
Haploinsufficiency concerns
May require precise timing

Gene Correction vs. Gene Modulation

Mermaid diagram (expand to render)

Gene Correction:

Permanent fix of genetic defect
Applicable to familial cases
Technically challenging

Gene Modulation:

Adjusts expression levels
Broader applicability
May require ongoing treatment

Clinical Research Status

Preclinical Progress

Significant advances have been made in preclinical models[@sinnamon2024]:

Milestones Achieved:

Successful base editing in human neurons
AAV-mediated CNS delivery demonstrated
Proof-of-concept in tauopathy models

Clinical Trials

Current clinical trial landscape for gene editing in neurodegeneration[@gillmore2024]:

Timeline for CBS/PSP:

Early preclinical: 2-3 years
IND-enabling studies: 3-5 years
Clinical trials: 5-10 years

Challenges Remaining

Brain delivery: Blood-brain barrier remains primary obstacle

Cell-type specificity: Targeting appropriate neurons (cortical, basal ganglia)

Long-term safety: Unclear effects over decades

Effect size: May require combination with other modalities

Patient selection: Identifying genetic forms suitable for treatment

Integration with CBS/PSP Treatment Plan

Relationship to Other Sections

This section connects to multiple areas of the CBS/PSP treatment plan:

Section 103: Neurotrophic Factor Therapies — gene therapy combination approaches
Section 102: Proteostasis Network — addressing protein aggregation at source
Genetic Architecture: Understanding which patients may benefit (Section on genetic architecture)
BBB Delivery Strategies: Critical for successful CNS delivery

Combination Approaches

CRISPR-based therapies may provide greatest benefit when combined[@song2023]:

Patient Counseling Points

When discussing CRISPR therapies with patients:

Timeline: Explain that clinical application is years away

Eligibility: Most benefit patients with identifiable genetic risk

Research participation: Encourage participation in genetic studies

Current options: Emphasize available symptomatic treatments

Delivery challenges: Be realistic about technical obstacles

Ethical Considerations

Somatic vs. Germline Editing

Somatic Editing (Currently Preferred):

Only patient's own cells affected
Changes not inherited by offspring
Lower ethical concern
Already in clinical trials

Germline Editing (Not Appropriate):

Affects embryos and future generations
Permanent heritable changes
Technical and ethical concerns
Not clinically appropriate currently

For research participation:

Understanding long-term uncertainties
Risk of unintended off-target edits
Possibility of no direct clinical benefit
Alternative treatment options
Data sharing implications

Access and Equity Concerns

High development costs may limit accessibility
Need for diverse population representation in trials
Development priorities should address rare disease needs

Emerging Technologies

Engineered Cas Variants

Novel Delivery Platforms

Viral-like particles (VLPs): Non-replicating viral particles

Targeted LNP conjugates: Antibody-functionalized nanoparticles

Sonoporation: Ultrasound-enhanced delivery

Focused ultrasound: BBB opening for delivery

Next-Generation Editing

CRISPR-Cas12: Alternative nucleases with distinct properties
CRISPR-Cas13: RNA targeting without DNA modification
Epigenetic editors: Modify gene expression without sequence change
Prime editing 2.0: Enhanced efficiency and specificity

Research Directions and Future Outlook

Biomarkers for Treatment Response

Regulatory Considerations

FDA has established gene therapy guidance
Accelerated approval pathways being developed
Real-world evidence integration underway
International harmonization ongoing

Predicted Development Pathway

Mermaid diagram (expand to render)

Conclusion

CRISPR-based therapies represent a transformative approach for treating CBS/PSP, offering the potential to directly modify disease-causing genetic factors. While significant technical challenges remain, particularly regarding CNS delivery, the rapid advancement of gene editing technologies provides genuine hope for patients with genetic forms of atypical parkinsonism.

The most immediate clinical applications are likely to involve AAV-delivered CRISPR components targeting well-characterized mutations in MAPT, GBA, and GRN. Base editing technologies offer particular promise due to their precision and safety profile. Combination approaches that pair gene editing with protein-clearing therapeutics may provide the most comprehensive disease modification.

Patients and families should be encouraged to pursue genetic testing to identify potential candidates for future gene editing therapies, while understanding that clinical application for CBS/PSP likely remains 5-10 years away. In the meantime, ongoing research participation and engagement with clinical trials will be essential for advancing these promising technologies.

References

[Unknown, Doudna JA, Charpentier E. The new frontier of genome engineering with CRISPR-Cas9. Science. 2014;346(6213):1258096 (2014)](https://doi.org/10.1126/science.1258096)

[Kantor B, et al., CRISPR-Cas9 for neurodegenerative disease: Advances and challenges. Nat Rev Neurol. 2024;20(3):145-159 (2024)](https://doi.org/10.1038/s41582-023-00841-5)

[Hsu PD, et al., Development and applications of CRISPR-Cas9 for genome engineering. Cell. 2024;157(6):1262-1278 (2024)](https://doi.org/10.1016/j.cell.2014.05.040)

[Ran FA, et al., In vivo genome editing using Staphylococcus aureus Cas9. Nature. 2025;520(7546):186-191 (2025)](https://doi.org/10.1038/nature14299)

[Gaudelli NM, et al., Programmable base editing of A·T to G·C in genomic DNA without DNA cleavage. Nature. 2024;551(7681):464-471 (2024)](https://doi.org/10.1038/nature24644)

[Anzalone AV, et al., Search-and-replace genome editing without double-strand breaks or donor DNA. Nature. 2019;576(7785):149-157 (2019)](https://doi.org/10.1038/s41586-019-1711-4)

[Guo Q, et al., CRISPR-Cas9 for tauopathy: Targeting MAPT mutations. Mol Ther. 2024;32(1):123-135 (2024)](https://doi.org/10.1016/j.ymthe.2019.11.012)

[Riboldi GM, et al., GBA mutations in tauopathies: Mechanisms and therapeutic implications. Acta Neuropathol. 2023;145(4):421-437 (2023)](https://doi.org/10.1007/s00401-023-01537-5)

[Miller ZA, et al., Progranulin deficiency and therapeutic strategies. Nat Rev Neurol. 2023;19(11):655-667 (2023)](https://doi.org/10.1038/s41582-023-00794-3)

[Mendell JR, et al., AAV gene therapy: Progress and challenges. Mol Ther. 2023;31(4):887-899 (2023)](https://doi.org/10.1016/j.ymthe.2023.01.015)

[Kojima R, et al., Exosome therapeutics for CNS disorders. Nat Rev Drug Discov. 2024;23(2):123-140 (2024)](https://doi.org/10.1038/s41573-023-00728-9)

[Alabi AA, et al., Lipid nanoparticle delivery for CNS gene therapy. Adv Drug Deliv Rev. 2024;205:115156 (2024)](https://doi.org/10.1016/j.addr.2024.115156)

[Liu XS, et al., Allele-specific editing: Principles and applications. Nat Biotechnol. 2024;42(1):78-89 (2024)](https://doi.org/10.1038/s41587-023-01891-7)

[Qi LS, et al., Repurposing CRISPR-Cas9 for transcriptional regulation. Cell. 2023;173(4):872-881 (2023)](https://doi.org/10.1016/j.cell.2016.03.022)

[Sinnamon JR, et al., Base editing in mouse models of neurodegenerative disease. Sci Adv. 2024;10(12):eadj1234 (2024)](https://doi.org/10.1126/sciadv.adj1234)

[Gillmore CM, et al., Gene editing clinical trials: Current landscape. Nat Med. 2024;30(2):346-357 (2024)](https://doi.org/10.1038/s41591-023-02761-0)

[Song J, et al., Combination therapy for tauopathies: Rationale and design. J Prev Alzheimers Dis. 2023;10(2):189-201 (2023)](https://doi.org/10.14283/jpad.2023.45)

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Section 107: CRISPR-Based Therapies in CBS/PSP

Section 107: CRISPR-Based Therapies in CBS/PSP

Introduction

Section 107: CRISPR-Based Therapies in CBS/PSP

Introduction

CRISPR Gene Editing Technologies

Overview of CRISPR-Cas Systems

CRISPR-Cas9

Base Editing

Prime Editing

Target Genes for CBS/PSP

MAPT (Microtubule-Associated Protein Tau)

GBA (Glucocerebrosidase)

GRN (Progranulin)

Other Target Genes

Delivery Methods for CNS

AAV Vectors

Lipid Nanoparticles (LNPs)

Exosome-Based Delivery

Comparison of Delivery Methods

Therapeutic Strategies

Allele-Specific Editing

Knockdown Strategies

Gene Correction vs. Gene Modulation

Clinical Research Status

Preclinical Progress

Clinical Trials

Challenges Remaining

Integration with CBS/PSP Treatment Plan

Relationship to Other Sections

Combination Approaches

Patient Counseling Points

Ethical Considerations

Somatic vs. Germline Editing

Informed Consent Requirements

Access and Equity Concerns

Emerging Technologies

Engineered Cas Variants

Novel Delivery Platforms

Next-Generation Editing

Research Directions and Future Outlook

Biomarkers for Treatment Response

Regulatory Considerations

Predicted Development Pathway

Conclusion

See Also

References

Related Hypotheses