Antisense oligonucleotide (ASO) therapies have demonstrated clinical proof-of-concept across multiple neurodegenerative , from nusinersen (SMA, 2016) to tofersen (SOD1-ALS, 2023). While the C9orf72 ASO program has received significant attention for ALS/FTD, a parallel and equally compelling landscape of ASO targets exists for Alzheimer's disease, Parkinson's disease, and broader ALS genetics. This page surveys ASO programs targeting SOD1, TDP-43 (TARDBP), alpha-synuclein (SNCA), LRRK2, and MAPT (tau) — assessing clinical stage, evidence strength, competitive positioning, and strategic gaps.
The ASO platform offers a unique combination: direct intracellular delivery to neurons, durable target engagement (weeks to months per dose), and the ability to modulate disease-causing at their source rather than after secretion. This makes ASOs particularly valuable for intracellular pathology targets like tau, alpha-synuclein, and TDP-43 that are poorly addressed by antibody approaches.
Status: FDA-Approved (tofersen, Qalsody)
SOD1 was the first genetic target with a commercially available ASO therapy. Tofersen (BIIB067, Biogen/Ionis) received accelerated FDA approval in 2023 for ALS patients with SOD1 mutations based on biomarker reduction (CSF SOD1 decreased up to 60%) and signals of clinical benefit in the VALOR trial and open-label extension. @miller2023tofersen
Key programs:
Evidence quality: Strong. The tofersen program established the template: genetic target → ASO design → preclinical validation → Phase 1/3 clinical data → regulatory approval. CSF SOD1 as a pharmacodynamic biomarker is well-validated, enabling dose selection and target engagement assessment.
Status: Preclinical to Early Clinical
TDP-43 pathology is present in ~95% of ALS cases and ~50% of FTD cases, making it one of the most broadly relevant targets in neurodegenerative disease. TDP-43 aggregates are the defining pathology of ALS and limbic-predominant age-related TDP-43 encephalopathy (LATE). Unlike SOD1 (a monogenic cause), TDP-43 reduction could theoretically benefit both familial and sporadic ALS/FTD patients. @fallini2023tdp
Key programs:
Therapeutic hypothesis: Partial TARDBP reduction or splice correction could address the loss-of-function component of TDP-43 pathology while avoiding complete ablation (TDP-43 is essential for neuronal survival).
Evidence quality: Moderate. TDP-43 reduction is well-validated in animal models. The challenge is that sporadic ALS lacks a clear monogenic trigger, complicating patient selection. Emerging understanding of TDP-43 granule dynamics and phase separation may enable allele-selective approaches.
Status: Clinical (discontinued lead program, early-stage follow-ons)
Alpha-synuclein is the defining protein of Parkinson's disease pathology. The SNCA gene multiplication evidence (duplications/triplications sufficient to cause PD) provides the strongest genetic proof-of-concept for ASO targeting. The Ionis/Biogen program BIIB101 (IONIS-SNAS) reached Phase 1/2 but was discontinued in 2023 after insufficient target engagement signals. @mcgrew2020snca @biogen2023
Key programs:
Why it failed (lessons): The Biogen discontinuation highlighted three critical challenges:
Evidence quality: Moderate (was high until Phase 1/2 failure). The genetic evidence (SNCA multiplications) remains compelling. New delivery approaches (conjugate ASOs, focused ultrasound-assisted delivery) may revive the target.
Status: Phase 1 (BIIB132) + Preclinical
LRRK2 mutations (particularly G2019S) are the most common genetic cause of familial PD. ASOs offer a complementary mechanism to kinase inhibitors (which are in Phase 2) by reducing LRRK2 protein levels rather than just inhibiting kinase activity. BIIB132 (Biogen/Ionis) demonstrated dose-dependent CSF LRRK2 reduction in Phase 1 (NCT03976375). @lrrk2_aso
Key programs:
Advantage over kinase inhibitors: ASOs provide complete pathway suppression (not partial enzymatic inhibition) and longer duration of action (weeks vs. hours). Could be used in combination or sequentially.
Evidence quality: Moderate. LRRK2 is well-validated genetically and biochemically. ASO approach adds a new dimension to LRRK2 targeting, with BIIB132 providing first-in-human data.
Status: Phase 1/2
Tau protein reduction via ASO represents one of the most actively developed strategies for Alzheimer's disease and tauopathies. IONIS-MAPT (Biogen/Ionis) completed Phase 1 in AD, with dose-dependent CSF tau reduction demonstrated. @maptasopre2021
Key programs:
Therapeutic rationale: Tau reduction is supported by:
Evidence quality: Strong. Tau ASOs have the strongest clinical development pipeline among AD targets, with IONIS-MAPT providing Phase 1 data. Tau as a biomarker in CSF is well-established, enabling dose selection.
| Target | Disease | Stage | Key Program | Status |
|---|---|---|---|---|
| SOD1 | ALS (familial) | Approved | Tofersen (Qalsody) | FDA-approved 2023 |
| TDP-43 | ALS/FTD | Preclinical/Phase 1 | Multiple programs | Active development |
| SNCA | Parkinson's Disease | Phase 1 (discontinued lead) | BIIB101 | Discontinued 2023; follow-ons active |
| LRRK2 | Parkinson's Disease | Phase 1 | BIIB132 | Active, NCT03976375 |
| MAPT | AD/Tauopathies | Phase 1/2 | IONIS-MAPT (BIIB080) | Active, NCT05399888 |
| Program | Company | Chemistry | Delivery | Target Reduction |
|---|---|---|---|---|
| Tofersen | Biogen/Ionis | 2'-MOE PS | Intrathecal | ~60% CSF SOD1 |
| BIIB101 | Biogen/Ionis | 2'-MOE PS | Intrathecal | Insufficient engagement |
| BIIB132 | Biogen/Ionis | 2'-MOE PS | Intrathecal | Dose-dependent LRRK2 reduction |
| IONIS-MAPT | Biogen/Ionis | 2'-MOE PS | Intrathecal | Dose-dependent CSF tau |
| Wave stereopure | Wave Life Sciences | Stereopure PS | Intrathecal | Preclinical |
All CNS-targeting ASOs face the same fundamental challenge: the blood-brain barrier. The comparative analysis reveals:
| Target | Genetic Validation | Pathological Role | Therapeutic Window | Biomarker |
|---|---|---|---|---|
| SOD1 | Strong (monogenic) | Gain-of-toxicity | Wide | CSF SOD1 (validated) |
| TDP-43 | Moderate (complex) | Gain + loss-of-function | Narrow | CSF TDP-43 |
| SNCA | Strong (dose-dependent) | Gain-of-toxicity | Moderate | CSF alpha-syn |
| LRRK2 | Strong (monogenic) | Gain-of-function | Wide | CSF pSer935-LRRK2 |
| MAPT | Strong (monogenic) | Gain-of-toxicity | Wide | CSF tau (validated) |
SNCA revival: The discontinuation of BIIB101 left a gap for alpha-synuclein ASOs. New delivery technologies (conjugates, focused ultrasound) may enable a successful revival. The genetic evidence (SNCA multiplication → PD) remains the strongest in PD therapeutics.
TDP-43 sporadic ALS: The absence of a monogenic trigger for sporadic ALS/FTD complicates patient selection. Biomarkers distinguishing TDP-43 pathologically-defined subtypes could enable targeted therapy.
Combination approaches: No ASO programs currently target multiple genes simultaneously. Multi-target ASOs or ASO combinations could address the complex pathophysiology of AD and PD.
Allele-selective ASOs: For SOD1 and HTT, allele-selective approaches spare the wild-type allele — a strategy not yet applied to SNCA, LRRK2, or MAPT for their respective .
Preventive ASOs: All current programs target established disease. ASO therapy in prodromal or genetic risk populations remains unexplored.
| Company | ASO Platform | Targets | Stage |
|---|---|---|---|
| Biogen/Ionis | 2'-MOE PS | SOD1 (approved), LRRK2 (Ph1), MAPT (Ph1/2), TDP-43 | Multiple |
| Wave Life Sciences | Stereopure | LRRK2 (preclinical), C9orf72 (Ph1/2) | Active |
| Roche | ASO (NY--1) | HTT (Ph3), SOD1 | Advanced |
| Pfizer/Wyatt | ASO | TDP-43 (preclinical) | Early |
| Novartis | ASO | SNCA (discovery) | Early |