Amyotrophic Lateral Sclerosis

Overview

Amyotrophic lateral sclerosis (ALS) is a progressive disease in which motor neurons—the nerve cells that control voluntary movement—gradually die. This causes worsening weakness, problems speaking and swallowing, loss of mobility, and eventually failure of the breathing muscles. ALS most often begins between ages 40 and 70, and most people die within three to five years of symptom onset, although progression varies substantially between individuals. NINDS ALS overview FDA Qalsody drug snapshot

There is not yet a cure. Current care combines multidisciplinary symptom management—including respiratory support, nutrition, mobility and communication technology, and palliative care—with disease-modifying medicines. Riluzole and edaravone are available for broader ALS populations, while tofersen is approved in the United States for adults whose ALS is caused by a mutation in the SOD1 gene. NINDS ALS overview FDA Qalsody drug snapshot

Scope of Recent Research (2020–present)

ALS research since 2020 has become more genetically precise, with major efforts directed at lowering toxic gene products, detecting disease before symptoms begin, correcting or removing disease-causing DNA changes, and targeting shared processes such as protein aggregation, inflammation, and impaired cellular energy handling. The field is highly active and has produced the first approved gene-targeted ALS therapy, but no treatment has yet demonstrated that it can reliably stop or reverse ALS across the broader patient population. FDA Qalsody drug snapshot ALS therapies targeting genetic mutations

Major Breakthroughs and Emerging Therapies

The clearest clinical advance is tofersen (Qalsody), an antisense oligonucleotide (ASO): a short synthetic strand of nucleic acid designed to bind SOD1 messenger RNA and reduce production of SOD1 protein. In the phase 3 VALOR trial, tofersen substantially lowered SOD1 protein in cerebrospinal fluid and neurofilament light chain (NfL), a blood marker of ongoing nerve-cell injury, but it did not significantly improve the trial’s primary functional outcome at 28 weeks. The FDA nevertheless granted accelerated approval on April 25, 2023 for SOD1-ALS based on the NfL reduction, which is considered reasonably likely to predict clinical benefit. VALOR tofersen trial FDA Qalsody drug snapshot Longer follow-up through the VALOR open-label extension found that earlier tofersen treatment was associated with less numerical decline in function, respiratory capacity, strength, and quality of life than delayed initiation, although the comparison is less definitive than the original randomized phase. Long-term tofersen study

Other RNA-directed therapies aim to extend this precision-medicine model to rarer genetic forms of ALS. Jacifusen, also called ulefnersen or ION363, is an ASO intended to lower FUS RNA and is in a phase 3 trial for FUS-associated ALS. AMT-162 is a first-in-human phase 1/2 gene-therapy program that uses an adeno-associated virus (AAV) vector to deliver a microRNA designed to suppress SOD1 expression after a single injection into spinal fluid. These programs remain experimental; their central questions are whether enough target reduction can be achieved safely and whether a durable molecular effect translates into preserved motor neurons and clinical function. ALS therapies targeting genetic mutations AMT-162 trial record

Gene editing remains preclinical but is particularly compelling for C9orf72-related ALS, a common genetic cause of ALS and frontotemporal dementia. In 2022, researchers used AAV-delivered CRISPR-Cas9 to excise the expanded DNA repeat in mouse models, patient-derived induced pluripotent stem cell (iPSC) motor neurons, and brain organoids. The intervention reduced several disease-associated features, including RNA foci and toxic dipeptide-repeat proteins. This is proof of biological feasibility, not evidence of safety or efficacy in people; permanent editing, brain-wide delivery, immune responses to AAV or Cas9, and unintended DNA changes remain major hurdles. CRISPR excision of C9orf72 repeat expansion

Researchers are also pursuing treatments that could help genetically diverse ALS populations. PrimeC, an extended-release combination of celecoxib and ciprofloxacin intended to influence inflammation, iron handling, and microRNA biology, showed acceptable short-term safety in the 68-person phase 2b PARADIGM trial and a numerically slower functional decline over six months; however, the study was small, and its efficacy outcomes were exploratory rather than confirmatory. PARADIGM PrimeC trial In contrast, the first published results from several broad-population arms of the adaptive HEALEY ALS Platform Trial—including CNM-Au8 and pridopidine—did not show benefit on their primary measures of ALS progression over 24 weeks. These negative findings are scientifically valuable because they rapidly eliminate weak candidates and redirect resources. CNM-Au8 HEALEY trial Pridopidine HEALEY trial

Clinical Trials and Experimental Approaches

As of October 9, 2026, the most consequential ongoing prevention-oriented study is Biogen’s phase 3 ATLAS trial of tofersen in clinically presymptomatic adults with certain SOD1 variants and elevated NfL. It tests whether starting molecular treatment before weakness begins can delay or prevent clinically manifest ALS—a much stronger definition of success than slowing decline after motor neurons have already been lost. The study record listed an estimated enrollment of approximately 150 participants and no posted results. ATLAS trial record ALS therapies targeting genetic mutations

The HEALEY ALS Platform Trial, led through Massachusetts General Hospital and the Northeast ALS Consortium, remains a major experimental infrastructure effort. It uses a shared master protocol, common placebo data, and adaptive decision-making to test several therapies more efficiently than a series of fully separate trials. The platform was recruiting as of its June 2026 registry update. HEALEY ALS Platform Trial Other notable programs include the phase 3 FUS-ALS ASO trial of jacifusen and the phase 1/2 AMT-162 AAV-microRNA gene-therapy study for SOD1-ALS. ALS therapies targeting genetic mutations AMT-162 trial record

Methodologies and Scientific Approaches

Modern ALS studies increasingly combine genetic testing with molecular biomarkers. Blood NfL is used to measure axonal injury and to enrich prevention trials for people approaching symptom onset; cerebrospinal-fluid target proteins, digital measures of movement and speech, lung-function testing, and the ALS Functional Rating Scale–Revised are used alongside survival and ventilation outcomes. The tofersen program has been especially influential because it linked a direct molecular target, SOD1 reduction, to a biomarker response and then to longer-term clinical follow-up. FDA accelerated-approval case study for tofersen Long-term tofersen study

Before human testing, investigators use genetically engineered mice, zebrafish, patient-derived iPSC motor neurons, co-cultures containing glial cells, and brain or spinal-cord organoids. These systems allow researchers to test toxic protein accumulation, RNA defects, inflammation, and motor-neuron vulnerability in disease-relevant cells. AAV vectors, ASOs, small interfering RNAs, and CRISPR systems are then compared for their ability to reach the central nervous system, engage their intended molecular target, and avoid toxic effects. CRISPR excision of C9orf72 repeat expansion Selective C9orf72-targeting siRNAs

Leading Institutions and Funding

Major centers include Massachusetts General Hospital’s Sean M. Healey & AMG Center for ALS, the Northeast ALS Consortium, Washington University in St. Louis, Columbia University, Johns Hopkins University, University College London, King’s College London, the University of Sheffield, and international ALS trial networks. Biogen leads the tofersen and ATLAS programs; Ionis Pharmaceuticals developed jacifusen; uniQure is developing AMT-162; and numerous smaller biotechnology companies are pursuing RNA, gene-delivery, protein-clearance, and neuroprotection strategies. HEALEY ALS Platform Trial ALS therapies targeting genetic mutations

Public and philanthropic funding have expanded the research base. For fiscal year 2025, the U.S. Department of Defense ALS Research Program received $40 million, while the National Institute of Neurological Disorders and Stroke announced up to $35 million for an expanded-access clinical-trial initiative under the ACT for ALS framework. The ALS Association reports supporting more than 150 active research projects and committing nearly $4 million to clinical-trial support through its Hoffman ALS Clinical Trial Awards Program. DoD FY2025 research funding NINDS ACT for ALS funding opportunity ALS Association 2024 progress report

Strengths, Limitations, and Challenges

The strongest recent result is the demonstration that an RNA-targeting medicine can lower a causal protein in the central nervous system and may be more effective when started earlier. This establishes a practical path toward gene-specific treatment and prevention for some inherited forms of ALS. Platform trials, longitudinal biomarker collection, and open data collaborations should also make it faster to identify ineffective treatments and prioritize better ones. Long-term tofersen study HEALEY ALS Platform Trial

The limitations are substantial. SOD1-ALS represents only a small fraction of cases, while most ALS is not yet linked to a single druggable genetic cause. A biomarker improvement does not automatically prove meaningful functional benefit, and tofersen requires repeated lumbar punctures and can cause cerebrospinal-fluid abnormalities and, rarely, serious inflammatory neurologic events. The unsuccessful C9orf72 ASO BIIB078 trial—where there was no NfL reduction or clinical benefit—also shows that lowering an RNA target can fail if the target, dose, timing, or disease biology is wrong. VALOR tofersen trial BIIB078 C9orf72 trial

Outlook and Future Directions

ALS is not close to a universal cure, but the field is closer to rational, potentially preventive treatment for defined genetic subtypes than it was in 2020. The milestones to watch are whether ATLAS shows that presymptomatic tofersen delays disease onset, whether FUS and SOD1 gene-silencing programs confirm durable clinical benefit, whether AAV-based delivery can safely provide long-lasting target suppression, and whether molecularly stratified trials can uncover therapies for the much larger non-SOD1 ALS population. A realistic near-term goal is not one cure for all ALS, but a growing set of treatments that prevent, stop, or substantially slow distinct biological forms of the disease. ATLAS trial record ALS therapies targeting genetic mutations

References

• NINDS ALS overview — National Institute of Neurological Disorders and Stroke, 2026.
• FDA Qalsody drug snapshot — U.S. Food and Drug Administration, 2023.
• VALOR tofersen trial — Miller et al., New England Journal of Medicine, 2022.
• Long-term tofersen study — Miller et al., JAMA Neurology, 2026.
• FDA accelerated-approval case study for tofersen — U.S. Food and Drug Administration, 2024.
• ATLAS trial record — ClinicalTrials.gov, 2026.
• ALS therapies targeting genetic mutations — The ALS Association, 2026.
• AMT-162 trial record — ICH GCP Clinical Trials Registry, 2026.
• CRISPR excision of C9orf72 repeat expansion — Ababneh et al., Molecular Therapy, 2022.
• Selective C9orf72-targeting siRNAs — Al-Ramahi et al., Molecular Therapy Nucleic Acids, 2024.
• PARADIGM PrimeC trial — Gurevich et al., JAMA Neurology, 2026.
• CNM-Au8 HEALEY trial — HEALEY ALS Platform Trial Writing Committee, JAMA, 2025.
• Pridopidine HEALEY trial — HEALEY ALS Platform Trial Writing Committee, JAMA, 2025.
• HEALEY ALS Platform Trial — ClinicalTrials.gov, 2026.
• BIIB078 C9orf72 trial — van den Berg et al., Lancet Neurology, 2024.
• DoD FY2025 research funding — Congressionally Directed Medical Research Programs, 2025.
• NINDS ACT for ALS funding opportunity — National Institutes of Health, 2024.
• ALS Association 2024 progress report — The ALS Association, 2024.