At the 2026 European Epilepsy Congress (EEC), Stoke Therapeutics and partner Biogen unveiled new long-term data from open-label extensions (OLEs) of their phase I/IIa studies of zorevunersen. The four-year OLE results showed substantial and durable seizure reductions, as well as continued improvements in cognition and behavior. The results are pivotal and could mark a shift in the treatment paradigm for Dravet syndrome (DS), according to GlobalData, a leading intelligence and productivity platform.

The study results showed that zorevunersen elicited substantial reductions in generalized tonic-clonic and focal-to-bilateral tonic-clonic seizures through three years of the OLEs compared with patients’ baseline at study entry.

Jos Opdenakker, Neurology Analyst at GlobalData, comments: “The results demonstrate zorevunersen’s potential to address critical unmet needs in the treatment of DS. Most, if not all, DS patients are refractory, so the market is ripe for a new agent that is able to achieve sustained efficacy, without compromising on tolerability. Stoke and Biogen’s results are impressive given the disease-modifying potential of zorevunersen, but there are other therapies in the pipeline that boast disease-modifying potential.”

There is another therapy in the late-stage pipeline, Encoded Therapeutics’ ETX-101, which addresses SCN1A deficiency by increasing its expression in inhibitory interneurons. ETX-101 displayed a median seizure reduction of 78% through seven months, with no treatment-related serious adverse events. Furthermore, ETX-101 is administered only once, which is highly attractive versus chronic symptomatic dosing or even dosing cycles.

Key opinion leaders (KOLs) previously interviewed by GlobalData have lauded zorevunersen’s disease-modifying potential but have expressed concerns over the logistics of administering the treatment, as it needs to be injected intrathecally through a lumbar puncture. This is not a simple procedure, and patients will need to be sedated to receive the treatment, creating an additional logistical burden.

Opdenakker adds: “Zorevunersen will compete directly with ETX-101 in DS should both come to market, so it will be important for Stoke and Biogen to show that their asset is superior. With multiple DMTs entering the market, tolerability and durability of response will be key differentiators.”

Opdenakker continues: “In addition to its rivalry with ETX-101 in clinical development, zorevunersen would be entering a highly competitive and crowded DS market, with the current landscape comprising valproate, clobazam, stiripentol, SV2A ligands, and other mixed-mechanism agents such as cannabidiol, fenfluramine, and cenobamate. As a complex, potentially disease-modifying treatment, it would likely be reserved for later in the treatment algorithm, once the aforementioned therapies have been trialed.”

Opdenakker concludes: “Stoke and Biogen are progressing with their development program for zorevunersen. If the results of their phase III EMPEROR study build upon the OLE data, zorevunersen will have a good chance of entering the market in a strong position. The results of EMPEROR should be pivotal in outlining zorevunersen’s trajectory moving forward.”