How Zorevunersen Works: The Mechanism of Action

Unlike the antiseizure medications used to manage Dravet syndrome, which act on downstream targets to modulate seizure activity, zorevunersen is designed to address the root cause of the disease at the molecular level. Its mechanism begins with the observation that children with Dravet carry one loss-of-function SCN1A variant and one wild-type copy -- and that the wild-type copy contains a built-in regulatory mechanism that limits its own production.

Dr. Wirrell explains the antisense oligonucleotide mechanism in detail. In the pre-messenger RNA of the wild-type SCN1A allele, there is a nonsense-mediated decay exon. When this exon is incorporated into the messenger RNA, it signals degradation, preventing production of NaV1.1 protein. Zorevunersen is an ASO that causes alternative splicing, specifically splicing out this nonsense-mediated decay exon. The result is increased production of functional messenger RNA and, consequently, increased NaV1.1 protein production -- in many cases approaching wild-type levels. She also highlights why this approach is particularly well suited to Dravet: because the SCN1A gene is very large and carries hundreds of different pathogenic variants, a therapy that targets only one specific mutation would apply to only a small subset of patients. By targeting the wild-type allele instead, zorevunersen is broadly applicable across the Dravet population regardless of which specific SCN1A variant a patient carries.

Dr. Wheless adds context on what makes this mechanistically distinct from existing therapies. Standard antiseizure medications work downstream of the genetic abnormality and are aimed at modulating neuronal excitability; the goal with zorevunersen is to restore the protein that should have been produced in the first place, essentially correcting the upstream insufficiency. He also notes an important feature of ASO-based therapeutics: because this approach affects RNA rather than permanently altering the genome, it does not produce a durable genetic change. Messenger RNA has a finite lifespan, which means that to maintain the therapeutic effect and sustained protein production, zorevunersen must be re-administered at regular intervals.

Dr. Schreiber addresses the delivery route. Because the target is in the central nervous system, zorevunersen is administered intrathecally, an important practical consideration for clinicians and families that distinguishes it further from oral antiseizure medications and shapes both the dosing logistics and the safety profile discussion that follows.

In the next episode, the panelists walk through the clinical development program behind zorevunersen, explaining how four studies across the United States and United Kingdom built the evidence base published in the New England Journal of Medicine.