The US Food and Drug Administration has granted Breakthrough Therapy Designation to elsunersen (PRAX-222), an investigational treatment for seizures associated with SCN2A developmental and epileptic encephalopathy (SCN2A-DEE) caused by gain-of-function variants. Praxis Precision Medicines announced the designation on 22 June 2026.
Elsunersen is an antisense oligonucleotide (ASO) designed to reduce SCN2A gene expression, targeting the underlying cause of the condition rather than the symptoms alone.
The designation was based on results from the EMBRAVE Part A trial, a randomised, sham-controlled Phase 1/2 study in nine children aged 2 to 12 with early-seizure-onset SCN2A-DEE.
What the trial reported.
Reported results from the randomised, sham-controlled Phase 1/2 study that supported the designation.
Improvements across sleep, motor function, muscle tone, attention or neuropsychomotor development were reported in all treated children and none of those on sham.
Praxis reported that elsunersen was well tolerated, with no drug-related serious adverse events, no discontinuations, and no neuroinflammation signals at doses up to 8 mg. Most adverse events were mild to moderate.
Elsunersen now holds Breakthrough Therapy, Orphan Drug and Rare Pediatric Disease designations from the FDA, and Orphan Drug and PRIME designations from the European Medicines Agency.
The pivotal EMBRAVE3 study
The pivotal EMBRAVE3 study is enrolling around 30 patients under a single-arm, baseline-controlled design. All participants receive elsunersen for 24 weeks, followed by a further 24-week extension. The primary analysis measures the change from baseline in countable motor seizures. The programme is being run in collaboration with Ionis Pharmaceuticals and RogCon.