FDA Grants Breakthrough Status to Elsunersen After Strong Seizure Reduction Data

Praxis Precision Medicines has received U.S. Food and Drug Administration (FDA) Breakthrough Therapy Designation (BTD) for elsunersen (PRAX-222), an investigational antisense oligonucleotide (ASO) therapy for seizures associated with SCN2A developmental and epileptic encephalopathy (SCN2A-DEE) caused by gain-of-function (GoF) variants.

The designation was supported by positive results from the Phase 1/2 EMBRAVE Part A study (NCT05737784), where elsunersen produced a 77% sham-adjusted reduction in monthly seizures compared with baseline. The therapy also showed durable benefits during the open-label extension phase, with improvements maintained for up to one year.

The FDA grants Breakthrough Therapy Designation to investigational treatments for serious conditions when early clinical evidence suggests substantial improvement over available therapies. The status provides intensive FDA guidance and may accelerate both development and regulatory review.

Targeting the Genetic Cause of SCN2A-DEE

SCN2A-DEE is a rare and severe genetic epilepsy that typically begins during infancy. The condition is caused by gain-of-function mutations in the SCN2A gene, which lead to excessive neuronal activity, recurrent seizures, developmental delays, and significant neurological impairment.

Elsunersen is an antisense oligonucleotide that lowers SCN2A gene expression, directly addressing the underlying genetic driver of the disease. Unlike conventional anti-seizure medications that primarily manage symptoms, the therapy aims to modify disease biology by reducing abnormal sodium channel activity.

Currently, no approved treatment specifically targets the genetic cause of SCN2A-DEE.

EMBRAVE Study Demonstrated Meaningful Seizure Reduction

The randomized, sham-controlled EMBRAVE Part A trial enrolled nine children aged 2 to 12 years with early-seizure-onset SCN2A-DEE.

Key findings included:

• 77% sham-adjusted reduction in monthly seizures (p=0.015)
• 71% of treated patients achieved greater than 50% seizure reduction
• 57% experienced at least 28 consecutive days without seizures during the six-month treatment period
• Benefits remained durable during the open-label extension for up to one year

Beyond seizure control, all elsunersen-treated patients experienced improvements in at least one additional clinical domain, including sleep, motor function, muscle tone, attention, or neuropsychomotor development. No such improvements were reported in the sham group.

The therapy demonstrated a favorable safety profile. Investigators reported no drug-related serious adverse events, no treatment discontinuations, and no evidence of neuroinflammation at doses up to 8 mg. Most treatment-emergent adverse events were mild to moderate.

Regulatory Pathway Advances Toward Registration

Praxis noted that the FDA designation strengthens the development pathway for elsunersen and supports ongoing discussions with regulators.

Following FDA alignment reached in late 2025, the pivotal EMBRAVE3 trial was converted into a streamlined single-arm, baseline-controlled registrational study. Approximately 30 patients are expected to enroll, with the primary analysis evaluating changes in countable motor seizures after 24 weeks of treatment.

Company leadership said the designation recognizes both the severity of unmet medical need in SCN2A-DEE and the strength of the clinical data generated to date.

 Path Forward

Elsunersen now holds FDA Breakthrough Therapy, Orphan Drug, and Rare Pediatric Disease designations, in addition to Orphan Drug and PRIME designations from the European Medicines Agency. These regulatory incentives could help accelerate development and review in both the United States and Europe.

As enrollment continues in the pivotal EMBRAVE3 study, Praxis is positioning elsunersen as a potential first disease-modifying therapy for patients with gain-of-function SCN2A-DEE, a population that currently lacks targeted treatment options.

Reference

Praxis Precision Medicines Receives FDA Breakthrough Therapy Designation for Elsunersen for the Treatment of Seizures Associated with SCN2A Developmental and Epileptic Encephalopathy Caused by Gain of Function Variants – Praxis Precision Medicines, Inc.