This (DEEp SEA Study) is a double-blind, randomized, placebo-controlled, multicenter study to investigate the efficacy, safety, and tolerability of LP352 in the treatment of seizures in children and adults with DS. The study consists of 3 main phases: Screening, Titration period, and Maintenance period, followed by a Taper period and Follow-Up. Participants will be randomized to LP352 or placebo. The total duration of the study will be approximately 24 months.

Inclusion Criteria:

• Diagnosis of DS must fulfill all of the following criteria:

  1. Participants with seizure onset age >1 and <20 months
  2. The participant has a history of at least 1 of the following seizure type(s): prolonged generalized tonic-clonic, hemiclonic, myoclonic, tonic, atonic, atypical absence, focal impaired awareness, nonconvulsive status epilepticus

• The participant has a current occurrence of at least 1 of the following countable motor seizure types: generalized tonic-clonic, tonic (bilateral), clonic (bilateral), atonic (bilateral) with truncal/leg involvement, focal motor (including hemiclonic), and focal to bilateral tonic-clonic

• The participant has demonstrated an average of at least 4 countable motor seizures per month for the 3 months prior to Screening.

• The participant has been taking 1 to 4 antiseizure medications (ASMs) at a stable dose for at least 4 weeks prior to Screening.

• The participant, parent, or caregiver is willing and able (in the judgment of the investigator) to comply with completion of the diaries throughout the study.

• The participant must be willing and able to provide written informed consent.

Exclusion Criteria:

• The participant has a history of infantile/epileptic spasms.
• The participant has been admitted to a medical facility for treatment of status epilepticus requiring mechanical ventilation within 3 months prior to Screening.
• The participant has a neurodegenerative disorder as indicated by magnetic resonance imaging or genetic testing.
• The participant has an acquired lesion/injury unrelated to the primary etiology that could contribute as a secondary cause of seizures.
• The participant is receiving exclusionary medications.
• The participant is currently using any cannabis product or cannabidiol that is not in oral solution/capsule/tablet form, not obtained from a government-approved dispensary, or contains ≥50% Delta-9-tetrahydrocannabinol (THC).
• The participant has unstable, clinically significant neurologic (other than the disease being studied, eg, recurrent strokes), psychiatric, cardiovascular (eg, pulmonary arterial hypertension, cardiac valvulopathy, orthostatic hypotension/tachycardia), pulmonary, hepatic, renal, metabolic, gastrointestinal, urologic, immunologic, hematopoietic, or endocrine disease or other abnormality which may impact the ability of the participant to participate or potentially confound the study results.
• The participant is unwilling to comply with any of the study requirements or timelines.