A Study to Investigate LP352 in Children and Adults With Developmental and Epileptic Encephalopathies (DEE)

Inclusion Criteria:

• Participants who are characterized as having Lennox-Gastaut Syndrome (LGS) mustfulfill all of the following criteria:

• Onset of seizures at ≤8 years old

• History of tonic/tonic-atonic seizures plus at least 1 of the following seizuretype(s): atypical absence, atonic, myoclonic, focal impaired awareness,generalized tonic-clonic, nonconvulsive status epilepticus, or epileptic spasms

• Presence of developmental plateauing or regression

• History of electroencephalogram (EEG) showing generalized slow (<2.5 Hertz [Hz]) spike-and-wave complexes

• Participants who are characterized as having DEE (Other) must fulfill all of thefollowing criteria:

• Does not meet criteria for LGS

• Onset of seizures at ≤5 years old

• Presence of developmental plateauing or regression

• History of multiple seizure types

• History of interictal EEG background showing diffuse or multifocal slowing (with or without epileptiform activity)

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

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

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

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

• The participant must be willing and able to provide written informed consent; ininstances where the participant is unable to provide consent, an appropriate legalrepresentative.

Exclusion Criteria:

• The participant has a diagnosis of Dravet Syndrome (DS) or has a mutation of theSodium channel protein type 1 subunit alpha (SCN1A) gene consistent with DS.

• The participant has been admitted to a medical facility for treatment of statusepilepticus requiring mechanical ventilation within 3 months prior to Screening.

• The participant has a neurodegenerative disorder as indicated by magnetic resonanceimaging or genetic testing.

• The participant has an acquired lesion/injury unrelated to the primary etiology thatcould 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 notin oral solution/capsule/tablet form, not obtained from a government-approveddispensary, or contains ≥50% Delta-9-tetrahydrocannabinol (THC).

• The participant has unstable, clinically significant neurologic (other than thedisease being studied; eg, recurrent strokes), psychiatric, cardiovascular (eg,pulmonary arterial hypertension, cardiac valvulopathy, orthostatichypotension/tachycardia), pulmonary, hepatic, renal, metabolic, gastrointestinal,urologic, immunologic, hematopoietic, or endocrine disease or other abnormalitywhich may impact the ability of the participant to participate or potentiallyconfound the study results.

• The participant is unable or unwilling to comply with any of the study requirementsor timelines.