A PHASE II, RANDOMIZED, DOUBLE-BLIND, PLACEBO-CONTROLLED, PARALLEL GROUP STUDY TO EVALUATE THE SAFETY, EFFICACY, AND PHARMACODYNAMICS OF 52 WEEKS OF TREATMENT WITH BASMISANIL IN PARTICIPANTS AGED 2 TO 14 YEARS OLD WITH DUP15Q SYNDROME FOLLOWED BY A 2-YEAR OPTIONAL OPEN-LABEL EXTENSION

PART 1
• Participants aged 2 to 14 years inclusive at the time the caregiver signs
the
informed consent.
• Documented maternal duplication (3 copies) or triplication (4 copies) of the
chromosome 15q11.2-q13.1 region that includes the Prader-Willi/Angelman
critical region defined as [BP2-BP3] segment
• Dup15q syndrome Clinician Global Impression of Severity scale (Dup15q CGI-S)
overall severity score >= 4 (at least moderately ill)
• Stage 1 specific inclusion criterion: Participants aged 6 to 14 years with
epilepsy.
• Body weight equal to or above the third percentile for age
• Male and female participants: Some of the provisions that follow may have
limited applicability based on the age range of study participants (i.e., up to
the age of 14) and the nature of the disease under study
• Female Participants: A female participant is eligible to participate if she
is not pregnant, not breastfeeding
• Male Participants: Male contraception is not required in this study because
of the minimal seminal dose transmitted through sexual intercourse
• The participant has a parent, caregiver, or legally authorized
representative (hereinafter *caregiver*) of at least 18 years of age, who is
fluent in the local language at the site, and capable and willing to provide
written informed consent for the participant according to International Council
for Harmonisation and local regulations
• The participant*s caregiver must be living with the participant and, in the
opinion of the Investigator, able and willing to reliably assess the
participant*s ongoing condition, to accompany the participant to all clinic
visits, and ensure compliance to study treatment throughout the study. The same
caregiver is able and willing to complete the caregiver assessments and is
available to the Investigational Site by telephone or email if needed
• The participant*s caregiver is able and willing to use electronic devices to
record information on the participant*s condition and to complete assessments
at home and agrees to home nursing visits, if local regulations allow for it
and if home nursing service is available in the country/region.

PART 2:
All participants who complete the 52 weeks of study treatment in Part 1 will be
offered the option to roll over into an OLE to receive basmisanil treatment for
a duration of approximately 2 years (Part 2). Participants will be required to
sign a separate ICF for participation in Part 2.

PART 1
• Uncontrolled epilepsy at Screening as indicated by:
Use of rescue medication(s) to treat more than one seizure cluster per month on
average in the past 6 months; OR
Concomitant chronic use of more than 4 anti-epileptic medications or status
epilepticus within the past 6 months requiring hospitalization for treatment of
the status epilepticus; OR
any implanted devices to treat drug-resistant epilepsy
• Lymphoma, leukemia, or any malignancy within the past 5 years, except for
basal cell or squamous epithelial carcinomas of the skin that have been
resected with no evidence of metastatic disease for 3 years
• Clinically significant ECG abnormalities at Screening, including an average
triplicate QTcF > 450 ms for participants > 10 years or QTcB > 450 ms for
children up to and including age 10 years
• Clinically significant abnormalities in laboratory test results at screening
(including positive results for HIV, hepatitis B and/or hepatitis C). ALT
values > 1.5 × the upper limit of normal. GFR < 90 mL/min per 1.73 m2 (Grade 1
CKD) as estimated using Schwarz formula.
• Allowed prior existing medication should be on a stable regimen (or frequency
of intervention) for at least 6 weeks, and at least 8 weeks for anti-epileptic
treatment, prior to Screening
• Non-pharmacological / behavioral therapies should not be stopped or newly
started at least 6 weeks prior to Screening and are expected to remain stable
for the entire study duration (excluding changes related to standard age and
educational interventional programs and minor interruptions such as illness or
vacation
• Concomitant use of prohibited medications
• Participation in an investigational drug study within one month or within 6 ×
the elimination half-life, whichever is longer, prior to dosing in the study
• Significant risk for suicidal behavior, as assessed through the suicidal
behavior question adapted from the Columbia Classification Algorithm for
Suicide Assessment (C-CASA) (participants >= 6 years of age only)
• Known sensitivity to any of the study treatments or components thereof, or
drug or other allergy that, in the opinion of the Investigator, contraindicates
the participation in the study, including severe lactose intolerance
• Concomitant clinically relevant disease or condition or any clinically
significant finding at screening that could interfere with, or for which, the
treatment might interfere with, the conduct of the study or that would pose an
unacceptable risk to the participants in this study
• Known active or uncontrolled bacterial, viral, or other infection or any
major clinically significant episode of infection or hospitalization (relating
to the completion of the course of antibiotics) within 6 weeks prior to the
start of drug administration.

PART 2
A participant will not be eligible to receive study treatment after the end of
Part 1 of the study if any of the following conditions are met:
• The study treatment is commercially marketed in the participant's country and
is reasonably accessible to the participant (e.g., is covered by the
participant's insurance or would not otherwise create a financial hardship for
the participant).
• The Sponsor has discontinued development of the study treatment or data
suggest that the study treatment is not effective for Dup15q syndrome.
• The Sponsor has reasonable safety concerns with regards to the study
treatment.
• Provision of study treatment is not permitted under the laws and regulations
of the participant's country.
• The participant discontinued prematurely from study treatment or withdrew
from the study before completing 52 weeks of treatment.