A Study to Evaluate the Safety and Efficacy of Basmisanil Treatment in Children Aged 2-14 Years With Dup15q Syndrome

Inclusion Criteria: * 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) * Body weight equal to or above the third percentile for age * 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 * 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 * 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 Exclusion Crit…