An Open-Label Study of the Safety, Tolerability, and Pharmacokinetics of Oral NNZ-2591 in Angelman Syndrome

Inclusion Criteria: 1. Clinical diagnosis of AS with a documented disease-causing genetic etiology known to impact maternally derived UBE3A expression in brain. 2. Males or females aged 3-17 years 3. Body Weight of \>12Kg 4. Subjects with a Clinical Global Impression - Severity (CGI-S) score of 3 or greater 5. Not actively undergoing regression or loss of skills, defined as no persistent loss of previously acquired developmental skills for a period within 3 months of the Screening visit 6. Each subject must be able to swallow the study medication provided as a liquid solution. 7. Caregiver(s) must have sufficient English language skills. Exclusion Criteria: 1. Mosaicism for disease-causing mutation. 2. Clinically Significant abnormalities in safety laboratory testing or vital signs at screening 3. Abnormal QTcF interval or prolongation at Screening. 4. Positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and previous COVID 19 infection with last 12 months that required hospitalization. 5. Unstable or changes to Psychotropic treatment 2 weeks prior to screening . 6. Excluded concomitant treatments 7. Actively undergoing regression or loss of skills. 8. Unstable seizure profile. 9. Current clinically significant renal conditions and abnormalities 10. Current clinically significant cardiovascular, hepatic, gastrointestinal, respiratory, endocrine disease, or clinically significant organ impairment. 11. Current clinically significant hypo or hyperthyroidism, Type 1 or Type 2 diabetes mellitus requiring insulin (whether well controlled or uncontrolled), or uncontrolled Type 1 or Type 2 diabetes. 12. Has planned surgery during the study. 13. History of, or current, cerebrovascular disease or brain trauma. 14. History of, or current catatonia or catatonia-like symptoms. 15. History of, or current, malignancy. 16. Current major or persistent depressive disorder (including bipolar depression). 17. Significant, uncorrected visual or uncorrected hearing impairment. 18. Allergy to strawberry. 19. Positive pregnancy test 20. Subject is judged by the Investigator or Medical Monitor to be inappropriate for the study