An Open-Label Study of Oral NNZ-2591 in Pitt Hopkins Syndrome (PTHS-001)

Open to people ages 3-17

1. Clinical diagnosis of PTHS with a documented disease-causing genetic etiology for the disorder.
2. Males or females aged 3-17 years.
3. Body weight of 12kg or higher at screening
4. Subjects with a Clinical Global Impression- Severity (CGI-S) score of 4 or greater at the Screening visit.
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.

1. Body weight <12kg at screening
2. Clinically significant abnormalities in safety laboratory tests and vital signs at Screening.
3. Abnormal QTcF interval or prolongation at Screening.
4. Any other clinically significant finding on ECG at the Screening visit.
5. Positive for severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) and previous COVID 19 infection with last 12 months that required hospitalization.
6. Unstable or changes Psychotropic treatment 2 weeks prior to screening
7. Excluded concomitant treatments.
8. Actively undergoing regression or loss of skills.

9. Unstable seizure profile.

   10. Current clinically significant renal conditions and abnormalities 11. Current clinically significant cardiovascular, hepatic, gastrointestinal, respiratory,

   endocrine disease, or clinically significant organ impairment.

   12. 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.

   13. Has planned surgery during the study. 14. History of, or current, cerebrovascular disease or brain trauma. 15. History of, or current catatonia or catatonia-like symptoms. 16. History of, or current, malignancy. 17. Current major or persistent depressive disorder (including bipolar depression). 18. Significant, uncorrected visual or uncorrected hearing impairment. 19. Allergy to strawberry. 20. Positive pregnancy test 21. Subject is judged by the Investigator or Medical Monitor to be inappropriate for the

   study