MZ-1866

The goal of this clinical trial is to learn if MZ-1866 is a safe and tolerable treatment for children and adults with Pitt Hopkins Syndrome.
To evaluate the safety of MZ-1866, the following will be evaluated:
* frequency and severity of adverse events
* physical exam, laboratory results and electrocardiogram findings
Participants will:
* receive a single dose of MZ-1866 by intracerebroventricular injection
* be seen by the study physician and site staff periodically to assess changes to their health status
* be periodically evaluated using neurodevelopmental tools
Caregivers will:
* be interviewed periodically about the health status and development of the participant
* keep diaries and complete periodic questionnaires regarding participant symptoms