Phase 1/2 Study of MZ-1866, an AAV-9 Gene Therapy Delivered by Intracerebroventricular Injection to Participants With Pitt Hopkins Syndrome

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