Study of Zatolmilast (BPN14770) in Participants With PPP2R5D Neurodevelopmental Disorder (Jordan's Syndrome [JS])

Inclusion Criteria: 1. Participant is aged 9 to 45 years, inclusive. 2. Participant has confirmed/documented history of PPP2R5D Neurodevelopmental Disorder. 3. Current treatment with no more than 3 prescribed psychotropic medications. 4. Participant has a parent, legal authorized guardian or consistent caregiver. Exclusion Criteria: 1. Participant has body weight less than 25 kilograms (kg). 2. Clinically significant abnormalities, in the investigator's judgment, in safety laboratory tests, vital signs, or electrocardiogram (ECG), as measured during Screening. 3. Concurrent major psychiatric condition (e.g., Major Depressive Disorder, Schizophrenia or Bipolar Disorder) as diagnosed by the investigator. Participants with additional diagnosis of Autism Spectrum Disorder or Anxiety Disorder will be allowed. 4. Participant is planning to commence psychotherapy or cognitive behavior therapy (CBT) during the period of the study or had begun psychotherapy or CBT within 4 weeks prior to Screening.