This study is about finding out how well a new medicine called ZX008 works and how safe it is for people with a condition called CDKL5 Deficiency Disorder (CDD). CDD is a problem that affects the brain and causes seizures. Seizures are like sudden bursts of electricity in the brain that make it hard for the person to control their body. This study will include children and adults who have a hard time controlling their seizures even though they already take medicine for it. The study has two parts.

Part 1 lasts 20 weeks and involves taking the new medicine or a dummy pill (placebo) in addition to their current medicine. Part 2 is a longer 54-week part where everyone gets the real medicine to see how it works over time. To join, participants need to have tried at least two other seizure medicines without success, and must be between 1 to 35 years old.

Key points to consider:

• The first part of the study is 20 weeks long.
• Participants will need to have regular check-ups.
• The study involves taking a new medicine along with current treatments.