A Novel, Regulated Gene Therapy (NGN-401) Study for Female Children with Rett Syndrome

Inclusion Criteria:

• Diagnosis of typical Rett syndrome with a documented disease-causing mutation in themethyl-CpG-binding protein 2 (MECP2) gene

• Current anti-epileptic drug regimen has been stable for at least 12 weeks

• Participant and caregiver should reside within a 2-hour drive of the study centerfor at least 3 months following treatment

• Participant must have never taken trofinetide or have taken trofinetide anddiscontinued due to tolerability, lack of efficacy, or other reasons. FollowingNGN-401 dosing, trofinetide may be initiated after a specified time period and withthe support of the treating clinician

Exclusion Criteria:

• Normal or near normal hand function

• Has a current clinically significant condition other than Rett syndrome

• Presence of a concomitant medical condition that precludes intracerebroventricularadministration, or use of anesthetics needed for study related procedures

• Grossly abnormal psychomotor development in the first 6 months of life

• A history of other genetic disorders or neurological conditions, such as stroke,brain tumor, or autoimmune processes affecting the central nervous system

Other inclusion or exclusion criteria apply.