Safety and Efficacy of TSHA-102 in Pediatric Females With Rett Syndrome (REVEAL Pediatric Study)

Inclusion Criteria:

• Participant has a confirmed diagnosis of classical/typical Rett Syndrome with adocumented mutation of the MECP2 gene that results in loss of function.

• Participant is between ≥5 to ≤8 years of age at the time of consent.

• Participant must be up to date with all relevant local vaccination requirements,with last vaccination dose received at least 42 days prior to the start of theimmunosuppression regimen.

• Participant's parent/caregiver must be willing to allow participant to receive bloodor blood products for the treatment of an AE if medically needed.

Exclusion Criteria:

• Participant has another neurodevelopmental disorder independent of the MECP2 geneloss of function mutation, or any other genetic syndrome with a progressive course.

• Participant has a history of brain injury that causes neurological problems.

• Participant had grossly abnormal psychomotor development in the first 6 months oflife.

• Participant has a diagnosis of atypical Rett syndrome.

• Participant has an MECP2 mutation that does not cause Rett syndrome.

• Participant requires non-invasive and invasive ventilatory support.

• Participant has contraindications for IT administration of TSHA-102 or lumbarpuncture procedure, other medical conditions, or contraindications to anymedications required for IT administration.

• Participant has acute or chronic hepatitis B or C infections.