Rett syndrome (RTT) is a serious neurodevelopmental disorder that has a significant impact on patients and their families. Patients suffer from severe social dysfunction and poor quality of life, and there is currently no effective treatment available. The MECP2 functional loss mutation is the clear pathogenic factor. In recent years, gene therapy has been applied in neuromuscular diseases such as SMA and has achieved good safety and effectiveness. Professor Qiu Zilong's self-developed AAV-MECP2 gene therapy product for RTT was found to significantly improve disease symptoms in RTT model mice, and demonstrated good safety in heath injection testing in monkeys. The dose exploration study of AAV-MECP2 initiated by our researchers is a multicenter, single arm, single intrathecal injection. The plan is to explore two target doses, with three subjects enrolled in each dose, to evaluate the safety, tolerability, and preliminary efficacy of single intrathecal injection of AAV-MECP2 in the treatment of RTT.