This is an exploratory, Phase 2, multicenter, double-blind, parallel-group, placebo-controlled study to assess the safety, tolerability, and efficacy of oral treatment with VYNT-0126 in female subjects 18-45 years of age with Rett syndrome.

Inclusion Criteria:

• Females age 18-45 (inclusive)
• Diagnosis of classic/typical Rett syndrome with a documented mutation of the MeCP2 gene
• Severity rating of between 10 and 36 (Rett Syndrome Natural History/Clinical Severity Scale)
• Concomitant medications (including approved medications for treatment of Rett syndrome) must be stable for >4 weeks prior to enrollment
• Able to receive liquid study drug orally or via gastrostomy tube (G-tube)

Exclusion Criteria:

• Actively undergoing neurological regression;
• Abnormal QT interval, prolongation or significant cardiovascular history
• Excluded concomitant medications
• Current clinically significant (as determined by the investigator). cardiovascular, endocrine, hepatic, renal, or respiratory disease
• Gastrointestinal disease which may interfere with the absorption, distribution, metabolism or excretion of the study medication
• History of, or current cerebrovascular disease or brain trauma
• History of, or current, malignancy
• Clinically significant abnormalities in safety laboratory tests, vital signs, or ECG, as measured at screening or baseline
• Any condition which in the investigator's opinion would affect the ability of the subject to participate in the study
• Allergy to VYNT-0126 or any ingredients of the liquid formulation