Study of VYNT-0126 in the Treatment of Rett Syndrome in Adult Patients

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