A Safety Study of NNZ-2566 in Patients With Rett Syndrome

Inclusion Criteria: * Diagnosis of Rett Syndrome with proven mutation of the MeCP2 gene * Age 16 to 45 years * Severity rating of between 10 and 36 (Rett Syndrome Natural History/Clinical Severity Scale) * Concomitant medications must be stable for \>4 weeks prior to enrollment. The following concomitant medications are permitted: anticonvulsants which do not have liver inducing effects; beta-blockers; medications for the treatment of gastroesophageal reflux disease (GERD); medications for the treatment of chronic respiratory conditions such as asthma; medications for the treatment of anxiety, of depression and of psychosis, hormonal contraceptives. Melatonin for difficulties with sleep onset. * Ability to swallow study medication provided as a liquid solution, or via gastrostomy tube Exclusion Criteria: * No detectable abnormality of the EEG during screening period * Actively undergoing regression * QTcF exclusions (any of the following): baseline/screening QT/QTcF interval of 450 msec; history of risk factors for torsade de pointes (e.g. heart failure, hypokalemia (serum potassium at screening \< 3.0 mmol/L) or family history of long QT syndrome; QT/QTcF prolongation previously or currently controlled with medication * Current treatment with insulin * Hgb A1C values outside the normal reference range at screening * Current or past treatment with IGF-1 * Current or past treatment with growth hormone * Current treatment with N-methyl-D-aspartate (NMDA) antagonists * Current or planned use of non-medication based interventional therapy during the period of the study (defined as 4-6 week screening period followed by 4 week dosing and 2 week follow-up period) * Current clinically significant cardiovascular, renal, hepatic or respiratory disease * Gastrointestinal disease which may interfere with the absorption, distribution, metabolism or excretion of the the study medication * History of, or current cerebrovascular disease or brain trauma * History of, or current significant endocrine disorder e.g. hypo or hyperthyroidism or diabetes mellitus * History of, or current malignancy * Clinically significant abnormalities in safety laboratory tests, vital signs or ECG, as measured at screening or baseline * Confirmed pregnancy * Significant hearing and/or visual impairment that may affect ability to complete the test procedures * Enrollment in another clinical trial within the previous 30 days * Previously randomized in this clinical trial * Allergy to strawberries