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Rett syndrome is one of the most common genetic causes of intellectual disabilities in women Rett Syndrome is caused by mutations in the X-linked MECP2 gene MeCP2 regulates the expression of many genes involved in normal brain function A brief period of normal development is followed by a devastating loss of speech and purposeful hand use along with the emergence breathing abnormalities Disease reversibility described in animal models as demonstrated by Sir Adrian Bird¹ The estimated prevalence of Rett syndrome is 25,000 patients in the US and EU 1. Guy J et al. Science 2007 = || & STAGE I 6-18 months (typical) 36 months (early) Developmental Arrest Symptom Onset STAGE II 1-4 years Rapid Deterioration Symptom progression-regression STAGE III 4-10 years Pseudo stationary Symptoms stabilize/improve 00 Infants are generally described as having normal development until approximately 6 to 18 months of age Hallmark Rett symptoms appear: Hand wringing or squeeze, clapping. rubbing, washing, or hand to mouth movements After a period of rapid deterioration neurological symptoms stabilize, with some even showing slight improvements STAGE IV >10 years Late Motor Deterioration Muscle wasting that worsens with age wasting with age 85-90% of affected people may experience growth failure and muscle 28

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