The invention concerns the use of a toxin selected from the group consisting of: type 1 (CNF1 ), type 2 (CNF2) or type 3 (CNF3) Cytotoxic Necrotizing Factor from Escherichia coli or CNFY from Yersinia spp. or DNT from Bordetella spp, active fragments or mixtures thereof for the preparation of a medicament for the treatment and/or prevention of symptomatology associated with Rett syndrome (RTT).