MECP2 and atypical Rett syndrome: It may be possible to deliver MUSE to the brain using the brain tropism serotype AAV-PHP.eB54 to control production of a therapeutic protein (e.g., methyl-CpG binding protein 2, MECP2) for treating Rett syndrome (RTT), which could avoid promotion of neurological disorders known to result from aberrant overexpression of MECP255.