Rett Syndrome strikes at random in early childhood, affecting little girls almost exclusively. Each of these girls will lose the ability to walk, talk and use their hands. Most will have difficulty breathing and eating. All are at increased risk of sudden and unexplained death. Many girls live into adulthood, requiring total, 24-hour-a-day care. There is currently no effective treatment.

The concept behind gene therapy is simple: deliver a healthy gene to compensate for one that is mutated. The genetic target in Rett is known: MECP2. Another advantage is that Rett is not neurodegenerative – neurons don’t die. And we know that restoring the proper level of MeCP2, even later in life, at least in a mouse, results in dramatic improvements. Finally, we already know that a single one-time administration of a gene therapeutic can restore health in the mouse model of this disease.