Rett syndrome is a rare, progressive neurodevelopmental disorder that typically affects girls, causing severe intellectual disability, loss of motor skills, and autism-like symptoms, and there is currently no cure. Rett syndrome is caused by a loss-of-function mutation in the X chromosome gene MECP2. Females typically have two copies of MECP2—one on each X chromosome—and in most cases of Rett syndrome, only one copy has the mutation. The disease occurs because the other, normal copy of MECP2 is turned off in neurons by a process called X chromosome inactivation.
