How can you tell a child has mild rett syndrome?

Genetic testing. Rett´s syndrome is a genetic disorder almost always affecting girls. Genetic testing as well as a very detailed exam can give you answers. Typically girls start off with normal development up until about 18 months, sometimes the first symptom is the arms and legs get floppy, and loss of hand movements that are purposeful. It afects the brain, cognition and breathing patterns amongst other things.