Girls with Rett Syndrome are able to understand everything you say and everything you do. They hear you when you say, "hi" and see you when you wave. They have a hard time responding back correctly. Let me explain why . . .
Everyone has brain cells that die and get cleaned out by a protein in their brain and then they get new brain cells. Well, girls with Rett Syndrome are lacking that protein that cleans the brain of the dead brain cells. What happens is that the girls are born like any other child. They have all finger and toes and look perfect. They start developing normally. What we don't see is that as they are developing normally, their brain is accumulating the dead brain cells that aren't being cleaned out. All of the sudden the girls stop doing what they once could do. This is because of the dead brain cells. Their brain starts to get "foggy" with dead brain cells that their brain starts having a hard time sending signals to the rest of the body. So this is why over time, they stop doing things. Because the connection get's "foggy". So as time goes on, they start loosing the ability to do more and more because more brain cells are clogging the signal the brain is trying to send to the body.
This is also why girls with rett syndrome have a high pain tolerance. Signals sent to the rest of the body are sent by your nerves. Because of the dead brain cells, the nerves aren't firing off like yours and mine and the nerves are what tell us we are in pain.
Our girls with Rett Syndrome do not have mental retardation (although it may seem like that just by looking at them and how they look like they aren't paying attention). Their brain is all there and they do understand you and know what is going on. That is why I ask that people treat my daughter like any other 2 year old. Hold her hand (she may pull away but it's not because she doesn't want to hold your hand, she can't control her body). Talk to her (she may not make eye contact all the time, but that's because she can't always control her eyes). Play with her. Sing to her. You'll eventually notice that she reacts to you and what you are doing the best she can. You will come to realize just how much she understands you.
Just be patient with her (and other girls with Rett Syndrome). If you give them enough time to respond, her brain just may be able to send a signal every once and a while. She can do great things if you just give her a little time.
I know this isn't a medical explanation This is just my way of explaining it, the way I understand it. Hopefully this makes sense and if anyone has any questions, please ask!