Unfortunately, being non-verbal is very common in children with genetic diseases. No one is able to pinpoint an exact reason. But it seems to be that the speech portion of the brain is often left underdeveloped due to the complications of the disorder.
What's interesting is that I often forget that she doesn't speak. I forget that this is one of her many (very) delayed areas of development. We have so many obstacles that we face on any given day that this usually ranks near the bottom of the list. Often, I don't even realize it until we cross paths with another young child. Or when someone speaks directly to her and waits for a response.
You see, her and I have a way that allows us to connect without the use of language. Since the first moment I have been able to communicate with her in a way that defies science or reason. She does not make eye contact. She does not point. But I always seem to get the message she is sending.
I have learned to listen to the changes in her breathing. The rapid movement of her body. I can sense her mood based on her posture or muscle tone at the moment.
I know the purr of her breathing when she has finally drifted off to sleep.
I know the exact pitch of her cry when she is angry/bratty/hungry.
Her soft bounce means she is excited.
I know that her slouch means that she is feeling lazy or under the weather.
Her head tilt means that she is not happy with something.
I know that she drags her fingernails over the floorboards when she is bored or ready to move on to some other task.
She slams her fists into the mattress repetitively when she wants to get up from her nap.
I know that she mouths her keys when she is content.
When she wants something, she pants excitedly upon sight of said object.
Our connection is based solely on instinct and observation.
There is no way to know for sure if she will ever speak. We can't be sure if this is just a significant delay and she will eventually grow to have some, if any, language skills. (It doesn't seem impossible.)
She may never speak...but she may never have to.