Yes, I do know of a Deaf-Blind girl that was born that way at my elementary school. She was in a special-need program-- she wasn't able to communicate much. I never really feel that she was PART of a class (sometime Deaf and Special-Need are put together due to lack of space or too few students to own a big classroom) because the aide didn't fingerspell everything what the Teacher said (mostly because the aide was a hearie-- probably couldn"t understand everything the teacher signed)
But then now I realized-- I am not sure if she is mentally-challenged or not. She does know some signs like yes, no, bathroom, please, etc. She does "read" fingerspelling with her hands, but I am not sure if she does understand everything or few words that she already knows.
Last time I saw her was in a high school (in a special classroom) and she looked the same.