"Our folks’ third and last child, Molly, born in Palo Alto, was, sadly, not what anybody had thought. By four or so, Molly was visibly abnormal — not saying any words at all, nor absorbing any. It wasn’t autism; it was a profound brain malfunction, probably dating from birth or prior to birth, but what was wrong, nobody could say — no diagnosis. Molly just didn’t pick up any words, who knows why, and our Mom and Dad had such anguish for so long on Molly’s account, as did Laura and I. What bad luck."
https://prelectur.stanford.edu/lecturers/hofstadter/autolipo...
The second sentence of the quote does seem strongly opposed to what I know of Dennett's position.
I can't imagine a "normal functioning" human that cannot communicate in any way with others. Surely there are things she can do to express herself and understand others?
That's an interesting position for him, considering (IIRC) his co-author Douglas Hofstadter (The Mind's I) has a sister who is a perfectly normal & functional adult except for her complete incapacity for language.