It means that too little attention is paid to the issues of adults, and autistic development is too often tracked only by children. Many, many autistic adults lose speech some of the time, whether or not they had a speech delay. A fair-sized minority of autistic people have a movement disorder that can lead to permanent loss of speech (regardless of speech history or which spectrum diagnosis a person has) in adolescence or adulthood, although sometimes this takes the form of periodic loss of speech that just becomes more and more frequent until there's no communicative-type speech left at a certain point. (Which is what happened to me and a few other people I know.) There are a very large number of reasons why people have trouble with speech, from emotional, to cognitive, to motor, and each one of those reasons has a number of variants.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams