Children with autism show measurable brain-structure changes around ages 2-3, when symptoms typically emerge. What looks like regression is often a halt in development: kids stop learning new words and social skills, creating the impression they've lost abilities they once had.
Up till now, we have had some research showing that ASD children in general, at around 2 or 3, their brain structure, it develops differently from a typical developing child. What it means is that these changes biologically in the brain also translates to the symptoms of ASD surfacing at similar ages. So when these symptoms come out, the symptoms of asd, the most predominant one is obviously the inability to social. Like they don't know why they should talk to you, why use sounds, they don't get it. So you pair that with the onset time and the regression time. Then therefore, it becomes clear that it's because of the onset of ASD that makes it feel like they start to regress back behind. It's actually their development has halted and they haven't been learning new words, learning how to use those words, learning how to interact with people with the words that they know, and therefore it feels like it's gone back because their social abilities have stagnated and therefore it's very difficult for them to learn any more words.
