I really have to wonder, unless it is some morbid case that renders a person utterly disabled and unable to function at even a basic level, whether there even is such a thing as ADD or ADHD. Ditto autism. Again, there could be morbid, extreme cases, but I have to suspect that a lot of "high-functioning autistic" people are simply a bit eccentric and have keener (and possibly more easily disturbed) senses than the norm. What I am seeing in modern society, is a tendency to create this ideal "normal person", someone who doesn't deviate too far from what society accepts as desirable, and is also more easily directed towards desired behaviors and attitudes by TPTB. Anyone falling outside that norm is seen as in need of medication, therapy, or just labeling or "othering".
As to ADD/ADHD, it may simply be that some people aren't cut out to sit still for long periods of time, to sit at a desk or in a classroom, and to pay attention to something that someone else has decided is worthy of X amount of attention. On the other side of the coin, what about contemplative monks and nuns? I wouldn't be a bit surprised to see someone come along and label them, saying "they're autistic, all they think about day and night is adoring God, they're unable to do anything else, a normal person would be more well-rounded than that".
Just my two cents.