Then you should ask yourself what subcategories might make sense?
We already have that speech development that divides a part of the spectrum from classical autism, calling it 'AS'.
However, in that subgroup of AS, there are at least 5 groups:
1. those with perfectly normal and average language development (no echolalia, no confusion with semantics)
2. those with a very early and very fast language development
3. those with normally delayed and atypical language development
4. those who don't fit either of these categories
5. those with an AS diagnosis and language delay in early childhood (hey, what about that criterion if there are professionals who don't care?)
All others symptoms and traits would be disregarded in favour of the language development of a person. Doesn't seem so sensible to me when there are those with classical autism who also gain language and speech to an age appropriate level.
The use of the criterion of repetitive behaviours to divide AS into subtypes would also lead to confusion, I think. There are those with a diagnosis of AS that:
1. have a special interest (however, classical autism doesn't exclude a special interest and many kfolks with classical have or develop one)
2. that have no special interest (a fleeting minority, I'd think)
3. that have routines:
3a. that have routines that if broken distress the individual
3b. that have routines that if broken render the individual non-functional
3c. that have routines and fulfil both 3a. and 3b.
4. that have 'no' routines (=no clinically significant routines, no more than the average person)
5. that have stereotypical mannerisms
...
X. that have a combination of several of the above in various forms.
Which could then again lead to create new subtypes such as '1+3c+6' and '2+4+5' and so on.
And that all isn't even taking the social interaction part into consideration.
So maybe finding the cause for some types of AS would help some.
But there's always the (likely) possibility that a large part of the diagnosed AS population will have the same cause but show a spectrum of symptoms all the same.
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett