Hmmm...interesting question and one I am now pondering myself having received an official diagnosis of AS yesterday. I'm torn. On the one hand I feel, as mentioned previously, that it would go some way towards them maybe understanding me a little better. I would also hope that it might do some good for others on the autistic spectrum too because my family would likely be more sympathetic and understanding about it and be able to relate in some small way with anyone they encountered with it. I know my younger brother worked for a while as a carer in a residential home for young adults with LFA, so he has some understanding of the spectrum and I have mentioned to him in passing that we have traits. The other reason I am keen to tell is because my dad is remarried with a 7 yr old boy, who, I believe, shows some pretty unusual behaviour, so at least he would be aware of the genetic possiblity and could keep his eye on my half-brother in case his behaviour gets unmanageable.
On the other hand, I don't want the little guy labelled and treated as 'special' or a freak...I did quite fine getting myself to 33 years of age without a diagnosis or any special treatment. I want him to have a'normal' childhood, especially if he is atypical! I am also hesitant about telling them all because it could just be one other way in which I 'disappoint' them or get to be the 'black sheep' in the family. At this stage they probably think it's enough to deal with having a gay daughter/sister, let alone one who has a neurological disorder as well.
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"Burn brightly without burning out" -Richard K. Biggs