Thought I'd throw in my
EUR 0.02I have a son with autism (officially: Asperger Syndrome, which is on the "autistic spectrum", as they say), and have a few relatives and acquaintances that seem like they might also be autistic to some degree.
The main thing I've noticed is that figuring out social interactions and social situations is difficult for them. The doctor who diagnose my son at age 5 called it "a learning disability in the social area." The social skills (for example, picking up on how people are reacting to him) that people normally learn completely unconsciously by age 4 or 5 are things that he has to think about even now, at age 24. We found a good therapist for him who worked with him for 12 years and helped him with a lot of these things, and, IMHO even more important, gave him the feeling that relating to people was worth the effort and the pain. But there's still a lot of stuff he doesn't get unless you explain it to him.
That's why groups of people are a problem -- he has to figure out each person who he might have to deal with as if they were a new species of extraterrestrial alien[ 1 ], all at the same time, all the time. This is exhausting. Also, people he doesn't know well are a problem (it used to be a _big_ problem in school when he'd get a new teacher or have to deal with someone other than his regular teacher.) He also has social anxiety, which most people aren't aware of because he doesn't give the sort of cues to his emotions that neurotypical people do. I've always suspected that a lot of the anxiety comes from not knowing what's going to happen when he goes into a social situation.
Autism seems to come with a bunch of other issues. What I've mostly noticed in my son are sensitivities to touch and taste and noise. There are a lot of foods he won't eat because of the texture, clothes he won't wear because of how they feel on his body. He is also is easily overloaded by sensation, especially noise.
As others have said, the best thing you can do is to talk and listen to him, to not assume he understands something if you have not talked it out with him, and to keep in mind that things might be very stressful for him that are not stressful for you. Also, don't assume that what he appears to be feeling is what he is in fact feeling. You need to ask.
BTW, I remember when my son was younger, he often did not know what he was feeling himself. He would get angry, for example, and not know that he was angry. We would notice that he was doing things that he would only do if he were angry, and then we would have to explain to him that he was angry. So sometimes, you and he will have to figure out together what he is feeling.
Another thing: at least here in the USA, a lot of people, including a lot of mental health professionals, assume that autistic people don't have emotions (because autistic people don't express their emotions the same way neurotypical people do), and treat them like robots or like animals that don't have feelings. They say you should just "train" them to not be too socially unacceptable. So be on guard against "professional" advice or treatments that are actually useless or even cruel. (We avoided this, but some of our friends were not so lucky.)
[ 1 ] One well-known high-functioning autistic person -- Temple Grandin -- described it as "like being an anthropologist on Mars."
Oh, and for the record: girls can be autistic, too. But doctors often don't recognize it, because (a) they aren't boys and (b) it looks somewhat different in girls. A lot of times women don't find out they are autistic until they have a child who is diagnosed with autism and they notice that they have the same problems as their child.
