Missy Alexander I believe Reid and his father are just very intelligent in math especially, however if you paid attention his mother also was very organized and with having 7 kids and all of them seem to be bright Reid was just exceptionally bright in mathematics. He does not have any issues connecting physically with especially we see with Meg, emotions is that he has to find like-minded individuals. That is my opinion though.
Marlena I'm not sure. A lot of his behavior was stress induced, his personality was completely different at the end of the book.
Mary I believe that Reid, and possibly Meg, is on the spectrum. Having a grandson on the spectrum, I noticed many of the signs in both of them.
Shir The author never discusses it but I also thought there were a lot of autism spectrum symptoms in Reid as well as his father.
Kristy Moore As someone with two autistic kids and some autistic traits myself, I see a lot of autistic traits in Reid. That doesn't mean he IS autistic, but I find him relatable, especially when he was standing in the rain asking the inappropriately invasive questions about Meg's business. I immediately picked up that he was showing concern in an especially awkward way, as that's something I do to my sisters (who call me "smothering") and sometimes even strangers.
Joy I don’t think so. I can see in hindsight how you might be tempted to think that, but I find Reid to be a bit more socially awkward than on the spectrum. He’s never felt as if he’s fit in, but once he’s comfortable with Meg he warms up. As another poster mentioned he was highly stressed throughout most of the book, and due to the circumstances we discover near the end, I believe that would put anyone on guard.