Asperger’s syndrome, like other autism spectrum disorders, is in many senses poorly understood (as you can see in the Wikipedia writeup, which includes only speculation as the biological basis; it was introduced as a formal classification only in 1994). Asperger’s is often characterized by a lack of recognition of social “rules”, compensated sometimes by exceptional (though highly literal) linguistic abilities and/or the ability to focus intently on certain subjects of interest. In this latter respect, of course, it bears some similarity to some forms of attention deficit/hyperactive disorder, although what little is known about the biological basis of Asperger’s suggests it’s quite different from ADHD. (I am still pouring over brain maps in an attempt to clarify this – I’m well out of my water there.)
My colleague Michael Goldberg maintains the Autism Bulletin blog, which has become a well-known resource for parents with autism spectrum kids, and recently summarized a powerful first-person account in The New Yorker of growing up with Asperger’s. I found even this small excerpt enlightening and moving.