This week I learned of a condition called Hyperlexia. It's the opposite of Dyslexia: a person can easily read words, but can not comprehend what he has read. According to Hyperlexia.net, children with this syndrome have a precocious ability to read words, or an intense fascination with letters or number, but difficulty in understanding verbal language or socializing with other people. Like PDD, hyperlexia may be characterized by echolalia; difficulty with conversations, abstract concepts, or WH questions; sensory issues; awkward social skills; and a need to stick to strict routines.
This sounds very familiar. Ryan's been reciting the entire alphabet since before he was two, can count to 100, and is fascinated by all things letter-related. I wouldn't say he can exactly read yet, but he has a lot of sight-words and a basic understanding of phonics. But the echolalia, the difficulty with conversations, the sensory stuff, and the difficulty with answering questions - yeah, we got that.
We have no diagnosis on this, and I don't know that it would matter if we did - according to a couple of friends of mine who are speech therapists, adding this label probably wouldn't redirect Ryan's course of therapy. But how fascinating that there are enough brains out there that process language in this way that there's a fancy name for them.