Hyperlexia is when a child can read words way before their chronological age, as well has have an extreme liking to letters and numbers. If you see your child exhibiting these types of behaviors, your child could have this.
Children with autism and this dosorder share some of the same characteristics such as: difficulty with social skills, hard to understand expressive language, learn expressive language rote or by echolalia, exhibit some self stimulatory behaviors, and like to stick to routine.
You can go with his or her skills and teach them to read more then one word together for conversational skills. This shold be done in a systematic way to keep the frustration down and the success rate up. This can all be taught using ABA. Just make sure you don't skip skills your child needs to learn.
Because your child could become a bit ocd over numbers and letters, they might want to only play with those type of activities as well as play with them only one way, you need to teach flexibility. For example if you are doing a letters puzzle and the only whay your child will put the pieces in is in order, you need to have them mix them up. You do this hand over hand, even if he or she is having tantrum. Continue until you finish the activity. After doing this a few times or more, usually the child starts to understand that it is okay to do the puzzle different ways.