What condition did River have in To the Moon?

Throughout To the Moon, Eva and Neil mention that River had a certain condition that causes someone to answer questions literally (that's how I took it but it probably had another effect).

What condition are they referring to?

River has Asperger's syndrome, which is an autism spectrum disorder than can cause difficulties in social interaction.

This is evidenced by the doctor's recommendation that Johnny read some of the books written by Tony Attwood, a psychologist who has written several books on Asperger's syndrome.

River's condition is known as Asperger's syndrome, a form of autism that make social interaction hard and unwanted. The signs that she shows are:

• She shies away from new people.
• She's assigned several books on the condition to read.
• The sound of a ticking clock makes her nervous