What is the difference between asperger disorder and autism in terms of intense interest in subjects?

Aspergers: Both have poor social skills. Children with aspergers are higher functioning academically and, therefore tend to show more interest in subjects they like.

IQ & language: Many studies have shown that the main difference between autism and asperger's disorder is overall intelligence and functional language. Matched for iq, there are few differences, which is why the next diagnostic manual proposes to do away with the distinction. Intense interest in a narrow topic can and does occur with both disorders but probably more commonly with asperger's disorder.