While the DSM-5 may not directly list deficit in demonstrated empathy among diagnostic symptomology for ASD, it is my understanding empathy is assessed by the Autism Diagnostic Observation Schedule (ADOS).

The CDC has an "act early" campaign which shares milestones, free downloadable resources, and tips on steps to take if there is a concern.

The descriptipn of Asperger's and Glossary of Terms, by Autism Speaks, may also be helpful.