Is there a genetic marker for Autism Spectrum Disorders?

I was diagnosed with Aspergers Syndrome (in the autism spectrum) about two years ago. Since then I have been reading everything I can get my hands on about the topic.

Experts believe that autism spectrum disorders are an inherited condition. From my reading (I’m not a biologist or geneticist) I understand that the condition has not been traced to single-gene mutation or single-chromosome abnormality.

Has a marker pattern, or combination of markers been discovered that directly points to or labels ASD? What is the likelihood of a genetic test being developed that either gives a probability of an individual or couple producing ASD offspring or an in-utero test such as for Downs Syndrome?