"Autism" is a vast diagnostic umbrella under which a variety of disorders are shoved, primarily because we don't know how else to label unusual behaviors. My 9-year-old son was declared to be a high-functioning autistic — even though he's never displayed many of the so-called classic markers — by a team of researchers looking for an autistic diagnosis. They admitted they didn't know how else to categorize his excessive quirkiness.
Until we become far more specific identifying disorders, instead of lumping them all under one term, we'll never discover the causes or find cures for autism and the many other disorders inappropriately named as such. The current method of looking at autism is as ineffective as prescribing a Tums for every person who has a stomachache, be it from a punch to the gut or appendicitis. While there may be similar symptoms, the causes and treatments are very different.