Experts have long believed autism involves disruptions in typical brain development, going back to pregnancy. The new study, reported online March 27 in the New England Journal of Medicine, offers more direct evidence of such early origins.

For the study, researchers examined samples of brain tissue from 22 children after death -- 11 with autism and 11 without. They were able to spot tiny patches of disrupted development dotting the outer layers of the brain in the children with autism.

Differences like that would take shape during prenatal development, said Ed Lein, a researcher at Seattle's Allen Institute for Brain Science, who worked on the study.