Investigators from University of California, San Diego, and other centers in the US, assayed markers for neurons and glia and genes implicated in the risk of autism, in prefrontal, temporal, and occipital neocortex. Postmortem tissue samples were obtained from children with autism and unaffected children between the ages of 2 and 15 years. Prefrontal and temporal cortical tissue from 10 of 11 children with autism and from 1 of 11 unaffected children showed focal patches of abnormal laminar cytoarchitecture and cortical disorganization of neurons, but not glia. No cortical layer was spared, layers 4 and 5 being most affected. A probable dysregulation of layer formation and neuronal differentiation is proposed at prenatal developmental stages of children with autism. 
COMMENTARY. The authors suggest that the mechanism of this laminar disorganization might result from migration defects or de novo changes in early prenatal development. Both genetic and environmental factors contribute to autism liability. In a Swedish population study , the risk of autism spectrum disorder (ASD) in family members of persons with ASD was significantly higher than the risk in the general population, and the risk of ASD recurrence among family members decreased with decreasing genetic relatedness, from a 10-fold increased risk of recurrence in full siblings to a 2-fold increased risk of recurrence in cousins. Genetic factors explained half of the liability for autism . Another population-based Swedish study based only on twins estimated a heritability of 80% .