Editors' ChoiceAutism

Nature versus nurture in autism

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Science Translational Medicine  06 Mar 2019:
Vol. 11, Issue 482, eaaw7626
DOI: 10.1126/scitranslmed.aaw7626

Abstract

Structural MRI study of twins with autism reveals both genetic and environmental factors contribute to abnormal neural growth patterns.

If you’ve met one child with autism, you’ve met one child with autism is a common phrase heard in the clinic highlighting the heterogeneity associated with this disorder. Structural brain studies have demonstrated atypical growth patterns in individuals with autism, with overgrowth early in life followed by a plateau. Yet, there is significant variability in the degree of overgrowth and what brain regions are affected among individuals. To test the hypothesis that both genetic and environmental factors influence this variability, Hegarty and colleagues recruited monozygotic and dizygotic twins (6–15 years of age) who either had autism or were typically developing, to complete a structural magnetic resonance imaging (MRI) brain scan. Cerebral and cerebellar gray and white matter volume, surface area, and cortical thickness were mostly influenced by genetic factors in twins who were typically developing. Mean curvature of the brain, which is associated with folding of the cerebral cortex, was more influenced by environmental factors. In children with autism, although there was also strong genetic effect on brain structure, it was mostly concentrated in subcortical gray matter. In contrast, cortical thickness and cerebellar white matter were more influenced by environmental factors.

These findings provide an important contribution to understanding how both genetic and environmental factors contribute to the varying neural trajectories in autism. These results suggest that, whereas brain size is largely determined by genetic factors in both typically developing children and those with autism, environmental factors seem to have a larger influence in the latter. However, what these environmental factors actually are is not known yet. Future work that tests children younger than those recruited in this study, as well as a larger dataset to compare males and females, might be able to help us better understand the etiology of the significant neural overgrowth observed in autism early in life, as well as the predominance of autism in males.

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