Brain overgrowth has been noted among children with autism spectrum disorder (ASD). Now, a new imaging study suggests that the accelerated brain growth appears before 2 years of life, offering new avenues for early identification and intervention of ASD. Investigators conducted a longitudinal magnetic resonance imaging (MRI) study of 59 children with ASD and 38 control children. The children were evaluated at 2 years of age with behavioral assessments, and brain measurements were obtained through MRI. Both behavioral and MRI evaluations were repeated 24 months later, when the children were 4 to 5 years old.

Overall, the cerebral cortex of children with ASD was larger than the cerebral cortex of control children at all ages studied. The rate of growth, however, of the cerebral cortex was the same in both groups over the period of the study, indicating that the brain enlargement is due to accelerated brain growth before 2 years of age. Children with ASD also had an increase in white matter in the temporal lobe, compared to other children.

Brain enlargement is not a new finding in autism research. But, the onset and mechanism of brain overgrowth has yet to be accurately defined. Age-specific changes take place in the brain of children and adults with ASD, resulting from not only anatomic abnormalities, but also altered gene expression and molecular abnormalities. The brains of children with ASD appear to undergo accelerated growth early in life, followed by decelerated maturation. Several studies have noted that the brains of infants that will later be diagnosed with ASD are smaller than controls at birth, but experience an accelerated growth during the first year of life. Brain growth then slows, so that brain size is not different from controls by adolescence and adulthood.

ASD is most commonly diagnosed between the ages of 2 and 3 years, but symptoms can begin to appear as early as 6 and 12 months of age. As evidenced by the current study, published in the Archives of General Psychiatry, accelerated brain growth is already taking place or completed by the time the symptoms of ASD appear. If these patterns of brain growth are noted early, therapeutic interventions might be initiated early, improving outcomes for children with ASD. In the future, if genes are identified that control brain growth, they may become targets for additional therapy.

ASD is still an elusive disorder, often without clear-cut causes and diagnoses. Each clue that is uncovered offers new hope for understanding the biology and pathophysiology of ASD and directing future therapies.

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