Abstract | Summary | Original Article

Longitudinal Magnetic Resonance Imaging Study of Cortical Development Through Early Childhood in Autism

Schumann CM, Bloss CS, Barnes CC, Wideman GM,
Carper RA, Akshoomoff N, et al.

The Journal of Neuroscience, 2010; 30(12): 4419-4427.

Question: Do young children with signs of developing autism who are later diagnosed with Autism Spectrum Disorder show regions of abnormal brain growth?

Background: Previous studies have shown that young children with Autism Spectrum Disorder (ASD) have larger amounts of both grey and white brain matter than typically developing children. This tissue overgrowth is in areas of the brain that are associated with the behavioural symptoms of ASD. The goal of the study was to try to detect where and when this brain overgrowth began.

Participants: The participants were 118 toddlers (87 boys and 31 girls) who began the study between the ages of 18 and 48 months. Seventy-four of the children were deemed at risk for developing ASD because they displayed early signs of the condition. By 48 months of age, tests identified 41 children as having ASD (32 boys and 9 girls). Forty-four typically developing children (32 boys and 12 girls) made up the comparison group. .

Methods: When they entered study, all of the children were given tests of intelligence, social and communication skills and ability to perform activities of daily living. These tests were repeated every six months and then at the conclusion of the study, when the children were between 48 and 60 months. The MRI scans were also scheduled after each of these test sessions. Measurements of brain growth were standardized by specialists in brain anatomy and radiology.

Main Results: A total of 193 scans were performed on the children who received a formal diagnosis of ASD and the controls. Approximately half of each group had two successful scans. The MRIs of children who were formally diagnosed with ASD were examined. The scans showed that by age 2 ½ years, the age at which symptoms often appear, all of the children diagnosed with ASD had abnormal growth in all areas of the white matter and all areas of grey matter except for an area in the back of the brain. All of the brain areas with overgrowth are related to intelligence and symptoms of ASD. The overgrowth was worse in girls than in boys, which may explain why girls with ASD have worse symptoms and lower intelligence.

Conclusions: This study showed that there is a pattern of brain tissue overgrowth that begins by age 2 ½ at the latest in children with a diagnosis of ASD. These findings help to explain the symptoms of ASD, as the regions of overgrowth are those associated with the condition’s behavioural symptoms.