Increased Surface Area, but not Cortical Thickness, in a Subset of Young Boys With Autism Spectrum Disorder

Area of Science:

• Neuroimaging
• Developmental Neuroscience
• Autism Spectrum Disorder Research

Background:

• Autism Phenome Project is a large, longitudinal MRI study of young children with autism spectrum disorder (ASD).
• Previous analyses revealed larger total brain volume in children with ASD compared to typically developing (TD) children.
• A subset of boys with ASD exhibit disproportionate megalencephaly (ASD-DM), characterized by significantly larger brain size relative to height.

Purpose of the Study:

• To investigate cerebral cortical grey matter volume, thickness, and surface area in 3-year-old boys with ASD.
• To differentiate the contributions of cortical thickness versus surface area to early brain overgrowth in ASD.
• To analyze ASD-DM subgroups separately to understand their specific contributions to observed brain differences.

Main Methods:

• Magnetic resonance imaging (MRI) scans of 112 boys with ASD and 50 age-matched TD boys were analyzed.
• Cerebral cortical grey matter volume, thickness, and surface area were quantified.
• Boys with ASD were categorized into ASD-DM (n=17) and ASD-Normal brain size (ASD-N, n=95) groups for separate analysis.

Main Results:

• Cortical thickness was comparable between ASD and TD groups.
• Significantly greater cortical surface area was observed in the ASD group compared to the TD group.
• The increased surface area in ASD was largely driven by the ASD-DM subgroup, though not uniformly across all cortical regions.

Conclusions:

• Early brain overgrowth in autism spectrum disorder is predominantly characterized by an expansion of cortical surface area.
• Increased cortical thickness does not appear to be a primary driver of larger brain size in young children with ASD.
• These findings highlight surface area expansion as a key neurodevelopmental feature in a subset of young boys with ASD.