Subcortical Brain Development in Autism and Fragile X Syndrome: Evidence for Dynamic, Age- and Disorder-Specific...

Area of Science:

• Neuroscience
• Developmental Psychology
• Pediatric Radiology

Background:

• Previous studies indicate enlarged amygdala in children with autism spectrum disorder (ASD).
• The precise onset of amygdala enlargement during infancy and its relation to behavioral outcomes remain unclear.
• It is unknown if amygdala enlargement is specific to ASD or present in other neurodevelopmental disorders like fragile X syndrome.

Purpose of the Study:

• To investigate the onset and developmental trajectory of amygdala enlargement in infants at high risk for ASD.
• To compare brain development patterns in infants with fragile X syndrome and ASD.
• To examine the relationship between early brain changes and later behavioral deficits.

Main Methods:

• Longitudinal MRI scans were collected from 6 to 24 months of age.
• Participants included infants with fragile X syndrome, high-risk infants later diagnosed with ASD, high-risk infants without ASD, and controls.
• A total of 1,099 scans were analyzed from 400 infants.

Main Results:

• Infants later diagnosed with ASD showed typical amygdala volumes at 6 months but significantly faster growth between 6-24 months, with larger volumes by 12 months.
• Faster amygdala growth from 6-12 months correlated with greater social deficits at 24 months in the ASD group.
• Infants with fragile X syndrome exhibited persistently enlarged caudate volumes from 6-24 months, associated with repetitive behaviors.

Conclusions:

• ASD-related brain changes, specifically amygdala growth, emerge gradually during the first two years of life.
• Fragile X syndrome shows early and persistent caudate enlargement, distinct from ASD's developmental trajectory.
• These findings suggest age- and disorder-specific patterns of brain development preceding ASD diagnosis.