Amygdala overgrowth begins in first year of life in infants with ASD

The amygdala, which is enlarged in children aged 2 years who are diagnosed with autism spectrum disorder, appears to accelerate in growth in the first 6 to 12 months of life, researchers reported in The American Journal of Psychiatry.

“This suggests that early, presymptomatic brain changes in infancy may represent a cascade of linked brain and behavior changes that lead to the emergence of the full syndrome of autism, consolidating into a clinically diagnosable condition in the [second] and [third] years of life,” Mark D. Shen, PhD, an assistant professor and translational neuroscientist at the University of North Carolina School of Medicine, and colleagues wrote.

Expanding on previous research on amygdala enlargement in children with ASD, Shen and colleagues assessed 408 infants, 270 of whom were at risk for ASD because an older sibling had been diagnosed (109 were typically developing infants and 29 had Fragile X syndrome). MRI scans were conducted on each infant at 6, 12 and 24 months of age.

According to study results, 58 infants — all at risk for developing ASD —were diagnosed with the disorder and had normal-sized amygdala at 6 months and significantly larger volume at 12 and 24 months. Accelerated amygdala overgrowth also correlated with more severe ASD symptoms at 24 months.

In contrast, infants with Fragile X syndrome did not have enlarged amygdala; however, they had enlarged caudate volumes at all ages during MRI testing, which was significantly associated with greater repetitive behaviors, the authors wrote.

“This is the first MRI study comparing Fragile X syndrome and ASD in infancy, demonstrating strikingly different patterns of brain and behavior development,” Shen and colleagues wrote. “Fragile X syndrome-related changes were present from 6 months of age, whereas ASD-related changes unfolded over the first 2 years of life, starting with no detectable group differences at 6 months.”

References:

Amygdala overgrowth that occurs in autism spectrum disorder may begin during infancy. https://www.nih.gov/news-events/news-releases/amygdala-overgrowth-occurs-autism-spectrum-disorder-may-begin-during-infancy. Published March 30, 2022. Accessed March 30, 2022.

Shen MD, et al. Am J Psychiatry. 2022;doi:10.1176/appi.ajp.21090896.