Amygdala Overgrowth May Predict Autism in Babies, Study Suggests

Researchers have long known that autism is a disorder related to the amygdala but have been unable to tell when it starts. A new study by a team from North Carolina has for the first time provided insights on when the condition begins to develop.


Amygdala. Credit Amber Rieder

Autism is linked to the enlargement of the amygdala. This new research solves a puzzle by showing that the overgrowth of this vital brain structure begins when a baby is between the age of six and 12 months. The discovery could enable a much earlier diagnosis of the disorder than is currently possible.

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The study which appeared in the American Journal of Psychiatry showed differences between cases of autism and fragile X syndrome, another brain disorder. There was no abnormal amygdala growth in the latter disorder.

The research was carried out by scientists from the Infant Brain Imaging Study (IBIS) Network, which comprises 10 universities across the U.S. and Canada.

Amygdala and autism

The amygdala is a tiny cluster of cells shaped like an almond and situated around the lower part of the brain. Humans have two cell groups, with one in each of the brain’s hemispheres.

This brain structure is vital for decoding social and emotional clues, including being able to interpret facial expressions and recognize possible threats around us.

For a long time, scientists have long believed that the amygdala plays a key role in social behavior challenges that are seen in autism. School-age children that have the disorder typically exhibit an abnormal size of this brain structure.

However, it was not known before now at what point the amygdala begins to increase in size.

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Amygdala overgrowth in infants

To investigate when this brain structure starts to grow, researchers recruited 408 infants. These comprise 58 at a higher risk of having autism (have an autistic older sibling) and who later developed the disorder. The remaining included 212 infants more prone to developing autism but who failed to, 109 normally developing infants, and 29 infants having fragile X disorder.

The IBIS team carried out magnetic resonance imaging (MRI) scans on these babies during natural sleep. It did this when they were six, 12, and 24 months old.

At six months, researchers found nothing unusual about the size of the amygdala in infants who later developed autism. But the story changed after that point, with sizes increasing faster than in other babies. The amygdala of infants that developed autism became markedly enlarged by 12 months.

The enlargement of the brain structure continues through 24 (or age two), the scientists said. It is at this stage that the disorder is typically diagnosed, with autistic behaviors clearly evident.

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“Our research suggests an optimal time to start interventions and support children who are at highest likelihood of developing autism may be during the first year of life,” said Joseph Piven, MD, the study’s senior author and Professor of Psychiatry and Pediatrics at the University of North Carolina at Chapel Hill. “The focus of a pre-symptomatic intervention might be to improve visual and other sensory processing in babies before social symptoms even appear.”

This research showed that babies having fragile X syndrome were already showing cognitive deficits when six months old. Those who later developed autism did not exhibit such at that point, but a slow cognitive decline sets in between six months and two years of age.

On what could be responsible for the amygdala overgrowth, researchers theorized that increased stress on the structure may be to blame.

Research into other mental health conditions, including anxiety and depression, has shown a link between amygdala overgrowth and chronic stress. Researchers are now hoping this may help to understand autism development in infants.

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



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