'The faster the amygdala grew in infancy, the more social difficulties the child showed when diagnosed with autism a year later.' 'We also found that the rate of amygdala overgrowth in the first year is linked to the child's social deficits at age two,' said first author Mark Shen, PhD, Assistant Professor of Psychiatry and Neuroscience at UNC Chapel Hill and faculty of the Carolina Institute for Developmental Disabilities (CIDD). This amygdala enlargement continues through 24 months, an age when behaviors are often sufficiently evident to warrant a diagnosis of autism. However, their amygdala begins growing faster than other babies (including those with fragile X syndrome and those who do not develop autism), between six and 12 months of age, and is significantly enlarged by 12 months. Babies who go on to develop autism show no difference in the size of their amygdala at six months. Published in the American Journal of Psychiatry, the official journal of the American Psychiatric Association, this research demonstrated that infants with fragile X syndrome already exhibit cognitive delays at six months of age, whereas infants who will later be diagnosed with autism do not show any deficits in cognitive ability at six months of age, but have a gradual decline in cognitive ability between six and 24 months of age, the age when they were diagnosed with Autism Spectrum Disorder in this study. Increased growth of the amygdala in infants who were later diagnosed with autism differed markedly from brain-growth patterns in babies with another neurodevelopmental disorder, fragile X syndrome, where no differences in amygdala growth were observed. Overgrowth begins between six and 12 months of age, prior to the age when the hallmark behaviors of autism fully emerge, enabling the earliest diagnosis of this condition.

Now, for the first time, researchers from the Infant Brain Imaging Study (IBIS) Network, used magnetic resonance imaging (MRI) to demonstrate that the amygdala grows too rapidly in infancy. Researchers have long known the amygdala is abnormally large in school-age children with autism, but it was unknown precisely when that enlargement occurs.

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