Role of brain development in hereditary autism spectrum disorder

Researchers investigated brain development in the younger siblings of children who were diagnosed with autism spectrum disorder. Nikolay Bassov / Shutterstock

Autism spectrum disorder, or ASD, tends to run in families. If a child has ASD, their younger siblings are more likely to be diagnosed with ASD than the general population.

Researchers have used MRI to study brain development in infant siblings of children with ASD. These studies have identified changes to brain development during the first two years of life that precede ASD diagnosis. But it isn’t clear what developmental changes are hereditary.

An NIH-funded team of researchers led by Dr. Jessica Girault at the University of North Carolina at Chapel Hill previously showed that younger siblings are more likely to be diagnosed with ASD as the level of ASD traits in the older sibling increases. Building on this result, the team sought to determine whether ASD traits in older siblings also predict ASD-associated brain development in younger siblings. Results appeared in the American Journal of Psychiatry on May 26, 2022.

The researchers examined 384 sibling pairs in which the older sibling was diagnosed with ASD. In 89 of these pairs, the younger sibling also received an ASD diagnosis at 24 months of age. Participants were recruited from the NIH-funded Infant Brain Imaging Study Network. The scientists assessed the level of ASD traits in the older siblings using standard questionnaires. Younger siblings underwent MRI scans at 6, 12, and 24 months of age. 

Brain volume and surface area in the younger siblings increased with the level of ASD traits in their older siblings. The surface area of a specific brain region, the occipital cortex, exhibited a similar trend in younger siblings. This region includes parts of the brain involved in vision.

The team also examined white matter in a brain structure called the splenium. Previous research has shown that this structure is related to how quickly infants orient to visual stimuli. This behavior differs in infants who later develop ASD from those who don’t. Greater ASD traits in older siblings were associated with differences in splenium white matter at 6 months of age.

Finally, the researchers measured functional brain connections in the younger siblings at 6 months of age. ASD traits in older siblings were associated with weaker connections among brain networks that process visual information. Taken together, these findings suggest that genetic factors associated with ASD play a role in the development of visual circuitry during infancy. 

“We think aberrant visual circuitry is a fundamental cog in the cascade of events leading to later autism,” says Dr. Joseph Piven, one of the study’s co-senior authors. “We think this circuitry alters how infants experience the world, and how they experience the world alters how their brains subsequently develop. It’s this secondary altered brain development that may result in what we call autism that typically emerges in the latter part of the first and second years of life.”

—by Brian Doctrow, Ph.D.