Brain Overgrowth Could Explain Differences in Autism Severity

Researchers suggest that specific parts of an autistic child's brain grow faster during pregnancy, and those that have the largest growth also experience more severe social and language challenges.

Autism spectrum disorder (ASD) impacts people differently. Some autistic individuals need minimal help, while others experience more severe challenges and require substantial support.

DSM-5 diagnostic criteria classifies this spectrum of severity into three levels:

  • Level 1 autistic people "require support " with things like social interactions and organizational skills and may have difficulties with inflexible behavior and switching between activities.
  • Level 2 autistic individuals "require substantial support " during daily activities due to more challenges with language and social communication and may have more difficulty self-regulating.
  • Level 3 autistic people "require very substantial support" from others due to significant challenges with verbal and non-verbal communication, extreme difficulties coping with change, and more noticeable repetitive behaviors.

However, autistic individuals within each level aren't the same, as each person has their own strengths and challenges.

While scientists understand that autism is a spectrum of symptoms and behaviors, they are just beginning to comprehend the neurobiological differences between autistic and non-autistic people.

Now, a new study conducted by researchers from the University of California San Diego revealed more of those differences, and what they discovered may help explain why autism is a spectrum disorder.

Brain growth in autistic children

In the study, published in Molecular Autism, scientists created brain cortical organoids (BCOs) or models of fetal cortex out of blood-based stem cells from 10 toddlers with ASD. The brain's cortex begins to develop in early pregnancy and consists of nerve cells that play roles in cognitive functions such as thinking, memory, and emotions.

The team also created organoids using stem cells from six non-autistic toddlers.

They found that the BCOs derived from autistic children grew around three times faster than those created from non-autistic youngsters. Moreover, the size of an autistic toddler's BCOs was around 40% larger than those derived from non-autistic kids.

When they compared BCO size with symptoms and behaviors, the researchers discovered that the larger the BCO, the more severe the child's language and social symptoms were as they grew older. Moreover, brain scans showed that toddlers with larger BCOs also had more enlarged brain areas tied to sensory, language, and social functions.

"We found that in the brain organoids from toddlers with profound autism, there are more cells and sometimes more neurons — and that's not always for the best," said Alysson Muotri, Ph.D., director of the Sanford Stem Cell Institute (SSCI) Integrated Space Stem Cell Orbital Research Center, in a news release.

Because BCO overgrowth begins in the early stages of pregnancy, the scientists hope to investigate why this occurs and develop strategies to lessen its impact.

"The core symptoms of autism are social affective and communication problems," said co-study author Eric Courchesne, Ph.D., a professor in the School of Medicine's Department of Neurosciences. "We need to understand the underlying neurobiological causes of those challenges and when they begin.”


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