A study by researchers at UC San Diego has found an unusually large brain may be the first sign of autism, an indicator visible as early as the first trimester.

The disparity in autism outcomes – some children with autism experience profound, lifelong difficulties, while others experience more mild symptoms that improve with time – is also addressed in the new study, published in Molecular Autism by UCSD researchers.

Researchers used blood-based stem cells from 10 toddlers, ages 1 through 4, with idiopathic autism (in which no single-gene cause was identified) to create brain cortical organoids (BCOs), or models of the fetal cortex.

Often referred to as gray matter, the cortex lines the outside of the brain. It holds tens of billions of nerve cells and is responsible for essential functions like consciousness, thinking, reasoning, learning, memory, emotions and sensory functions.

The team also created BCOs from six neurotypical toddlers.

The researchers found the BCOs of toddlers with autism were about 40 percent larger than those of neurotypical controls, further discovering that abnormal BCO growth in toddlers with autism correlated with the severity of their disease presentation.

“The bigger the brain, the better isn’t necessarily true,” Alysson Muotri, director of the Sanford Stem Cell Institute at UCSD’s Integrated Space Stem Cell Orbital Research Center, said in a press release.

“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,” Muotri added.

The BCOs of all children with autism, regardless of severity, also grew roughly three times faster than those of neurotypical children.

The researchers hope now to pinpoint the cause of brain overgrowth to develop a therapy to ease intellectual and social functioning for those with the condition.