Research using three-dimensional replicas of the developing brain created in a lab dish is shedding new light on autism spectrum disorder.

Yale researchers found two paths to autism in the developing brain.

"It's amazing that children with the same symptoms end up with two distinct forms of altered neural networks," co-senior author Dr. Flora Vaccarino said in a university news release. She is director of the program in neurodevelopment and regeneration at the Child Study Center at Yale School of Medicine in New Haven, Conn.

These abnormalities, which arise just weeks after the start of brain development, have been associated with the emergence of autism, according to the new research.

They seem to be dictated by the size of the child's brain, the scientists said. That discovery may help to diagnose and treat autism in the future.

Researchers collected stem cells from 13 boys diagnosed with autism to create the brain organoids, which are lab-grown replicas of the developing brain that mimic neuronal growth in the fetus.

Patients were recruited from clinicians at the Yale Child Study Center.

Eight of the boys had a condition in which the head is enlarged, called macrocephaly.

About 20% of autism cases are in people with macrocephaly, in which the newborn's head size is in the 90th percentile or greater. These tend to be more severe autism cases.

Children with autism and macrocephaly exhibited excessive growth of excitatory neurons compared with their fathers, according to the study authors. The organoids of other children with autism had a deficit of the same type of neurons.

Excitatory neurons, which cause messages to be fired off in the brain, play a key role in functions like thinking, learning and memory, according to the Cleveland Clinic.

The ability to track the growth of these specific neurons could help doctors diagnose autism, researchers said. Symptoms of autism typically appear 18 to 24 months after birth.

Vaccarino said these findings may help identify autism cases that would benefit from existing drugs used to reduce symptoms of other disorders that involve excessive excitatory neuron activity, such as epilepsy. While autism patients with macrocephaly might benefit from these medications, those without enlarged brains may not.

Creating biobanks of patient-derived stem cells could be key to tailoring therapeutics to specific individuals, the authors noted.

Study findings were published Aug. 10 in Nature Neuroscience.