According to a 2023 study by Yale scientists published in the journal Nature Neuroscience, two distinct neurodevelopmental abnormalities that arise shortly after the start of brain development have been linked to the emergence of autism spectrum disorder (ASD). The researchers created brain organoids using stem cells from 13 boys with the disorder, including eight with macrocephaly, a condition in which the head is enlarged. The organoids were small replicas of developing brains that mimicked neuronal growth in the fetus.

The study found that children with ASD and macrocephaly showed an excessive growth of excitatory neurons, while those without macrocephaly exhibited a deficit of the same type of neurons. Measuring the prevalence of certain types of neurons, as was done in this study, could help doctors diagnose autism and also identify which autism cases might benefit from existing drugs that treat excessive excitatory neuron activity.