An imbalance in the number of excitatory neurons in early brain development may account for the difference.

Experiments offer clues to why certain mutations are associated with autism in some people and not others.

The mutation prevents certain amino acids from entering neurons, causing the cells to die early in development.

The changes may help explain the link between maternal infection and autism, though more research is needed.

Both human and mouse progenitor cells with the alterations struggle to become neurons and instead express genes that are typically active only in muscle or the heart.

The gene, linked to a little-known condition called Weiss-Kruszka syndrome, prevents embryonic stem cells from deviating from their neuronal destiny.

The developmental models have advantages over natural embryos and other synthetic models, such as organoids, but present technical and ethical challenges.