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

The variants are associated with slight differences in measures of intelligence, income and employment, but the relationship may not be causal.

Nonrandom mating — the propensity for people to partner with others who share their traits — can increase the likelihood of autism or other conditions across generations.

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

If a therapy for autism’s core traits makes it to market, it will likely take one of three forms, the researchers say.

Some conditions are too rare for conventional drug trials, leading some scientists to test bespoke treatments in single participants. Gleeson discusses the merits — and limitations — of these tiny trials.

This month’s issue of the Going on Trial newsletter examines personalized therapies for rare conditions, Acadia’s new drug for Rett syndrome and developments in a cord-blood program, among other autism-related drug trial news.

People whose brains look like those of people who carry autism-linked copy number variants also share markers of heart health.

The rare variants are also linked to ADHD and Tourette syndrome, two other conditions that disproportionately affect boys and men.

Common variants in five regions of the genome may determine whether someone has one condition versus the other.