Autistic and non-autistic girls’ brains differ in activity in a way that autistic and non-autistic boys’ brains do not, according to a new study. This sex difference may stem from distinct patterns of gene expression during early development.

The new findings lend support to the idea that autism has sex-specific biological roots. Such a difference may help explain the lower prevalence of autism in girls — and compound a diagnostic bias that leads some clinicians to overlook girls with the condition.