In a new study, resequencing the genomes of several thousands of children with autism spectrum disorders (ASDs) or developmental delay revealed a cohort of children with a diagnosis of ASD that carried mutations in chromodomain helicase DNA binding-protein 8 (CHD8). CHD8 mutations were also associated with an increased likelihood of certain other phenotypic markers of ASD, including increased head size and gastrointestinal (GI) dysfunction. Modelling Chd8 dysfunction in zebrafish produced both increased head size and GI motility problems. Thus, CHD8 mutations could result in a genetically based subtype of ASD in which both the brain and gut are affected.