ARID1B (AT-rich interaction domain 1B; also known as BAF250B) is a subunit of the SWI/SNF chromatin remodeling complex implicated in various neurodevelopmental, psychiatric, and cognitive disorders, including autism spectrum disorders (ASD), intellectual disability, and Coffin-Siris syndrome (1–6). Here, ARID1B is linked to Coffin-Siris syndrome.