Pathogenic variants in ARID1B are one of the top hits (~1%) in large-scale sequencing studies in intellectual disability (ID) populations [1,2] and ARID1B is also the most frequently mutated gene in Coffin–Siris syndrome (CSS) (OMIM 135900) (51–76%) [3,4,5]. Here, ARID1B is linked to Coffin-Siris syndrome.