Although several other genes encoding proteins in the SWI/SNF-like BAF complex including ARID1A, SMARCA2, SMARCA4, SMARCB1, and SMARCE1 have also been shown to cause the Coffin–Siris syndrome phenotype (Santen et al., 2013), and/or a CSS-like phenotype, ARID1B is recognized as one of the most frequently mutated genes causing intellectual disability (Hoyer et al., 2012; Santen et al., 2014; Yang et al., 2014; Liu et al., 2019). This evidence concerns the gene SMARCB1 and Coffin-Siris syndrome.