The most frequently mutated BAF subunit is ARID1B, accounting for 50–83% of CSS cases (Santen et al. 2013; Wieczorek et al. 2013; Tsurusaki et al. 2014; Kosho et al. 2014a), and 1% of all NDD cases (Hoyer et al. 2012; van der Sluijs et al. 2019; Gillentine et al. 2022; Valencia et al. 2023). The gene discussed is ARID1B; the disease is Coffin-Siris syndrome.