ARID1A and Coffin-Siris syndrome: Although human genetic studies suggest that both germ‐line mutations and microduplication of ARID1A could cause CSS (Tsurusaki et al, 2012; Santen et al, 2013; Bidart et al, 2017), the link between loss‐of‐function of ARID1A and the CSS pathogenesis remain unexplored.