16/272 (6.6%) of Arid1b+/- mice had hydrocephalus, the displacement of brain parenchyma by accumulated cerebrospinal fluid, a condition that frequently accompanies Dandy-Walker malformations seen in CSS patients (Schrier Vergano et al., 2013) (Figure 1—figure supplement 1E). The gene discussed is ARID1B; the disease is Coffin-Siris syndrome.