Our data readily explain the coincidence of impaired neurogenesis, gyrification and hydrocephalus, observed often in patients with cortical dysplasia and in our Pik3ca mouse model (Keppler-Noreuil et al., 2014; Jansen et al., 2015; Roy et al., 2015; Parrini et al., 2016; Furey et al., 2018). Here, PIK3CA is linked to Hydrocephalus.