In this issue of EBioMedicine, Najas et al. expand our knowledge of DS by showing that the dosage of the evolutionarily conserved tyrosine kinase Dyrk1a, encoded by a gene located on chromosome 21 and triplicated in DS, alters the cell cycle, and hence the fate, of neural stem cells (Najas et al., 2015-in this issue). This evidence concerns the gene DYRK1A and Dravet syndrome.