Given that fibroblast cells from DS individuals have less Cyclin D1 and enlarged G1 phases due to the overexpression of DYRK1A (Chen et al., 2013), and that the role of DYRK1A on brain development and growth is conserved across evolution (Tejedor and Hammerle, 2011), it is likely that the overexpression of DYRK1A in DS also increases G1 phase duration in RG progenitors of the developing neocortex thereby changing their neurogenic potential and final neuronal output. The gene discussed is CCND1; the disease is Dravet syndrome.