In addition to supporting the idea that NDE1 isoforms may influence the development and evolution of gyrencephaly, these data also raise two possibilities: (1) the earliest mammals expressed the Nde1 isoform with the Myh11-overlapping, human-linked terminal exon, and the mouse/lissencephaly-linked isoform evolved later to trigger the production of a lissencephalic brain; or (2) the gyrencephaly-linked isoform is essential for producing a highly gyrencephalic cortex, as opposed to simple gyrification, so they are found in lineages characterized by high gyrencephaly. Here, NDE1 is linked to lissencephaly spectrum disorders.