DYRK1A and Dravet syndrome: To assess the role of DYRK1A in the pathogenesis of ML-DS arising from fetal progenitors, we measured its expression in euploid and T21 fetal liver–derived megakaryocytes, as well as in undifferentiated euploid and T21 iPSCs and iPSC-derived megakaryocytes with and without the GATA1s mutation.