The genes encoding hematopoietic transcription factors ETS1 and FLI1 are located on chromosome 11q24.3, which is deleted in PTS. Using PTS-specific (11q23.3 deletion) and genome-edited (FLI1 deletion) induced pluripotent stem cell–derived iMegs, Vo et al find that the megakaryocyte/platelet defects observed in patients with PTS are due solely to hemizygous deletion of the TF FLI1.