DYRK1A and polycythemia: The species-specific divergence of our findings that DYRK1A restrains megakaryocyte proliferation in human hematopoietic cells versus a proliferative role in murine megakaryopoiesis is reminiscent of contrasting observations that T21 in mice results in anemia, while human T21 is associated with polycythemia, and T21 combined with the Gata1s mutation in mice does not recapitulate human TAM (29–31).