The report in Chk1-haploinsufficient mice of an hematopoietic disorder highly reminiscent of the one we evidenced in our Mcph1-KO mice, with multiple mitotic defects, increased binucleation, and frequent macrocytic anemia during their first year of life (Peddibhotla et al, 2009), supports this hypothesis. The gene discussed is MCPH1; the disease is anemia.