Given the previously characterized roleof Rho GTPases in hematopoietic cell localization within the marrowmicroenvironment [8, 31] and the disruption of this processobserved in PMF [23], wehypothesized that the severe infantile myelofibrosis phenotype that results fromthe CDC42 R186C mutation may provide insights into the more common acquired PMFcases. This evidence concerns the gene CDC42 and myelofibrosis.