Certain site specific point mutations in the KIX domain of p300 can disrupt the interaction between p300 and CREB/c-Myb, and mice homozygous for these mutations have many hematopoietic defects, such as anemia, thrombocytosis, megakaryocytosis, thymic hypoplasia, and B cell deficiency. This evidence concerns the gene EP300 and Thrombocytosis.