Exon 3 was replaced with an exon 3 containing the transition 298G>A that resulted in an amino acid substitution of methionine for valine at position 72 (V72M). A floxed neo was also inserted downstream of exon 5 and subsequently removed by cre-mediated recoombination. This mutation was originally identified in two unrelated patients with severe cognital neutropenia, one of whom had acute myeloid leukemia.