NPM1 and acute myeloid leukemia: In all of these situations, at least one of two tryptophan (W) residues in positions 288 and 290 (WQWRKSL), which are necessary for the nucleolar localization of NPM1, shift into other amino acids.31 Of 23 patients who had mutant NPM1 in our study,14 (60.8%) patients had mutant allele A; 5 (21.7%), allele D; and 4 (17.4%), allele B. Our results showed a high frequency of allele D of the mutant NPM1 gene among Iranian AML patients.