The transcription factor PU. 1 plays an important role in the differentiation of myelopoiesis by regulating the expression of a number of myeloid target genes. 1 Recently, Mueller et al2, 3 identified 10 mutant alleles of the PU. 1 gene in 9 of 126 acute myeloid leukemia (AML) patients. However, these findings could not be confirmed in 2 subsequent studies. 4, 5 Vegesna et al4 analyzed 381 samples of hematopoietic and solid malignancies, including 60 cases of de novo AML and 60 cases of myelodysplastic syndromes (MDSs), and were not able to identify PU. 1 coding region mutations. Similarly, Lamandin et al5 failed to detect PU. 1 gene mutations in 77 primary AML samples. We performed PU. 1 mutation analysis in 112 AML patients (normal karyotype, n 93; various chromosome abnormalities, n 19) entered into the AML HD93 treatment trial of the AML Study Group Ulm. 6 Mutation screening was performed by direct sequencing of genomic DNA after polymerase chain reaction (PCR) amplification of each single exon using intronic primer pairs. We detected a biallelic mutation (AC transversion; K216Q) in the DNA-binding domain in one patient. Since nonhematopoietic tissue was not available in this patient we analyzed bone marrow cells at the time of complete remission and identified the identical sequence pattern. We conclude that this point mutation was constitutional rather than disease-associated. However, one could not exclude that the mutation represented residual disease. In a second patient, a silent mutation in exon 5 (GA transversion; L203L) was detected.

Our results are at variance to those of Mueller et al, 2, 3 but they confirm the data published by Vegesna et al4 and Lamandin et al5 who did not identify a significant number of PU. 1 mutations in AML and MDS. There are 2 issues that may explain these controversial findings: the methodology applied and patient selection. In contrast to Mueller et al, who used direct sequencing of cDNA in 99 of 126 AML samples, Vegesna et al screened with PCR single-strand conformation polymorphism (SSCP) of genomic DNA by confirmatory sequencing, and Lamandin et al and our group used direct sequencing of genomic DNA. Specifically, the use of genomic DNA could miss large deletions, of which 2 were detected by Mueller et al. The second