Blood, Vol. 93 No. 1 (January 1), 1999:
pp. 293-299
ETV6-AML1 Translocation Breakpoints Cluster Near a Purine/Pyrimidine
Repeat Region in the ETV6 Gene
Srinivas P. Thandla,
Jonathan E. Ploski,
Samina Z. Raza-Egilmez,
Pradheepkumar P. Chhalliyil,
AnneMarie W. Block,
Pieter J. de Jong, and
Peter D. Aplan
From the Departments of Cancer Genetics, Pediatrics, Immunology,
Clinical Cytogenetics, Roswell Park Cancer Institute; and the
Department of Pediatric Hematology-Oncology, Children's Hospital of
Buffalo, Buffalo, NY.
The t(12;21)(p13;q22) translocation, fusing the ETV6 and
AML1 genes, is the most frequent chromosomal translocation
associated with pediatric B-cell precursor acute lymphoblastic
leukemia. Although the genomic organization of the ETV6 gene
and a breakpoint cluster region (bcr) in ETV6 intron 5 has been
described, mapping of AML1 breakpoints has been hampered
because of the large, hitherto unknown size of AML1 intron 1. Here, we report the mapping of the AML1 gene between exons 1 and 3, cloning of ETV6-AML1 breakpoints from different
patients, and localization of the AML1 breakpoints within
AML1 intron 1. In contrast to the tightly clustered ETV6 breakpoints, the AML1 breakpoints were found to be
dispersed throughout AML1 intron 1. Although nucleotide
sequence analysis of the breakpoint junctions showed several 5/7
matches for the V(D)J consensus heptamer recognition
sequence, these matches were present only on the ETV6 alleles
and not on the AML1 alleles, making it unlikely that the translocations were mediated by a simple V(D)J recombination mistake. Interestingly, several breakpoints as well as a stable insertion polymorphism mapped close to a polymorphic, alternating
purine-pyrimidine tract in the ETV6 gene, suggesting that this
region may be prone to DNA recombination events such as insertions or
translocations. Finally, the presence of an insertional polymorphism
within the ETV6 bcr must be recognized to avoid incorrect
genotype designation based on Southern blot analysis.
