Common 4q24 deletion in four cases of hematopoietic malignancy: early stem cell involvement?

We determined bone marrow karyotype at diagnosis in four female acute myeloid leukemia (AML) or myelodysplasia patients, aged between 52 and 56 years. In each case, we observed chromosome rearrangement involving the same 4q24 band. Three patients had a balanced reciprocal translocation as the sole abnormality - t(3;4)(q26;q24), t(4;5)(q24;p16) and t(4;7)(q24;q21) - and the fourth had del(4)(q23q24), +4. We used a set of 4q BAC probes for fluorescent in situ hybridization (FISH) in these four cases. We found a 4q24 submicroscopic deletion in all three translocations, with a common deletion of approximately 0.5 Mb. In three cases, we concluded that rearrangement occurred in an early hematopoietic stem cell, as it was detected, in mosaic with a normal karyotype, in a fraction of remission bone marrow cells, peripheral T and B lymphocytes, malignant lymph node T-lymphoma cells in one case and B-lymphoblastoid cell lines established in two cases. Moreover, one of 10 additional AML patients tested by FISH had a normal karyotype and deletion of one of the commonly deleted probe sequences. A tumor suppressor gene may therefore be involved, especially as two patients developed malignant lymphoma at the same time as myeloid proliferation.