HOXA gene cluster rearrangement in a t(7;9)(p15;q34) in a child with MDS

Control of vertebrate Hox clusters by remote and global cis-acting regulatory sequences

Despite apparently shared structural organisation and functional roles, vertebrate Hox genes are controlled by regulatory mechanisms rather distinct from those of the prototypic Drosophila Antennapedia (ANT-C) and Bithorax (BX-C) Complexes. If individual regulatory modules have been shown to recapitulate specific Hox expression patterns, other experimental studies underscore that vertebrate Hox clusters are controlled in many of their functions in a global manner, through distinct mechanisms. We will discuss the different models that have been proposed to account for these global regulatory modes. In this context, the studies of the regulation of the HoxD complex during limb development highlighted the role of global regulatory elements and the different mechanisms associated to transform a structural organisation into distinct temporal and spatial expression domains. We will further discuss how these mechanisms may have benefited from the structure of the vertebrate homeotic clusters and reciprocally contribute to shape their evolution towards an increased level of organisation and compaction.

Translocation (7;9)(q22;q34) in therapy-related myelodysplastic syndrome after allogeneic bone marrow transplantation for acute myeloblastic leukemia

Reciprocal translocations involving the long arm of chromosome 7 are relatively rare cytogenetic aberrations in myelodysplastic syndrome (MDS) and acute myeloblastic leukemia (AML). A 44-year-old woman was initially given a diagnosis of de novo AML M6A with a normal karyotype. After achieving complete remission, she received allogeneic bone marrow transplantation from an unrelated male donor. Seven months later, pancytopenia appeared with 14.8% myeloblasts and dysplastic changes of neutrophils and megakaryocytes in the bone marrow. Chromosome analysis revealed complex karyotypes, with add(7)(q22) and add(9)(q34) detected in all abnormal metaphase spreads; spectral karyotyping revealed these chromosomal aberrations to be derived from a reciprocal translocation t(7;9)(q22;q34). Fluorescence in situ hybridization analyses showed that D7S486 at 7q31 was translocated to the der(9)t(7;9), and that the ABL gene at 9q34 remained on the der(9)t(7;9). Because the same translocation reappeared and sustained for more than 8 months after second stem cell transplantation, we revised the diagnosis as therapy-related MDS after allogeneic transplantation. The t(7;9)(q22;q34) was supposed to have a crucial role in the pathogenesis of MDS. Considering two other such reported cases of AML, the t(7;9)(q22;q34) may be a novel recurrent translocation in myeloid malignancies.