Molecular characterization of a myelodysplasia-associated chromosome 7 inversion

Chromosome 7 abnormalities are observed in a wide range of myeloid disorders, particularly myelodysplasia (MDS) and acute myeloid leukaemia (AML). Monosomy 7 and 7q deletions are the most frequent abnormalities, although translocations and inversions involving 7q also occur. The region 7q22--q34 may contain as many as four distinct minimal regions of deletion (MDRs), which are thought to contain one or more myeloid tumour-suppressor genes. We have defined previously the proximal breakpoint of a constitutional 7q22--q34 inversion, carried in a cell line derived from a member of a family with a history of MDS. A YAC clone spanning this breakpoint was identified. Both inversion breakpoints have now been cloned and sequenced, placing the proximal breakpoint 40 kb centromeric to the TAC2 (tachykinin 2) gene and the distal breakpoint 42 kb telomeric to the SSBP (mitochondrial single-stranded DNA-binding protein) gene. Sequence alignments revealed small (3--4 bp) duplications at the inversion breakpoints, suggesting that the mechanism of inversion involved the creation of staggered breaks and filling in of the overhanging ends. A 190-bp Alu--Alu deletion close to the distal breakpoint was also detected and may have contributed to the inversion.