-7/del(7q) Deletion Probe

Abnormalities of chromosome 7 are very common in myeloid malignancies occurring in 5-10% of de novo AML (M4 & M6), ~15% adult MDS (30% of RAEB/RAEBT), 40% of paediatric MDS and 50% of treatment related AML/MDS. In children it is often associated with juvenile Chronic Myeloid Leukaemia (jCML).1,2,3,4 There is also a predominance in leukaemias associated with a constitutional predisposition caused by disorders including neurofibromatosis 1 (NF1), Fanconi Anaemia and possibly Down syndrome, which produces a distinct clinical picture known as Monosomy 7 syndrome.5 Another rearrangement, -5/del(5q), is found as an additional abnormality in 40-60% of secondary MDS cases, +8 is less frequently seen.4 Studies of myeloid disorders involving -7/del(7q) have found that signalling pathways using RAS proteins are affected. There are two commonly deleted regions (CDRs), one at 7q22 determined through LOH studies and the use of YAC libraries, the second at 7q31-34.2,6,7,8,9 RELN (7q22) encodes a large secreted protein related to extracellular matrix proteins which contains multiple epidermal growth factor (EGF)-like proteins.

The proximal 7q probe, labelled in red, covers a 368kb region of 7q22.1, including 235kb of the 5’ end of RELN to beyond the marker D7S658. The distal 7q probe, labelled in green, covers a 203kb region of 7q31 encompassing TES.