Fluorescence in situ hybridisation studies to characterise complete and partial monosomy 7 in myeloid disorders

Eight patients with myeloid disorders characterised by a karyotype including apparent monosomy or partial monosomy 7, in the presence of a ring or marker chromosome, were investigated by fluorescence in situ hybridisation (FISH) with a chromosome 7 centromere-specific probe and an Alu-PCR derived chromosome 7 paint. In 4 of 5 cases a ring chromosome was shown to be of chromosome 7 origin; in one of these the apparent ring was shown to consist solely of chromosome 7 centromeric material, and in the fifth case the ring was derived from chromosome 18. In three cases monosomy 7 had arisen during the course of karyotype evolution and was clearly not the primary cytogenetic abnormality. One further case demonstrated fragmentation and cryptic translocation of chromosome 7 material. In the last case a chromosome described as der(l)t(1;7)(p11;p11) was redefined as dic(1;7)(p11;q11). The application of FISH has enabled a more accurate characterisation of chromosome abnormalities, and extended studies of this type may eventually lead to more precise prognostic groups defined by karyotype.