COMPLETE AND PRECISE CHARACTERIZATION OF MARKER CHROMOSOMES BY APPLICATION OF MICRODISSECTION IN PRENATAL-DIAGNOSIS

A straightforward and extremely efficient reverse chromosome painting technique is described which allows the rapid and unequivocal identifi cation of any cytogenetically unclassifiable chromosome rearrangement. This procedure is used to determine the origin of unknown marker chro mosomes found at prenatal diagnosis. After microdissection of the mark er chromosome and amplification of the dissected fragment by a degener ate oligonucleotide-primed polymerase chain reaction (DOP-PCR), fluore scence in situ hybridization (FISH) to aberrant and normal metaphase c hromosomes with the marker-derived probe pool is performed. With this strategy, marker chromosomes present in amniotic fluid samples were su ccessfully identified in three cases. The origin of the supernumerary markers was ascertained as deriving from 3p(p12-cen), 18p(pter-cen) an d 9p(p12-cen), respectively. Since a specific FISH signal on chromosom es can be obtained within 2 working days using a probe generated witho ut any pretreatment from one chromosomal fragment only and without add itional image processing devices, this technique is considered to be h ighly suitable for routine application in pre- and postnatal cytogenet ic analysis.