MOLECULAR CYTOGENETIC CHARACTERIZATION OF MARKER CHROMOSOMES FOUND ATPRENATAL-DIAGNOSIS

The nature and origin of two de novo small marker chromosomes found at prenatal diagnosis were determined by fluorescence in situ hybridizat ion using chromosome centromere-specific probes and chromosome-specifi c plasmid libraries. One marker was found in a mosaic state and was sh own to be an i(18p). The second marker was characterized as an inv dup (22). We conclude that molecular cytogenetic analysis contributes to t he identification of marker chromosomes and therefore facilitates gene tic counselling and decision-making for the parents.