PRENATAL-DIAGNOSIS OF MOSAIC TRISOMY-8 WITH INVESTIGATIONS OF THE EXTENT AND ORIGIN OF TRISOMIC CELLS

A case of trisomy 8 mosaicism, which presented at obstetric ultrasound at is weeks' gestation with a distended bladder and absence of amniot ic fluid. is described. Analysis of DNA microsatellite polymorphisms i ndicates that the trisomic cell line most likely arose as the result o f a post-fertilization non-dysjunction event in early development of a chromosomally normal pre-implantation embryo. The distribution of nor mal and trisomy 8 cells suggests that in this pregnancy there has been either uneven allocation of abnormal cells to the extra-embryonic mes oderm, or selection against the proliferation of trisomic cells in tro phoblast derived cell lineages. This prenatal detection of trisomy wou ld not have been possible if only analysis of direct preparations had been undertaken. (C) 1998 John Wiley & Sons, Ltd.