Prenatal diagnosis of mosaic trisomy 8 with investigations of the extent and origin of trisomic cells.

ABSTRACT

A case of trisomy 8 mosaicism, which presented at obstetric ultrasound at 18 weeks' gestation with a distended bladder and absence of amniotic fluid, is described. Analysis of DNA microsatellite polymorphisms indicates that the trisomic cell line most likely arose as the result of a post-fertilization non-dysjunction event in early development of a chromosomally normal pre-implantation embryo. The distribution of normal and trisomy 8 cells suggests that in this pregnancy there has been either uneven allocation of abnormal cells to the extra-embryonic mesoderm, or selection against the proliferation of trisomic cells in trophoblast derived cell lineages. This prenatal detection of trisomy would not have been possible if only analysis of direct preparations had been undertaken.