PROSPECTIVE PRENATAL INVESTIGATIONS ON POTENTIAL UNIPARENTAL DISOMY IN CASES OF CONFINED PLACENTAL TRISOMY

In most reported cases of uniparental disomy (UPD) associated with con fined placental mosaicism (CPM), a high level of mosaicism or a full t risomy was found in chorionic villi. At the time that we started our i nvestigations, it was not quite clear whether fetal UPD also existed i n the more frequently occurring low levels of mosaicism. During a 4-ye ar period, a follow-up amniocentesis was performed in all cases of mos aic or non-mosaic trisomy detected in chorionic villus (CV) semi-direc t preparations and suspected to be confined to the placenta. We perfor med fluorescent in situ hybridization (FISH) on uncultured amniotic fl uid cells to differentiate between generalized mosaicism and CPM. We f ound 29 cases of CPM and we determined the incidence of UPD in 23 of t hese cases. Normal biparental chromosome contributions were found in 2 2 cases. In one case, we detected a maternal heterodisomy for chromoso me 16. UPD appeared to be a rare phenomenon in the cases of CPM (type I and/or type III) that we encountered in 3958 consecutively investiga ted CV samples, and is not the cause of the pregnancy complications fo und in seven out of 23 cases with CPM. (C) 1998 John Wiley & Sons, Ltd .