ANALYSIS OF 9 PREGNANCIES WITH CONFINED PLACENTAL MOSAICISM FOR TRISOMY-2

Karyotypically normal fetuses with completely trisomic or mosaic place ntae may be at increased risk for intrauterine growth restriction (IUG R). Molecular and cytogenetic analyses on nine pregnancies with confin ed placental mosaicism (CPM) for trisomy 2 were performed at two colla borating centres. Seven cases were identified through prenatal testing of chorionic villi (CVS). Two of these seven cases demonstrated compl ete trisomy 2 while the remaining five cases showed various levels of trisomy 2 (33 per cent-75 per cent cells). Two cases identified after IUGR was observed in newborn infants demonstrated 65 per cent and 100 per cent trisomy 2 in cultured villi from term placentae. In all nine cases, blood chromosome analysis (n=4), chromosome analysis of amnioti c fluid cultures (n=4), and cultured amnion (n=5) were normal, failing to demonstrate any trisomic cells in tissues of fetal origin. Molecul ar studies on the fetal or newborn tissues using dinucleotide repeat p olymorphisms on chromosome 2 revealed normal biparental inheritance of chromosome 2 in all nine cases. The parental origin studies of the ex tra chromosome 2 in the placenta showed that three cases were maternal in origin, at least two of which were consistent with a maternal meio tic non-disjunction giving rise to the trisomy 2, while in one case a paternal origin of the extra chromosome 2 was established.