Severe fetal malformations associated with trisomy 16 confined to the placenta.

Chorionic villus sampling (CVS) and amniocentesis were performed on a pregnant woman during her 24th week of amenorrhoea following an ultrasound scan which showed a fetus with hydrocephaly, intrauterine growth retardation (IUGR), and a single umbilical artery. The direct karyotype from the cytotrophoblast was non-mosaic 47,XXX,+16, while in amniotic fluid and several fetal tissues, studied post-mortem, a normal 46,XX karyotype was found in more than 400 cells. Uniparental disomy (UPD) was excluded by molecular genetic studies. Autopsy confirmed the echographic findings; in addition, agenesis of the corpus callosum and polysplenia were observed. This is the second example of congenital abnormality associated with confined placental mosaicism (CPM) for trisomy 16, without evidence of either UPD or an apparent contribution of abnormal cells to the fetus.