[Chromosomal mosaicism in the placenta].

Chromosomal mosaicism is when two (or more) cell lines with different chromosomal complements are found within one individual. Mosaicism can be found in all tissues but may also be confined to a specific tissue. During pregnancy the aberrant cell line, often with a trisomy, may be confined to the placenta. In prenatal diagnosis, more specifically in chorionic villus sampling, this can interfere with the results and may necessitate follow-up investigation with amniotic fluid cell culture. Confined placental mosaicism can have no visible effect whatsoever on foetal development, but can also lead to serious foetal problems, depending on the chromosome involved. Uniparental disomy in the diploid cell line of the mosaicism may also have a negative effect on the foetal phenotype. In the case of the reverse situation, where the normal diploid cell line is confined to the placenta and the foetus has trisomy 13 or 18, it has been suggested that the diploid cell line might play a role in intrauterine survival; a recent study by the present authors could not confirm this view.