The Principles of Clinical Cytogenetics - Extra Materials - Springer

Prenatal Cytogenetics 285
Table 10
Distribution of Specific Single Autosomal Trisomies in Each of
the Groups of Mosaicism/Discrepancy in Chorionic Villus Tissue
True fetal
CPM a mosaicism
Trisomy (no. of case s ) (no. of cases)
2 11
3 10
5 3
7 32
8 11 1
9 9 1
10 6
11 1
12 2 1
13 15 2
14 3
15 11 1
16 11
17 1
18 29 4
20 12 1
21 22 9
22 3
Total 192 20
a Includes all types of confined placental mosaicism, including directonly,
long-term culture-only, and both.
Source: Data from ref. 121.
fetal loss rate among pregnancies with CPM. Wolstenhome et al. found 73 cases of CPM in 8004
CVS specimens from women referred for advanced maternal age, previous child with aneuploidy, or
family history thereof (119). Comparison at delivery with the control population did not show a
marked increase in adverse pregnancy outcome. In 108 other cases referred for ultrasound detection
of isolated IUGR, 7 were shown to have CPM involving the following chromosomes: 2 and 15 (1), 9
(1), 16 (3), del(13) (1) and 22 (1).
Hahnemann and Vejerslev (121) evaluated cytogenetic outcomes of 92,246 successfully
karyotyped CVS specimens from 79 laboratories from 1986 to 1994. CVS mosaicism or nonmosaic
fetoplacental discrepancy was found in 1415 (1.5%) of the specimens. Table 10 shows the mosaic
and nonmosaic chromosome findings. Their work on several cell lineages indicated that mosaic or
nonmosaic trisomies found in cytotrophoblasts, with a normal karyotype in the villus mesenchyme,
were not seen in fetal cells. However, if such trisomies were seen on cultured preparations, a risk of
fetal mosaic or nonmosaic trisomy existed. They recommended amniocentesis in all pregnancies
involving mosaic autosomal trisomy in villus mesenchyme.
Uniparental Disomy in Confined Placental Mosaicism
When a conceptus is trisomic, this aneuploidy is said to be “corrected” if by chance there is early
loss of one of the trisomic chromosomes. Depending on the parental origin of the trisomy and of the
chromosome that is lost, this can lead to an apparently normal diploid cell line with uniparental
disomy (UPD) (both chromosomes in a pair from one parent) for that chromosome. Because most
trisomies are maternally derived, the disomy seen is often maternal, as was the case in two previously