The Principles of Clinical Cytogenetics - Extra Materials - Springer

Prenatal Cytogenetics 311
Table 18
Rare Trisomy Mosaicism Cases Diagnosed in Amniocytes Involving Autosomes
Other Than Chromosomes 13, 18, 20, and 21, Along with Risk of Abnormal Outcome
As Determined by Ultrasound and/or Physical Examination at Termination or Birth
Chromosome No. of Degree of risk
number cases for abnormal outcome
2 11 Very high
3 2 Undetermined
4 2 Undetermined
5 5 High
6 3 Undetermined
7 8 Moderate
8 14 Moderate
9 25 High
11 2 Undetermined
12 23 Moderately high
14 5 High
15 11 High
16 21 Very high
17 7 Low
19 1 Undetermined
22 11 Very high
Note: Very high = >60% risk; high = 40–59% risk; moderately high = 20–39% risk; moderate = up to 19% risk; lowrisk,
no abnormalities seen; undetermined-no cases for evaluation.
Source: From ref. 278.
Mosaicism of an Autosomal Structural Abnormality
In 78 reported cases of mosaicism for a balanced autosomal structural abnormality, phenotypic
information was available in 16 cases, and all were associated with a normal phenotype (30). However,
for unbalanced autosomal structural abnormality mosaicism, 25/52 (48%) were reported to be
phenotypically abnormal and 28/48 (58.3%) were cytogenetically confirmed. Such a finding thus
merits consideration of PUBS and ultrasound examination.
Culture Failure
Rates of culture failure vary from lab to lab, and guidelines for acceptable rates exist (see Chapter
6). Cell culture failure is more likely to occur in advanced-gestation amniocentesis specimens,
because the number of nonviable cells in the fluid is very high and they appear to slow the growth of
the viable cells. The usual counseling provided in such cases is that the fetal outcome is not related to
the lack of cell growth. However, there is a report describing 32 of 7852 (0.4%) amniocentesis specimens
classified as unexplained growth failures, and, in this group, 10 women did not repeat the
procedure and 22 did (279). Of the 10 who did not, a fetal bladder-outlet obstruction, two stillbirths,
and one acardiac twin resulted. Of the 22 who repeated, 18 had normal fetal karyotypes, but 4 were
aneuploid. Of these, two had trisomy 21, one had trisomy 13, and one had Pallister–Killian syndrome,
or tetrasomy 12p.
Maternal Cell Contamination
After cell culture and cytogenetic analysis of amniotic fluid specimens, maternal cell contamination
is rarely found. Maternal cells were detected in 0.17% of 44,170 cultured amniotic fluid samples
in one study (280). Because one would expect to detect this in only male pregnancies (as a mixture of