TRISOMY 8 MOSAICISM: CELL CYCLE KINETICS AND ...

original finding of La Marche in their patients with T8m. The growth advantage of
normal cells over the trisomic cells resulted in the decrease of trisomic cells and lead to
the complete disappearance of trisomic cells over time (Mark and Bier 1997).
Support for selective growth advantage of normal cells is evident from the
decrease of trisomy 8 cells from interphase to metaphase found in the transformed blood,
peripheral blood, umbilical cord, and chorion (Table 3). The significant difference
suggests there is a mechanism resulting in the decrease of trisomic cells in metaphase.
Alpha-satellite probes used in the FISH interphase study are known to give a large signal
and hence have a greater chance of overlap within the cell (Moore et al. 2000). The
sensitivity of the DNA probes has been reported as 80-90% efficiency for detecting the
specific region if present on the chromosome (Moore et al. 2000 and Ruangvutilert et al.
2000). Therefore, the efficiency of FISH probes would explain a decrease in trisomic
interphases compared to metaphase, but would not explain the reverse.
Mechanisms
Mechanisms that may be responsible for the significant decrease in trisomy 8
metaphases include varying cellular growth rates, apoptosis or cell death, and entry into
the GO phase. First we suggested a growth rate difference between the normal and
trisomy 8 cells. Trisomy 8 cells may have a more difficult time undergoing mitosis due
to the extra chromosome and therefore genetic information imbalance, while the normal
cells would divide as usual. This would possibly slow down the division rate since
replication, chromosomal alignment, and division times must be in synchrony for proper
cellular division. Growth disadvantage has been reported in a comparison of 45,X and
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