116
RENATE ULMER
In most of the above mentioned situations, a method which provides a
rapid and accurate identification of two thirds of all chromosomal defects
(Philip et aI., 1994) is a useful adjunctive diagnostic test to conventional
cytogenetic analysis.
There are two more situations, where a rapid testing for aneuploidy can
also be useful in a prenatal diagnostic laboratory.
First: the amniocytes of a special case show no or only very poor
growth in culture. With FISH on the uncultivated cells, are-amniocentesis
can be avoided in some instances.
Second: one or more aneuploid cell colonies (after in situ culture) or
metaphases (after flask culture) are found by analyzing the metaphase
spreads. For distinguishing between pseudomosaicism and true mosaicism, FISH on both uncultured (interphases) and cultured cells (interphases and metaphases) can be useful.
For each of the above-mentioned purposes a suspension of amniotic
fluid cells is necessary. Normally, there is no amniotic fluid left after setting up the culture. When the culture-medium is changed (as a rule 4 or 5
days after setting up the cultures), many amniocytes that did not settle
down are discarded. This medium from each amniotic fluid sample
can be kept in the refrigerator until the case is finished. If necessary,
FISH studies can be performed on this material.
FISH has become a powerful diagnostic tool, which allows a detection
of the aneuploidies of chromosomes 13, 18,21, X and Ywithin 24 h. As has
been shown by Liehr et aL (1999), even a translocation trisomy dup(21q)
can be distinguished from a free trisomy 21 by interphase-FISH. The reliability of the FISH- technique depends highly on the specificity and hybridization efficiency of the DNA-probes used.
Rapid and accurate detection of chromosomal aneuploidies has been
demonstrated in a blinded prospective study which compared aneuploid
detection by FISH for chromosomes 13, 18,21, X and Y to results obtained
by cytogenetics (Klinger et aL 1992). The first clinical application of this
technology was published by Ward et aL (1993, 1997). They reported informative results on 89.5% of 10,342 processed uncultured amniotic fluid
samples.
The breakthrough in using FISH on uncultured amniocytes was made
possible by the development of new DNA-probes. Up to 1992, probes specific for chromosome 18, X and Y were commercially available but the
detection of trisomy 13 and 21 in interphase cells was hampered by
the fact that available probes could not distinguish between chromosome
types 13 and 21 because of cross-hybridization (Philip et aI., 1994). While
Klinger (1992) and Ward (1993) constructed their own cosmid probes for
RENATE ULMER
In most of the above mentioned situations, a method which provides a
rapid and accurate identification of two thirds of all chromosomal defects
(Philip et aI., 1994) is a useful adjunctive diagnostic test to conventional
cytogenetic analysis.
There are two more situations, where a rapid testing for aneuploidy can
also be useful in a prenatal diagnostic laboratory.
First: the amniocytes of a special case show no or only very poor
growth in culture. With FISH on the uncultivated cells, are-amniocentesis
can be avoided in some instances.
Second: one or more aneuploid cell colonies (after in situ culture) or
metaphases (after flask culture) are found by analyzing the metaphase
spreads. For distinguishing between pseudomosaicism and true mosaicism, FISH on both uncultured (interphases) and cultured cells (interphases and metaphases) can be useful.
For each of the above-mentioned purposes a suspension of amniotic
fluid cells is necessary. Normally, there is no amniotic fluid left after setting up the culture. When the culture-medium is changed (as a rule 4 or 5
days after setting up the cultures), many amniocytes that did not settle
down are discarded. This medium from each amniotic fluid sample
can be kept in the refrigerator until the case is finished. If necessary,
FISH studies can be performed on this material.
FISH has become a powerful diagnostic tool, which allows a detection
of the aneuploidies of chromosomes 13, 18,21, X and Ywithin 24 h. As has
been shown by Liehr et aL (1999), even a translocation trisomy dup(21q)
can be distinguished from a free trisomy 21 by interphase-FISH. The reliability of the FISH- technique depends highly on the specificity and hybridization efficiency of the DNA-probes used.
Rapid and accurate detection of chromosomal aneuploidies has been
demonstrated in a blinded prospective study which compared aneuploid
detection by FISH for chromosomes 13, 18,21, X and Y to results obtained
by cytogenetics (Klinger et aL 1992). The first clinical application of this
technology was published by Ward et aL (1993, 1997). They reported informative results on 89.5% of 10,342 processed uncultured amniotic fluid
samples.
The breakthrough in using FISH on uncultured amniocytes was made
possible by the development of new DNA-probes. Up to 1992, probes specific for chromosome 18, X and Y were commercially available but the
detection of trisomy 13 and 21 in interphase cells was hampered by
the fact that available probes could not distinguish between chromosome
types 13 and 21 because of cross-hybridization (Philip et aI., 1994). While
Klinger (1992) and Ward (1993) constructed their own cosmid probes for