Book of Medical Disorders in Pregnancy - Tintash

least maceration: placenta, lung, and
diaphragm. Obtaining tissue from more
than one site can increase the yield by
avoiding contamination or by detection
of mosaicism.
FISH (performed on fresh tissue or
paraffin blocks):
In addition to karyotyping, fluorescence
in situ hybridization (FISH) can be
useful. A wide variety of probes are
available. It is useful for detecting
aneuploid conditions (trisomies, mono
somies). Fresh cells are desirable, but the
method can be applied even to fixed
tissues stored in paraffin blocks, though
working with paraffin blocks is much
more time consuming and interpretation
can be difficult. The ability to use FISH
on paraffin blocks means that archival
tissues can be examined in cases where
karyotyping was not performed, or cells
didn't grow in culture. FISH technique
diagram and FISH abnormalities, diagram.
DNA Probes:
Fetal cells obtained via amniocentesis or
CVS can be analyzed by probes specific
for DNA sequences. One method
employs restriction fragment length
polymorphism (RFLP) analysis. This
method is useful for detection of mutations
involving genes that are closely
linked to the DNA restriction fragments
generated by the action of an Endonuclease.
The DNA of family members
is analyzed to determine differences by
RFLP analysis. In some cases, if the
DNA sequence of a gene is known, a
probe to a DNA sequence specific for a
genetic marker is available, and the
polymerase chain reaction (PCR) technique
can be applied for diagnosis.
199
There are many genetic diseases, but
only in a minority have particular genes
been identified, and tests to detect them
have been developed in some of these.
Thus, it is not possible to detect all
genetic diseases. Moreover, testing is
confounded by the presence of different
mutations in the same gene, making
testing more complex.
Biochemical analysis:
Tissues can be obtained for cell culture
or for extraction of compounds that can
aid in identification of inborn errors of
metabolism. Examples include: Longchain
fatty acids (adrenoleukodystrophy)
amino acids (aminoacidurias).
Flow cytometry:
Flow cytometry is useful only for
determination of the amount of DNA
and can yield no information about
individual chromosomes with aneuploidy.
Thus, the condition that flow
cytometry can routinely detect is triploidy.
Very little sample (0.1 gm) is required.
The technique can also be applied to
fixed tissues in paraffin blocks.
Electron microscopy: Rarely used and
requires prompt fixation with no maceration.
Examples of conditions to be
diagnosed with EM include: mitochondrial
myopathies and viral infections.
Overview of fetal placental
abnormalities:
Chromosomal abnormalities:
The risk for chromosomal abnormalities
increases with increasing maternal age,
mainly because non dysfunctional events