Down's syndrome has been identified from maternal blood samples in an
non-invasive technique developed by Chinese clinicians.
In a preliminary study, the genetic marker for Down's syndrome was identified in
plasma samples obtained from three women. Analysis compared the findings among
seven control fetuses who did not have Down's syndrome.
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Aneuploidy:
(a"u-ploi'de) any deviation from an exact multiple of the haploid
number of chromosomes, whether fewer (hyperploidy, as in Turner's
syndrome) or more (hyperploidy, as in Down syndrome). source of definitions: Dorland's Illustrated Medical Dictionary, 29th ed.(2000) Also see: Danger in Plastic Baby Bottles? Common Plastics Chemical Linked to Genetic Damage DANIEL DeNOON / WebMD Medical News 31mar03 |
Dr. Y.M. Dennis Lo and colleagues from the Chinese University of Hong Kong used
the fluorescence in-situ hybridisation (FISH) technique on the maternal
plasma samples. Fluorescence in-situ hybridisation involved hybridising
coloured markers from a given chromosome -- in this study chromosome 21 -- to
cells from the patient. Normal individuals have two copies, but those with
Down's syndrome have three.
Among the plasma samples from the women with fetuses affected by Down's
syndrome, Dr. Lo and colleagues identified fetal cells with three chromosome 21
signals, the genetic marker for the disease.
The researchers point out: "A longstanding aim in medical genetics is the
development of safe and non-invasive prenatal genetic tests. One candidate
technique is the isolation of fetal cells from the cellular fraction of maternal
blood, an approach that generally needs expensive and advanced equipment because
of the rarity of such cells. Fetal DNA has been identified in the plasma of
pregnant women, at concentrations much higher than those present in the cellular
fraction, thus opening up new possibilities for non-invasive prenatal
diagnosis."
Until recently, it was assumed that fetal DNA detected in maternal plasma was
cell free and a definitive diagnosis of fetal chromosomal aneu~ploidies was not
thought possible. Studies now indicate that some fetal DNA originates from
intact fetal cells.
Researchers said their technique is simple for the prenatal detection of fetal
trisomy 21 by FISH analysis of fetal cells harvested from maternal plasma, and
it does not require expensive fetal cell enrichment equipment.
"Our data suggest that future large-scale trials should be initiated to
assess the diagnostic accuracy of this method for fetal aneuploidy detection.
Ultimately, with further technical refinements, prenatal diagnosis by maternal
plasma DNA analysis could reduce our reliance on invasive methods, leading to
safer investigative protocols for mother and fetus," they conclude.
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