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| 1 | 2008
Klinisk Biokemi i Norden
(Fortsat fra side 25)
(Fortsætter side 30)
rionic villus sampling, are invasive and constitute a
finite risk to the fetus. This picture changed upon the
discovery by Lo et al in 1997 (40) that fetal DNA (on
the Y-chromosome) was present in maternal plasma
and serum.
Fetal DNA in maternal plasma has been shown to
be useful for the prenatal diagnosis of certain neuro-
logical diseases, fetal chromosomal aneuploidies, sex-
linked disorders and fetal rhesus D (RhD) status (35).
Fetal RhD genotyping from maternal plasma has
become an adopted protocol in routine prenatal diag-
nosis in several centers (http://www.bloodnet.nbs.uk/
ibgrl/Refernce%20Services/refSer_genotyping.htm)
Quantitative aberrations of fetal DNA in maternal
plasma have been reported in various disease condi-
tions, ie pre-eclampsia, fetal-maternal haemorrhage
and polyhydramnion (35), primarily based on the
detection of Y-chromosomal sequences in maternal
plasma, thus limiting their applications to the 50% of
pregnancies involving male fetuses.
Using RT-PCR fetal RNA of placental origin has
recently been detected in maternal plasma (37). An
important extension of this placental avenue has late-
ly been shown by Tsui et al (41), who used systematic
micro array based identification of placental mRNA
in maternal plasma by subtractive gene expression
analysis.
Circulating DNA and RNA in Cancer testing
Application of circulating DNA in plasma in can-
cer testing depends on the accumulation of genetic
and epigenetic changes, such as 1) point mutations
2) chromosomal rearrangements 3) microsatellite
instability and 4) hypermethylation (35). Circulating
N-ras and K-ras gene mutations have been observed
in circulating DNA in various cancer forms and per-
sistence of mutated circulating K-ras sequences has
been related to recurrence or progressive disease (42).
Microsatellite instability, particularly loss of hetero-
zygosity (LOS) has been observed both in the tumor
itself and in the corresponding circulating DNA. Also
these changes have been correlated with disease pro-
gression or recurrence. Real time methylation specific
polymerase chain reaction (RT-MSP-PCR) allows
quantitative estimates of promoter hypermethylated
circulating DNA. Finally particular viral sequences
has been reported in circulation in patients suffer-
ing from some Epstein-Barr virus (EBV) associated
cancers( nasopharyngeal carcinoma, EBV-associated
Hodgkin’s disease) as has circulating human papil-
loma virus ( HPV) DNA sequences in plasma of cer-
vical cancer patients associated with metastasis (43).
Circulating mRNA
It came as a surprise the finding of mRNA in plas-
ma from patients with malignant melanoma (44).
Apparently cell-derived circulating mRNA is protect-
ed from degradation in plasma (45), possibly because
of “apoptotic packing”. Telomerase mRNAs (hTERT-
Telomerase Reverse Transcriptase) in plasma has
been found in several cancer forms (1;46). Lung
cancer disease was detected in 100% of patients using
Her2/neu and hnRNP-B1 serum mRNA as markers
(47). Several mRNA markers in plasma have been
demonstrated in breast cancer, and of lately
erbB2
mRNA in plasma has been associated with circulating
tumor cells and negative estrogen and progesterone
receptor status (48).
What holds for the future?
Scientists frequently display low predictive powers in
forecasting future scientific forthcomings. We shall
therefore be careful in trying to outline the future
developments. We feel sure, however, that the genera-
tion of databases containing large number of SNPs,
the characterization of haplotypes and patterns of
linkage disequilibrium throughout the genome will
provide an opportunity for the better understand-
ing of susceptibility to disease, prognosis of disease
and responses to drugs. Only the careful use of these
strategies and a clear understanding of their statistical
limits will allow novel genetic variants for many of the
common diseases to be determined as biomarkers.
Furthermore, we would predict various types of
cards to profile genes predictive of cardiovascular -,
diabetic - and cancer diseases. As to what extent the
public, the life insurance companies or the medical
profession will advocate such use may be both an
ethical and a political question. We also foresee the
increasing use of extracted DNA information from
non-coding sequences and from epigenetic changes
for the understanding of common diseases.
The application of quantitative estimate of mRNAs,
whether obtained on global expression platforms or
by low density arrays, to understand disease signa-
tures in circulating leukocytes will obviously increase
