Hum. Reprod. Advance Access originally published online on January 29, 2004
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Human Reproduction, Vol. 19, No. 3, 723-724,
March 2004
© 2004 European Society of Human Reproduction and Embryology
Circulating cell-free fetal DNA in maternal serum appears to originate from cyto- and syncytio-trophoblastic cells. Case report
1 Laboratoire de Cytogénétique, Hôpital de Hautepierre, Strasbourg, 2 Laboratoire de Biologie Moléculaire M.Dassault, Centre de Diagnostic Prénatal, Hôpital Américain de Paris, Neuilly-sur-Seine and 3 Service de Gynécologie-Obstétrique, CMCO-SIHCUS, Schiltigheim, France
4 To whom correspondence should be addressed. e-mail: jean-marc.costa{at}ahparis.org
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Abstract |
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Circulating cell-free fetal DNA in maternal serum offers an early and non-invasive method for prenatal diagnosis, but the origin of this DNA is still unknown. We report the absence of the SRY gene in maternal serum of a pregnant woman despite male genitalia at ultrasound. The karyotype was 45,X after direct trophoblast analysis and 45,X/46,Xidic(Yp) after culture and in all fetal tissues studied. Due to the absence of the SRY sequence in maternal blood and in the cytotrophoblast, we presume that free fetal DNA in this case originates from trophoblastic cells. As the case presented here is exceptional, it only has a minor impact on the accuracy of fetal sex determination by maternal serum analysis, but highlights the importance of and the necessity for the complementary ultrasonographic control.
Key words: fetal DNA/maternal serum/trophoblastic cells/case report
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Introduction |
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Since its first demonstration (Lo et al., 1997
), cell-free fetal DNA is known to be present in blood of pregnant women, but the source of this DNA remains unclear. It has been suggested recently that cell types other than fetal erythroblasts are responsible for the release of fetal DNA into the maternal circulation (Zhong et al., 2002). Furthermore, many reports strongly suggest that placental cells are the main source of cell-free fetal DNA in maternal serum. However, there is no direct proof to date to support this hypothesis (Guibert et al., 2003). |
Case report |
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In the case reported here, a pregnant woman carrier of severe haemophilia A was referred for prenatal diagnosis. As fetal sex determination can be achieved efficiently by maternal serum analysis early in pregnancy (Costa et al., 2001
), this new strategy (Costa et al., 2002) was proposed to the parents who gave written informed consent for the procedure. Given that no SRY gene was detected in the maternal serum at 13 weeks’ gestation, the fetus was identified as probably female. However, 3 weeks later, ultrasonographic examination revealed male genitalia, and chorionic villus sampling (CVS) was performed. Direct chromosomal analysis showed a 45,X karyotype on all the 100 analysed mitoses whereas, following CVS culture, a 45,X (51 mitoses)/46,XY (11 mitoses) mosaic karyotype with a non-fluorescent Y chromosome was identified. After fluorescent in situ hybridization (FISH) using a specific SRY probe, the abnormal Y was identified as an isodicentric (Yp) chromosome. The parents were informed that the fetus in all likelihood was affected by haemophilia. They opted for termination of pregnancy (TOP). A second maternal serum sample was tested before TOP, and the absence of the SRY sequence was confirmed. However, the SRY DNA sequence was detected in fetal blood, amniotic cells and chorionic villi obtained following TOP, and a technical problem could thus be eliminated. Fetal karyotypes established on in situ cultured amniocytes and blood lymphocytes confirmed the 45,X/46,Xidic(Yp) mosaicism, which was more complex in blood, with up to six cell lines observed (Table I). Fetal examination confirmed that genitalia were unambiguously male.
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The discrepancy between cytotrophoblast direct analysis (finding a 45,X karyotype only) and the other fetal tissues examined [showing mosaicisms including an isodic(Yp) cell line] can be explained by the embryological derivation of fetal and placental tissues. In the zygote, the inner cell mass (ICM) forming the extraembryonic mesenchyme (analysed by cultured chorionic villi), the embryo and the amnion is distinguished early from the trophoblast which results in the syncytiotrophoblast and cytotrophoblast (analysed by direct analysis). The mosaicism observed can be explained by two successive events (Kalousek et al., 1992
): first a confined placental mosaicism due to early anaphase lag in a diploid zygote carrying an idic(Yp) leads to a cytotrophoblast non-mosaic 45,X karyotype; secondly, a 45,X/46,Xidic(Yp) mosaicism occurred in all tissues derived from the ICM due to the unstable nature of the abnormal Y chromosome. As Y chromosome material was present in all fetal tissues examined but not in cytotrophoblastic cells and in maternal serum, it may be hypothesized that circulating non-cellular fetal DNA mainly originates from cytotrophoblastic cells. These cells might be discharged in the maternal circulation, trapped by her lungs and degraded by alveolar macrophages, or trophoblast might actively release DNA into maternal blood. |
Acknowledgements |
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We thank Dr S.Valleix, Hôpital Cochin, Paris for prenatal diagnosis of haemophilia, and all the technicians of the Cytogenetic Unit, Hôpital de Hautepierre, Strasbourg, for their technical assistance
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References |
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Costa JM, Benachi A, Gautier E, Jouannic JM, Ernault P and Dumez Y (2001) First-trimester fetal sex determination in maternal serum using real-time PCR. Prenat Diagn21, 1070–1074.[CrossRef][ISI][Medline]
Costa JM, Benachi A and Gautier E (2002) New strategy for prenatal diagnosis of X-linked disorders. N Eng J Med 346,1502.
Guibert J, Benachi A, Grebille AG, Ernault P, Zorn JR and Costa JM (2003) Kinetics of SRY gene appearance in maternal serum: detection by real-time PCR in early pregnancy after assisted reproductive technique. Hum Reprod 18,1733–1736.
Kalousek DK, Barrett IJ and Gärtner AB (1992) Spontaneous abortion and confined chromosomal mosacisim. Hum Genet 88,642–646.[Medline]
Lo YM, Corbetta N, Chamberlain PF, Rai V, Sargent IL, Redman CW and Wainscot JS (1997) Presence of fetal DNA in maternal plasma and serum. Lancet 350,485–487.[CrossRef][ISI][Medline]
Zhong X., Holzgreve W and Hahn S (2002) Cell-free fetal DNA in the maternal circulation does not stem from the transplacental passage of fetal erythroblasts. Mol Hum Reprod 8,864–870.
Submitted on October 10, 2003; accepted on November 17, 2003.
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