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This Article Full Text Full Text (PDF) Data Supplement All Versions of this Article: clinchem.2006.076851v1 52/12/2194    most recent Submit an electronic Letter to the Editor about this paper Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Tong, Y. K. Articles by Lo, Y.M. D. Search for Related Content PubMed PubMed Citation Articles by Tong, Y. K. Articles by Lo, Y.M. D. Related Collections Molecular Diagnostics and Genetics

Noninvasive Prenatal Detection of Fetal Trisomy 18 by Epigenetic Allelic Ratio Analysis in Maternal Plasma: Theoretical and Empirical Considerations

¹ Department of Chemical Pathology, ² Centre for Emerging Infectious Diseases, ³ Li Ka Shing Institute of Health Sciences, and ⁴ Department of Obstetrics and Gynaecology, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China.
⁵ Harris Birthright Research Centre for Fetal Medicine, King’s College Hospital, London, United Kingdom.

^aAddress correspondence to this author at: Department of Chemical Pathology, Rm. 38023, 1/F, Clinical Sciences Bldg., Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, Hong Kong SAR, China. Fax 852-2194-6171; e-mail loym{at}cuhk.edu.hk.

Background: The discovery of cell-free fetal DNA in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. However, the use of maternal plasma fetal DNA for the direct detection of fetal chromosomal aneuploidies has not been reported. We postulate that the aneuploidy status of a fetus could be revealed by an epigenetic allelic ratio approach, i.e., by analyzing the allelic ratio of a single-base variation present within DNA molecules exhibiting a placental-specific epigenetic signature in maternal plasma.

Methods: Placental-derived fetal-specific unmethylated maspin (SERPINB5) promoter sequences on human chromosome 18 were detectable in placental–maternal DNA mixtures and in maternal plasma by bisulfite modification followed by methylation-specific PCR (MSP) and primer extension. The ratios between the extension products of the 2 alleles were calculated for heterozygous placentas, placental–maternal blood cell DNA mixtures, and maternal plasma samples. The allelic ratios were compared between pregnancies carrying trisomy 18 and euploid fetuses.

Results: The epigenetic allelic ratios of all tested trisomy 18 samples deviated from the reference range obtained from euploid samples (placental DNA, 1.135 to 2.052; placental–maternal DNA mixtures, 1.170 to 1.985; maternal plasma, 0.330 to 3.044; without skew correction on the raw mass spectrometric data). A theoretical model was established and validated that predicted that a minimum of 200 copies of genomic DNA after bisulfite conversion were required for distinguishing euploid and aneuploid fetuses with confidence.

Conclusion: Epigenetic allelic ratio analysis of maternal plasma DNA represents a promising approach for noninvasive prenatal diagnosis of fetal chromosomal aneuploidies.

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				D. W. Bianchi Will Epigenetic Allelic Ratio Analysis Turn Prenatal Diagnosis of Trisomy 18 on Its EAR? Clin. Chem., December 1, 2006; 52(12): 2182 - 2183. [Full Text] [PDF]