A multicenter randomized controlled trial (RCT) of adjuvant chemotherapy (CT) in nasopharyngeal carcinoma (NPC) with residual plasma EBV DNA (EBV DNA) following primary radiotherapy (RT) or chemoradiation (CRT)

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Background: The benefit of adjuvant CT in NPC is unclear. Post-RT EBV DNA predicts poor survival and may be a biomarker of subclinical residual disease. We conducted a biomarker driven RCT using post-RT EBV DNA to select high risk NPC patients (pts) for adjuvant CT while sparing low risk pts from unnecessary toxicity. Methods: Eligible pts had biopsy proven NPC of AJCC (6th Ed) stage IIB-IVB, detectable EBV DNA ( > 0 copy/ml) at 6-8 weeks post-RT, no persistent locoregional disease or distant metastasis, ECOG 0 or 1, and adequate organ function. Pts were randomized with stratification for primary therapy (RT Vs CRT) and tumor stage (II/III Vs IV) to arm A (adjuvant cisplatin 40 mg/m2 and gemcitabine 1000 mg/m2, both given on D1+8 q3w x 6 cycles) or arm B (clinical follow-up). Primary endpoint was relapse free survival (RFS). With a hazard ratio (HR) of 2, 100 pts were required with a power of 0.8 and an alpha at 0.05. Results: From 9/2006 to 7/2015, 789 pts consented for EBV DNA screening, 218 (27.6%) pts had detectable EBV DNA, and 104 (13.2%) pts were randomized (arm A: 52; arm B: 52). The two arms were well balanced in baseline characteristics. 84.6% received prior neoadjuvant and/or concurrent CT and all received curative RT. Staging distribution: IIB 27.9%, III 37.5%, IVA 19.2%, IVB 15.4%. 8 pts refused adjuvant CT after randomization. Overall 69% and 50% completed 3 and 6 cycles of adjuvant CT respectively. After median follow up of 6.5 years (yr), the 3-yr and 5-yr survival outcomes were summarized in Table. Conclusions: In NPC pts who had residual EBV DNA after curative RT/CRT, adjuvant CT with cisplatin-gemcitabine did not improve survival. Clinical trial information: NCT00370890. [Table: see text]

Noninvasive Prenatal Methylomic Analysis by Genomewide Bisulfite Sequencing of Maternal Plasma DNA

BACKGROUND

Epigenetic mechanisms play an important role in prenatal development, but fetal tissues are not readily accessible. Fetal DNA molecules are present in maternal plasma and can be analyzed noninvasively.

METHODS

We applied genomewide bisulfite sequencing via 2 approaches to analyze the methylation profile of maternal plasma DNA at single-nucleotide resolution. The first approach used maternal blood samples and polymorphic differences between the mother and fetus to analyze the fetal methylome across the genome. The second approach used the methylation profile of maternal blood cells and the fractional fetal DNA concentration in maternal plasma to deduce the placental methylomic profile from maternal plasma DNA-sequencing data.

RESULTS

Because of the noninvasive nature of these approaches, we were able to serially assess the methylation profiles of fetal, placental, and maternal plasma with maternal blood samples collected in the first and third trimesters and after delivery. Gestation-related changes were observed. The fetal methylation profile deduced from maternal plasma data resembled that of the placental methylome, both on a genomewide level and per CpG site. Imprinted genes and differentially methylated regions were identified from the maternal plasma data. We demonstrated one potential clinical application of maternal plasma bisulfite sequencing with the successful detection of fetal trisomy 21.

CONCLUSIONS

We successfully analyzed fetal and placental methylomes on a genomewide scale, noninvasively and serially. This development offers a powerful method for research, biomarker discovery, and clinical testing for pregnancy-related disorders.

Noninvasive Prenatal Determination of Twin Zygosity by Maternal Plasma DNA Analysis

BACKGROUND

The current methods for distinguishing the zygosities of twins include ultrasound scanning, which is nondefinitive, and amniocentesis, which is invasive. We explored the use of massively parallel sequencing of maternal plasma DNA for the noninvasive prenatal assessment of the zygosities of twin pregnancies.

METHODS

Plasma DNA was extracted from blood collected from 8 women pregnant with twins. Target enrichment and massively parallel sequencing were performed for each plasma DNA library. Apparent fractional fetal DNA concentrations were calculated for multiple genomic regions by determining the ratio of minor to major alleles among single-nucleotide polymorphism sites. Variations in the apparent fractional fetal DNA concentrations between genomic regions were used to infer whether individual fetuses in a twin pair were genotypically different and hence dizygotic.

RESULTS

The extent of the variation in the apparent fractional fetal DNA concentration across chromosomes was 0.82–1.35 SDs for monozygotic twin pregnancies and 2.42–4.80 SDs for dizygotic twin pregnancies. The proportions of apparent fractional fetal DNA concentration values that deviated beyond the range expected for stochastic variation were 0.00%–1.93% for monozygotic twin pregnancies and 36.2%–78.1% for dizygotic twin pregnancies. After identifying a pair of twins as likely dizygotic, the method also allowed determination of the fractional fetal DNA concentrations contributed by the individual fetuses of a dizygotic twin pair.

CONCLUSIONS

Noninvasive prenatal determination of twin zygosity by maternal plasma DNA sequencing is feasible. It is also possible to determine the relative fractional fetal DNA concentrations for each fetus for dizygotic twin pregnancies.

Maternal Plasma DNA Analysis with Massively Parallel Sequencing by Ligation for Noninvasive Prenatal Diagnosis of Trisomy 21

Background: Noninvasive prenatal diagnosis of trisomy 21 (T21) has recently been shown to be achievable by massively parallel sequencing of maternal plasma on a sequencing-by-synthesis platform. The quantification of several other human chromosomes, including chromosomes 18 and 13, has been shown to be less precise, however, with quantitative biases related to the chromosomal GC content.

Methods: Maternal plasma DNA from 10 euploid and 5 T21 pregnancies was sequenced with a sequencing-by-ligation approach. We calculated the genomic representations (GRs) of sequenced reads from each chromosome and their associated measurement CVs and compared the GRs of chromosome 21 (chr21) for the euploid and T21 pregnancies.

Results: We obtained a median of 12 × 106 unique reads (21% of the total reads) per sample. The GRs deviated from those expected for some chromosomes but in a manner different from that previously reported for the sequencing-by-synthesis approach. Measurements of the GRs for chromosomes 18 and 13 were less precise than for chr21. z Scores of the GR of chr21 were increased in the T21 pregnancies, compared with the euploid pregnancies.

Conclusions: Massively parallel sequencing-by-ligation of maternal plasma DNA was effective in identifying T21 fetuses noninvasively. The quantitative biases observed among the GRs of certain chromosomes were more likely based on analytical factors than biological factors. Further research is needed to enhance the precision for measuring for the representations of chromosomes 18 and 13.

Mass Spectrometry–Based Detection of Hemoglobin E Mutation by Allele-Specific Base Extension Reaction

Background: The specific detection of a minor population of mutant DNA molecules requires methods of high specificity and sensitivity. While the single-allele base extension reaction (SABER) was shown to be useful for the detection of certain beta-thalassemia mutations, we encountered problems with false positivity during development of SABER for the noninvasive prenatal diagnosis of the hemoglobin E (HbE) disease. Systematic optimization resulted in an alternative protocol, the allele-specific base extension reaction (ASBER).

Methods: An artificial model was established by mixing genomic DNA of HbE carriers and normal individuals. Effects of terminator concentration and annealing temperature on the nonspecificity of SABER were then studied. The use of a single relevant terminator and the other 3 types of dideoxynucleotide as competing terminators were also compared in the development of the ASBER protocol. Thirteen cases of HbE-susceptible pregnancies were tested to compare the SABER and the ASBER protocols.

Results: Decreasing the single relevant terminator concentration and increasing the annealing temperature in SABER were found to improve specificity. The use of the other 3 types of dideoxynucleotide as competing terminators was shown to offer better detection sensitivity than a single terminator in ASBER. Genotyping results were all correctly determined by ASBER, except one false-negative detection (sensitivity: 80%, specificity: 100%).

Conclusions: An alternative mass spectrometry–based protocol for noninvasive prenatal diagnosis, ASBER, has been successfully developed to allow the detection of a minor DNA population with a point mutation.

Quantitative Subtyping of Hepatitis B Virus Reveals Complex Dynamics of Ymdd Motif Mutants Development during Long-Term Lamivudine Therapy

Background/aims

Treatment of chronic hepatitis B (CHB) with lamivudine (3TC) is limited by development of drug-resistant mutants at the YMDD motif. We aimed to validate the use of mass spectrometry to detect YMDD mutants and quantify viral subpopulations.

Methods

A total of 21 Chinese patients with severe acute exacerbation of CHB treated with 3TC were studied. Serial serum samples were tested for wild-type and YMDD mutants using matrix assisted laser desorption/ionization time-of-flight mass spectrometry. INNO-LiPA assay was performed for comparison.

Results

At a median follow-up of 192 weeks, 11 patients developed YMDD mutants (six had YIDD, four had YVDD and one had YV/IDD). Mass spectrometry was concordant with INNO-LiPA in all but one patient, in which INNO-LiPA detected coexistence of YIDD and YVDD but mass spectrometry and direct sequencing detected YVDD only. Mass spectrometry was able to reliably detect a minor hepatitis B virus (HBV) subtype at 5% or above. By serial quantitative measurement, several patterns of viral dynamics were observed. In some cases, YMDD mutants dominated the whole viral population. In other cases, the proportion of YMDD mutants fluctuated with time. When more than one mutant was present (that is, YIDD and YVDD), the different mutants might dominate during different time periods.

Conclusions

Mass spectrometry is an accurate and cheap method for the detection of YMDD mutants, even in the presence of overwhelming wild-type HBV. We observed some intriguing mutant viral dynamics during 3TC treatment. Further studies are needed to clarify whether they have any clinical significance.

Automated extraction protocol for quantification of SARS-coronavirus RNA in serum: an evaluation study

BACKGROUND

We have previously developed a test for the diagnosis and prognostic assessment of the severe acute respiratory syndrome (SARS) based on the detection of the SARS-coronavirus RNA in serum by real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR). In this study, we evaluated the feasibility of automating the serum RNA extraction procedure in order to increase the throughput of the assay.

METHODS

An automated nucleic acid extraction platform using the MagNA Pure LC instrument (Roche Diagnostics) was evaluated. We developed a modified protocol in compliance with the recommended biosafety guidelines from the World Health Organization based on the use of the MagNA Pure total nucleic acid large volume isolation kit for the extraction of SARS-coronavirus RNA. The modified protocol was compared with a column-based extraction kit (QIAamp viral RNA mini kit, Qiagen) for quantitative performance, analytical sensitivity and precision.

RESULTS

The newly developed automated protocol was shown to be free from carry-over contamination and have comparable performance with other standard protocols and kits designed for the MagNA Pure LC instrument. However, the automated method was found to be less sensitive, less precise and led to consistently lower serum SARS-coronavirus concentrations when compared with the column-based extraction method.

CONCLUSION

As the diagnostic efficiency and prognostic value of the serum SARS-CoV RNA RT-PCR test is critically associated with the analytical sensitivity and quantitative performance contributed both by the RNA extraction and RT-PCR components of the test, we recommend the use of the column-based manual RNA extraction method.

Serum proteomic fingerprints of adult patients with severe acute respiratory syndrome

BACKGROUND

Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a new coronavirus strain, SARS-CoV. Specific proteomic patterns might be present in serum in response to the infection and could be useful for early detection of the disease.

METHODS

Using surface-enhanced laser desorption/ionization (SELDI) ProteinChip technology, we profiled and compared serum proteins of 39 patients with early-stage SARS infection and 39 non-SARS patients who were suspected cases during the SARS outbreak period. Proteomic patterns associated with SARS were identified by bioinformatic and biostatistical analyses. Features of interest were then purified and identified by tandem mass spectrometry.

RESULTS

Twenty proteomic features were significantly different between the 2 groups. Fifteen were increased in the SARS group, and 5 were decreased. Their concentrations were correlated with 2 or more clinical and/or biochemical variables. Two were correlated with the SARS-CoV viral load. Hierarchical clustering analysis showed that a majority of the SARS patients (95%) had similar serum proteomic profiles and identified 2 subgroups with poor prognosis. ROC curve analysis identified individual features as potential biomarkers for SARS diagnosis (areas under ROC curves, 0.733-0.995). ROC curve areas were largest for an N-terminal fragment of complement C3c alpha chain (m/z 28 119) and an internal fragment of fibrinogen alpha-E chain (m/z 5908). Immunoglobulin kappa light chain (m/z 24 505) positively correlated with viral load.

CONCLUSIONS

Specific proteomic fingerprints in the sera of adult SARS patients could be used to identify SARS cases early during onset with high specificity and sensitivity.

A simple and rapid approach for screening of SARS-coronavirus genotypes: an evaluation study

BACKGROUND

The Severe Acute Respiratory Syndrome (SARS) was a newly emerged infectious disease which caused a global epidemic in 2002-2003. Sequence analysis of SARS-coronavirus isolates revealed that specific genotypes predominated at different periods of the epidemic. This information can be used as a footprint for tracing the epidemiology of infections and monitor viral evolution. However, direct sequencing analysis of a large number of clinical samples is cumbersome and time consuming. We present here a simple and rapid assay for the screening of SARS-coronavirus genotypes based on the use of fluorogenic oligonucleotide probes for allelic discrimination.

METHODS

Thirty SARS patients were recruited. Allelic discrimination assays were developed based on the use of fluorogenic oligonucleotide probes (TaqMan). Genotyping of the SARS-coronavirus isolates obtained from these patients were carried out by the allelic discrimination assays and confirmed by direct sequencing.

RESULTS

Genotyping based on the allelic discrimination assays were fully concordant with direct sequencing. All of the 30 SARS-coronavirus genotypes studied were characteristic of genotypes previously documented to be associated with the latter part of the epidemic. Seven of the isolates contained a previously reported major deletion but in patients not epidemiologically related to the previously studied cohort.

CONCLUSION

We have developed a simple and accurate method for the characterization and screening of SARS-coronavirus genotypes. It is a promising tool for the study of epidemiological relationships between documented cases during an outbreak.

Absence of association between angiotensin converting enzyme polymorphism and development of adult respiratory distress syndrome in patients with severe acute respiratory syndrome: a case control study

BACKGROUND

It has been postulated that genetic predisposition may influence the susceptibility to SARS-coronavirus infection and disease outcomes. A recent study has suggested that the deletion allele (D allele) of the angiotensin converting enzyme (ACE) gene is associated with hypoxemia in SARS patients. Moreover, the ACE D allele has been shown to be more prevalent in patients suffering from adult respiratory distress syndrome (ARDS) in a previous study. Thus, we have investigated the association between ACE insertion/deletion (I/D) polymorphism and the progression to ARDS or requirement of intensive care in SARS patients.

METHOD

One hundred and forty genetically unrelated Chinese SARS patients and 326 healthy volunteers were recruited. The ACE I/D genotypes were determined by polymerase chain reaction and agarose gel electrophoresis.

RESULTS

There is no significant difference in the genotypic distributions and the allelic frequencies of the ACE I/D polymorphism between the SARS patients and the healthy control subjects. Moreover, there is also no evidence that ACE I/D polymorphism is associated with the progression to ARDS or the requirement of intensive care in the SARS patients. In multivariate logistic analysis, age is the only factor associated with the development of ARDS while age and male sex are independent factors associated with the requirement of intensive care.

CONCLUSION

The ACE I/D polymorphism is not directly related to increased susceptibility to SARS-coronavirus infection and is not associated with poor outcomes after SARS-coronavirus infection.

Fetal DNA Clearance from Maternal Plasma Is Impaired in Preeclampsia

Background: Increased fetal DNA in maternal plasma/serum has been reported in pregnancies complicated by preeclampsia. We hypothesized that impaired clearance of fetal DNA might contribute, at least in part, to the above-mentioned phenomenon.

Methods: We studied 7 preeclamptic and 10 control pregnant women. All had male fetuses. Serial blood samples were obtained from before delivery to 6 h postpartum. Male fetal DNA in maternal plasma was measured by real-time quantitative PCR for the SRY gene on the Y chromosome.

Results: The median fetal DNA concentrations before delivery were significantly higher in the preeclamptic women than in the controls (521 vs 227 genome-equivalents/mL for preeclamptic and control women, respectively; Mann–Whitney rank-sum test, P = 0.017). The median fetal DNA concentrations at 6 h after delivery were also significantly different between the two groups (208 vs 0 genome-equivalents/mL for preeclamptic and control women, respectively; Mann–Whitney rank-sum test, P = 0.002). A first-order clearance model was found to best describe the kinetics of maternal plasma fetal DNA clearance. Moreover, we observed a significant difference in the median apparent clearance half-lives of fetal DNA between the preeclamptic women (114 min) and controls (28 min; Mann–Whitney rank-sum test, P = 0.007).

Conclusions: This study represents the first documentation of impaired fetal DNA clearance from maternal plasma in preeclampsia. Such an abnormality in circulating DNA clearance may also be present in other medical conditions associated with quantitative aberrations in circulating DNA concentrations.

Stability of Endogenous and Added RNA in Blood Specimens, Serum, and Plasma

Background: Circulating RNA in plasma/serum is an emerging field for noninvasive molecular diagnosis. Because RNA is widely thought to be labile in the circulation, we investigated the stability and various preanalytical factors that may affect RNA concentrations in blood specimens.

Methods: Blood samples were collected from 65 healthy volunteers. The effects of two preanalytical variables were studied: (a) time delay in processing of EDTA blood and clotted blood after venesection, and (b) freezing and thawing of plasma and serum. The lability of free added RNA in plasma was also investigated. Plasma/serum RNA was measured by a real-time quantitative reverse transcription-PCR assay for glyceraldehyde 3-phosphate dehydrogenase mRNA, whereas DNA was measured by a real-time quantitative PCR assay for the β-globin gene.

Results: No significant difference was found for plasma RNA concentrations obtained from uncentrifuged EDTA blood that had been left at 4 °C for 0, 6, and 24 h (P =0.182). On the other hand, the serum RNA concentrations increased significantly over 24 h when uncentrifuged clotted blood was stored at 4 °C (P <0.05). In comparison, >99% of the free added RNA could no longer be amplified after incubation in plasma for 15 s. Never-frozen plasma, freeze-thawed plasma, and thawed plasma left at room temperature for 1 h showed no significant differences in RNA concentration (P =0.465). No significant difference was observed for freeze-thawed serum (P = 0.430).

Conclusions: Plasma RNA is stable in uncentrifuged EDTA blood stored at 4 °C, but to obtain a stable serum RNA concentration, uncentrifuged clotted blood should be stored at 4 °C and processed within 6 h. A single freeze/thaw cycle produces no significant effect on the RNA concentration of plasma or serum.

Presence of Filterable and Nonfilterable mRNA in the Plasma of Cancer Patients and Healthy Individuals

Background: As RNA is labile, we investigated whether circulating RNA in human plasma may be present in a particle-associated form.

Methods: Blood was collected from 27 healthy individuals and 16 hepatocellular carcinoma (HCC) patients. The plasma from each individual was processed by two means: filtration through filters with different pore sizes (from 5 μm to 0.22 μm) and ultracentrifugation. We assessed plasma RNA content by a real-time quantitative reverse transcription-PCR assay for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) transcripts and plasma DNA by a real-time quantitative PCR assay for the β-globin gene.

Results: The plasma GAPDH mRNA concentrations in the healthy individuals were significantly different in every pair of these filter sizes (P <0.05 for each pair). Overall, the plasma GAPDH mRNA concentration was higher by a median of 15-fold (interquartile range, 10- to 24-fold) in the paired unfiltered sample than in the sample filtered through a 0.22 μm filter. In contrast, no significant difference was seen in β-globin DNA concentrations among different pore-size-filtered plasma samples (P = 0.455). Similarly, a significant difference was observed for RNA, but not DNA, between unfiltered plasma and ultracentrifuged plasma (P <0.05). No significant difference in GAPDH mRNA concentrations was seen between the 0.22-μm-filtered plasma samples and the ultracentrifuged plasma samples (P >0.05). In HCC patients, filtration with a 0.22 μm filter produced a median 9.3-fold (interquartile range, 6.9- to 311-fold) reduction in GAPDH mRNA concentration in plasma. Plasma GAPDH mRNA concentrations in HCC patients were significantly higher than those in healthy individuals, both with or without filtration (P <0.0 5 for filtered plasma samples; P <0.005 for unfiltered plasma samples).

Conclusions: A substantial proportion of plasma mRNA species is particle-associated. In HCC patients, both circulating particle- and non-particle-associated plasma RNA are increased.

Plasma Nucleic Acids in the Diagnosis and Management of Malignant Disease

Background: There is a need for development of molecular markers of cancer that can be used clinically for the detection, prognostication, and monitoring of cancer. Recently, there has been much interest in the potential use of nucleic acid markers in plasma and serum for this purpose.

Approach: We reviewed published literature up to 2002 on the topic, with a particular emphasis on reports published between 1996 and 2002.

Content: The nucleic acid markers described in plasma and serum include oncogene mutations/amplifications, microsatellite alterations, and gene rearrangements. Such markers have been described in many cancer types, including lung, colon, and breast. Epigenetic alterations, such as aberrant promoter methylation, have been identified in plasma and serum. Viral nucleic acid markers, such as Epstein–Barr virus DNA in plasma and serum, are reviewed in detail with regard to their application to virus-associated cancers such as nasopharyngeal carcinoma and various lymphomas. More recently, mitochondrial DNA and tumor-related mRNAs have been identified in plasma and serum from patients with several types of tumors.

Conclusions: Circulating nucleic acids are an emerging class of molecular tumor markers. Their wide applicability and clinical relationship with the malignant state will likely grant them increasing clinical importance in the near future.

Differential DNA Methylation between Fetus and Mother as a Strategy for Detecting Fetal DNA in Maternal Plasma

Background: Fetal DNA has been detected in maternal plasma by the use of genetic differences between mother and fetus. We explore the possibility of using epigenetic markers for the specific detection of fetal DNA in maternal plasma.

Methods: A differentially methylated region in the human IGF2-H19 locus and a single-nucleotide polymorphism in this region were chosen for the study. The methylation status in this region is maintained in such a way that the paternal allele is methylated and the maternal allele is unmethylated. The single-nucleotide polymorphism was typed by direct sequencing of PCR products. The methylation status of this region was ascertained by bisulfite conversion and methylation-specific PCR. Differentially methylated fetal alleles were detected in maternal plasma by direct sequencing and a primer-extension assay.

Results: Women in the second (n = 21; 17–21 weeks) and third (n = 18; 37–42 weeks) trimesters of pregnancy were recruited. Among these 39 volunteers, the 16 who were heterozygous for the single-nucleotide polymorphism were chosen for further analysis. In 11 of these 16 cases, paternally inherited methylated fetal alleles were different from the methylated alleles of the respective mothers. Using direct sequencing, we detected paternally inherited methylated fetal DNA in 6 of 11 (55%) cases. In 8 of the 16 heterozygous cases, the fetuses possessed an unmethylated maternally inherited allele that was different from the unmethylated allele of the mother. Using a primer-extension assay, we detected fetal-derived maternally inherited alleles in maternal plasma of four of eight (50%) cases.

Conclusions: These results represent the first use of fetal epigenetic markers in noninvasive prenatal analysis. These data may also have implications for the investigation of other types of chimerism.

Increased Fetal DNA Concentrations in the Plasma of Pregnant Women Carrying Fetuses with Trisomy 21

Background: The recent discovery of the presence of circulating cell-free fetal DNA in maternal plasma opens up new prenatal diagnostic applications and provides new avenues for clinical investigation. It is of research and potential diagnostic interest to determine whether fetal trisomy 21 may be associated with quantitative abnormalities of circulating fetal DNA in maternal plasma.

Methods: Maternal plasma samples were prospectively collected from two centers situated in Hong Kong and Boston. Samples collected from Boston consisted of 7 women carrying male trisomy 21 fetuses, 19 carrying euploid male fetuses, and 13 carrying female fetuses. Samples collected from Hong Kong consisted of 6 women carrying male trisomy 21 fetuses, 18 carrying euploid male fetuses, and 10 carrying female fetuses. Male fetal DNA in maternal plasma was measured using real-time quantitative Y-chromosomal PCR.

Results: For patients recruited from Boston, the median circulating fetal DNA concentrations in women carrying trisomy 21 and euploid male fetuses were 46.0 genome-equivalents/mL and 23.3 genome-equivalents/mL, respectively (P = 0.028). For patients recruited from Hong Kong, the median circulating fetal DNA concentrations in women carrying trisomy 21 and euploid male fetuses were 48.2 genome-equivalents/mL and 16.3 genome-equivalents/mL, respectively (P = 0.026). None of the samples from women carrying female fetuses had detectable Y-chromosomal signals.

Conclusions: Abnormally high concentrations of circulating fetal DNA are found in a proportion of women carrying fetuses with trisomy 21. The robustness and reproducibility of real-time PCR analysis of maternal plasma makes it a valuable tool for cross-institutional collaboration involving centers located in different parts of the world.

Quantitative Abnormalities of Fetal DNA in Maternal Serum in Preeclampsia

Background: There is much recent interest in the biologic and diagnostic implication of cell-free non-host DNA in the plasma and serum of human subjects. To determine if quantitative abnormalities of circulating non-host DNA may be associated with certain pathologic processes, we used circulating fetal DNA in preeclampsia as a model system. Methods: We studied 20 preeclamptic women and 20 control subjects of comparable gestational age (means, 32 and 33 weeks, respectively). Male fetal DNA in maternal serum was measured using real-time quantitative PCR for the SRY gene on the Y chromosome. Results: The imprecision (CV) of the assay was 2.7%. The median circulating fetal DNA was increased fivefold in 20 preeclamptic women compared with 20 control pregnant women (381 vs 76 genome-equivalents/mL, P <0.001). Conclusions: These observations suggest that preeclampsia is associated with disturbances in the liberation and/or clearance mechanisms of circulating DNA. These results also raise the possibility that measurement of circulating DNA may prove useful as a marker for the diagnosis and/or monitoring of preeclampsia.