Size-based molecular diagnostics using plasma DNA for noninvasive prenatal testing.

Noninvasive prenatal testing using fetal DNA in maternal plasma is an actively researched area. The current generation of tests using massively parallel sequencing is based on counting plasma DNA sequences originating from different genomic regions. In this study, we explored a different approach that is based on the use of DNA fragment size as a diagnostic parameter. This approach is dependent on the fact that circulating fetal DNA molecules are generally shorter than the corresponding maternal DNA molecules. First, we performed plasma DNA size analysis using paired-end massively parallel sequencing and microchip-based capillary electrophoresis. We demonstrated that the fetal DNA fraction in maternal plasma could be deduced from the overall size distribution of maternal plasma DNA. The fetal DNA fraction is a critical parameter affecting the accuracy of noninvasive prenatal testing using maternal plasma DNA. Second, we showed that fetal chromosomal aneuploidy could be detected by observing an aberrant proportion of short fragments from an aneuploid chromosome in the paired-end sequencing data. Using this approach, we detected fetal trisomy 21 and trisomy 18 with 100% sensitivity (T21: 36/36; T18: 27/27) and 100% specificity (non-T21: 88/88; non-T18: 97/97). For trisomy 13, the sensitivity and specificity were 95.2% (20/21) and 99% (102/103), respectively. For monosomy X, the sensitivity and specificity were both 100% (10/10 and 8/8). Thus, this study establishes the principle of size-based molecular diagnostics using plasma DNA. This approach has potential applications beyond noninvasive prenatal testing to areas such as oncology and transplantation monitoring.

Cancer genome scanning in plasma: detection of tumor-associated copy number aberrations, single-nucleotide variants, and tumoral heterogeneity by massively parallel sequencing.

BACKGROUND: Tumor-derived DNA can be found in the plasma of cancer patients. In this study, we explored the use of shotgun massively parallel sequencing (MPS) of plasma DNA from cancer patients to scan a cancer genome noninvasively. METHODS: Four hepatocellular carcinoma patients and a patient with synchronous breast and ovarian cancers were recruited. DNA was extracted from the tumor tissues, and the preoperative and postoperative plasma samples of these patients were analyzed with shotgun MPS. RESULTS: We achieved the genomewide profiling of copy number aberrations and point mutations in the plasma of the cancer patients. By detecting and quantifying the genomewide aggregated allelic loss and point mutations, we determined the fractional concentrations of tumor-derived DNA in plasma and correlated these values with tumor size and surgical treatment. We also demonstrated the potential utility of this approach for the analysis of complex oncologic scenarios by studying the patient with 2 synchronous cancers. Through the use of multiregional sequencing of tumoral tissues and shotgun sequencing of plasma DNA, we have shown that plasma DNA sequencing is a valuable approach for studying tumoral heterogeneity. CONCLUSIONS: Shotgun DNA sequencing of plasma is a potentially powerful tool for cancer detection, monitoring, and research.

FetalQuant: deducing fractional fetal DNA concentration from massively parallel sequencing of DNA in maternal plasma.

MOTIVATION: The fractional fetal DNA concentration is one of the critical parameters for non-invasive prenatal diagnosis based on the analysis of DNA in maternal plasma. Massively parallel sequencing (MPS) of DNA in maternal plasma has been demonstrated to be a powerful tool for the non-invasive prenatal diagnosis of fetal chromosomal aneuploidies. With the rapid advance of MPS technologies, the sequencing cost per base is dramatically reducing, especially when using targeted MPS. Even though several approaches have been developed for deducing the fractional fetal DNA concentration, none of them can be used to deduce the fractional fetal DNA concentration directly from the sequencing data without prior genotype information. RESULT: In this study, we implement a statistical mixture model, named FetalQuant, which utilizes the maximum likelihood to estimate the fractional fetal DNA concentration directly from targeted MPS of DNA in maternal plasma. This method allows the improved deduction of the fractional fetal DNA concentration, obviating the need of genotype information without loss of accuracy. Furthermore, by using Bayes' rule, this method can distinguish the informative single-nucleotide polymorphism loci where the mother is homozygous and the fetus is heterozygous. We believe that FetalQuant can help expand the spectrum of diagnostic applications using MPS on DNA in maternal plasma. AVAILABILITY: Software and simulation data are available at http://sourceforge.net/projects/fetalquant/. CONTACT: haosun@cuhk.edu.hk. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Nonhematopoietically derived DNA is shorter than hematopoietically derived DNA in plasma: a transplantation model.

BACKGROUND: Plasma DNA is predominantly hematopoietic in origin. The size difference between maternal- and fetal-derived DNA in maternal plasma prompted us to investigate whether there was any discrepancy in molecular size between hematopoietically and nonhematopoietically derived DNA in plasma. METHODS: Plasma DNA samples from 6 hematopoietic stem cell transplant recipients and 1 liver transplant recipient were analyzed by massively parallel paired-end sequencing. The size of each fragment was deduced from the alignment positions of the paired reads. In sex-mismatched transplant recipients, the reads from chromosome Y were used as markers for the male donor/recipient. For other transplant recipients, the reads of the donor- and recipient-specific alleles were identified from the single-nucleotide polymorphism genotypes. RESULTS: In male patients receiving female hematopoietic stem cells, more chromosome Y-derived DNA molecules (nonhematopoietically derived) were ≤150 bp than the autosome-derived ones (mainly hematopoietically derived) (median difference, 9.9%). In other hematopoietic stem cell transplant recipients, more recipient-specific DNA molecules (nonhematopoietically derived) were ≤150 bp than the donor-specific ones (hematopoietically derived) (median difference, 14.8%). In the liver transplant recipient, more donor-derived DNA molecules (liver derived) were ≤150 bp than the recipient-derived ones (mainly hematopoietically derived) (difference, 13.4%). The nonhematopoietically derived DNA exhibited a reduction in a 166-bp peak compared with the hematopoietically derived DNA. A 10-bp periodicity in size distribution below approximately 143 bp was observed in both DNA populations. CONCLUSIONS: Massively parallel sequencing is a powerful tool for studying posttransplantation chimerism. Plasma DNA molecules exhibit a distinct fragmentation pattern, with the nonhematopoietically derived molecules being shorter than the hematopoietically derived ones.

Noninvasive prenatal diagnosis of fetal trisomy 18 and trisomy 13 by maternal plasma DNA sequencing.

Massively parallel sequencing of DNA molecules in the plasma of pregnant women has been shown to allow accurate and noninvasive prenatal detection of fetal trisomy 21. However, whether the sequencing approach is as accurate for the noninvasive prenatal diagnosis of trisomy 13 and 18 is unclear due to the lack of data from a large sample set. We studied 392 pregnancies, among which 25 involved a trisomy 13 fetus and 37 involved a trisomy 18 fetus, by massively parallel sequencing. By using our previously reported standard z-score approach, we demonstrated that this approach could identify 36.0% and 73.0% of trisomy 13 and 18 at specificities of 92.4% and 97.2%, respectively. We aimed to improve the detection of trisomy 13 and 18 by using a non-repeat-masked reference human genome instead of a repeat-masked one to increase the number of aligned sequence reads for each sample. We then applied a bioinformatics approach to correct GC content bias in the sequencing data. With these measures, we detected all (25 out of 25) trisomy 13 fetuses at a specificity of 98.9% (261 out of 264 non-trisomy 13 cases), and 91.9% (34 out of 37) of the trisomy 18 fetuses at 98.0% specificity (247 out of 252 non-trisomy 18 cases). These data indicate that with appropriate bioinformatics analysis, noninvasive prenatal diagnosis of trisomy 13 and trisomy 18 by maternal plasma DNA sequencing is achievable.

SFRS7-mediated splicing of tau exon 10 is directly regulated by STOX1A in glial cells.

BACKGROUND: In this study, we performed a genome-wide search for effector genes bound by STOX1A, a winged helix transcription factor recently demonstrated to be involved in late onset Alzheimer's disease and affecting the amyloid processing pathway. METHODOLOGY/PRINCIPAL FINDINGS: Our results show that out of 218 genes bound by STOX1A as identified by chromatin-immunoprecipitation followed by sequencing (ChIP-Seq), the serine/arginine-rich splicing factor 7 (SFRS7) was found to be induced, both at the mRNA and protein levels, by STOX1A after stable transfection in glial cells. The increase in SFRS7 was followed by an increase in the 4R/3R ratios of the microtubule-associated protein tau (MAPT) by differential exon 10 splicing. Secondly, STOX1A also induced expression of total tau both at the mRNA and protein levels. Upregulation of total tau expression (SFRS7-independent) and tau exon 10 splicing (SFRS7-dependent), as shown in this study to be both affected by STOX1A, is known to have implications in neurodegeneration. CONCLUSIONS: Our data further supports the functional importance and central role of STOX1A in neurodegeneration.

Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: large scale validity study.

OBJECTIVES: To validate the clinical efficacy and practical feasibility of massively parallel maternal plasma DNA sequencing to screen for fetal trisomy 21 among high risk pregnancies clinically indicated for amniocentesis or chorionic villus sampling. DESIGN: Diagnostic accuracy validated against full karyotyping, using prospectively collected or archived maternal plasma samples. SETTING: Prenatal diagnostic units in Hong Kong, United Kingdom, and the Netherlands. PARTICIPANTS: 753 pregnant women at high risk for fetal trisomy 21 who underwent definitive diagnosis by full karyotyping, of whom 86 had a fetus with trisomy 21. Intervention Multiplexed massively parallel sequencing of DNA molecules in maternal plasma according to two protocols with different levels of sample throughput: 2-plex and 8-plex sequencing. MAIN OUTCOME MEASURES: Proportion of DNA molecules that originated from chromosome 21. A trisomy 21 fetus was diagnosed when the z score for the proportion of chromosome 21 DNA molecules was >3. Diagnostic sensitivity, specificity, positive predictive value, and negative predictive value were calculated for trisomy 21 detection. RESULTS: Results were available from 753 pregnancies with the 8-plex sequencing protocol and from 314 pregnancies with the 2-plex protocol. The performance of the 2-plex protocol was superior to that of the 8-plex protocol. With the 2-plex protocol, trisomy 21 fetuses were detected at 100% sensitivity and 97.9% specificity, which resulted in a positive predictive value of 96.6% and negative predictive value of 100%. The 8-plex protocol detected 79.1% of the trisomy 21 fetuses and 98.9% specificity, giving a positive predictive value of 91.9% and negative predictive value of 96.9%. CONCLUSION: Multiplexed maternal plasma DNA sequencing analysis could be used to rule out fetal trisomy 21 among high risk pregnancies. If referrals for amniocentesis or chorionic villus sampling were based on the sequencing test results, about 98% of the invasive diagnostic procedures could be avoided.

Targeted massively parallel sequencing of maternal plasma DNA permits efficient and unbiased detection of fetal alleles.

BACKGROUND: Massively parallel sequencing has recently been used in noninvasive prenatal diagnosis. The current costs of this technology are still relatively expensive, however, and sample throughput is still relatively low when it is used as a molecular diagnostic tool. Rather than nonselectively sequencing the genome, target enrichment provides a logical approach for more efficient and cost-effective massively parallel sequencing because it increases the proportion of informative data from the targeted region(s). Existing applications of targeted sequencing have mainly been qualitative analyses of genomic DNA. In this study, we investigated its applicability in enriching selected genomic regions from plasma DNA and the quantitative performance of this approach. METHODS: DNA was extracted from plasma samples collected from 12 pregnant women carrying female fetuses. The SureSelect Target Enrichment System (Agilent Technologies) was used to enrich for exons on chromosome X. Plasma DNA libraries with and without target enrichment were analyzed by massively parallel sequencing. Genomic DNA samples of the mother and fetus for each case were genotyped by microarray. RESULTS: For the regions targeted by the enrichment kit, the mean sequence coverage of the enriched samples was 213-fold higher than that of the nonenriched samples. Maternal and fetal DNA molecules were enriched evenly. After target enrichment, the coverage of fetus-specific alleles within the targeted region increased from 3.5% to 95.9%. CONCLUSIONS: Targeted sequencing of maternal plasma DNA permits efficient and unbiased detection of fetal alleles at genomic regions of interest and is a powerful method for measuring the proportion of fetal DNA in a maternal plasma sample.