Impact of long-term storage of plasma and cell-free DNA on measured DNA quantity and fetal fraction.

BACKGROUND AND OBJECTIVE: Optimal sample storage conditions are essential for non-invasive prenatal testing of cell-free fetal and total DNA. We investigated the effect of long-term storage of plasma samples and extracted cfDNA using qPCR. MATERIALS AND METHODS: Fetal and total cfDNA yield and fetal fraction were calculated before and after storage of plasma for 0-6 years at -25°C. Dilution experiments were performed to investigate PCR inhibition. Extraction with or without proteinase K was used to examine protein dissociation. Storage of extracted cfDNA was investigated by testing aliquots immediately, and after 18 months and 3 years of storage at -25°C. RESULTS: We observed a marked increase in the levels of amplifiable fetal and total DNA in plasma stored for 2-3 years, and fetal fraction was slightly decreased after 3 years of storage. cfDNA detection was independent of proteinase K during DNA extraction in plasma samples stored >2 years, indicating a loss of proteins from DNA over time, which was likely to account for the observed increase in DNA yields. Measured fetal and total DNA quantities, as well as fetal fraction, increased in stored, extracted cfDNA. CONCLUSION: Fetal and total cell-free DNA is readily detectable in plasma after long-term storage at -25°C. However, substantial variation in measured DNA quantities and fetal fraction means caution may be required when using stored plasma and extracted cfDNA for test development or validation purposes.

Biology of human primitive erythroblasts for application in noninvasive prenatal diagnosis.

OBJECTIVE: Human primitive erythroblasts produced during early embryogenesis have been found in maternal circulation at early gestation and are considered good target cells for noninvasive prenatal diagnosis. We aimed to gain a better understanding of the biology of primitive erythroblasts and maximize their potential utility for noninvasive prenatal diagnosis. METHODS: Cells were obtained from first trimester human placental tissues. Biological properties including surface antigen composition, differentiation, proliferation, enucleation, and degeneration were studied as gestation progressed. A microdroplet culture system was developed to observe the behavior of these cells in vitro. RESULTS: Histology showed that primitive erythroblasts undergo maturation from polychromatic to orthochromatic erythroblasts and can differentiate spontaneously in vitro. Cell surface markers and nuclear gene expression suggest that the cells do not possess stemness properties, despite being primitive in nature. They have limited proliferative activity and highly deacetylated chromatin, but a microdroplet culture system can prolong their viability under normoxic conditions. No apoptosis was seen by 11 weeks' gestation, and there was no enucleation in vitro. CONCLUSION: These properties confirm that viable cells with intact nuclei can be obtained at very early gestation for genetic analysis.

Challenges in non-invasive prenatal screening for sub-chromosomal copy number variations using cell-free DNA.

Non-invasive prenatal screening (NIPS) has revolutionized the approach to prenatal fetal aneuploidy screening. Many commercial providers now offer analyses for sub-chromosomal copy number variations (CNVs). Here, we review the use of NIPS in the context of screening for microdeletions and microduplications, issues surrounding the choice of disorders tested for, and the advantages and disadvantages associated with the inclusion of microdeletions to current NIPS. Several studies have claimed benefits; however, we suggest that microdeletions have not demonstrated a low enough false positive rate to be deemed practical or ethically acceptable, especially considering their low positive predictive values. Because a positive NIPS result should be confirmed using diagnostic techniques, and false positive rates are as high as 90% for some microdeletions, diagnostic testing seems preferable when the goal is to maximize the detection of microdeletion or microduplication syndromes.

Synthetic combinations of missense polymorphic genetic changes underlying Down syndrome susceptibility.

Single nucleotide polymorphisms (SNPs) are important biomolecular markers in health and disease. Down syndrome, or Trisomy 21, is the most frequently occurring chromosomal abnormality in live-born children. Here, we highlight associations between SNPs in several important enzymes involved in the one-carbon folate metabolic pathway and the elevated maternal risk of having a child with Down syndrome. Our survey highlights that the combination of SNPs may be a more reliable predictor of the Down syndrome phenotype than single SNPs alone. We also describe recent links between SNPs in p53 and its related pathway proteins and Down syndrome, as well as highlight several proteins that help to associate apoptosis and p53 signaling with the Down syndrome phenotype. In addition to a comprehensive review of the literature, we also demonstrate that several SNPs reside within the same regions as these Down syndrome-linked SNPs, and propose that these closely located nucleotide changes may provide new candidates for future exploration.

Non-invasive prenatal diagnosis of achondroplasia and thanatophoric dysplasia: next-generation sequencing allows for a safer, more accurate, and comprehensive approach.

OBJECTIVE: Accurate prenatal diagnosis of genetic conditions can be challenging and usually requires invasive testing. Here, we demonstrate the potential of next-generation sequencing (NGS) for the analysis of cell-free DNA in maternal blood to transform prenatal diagnosis of monogenic disorders. METHODS: Analysis of cell-free DNA using a PCR and restriction enzyme digest (PCR-RED) was compared with a novel NGS assay in pregnancies at risk of achondroplasia and thanatophoric dysplasia. RESULTS: PCR-RED was performed in 72 cases and was correct in 88.6%, inconclusive in 7% with one false negative. NGS was performed in 47 cases and was accurate in 96.2% with no inconclusives. Both approaches were used in 27 cases, with NGS giving the correct result in the two cases inconclusive with PCR-RED. CONCLUSION: NGS provides an accurate, flexible approach to non-invasive prenatal diagnosis of de novo and paternally inherited mutations. It is more sensitive than PCR-RED and is ideal when screening a gene with multiple potential pathogenic mutations. These findings highlight the value of NGS in the development of non-invasive prenatal diagnosis for other monogenic disorders.

Non-invasive prenatal diagnostic testing for ß-thalassaemia using cell-free fetal DNA and next generation sequencing.

OBJECTIVE: To develop an accurate non-invasive prenatal test using next generation sequencing (NGS) for HbE and the four most common ß-thalassaemia mutations found in South East Asia (namely -28A > G, CD17A > T, CD41/42(-TTCT) and IVS-II-654C > T). METHODS: Cell-free DNA was extracted from maternal plasma from 83 families where both parents were carriers of the HbE mutation or one of four common ß-thalassaemia mutations. Overlapping PCR amplicons covering each mutation were generated, pooled and sequenced using the Illumina MiSeq. Fastq files were analysed to detect inheritance of the paternal mutation. RESULTS: In two cases where the fathers were compound heterozygotes for HbE and -28A > G, the fetus was correctly diagnosed as having inherited one of the paternal mutations. In 35/85 cases, the paternal mutation was not detected, and in 50/85 cases, it was classified as inherited. Overall sensitivity for detection of paternal mutations was 100% (95% CI: 92.4-100%), and specificity was 92.1% (95% CI: 79.2-97.3%). CONCLUSION: We demonstrated that detection of paternal mutations using NGS can be readily achieved with high sensitivity and specificity, removing the need for an invasive test in 50% of pregnancies at risk of a thalassaemia in cases where the father and mother carry a different mutation. © 2014 John Wiley & Sons, Ltd.

Detection of aneuploidy from single fetal nucleated red blood cells using whole genome sequencing.

OBJECTIVE: The objective of the study was to detect aneuploidy in single fetal nucleated red blood cells (FNRBCs) from placental villi using whole genome amplification (WGA) and next generation sequencing. METHODS: Three single FNRBCs per sample were manually picked from villi collected from ten women undergoing elective first-trimester termination of pregnancy, and one or two cells were picked from each of four aneuploid chorionic villus samples. Following WGA and addition of adaptor and index sequences, samples were sequenced on the Illumina MiSeq. Leading and trailing 15 bases were trimmed, and reads were aligned to the human reference genome. Z-scores were calculated to determine deviation of the mean of the test from reference samples, with a score of 3 used as the threshold for classification of a particular chromosome as trisomic. RESULTS: We successfully made correct diagnoses from ten single cells isolated from villi from two cases of trisomy 21 (one case from a single cell and one from two cells), two cases of trisomy 18 (two cells each), and a case of trisomy 15 (three cells). CONCLUSION: With their faithful representation of fetal genome, diagnosis using single FNRBCs provides a definitive result compared with non-invasive prenatal testing using cell-free fetal DNA, and is a safer alternative to invasive amniocentesis.

Stability of cell-free DNA from maternal plasma isolated following a single centrifugation step.

OBJECTIVE: Cell-free fetal DNA can be used for prenatal testing with no procedure-related risk to the fetus. However, yield of fetal DNA is low compared with maternal cell-free DNA fragments, resulting in technical challenges for some downstream applications. To maximize the fetal fraction, careful blood processing procedures are essential. We demonstrate that fetal fraction can be preserved using a single centrifugation step followed by postage of plasma to the laboratory for further processing. METHODS: Digital PCR was used to quantify copies of total, maternal, and fetal DNA present in single-spun plasma at time points over a two-week period, compared with immediately processed double-spun plasma, with storage at room temperature, 4°C, and -80°C representing different postage scenarios. RESULTS: There was no significant change in total, maternal, or fetal DNA copy numbers when single-spun plasma samples were stored for up to 1 week at room temperature and 2 weeks at -80°C compared with plasma processed within 4 h. Following storage at 4°C no change in composition of cell-free DNA was observed. CONCLUSIONS: Single-spun plasma can be transported at room temperature if the journey is expected to take one week or less; shipping on dry ice is preferable for longer journeys.

Safe, accurate, prenatal diagnosis of thanatophoric dysplasia using ultrasound and free fetal DNA.

OBJECTIVE: To improve the prenatal diagnosis of thanatophoric dysplasia by defining the change in fetal size across gestation and the frequency of sonographic features, and developing non-invasive molecular genetic diagnosis based on cell-free fetal DNA (cffDNA) in maternal plasma. METHODS: Fetuses with a confirmed diagnosis of thanatophoric dysplasia were ascertained, records reviewed, sonographic features and measurements determined. Charts of fetal size were then constructed using the LMS (lambda-mu-sigma) method and compared with charts used in normal pregnancies and those complicated by achondroplasia. Cases in this cohort referred to our Regional Genetics Laboratory for molecular diagnosis using cffDNA were identified and results reviewed. RESULTS: Forty-two cases were scanned in our units. Commonly reported sonographic features were very short and sometimes bowed femora, frontal bossing, cloverleaf skull, short fingers, a small chest and polyhydramnios. Limb shortening was obvious from as early as 13 weeks' gestation, with minimal growth after 20 weeks. Analysis of cffDNA in three of these pregnancies confirmed the presence of the c.742C>CT (p.Arg248Cys) or the c.1948A>AG (p.Lys650Glu) mutation in the fibroblast growth factor receptor 3 gene. CONCLUSION: These data should improve the accuracy of the sonographic diagnosis of thanatophoric dysplasia and have implications for reliable and safe targeted molecular confirmation using cffDNA.

Digital PCR analysis of maternal plasma for noninvasive detection of sickle cell anemia.

BACKGROUND: Cell-free fetal DNA (cffDNA) constitutes approximately 10% of the cell-free DNA in maternal plasma and is a suitable source of fetal genetic material for noninvasive prenatal diagnosis (NIPD). The objective of this study was to determine the feasibility of using digital PCR for NIPD in pregnancies at risk of sickle cell anemia. METHODS: Minor-groove binder (MGB) TaqMan probes were designed to discriminate between wild-type hemoglobin A and mutant (hemoglobin S) alleles encoded by the HBB (hemoglobin, beta) gene in cffDNA isolated from maternal plasma samples obtained from pregnancies at risk of sickle cell anemia. The fractional fetal DNA concentration was assessed in male-bearing pregnancies with a digital PCR assay for the Y chromosome-specific marker DYS14. In pregnancies with a female fetus, a panel of biallelic insertion/deletion polymorphism (indel) markers was developed for the quantification of the fetal DNA fraction. We used digital real-time PCR to analyze the dosage of the variant encoding hemoglobin S relative to that encoding wild-type hemoglobin A. RESULTS: The sickle cell genotype was correctly determined in 82% (37 of 45) of male fetuses and 75% (15 of 20) of female fetuses. Mutation status was determined correctly in 100% of the cases (25 samples) with fractional fetal DNA concentrations >7%. The panel of indels was informative in 65% of the female-bearing pregnancies. CONCLUSIONS: Digital PCR can be used to determine the genotype of fetuses at risk for sickle cell anemia. Optimization of the fractional fetal DNA concentration is essential. More-informative indel markers are needed for this assay's comprehensive use in cases of a female fetus.

Whole-Chromosome Karyotyping of Fetal Nucleated Red Blood Cells Using the Ion Proton Sequencing Platform.

The current gold standard for the definitive diagnosis of fetal aneuploidy uses either chorionic villus sampling (CVS) or amniocentesis, both of which are which are invasive procedures carrying a procedure-related risk of miscarriage of up to 0.1-0.2%. Non-invasive prenatal diagnosis using fetal nucleated red blood cells (FNRBCs) isolated from maternal peripheral venous blood would remove this risk of miscarriage since these cells can be isolated from the mother's blood. We aimed to detect whole-chromosome aneuploidies from single nucleated fetal red blood cells using whole-genome amplification followed by massively parallel sequencing performed on a semiconductor sequencing platform. Twenty-six single cells were picked from the placental villi of twelve patients thought to have a normal fetal genotype and who were undergoing elective first-trimester surgical termination of pregnancy. Following karyotyping, it was subsequently found that two of these cases were also abnormal (one trisomy 15 and one mosaic genotype). One single cell from chorionic villus samples for two patients carrying a fetus with trisomy 21 and two single cells from women carrying fetuses with T18 were also picked. Pooled libraries were sequenced on the Ion Proton and data were analysed using Ion Reporter software. We correctly classified fetal genotype in all 24 normal cells, as well as the 2 T21 cells, the 2 T18 cells, and the two T15 cells. The two cells picked from the fetus with a mosaic result by CVS were classified as unaffected, suggesting that this was a case of confined placental mosaicism. Fetal sex was correctly assigned in all cases. We demonstrated that semiconductor sequencing using commercially available software for data analysis can be achieved for the non-invasive prenatal diagnosis of whole-chromosome aneuploidy with 100% accuracy.

Human Wharton's Jelly Mesenchymal Stem Cells Show Unique Gene Expression Compared with Bone Marrow Mesenchymal Stem Cells Using Single-Cell RNA-Sequencing.

Human Wharton's jelly stem cells (hWJSCs) isolated from the human umbilical cord are a unique population of mesenchymal stem cells (MSCs) with significant clinical utility. Their broad differentiation potential, high rate of proliferation, ready availability from discarded cords, and prolonged maintenance of stemness properties in culture make them an attractive alternative source of MSCs with therapeutic value compared with human bone marrow MSCs (hBMMSCs). We aimed to characterize the differences in gene expression profiles between these two stem cell types using single-cell RNA sequencing (scRNA-Seq) to determine which pathways are involved in conferring hWJSCs with their unique properties. We identified 436 significantly differentially expressed genes between the two cell types, playing roles in processes, including immunomodulation, angiogenesis, wound healing, apoptosis, antitumor activity, and chemotaxis. Expression of immune molecules is particularly high in hWJSCs compared with hBMMSCs. These differences in gene expression may help to explain many of the advantages that hWJSCs have over hBMMSCs for clinical application. Although cell surface protein marker expression indicates that isolated hWJSCs and hBMMSCs are both homogenous populations, using scRNA-Seq we can clearly identify extreme variability in expression levels between individual cells within a certain cell type. If the cells are examined as bulk populations, it is not possible to appreciate that a single cell may be making a major unique contribution to the apparent overall expression level. We demonstrated how the fine tuning of expression within hWJSCs and hBMMSCs may be achieved by expression of molecules with opposing function between two cells. We hypothesize that a greater understanding of these differences in gene expression between the two cell types may aid in the development of new therapies using hWJSCs.

Thalassaemia screening and confirmation of carriers in parents.

Haemoglobinopathies are among the most common inherited monogenic disorders worldwide. Thalassaemia screening for carrier status is recommended for adults of reproductive age if suspected of being at risk. Conventional laboratory methods for screening include the assessment of haematological indices, and high-performance liquid chromatography, capillary electrophoresis or isoelectric focusing to measure the levels of HbA2 and HbF, and to identify haemoglobin variants. Each screening method has its advantages and disadvantages, the main disadvantage being that none can fully resolve all variants. The complex nature of the genetics of haemoglobinopathies necessitates expertise in the interpretation of screening results to evaluate the most likely genotypes, which must then be confirmed using the DNA diagnosis. This review highlights the limits and pitfalls of each screening technique, and outlines a rational combination of different methods to overcome issues in thalassaemia carrier detection.

Measurement of fetal fraction in cell-free DNA from maternal plasma using a panel of insertion/deletion polymorphisms.

OBJECTIVE: Cell-free DNA from maternal plasma can be used for non-invasive prenatal testing for aneuploidies and single gene disorders, and also has applications as a biomarker for monitoring high-risk pregnancies, such as those at risk of pre-eclampsia. On average, the fractional cell-free fetal DNA concentration in plasma is approximately 15%, but can vary from less than 4% to greater than 30%. Although quantification of cell-free fetal DNA is straightforward in the case of a male fetus, there is no universal fetal marker; in a female fetus measurement is more challenging. We have developed a panel of multiplexed insertion/deletion polymorphisms that can measure fetal fraction in all pregnancies in a simple, targeted sequencing reaction. METHODS: A multiplex panel of primers was designed for 35 indels plus a ZFX/ZFY amplicon. cfDNA was extracted from plasma from 157 pregnant women, and maternal genomic DNA was extracted for 20 of these samples for panel validation. Sixty-one samples from pregnancies with a male fetus were subjected to whole genome sequencing on the Ion Proton sequencing platform, and fetal fraction derived from Y chromosome counts was compared to fetal fraction measured using the indel panel. A total of 157 cell-free DNA samples were sequenced using the indel panel, and informativity was assessed, along with the proportion of fetal DNA. RESULTS: Using gDNA we optimised the indel panel, removing amplicons giving rise to PCR bias. Good correlation was found between fetal fraction using indels and using whole genome sequencing of the Y chromosome (Spearmans r = 0.69). A median of 12 indels were informative per sample. The indel panel was informative in 157/157 cases (mean fetal fraction 14.4% (±0.58%)). CONCLUSIONS: Using our targeted next generation sequencing panel we can readily assess the fetal DNA percentage in male and female pregnancies.

Preferences for prenatal tests for Down syndrome: an international comparison of the views of pregnant women and health professionals.

Non-invasive prenatal testing is increasingly available worldwide and stakeholder viewpoints are essential to guide implementation. Here we compare the preferences of women and health professionals from nine different countries towards attributes of non-invasive and invasive prenatal tests for Down syndrome. A discrete choice experiment was used to obtain participants' stated preference for prenatal tests that varied according to four attributes: accuracy, time of test, risk of miscarriage, and type of information. Pregnant women and health professionals were recruited from Canada, Denmark, Iceland, Israel, Italy, the Netherlands, Portugal, Singapore, and the United Kingdom. A total of 2666 women's and 1245 health professionals' questionnaires were included in the analysis. Differences in preferences were seen between women and health professionals within and between countries. Overall, women placed greater emphasis on test safety and comprehensive information than health professionals, who emphasised accuracy and early testing. Differences between women's and health professionals' preferences are marked between countries. Varied approaches to implementation and service delivery are therefore needed and individual countries should develop guidelines appropriate for their own social and screening contexts.

Developing noninvasive diagnosis for single-gene disorders: the role of digital PCR.

Cell-free fetal DNA constitutes approximately 10 % of the cell-free DNA found in maternal plasma and can be used as a reliable source of fetal genetic material for noninvasive prenatal diagnosis (NIPD) from early pregnancy. The relatively high levels of maternal background can make detection of paternally inherited point mutations challenging. Diagnosis of inheritance of autosomal recessive disorders using qPCR is even more challenging due to the high background of mutant maternal allele. Digital PCR is a very sensitive modified method of quantitative real-time PCR (qPCR), allowing absolute quantitation and rare allele detection without the need for standards or normalization. Samples are diluted and then partitioned into a large number of small qPCR reactions, some of which contain the target molecule and some which do not; the proportion of positive reactions can be used to calculate the concentration of targets in the initial sample. Here we discuss the use of digital PCR as an accurate approach to NIPD for single-gene disorders.

Uses of cell free fetal DNA in maternal circulation.

For over a decade, researchers have focused their attention on the development of non-invasive prenatal diagnosis tests based on cell-free fetal DNA circulating in maternal blood. With the possibility of earlier and safer testing, non-invasive prenatal diagnosis has the potential to bring many positive benefits to prenatal diagnosis. Non-invasive prenatal diagnosis for fetal sex determination for women who are carriers of sex-linked conditions is now firmly established in clinical practice. Other non-invasive prenatal diagnosis-based tests are set to follow, as future applications, such as the detection of single-gene disorders and chromosomal abnormalities, are now well within reach. Here, we review recent developments in non-invasive prenatal diagnosis for genetic conditions and chromosomal abnormalities, and provide an overview of research into ethical concerns, social issues and stakeholder view points.

Implementing prenatal diagnosis based on cell-free fetal DNA: accurate identification of factors affecting fetal DNA yield.

OBJECTIVE: Cell-free fetal DNA is a source of fetal genetic material that can be used for non-invasive prenatal diagnosis. Usually constituting less than 10% of the total cell free DNA in maternal plasma, the majority is maternal in origin. Optimizing conditions for maximizing yield of cell-free fetal DNA will be crucial for effective implementation of testing. We explore factors influencing yield of fetal DNA from maternal blood samples, including assessment of collection tubes containing cell-stabilizing agents, storage temperature, interval to sample processing and DNA extraction method used. METHODS: Microfluidic digital PCR was performed to precisely quantify male (fetal) DNA, total DNA and long DNA fragments (indicative of maternal cellular DNA). Real-time qPCR was used to assay for the presence of male SRY signal in samples. RESULTS: Total cell-free DNA quantity increased significantly with time in samples stored in K(3)EDTA tubes, but only minimally in cell stabilizing tubes. This increase was solely due to the presence of additional long fragment DNA, with no change in quantity of fetal or short DNA, resulting in a significant decrease in proportion of cell-free fetal DNA over time. Storage at 4 °C did not prevent these changes. CONCLUSION: When samples can be processed within eight hours of blood draw, K(3)EDTA tubes can be used. Prolonged transfer times in K(3)EDTA tubes should be avoided as the proportion of fetal DNA present decreases significantly; in these situations the use of cell stabilising tubes is preferable. The DNA extraction kit used may influence success rate of diagnostic tests.

Great vessel development requires biallelic expression of Chd7 and Tbx1 in pharyngeal ectoderm in mice.

Aortic arch artery patterning defects account for approximately 20% of congenital cardiovascular malformations and are observed frequently in velocardiofacial syndrome (VCFS). In the current study, we screened for chromosome rearrangements in patients suspected of VCFS, but who lacked a 22q11 deletion or TBX1 mutation. One individual displayed hemizygous CHD7, which encodes a chromodomain protein. CHD7 haploinsufficiency is the major cause of coloboma, heart defect, atresia choanae, retarded growth and development, genital hypoplasia, and ear anomalies/deafness (CHARGE) syndrome, but this patient lacked the major diagnostic features of coloboma and choanal atresia. Because a subset of CHARGE cases also display 22q11 deletions, we explored the embryological relationship between CHARGE and VCSF using mouse models. The hallmark of Tbx1 haploinsufficiency is hypo/aplasia of the fourth pharyngeal arch artery (PAA) at E10.5. Identical malformations were observed in Chd7 heterozygotes, with resulting aortic arch interruption at later stages. Other than Tbx1, Chd7 is the only gene reported to affect fourth PAA development by haploinsufficiency. Moreover, Tbx1+/-;Chd7+/- double heterozygotes demonstrated a synergistic interaction during fourth PAA, thymus, and ear morphogenesis. We could not rescue PAA morphogenesis by restoring neural crest Chd7 expression. Rather, biallelic expression of Chd7 and Tbx1 in the pharyngeal ectoderm was required for normal PAA development.