Feasibility Study for a Microchip-Based Approach for Noninvasive Prenatal Diagnosis of Genetic Diseases

Non-invasive prenatal diagnostic test accuracy for fetal sex using cell-free DNA a review and meta-analysis

Background

Cell-free fetal DNA (cffDNA) can be detected in maternal blood during pregnancy, opening the possibility of early non-invasive prenatal diagnosis for a variety of genetic conditions. Since 1997, many studies have examined the accuracy of prenatal fetal sex determination using cffDNA, particularly for pregnancies at risk of an X-linked condition. Here we report a review and meta-analysis of the published literature to evaluate the use of cffDNA for prenatal determination (diagnosis) of fetal sex. We applied a sensitive search of multiple bibliographic databases including PubMed (MEDLINE), EMBASE, the Cochrane library and Web of Science.

Results

Ninety studies, incorporating 9,965 pregnancies and 10,587 fetal sex results met our inclusion criteria. Overall mean sensitivity was 96.6% (95% credible interval 95.2% to 97.7%) and mean specificity was 98.9% (95% CI = 98.1% to 99.4%). These results vary very little with trimester or week of testing, indicating that the performance of the test is reliably high.

Conclusions

Based on this review and meta-analysis we conclude that fetal sex can be determined with a high level of accuracy by analyzing cffDNA. Using cffDNA in prenatal diagnosis to replace or complement existing invasive methods can remove or reduce the risk of miscarriage. Future work should concentrate on the economic and ethical considerations of implementing an early non-invasive test for fetal sex.

Noninvasive fetal sex determination using cell-free fetal DNA: a systematic review and meta-analysis

CONTEXT

Noninvasive prenatal determination of fetal sex using cell-free fetal DNA provides an alternative to invasive techniques for some heritable disorders. In some countries this testing has transitioned to clinical care, despite the absence of a formal assessment of performance.

OBJECTIVE

To document overall test performance of noninvasive fetal sex determination using cell-free fetal DNA and to identify variables that affect performance.

DATA SOURCES

Systematic review and meta-analysis with search of PubMed (January 1, 1997-April 17, 2011) to identify English-language human studies reporting primary data. References from review articles were also searched.

STUDY SELECTION AND DATA EXTRACTION

Abstracts were read independently to identify studies reporting primary data suitable for analysis. Covariates included publication year, sample type, DNA amplification methodology, Y chromosome sequence, and gestational age. Data were independently extracted by 2 reviewers.

RESULTS

From 57 selected studies, 80 data sets (representing 3524 male-bearing pregnancies and 3017 female-bearing pregnancies) were analyzed. Overall performance of the test to detect Y chromosome sequences had the following characteristics: sensitivity, 95.4% (95% confidence interval [CI], 94.7%-96.1%) and specificity, 98.6% (95% CI, 98.1%-99.0%); diagnostic odds ratio (OR), 885; positive predictive value, 98.8%; negative predictive value, 94.8%; area under curve (AUC), 0.993 (95% CI, 0.989-0.995), with significant interstudy heterogeneity. DNA methodology and gestational age had the largest effects on test performance. Methodology test characteristics were AUC, 0.988 (95% CI, 0.979-0.993) for polymerase chain reaction (PCR) and AUC, 0.996 (95% CI, 0.993-0.998) for real-time quantitative PCR (RTQ-PCR) (P = .02). Gestational age test characteristics were AUC, 0.989 (95% CI, 0.965-0.998) (<7 weeks); AUC, 0.994 (95% CI, 0.987-0.997) (7-12 weeks); AUC, 0.992 (95% CI, 0.983-0.996) (13-20 weeks); and AUC, 0.998 (95% CI, 0.990-0.999) (>20 weeks) (P = .02 for comparison of diagnostic ORs across age ranges). RTQ-PCR (sensitivity, 96.0%; specificity, 99.0%) outperformed conventional PCR (sensitivity, 94.0%; specificity, 97.3%). Testing after 20 weeks (sensitivity, 99.0%; specificity, 99.6%) outperformed testing prior to 7 weeks (sensitivity, 74.5%; specificity, 99.1%), testing at 7 through 12 weeks (sensitivity, 94.8%; specificity, 98.9%), and 13 through 20 weeks (sensitivity, 95.5%; specificity, 99.1%).

CONCLUSIONS

Despite interstudy variability, performance was high using maternal blood. Sensitivity and specificity for detection of Y chromosome sequences was greatest using RTQ-PCR after 20 weeks' gestation. Tests using urine and tests performed before 7 weeks' gestation were unreliable.

Prenatal Diagnosis of β-Thalassemias and Hemoglobinopathies

Prenatal diagnosis of β-thalassemia was accomplished for the first time in the 1970s by globin chain synthesis analysis on fetal blood obtained by placental aspiration at 18-22 weeks gestation. Since then, the molecular definition of the β-globin gene pathology, the development of procedures of DNA analysis, and the introduction of chorionic villous sampling have dramatically improved prenatal diagnosis of this disease and of related disorders. Much information is now available about the molecular mechanisms of the diseases and the molecular testing is widespread. As prenatal diagnosis has to provide an accurate, safe and early result, an efficient screening of the population and a rapid molecular characterization of the couple at risk, are necessary prerequisites. In the last decades earlier and less invasive approaches for prenatal diagnosis were developed. A overview of the most promising procedure will be done. Moreover, in order to reduce the choice of interrupting the pregnancy in case of affected fetus, Preimplantation or Preconceptional Genetic Diagnosis (PGD) has been setting up for several diseases including thalassemias.

High-sensitive microarray substrates specifically designed to improve sensitivity for the identification of fetal paternally inherited sequences in maternal plasma

BACKGROUND

The identification of very low-levels of minority sequences has interesting clinical and diagnostic applications. Among these, non-invasive prenatal diagnosis of genetic diseases on fetal DNA circulating in maternal plasma is an emerging field of application.

METHODS

A combined approach based on innovative microarray slides coated with a special copolymer was developed for the identification of three polymorphisms located in the causative gene for cystic fibrosis (CF). This technique was applied to the analysis of fetal DNA in maternal plasma from four couples that carried different allelic variants.

RESULTS

The use of highly sensitive slides correctly identified fetal paternally inherited alleles without any enrichment strategy.

CONCLUSIONS

Our results confirm that the high fluorescence signal provided by the optimized substrate may be applied to the identification of any fetal paternally inherited sequence. This helps extend the application of non-invasive prenatal diagnosis to genetic diseases caused by predominant mutations or minor rare molecular defects.

Development of new substrates for high-sensitive genotyping of minority mutated alleles

An unsurpassed level of sensitivity was reached in the detection of minority mutated alleles. A low-density microarray was printed on a substrate specifically designed to provide an interference effect which amplifies the collection of the light emitted on the support and reinforces the intensity of excitation light. Optimal performance of the array was obtained by maximizing the probe density and the binding efficiency to the target through a polymeric coating made by the adsorption of a copolymer of N,N-dimethylacrylamide (97% of moles), N,N-acryloyloxysuccinimide (2%) and 3-(trimethoxysilyl)propyl methacrylate (1%) synthesized by free radical copolymerization. The new substrate was used in the identification of fetal mutations in the maternal plasma DNA. Amino-modified amplicons from genomic DNA corresponding to the locus of eight beta-thalassemia mutations were immobilized and interrogated with dual-color oligonucleotide targets. Compared with the conventional glass substrates, the new substrate showed a great enhancement of fluorescence signals thanks to the combination of the optics with the highly efficient polymeric coating, allowing specific detection of all mutations. The high sensitivity and selectivity obtained made it possible to develop assays for the identification of paternally inherited mutations on fetal DNA in the maternal plasma in couples at risk for beta-thalassemia.

Different approaches for noninvasive prenatal diagnosis of genetic diseases based on PNA-mediated enriched PCR

The aim of this work was to develop advanced and accessible protocols for noninvasive prenatal diagnosis of genetic diseases. We are evaluating different technologies for mutation detection, based on fluorescent probe hybridization of the amplified product and pyrosequencing, a technique that relies on the incorporation of nucleotides in a primer-directed polymerase extension reaction. In a previous investigation, we have already proven that these approaches are sufficiently sensitive to detect a few copies of a minority-mutated allele in the presence of an excess of wild-type DNA, In this work, in order to further enhance the sensitivity, we have employed a mutant enrichment amplification strategy based on the use of peptide nucleic acids (PNAs). These DNA analogues bind wild-type DNA, thus interfering with its amplification while still allowing the mutant DNA to become detectable. We have synthesized different PNAs, which are highly effective in clamping wild-type DNA in the beta-globin gene region, where four beta-thalassemia mutations are located (IVSI.110, CD39, IVSI.1, IVSI.6) plus HbS. The fluorescence microchip readout allows us to monitor the extent of wild-type allele inhibition, thus facilitating the assessment of the optimal PNA concentration.

Blood group chimerism

PURPOSE OF REVIEW

With improved methods for detecting chimeras and growing numbers of stem cell transplantations, blood group and other forms of chimerism are observed with increasing frequency. This review will focus on the state of science and new insights into the multifaceted subject of blood group chimerism.

RECENT FINDINGS

Recognition that the immune system tolerates chimeric cells under certain conditions has led to efforts to elucidate related immune-modulating processes. The chimeric state following transplantation of hematopoietic stem cells, as well as after solid organ transplantation, is of special interest. Also, chimerism is considered to be a potential trigger for certain autoimmune diseases. Natural chimerism is more frequent than previously recognized. Using improved laboratory techniques, investigators can often trace chimeric tissues to their origin. New therapeutic strategies have been applied after stem cell transplantation depending on the chimeric state. Also, recent research has resulted in methods for determining chimerism in maternal peripheral blood that reflect fetal blood type and certain congenital diseases.

SUMMARY

The subject of human chimerism has evolved from a curiosity of nature to an important field of research and, potentially, holds the key to advancing our understanding of the fundamental mechanisms of immune tolerance.

Microelectronic DNA chip for hereditary hyperferritinemia cataract syndrome, a model for large-scale analysis of disorders of iron metabolism

Hereditary hyperferritinemia cataract syndrome (HHCS) is caused by mutations in the regulatory iron responsive element (IRE) in the 5'UTR of the L-ferritin transcript that reduce binding affinity to the iron regulatory proteins (IRPs) and lead to a constitutive upregulation of the protein in tissue and serum. Twenty-nine mutations have been reported within the L-ferritin (FTL) IRE sequence, 21 of which were available to us. In addition, we included in this study three new mutations. Thus, we analyzed 24 mutations spanning over a DNA stretch of 48 nucleotides, including four deletions 2-29 nucleotides long and 20 substitutions, seven of which were conservative transversions. With this unique experimental model we developed a microchip diagnostic platform for identifying known molecular defects in the L-ferritin IRE structure with a microelectronic array approach, which we optimized after studying the effects of various parameters. The system enables electronic deposition of biotinylated amplicons to selected pads. Under optimized conditions, no cross-hybridization was found, even for mutations that affected the same or adjacent nucleotide positions. The same cartridge could be serially hybridized with all the 24 reporter probe sets, which allowed correct genotyping right up until the end of the analysis. Extensive validation on 200 samples in a blinded fashion gave total concordance of results. This pilot study represents a first step toward developing a diagnostic microchip for large-scale analyses for epidemiological studies and screening of mutations associated with iron disorders.

Non-invasive diagnosis of fetal sex; utilisation of free fetal DNA in maternal plasma and ultrasound

Non-invasive prenatal diagnosis is now a clinical reality, using both early ultrasound and molecular DNA methods. Technical advances in the sensitivity of the polymerase chain reaction (PCR), coupled with the finding that significant levels of fetal DNA (ffDNA) are found in maternal plasma and serum, has enabled the ready detection of paternally inherited genes or polymorphisms. Routine maternal plasma-based genotyping is now available for the determination of fetal sex and RHD blood group status (Van der Schoot et al., 2003). This review touches briefly on the ultrasound diagnoses and then focuses on the application of free ffDNA for fetal sex determination, indicating the Y-chromosome targets exploited in this strategy and the merits of their utilisation.

Present and future of rapid and/or high-throughput methods for nucleic acid testing

BACKGROUND

Behind the success of 'completing' the human genome project was a more than 30-year history of technical innovations for nucleic acid testing.

METHODS

Discovery of specific restriction endonucleases and reverse transcriptase was followed shortly by the development of the first diagnostic nucleic acid tests in the early 1970s. Introduction of Southern, Northern and dot blotting and DNA sequencing later in the 1970s considerably advanced the diagnostic capabilities. Nevertheless, it was the discovery of the polymerase chain reaction (PCR) in 1985 that led to an exponential growth in molecular biology and the introduction of practicable nucleic acid tests in the routine laboratory. The past two decades witnessed a continuing explosion of technological innovations in molecular diagnostics. In addition to classic PCR and reverse transcriptase PCR, numerous variations of PCR and alternative amplification techniques along with an ever-increasing variety of detection chemistries, closed tube (homogeneous) assays, and automated systems were developed. Discovery of real-time quantitative PCR and the development of oligonucleotide microarrays, the 'DNA chip', in the 1990s heralded the beginning of another revolution in molecular biology and diagnostics that is still in progress.

Fetal DNA detection in maternal plasma throughout gestation

The presence of fetal DNA in maternal plasma may represent a source of genetic material which can be obtained noninvasively. We wanted to assess whether fetal DNA is detectable in all pregnant women, to define the range and distribution of fetal DNA concentration at different gestational ages, to identify the optimal period to obtain a maternal blood sample yielding an adequate amount of fetal DNA for prenatal diagnosis, and to evaluate accuracy and predictive values of this approach. This information is crucial to develop safe and reliable non-invasive genetic testing in early pregnancy and monitoring of pregnancy complications in late gestation. Fetal DNA quantification in maternal plasma was carried out by real-time PCR on the SRY gene in male-bearing pregnancies to distinguish between maternal and fetal DNA. A cohort of 1,837 pregnant women was investigated. Fetal DNA could be detected from the sixth week and could be retrieved at any gestational week. No false-positive results were obtained in 163 women with previous embryo loss or previous male babies. Fetal DNA analysis performed blindly on a subset of 464 women displayed 99.4, 97.8 and 100% accuracy in fetal gender determination during the first, second, and third trimester of pregnancy, respectively. No SRY amplification was obtained in seven out of the 246 (2.8%) male-bearing pregnancies. Fetal DNA from maternal plasma seems to be an adequate and reliable source of genetic material for a noninvasive prenatal diagnostic approach.

Accurate and robust quantification of circulating fetal and total DNA in maternal plasma from 5 to 41 weeks of gestation

BACKGROUND

Detection of fetal DNA in maternal plasma is achievable at 5 weeks of gestation, but few large-scale studies have reported circulating fetal and maternal DNA across all trimesters.

METHODS

Blood samples were collected from 201 women between 5 and 41 weeks of pregnancy. Quantitative PCR was used to assess total and fetal DNA concentrations, and allelic discrimination analysis was investigated as a route to detecting specifically fetal DNA.

RESULTS

Male fetuses were detectable from 5 weeks amenorrhea with increasing fetal DNA concentrations across gestation. The sensitivity of fetal male gender determination in pregnancies with live birth confirmation was 99%, with 100% specificity. Total DNA concentrations did not correlate with gestational age, but appeared slightly higher in the first and third trimesters than in mid-pregnancy. Analysis of short tandem repeats demonstrated that significant improvements in the detection limit are required for specific detection of fetal DNA.

CONCLUSIONS

The high sensitivity of PCR-based detection, together with quantification provided by real-time DNA analysis, has clear potential for clinical application in noninvasive prenatal diagnosis. However, accurate quantification using best-fit data analysis, standardization of methods, and performance control indicators are necessary for robust routine noninvasive diagnostics.