Evaluation of molecular tests for prenatal diagnosis of chromosome abnormalities

An economic analysis of chromosome testing in couples with children who have structural chromosome abnormalities

Background

Structural chromosome abnormalities can cause significant negative reproductive outcomes as they typically result in morbidity and mortality of newborns. The prevalence of structural chromosomal abnormalities in live births is at least 0.05%, of which many of them have parental origins. It is uncommon to predict structural chromosome abnormalities at birth in the first child but it is possible to prevent repeated abnormalities through screening and diagnostic programmes. This study will provide an economic analysis of the prenatal detection of these abnormalities.

Methods

A cost-benefit analysis using a decision analytic model was employed to compare the status quo (doing nothing) with two interventional strategies. The first strategy (Strategy I) is preconceptional screening plus amniocentesis, and the second strategy (Strategy II) is amniocentesis alone. The monetary values in Thai baht (THB) were adjusted to international dollars (I$) using purchasing power parity (PPP) (I$1 = THB 17.60 for the year 2013). The robustness of the results was tested by applying a probabilistic sensitivity analysis.

Results

Both diagnostic strategies can reduce approximately 10.7–11.1 births with abnormal chromosomes per 1,000 diagnosed couples. The benefit cost ratios were 1.62 for Strategy I and 1.24 for Strategy II. Net present values per 1,000 diagnoses in couples were I$464,000 for Strategy I and I$267,000 for Strategy II. The probabilistic sensitivity analysis suggested that the cost-benefit analysis was sufficiently robust, confirming that both strategies provided higher benefits than costs.

Conclusions

Since the benefits of both diagnostic strategies exceeded their costs, both strategies are economical–with Strategy I being more economically attractive. Strategy I is superior to Strategy II because it decreases the risk of normal children potentially dying from the amniocentesis process.

Bisulfite Conversion of DNA: Performance Comparison of Different Kits and Methylation Quantitation of Epigenetic Biomarkers that Have the Potential to Be Used in Non-Invasive Prenatal Testing

INTRODUCTION

Epigenetic alterations, including DNA methylation, play an important role in the regulation of gene expression. Several methods exist for evaluating DNA methylation, but bisulfite sequencing remains the gold standard by which base-pair resolution of CpG methylation is achieved. The challenge of the method is that the desired outcome (conversion of unmethylated cytosines) positively correlates with the undesired side effects (DNA degradation and inappropriate conversion), thus several commercial kits try to adjust a balance between the two. The aim of this study was to compare the performance of four bisulfite conversion kits [Premium Bisulfite kit (Diagenode), EpiTect Bisulfite kit (Qiagen), MethylEdge Bisulfite Conversion System (Promega) and BisulFlash DNA Modification kit (Epigentek)] regarding conversion efficiency, DNA degradation and conversion specificity.

METHODS

Performance was tested by combining fully methylated and fully unmethylated λ-DNA controls in a series of spikes by means of Sanger sequencing (0%, 25%, 50% and 100% methylated spikes) and Next-Generation Sequencing (0%, 3%, 5%, 7%, 10%, 25%, 50% and 100% methylated spikes). We also studied the methylation status of two of our previously published differentially methylated regions (DMRs) at base resolution by using spikes of chorionic villus sample in whole blood.

RESULTS

The kits studied showed different but comparable results regarding DNA degradation, conversion efficiency and conversion specificity. However, the best performance was observed with the MethylEdge Bisulfite Conversion System (Promega) followed by the Premium Bisulfite kit (Diagenode). The DMRs, EP6 and EP10, were confirmed to be hypermethylated in the CVS and hypomethylated in whole blood.

CONCLUSION

Our findings indicate that the MethylEdge Bisulfite Conversion System (Promega) was shown to have the best performance among the kits. In addition, the methylation level of two of our DMRs, EP6 and EP10, was confirmed. Finally, we showed that bisulfite amplicon sequencing is a suitable approach for methylation analysis of targeted regions.

Rapid Aneuploidy Detection of Chromosomes 13, 18, 21, X and Y Using Quantitative Fluorescent Polymerase Chain Reaction with Few Microdissected Fetal Cells

Objectives: Analysis of DNA from small numbers of cells, such as fetal cells in maternal blood, is a major limiting factor for their use in clinical applications. Traditional methods of single-cells whole genome amplification (SCs-WGA) and accurate analysis have been challenging to date. Our purpose was to assess the feasibility of using a few fetal cells to determine fetal sex and major chromosomal abnormalities by quantitative fluorescent polymerase chain reaction (QF-PCR). Methods: Cultured cells from 26 amniotic fluid samples were used for standard DNA extraction and recovery of 5 fetal cells by laser-capture microdissection. SCs-WGA was performed using the DNA from the microdissected cells. PCR amplification of short tandem repeats specific for chromosomes 13, 18, 21, X and Y was performed on extracted and amplified DNA. Allele dosage and sexing were quantitatively analyzed following separation by capillary electrophoresis. Results: Microsatellite QF-PCR analysis showed high concordance in chromosomal copy number between extracted and amplified DNA when 5 or more cells were used. Results were in concordance with that of conventional cytogenetic analysis. Conclusion: Satisfactory genomic coverage can be obtained from SCs-WGA. Clinically, SCs-WGA coupled with QF-PCR can provide a reliable, accurate, rapid and cost-effective method for detection of major fetal chromosome abnormalities.

Performance of QF-PCR in targeted prenatal aneuploidy diagnosis: Indian scenario

OBJECTIVE

Among the rapid aneuploidy detection methods, QF-PCR has now become an alternative tool for prenatal aneuploidy diagnosis concomitant with karyotyping. This method has been validated in many of the western clinics but in India no study was conducted to assess its utility as standalone procedure. The study was designed to answer the question whether QF-PCR can be implemented as a standalone diagnostic method for rapid aneuploidy diagnosis in our present clinical setup?

MATERIALS AND METHODS

Study was conducted during March 2012 to August 2014 consisting of 270 prenatal samples that underwent for aneuploidy diagnosis. In addition to karyotyping, QF-PCR was also performed on these samples and the results were compared.

RESULTS

Of 270 samples screened, 262 samples showed euploid genome (125 normal male and 137 normal female). Eight samples were consistent with aneuploidy--four trisomy 21 male sample, 2 trisomy 21 female sample, 1 trisomy 18 samples and 1 Klinefelter sample. The specificity, sensitivity, positive prediction value and negative prediction values were 100% while false positive rate and false negative rate were 0%.

CONCLUSION

Outcome of this study strongly suggests that QF-PCR can be used as standalone procedure for targeted rapid aneuploidy diagnosis.

Rapid aneuploidy screening (FISH or QF-PCR): the changing scene in prenatal diagnosis?

The accuracy of new molecular diagnostics, fluoresence in situ hybridization or quantitative fluorescence-PCR (collectively known as rapid aneuploidy screening), in prenatal diagnosis has already been demonstrated in a number of large studies. The challenge now is how to apply them clinically in the most cost-effective manner. It is now time to appraise whether rapid aneuploidy screening can replace traditional karyotyping when amniocenteses are performed for increased risk of Down's syndrome by maternal serum screening or advanced maternal age in the absence of ultrasound abnormality. The ten most recent studies from the literature within this research theme are reviewed and the pros and cons of this new approach in prenatal diagnosis are discussed, including the suggestion of future studies.

Disease specific characteristics of fetal epigenetic markers for non-invasive prenatal testing of trisomy 21

Background

Non-invasive prenatal testing of trisomy 21 (T21) is being actively investigated using fetal-specific epigenetic markers (EPs) that are present in maternal plasma. Recently, 12 EPs on chromosome 21 were identified based on tissue-specific epigenetic characteristics between placenta and blood, and demonstrated excellent clinical performance in the non-invasive detection of fetal T21. However, the disease-specific epigenetic characteristics of the EPs have not been established. Therefore, we validated the disease-specific epigenetic characteristics of these EPs for use in non-invasive detection of fetal T21.

Methods

We performed a high-resolution tiling array analysis of human chromosome 21 using a methyl-CpG binding domain-based protein (MBD) method with whole blood samples from non-pregnant normal women, whole blood samples from pregnant normal women, placenta samples of normal fetuses, and placenta samples of T21 fetuses. Tiling array results were validated by bisulfite direct sequencing and qPCR.

Results

Among 12 EPs, only four EPs were confirmed to be hypermethylated in normal placenta and hypomethylated in blood. One of these four showed a severe discrepancy in the methylation patterns of T21 placenta samples, and another was located within a region of copy number variations. Thus, two EPs were confirmed to be potential fetal-specific markers based on their disease-specific epigenetic characteristics. The array results of these EPs were consisted with the results obtained by bisulfite direct sequencing and qPCR. Moreover, the two EPs were detected in maternal plasma.

Conclusions

We validated that two EPs have the potential to be fetal-specific EPs which is consistent with their disease-specific epigenetic characteristics. The findings of this study suggest that disease-specific epigenetic characteristics should be considered in the development of fetal-specific EPs for non-invasive prenatal testing of T21.

The importance of rapid aneuploidy screening and prenatal diagnosis in the detection of numerical chromosomal abnormalities

Objectives

Evaluation of Fluorescent in situ hybridization (FISH) as a tool for rapid aneuploidy screening (RAS) of high risk pregnancies, before its approval in the national antenatal screening and genetic diagnosis program in Egypt.

Methods

The cytogenetic data of prenatal specimens, and results of FISH of 100 patients performed between, January 2009 and December 2009, at the Medical Genetics Center (MGC) laboratory were retrieved and reviewed. AneuVysion Assay kit was used for detection of 13, 21, X, Y, 18 aneuploidies.

Results

Maternal age varied from 21 to 44 years (mean was 35.6 year). Ninety percent of pregnancies had normal chromosomes and 10% of the cases had numerical chromosomal abnormalities. Trisomy 21 was the most frequent chromosomal disorder across all indications (5%), followed by Turner syndrome (2%), trisomy 18 (2%), and trisomy 13 (1%). When comparing the FISH data with karyotype results for chromosomes 13, 18, 21, X, and Y in the 83 individual tested, no false positive or negative results were detected by the FISH assay. The result obtained by FISH and the banding cytogenetic were in complete accordance.

Conclusion

This study supports the integration of amniotic fluid (AF) FISH as a RAS test, in to routine antenatal practice for identification of chromosome aneuploidies. There are trends towards delayed childbearing and most cases of Down Syndrome (DS) are currently detected post-nataly in the Egyptian population. Consequently, the live birth prevalence of DS has increased, which might lead to a serious negative public health effects.

Rapid detection of fetal aneuploidies by quantitative fluorescent-polymerase chain reaction for prenatal diagnosis in the Turkish population

Prenatal diagnosis is testing for diseases or conditions in a fetus or embryo before it is born. It employs a variety of techniques to determine the health and condition of an unborn fetus. The main goal of this process is to perform prenatal diagnosis at the earliest possible stage of gestation. In this regard, quantitative fluorescent-polymerase chain reaction (QF-PCR), a novel technique that is fast and reliable, was employed to detect aneuploidies (13, 18, 21, X and Y) without the need of the time-consuming culturing process. The QF-PCR method can detect five different chromosome aneuploidies with 98.6% accuracy. In this study, 1874 amniotic fluid samples of pregnant subjects, who were referred to the Department of Medical Biology and Genetics, Adana, Turkey (molecular biology section), were analyzed with the QF-PCR technique by employing 27 short tandem repeat (STR) markers to detect chromosomes 13, 18, 21, X and Y aneuploidies. We detected 31 subjects (1.7%) with aneuploidies or euploidies out of the 1874 subjects. The average age of the pregnant subjects was 32 (range: 14-49). Abnormal karyotypes detected were as follows: 47,XX,+21 (19.4%, 6/31), 47,XY,+21 (48.4%, 15/31), 48,XXX,+21 (3.2%, 1/31), 69,XXX (3.2%, 1/31), 47,XY,+13 (3.2%, 1/31), 47,XXY (9.6%, 3/31), 47,XXX (9.6%, 3/31) and 45,X (3.2%, 1/31). Moreover, some STR markers were found to be more specific to the Turkish population. In conclusion, QF-PCR can be regarded as an alternative method of conventional cytogenetic analysis as it is a rapid and reliable method; however, in most cases it is required to be supported or validated with conventional cytogenetic karyotyping and some STR markers employed for QF-PCR can be more informative for a given population.

Prenatal screening methods for aneuploidies

Aneuploidies are a major cause of perinatal morbidity and mortality. Therefore, it is the most common indication for invasive prenatal diagnosis. Initially, screening for aneuploidies started with maternal age risk estimation. Later on, serum testing for biochemical markers and ultrasound markers were added. Women detected to be at high-risk for aneuploidies were offered invasive testing. New research is now focusing on non-invasive prenatal testing using cell-free fetal DNA in maternal circulation. The advantage of this technique is the ability to reduce the risk of miscarriage associated with invasive diagnostic procedures. However, this new technique has its own set of technical limitations and ethical issues at present and careful consideration is required before broad implementation.

Women's Attitudes towards the Option to Choose between Karyotyping and Rapid Targeted Testing during Pregnancy

Objectives. Pregnant women, referred because of an increased risk of fetal Down syndrome, who underwent an invasive prenatal procedure were offered a choice between karyotyping and rapid targeted testing. This study aims to assess women's attitudes and experiences towards what option to choose. Methods. A retrospective multicentre survey (2008–2010) was conducted among 1370 women. General questions were asked about decision making issues, followed by personal questions about their experiences in choice making, test preference, influence of others, and possible regrets. Results. In total, 90.1% of the respondents (N = 825) indicated that pregnant women are able to choose, although 33.1% stated that the choice can best be made by a professional. 18.4% indicated that making a choice places a burden on women. In 96.4%, respondents preferred to have the option to choose again in case of a next pregnancy, whereas 2.7% preferred the choice to be made by a professional. Regret was indicated by 1.2%. Decision making was influenced by others in 64.9%. A slightly higher preference for karyotyping was indicated by 52.7% of the respondents. Conclusions. Positive attitudes and experiences were expressed towards the option to choose. Respondents took decisions freely, although sometimes influenced by a partner or a professional, to follow their individual perspectives.

Non-invasive prenatal diagnosis of fetal trisomy 21 using cell-free fetal DNA in maternal blood

Since the existence of cell-free fetal DNA (cff-DNA) in maternal circulation was discovered, it has been identified as a promising source of fetal genetic material in the development of reliable methods for non-invasive prenatal diagnosis (NIPD) of fetal trisomy 21 (T21). Currently, a prenatal diagnosis of fetal T21 is achieved through invasive techniques, such as chorionic villus sampling or amniocentesis. However, such invasive diagnostic tests are expensive, require expert technicians, and have a miscarriage risk approximately 1%. Therefore, NIPD using cff-DNA in the detection of fetal T21 is significant in prenatal care. Recently, the application of new techniques using single-molecular counting methods and the development of fetal-specific epigenetic markers has opened up new possibilities in the NIPD of fetal T21 using cff-DNA. These new technologies will facilitate safer, more sensitive and accurate prenatal tests in the near future. In this review, we investigate the recent methods for the NIPD of fetal T21 and discuss their implications in future clinical practice.

The scope of prenatal diagnosis for women at increased risk for aneuploidies: views and preferences of professionals and potential users

The increasing number of prenatal diagnostic tests in prenatal screening strategies, raises the question what tests to offer and why. This qualitative study investigated the views and preferences of professionals and potential users regarding four diagnostic test options for women at increased risk for common aneuploidies. Seven focus group sessions were conducted in The Netherlands between October 2009 and June 2010, with various categories of participants (n = 55): professionals engaged in prenatal testing and potential users of this testing (meaning pregnant women and parents of young children). Participants were invited to mention all pros and cons and their preferences regarding four hypothetical diagnostic test options, presented on vignettes: a standard offer of rapid aneuploidy detection, karyotyping or array comparative genomic hybridization, representing a narrow, traditional and broad test, respectively, and the option of individualised choice. Then, a semi-structured group interview was conducted. The data were analysed by the constant comparative method. Participants identified similar test-specific pros and cons but showed different preferences. Users' opinion on what test to offer as a general policy differed from what they would choose themselves. All participants agreed that in theory, users should be enabled to make an informed choice about what test to apply, but they disagreed about the feasibility of this ideal. Standard narrow testing was favoured for its limiting effects on emotional and organisational burdens; individualised choice was preferred for assuring women's decisive influence. The varying opinions reflect different views on what autonomy in the prenatal screening context means, suggest that a single standard test offer is inadequate and that differentiation will be needed.

Economic evaluations conducted for assessment of genetic testing technologies: a systematic review

AIMS

To systematically review the methods used in economic evaluations (EEs) included in health technology assessments (HTAs) of genetic testing technologies (GTTs).

METHODS

A systematic search using bibliographic databases and gray literature was undertaken to identify HTA reports on GTTs that included EEs in addition to clinical effectiveness results. Studies were reviewed in terms of methodology and reporting.

RESULTS

Of 361 identified citations, 15 HTAs consisting of 11 model-based and 4 trial-based EEs were included, more than 50% of which had moderate-to-low-quality scores mainly due to not reporting information on basic elements of a standard EE and inadequate management of uncertainty. Cost-effectiveness analysis accounted for 62% of studies. Approximately 66% of the studies adopted a third-party payer perspective, and 46% used a lifelong time horizon. The majority of studies exclusively included technical costs of testing (100%) and therapeutic or preventive interventions (60%). The most frequent variables tested in sensitivity analysis included costs (66%), effects (50%), and transition probabilities (58%).

CONCLUSIONS

We found several methodological challenges in the reviewed EEs, including identification of a proper analytical perspective, inclusion of wider range of outcomes and costs, allowing for long-term medical and nonmedical impacts of genetic tests, and sufficient management of uncertainty. These issues should be carefully considered in future EEs of GTTs.

Non-invasive prenatal diagnosis of aneuploidies: new technologies and clinical applications

Non-invasive prenatal diagnosis (NIPD) has substantial medical importance as it targets the development of safer and more effective methods to avoid the risk of fetal loss associated with currently used invasive methods. Several approaches have been demonstrated as being proof-of concept for NIPD of chromosomal aneuploidies. These approaches include cell-based and cell-free detection methods, involving the investigation of fetal cells in the maternal circulation, formaldehyde treatment of maternal plasma, DNA methylation studies using sodium bisulfite or restriction enzymes, protein-based studies, identification of fetal-specific mRNAs and digital polymerase chain reaction (PCR) approaches, and recently next-generation sequencing and methylated DNA immunoprecipitation real-time quantitative PCR-based approaches. Although all these NIPD methods have both advantages and limitations, some are moving closer to clinical implementation. Biotechnology companies dedicated to the development of NIPD tests such as the sequencing- or methylation-based approaches are finalizing large clinical trials. It is expected that these new technologies will facilitate safer, more sensitive and accurate prenatal diagnostic tests in the near future. In this review, we highlight the most recent advances in methods for NIPD of aneuploidies, and we discuss their future implications in clinical practice.

Dual testing with QF-PCR and karyotype analysis for prenatal diagnosis of chromosomal abnormalities. Evaluation of 13,500 cases with consideration of using QF-PCR as a stand-alone test according to referral indications

OBJECTIVE

Evaluate the results obtained from Quantitative Fluorescent (QF)-PCR and conventional karyotype analysis to determine the advantages and disadvantages of dual testing in prenatal diagnosis.

METHODS

From 1 June 2006 to 1 June 2010, dual testing by QF-PCR and karyotype analysis was performed in 13,500 prenatal samples. The rates of concordant results between the two methods were evaluated and the rates of clinically significant chromosomal abnormalities undetected by QF-PCR were assessed.

RESULTS

Abnormal karyotype was found in 320 out of 13,500 cases (2.37%, 95% confidence interval (CI) 2.11-2.63%). From these, QF-PCR did not detect the abnormality in 70 cases (0.52%, 95% CI 0.4-0.64%), whereas 34 had a high/unknown risk of adverse outcome (0.25%, 95% CI 0.17-0.33%). By selectively applying dual testing only at cases with ultrasound findings and/or genetic history, 13 cases of high/unknown risk would have been missed (0.1%, 95% CI 0.05-0.15%).

CONCLUSION

Selective dual testing is expected to achieve a serious beneficial economical outcome and reduce parental anxiety produced by ambiguous cytogenetic findings. However, the percentage of 0.1% undetected clinically significant abnormalities cannot be ignored. A suggestion would include the offering of a choice to the pregnant women, undergoing prenatal screening, by informing them about different approaches and various complications.

Is routine karyotyping required in prenatal samples with a molecular or metabolic referral?

As a routine, karyotyping of invasive prenatal samples is performed as an adjunct to referrals for DNA mutation detection and metabolic testing. We performed a retrospective study on 500 samples to assess the diagnostic value of this procedure. These samples included 454 (90.8%) chorionic villus (CV) and 46 (9.2%) amniocenteses specimens. For CV samples karyotyping was based on analyses of both short-term culture (STC) and long-term culture (LTC) cells. Overall, 19 (3.8%) abnormal karyotypes were denoted: four with a common aneuploidy (trisomy 21, 18 and 13), two with a sex chromosomal aneuploidy (Klinefelter syndrome), one with a sex chromosome mosaicism and twelve with various autosome mosaicisms. In four cases a second invasive test was performed because of an abnormal finding in the STC. Taken together, we conclude that STC and LTC karyotyping has resulted in a diagnostic yield of 19 (3.8%) abnormal cases, including 12 cases (2.4%) with an uncertain significance. From a diagnostic point of view, it is desirable to limit uncertain test results as secondary test findings. Therefore, we recommend a more targeted assay, such as e.g. QF-PCR, as a replacement of the STC and to provide parents the autonomy to choose between karyotyping and QF-PCR.

Rapid aneuploidy detection or karyotyping? Ethical reflection

No consensus exists whether women at increased risk for trisomy 21, 13, and 18 should be offered stand-alone rapid aneuploidy detection (RAD) or karyotyping. In this paper, the ethical implications of a fast, relatively cheap and targeted RAD are examined. The advantages of RAD seem less robust than its proponents suggest. Fast test results only give a short-term psychological benefit. The cost advantage of RAD is apparent, but must be weighed against consequences like missed abnormalities, which are evaluated differently by professionals and pregnant women. Since pre-test information about RAD will have to include telling women about karyotyping as a possible alternative, the advantage of RAD in terms of the quantity of information that needs to be given may also be smaller than suggested. We conclude that none of the supposed arguments in favour of RAD is decisive in itself. Whether the case for RAD may still be regarded as convincing when taking these arguments together seems to depend on one's implicit view of what prenatal screening is about. Are we basically dealing with a test for trisomy 21 and a few conditions more? Or are there good grounds for also testing for the wider range of abnormalities that karyotyping can detect? As professionals and pregnant women may have different views about this, we suggest that the best approach is to offer women a choice between RAD and karyotyping. This approach is most in line with the general aim of prenatal screening: providing opportunities for autonomous reproductive choice.

Economic evaluation of multiplex ligation-dependent probe amplification and karyotyping in prenatal diagnosis: a cost-minimization analysis

Purpose

To assess the cost-effectiveness of Multiplex Ligation-dependent Probe Amplification (MLPA, P095 kit) compared to karyotyping.

Methods

A cost-minimization analysis alongside a nationwide prospective clinical study of 4,585 women undergoing amniocentesis on behalf of their age (≥36 years), an increased risk following first trimester prenatal screening or parental anxiety.

Results

Diagnostic accuracy of MLPA (P095 kit) was comparable to karyotyping (1.0 95% CI 0.999–1.0). Health-related quality of life did not differ between the strategies (summary physical health: mean difference 0.31, p = 0.82; summary mental health: mean difference 1.91, p = 0.22). Short-term costs were lower for MLPA: mean difference €315.68 (bootstrap 95% CI €315.63–315.74; −44.4%). The long-term costs were slightly higher for MLPA: mean difference €76.42 (bootstrap 95% CI €71.32–81.52; +8.6%). Total costs were on average €240.13 (bootstrap 95% CI €235.02–245.23; −14.9%) lower in favor of MLPA. Cost differences were sensitive to proportion of terminated pregnancies, sample throughput, individual choice and performance of tests in one laboratory, but not to failure rate or the exclusion of polluted samples.

Conclusion

From an economic perspective, MLPA is the preferred prenatal diagnostic strategy in women who undergo amniocentesis on behalf of their age, following prenatal screening or parental anxiety.

Electronic supplementary material

The online version of this article (doi:10.1007/s00404-011-1921-y) contains supplementary material, which is available to authorized users.

Rapid methods for targeted prenatal diagnosis of common chromosome aneuploidies

Improvements in non-invasive screening methods for trisomy 21 (Down syndrome) and other aneuploidies during the first and second trimester of pregnancy have radically changed the indications for prenatal diagnosis over the last decade. Consequently, there was a need for rapid tests for the detection of common chromosome aneuploidies resulting in the development of molecular methods for the rapid, targeted detection of (an)euploidies of the chromosomes 13, 18, 21 and the sex chromosomes. The analysis of large series of prenatal samples has shown that such tests can detect the great majority of chromosome abnormalities in prenatal diagnosis. This resulted in lively discussions on whether conventional karyotyping should remain the standard method for the majority of prenatal cases or can be replaced by rapid tests only. This review gives an overview of different aspects of the three most common tests for rapid, targeted prenatal detection of (an)euploidies, i.e. interphase fluorescence in-situ hybridisation (iFISH), quantitative fluorescent polymerase chain reaction (QF-PCR) and multiplex ligation-dependent probe amplification (MLPA).

A new fetal RHD genotyping test: costs and benefits of mass testing to target antenatal anti-D prophylaxis in England and Wales

BACKGROUND

Postnatal and antenatal anti-D prophylaxis have dramatically reduced maternal sensitisations and cases of rhesus disease in babies born to women with RhD negative blood group. Recent scientific advances mean that non-invasive prenatal diagnosis (NIPD), based on the presence of cell-free fetal DNA in maternal plasma, could be used to target prophylaxis on "at risk" pregnancies where the fetus is RhD positive. This paper provides the first assessment of cost-effectiveness of NIPD-targeted prophylaxis compared to current policies.

METHODS

We conducted an economic analysis of NIPD implementation in England and Wales. Two scenarios were considered. Scenario 1 assumed that NIPD will be only used to target antenatal prophylaxis with serology tests continuing to direct post-delivery prophylaxis. In Scenario 2, NIPD would also displace postnatal serology testing if an RhD negative fetus was identified. Costs were estimated from the provider's perspective for both scenarios together with a threshold royalty fee per test. Incremental costs were compared with clinical implications.

RESULTS

The basic cost of an NIPD in-house test is £16.25 per sample (excluding royalty fee). The two-dose antenatal prophylaxis policy recommended by NICE is estimated to cost the NHS £3.37 million each year. The estimated threshold royalty fee is £2.18 and £8.83 for Scenarios 1 and 2 respectively. At a £2.00 royalty fee, mass NIPD testing would produce no saving for Scenario 1 and £507,154 per annum for Scenario 2. Incremental cost-effectiveness analysis indicates that, at a test sensitivity of 99.7% and this royalty fee, NIPD testing in Scenario 2 will generate one additional sensitisation for every £9,190 saved. If a single-dose prophylaxis policy were implemented nationally, as recently recommended by NICE, Scenario 2 savings would fall.

CONCLUSIONS

Currently, NIPD testing to target anti-D prophylaxis is unlikely to be sufficiently cost-effective to warrant its large scale introduction in England and Wales. Only minor savings are calculated and, balanced against this, the predicted increase in maternal sensitisations may be unacceptably high. Reliability of NIPD assays still needs to be demonstrated rigorously in different ethnic minority populations. First trimester testing is unlikely to alter this picture significantly although other emerging technologies may.

Individualized choice in prenatal diagnosis: the impact of karyotyping and standalone rapid aneuploidy detection on quality of life

OBJECTIVE

To assess the reasons and perceptions of women who are offered a choice between karyotyping and standalone rapid aneuploidy detection (RAD) and to compare the impact of both tests on anxiety and health-related quality of life.

METHODS

In this prospective comparative study, women undergoing amniocentesis on behalf of their age or for an increased Down syndrome risk were offered a choice between karyotyping (group 1, n = 68) and standalone RAD (group 2, n = 61). Follow-up was 9 weeks post amniocentesis.

RESULTS

The most commonly cited reason for choosing karyotyping was obtaining as much information as possible, while for choosing standalone RAD, it was the short waiting time. Prenatal screening (OR 7.09), no knowledge of karyotyping (OR 4.2), and an intermediate perceived risk for chromosomal abnormalities (OR 3.6) were associated with choosing standalone RAD. There were no systematic differences in time of karyotyping and standalone RAD in terms of anxiety (P = 0.11), generic physical and mental health (P = 0.94, 0.52; P = 0.66, 0.07), personal perceived control (PPC; P = 0.69), and stress (P = 0.66).

CONCLUSION

Offering a choice between karyotyping and standalone RAD does not influence anxiety, stress, PPC, or generic health. Individual choice in prenatal diagnosis meets individual needs and thereby could reduce anxiety and stress.

Rapid and novel prenatal molecular assay for detecting aneuploidies and microdeletion syndromes

OBJECTIVES

To develop a targeted aneuploidy and microdeletion detection platform for use in the prenatal setting, to assess the integrity of the platform with a robust validation system, and to prospectively determine the performance of the platform under routine clinical conditions.

METHODS

To generate proxies for the various disorders assessed by the assay for analytical validation purposes, cells from ten microdeletion syndromes as well as from common aneuploidies were spiked into cleared amniotic fluid. Genomic DNA was isolated, labeled, and hybridized to microbeads that have been coupled to DNA derived from Bacterial Artificial Chromosome (BAC) from the relevant regions targeted by the array. Beads were read using a flow cytometric multiplex bead array detection system. In the prospective part of the study, 104 amniotic fluid samples were collected and analyzed.

RESULTS

All microdeletion syndromes and aneuploidies were validated in a blinded fashion. In the prospective study, the total number of readable samples was 101 of 104 (97%). All sample results were confirmed independently.

CONCLUSION

The bead array approach is a rapid and reliable test for detecting aneuploidies and microdeletions. This assay has the potential to provide the benefit of expanded molecular cytogenetic testing to pregnant women undergoing invasive prenatal diagnosis. This approach may be especially useful in parts of the world where cytogenetic personnel and facilities may be limited.

Rapid testing versus karyotyping in Down's syndrome screening: cost-effectiveness and detection of clinically significant chromosome abnormalities

In all, 80% of antenatal karyotypes are generated by Down's syndrome screening programmes (DSSP). After a positive screening, women are offered prenatal foetus karyotyping, the gold standard. Reliable molecular methods for rapid aneuploidy diagnosis (RAD: fluorescence in situ hybridization (FISH) and quantitative fluorescence PCR (QF-PCR)) can detect common aneuploidies, and are faster and less expensive than karyotyping.In the UK, RAD is recommended as a standalone approach in DSSP, whereas the US guidelines recommend that RAD be followed up by karyotyping. A cost-effectiveness (CE) analysis of RAD in various DSSP is lacking. There is a debate over the significance of chromosome abnormalities (CA) detected with karyotyping but not using RAD. Our objectives were to compare the CE of RAD versus karyotyping, to evaluate the clinically significant missed CA and to determine the impact of detecting the missed CA. We performed computer simulations to compare six screening options followed by FISH, PCR or karyotyping using a population of 110948 pregnancies. Among the safer screening strategies, the most cost-effective strategy was contingent screening with QF-PCR (CE ratio of $24084 per Down's syndrome (DS) detected). Using karyotyping, the CE ratio increased to $27898. QF-PCR missed only six clinically significant CA of which only one was expected to confer a high risk of an abnormal outcome. The incremental CE ratio (ICER) to find the CA missed by RAD was $66608 per CA. These costs are much higher than those involved for detecting DS cases. As the DSSP are mainly designed for DS detection, it may be relevant to question the additional costs of karyotyping.

Rapid aneuploidy testing versus traditional karyotyping in amniocentesis for certain referral indications

OBJECTIVE

(1) To determine the suitability of replacing full karyotype analysis with quantitative fluorescent polymerase chain reaction (QF-PCR) for prenatal diagnosis in amniotic fluid samples obtained by amniocentesis. (2) To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

METHODS

We reviewed all fetal karyotypes obtained by amniocentesis between January 2004 and December 2008. We compared the cytogenetic findings obtained through conventional karyotype with those that would have been theoretically obtained using QF-PCR.

RESULTS

Of the 4007 karyotypes obtained, 110 abnormal karyotypes were found (2.8%). Out of these, 30 (27%) were chromosomal abnormalities (CA) which would not have been detected by PCR alone. These included 16 cases (53%) predicted to confer no increased risk, 9 (30%) predicted to have a low risk, and 5 (17%) with an uncertain or high risk of fetal abnormality. A policy of QF-PCR alone would have identified 80 of 85 (94%) clinically significant CA. When QF-PCR shows a normal result, the overall residual risk is 0.75% for any CA and 0.12% for a clinical significant CA.

CONCLUSION

In our population, a policy of QF-PCR alone would miss 0.12% clinically relevant CA. QF-PCR directed to common aneuploidies can be considered as an economically and clinically acceptable prenatal diagnosis policy, offering full karyotype only for specific indications.

The impact of rapid aneuploidy detection (RAD) in addition to karyotyping versus karyotyping on maternal quality of life

OBJECTIVE

To assess the impact of rapid aneuploidy detection (RAD) combined with fetal karyotyping versus karyotyping only on maternal anxiety and health-related quality of life.

METHODS

Women choosing to undergo amniocentesis were selected into group 1, i.e. receiving a karyotype result only (n = 132) or to group 2, i.e. receiving both the result of RAD and karyotyping (n = 181).

RESULTS

There were no systematic differences in time of RAD combined with karyotyping versus karyotyping only in terms of anxiety (P = 0.91), generic physical health (P = 0.76, P = 0.46), generic mental health (P = 0.52, P = 0.72), personal perceived control (P = 0.91) and stress (P = 0.13). RAD combined with karyotyping reduced anxiety and stress two weeks earlier compared to karyotyping only.

CONCLUSION

RAD as add-on to karyotyping reduces anxiety and stress in the short term but it does not influence overall anxiety, stress, personal perceived control, and generic mental and physical health when compared to a karyotype-only strategy.

Using population-based data to predict the impact of introducing noninvasive prenatal diagnosis for Down syndrome

PURPOSE

To compare the number and types of chromosome abnormalities prenatally diagnosed and the number of invasive procedures between current prenatal testing pathways and a pathway where noninvasive prenatal diagnosis for Down syndrome replaces Down syndrome screening tests.

METHODS

Numbers and types of chromosome abnormalities for each referral category were extracted from prenatal diagnostic testing reports routinely collected in Victoria, Australia, in 2006 and 2007. These data were then applied to the proposed implementation strategy.

RESULTS

If noninvasive prenatal diagnosis for Down syndrome had replaced Down syndrome screening tests in 2006 and 2007, in Victoria, there would have been 25 (7%) additional Down syndrome diagnosed, 6896 (84%) fewer invasive procedures, and 231 (56%) non-Down syndrome chromosome abnormalities no longer detected. These include trisomy 13, trisomy 18, sex chromosome abnormalities, balanced and unbalanced rearrangements, polyploidy, and mosaic results.

CONCLUSIONS

The potential loss of information about chromosome abnormalities other than Down syndrome with noninvasive prenatal diagnosis compared with full karyotyping with traditional prenatal diagnosis should be considered when planning for the implementation of new technologies.

Karyotyping or rapid aneuploidy detection in prenatal diagnosis? The different views of users and providers of prenatal care

Developments in prenatal diagnosis raise the question which test strategy should be implemented. However, preferences of women and caregivers are underexposed. This study investigates what kind of prenatal test pregnant women and caregivers prefer and if differences between the groups exist, using self-report questionnaires. Women preferred either karyotyping (50%) or rapid aneuploidy detection (43%). Caregivers opted for the latter (78%). A test targeted on Down syndrome was the least preferred in both groups. We recommend the use of individualised choice for genetic test in prenatal diagnosis, overcoming the existing differences in preferences between women and caregivers.

Rapid prenatal diagnosis of common chromosome aneuploidies by QF-PCR, results of 9 years of clinical experience

BACKGROUND

Despite being deliberately targeted to common chromosome aneuploidies, the rapid quantitative fluorescent polymerase chain reaction (QF-PCR) tests can detect the majority of chromosome abnormalities in prenatal diagnosis. The main advantages of this assay are low cost, speed and automation allowing large-scale application.

METHODS

We developed a QF-PCR test that was applied on 43 000 clinical samples reporting results in 24 h. Most common indications were biochemical risk (32%) and advanced maternal age (30%). Samples were also tested by cytogenetic analysis and the results compared.

RESULTS

Aneuploidies involving chromosomes 21, 18, 13, X and Y were detected with 100% specificity. Several cases of partial trisomies and mosaicism were also identified. Overall 95% of clinically relevant abnormalities were readily detected and termination of affected pregnancies could be performed without waiting for the cytogenetic results.

CONCLUSIONS

Our study supports the possibility of reducing the load of prenatal cytogenetic tests if the pregnancies are carefully monitored by non-invasive screening. In case of abnormal QF-PCR results, medical action can be taken within few hours from sampling. In cases of negative QF-PCR results, cytogenetic analyses might only be performed for fetuses with ultrasound abnormalities. In countries where large-scale cytogenetic tests are not available, QF-PCR may be used as the only prenatal diagnostic procedure.

Rapid aneuploidy detection with multiplex ligation-dependent probe amplification: a prospective study of 4000 amniotic fluid samples

The introduction of prenatal screening requires rapid high-throughput diagnosis of common aneuploidies. Multiplex ligation-dependent probe amplification (MLPA) allows for quick, easily automated multiplex testing of these aneuploidies in one polymerase chain reaction. We performed a large prospective study using MLPA on 4000 amniotic fluid (AF) samples including all indications and compared its value to karyotyping and fluorescence in situ hybridization (FISH). MLPA can reliably determine common aneuploidies with 100% sensitivity and 100% specificity. Moreover, some mosaic cases and structural chromosome aberrations were detected as well. In cases of a male fetus, triploidies can be detected by an aberrant pattern of probe signals, which mimics maternal cell contamination (MCC). Macroscopic blood contamination was encountered in 3.2% of the AF samples. In 20% of these samples, an MLPA pattern was found consistent with MCC, although there were no false negatives of the most common aneuploidies. As the vast majority of inconclusive results (1.7%) is due to potential MCC, we designed a protocol in which we determine whether MLPA can be performed on blood-contaminated AF samples by testing if blood is of fetal origin. Then, the number of inconclusive results could be theoretically reduced to 0.05%. We propose an alternative interpretation of relative probe signals for rapid aneuploidy diagnosis (RAD). We discuss the value of MLPA for the detection of (submicroscopic) structural chromosome anomalies. MLPA is a reliable method that can replace FISH and could be used as a stand-alone test for RAD instead of karyotyping.

Multiplex ligation-dependent probe amplification versus karyotyping in prenatal diagnosis: the M.A.K.E. study

Background

In the past 30 years karyotyping was the gold standard for prenatal diagnosis of chromosomal aberrations in the fetus. Traditional karyotyping (TKT) has a high accuracy and reliability. However, it is labor intensive, the results take 14–21 days, the costs are high and unwanted findings such as abnormalities with unknown clinical relevance are not uncommon. These disadvantages challenged the practice of karyotyping. Multiplex ligation-dependent probe amplification (MLPA) is a new molecular genetic technique in prenatal diagnosis. Previous preclinical evidence suggests equivalence of MLPA and traditional karyotyping (TKT) regarding test performance.

Methods/Design

The proposed study is a multicentre diagnostic substitute study among pregnant women, who choose to have amniocentesis for the indication advanced maternal age and/or increased risk following prenatal screening test. In all subjects, both MLPA and karyotyping will be performed on the amniotic fluid sample. The primary outcome is diagnostic accuracy. Secondary outcomes will be maternal quality of life, women's preferences and costs. Analysis will be intention to treat and per protocol analysis. Quality of life analysis will be carried out within the study population. The study aims to include 4500 women.

Discussion

The study results are expected to help decide whether MLPA can replace traditional karyotyping for 'low-risk' pregnancies in terms of diagnostic accuracy, quality of life and women's preferences. This will be the first clinical study to report on all relevant aspects of the potential replacement.

Trial Registration

The protocol is registered in the clinical trial register number ISRCTN47252164

A randomised trial of two methods of issuing prenatal test results: the ARIA (Amniocentesis Results: Investigation of Anxiety) trial

BACKGROUND

Many pregnant women experience anxiety while waiting for the results of diagnostic tests. Policies and practices intended to reduce this anxiety require evaluation.

OBJECTIVES

To test the following two hypotheses: * That giving amniocentesis results out on a fixed date alters maternal anxiety during the waiting period, compared with a policy of telling parents that the result will be issued "when available" (i.e. variable date). * That issuing early results from a rapid molecular test alters maternal anxiety during the waiting period, compared with not receiving any results prior to the karyotype. The effects of the two interventions on anxiety 1 month after receiving karyotype results were also examined.

DESIGN

A multicentre, randomised, controlled, open fixed sample, 2 x 2 factorial design trial, with equal randomisation.

SETTING

The prenatal diagnosis clinics in 12 hospitals in England offering amniocentesis as a diagnostic test for Down's syndrome.

SAMPLE

Two hundred and twenty-six women who had had an amniocentesis were randomised between June 2002 and July 2004. Eight women with abnormal results or test failure were excluded post-randomisation.

INTERVENTIONS

Issuing karyotype results on a prespecified fixed date, rather than issuing them as soon as they became available. Issuing karyotype results alone, or subsequent to issuing results from a rapid molecular test for the most common chromosomal abnormalities.

MAIN OUTCOME MEASURES

Average anxiety during the waiting period, calculated using daily scores from the short version of the Spielberger State-Trait Anxiety Inventory (STAI). Anxiety 1 month after receiving karyotype results, measured using the short form STAI.

RESULTS

Issuing early results from a partial but rapid test reduced maternal anxiety by a clinically significant amount during the waiting period (mean daily score 12.5 versus 14.8; scale score difference -2.36, 95% CI -1.2, -3.6), compared with receiving only the full karyotype results. There was no evidence that giving out karyotype results on a fixed or on a variable date altered maternal anxiety during the waiting period (mean daily score 13.2 versus 14.2; scale score difference -1.02, 95% CI -2.2, 0.2). One month after receiving normal karyotype results, anxiety was low in all groups, but women who had been given rapid test results tended to be more anxious than those who had not (mean single day score 9.2 versus 8.3; mean scale score difference 0.95, 95% CI -0.03, 1.9). This small to moderate effect did not reach conventional levels of statistical significance.

CONCLUSIONS

Rapid testing was a beneficial addition to karyotyping, at least in the short term. This does not necessarily imply that early results would be preferred to comprehensive ones if women had to choose between them. Because there are no clear advantages in anxiety terms of issuing karyotype results as soon as they become available, or on a fixed date, women could be given a choice between them.

Molecular cytogenetic and rapid aneuploidy detection methods in prenatal diagnosis

Cytogenetic analysis is an important component of prenatal diagnosis. The ability to rapidly detect aneuploidy and identify small structural abnormalities of fetal chromosomes has been greatly enhanced by the use of molecular cytogenetic technologies. In this review, we will present some of the molecular cytogenetic techniques available to the clinical cytogenetics laboratory. These include fluorescence in situ hybridization (FISH), quantitative fluorescence PCR (QF-PCR), multiplex ligation-dependent probe amplification (MLPA) and microarray-based comparative genomic hybridization (array CGH). The benefits and limitations of each technology will be discussed in the context of prenatal diagnosis.

A comparison of Australian and UK obstetricians' and midwives' preferences for screening tests for Down syndrome

OBJECTIVE

To establish and compare obstetricians' and midwives' preferences for hypothetical prenatal screening tests for Down syndrome.

METHODS

A cross-sectional questionnaire survey was completed by 296 obstetricians and midwives at two teaching hospitals: one in Melbourne, Australia (n = 175), and one in London, UK (n = 94). Conjoint analysis was undertaken using random effects probit regression.

RESULTS

No significant differences were seen in any measurements when comparing obstetricians in Australia and the UK or midwives in Australia and the UK. Obstetricians and midwives shared similar relative values regarding the importance of the detection rate of the screening tests. However, obstetricians placed higher relative values on both timing of prenatal tests and risk associated with the subsequent diagnostic test than did midwives when considering optimal tests to offer women. Marginal rates of substitution suggest that, compared with midwives, obstetricians would wait longer and accept a greater decrease in detection rate for a test if it was safer. Younger midwives placed higher value on both detection rate and safety of prenatal tests than older midwives. Female obstetricians placed higher value on the timing of a test than male obstetricians.

CONCLUSION

Obstetricians in Australia and UK placed almost identical importance on test attributes, as did the midwives in the two countries. However, different attitudes towards tests were seen between obstetricians and midwives.

Fetal nuchal translucency scan and early prenatal diagnosis of chromosomal abnormalities by rapid aneuploidy screening: observational study

OBJECTIVE

To investigate an approach for the analysis of samples obtained in screening for trisomy 21 that retains the advantages of quantitative fluorescent polymerase chain reaction (qf-PCR) over full karyotyping and maximises the detection of clinically significant abnormalities.

DESIGN

Observational study.

SETTING

Tertiary referral centre.

SUBJECTS

17,446 pregnancies, from which chorionic villous samples had been taken after assessment of risk for trisomy 21 by measurement of fetal nuchal translucency (NT) thickness at 11 to 13(+6) weeks of gestation.

INTERVENTIONS

Analysis of chorionic villous samples by full karyotyping and by qf-PCR for chromosomes 13, 18, 21, X, and Y.

MAIN OUTCOME MEASURE

Detection of clinically significant chromosomal abnormalities.

RESULTS

The fetal karyotype was normal in 15,548 (89.1%) cases and abnormal in 1898 (10.9%) cases, including 1722 with a likely clinically significant adverse outcome. Karyotyping all cases would lead to the diagnosis of all clinically significant abnormalities, and a policy of relying entirely on qf-PCR would lead to the diagnosis of 97.9% of abnormalities. An alternative strategy whereby qf-PCR is the main method of analysis and full karyotyping is reserved for those cases with a minimum fetal NT thickness of 4 mm would require full karyotyping in 10.1% of the cases, would identify 99.0% of the significant abnormalities, and would cost 60% less than full karyotyping for all.

CONCLUSIONS

In the diagnosis of chromosomal abnormalities after first trimester screening for trisomy 21, a policy of qf-PCR for all samples and karyotyping only if the fetal NT thickness is increased would reduce the economic costs, provide rapid delivery of results, and identify 99% of the clinically significant chromosomal abnormalities.

Full karyotyping, rapid aneuploidy diagnosis or both when invasive prenatal testing is performed for diagnosis of thalassaemia?

A retrospective study was performed to compare the detection rate of chromosomal abnormalities by different approaches of full karyotyping, rapid aneuploidy diagnosis (RAD) or both when invasive prenatal testing is performed for diagnosis of thalassaemia. The karyotype results of 1120 prenatal samples obtained from thalassaemia couples from January 1985 to December 2002 in a referral centre for prenatal diagnosis were studied. The detection rate of chromosomal abnormalities by four different approaches were compared: (i) karyotyping for all samples; (ii) RAD (21,18,13,X,Y) for all samples; (iii) RAD for all samples + karyotyping for cases with ultrasound abnormalities; and (iv) RAD (21,18,13) for all + RAD (X,Y) for cases with ultrasound abnormalities consistent with Turner syndrome + karyotyping for cases with ultrasound abnormalities. Normal karyotypes were found in 1103 samples (98.5%). There were 17 cases (1.5%) of chromosomal abnormalities: four cases (0.36%) were clinically significant, eight cases (0.7%) were of borderline clinical significance and five cases (0.44%) were not confirmed by subsequent prenatal or postnatal tests. The incidences of autosomal (7/1120 = 0.63%) and sex chromosomal (5/1120 = 0.45%) abnormalities were not higher than those (0.41 and 0.22%, respectively) from newborn surveys (Hook and Hamerton, 1977) (P = 0.398 and 0.216, respectively). Approach 1 would detect all 17 chromosomal abnormalities. Approach 2 would detect three of four clinically significant chromosomal abnormalities but not detect six of eight chromosomal abnormalities of borderline clinical significance and three of five chromosomal abnormalities not confirmed by subsequent prenatal or postnatal tests. Approach 3, in addition, would be able to detect all four clinically significant chromosomal abnormalities. Approach 4 would detect all four clinically significant chromosomal abnormalities but would not detect seven of eight chromosomal abnormalities of borderline clinical significance and four of five chromosomal abnormalities not confirmed by subsequent prenatal or postnatal tests. RAD (21,18,13) for all + RAD (X,Y) for cases with ultrasound abnormalities consistent with Turner syndrome + karyotyping for cases with ultrasound abnormalities seemed to be the best approach for the detection of chromosomal abnormalities when invasive prenatal testing is performed for diagnosis of thalassaemia.

Ultrasound findings before amniocentesis in selecting the method of analysing the sample

OBJECTIVE

To determine if the primary method of cytogenetic analysis in pregnant women undergoing amniocentesis should be quantitative fluorescent polymerase chain reaction (qf-PCR), with karyotyping being performed only on those with abnormal ultrasound findings.

METHODS

Amniocentesis was performed in 3854 cases. The median maternal age was 36 years and median gestational age was 18 weeks. The indication for karyotyping was an increased risk for aneuploidy in the absence or presence of sonographic abnormalities detected at the scan before amniocentesis. All samples were analysed by qf-PCR and full karyotyping. For each detectable fetal defect, the positive or negative likelihood ratio for aneuploidy was determined.

OUTCOME MEASURE

Detection rate of clinically significant chromosomal abnormalities.

RESULTS

The karyotype was normal in 3617 (93.9%) cases. In 237 (6.1%) cases, the karyotype was abnormal and the detection rate by qf-PCR was 92.4%. A policy of performing qf-PCR in all cases and karyotyping in only those with combined likelihood ratios of > 1, > 3, and > 5 would detect 98.3, 96.6, and 95.4% of all chromosomal abnormalities and would require karyotyping in 16.1, 8.0, and 5.4% of the cases, respectively.

CONCLUSIONS

More than 95% of the aneuploidies can be detected if karyotyping is performed in addition to qf-PCR in about 15% of the cases selected on the basis of ultrasound findings before amniocentesis.

The future of prenatal diagnosis: rapid testing or full karyotype? An audit of chromosome abnormalities and pregnancy outcomes for women referred for Down's Syndrome testing

OBJECTIVE

To assess the implications of a change in prenatal diagnosis policy from full karyotype analysis to rapid trisomy testing for women referred primarily for increased risk of Down's Syndrome.

DESIGN

Retrospective collection and review of data.

SETTING

The four London Regional Genetics Centres.

POPULATION

Pregnant women (32,674) in the London area having invasive prenatal diagnosis during a six-year three-month period.

METHODS

Abnormal karyotypes and total number of samples referred for raised maternal age, raised risk of Down's Syndrome following serum screening or maternal anxiety were collected. Abnormal karyotypes detected by molecular trisomy detection were removed, leaving cases with residual abnormal karyotypes. These were assessed for their clinical significance. Pregnancy outcomes were ascertained by reviewing patient notes or by contacting obstetricians or general practioners.

MAIN OUTCOME MEASURES

Proportion of prenatal samples with abnormal karyotypes that would not have been detected by rapid trisomy testing, and the outcome of those pregnancies with abnormal karyotypes.

RESULTS

Results from 32,674 samples were identified, of which 24,891 (76.2%) were from women referred primarily for Down's Syndrome testing. There were 118/24,891 (0.47%) abnormal sex chromosome karyotypes. Of the samples with autosomal abnormalities that would not be detected by rapid trisomy testing, 153/24,891 (0.61%) were in pregnancies referred primarily for Down's Syndrome testing. Of these, 98 (0.39%) had a good prognosis (46/98 liveborn, 3/98 terminations, 1/98 intrauterine death, 1/98 miscarriage, 47/98 not ascertained); 37 (0.15%) had an uncertain prognosis (20/37 liveborn, 5/37 terminations; 12/37 not ascertained) and 18 (0.07%) had a poor prognosis (1/18 liveborn, 2/18 miscarriage, 11/18 terminations, 4/18 not ascertained).

CONCLUSIONS

For pregnant women with a raised risk of Down's Syndrome, a change of policy from full karyotype analysis to rapid trisomy testing would result in the failure to detect chromosome abnormalities likely to have serious clinical significance in approximately 0.06% (1 in 1659) cases. However, it should be noted that this figure may be higher (up to 0.12%; 1 in 833) if there were fetal abnormalities in some of the pregnancies in the uncertain prognosis group for which outcome information was not available.

Small interfering RNA and gene expression analysis using a multiplex branched DNA assay without RNA purification

The authors have developed a novel multiplex detection system that quantitatively measures the expression level of 11 messenger RNAs (mRNAs) directly from cell lysates or tissue homogenates without RNA purification. The system incorporates branched DNA (bDNA) technology from Bayer and a multiplex bead array platform from Luminex. In this study, a 21-nt synthetic small interfering RNA (siRNA; specifically designed to knockdown interleukin-8 [IL-8] expression) was delivered into HeLa cells. Using the multiplex bDNA assay, gene expression levels were measured simultaneously from cell lysates for 11 genes. After treating the HeLa cells for 20 h with phorbol myristate acetate (PMA), IL-8 mRNA levels were induced by almost 50-fold; transfection with 30 nM IL-8-specific siRNA reduced the PMA-induced IL-8 mRNA by 80%. In addition, PMA induced mRNA expression in IL-1alpha (3-fold) and IL-6 (4-fold); however, the IL-8 siRNA did not affect the expression of either of these 2 cytokine genes, indicating that the siRNA was selective for IL-8 mRNA expression. Three housekeeping genes' expression levels were measured under all conditions tested. The multiplex bDNA assay provides a powerful tool for quantitative multiplex gene expression analysis directly from cell lysates, which could be extremely valuable for conservation of rare or difficult-to-obtain samples.

Prenatal detection of Down's syndrome by rapid aneuploidy testing for chromosomes 13, 18, and 21 by FISH or PCR without a full karyotype: a cytogenetic risk assessment

BACKGROUND

In 2004, the UK National Screening Committee (UKNSC) recommended that new screening programmes for Down's syndrome need not include karyotyping and can offer prenatal diagnosis for the syndrome with FISH (fluorescence in-situ hybridisation) or PCR as rapid diagnostic tests. The UKNSC also recommended that FISH or PCR tests should only include trisomies 13, 18, and 21. We undertook a retrospective cytogenetic audit to assess the probable clinical effect of these proposed policy changes.

METHODS

23 prenatal cytogenetic laboratories from the UK public sector submitted data for amniotic fluid or chorionic villus samples referred from April, 1999, to March, 2004. We obtained data for the details of all abnormal karyotypes by reason for referral and assessed the efficiency of FISH and PCR rapid tests for the detection of chromosome abnormalities.

FINDINGS

Of 119,528 amniotic fluid and 23,077 chorionic villus samples, rapid aneuploidy testing replacement of karyotyping would have resulted in about one in 100 and one in 40 samples having an undetected abnormal karyotype, respectively. Of these missed results, 293 (30%) of 1006 amniotic fluid samples and 152 (45%) of 327 chorionic villus samples were associated with a substantial risk of an abnormal phenotypic outcome. Of 34,995 amniotic fluid and 3049 chorionic villus samples that had karyotyping and a rapid test on the same sample, none of the three technologies was completely reliable to detect an abnormal karyotype, but the best protocol for an interpretable result was PCR and karyotyping or FISH and karyotyping.

INTERPRETATION

Replacement of full karyotyping with rapid testing for trisomies 13, 18, and 21 after a positive screen for Down's syndrome will result in substantial numbers of liveborn children with hitherto preventable mental or physical handicaps, and represents a substantial change in the outcome quality of prenatal testing offered to couples in the UK.