Rapid aneuploidy detection or karyotyping? Ethical reflection

Rapid and simultaneous detection of common aneuploidies by quadruplex real-time polymerase chain reaction combined with melting curve analysis

BACKGROUND

During the prenatal period, the number variation of chromosomes 13, 18, 21, X and Y accounts for more than 80% of the clinically significant chromosomal abnormalities diagnosed. Rapid tests for prenatal diagnosis of these abnormalities can improve pregnancy management and alleviate parental anxiety. Here, we present a molecular alternative method for detecting common aneuploidies.

METHODS

This method is based on co-amplification of segmental duplications located on two different chromosomes using a single pair of primers. Segmental duplications have a high degree of sequence identity, but have single-nucleotide differences in some regions. These sequence differences can be quantified using melting curve analysis of dual-labeled probes to estimate the relative dosages of different chromosomes. We designed two quadruplex real-time PCR assays to detect aneuploidies of chromosomes 13, 18, 21, X and Y.

RESULTS

We examined 75 aneuploid DNA samples and 56 unaffected DNA control samples using these two assays and correctly identified all samples. Four cases of unbalanced translocation were also accurately detected. The observed averaged ratio for each chromosomal disorder was similar to the theoretically expected value.

CONCLUSIONS

Our real-time assay is a robust, rapid, and easy to conduct technique for prenatal diagnosis of common aneuploidies, representing a competitive alternative for use in diagnostic laboratories.

Microarrays as a diagnostic tool in prenatal screening strategies: ethical reflection

Genomic microarray analysis is increasingly being applied as a prenatal diagnostic tool. Microarrays enable searching the genome at a higher resolution and with higher sensitivity than conventional karyotyping for identifying clinically significant chromosomal abnormalities. As yet, no clear guidelines exist on whether microarrays should be applied prenatally for all indications or only in selected cases such as ultrasound abnormalities, whether a targeted or genome-wide array should be used, and what these should include exactly. In this paper, we present some ethical considerations on the prenatal use of microarrays. There is a strong consensus, at least in Western countries, that the aim of prenatal screening for foetal abnormalities should be understood as facilitating autonomous reproductive choice for prospective parents. The tests offered should be valid and useful to reach that purpose. Against this background, we address several ethical issues raised by the prenatal application of microarrays. First, we argue that the general distinction between a targeted and a genome-wide microarray needs to be scrutinised. Then we examine whether microarrays are 'suitable tests' to serve either a screening or a diagnostic purpose. Given the wide range of findings possibly generated by microarrays, the question arises whether microarrays actually promote or interfere with autonomous reproductive decision-making. Moreover, if variants of unknown clinical significance are identified, this adds to the burden and complexity of reproductive decision-making. We suggest a qualified use of microarrays in the prenatal context.

The impact of national guidance for anomaly screening and invasive testing: unintended consequences

Recent guidance from the UK National Screening Committee (NSC) and the Fetal Anomaly Screening Programme (FASP) has led to important changes in prenatal ultrasound diagnosis and invasive testing. These relate to prenatal ultrasound investigation of what were previously known as 'soft markers' for Down's syndrome at the time of the detailed anomaly scan and as to whether full karyotype or FISH (fluorescent in situ hybridisation)/QFPCR (quantitative fluorescence PCR) testing for trisomies should be carried out when an invasive test is performed. Neither recommendation is directly related to the other but both in combination could have profound implications for the detection of chromosomal abnormalities other than trisomy 21 (Down's syndrome). In the light of two cases recently managed in one regional fetal medicine unit, we retrospectively reviewed cases where, with correct application of the NSC and FASP recommendations, non-lethal and clinically important chromosomal abnormalities would most likely not have been detected.

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.

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.

Multiplex ligation-dependent probe amplification (MLPA) and prenatal diagnosis

Multiplex ligation-dependent probe amplification (MLPA) is a recent technique for the relative quantitation of up to 40 to 45 nucleic acid targets. Due to its relative simplicity, low cost, and availability of laboratory-developed and more than 300 commercially-developed assays, MLPA has become more widely used for both research and diagnostic applications. The MLPA platform is now extensively applied for postnatal diagnosis of genetic disorders and has recently been used for prenatal diagnosis. The published uses of MLPA for prenatal diagnosis include detection of aneuploidies, common microdeletion syndromes and subtelomeric copy-number changes, identification of marker chromosomes, and detection of familial copy-number changes in single genes. This review describes the technique of MLPA in detail and offers considerations for the interpretation of results in the clinical diagnostic setting. © 2012 John Wiley & Sons, Ltd.

Advances in prenatal screening: the ethical dimension

Prenatal screening strategies are undergoing rapid changes owing to the introduction of new testing techniques. The overall tendency is towards broadening the scope of prenatal testing through increasingly sensitive ultrasound scans and genome-wide molecular tests. In addition, non-invasive prenatal diagnosis is likely to be introduced in the near future. These developments raise important ethical questions concerning meaningful reproductive choice, the autonomy rights of future children, equity of access and the proportionality of testing.