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Keywords:

  • BoBs;
  • karyotyping;
  • microdeletion;
  • QF-PCR

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Objective

To evaluate the diagnostic performance of the BACs-on-Beads (BoBs) assay for prenatal detection of chromosomal abnormalities.

Design

Retrospective study.

Setting

Tertiary prenatal diagnosis centre.

Population

Women referred for prenatal diagnosis.

Methods

We retrieved 2153 archived DNA samples collected between January 2010 and August 2011 for the BoBs assay. These samples had previously been tested by quantitative fluorescence polymerase chain reaction (QF-PCR) and karyotyping. In the BoBs assay a sample was defined as normal disomic when the ratio of the fluorescence intensities in a chromosome locus lay within the threshold (mean ratio ± 2SD), and as deleted or duplicated when the ratio was below the lower threshold (0.6–0.8) or above the upper threshold (1.3–1.4), respectively. The BoBs results were further validated by microarray and compared in a blinded manner with the original QF-PCR and karyotyping results.

Main outcome measures

Concordance of any numerical, structural, and submicroscopic chromosomal abnormalities between the methods.

Results

BACs-on-Beads was similar to karyotyping and QF-PCR in detecting trisomy 13, trisomy 18, trisomy 21, and sex chromosomal aneuploidies, and superior to QF-PCR in detecting major structural abnormalities (53.3 versus 13.3%) and mosaicism (28.6 versus 0%) involving chromosomal abnormalities other than the common aneuploidies. BoBs detected six microdeletion syndromes missed by karyotyping and QF-PCR; however, BoBs missed two cases of triploidy identified by QF-PCR. Therefore, the sensitivity of BoBs is 96.7% (95% CI 92.6–98.7%), and its specificity is 100% (95% CI 99.8–100%).

Conclusions

BACs-on-Beads can replace QF-PCR for triaging in prenatal diagnosis, and gives a better diagnostic yield than current rapid aneuploidy tests.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Karyotyping, a time- and labour-intensive method, has traditionally been regarded as the gold standard for the prenatal diagnosis of chromosomal abnormalities; however, for the diagnosis of common aneuploidies, involving chromosomes 13, 18, and 21, triploidy, and aneuploidy of the sex chromosomes, karyotyping is being progressively replaced by the introduction of rapid aneuploidy tests (RATs),[1, 2] such as quantitative fluorescence polymerase chain reaction (QF-PCR), fluorescence in situ hybridisation (FISH), and multiplex ligation-dependent probe amplification (MLPA). These common abnormalities account for more than 80% of the clinically significant chromosomal defects diagnosed in the prenatal period.[3] Furthermore, additional tests using chromosomal microarray-based analysis (CMA), such as array comparative genomic hybridisation (array CGH) or single nucleotide polymorphism (SNP) array platforms, may be required to provide a more comprehensive genome-wide identification of submicroscopic abnormalities.[4-7] CMA analysis is expensive, and creates uncertainties when copy number variations of unknown pathogenic significance are detected.[8] Although RATs are cheaper than conventional karyotyping, they nevertheless have limitations,[3, 9, 10] so bacterial artificial chromosomes (BACs)-on-Beads (BoBs) technology has been introduced for the detection of common aneuploidies and also for specific microdeletion syndromes.[11-14] The BoBs assay is a bead-based multiplex assay using beads impregnated with different concentrations of two different fluorochromes to create an array of up to 100 different unique probes; each probe is derived from a BAC DNA that can allow the diagnosis of common trisomies and nine microdeletions within 24 hours.[11, 12, 15]

The benefits of BoBs assay in terms of diagnostic yield and sensitivity compared with current RATs remain unclear. Several studies with sample sizes between 100 and 1650 have been used to demonstrate the additional diagnostic benefit of BoBs for detecting microdeletions with 93.8–97.0% readable results,[11-14] but no retrospective studies have yet evaluated BoBs against karyotyping and QF-PCR. We hypothesise that BoBs has the potential to become the main screening/triaging test in prenatal diagnosis. To test our hypothesis we conducted a retrospective cohort study on consecutive cases presented to us for prenatal diagnosis to compare the diagnostic accuracy of the BoBs assay against the known results of conventional karyotyping and QF-PCR.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Sample selection and preparation

The study institution is a referral centre for fetal medicine and prenatal diagnosis. Both conventional karyotyping and QF-PCR are part of the routine clinical service on offer. In our practice, after karyotyping and QF-PCR assessment of the fetal samples, the leftover DNA samples are routinely archived at −80°C, with written consent. For this study, consecutively archived DNA samples collected between January 2010 and August 2011 were retrieved for BoBs assay without knowledge of the original karyotype and QF-PCR results, and the results of the different tests were compared. The majority of these samples originated from chorionic villi (1473; 68.4%) and amniotic fluid (665; 30.9%), and only 15 samples (0.7%) were from either fetal blood or placental tissue. Archived DNA samples with less than 50 ng of total genomic DNA were excluded from this study. Ethics approval was obtained from the Joint Chinese University of Hong Kong–New Territories East Cluster Clinical Research Ethics Committee (CRE-2011.273).

Karyotyping and QF-PCR

The fetal chromosomes were examined using the standard G-banding method. QF-PCR analysis was performed based on polymorphic small tandem repeat (STR) markers on chromosomes 13, 18, 21, X, and Y. Genomic DNA was extracted from the prenatal samples according to the manufacturer's protocol (Qiagen, Hilden, Germany), except that a modified RNase A incubation step was added. In brief, 3–5 ml of amniotic fluid was centrifuged at 400 × g for 5 minutes. The cell pellet was suspended in 200 μl of 1× (working solution) phosphate-buffered saline and 20 μl of protease K, and 4 μl of RNase A was added followed by incubation at room temperature (24–27°C) for 2 minutes. After this, 200 μl of AL buffer was added and incubated at 56°C for 10 minutes. After washing and performing DNA elution according to the manufacturer's instructions, QF-PCR was performed according to the previously published protocol.[15]

BoBs assay

This assay was designed for the detection of gains and losses of DNA in chromosomal regions associated with nine microdeletion syndromes, as well as copy number changes of chromosomes 13, 18, 21, X, and Y. The assay was read using a Luminex 200 analyser, and the fluorescence data were analysed with BoBsoft® software developed by the assay manufacturer (PerkinElmer, Wallac Oy, Turku, Finland). Five independent probes were included for each of chromosomes 13, 18, 21, X, and Y, and between four and eight probes for each of the selected microdeletion regions. The BoBs assay was performed according to the manufacturer's protocol as described previously.[15] Briefly, 50–250 ng of genomic DNA was labelled with biotin-dNTP, purified and then hybridised in microplate wells overnight with the BoBs mix. Normal male and female DNA (Promega, Madison, WI, USA) was also labelled and hybridised in duplicate as a reference for each plate of samples. After a series of washes before and after incubation with streptavidin phycoerythrin reporter, the hybridised signals were detected by the Luminex xMAP system (Luminex Corp, Austin, TX, USA). BoBsoft® 1.0 generated the results with numerical and graphical presentations of probes and chromosome locus group ratios against both female (red line) and male (blue line) references. Sample acceptance requires a coefficient of variation (CV) of 6% or less. A sample was defined as normal disomic when the ratios of the fluorescence intensities for a chromosome region fell within the lower and upper threshold limits (mean ratio ± 2 SDs), with a ratio of about 1.0. A sample was defined as deleted/duplicated at a specific chromosomal locus when the ratios of the fluorescence intensities fell outside the threshold of the mean ratio ± 2 SDs, typically ranging between 0.6 and 0.8 (deleted) and between 1.3 and 1.4 (duplicated), respectively. If the intensity result is reported between 0.9 and 1.2 this could indicate mosaicism,[15] and the BoBs assay is repeated. Any microdeletion or microduplication detected by the BoBs assay is then validated with the Agilent arrayCGH platform (Agilent, Santa Clara, CA, USA) using the 44K Fetal DNA chip.[5, 8] All data analysis was performed by two independent technical staff members in a blinded fashion.

Comparison between BoBs assay, QF-PCR, and karyotyping

The results of the BoBs assay were compared with the original QF-PCR and karyotyping results, with karyotyping as the comparator analysed in blinded fashion, according to the following two main categories.

  1. Targets of routine QF-PCR testing that include aneuploidies involving chromosomes 13, 18, 21, and the sex chromosomes, trisomies, monosomies, and polyploidies. Mosaic trisomies or monosomies involving these chromosomes were also counted in this group.
  2. Chromosomal abnormalities other than category 1: such as structural chromosomal abnormalities involving all chromosomes, or trisomies or monosomies involving chromosomes other than chromosomes 13, 18, 21, and the sex chromosomes; mosaicism in chromosomes other than 13, 18, 21, and the sex chromosomes; microdeletion and microduplication in any chromosome; and balanced translocation/inversion and benign markers in any chromosome.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Sample quality and basic information

A total of 2153 archived DNA samples were retrieved and accepted for analysis, as the DNA content was more than 50 ng in all samples. The sample size was based on the assumption that the incidence of either one of these nine microdeletion syndromes is approximately 1 in 1400–1700.[11-13] Therefore, our sample is likely to have included at least one case of a microdeletion syndrome to be detected by the BoBs assay. The majority of these samples originated from chorionic villi (1473; 68.4%) and amniotic fluid (665; 30.9%), and only 15 samples (0.7%) were from fetal blood or placental tissue. The original indications for fetal karyotyping were positive screening for trisomy 21 (1532; 71.2%), the presence of fetal ultrasound abnormalities (221; 10.3%), advanced maternal age (259; 12.0%), and the presence of other risk factors such as a previous family history of chromosomal abnormalities and maternal anxiety (141; 6.5%); however, two samples did not pass the sample acceptance threshold for BoBs assay (autosomal ratio CV < 6%), giving a failure rate of 0.09%. Both samples originated from amniotic fluid samples. The turnaround time was 2 days, which is comparable with a turnaround time for QF-PCR of 1–2 days.

Common aneuploidies involving chromosomes 13, 18, 21, and the sex chromosomes

Of the 2151 qualifying samples in the final study cohort, 183 (8.5%) had one of the common aneuploidies involving chromosomes 13, 18, 21, and the sex chromosomes, as detected by karyotyping (Table S1). Trisomy 21 was the most common (T21 = 78/183, 42.6%), followed by trisomy 18 (T18 = 52/183, 28.4%, including one mosaic), Turner syndrome (27/183, 14.8%, including five mosaics), XXX or XXY (12/183, 6.6%), and trisomy 13 (T13 = 9/183, 4.9%, including one mosaic). There were also two cases of triploidy and two cases of mosaic tetraploidy.

Compared with karyotype results, the sensitivities of QF-PCR and BoBs assay were similar, at 97.8 and 96.7%, respectively (Table S1). The BoBs assay detected all cases of T21, T13, and T18, whereas QF-PCR failed to detect a case of T18, which was reported as ‘inconclusive due to borderline allelic ratio (1.4–1.6) and suggested mosaic trisomy 18’. The BoBs assay missed one case of mosaic trisomy 13 that was identified by QF-PCR, however. In addition, QF-PCR also picked up two cases of triploidy that were missed by BoBs. Neither test was able to detect the two cases of mosaic tetraploidy. For Turner syndrome, BoBs appeared superior to QF-PCR in detecting mosaic monosomy X (80.0 versus 60.0%). No false-positive results were observed in the QF-PCR or BoBs assays: the specificity was 100% with a confidence interval of 99.8–100%.

Other chromosomal abnormalities detected by karyotyping

There were 15 cases (0.7%) of major chromosomal abnormalities involving other chromosomes, as well as structural abnormalities in chromosomes 13, 18, and X (Table 1). Among them were four cases (26.6%) with abnormalities involving the targeted chromosomes, two of which were detected by QF-PCR. On the other hand, the BoBs assay detected eight of these 15 cases (53.3%), or eight out of ten cases involving the targeted chromosomal loci (80.0%). These eight cases had abnormalities involving the selected target loci in chromosomes 4, 5, 13, 18, 22, and X. Although the design of the BoBs assay also targeted some regions in chromosomes 15 and 22, it could not detect the case with ring chromosomes on 15 and 22. There were seven cases of mosaicism involving chromosomes 2, 7, 8, 15, 16, and 22. Excluding the two cases that involved chromosomes 2 and 16, which were not targeted by the BoBs assay, it was able to detect two out of the other five cases (40%). The QF-PCR test was negative in all seven cases, as the chromosome regions were not targeted (Table 1). In addition, there were three cases with marker chromosomes, and 11 and 34 cases with balanced translocation and inversion, respectively. None of these cases were detected by QF-PCR or BoBs assay (Table 1).

Table 1. Detection rate of other numerical and structural chromosomal abnormalities by quantitative fluorescence polymerase chain reaction (QF-PCR) and BACs-on-beads (BoBs) assay, in comparison with karyotyping
Chromosome involved n Karyotype resultDetected by QF-PCR (Y/N)Detected by BoBs (Y/N)
  1. a

    Including normal variant of inv(9)(p11q13).

Other numerical and structural chromosomal abnormalities
Chr4246,XX,del(4)(p15.2)NY
46,XX,der(4)t(4;7)(q34;p21)patNY
Chr5146,XY,der(5)t(5;18)(p13;q12.3)matNY
Chr9146,XX,der(9)?t(9;?)(p22;?)NN
Chr13146,XY,del(13)(q12q14)NY
Chr15146,XX,r(15)(p12q26)NN
Chr16146,XX,der(16)t(16;17)(p13.3;q25)NN
Chr18146,XX,der(18)t(Y;18)(q11.2;p11.2)patYN
Chr20147,XX,+20NN
Chr22446,XX,r(22)NN
47,XX,+der(22)t(11;22)(q23;q11.2)NY
47,XY,+22NY
47,XY,+der(22)t(11;22)(q23.3;q11.2)NY
ChrX246,X,der(X)t(X;4)(q21.2;q31)NN
46,X,der(X)del(X)(p11)del(X)(q13)YY
Total15 2 (13.3%)8 (53.3%)
Mosaicism involving chromosomes other than Chr13, 18, 21, and the sex chromosomes
Chr21mos 47,XY,+2[13]/46,XY[25]NN
Chr71mos 47,XX,+7[30]/46,XX[3]NN
Chr82mos 47,XX,+8[24]/46,XX[6]NN
mos 47,XY,+8[13]/46,XX[12]NN
Chr151mos 47,XX,+15[15]/46,XX[18]NY
Chr161mos 47,XX, +16 [21]/46XX[13]NN
Chr221mos 47,XY,+22[8]/46,XY[22]NY
Total7 0 (0%)2 (28.6%)
Marker chromosome  47,XY,+mar patNN
 48,XY,+mar1,+mar2[23]/47,XY,+mar1[7]NN
 mos 47,XY,+mar[15]/46,XY[7]NN
Total3 0 (0%)0 (0%)
Balanced translocation 11 0 (0%)0 (0%)
Inversion 34a 0 (0%)0 (0%)

Microdeletion/microduplication missed by karyotyping or QF-PCR, but detected by BoBs assay

Among the 1897 cases (88.2%) with normal karyotype results, BoBs successfully detected six cases of microdeletion and two cases of microduplication, which were all classed as normal by QF-PCR (Table 2). Four of the cases were recognised as deletions of the Di George syndrome region (22q11.2) (Figure 1A), characterised by increased nuchal translucency and tricupsid regurgitation detected in the first trimester, and the other three had cardiac malformations identified by ultrasound in the second trimester. There was one case of a deletion of the Miller–Dieker syndrome region (17p13.3), with multiple abnormalities identified in the first trimester, and one case of a deletion of the Prader–Willi syndrome region (15q11–q12), which was associated with a positive screening test for trisomy 21, but no obvious structural abnormality was detected (Figure 1B, C). There were two cases identified as duplications of the Di George syndrome region (22q11.2). All these abnormal results were subsequently confirmed by either arrayCGH or specific QF-PCR targeting the pathogenic region (Figure 2); however, as the microduplication at the Di George syndrome region is of ‘uncertain pathogenicity’, the last two cases were not regarded as pathogenic. Our results suggest that the performance of BoBs in terms of diagnostic yield compared with the other tests is driven by the prevalence of the targeted microdeletion syndromes, for example Di George syndrome is relatively more prevalent. Also, the timing of the sampling (i.e. first-trimester chorionic villus sampling or second-trimester amniocentesis) does not affect the test performance.

Table 2. Eight cases classified as normal by quantitative fluorescence polymerase chain reaction/karyotyping, and unmasked as microdeletion/duplication by BoBs assay
CaseSampleIndicationResults
  1. +, duplication; −, deletion; AF, amniotic fluid; CVS, chorionic villus sample; DGS, Di George syndrome region; MDS, Miller–Dieker syndrome region; PWS, Prader–Willi syndrome region.

1CVSPositive first-trimester trisomy 21 screening; increased nuchal translucency, tricuspid regurgitation−DGS, XY
2AFInterruption aortic arc, ventricular septal defect, hypertelorism, exophthalmos, micrognathia detected in second trimester−DGS, XY
3AFTetralogy of Fallot detected in second trimester−DGS, XY
4AFFetal congenital heart disease detected in second trimester−DGS, XY
5CVSPositive first-trimester trisomy 21 screening; general oedema, small nasal bone, exomphalos on ultrasonography−MDS, XY
6AFPositive second-trimester trisomy 21 screening−PWS, XY
7AFPositive second-trimester trisomy 21 screening; increased nuchal fold (7.8 mm) in the second trimester+DGS, XX
8CVSFirst-trimester ultrasound showed absent nasal bone, single umbilical artery+DGS, XY
image

Figure 1. Representative BoBs results for the common microdeletions detected. (A) Four cases with a deletion of the Di George syndrome region. (B) One case with a deletion of the Prader–Willi syndrome region. (C) One case with a deletion of the Miller–Dieker syndrome region.

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image

Figure 2. (A) Results of a BoBs assay showing cases with (i) Miller–Dieker syndrome and (ii) Prader–Willi/Angelman syndrome, which were confirmed by array comparative genomic hybridisation (arrows indicate the deletion region). (B) Di George syndrome was confirmed by QF-PCR for the Di George region (arrows indicated the markers located in the deletion region, showing a single allele).

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Main findings

The pioneering works by Gross et al.[11], Vialard et al.[12, 14], and Shaffer et al.[13] have demonstrated the ability of the BoBs assay to rapidly diagnose abnormalities of chromosomes 13, 18, 21, X, and Y, and another nine significant microdeletion syndromes. The results of our retrospective study on 2151 samples provided further assurance on the increased diagnostic yield of the BoBs assay compared with QF-PCR. Compared with the sensitivity of QF-PCR in detecting trisomies 13, 18, 21, and sex chromosome aneuploidies (97.8%; 95% CI 94.1–99.3%), that of BoBs was 96.7% (95% CI 94.1–99.3%). For Turner syndrome, the BoBs assay performed better in detecting mosaic cases (80.0 versus 60.0%) because of the intrinsic limitation on heterozygosity of the STR markers in QF-PCR. In addition, BoBs detected an additional 16 cases missed by QF-PCR. Another case of partial deletion of chromosome 13 was detected by karyotyping and BoBs assay, but not by QF-PCR; however, the BoBs assay missed one case of mosaic trisomy 13 that was detected by QF-PCR.

Strengths and limitations

From the cytogenetic point of view, the BoBs assay could offer extra diagnostic benefit compared with QF-PCR other than providing more diversity for detecting mosaicism.[15] This method was superior to QF-PCR in detecting eight of the 15 cases of structural chromosomal abnormalities diagnosed by karyotyping, as well as six cases of well-known microdeletion syndromes missed by conventional karyotyping, supporting the finding that the BoBs assay allowed an extra 0.75% (11/1599) diagnostic yield for microdeletion/microduplication syndromes.[14] It is known that conventional karyotyping might not be able to detect microdeletions/microduplications of less than 5 Mb in size, unless the resolution of banding is above the 750-band level. The false-negative diagnoses occurred because the comparator technique was incapable of detecting the microdeletion abnormality (of less than 5 Mb). For the identification of chromosomal rearrangement and low-level mosaicism, conventional cytogenetics still remains the gold standard.

The area in which the BoBs assay loses out to QF-PCR is in diagnosing polyploidies[15] and maternal contamination. This finding is consistent with the study of Vialard et al.,[12] in which they identified six false-negative cases, including five triploidies and a case of 48,XXXY that were only recognised by karyotyping. In the study of Shaffer et al.,[13] one normal male with maternal cell contamination was incorrectly identified as a 69,XXY sample. Another interesting finding of our study is a slightly higher rate of readable results (99.9 versus 94–97%),[11-13] attributable to the use of RNase A for the elimination of RNA from the DNA preparation; this might have helped to improve the quality of the DNA, thereby enhancing the success rate of the BoBs assay. False-positive cases have also been noted by Vialard et al.,[14] who reported three false-positive results out of 1653 cases (0.18%).

Interpretation

Compared with QF-PCR, the BoBs assay has additional diagnostic yield for microdeletion and identifying chromosomal abnormalities other than the three common trisomies. BoBs is easier, has a cheaper instrumental cost, and has a higher throughput of up to 92 samples per run,[16] when evaluated against standard karyotyping and RATs like QF-PCR, MLPA, and FISH.[17-22] Like FISH, this technique is both labour intensive and costly, with the use of expensive probes that are restricted to a single probe for each target region, but the BoBs assay uses five or six beads each with a different BAC probe at each locus, so that confidence in the detection of abnormalities is enhanced. Furthermore, Shaffer et al.[13] have also demonstrated the possibility of designing the chromosome regions targeted by the assay according to the prevalence and characteristics of the local population, so that BoBs is ideal for resource-limited countries with increasing demands for a rapid test for different conditions.

Recently it was suggested that karyotyping be replaced by CMA as the standard first-line investigation.[23] Compared with the BoBs assay, CMA analysis is more comprehensive and is preferable when prenatal ultrasonography reveals multiple structural abnormalities.[23] In our study, all 15 cases of structural chromosomal abnormalities and six cases of microdeletion syndromes should have been diagnosed with CMA within a week,[24] because CMA does not require cell culture and is able to identify deletion down to kilobase-pair resolution,[4-6, 23] with only a small quantity of DNA (500 ng). Hence the BoBs assay may not have a significant edge over CMA as a rapid diagnostic test. On the other hand, CMA is expensive and may not be affordable in many countries. The interpretation and counselling arising from the detection by CMA of copy-number variants of uncertain significance (VOUS) continue to be important clinical problems. Therefore, the BoBs assay would remain the preferred complementary test for countries that still rely on karyotyping. Furthermore, the highly successful first-trimester programme of combined screening for trisomy 21 has advanced prenatal diagnosis to before 14 weeks of gestation through chorionic villus sampling.[25-30] At this stage fetal structural abnormalities may not be obvious on ultrasonography, so that it is difficult to justify the use of high-cost CMA at this stage in most countries. In addition, non-invasive prenatal testing (NIPT) could detect a wide range of fetal, placental, and maternal chromosomal abnormalities.[31] Hence, the rapid exclusion or confirmation of common trisomies and microdeletion syndromes using the BoBs assay would be optimal for cases that screened positive by NIPT or first-trimester biochemistry.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

The BoBs assay is superior to QF-PCR or other RATs as a triaging test for prenatal diagnosis because of its high specificity, yet it has a similar cost and turnaround time to current RATs. BoBs can identify known microdeletion syndromes or additional structural chromosomal abnormalities undetected by current RATs that target only five chromosomes. It is cheaper than the CMA method and without the worry of creating the dilemma of finding variants of unknown significance.

Practical recommendations

Replacing QF-PCR or other RATs with BoBs assay would allow a higher diagnostic yield to detect additional chromosomal abnormalities and microdeletions undetected by current RATs.

Disclosure of interests

KWC, TYL, and CCW received a research grant from Wallac Oy to sponsor some of the Prenatal BACs-on-Beads reagents. MS and KA are employees of and stockholders in PerkinElmer, the parent company of Wallac Oy. The Luminex 200 analyser was provided by PerkinElmer Inc. None of the co-authors (except MS and KA) have any financial relationship with the commercial sponsors. We declare that we have no conflicts of interest.

Contribution to authorship

KWC and TYL designed the study; YKK, YYC, KMW, HKW, KL, and KYS performed the study; KA, CCW, and MJS contributed reagents and analytic tools; KWC, TKL, and TTL analysed the data; and KWC, YKK, TTL, and TYL wrote the article.

Details of ethics approval

This project was approved by the joint Chinese University of Hong Kong–New Territories East Cluster Clinical Research Ethics Committee on 12 July 2011 (CRE-2011.273).

Funding

This work was partially supported by the National Basic Research Programme of China (2012CB944600) and the Health and Medical Research Fund, Hong Kong (08090401).

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

We thank Dawn Lui and Anna Chan for their technical support during sample preparation.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. References
  10. Supporting Information
FilenameFormatSizeDescription
bjo12873-sup-0001-TableS1.pdfPDF document15KTable S1. Detection rate of common major aneuploidies by QF-PCR and BoBs assay, in comparison with karyotyping.

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