Single nucleotide polymorphism array (SNP-array) analysis for fetuses with abnormal nasal bone

PURPOSE

This study aims to evaluate the prevalence of submicroscopic chromosomal abnormalities found on single nucleotide polymorphism array (SNP array) in pregnancies with either an absent or hypoplastic nasal bone.

METHODS

This retrospective study included 333 fetuses with either nasal bone hypoplasia or absence identified on prenatal ultrasound. SNP array analysis and conventional karyotyping were performed in all the subjects. The prevalence of chromosomal abnormalities was adjusted for maternal age and other ultrasound findings. Fetuses with either an isolated nasal bone absence or hypoplasia, those that had additional soft ultrasound markers, and those where structural defects were found on ultrasound were divided into three groups: A, B, and C, respectively.

RESULTS

Among the total cohort of 333 fetuses, 76 (22.8%) had chromosomal abnormalities, including 47 cases of trisomy 21, 4 cases of trisomy 18, 5 cases of sex chromosome aneuploidy, and 20 cases of copy number variations of which 12 were pathogenic or likely pathogenic. The prevalence of chromosomal abnormalities in group A (n = 164), B (n = 79), and C (n = 90) was 8.5%, 29.1% and 43.3%, respectively. The incremental yields by SNP-array compared with karyotyping in group A, B, and C were 3.0%, 2.5% and 10.7%, respectively (p > 0.05). Compared to karyotype analysis, SNP array detected an additional 2 (1.2%), 1 (1.3%), and 5 (5.6%) pathogenic or likely pathogenic CNVs in groups A, B, and C, respectively. In the 333 fetuses, the prevalence of chromosomal abnormalities in women with advanced maternal age (AMA) was significantly higher than that in non-AMA women, (47.8% vs. 16.5%, p < 0.05).

CONCLUSION

In addition to Down's syndrome, many other chromosomal abnormalities are present in fetuses with abnormal nasal bone. SNP array can improve the prevalence of chromosomal abnormalities associated with nasal bone abnormalities, especially in pregnancies with non-isolated nasal bone abnormalities and advanced maternal age.

Detection of copy number variants associated with late-onset conditions in ~16 200 pregnancies: parameters for disclosure and pregnancy outcome

BACKGROUND

Copy number variants (CNVs) associated with late-onset medical conditions are rare but important secondary findings in chromosomal microarray analysis (CMA) performed during pregnancy. Here, we critically review the cases at two tertiary centres to assess the criteria which guide the disclosure of such findings and develop a disclosure decision tool (DDT) aimed at facilitating disclosure decision. Parental decisions on receiving CNVs associated with risks for late-onset conditions were also recorded.

METHODS

Prenatal CMAs in Hadassah and Shaare Zedek Medical Centers from November 2013 to October 2021 were reviewed for CNVs associated with late-onset conditions. The DDT proposed uses a five-parameter scoring system, which considers the severity, median age of onset, penetrance, understanding of genotype-phenotype correlation and actionability of the finding.

RESULTS

Out of 16 238 prenatal CMAs, 16 (0.1%) harboured CNVs associated with late-onset conditions, 15 of which were disclosed. Outcome information was available on 13 of the 16 pregnancies, all of which continued to delivery.

CONCLUSIONS

Our suggested DDT will help clinicians to quantitatively weigh the variables associated with CNVs of this type and arrive at a well thought out clinical decision regarding disclosure. Although the prevalence of late-onset conditions as a major finding in the prenatal setup is low, it is expected to rise with the increasing use of non-invasive CMA testing and whole exome and genome sequencing.

Optimizing the Diagnostic Strategy to Identify Genetic Abnormalities in Miscarriage

INTRODUCTION

The single most common cause of miscarriage is genetic abnormality.

OBJECTIVE

We conducted a prospective cohort study to compare the performance of conventional karyotyping and chromosomal microarray analysis (CMA) using array comparative genomic hybridization (array-CGH) and single nucleotide polymorphism array (SNP-array) to identify genetic abnormalities in miscarriage specimens.

METHODS

A total of 63 miscarriage specimens were included. Conventional karyotyping, array-CGH, and SNP-array were performed and the results compared.

RESULTS

Genetic abnormalities were detected in 31 cases (49.2%) by at least one testing modality. Single autosomal trisomy was the most common defect (71.0%), followed by polyploidy (16.1%), multiple aneuploidy (9.7%), and monosomy X (3.2%). Mosaicisms were identified in four cases and confirmed by fluorescence in situ hybridization (FISH) using appropriate probes. SNP-array had a higher detection rate of genetic abnormalities than array-CGH (93.5 vs. 77.4%), and conventional karyotyping had the lowest detection rate (76.0%). SNP-array enabled the detection of all types of genetic abnormalities, including polyploidy.

CONCLUSIONS

Although conventional karyotyping and FISH are still needed, SNP-array represents the first choice for miscarriage because the technique showed excellent performance in the detection of genetic abnormalities and minimized the probability of testing failure as well as time, costs, and labor.

Microarrays in prenatal diagnosis

In prenatal diagnosis, chromosomal microarray (CMA) has not yet fully replaced conventional karyotyping but has rapidly become the recommended test in pregnancies with ultrasound abnormalities. In this review, we provide an overview of the published data concerning this technology and the controversies concerning its use in the prenatal setting. There is abundant evidence indicating the added detection of pathogenic abnormalities with CMA in comparison to the traditional karyotyping, especially in fetuses with multiple or isolated ultrasound abnormalities such as congenital heart disease, increased nuchal translucency, or oral cleft. On the other hand, there is also a risk to detect variants of unknown significance, late-onset disorders, and variants in susceptibility loci. However, it has been shown that pregnant couples tend to prefer a maximum of information about the health of their unborn child. Taken together, CMA has considerable diagnostic and prognostic values during pregnancy and should therefore be the test of choice.

Chromosomal microarray analysis as a first-line test in pregnancies with a priori low risk for the detection of submicroscopic chromosomal abnormalities

In this study, we aimed to explore the utility of chromosomal microarray analysis (CMA) in groups of pregnancies with a priori low risk for detection of submicroscopic chromosome abnormalities, usually not considered an indication for testing, in order to assess whether CMA improves the detection rate of prenatal chromosomal aberrations. A total of 3000 prenatal samples were processed in parallel using both whole-genome CMA and conventional karyotyping. The indications for prenatal testing included: advanced maternal age, maternal serum screening test abnormality, abnormal ultrasound findings, known abnormal fetal karyotype, parental anxiety, family history of a genetic condition and cell culture failure. The use of CMA resulted in an increased detection rate regardless of the indication for analysis. This was evident in high risk groups (abnormal ultrasound findings and abnormal fetal karyotype), in which the percentage of detection was 5.8% (7/120), and also in low risk groups, such as advanced maternal age (6/1118, 0.5%), and parental anxiety (11/1674, 0.7%). A total of 24 (0.8%) fetal conditions would have remained undiagnosed if only a standard karyotype had been performed. Importantly, 17 (0.6%) of such findings would have otherwise been overlooked if CMA was offered only to high risk pregnancies.The results of this study suggest that more widespread CMA testing of fetuses would result in a higher detection of clinically relevant chromosome abnormalities, even in low risk pregnancies. Our findings provide substantial evidence for the introduction of CMA as a first-line diagnostic test for all pregnant women undergoing invasive prenatal testing, regardless of risk factors.

0.5 Mb array as a first-line prenatal cytogenetic test in cases without ultrasound abnormalities and its implementation in clinical practice

Using whole-genome array testing instead of karyotyping in prenatal diagnosis for all indications may be desirable because of the higher diagnostic yield and shorter reporting time. The goal of this research was finding the optimal array resolution that could replace routine prenatal karyotyping in cases without ultrasound abnormalities, for example, referred for advanced maternal age or abnormal first trimester screening. As variants of unknown clinical significance (VOUS), if reported, might complicate decision-making about continuation of pregnancy, such an optimal array resolution should have a high abnormality detection rate and reveal a minimal amount of VOUS. The array data of 465 fetuses were retrospectively evaluated with several resolution levels, and the Decipher microdeletion/microduplication syndrome list was reviewed to assess what could be theoretically missed with a lower resolution. A 0.5-Mb resolution showed a high diagnostic yield potential and significantly minimized the number of VOUS. Based on our experience, we recommend genomic SNP array as a first-tier test in prenatal diagnosis. The resolution should be chosen based on the indication. In cases of fetal ultrasound abnormalities or intrauterine fetal death (IUFD), high-resolution analysis should be done. In other cases, we advise replacing karyotyping by SNP array analysis with 0.5 Mb resolution.

Prenatal microarray analysis as second-tier diagnostic test: single-center prospective study

OBJECTIVE

To evaluate the usefulness of chromosome microarrays as a second-tier test in prenatal genetic testing.

METHODS

We prospectively analyzed 75 high-risk pregnancies undergoing invasive prenatal genetic testing in which the karyotype either was normal or had findings other than a common non-mosaic autosomal aneuploidy.

RESULTS

Chromosomal microarray analysis (CMA) was performed successfully in all cases. Pathological copy-number variations (CNVs) explaining the phenotypes were found in 11 cases (14.7%). Four cases were detected with an unbalanced translocation. In three of these cases, subsequent genetic analysis demonstrated that a parent was an unknown carrier of a balanced translocation. Among the 67 cases with normal karyo-types, submicroscopic rearrangements with pathological significance were detected in five (7.5%) and CNVs of unclear significance were detected in one (1.5%). CMA was able to discriminate correctly between true mosaicism and confined or pseudomosaicism in all six mosaic cases.

CONCLUSION

CMA is a valuable second-tier test in high-risk pregnancies for which identification or further delineation of genetic aberrations is important. Its higher resolution results in a higher detection rate of aberrant cases, with a clear clinical benefit for estimation of risk of recurrence.

Karyotype versus microarray testing for genetic abnormalities after stillbirth

BACKGROUND

Genetic abnormalities have been associated with 6 to 13% of stillbirths, but the true prevalence may be higher. Unlike karyotype analysis, microarray analysis does not require live cells, and it detects small deletions and duplications called copy-number variants.

METHODS

The Stillbirth Collaborative Research Network conducted a population-based study of stillbirth in five geographic catchment areas. Standardized postmortem examinations and karyotype analyses were performed. A single-nucleotide polymorphism array was used to detect copy-number variants of at least 500 kb in placental or fetal tissue. Variants that were not identified in any of three databases of apparently unaffected persons were then classified into three groups: probably benign, clinical significance unknown, or pathogenic. We compared the results of karyotype and microarray analyses of samples obtained after delivery.

RESULTS

In our analysis of samples from 532 stillbirths, microarray analysis yielded results more often than did karyotype analysis (87.4% vs. 70.5%, P<0.001) and provided better detection of genetic abnormalities (aneuploidy or pathogenic copy-number variants, 8.3% vs. 5.8%; P=0.007). Microarray analysis also identified more genetic abnormalities among 443 antepartum stillbirths (8.8% vs. 6.5%, P=0.02) and 67 stillbirths with congenital anomalies (29.9% vs. 19.4%, P=0.008). As compared with karyotype analysis, microarray analysis provided a relative increase in the diagnosis of genetic abnormalities of 41.9% in all stillbirths, 34.5% in antepartum stillbirths, and 53.8% in stillbirths with anomalies.

CONCLUSIONS

Microarray analysis is more likely than karyotype analysis to provide a genetic diagnosis, primarily because of its success with nonviable tissue, and is especially valuable in analyses of stillbirths with congenital anomalies or in cases in which karyotype results cannot be obtained. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.).

Genomic microarrays: a technology overview

Genomic microarrays are now widely used diagnostically for the molecular karyotyping of patients with intellectual disability, congenital anomalies and autistic spectrum disorder and have more recently been applied for the detection of genomic imbalances in prenatal genetic diagnosis. We present an overview of the different arrays, protocols used and discuss methods of genomic array data analysis.

Prenatal chromosomal microarray analysis in a diagnostic laboratory; experience with >1000 cases and review of the literature

OBJECTIVE

To evaluate the results of prenatal chromosomal microarray analysis (CMA) on >1000 fetal samples referred for testing at our institution and to compare these data to published reports.

METHODS

High resolution CMA was offered to women undergoing amniocentesis or chorionic villus sampling. Parental samples were obtained concurrently to exclude maternal cell contamination and assist interpretation of copy number variations.

RESULTS

Clinically significant copy number variations were observed in 85/1115 cases (7.6%) overall, and in 45/1075 cases (4.2 %) if 40 abnormal cases with known chromosome abnormalities or familial genomic imbalances were excluded. Eighteen of the 1115 cases had variants of unclear clinical significance (1.6%). Indications yielding the most clinically significant findings were abnormal karyotype/fluorescence in situ hybridization (26/61, 42.6%), family history of chromosomal abnormality (13/137, 9.5%), abnormal ultrasound (38/410, 9.3%), abnormal serum screening (2/37, 5.4%) and advanced maternal age (5/394, 1.3%). Of 1075 cases having no previously known cytogenetic abnormality or family history, 18 (1.7%) had clinically significant genomic changes undetectable by conventional prenatal chromosome analysis.

CONCLUSION

Current experience confirms that the detection rate of CMA for prenatal chromosomal abnormalities surpasses that of conventional karyotype analysis and continues to improve with higher resolution arrays, while maintaining a low frequency of results of unclear clinical significance.

The introduction of arrays in prenatal diagnosis: a special challenge

Genome-wide arrays are rapidly replacing conventional karyotyping in postnatal cytogenetic diagnostics and there is a growing request for arrays in the prenatal setting. Several studies have documented 1-3% additional abnormal findings in prenatal diagnosis with arrays compared to conventional karyotyping. A recent meta-analysis demonstrated that 5.2% extra diagnoses can be expected in fetuses with ultrasound abnormalities. However, no consensus exists as to whether the use of genome-wide arrays should be restricted to pregnancies with ultrasound abnormalities, performed in all women undergoing invasive prenatal testing or offered to all pregnant women. Moreover, the interpretation of array results in the prenatal situation is challenging due to the large numbers of copy number variants with no major phenotypic effect. This also raises the question of what, or what not to report, for example, how to deal with unsolicited findings. These issues were discussed at a working group meeting that preceded the European Society of Human Genetics 2011 Conference in Amsterdam. This article is the result of this meeting and explores the introduction of genome-wide arrays into routine prenatal diagnosis. We aim to give some general recommendations on how to develop practical guidelines that can be implemented in the local setting and that are consistent with the emerging international consensus.