Chromosomal Microarrays in Prenatal Diagnosis: Time for a Change of Policy?

C-banding and AgNOR-staining were still effective complementary methods to indentify chromosomal heteromorphisms and some structural abnormalities in prenatal diagnosis

BACKGROUND

In prenatal diagnosis, CMA has begun to emerge as a favorable alternative to karyotype analysis, but it could not identify balanced translocations, triploidies, inversion and heteromorphisms. Therefore, conventional cytogenetic and specific staining methods still play an important role in the work-up of chromosome anomaly. This study investigated the application of C-banding and AgNOR-staining techniques in prenatal diagnosis of chromosomal heteromorphisms and some structure abnormalities.

RESULTS

Among the 2970 samples, the incidence of chromosomal heteromorphisms was 8.79% (261/2970). The most frequent was found to be chromosome Y (2.93%, 87/2970), followed by chromosome 1 (1.65 %, 49/2970), 9 (1.52 %, 45/2970), 22 (0.77 %, 23/2970) and 15 (0.64 %, 19/2970). We compared the incidence of chromosomal heteromorphisms between recurrent spontaneous abortion (RSA) group and control group. The frequency of autosomal hetermorphisms in RSA group was 7.63% higher than that in control group (5.78%), while the frequency of Y chromosomal heteromorphisms was 4.76% lower than that in control group (5.71%). Here we summarized 4 representative cases, inv (1) (p12q24), psu dic (4;17) (p16.3;p13.3), r(X)(p11; q21) and an isodicentric bisatellited chromosome to illustrate the application of C-banding or AgNOR-staining, CMA or NGS was performed to detect CNVs if necessary.

CONCLUSIONS

This study indicated that C-banding and AgNOR-staining were still effective complementary methods to identify chromosomal heteromorphisms and marker chromosomes or some structural rearrangements involving the centromere or acrocentric chromosomes. Our results suggested that there was no evidence for an association between chromosomal heteromorphisms and infertility or recurrent spontaneous abortions. Undoubtedly, sometimes we needed to combine the results of CMA or CNV-seq to comprehensively reflect the structure and aberration of chromosome segments. Thus, accurate karyotype reports and genetic counseling could be provided.

Indications for genetic testing leading to termination of pregnancy

PURPOSE

In this study, we aimed to assess the distribution of genetic abnormalities leading to termination of pregnancy and its fluctuation during the past 8 years in light of those technical advances.

METHODS

Our cohort consisted of all pregnant women who underwent termination of pregnancy because of genetic aberrations in their fetuses from January 2010 through April 2018 in our medical center. The information that was gathered included: maternal age, results of the nuchal scan, results of the first- and second-trimester biochemical screening, ultrasonographic findings, reasons for conducting a genetic evaluation, gestational age at which termination of pregnancy was carried out, and the type of genetic aberration.

RESULTS

816 women underwent termination of pregnancy at our institution due to genetic aberrations, most of them because of positive biochemical screening (n = 297, 36%) or because of maternal anxiety (n = 283, 35%). Findings in chromosomal microarray led to termination of pregnancy in 100 women (100/816, 12%). Chromosomal microarray had been performed due to maternal choice and not because of accepted medical indications among most of the women who underwent termination of pregnancy due to findings on chromosomal microarray (69/100, 69%).

CONCLUSION

Performing chromosomal microarray on a structurally normal fetus and identifying abnormal copy number variants may give the parents enough information for deciding on the further course of the pregnancy.

Prevalence of chromosomal abnormalities identified by copy number variation sequencing in high-risk pregnancies, spontaneous abortions, and suspected genetic disorders

Objective

High-throughput sequencing based on copy number variation (CNV-seq) is commonly used to detect chromosomal abnormalities including aneuploidy. This study provides evidence for the prevalence of chromosomal abnormalities in target populations.

Methods

A total of 160 samples, including 83 high-risk pregnancies, 37 spontaneous abortions, and 40 suspected genetic disorders, were analyzed by CNV-seq. Relationships between the incidence of these chromosomal abnormalities and risk factors (e.g. advanced maternal age, abnormal pregnancy history, and family history of congenital disease) were further analyzed by subgroup.

Results

A total of 37 (44.6%) high-risk pregnancies, 25 (67.6%) spontaneous abortions, and 22 (55%) suspected genetic disorders had chromosomal abnormalities including aneuploidy and CNVs. There was an increased risk association between the prevalence of aneuploidy and pathogenic-relevant CNV in the fetus or abortive tissue and advanced maternal age. Moreover, a family history of congenital disease was also positively correlated with fetal chromosomal abnormalities in high-risk pregnancies.

Conclusion

A relatively high prevalence of chromosomal abnormalities was detected in high-risk pregnancies, spontaneous abortions, and suspected genetic disorders, indicating the importance of CNV detection in such populations.

CGH Array and Karyotype as Complementary Tools in Prenatal Diagnosis: Prenatal Diagnosis of a 4q Derivative Chromosome from Maternal 4q;11q Translocation

BACKGROUND

There is controversy whether chromosomal microarray (CMA) can replace karyotyping in prenatal diagnosis. Chromosomal microarray may detect more clinically significant chromosomal imbalances than karyotyping in a shorter time but does not detect inversions, triploidies or low mosaicisms.

CASE REPORT

Amniocentesis was performed in the late second trimester based on ultrasound abnormalities. A CMA, obtained at 10 days, demonstrated a terminal deletion in 4q34.3-q35.2 and a duplication in 11q21-q25. The karyotype results, obtained 1 week later, showed a derivative chromosome 4 inherited from a maternal balanced 4;11 translocation.

CONCLUSION

CMA and karyotype were complementary in this case, together permitting a more accurate diagnosis and genetic counseling than if only one method was used.

Dilemmas in genetic counseling for low-penetrance neuro-susceptibility loci detected on prenatal chromosomal microarray analysis

BACKGROUND

Chromosomal microarray analysis is standard of care in fetuses with malformations, detecting clinically significant copy number variants in 5-7% of cases over conventional karyotyping. However, it also detects variants of uncertain significance in 1.6-4.2% of the cases, some of which are low-penetrance neuro-susceptibility loci. The interpretation of these variants in pregnancy is particularly challenging because the significance is often unclear and the clinical implications may be difficult to predict.

OBJECTIVE

The purpose of this study was to describe counseling dilemmas regarding low-penetrance neuro-susceptibility loci that are detected by prenatal chromosomal microarray analysis.

STUDY DESIGN

During the study period (January 2014 to December 2015), 700 prenatal chromosomal microarray analyses were performed. Cases were categorized as "indicated" (n=375) if there were abnormal sonographic findings or suggestive medical history and "patient choice" (n=325) in the presence of a structurally normal fetus with no other particular indication. The laboratory reported on copy number variants ≥400 Kb in size in loci known to be associated with genetic syndromes and ≥1 Mb in other areas of genome. Results were classified as gross aneuploidy, copy number variants, and normal. Copy number variants were categorized according to the American College of Medical Genetics standards and guidelines: pathogenic, variants of uncertain significance, or benign. Variants of uncertain significance were further subdivided into categories of likely pathogenic, variants of uncertain significance with no subclassification, and likely benign. Statistical analysis was performed with the use of Chi square test and Fisher's exact test to compare intergroup differences in incidence of the different result categories and demographic data.

RESULTS

Patient choice cases became more prevalent with time (35.5% in the beginning of the study, compared with 48.4% at the end of the study period). Clinically significant copy number variants were found in 14 of 375 (3.7%) of indicated cases vs only 2 of 325 (0.6%) of patient choice cases (P=.009). All "likely benign" variants consisted of low-penetrance neuro-susceptibility loci. The incidence thereof was similar between the indicated and patient choice groups (3.7% vs 3.4%; P=.85). In the indicated group, some variants of uncertain significance may have contributed to the abnormal anatomic findings. Conversely, in the patient choice group, the finding of low-penetrance neuro-susceptibility loci was often unexpected and confounding for prospective parents.

CONCLUSION

Prenatal chromosomal microarray analysis added clinically significant information in both groups. However, it also detected low-penetrance neuro-susceptibility loci in approximately 3.5% of the cases. This fact should be conveyed during pretest counseling to allow patients to make informed choices, particularly when chromosomal microarray is to be performed for patient choice.