A two-year prospective study assessing the performance of fetal chromosomal microarray analysis and next-generation sequencing in high-risk pregnancies.

BACKGROUND: Introduction of cell-free fetal DNA (cff-DNA) testing in maternal blood opened possibilities to improve the performance of combined first-trimester screening (cFTS) in terms of better detection of trisomies and lowering invasive testing rate. The use of new molecular methods, such as chromosomal microarray analysis (CMA) and next-generation sequencing (NGS), has shown benefits in prenatal diagnosis of chromosomal and genetic diseases, which are not detectable with cff-DNA screening, but require an invasive procedure. METHODS: The objective of this study was to evaluate prospectively during two years performance of CMA and NGS in high-risk pregnancies. Initially, we investigated 14,566 singleton pregnancies with cFTS. A total of 334 high-risk pregnancies were selected for CMA diagnostic performance evaluation and 28 cases of highly dysmorphic fetuses for NGS analysis. CMA study group was divided into two groups based on the indications for testing; group A patients with high-risk for trisomies after cFTS, but normal ultrasound and group B patients who met criteria for CMA as a first-tier diagnostic test. RESULTS: The diagnostic yield of CMA was overall 3.6% (1.6% in Group A and 6.0% in Group B). In NGS analysis group, we report diagnostic yield of 17.9%. CONCLUSION: The use of CMA in high-risk pregnancies is justified and provides relevant clinical information in 3.6% of the cases. NGS analysis in fetuses with multiple anomalies shows promising results, but more investigations are needed for a better understanding of practical applications of this molecular diagnosis method in prenatal settings.

Creating basis for introducing non-invasive prenatal testing in the Estonian public health setting.

OBJECTIVE: The study aimed to validate a whole-genome sequencing-based NIPT laboratory method and our recently developed NIPTmer aneuploidy detection software with the potential to integrate the pipeline into prenatal clinical care in Estonia. METHOD: In total, 424 maternal blood samples were included. Analysis pipeline involved cell-free DNA extraction, library preparation and massively parallel sequencing on Illumina platform. Aneuploidies were determined with NIPTmer software, which is based on counting pre-defined per-chromosome sets of unique k-mers from sequencing raw data. SeqFF was implemented to estimate cell-free fetal DNA (cffDNA) fraction. RESULTS: NIPTmer identified correctly all samples of non-mosaic trisomy 21 (T21, 15/15), T18 (9/9), T13 (4/4) and monosomy X (4/4) cases, with the 100% sensitivity. However, one mosaic T18 remained undetected. Six false-positive (FP) results were observed (FP rate of 1.5%, 6/398), including three for T18 (specificity 99.3%) and three for T13 (specificity 99.3%). The level of cffDNA of <4% was estimated in eight samples, including one sample with T13 and T18. Despite low cffDNA level, these two samples were determined as aneuploid. CONCLUSION: We believe that the developed NIPT method can successfully be used as a universal primary screening test in combination with ultrasound scan for the first trimester fetal examination.

A prenatally diagnosed case of Meckel-Gruber syndrome with novel compound heterozygous pathogenic variants in the TXNDC15 gene.

BACKGROUND: Meckel-Gruber syndrome (MKS) is a well-known rare disease that can be detected on prenatal ultrasound. Meckel-Gruber syndrome has very heterogeneous etiology; at least, 17 genes have been described in association with MKS. The characteristic findings in fetuses affected by MKS are encephalocele (usually occipital), postaxial polydactyly, and polycystic dysplastic kidneys. However, the association of the TXNDC15 gene with MKS has been reported only once before in three consanguineous families. METHODS: We report a new case of MKS diagnosed at 12 + 1 weeks of gestation with typical ultrasound findings, but with novel compound heterozygous pathogenic variants in the TXNDC15 gene identified by whole-exome sequencing (WES). RESULTS: This is the second clinical report supporting TXNDC15 as a novel causative gene of MKS, and the first describing a case in a non-consanguineous family with causative compound heterozygous mutations. CONCLUSIONS: Meckel-Gruber syndrome is a very heterogeneous syndrome in terms of the associated causal genes. In the first-line diagnosis, we used an next-generation sequencing (NGS)-based large gene panel, but only 10 MKS genes were available on the platform used. In the case of prenatal ultrasound findings that are highly suggestive of MKS and a negative NGS MKS gene panel, WES should also be performed to not miss rare gene associations.

Two Consecutive Pregnancies with Simpson-Golabi-Behmel Syndrome Type 1: Case Report and Review of Published Prenatal Cases.

Fetal overgrowth and numerous congenital malformations can be detected in every trimester of pregnancy. New technologies in molecular testing, such as chromosomal microarray analysis and next-generation sequencing, continually demonstrate advantages for definitive diagnosis in fetal life. Simpson-Golabi-Behmel (SGB) syndrome is a rare but well-known overgrowth condition that is rarely diagnosed in the prenatal setting. We report 3 cases of SGB syndrome in 2 consecutive pregnancies. In our series, distinctive prenatal sonographic findings led to molecular diagnosis. Exome sequencing from fetal DNA revealed a hemizygous splice site variant in the GPC3 gene: NM_004484.3:c.1166+ 1G>T. The mother is a heterozygous carrier. We also provide an overview of the previously published 57 prenatal cases of SGB syndrome with prevalence estimation of the symptoms to aid prenatal differential diagnosis of fetal overgrowth syndromes.