Whole exome sequencing of fetal structural anomalies detected by ultrasonography

Spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) including renal parenchymal malformations during fetal life and the implementation of prenatal exome sequencing (WES)

OBJECTIVES AND BACKGROUND

Congenital malformations of the kidney and urinary tract (CAKUT) have a prevalence of 4-60 in 10,000 livebirths and constitute for 40-50% of all end stage pediatric kidney disease. CAKUT can have a genetic background due to monogenetic inherited disease, such as PKD or ciliopathies. They can also be found in combination with extra-renal findings as part of a syndrome. Upon detection of genitourinary malformations during the fetal anomaly scan the question arises if further genetic testing is required. The purpose of this study was to determine the phenotypic presentation of CAKUT cases and the results of exome analysis (WES).

METHODS

This is a retrospective analysis of 63 fetal cases with a diagnosis of CAKUT or DSD at a single center between August 2018 and December 2022.

RESULTS

A total of 63 cases (5.6%) out of 1123 matched CAKUT phenotypes including renal parenchyma malformations. In 15 out of 63 WES analysis a pathogenic variant was detected (23.8%). In fetuses with isolated CAKUT the rate of detecting a pathogenic variant on exome sequencing was five out of 44 (11.4%). Ten out of 19 fetuses (52.6%) that displayed extra-renal findings in combination with CAKUT were diagnosed with a pathogenic variant.

CONCLUSIONS

WES provides an increase in diagnosing pathogenic variants in cases of prenatally detected CAKUT. Especially in fetuses with extra-renal malformations, WES facilitates a gain in information on the fetal genotype to enhance prenatal counselling and management.

Prenatal whole-exome sequencing for fetal structural anomalies: a retrospective analysis of 145 Chinese cases

BACKGROUND

Whole-exome sequencing (WES) significantly improves the diagnosis of the etiology of fetal structural anomalies. This study aims to evaluate the diagnostic value of prenatal WES and to investigate the pathogenic variants in structurally abnormal fetuses.

METHODS

We recruited 144 fetuses with structural anomalies between 14 and 2020 and 15 December 2021 in the study. Genetic screening was performed by WES combined with karyotyping and chromosomal microarray analysis. The molecular diagnostic yield of prenatal WES for each type of fetal structural anomaly and the identified pathogenic genes and mutations were reported.

RESULTS

In this study, we retrospectively analyzed the clinical and genetic data of 145 structurally anomalous fetuses. These cases were classified into 9 phenotypic classes based on antenatal ultrasound findings. Thirty-eight pathogenic variants in 24 genes were identified in 35 of the 145 cases, including 14 novel variants in 13 genes (EP300, MYH3, TSC2, MMP9, CPLANE1, INVS, COL1A1, EYA1, TTC21B, MKS1, COL11A2, PDHA1 and L1CAM). Five additional pathogenic variants were classified as incidental findings. Our study showed that the overall diagnosis rate of WES was 28.1% (27/96) in the parent-fetus trio cases and 16.3% (8/49) in the proband-only cases. Fetuses with musculoskeletal anomalies had the highest diagnostic yield (51.4%, 19/37). In addition, FGFR3 and COL1A1 were the most common pathogenic genes.

CONCLUSIONS

Our work expands the mutation spectrum of the genes associated with fetal structural anomalies and provides valuable information for future parental genetic counselling and pregnancy management of the structurally anomalous fetuses.

Diagnostic yield with exome sequencing in prenatal severe bilateral ventriculomegaly: a systematic review and meta-analysis

OBJECTIVE

This study aimed to determine the incremental diagnostic yield of prenatal exome sequencing after negative chromosomal microarray analysis results in prenatally diagnosed bilateral severe ventriculomegaly or hydrocephalus; another objective was to categorize the associated genes and variants.

DATA SOURCES

A systematic search was performed to identify relevant studies published until June 2022 using 4 databases (Cochrane Library, Web of Science, Scopus, and MEDLINE).

STUDY ELIGIBILITY CRITERIA

Studies in English reporting on the diagnostic yield of exome sequencing following negative chromosomal microarray analysis results in cases of prenatally diagnosed bilateral severe ventriculomegaly were included.

METHODS

Authors of cohort studies were contacted for individual participant data, and 2 studies provided their extended cohort data. The incremental diagnostic yield of exome sequencing was assessed for pathogenic/likely pathogenic findings in cases of: (1) all severe ventriculomegaly; (2) isolated severe ventriculomegaly (as the only cranial anomaly); (3) severe ventriculomegaly with other cranial anomalies; and (4) nonisolated severe ventriculomegaly (with extracranial anomalies). To be able to identify all reported genetic associations, the systematic review portion was not limited to any minimal severe ventriculomegaly case numbers; however, for the synthetic meta-analysis, we included studies with ≥3 severe ventriculomegaly cases. Meta-analysis of proportions was done using a random-effects model. Quality assessment of the included studies was performed using the modified STARD (Standards for Reporting of Diagnostic Accuracy Studies) criteria.

RESULTS

A total of 28 studies had 1988 prenatal exome sequencing analyses performed following negative chromosomal microarray analysis results for various prenatal phenotypes; this included 138 cases with prenatal bilateral severe ventriculomegaly. We categorized 59 genetic variants in 47 genes associated with prenatal severe ventriculomegaly along with their full phenotypic description. There were 13 studies reporting on ≥3 severe ventriculomegaly cases, encompassing 117 severe ventriculomegaly cases that were included in the synthetic analysis. Of all the included cases, 45% (95% confidence interval, 30-60) had positive pathogenic/likely pathogenic exome sequencing results. The highest yield was for nonisolated cases (presence of extracranial anomalies; 54%; 95% confidence interval, 38-69), followed by severe ventriculomegaly with other cranial anomalies (38%; 95% confidence interval, 22-57) and isolated severe ventriculomegaly (35%; 95% confidence interval, 18-58).

CONCLUSION

There is an apparent incremental diagnostic yield of prenatal exome sequencing following negative chromosomal microarray analysis results in bilateral severe ventriculomegaly. Although the greatest yield was found in cases of nonisolated severe ventriculomegaly, consideration should also be given to performing exome sequencing in cases of isolated severe ventriculomegaly as the only brain anomaly identified on prenatal imaging.

Enhancing Molecular Testing for Effective Delivery of Actionable Gene Diagnostics

There is a deep need to navigate within our genomic data to find, understand and pave the way for disease-specific treatments, as the clinical diagnostic journey provides only limited guidance. The human genome is enclosed in every nucleated cell, and yet at the single-cell resolution many unanswered questions remain, as most of the sequencing techniques use a bulk approach. Therefore, heterogeneity, mosaicism and many complex structural variants remain partially uncovered. As a conceptual approach, nanopore-based sequencing holds the promise of being a single-molecule-based, long-read and high-resolution technique, with the ability of uncovering the nucleic acid sequence and methylation almost in real time. A key limiting factor of current clinical genetics is the deciphering of key disease-causing genomic sequences. As the technological revolution is expanding regarding genetic data, the interpretation of genotype-phenotype correlations should be made with fine caution, as more and more evidence points toward the presence of more than one pathogenic variant acting together as a result of intergenic interplay in the background of a certain phenotype observed in a patient. This is in conjunction with the observation that many inheritable disorders manifest in a phenotypic spectrum, even in an intra-familial way. In the present review, we summarized the relevant data on nanopore sequencing regarding clinical genomics as well as highlighted the importance and content of pre-test and post-test genetic counselling, yielding a complex approach to phenotype-driven molecular diagnosis. This should significantly lower the time-to-right diagnosis as well lower the time required to complete a currently incomplete genotype-phenotype axis, which will boost the chance of establishing a new actionable diagnosis followed by therapeutical approach.

Distal 2q duplication in a patient with intellectual disability

We report on a patient with a distal 16.4-Mb duplication at 2q36.3-qter, who presented with severe intellectual disability, microcephaly, brachycephaly, prominent forehead, hypertelorism, prominent eyes, thin upper lip, and progenia. Copy number analysis using whole exome data detected a distal 2q duplication. This is the first report describing a distal 2q duplication at the molecular level.

Exploring the diagnostic utility of genome sequencing for fetal congenital heart defects

OBJECTIVE

The diagnostic yield for congenital heart defects (CHD) with routine genetic testing is around 10-20% when considering the pathogenic CNVs or aneuploidies as positive findings. This is a pilot study to investigate the utility of genome sequencing (GS) for prenatal diagnosis of CHD.

METHODS

Genome sequencing (GS, 30X) was performed on 13 trios with CHD for which karyotyping and/or chromosomal microarray results were non-diagnostic.

RESULTS

Trio GS provided a diagnosis for 4/13 (30.8%) fetuses with complex CHDs and other structural anomalies. Findings included pathogenic or likely pathogenic variants in DNAH5, COL4A1, PTPN11, and KRAS. Of nine cases without a possibly genetic etiology by GS, we had follow-up on eight. For five of them (60%), the parents chose to keep the pregnancy. A balanced translocation [46,XX,t(14;22)(q32.33;q13.31)mat] was detected in a trio with biallelic DNAH5 mutations, which together explained the recurrent fetal situs inversus and dextrocardia that was presumably due to de novo Phelan-McDermid syndrome. A secondary finding of a BRCA2 variant and carrier status of HBB, USH2A, HBA1/HBA2 were detected in the trio.

CONCLUSIONS

GS expands the diagnostic scope of mutation types over conventional testing, revealing the genetic etiology for fetal heart anomalies. Patients without a known genetic abnormality indicated by GS likely opted to keep pregnancy especially if the heart issue could be repaired. We provide evidence to support the application of GS for fetuses with CHD. This article is protected by copyright. All rights reserved.

Molecular Approaches in Fetal Malformations, Dynamic Anomalies and Soft Markers: Diagnostic Rates and Challenges-Systematic Review of the Literature and Meta-Analysis

Fetal malformations occur in 2-3% of pregnancies. They require invasive procedures for cytogenetics and molecular testing. "Structural anomalies" include non-transient anatomic alterations. "Soft markers" are often transient minor ultrasound findings. Anomalies not fitting these definitions are categorized as "dynamic". This meta-analysis aims to evaluate the diagnostic yield and the rates of variants of uncertain significance (VUSs) in fetuses undergoing molecular testing (chromosomal microarray (CMA), exome sequencing (ES), genome sequencing (WGS)) due to ultrasound findings. The CMA diagnostic yield was 2.15% in single soft markers (vs. 0.79% baseline risk), 3.44% in multiple soft markers, 3.66% in single structural anomalies and 8.57% in multiple structural anomalies. Rates for specific subcategories vary significantly. ES showed a diagnostic rate of 19.47%, reaching 27.47% in multiple structural anomalies. WGS data did not allow meta-analysis. In fetal structural anomalies, CMA is a first-tier test, but should be integrated with karyotype and parental segregations. In this class of fetuses, ES presents a very high incremental yield, with a significant VUSs burden, so we encourage its use in selected cases. Soft markers present heterogeneous CMA results from each other, some of them with risks comparable to structural anomalies, and would benefit from molecular analysis. The diagnostic rate of multiple soft markers poses a solid indication to CMA.

Diagnostic yield of exome sequencing for prenatal diagnosis of fetal structural anomalies: A systematic review and meta-analysis

Objectives

We conducted a systematic review and meta‐analysis to determine the diagnostic yield of exome sequencing (ES) for prenatal diagnosis of fetal structural anomalies, where karyotype/chromosomal microarray (CMA) is normal.

Methods

Following electronic searches of four databases, we included studies with ≥10 structurally abnormal fetuses undergoing ES or whole genome sequencing. The incremental diagnostic yield of ES over CMA/karyotype was calculated and pooled in a meta‐analysis. Sub‐group analyses investigated effects of case selection and fetal phenotype on diagnostic yield.

Results

We identified 72 reports from 66 studies, representing 4350 fetuses. The pooled incremental yield of ES was 31% (95% confidence interval (CI) 26%–36%, p < 0.0001). Diagnostic yield was significantly higher for cases pre‐selected for likelihood of monogenic aetiology compared to unselected cases (42% vs. 15%, p < 0.0001). Diagnostic yield differed significantly between phenotypic sub‐groups, ranging from 53% (95% CI 42%–63%, p < 0.0001) for isolated skeletal abnormalities, to 2% (95% CI 0%–5%, p = 0.04) for isolated increased nuchal translucency.

Conclusion

Prenatal ES provides a diagnosis in an additional 31% of structurally abnormal fetuses when CMA/karyotype is non‐diagnostic. The expected diagnostic yield depends on the body system(s) affected and can be optimised by pre‐selection of cases following multi‐disciplinary review to determine that a monogenic cause is likely.

What's already known about this topic?

Prenatal exome sequencing (ES) increases genetic diagnoses in fetuses with structural abnormalities and a normal karyotype and chromosomal microarray.

Published diagnostic yields from ES are varied and may be influenced by study size, case selection and fetal phenotype.

What does this study add?

This study provides a comprehensive systematic review of the literature to date and investigates the diagnostic yield of ES for a range of isolated system anomalies, to support clinical decision‐making on how to offer prenatal ES.

Long-term course of early onset developmental and epileptic encephalopathy associated with 2q24.3 microduplication

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2q24.3 is a region containing a cluster of genes for multiple voltage-gated sodium channels and CNVs in the region cause developmental and epileptic encephalopathy.

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DEE associated with 2q24.3 duplication have been reported to show early-onset epilepsy, resistant to antiseizure drugs, and severe developmental delay.

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Drug-resistant epilepsy due to 2q24.3 duplication can be seizure free after infancy.

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Our case was considered pyridoxine dependent but identifying duplication of 2q24.3 led to the discontinuation of unnecessary medication.

Copy number variations (CNVs) have been related to developmental and epileptic encephalopathy (DEE). The 2q24.3 region includes a cluster of genes for voltage-gated sodium channels (SCN) and CNVs in this region cause DEE. However, the long-term course of DEE with a 2q24.3 duplication has not been described. A 20-year-old female developed epileptic encephalopathy in early infancy that was resistant to various antiseizure medications. Her seizures disappeared after starting vitamin B6 therapy. Therefore, her epilepsy was considered pyridoxine-dependent epilepsy. At 16 years old, whole exome sequencing revealed a 2q24.3 microduplication including SCN1A, SCN2A, SCN3A, SCN7A, and SCN9A. Quantitative PCR detected an increased copy number of 1.3 Mb on 2q24.3 involving these genes, but no gene mutation accounting for pyridoxine-dependent epilepsy. Considering that with this duplication she was reported to be seizure-free after infancy, she was able to be off antiseizure medications including vitamin B6. Our case involvingdrug-resistant epilepsy in early infancy had no recurrent seizures during long-term follow up. Detecting CNVs using whole exome sequencing data was useful to identify a 2q24.3 duplication unassociated with pyridoxine-dependent epilepsy, leading to cessation of unnecessary medications.

Biallelic null variants in ZNF142 cause global developmental delay with familial epilepsy and dysmorphic features

Biallelic variants in ZNF142 at 2q35, which encodes zinc-finger protein 142, cause neurodevelopmental disorder with seizures or dystonia. We identified compound heterozygous null variants in ZNF142, NM_001105537.4:c.[1252C>T];[1274-2A>G],p.[Arg418*];[Glu426*], in Malaysian siblings suffering from global developmental delay with epilepsy and dysmorphism. cDNA analysis showed the marked reduction of ZNF142 transcript level through nonsense-mediated mRNA decay by these novel biallelic variants. The affected siblings present with global developmental delay and epilepsy in common, which were previously described, as well as dysmorphism, which was not recognized. It is important to collect patients with ZNF142 abnormality to define its phenotypic spectrum.

Intellectual disability and microcephaly associated with a novel CHAMP1 mutation

Mutations in a number of genes related to chromosomal segregation reportedly cause developmental disorders, e.g., chromosome alignment-maintaining phosphoprotein 1 (CHAMP1). We report on an 8-year-old Japanese girl who presented with a developmental disorder and microcephaly and carries a novel nonsense mutation in CHAMP1. Therefore, CHAMP1 mutation should be considered as a differential diagnosis of global developmental delay and microcephaly.

Clinical course of epilepsy and white matter abnormality linked to a novel DYRK1A variant

Epilepsy and white matter abnormality have been reported in DYRK1A-related intellectual disability syndrome; however, the clinical course has yet to be elucidated. Here, we report the clinical course of an 18-year-old male with a novel heterozygous DYRK1A variant (NM_001396.4: c.957C>G, p.Tyr319*); based on previous reports, epilepsy with this syndrome tends to be well controlled. Follow-up MRIs of the patient’s lesion revealed slightly reduced signal intensity compared to the first image.

Novel CLTC variants cause new brain and kidney phenotypes

Heterozygous variants in CLTC, which encode the clathrin heavy chain protein, cause neurodevelopmental delay of varying severity, and often accompanied by dysmorphic features, seizures, hypotonia, and ataxia. To date, 28 affected individuals with CLTC variants have been reported, although their phenotypes have not been fully elucidated. Here, we report three novel de novo CLTC (NM_001288653.1) variants in three individuals with previously unreported clinical symptoms: c.3662_3664del:p.(Leu1221del) in individual 1, c.2878T>C:p.(Trp960Arg) in individual 2, and c.2430+1G>T:p.(Glu769_Lys810del) in individual 3. Consistent with previous reports, individuals with missense or small in-frame variants were more severely affected. Unreported symptoms included a brain defect (cystic lesions along the lateral ventricles of the brain in individuals 1 and 3), kidney findings (high-echogenic kidneys in individual 1 and agenesis of the left kidney and right vesicoureteral reflux in individual 3), respiratory abnormality (recurrent pneumonia in individual 1), and abnormal hematological findings (anemia in individual 1 and pancytopenia in individual 3). Of note, individual 1 even exhibited prenatal abnormality (fetal growth restriction, cystic brain lesions, high-echogenic kidneys, and a heart defect), suggesting that CLTC variants should be considered when abnormal prenatal findings in multiple organs are detected.

Prenatal Exome Sequencing: Background, Current Practice and Future Perspectives-A Systematic Review

The introduction of Next Generation Sequencing (NGS) technologies has exerted a significant impact on prenatal diagnosis. Prenatal Exome Sequencing (pES) is performed with increasing frequency in fetuses with structural anomalies and negative chromosomal analysis. The actual diagnostic value varies extensively, and the role of incidental/secondary or inconclusive findings and negative results has not been fully ascertained. We performed a systematic literature review to evaluate the diagnostic yield, as well as inconclusive and negative-result rates of pES. Papers were divided in two groups. The former includes fetuses presenting structural anomalies, regardless the involved organ; the latter focuses on specific class anomalies. Available findings on non-informative or negative results were gathered as well. In the first group, the weighted average diagnostic yield resulted 19%, and inconclusive finding rate 12%. In the second group, the percentages were extremely variable due to differences in sample sizes and inclusion criteria, which constitute major determinants of pES efficiency. Diagnostic pES availability and its application have a pivotal role in prenatal diagnosis, though more homogeneity in access criteria and a consensus on clinical management of controversial information management is envisageable to reach widespread use in the near future.