Next-Generation Sequencing Gene Panels and "Solo" Clinical Exome Sequencing Applied in Structurally Abnormal Fetuses

Guidelines for NGS procedures applied to prenatal diagnosis by the Spanish Society of Gynecology and Obstetrics and the Spanish Association of Prenatal Diagnosis

OBJECTIVE

This document addresses the clinical application of next-generation sequencing (NGS) technologies for prenatal genetic diagnosis and aims to establish clinical practice recommendations in Spain to ensure uniformity in implementing these technologies into prenatal care.

METHODS

A joint committee of expert obstetricians and geneticists was created to review the existing literature on fetal NGS for genetic diagnosis and to make recommendations for Spanish healthcare professionals.

RESULTS

This guideline summarises technical aspects of NGS technologies, clinical indications in prenatal setting, considerations regarding findings to be reported, genetic counselling considerations as well as data storage and protection policies.

CONCLUSIONS

This document provides updated recommendations for the use of NGS diagnostic tests in prenatal diagnosis. These recommendations should be periodically reviewed as our knowledge of the clinical utility of NGS technologies, applied during pregnancy, may advance.

Monogenic conditions and central nervous system anomalies: A prospective study, systematic review and meta-analysis

OBJECTIVES

Determine the incremental diagnostic yield of prenatal exome sequencing (pES) over chromosome microarray (CMA) or G-banding karyotype in fetuses with central nervous system (CNS) abnormalities.

METHODS

Data were collected via electronic searches from January 2010 to April 2022 in MEDLINE, Cochrane, Web of Science and EMBASE. The NHS England prenatal exome cohort was also included. Incremental yield was calculated as a pooled value using a random-effects model.

RESULTS

Thirty studies were included (n = 1583 cases). The incremental yield with pES for any CNS anomaly was 32% [95%CI 27%-36%; I2 = 72%]. Subgroup analysis revealed apparent incremental yields in; (a) isolated CNS anomalies; 27% [95%CI 19%-34%; I2 = 74%]; (b) single CNS anomaly; 16% [95% CI 10%-23%; I2 = 41%]; (c) more than one CNS anomaly; 31% [95% Cl 21%-40%; I2 = 56%]; and (d) the anatomical subtype with the most optimal yield was Type 1 malformation of cortical development, related to abnormal cell proliferation or apoptosis, incorporating microcephalies, megalencephalies and dysplasia; 40% (22%-57%; I2 = 68%). The commonest syndromes in isolated cases were Lissencephaly 3 and X-linked hydrocephalus.

CONCLUSIONS

Prenatal exome sequencing provides a high incremental diagnostic yield in fetuses with CNS abnormalities with optimal yields in cases with multiple CNS anomalies, particularly those affecting the midline, posterior fossa and cortex.

Prenatal Exome Sequencing Analysis in Fetuses with Various Ultrasound Findings

OBJECTIVES

To evaluate the use of Exome Sequencing (ES) for the detection of genome-wide Copy Number Variants (CNVs) and the frequency of SNVs-InDels in selected genes related to developmental disorders in a cohort of consecutive pregnancies undergoing invasive diagnostic procedures for minor or simple ultrasound findings with no indication of ES.

METHODS

Women undergoing invasive diagnostic testing (chorionic villus sampling or amniocentesis) for QF-PCR and chromosomal microarray analysis (CMA) due to prenatal ultrasound findings without an indication for ES were selected over a five-month period (May-September 2021). ES was performed to compare the efficiency of genome-wide CNV detection against CMA analysis and to detect monogenic disorders. Virtual gene panels were selected to target genes related to ultrasound findings and bioinformatic analysis was performed, prioritizing variants based on the corresponding HPO terms. The broad Fetal Gene panel for developmental disorders developed by the PAGE group was also included in the analysis.

RESULTS

A total of 59 out of 61 women consented to participate in this study. There were 36 isolated major fetal anomalies, 11 aneuploidy markers, 6 minor fetal anomalies, 4 multiple anomalies, and 2 other ultrasound signs. Following QF-PCR analysis, two uncultured samples were excluded from this study, and six (10%) common chromosome aneuploidies were detected. In the remaining 51 cases, no pathogenic CNVs were detected at CMA, nor were any pathogenic variants observed in gene panels only targeting the ultrasound indications. Two (3.9%) monogenic diseases, apparently unrelated to the fetal phenotype, were detected: blepharo-cheilo-odontic syndrome (spina bifida) and Duchenne muscular dystrophy (pyelocaliceal dilation).

CONCLUSIONS

In our series of pregnancies with ultrasound findings, common aneuploidies were the only chromosomal abnormalities present, which were detected in 10% of cases. ES CNV analysis was concordant with CMA results in all cases. No additional findings were provided by only targeting selected genes based on ultrasound findings. Broadening the analysis to a larger number of genes involved in fetal developmental disorders revealed monogenic diseases in 3.9% of cases, which, although apparently not directly related to the indications, were clinically relevant.

Whole exome sequencing in fetuses with isolated increased nuchal translucency: a systematic review and meta-analysis

OBJECTIVE

To estimate the incremental yield of detecting pathogenic or likely pathogenic diagnostic genetic variants (DGV) by whole exome sequencing (WES) over standard karyotype and chromosomal microarray (CMA) analyses in fetuses with isolated increased nuchal translucency (NT) and normal fetal anatomy at the time of 11-14 weeks scan.

MATERIALS AND METHODS

Medline and Embase databases were searched. Inclusion criteria were fetuses with NT >95^th percentile, normal karyotype and CMA and no associated structural anomalies at the time of the 11-14 weeks scan. The primary outcome was to estimate the incremental yield of detecting pathogenic or likely pathogenic genetic variants by WES over standard karyotype and CMA analyses in fetuses with isolated increased nuchal translucency. The secondary outcomes were the detection of a genetic variant of unknown significance. Sub-analysis according to different NT cutoffs (between 3.0 and 5.5 mm and > 5.5 mm) and considering fetuses with isolated NT in which fetal anatomy was confirmed to be normal at the anomaly scan were also performed. Random effects model meta-analyses of proportion were used to analyze the data.

RESULTS

Eight articles (324 fetuses) were included in the systematic review. Of the fetuses with negative standard karyotype and CMA analysis, the 8.07% (95% CI 5.4-11.3) had pathogenic or likely pathogenic genetic variants detected exclusively by WES. When stratifying the analysis according to NT cutoffs, genetic anomalies detected exclusively at WES analysis were found in 44.70% (95% CI 26.8-63.4) of fetuses with NT between 3.0 mm and 5.5 mm and 55.3% (95% CI 36.6-73.2) in those fetuses with NT >5.5 mm and positive WES results. The 7.84% (95% CI 1.6-18.2) had variants of unknown significance identified by WES. When considering fetuses with isolated increased NT and normal fetal anatomy at the anomaly scan, the rate of pathogenic or likely pathogenic genetic variants detected by WES was 3.87% (95% CI 1.6-7.1), while variants of unknown significance were detected in 4.27% (95% CI 2.2-7.0) of cases.

CONCLUSIONS

Pathogenic and likely pathogenic genetic variants detected by WES are present in a significant proportion of fetuses with increased NT but normal standard karyotype and CMA analysis, also when no anomalies are detected at the anomaly scan. Further large studies sharing objective protocols of imaging assessment are needed to confirm these findings and to elucidate which gene panels should be assessed in fetuses with isolated increased NT to rule out associated genetic anomalies, which may potentially impact post-natal outcomes.

Postnatal genetic and neurodevelopmental assessment in infants born at term with severely low birth weight of non-placental origin

OBJECTIVE

To determine the frequency of genetic syndromes and childhood neurodevelopmental impairment in non-malformed infants born at term with severely low birth weight and no evidence of placental insufficiency.

METHODS

This case series was constructed from the data of infants delivered at term between 2013 and 2018 with severely low birth weight, defined as birth weight more than 2.5 SD below the mean, with normal maternal and fetal Doppler (umbilical artery, fetal middle cerebral artery, cerebroplacental ratio and uterine artery) and no maternal hypertensive disorder during pregnancy or fetal structural anomaly on prenatal ultrasound examination. Clinical exome sequencing and copy number variation (CNV) analysis were performed using DNA extracted from the children's saliva. Cognitive and psychomotor development was evaluated using the Bayley Scales of Infant and Toddler Development, 3rd edition or the Wechsler Intelligence Scale for Children, 5th edition tests, according to the child's age at testing.

RESULTS

Among the 36 405 infants born within the study period, 274 (0.75%) had a birth weight below -2.5 SD, of whom 98 met the inclusion criteria. Among the 63 families contacted, seven (11%) reported a postnatal diagnosis of a genetic syndrome and a further 18 consented to participate in the study. Median gestational age at delivery was 38.0 (interquartile range (IQR), 37.3-38.5) weeks and median birth weight was 2020 (IQR, 1908-2248) g. All 18 children showed a normal result on clinical exome sequencing and CNV analysis, but six (33%) obtained a low score on neurodevelopmental testing.

CONCLUSION

Non-malformed severely small term infants with no clinical or Doppler signs of placental insufficiency present a high rate of genetic syndromes and neurodevelopmental impairment during childhood. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Diagnostic yield of exome sequencing in fetuses with multisystem malformations: systematic review and meta-analysis

OBJECTIVE

To determine the diagnostic yield of exome sequencing (ES) above that of chromosomal microarray analysis (CMA) or karyotyping in fetuses with multisystem structural anomalies (at least two major anomalies in different anatomical systems).

METHOD

This was a systematic review conducted in accordance with PRISMA guidelines. Searching PubMed, Web of Knowledge and Cochrane database, we identified studies describing ES, whole-genome and/or next-generation sequencing in fetuses with multisystem malformations. Included were observational studies involving five or more eligible fetuses. A fetus was eligible for inclusion if it had at least two major anomalies of different anatomical systems and a negative CMA or karyotyping result. Only positive variants classified as likely pathogenic or pathogenic determined to be causative of the fetal phenotype were considered. A negative CMA or karyotype result was treated as the reference standard. The diagnostic yield of the primary outcome was calculated by single-proportion analysis using random-effects modeling. A subgroup analysis was performed to compare the diagnostic yield of the solo approach (fetus alone sequenced) with that of the trio approach (fetus and both parents sequenced).

RESULTS

Seventeen articles with data on ES diagnostic yield, including 694 individuals with multisystem malformations, were identified. Overall, a pathogenic or likely pathogenic variant potentially causative of the fetal phenotype was found in 213 fetuses, giving a 33% (95% CI, 27-40%) incremental yield of ES. A stratified analysis showed similar diagnostic yields of ES using the solo approach (30%; 95% CI, 11-52%) and the trio approach (35%; 95% CI, 26-44%).

CONCLUSIONS

ES applied in fetuses with multisystem structural anomalies was able to identify a potentially causative gene when CMA or karyotyping had failed to do so in an additional one-third of cases. No differences were observed between the solo and trio approaches for ES. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

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.