The many etiologies of nonimmune hydrops fetalis diagnosed by exome sequencing

A systematic review to assess the utility of genomic autopsy using exome or genome sequencing in cases of congenital anomalies and perinatal death

PURPOSE

Exome or genome sequencing (ES or GS) can identify genetic causes of otherwise unexplained congenital anomaly and perinatal death (PND) but is not routine practice. The evidence base for "genomic autopsy" after termination of pregnancy for fetal anomaly (TOPFA) and PND has been synthesized to determine the value of this investigation.

METHODS

We conducted a systematic review and meta-analysis of studies meeting prespecified inclusion criteria and containing ≥10 cases of TOPFA or PND (with or without major congenital abnormality), in which ES or GS was conducted. We determined test performance, including diagnostic yield, accuracy, and reliability. We also reported outcomes associated with clinical utility and harms, where described.

RESULTS

From 2245 potentially eligible studies, 32 publications were eligible and had data extracted, representing 2120 cases that could be meta-analyzed. No diagnostic accuracy or comparative studies were identified, although some analysis of concordance between different ES/GS methodologies could be performed. Studies reporting parent-related outcomes or long-term follow-up did not do so in a systematic or quantifiable manner.

CONCLUSION

Evidence suggests that approximately one-fourth to one-third of fetal losses associated with TOPFA or unexplained PND are associated with a genetic cause identifiable on ES or GS-albeit this estimate varies depending on phenotypic and background risk factors. Despite the large body of evidence on ES and GS, little research has attempted to validate the accuracy of testing, nor measure the clinical or societal outcomes in families that follow the diagnostic investigation in this context.

RASopathies are the most common set of monogenic syndromes identified by exome sequencing for nonimmune hydrops fetalis: A systematic review and meta-analysis

RASopathies are a group of malformation syndromes known to lead to nonimmune hydrops fetalis (NIHF) in severe presentations. Pathogenic variants can be de novo or parentally inherited. Despite being a known frequent presentation, the fraction of monogenic NIHF cases due to RASopathies is limited in the literature. Also, the specific parental contribution of RASopathies to NIHF is not well described. Our objective was to review pooled exome sequencing (ES) diagnostic yield of RASopathies for NIHF and to determine the parental contribution of RASopathy to NIHF. We performed a systematic review of prenatal ES studies from January 1, 2000 to August 1, 2022. Thirty-six studies met inclusion criteria. Cases with RASopathy gene variants were reviewed. NIHF cases were further classified as isolated or non-isolated. Thirty-six ES studies including 46 pregnancies with NIHF and a diagnosed RASopathy were reviewed. Forty-four diagnostic variants and 2 variants of uncertain significance in 12 RASopathy genes were identified. Expanding on what was previously published, a total of 506 NIHF cases were extracted with 191 cases yielding a positive diagnosis by ES. The overall rate of RASopathy diagnosis in clinically diagnosed NIHF cases was 9% (44/506). The rate of RASopathy diagnosis among NIHF cases with positive genetic diagnosis by ES was 23% (44/191). Of the 46 cases identified, 13 (28%) variants were parentally inherited; specifically, 5/13 (38%) maternal, 3/13 (23%) paternal, 2/13 (15%) biparental, and 3/13 (23%) unspecified. Majority of NIHF cases 29/46 (63%) were isolated. Among NIHF cases with positive ES diagnoses, RASopathy diagnostic yield by ES was 23%. NIHF secondary to RASopathies was parentally inherited in 28% of cases. Most cases of NIHF due to RASopathy were isolated, with no prenatal detection of associated anomalies.

Outcome and etiology of fetal pleural effusion, fetal ascites and hydrops fetalis after fetal intervention: retrospective observational cohort from a single institution

OBJECTIVES

Non-immune hydrops fetalis (NIHF) is the pathological accumulation of fluids in fetal compartments, without maternal isoimmunization. Fetal interventions (e.g. shunting, fetal paracentesis, fetal thoracocentesis, fetal pleurodesis) are used to alleviate fluid accumulations, but the outcome is uncertain because the underlying causes of NIHF vary. We aimed to explore the etiology and long-term outcome of NIHF after fetal intervention.

METHODS

This was a retrospective review of fetuses with NIHF, defined by the presence of fetal ascites, pleural or pericardial effusion, skin edema or cystic hygroma, or a combination of these features, who underwent intervention at our institution during the period 2012-2021. Clinical surveillance, genetic analysis and viral infection screening were used to define the etiology. Chart reviews and telephone interviews were conducted to assess the long-term outcomes.

RESULTS

In total, 55 fetuses were enrolled and 46 cases had final follow-up data after delivery. Etiology was identified in 33 cases, including four for which the underlying causes were not identified initially using small-gene-panel tests but which were later diagnosed with monogenic disorders by whole-exome sequencing (WES). Twenty-three cases with follow-up survived, having a follow-up period of 2-11 years at the time of writing, of which 17 were healthy. All 11 cases initially presenting as congenital chylothorax survived with favorable outcome.

CONCLUSIONS

The etiologies of NIHF are heterogeneous, and the long-term (spanning 2-11 years) outcome of fetal intervention varies, according to the underlying etiology, with cases caused by congenital chylothorax having the best prognosis. Genome-wide tests, such as WES, may be helpful in determining the underlying condition in cases caused by a genetic disorder, and this may affect fetal therapy approaches in the future. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

PIEZO1 is the most common monogenic etiology of non-immune hydrops fetalis detected by prenatal exome sequencing

OBJECTIVE

To clarify the relevance of PIEZO1 variants detected by prenatal exome in the context of non-immune hydrops fetalis (NIHF).

METHODS

A systematic review of prenatal exome studies from 1/1/2000-8/1/2022 was performed. Thirty-six studies met the inclusion criteria. PIEZO1 variants were categorized by disease mode (dominant (AD) versus recessive (AR)) and classified by the American College of Medical Genetics and Genomics (ACMG) guidelines.

RESULTS

Twenty-two pregnancies with 35 distinct PIEZO1 variants were included. We deemed PIEZO1 variants to be "likely diagnostic" in 12/22 pregnancies, "possibly diagnostic" in 7/22, and "unlikely diagnostic" in 3/22. In total, 19 of 191 NIHF cases diagnosed by prenatal exome were attributed to PIEZO1. Among likely diagnosed cases, the disease mode was AR in eight and AD in four. PIEZO1 variants causing AR NIHF were characterized by loss of function and isolated NIHF phenotype. PIEZO1 variants causing AD NIHF were characterized by gain of function in red blood cells, scarcity in databases, and sporadic inheritance. Missense variants associated with NIHF were clustered in three domains: transmembrane helical unit 4 (THU4), THU5, and the Cap.

CONCLUSION

PIEZO1 variants were reported in 10% of NIHF cases diagnosed by prenatal exome, making PIEZO1 the most common single gene reported in NIHF.

Genetic disorders and pregnancy outcomes of non-immune hydrops fetalis in a tertiary referral center

OBJECTIVES

Non-immune hydrops fetalis (NIHF) is a non-specific symptom associated with a wide range of disorders. The prognosis of NIHF depends on the underlying etiology. In this study, we investigated the incidence of chromosomal abnormalities and Bart's hydrops fetalis in pregnancies associated with NIHF in South China.

METHODS

We conducted a retrospective review of NIHF pregnancies referred to the Fujian Provincial Maternity and Children's Hospital between 2014 and 2018, excluding pregnancies with maternal alloimmunization. Routine karyotyping was performed on all 129 enrolled patients, and chromosomal microarray analysis was performed for 35 cases with a normal karyotype. In addition, α-thalassemia genotyping was performed to confirm the presence of Bart's hydrops fetalis.

RESULTS

Chromosomal abnormalities were detected in 29.5% (38/129) of the cohort, including 37 cases with aneuploidy and one case with unbalanced structural rearrangement. Chromosomal microarray analysis performed on the 35 cases with a normal karyotype did not reveal any additional pathogenic variants. The proportions of chromosomal abnormalities declined with trimester progression, with frequencies of 65%, 30.1%, and 8.3% in the first, second, and third trimesters, respectively (p < 0.05). Bart's hydrops fetalis was detected in 34.9% (45/129) of the cohort. Among the 46 (35.6%) cases with unknown etiology, 23 cases had other ultrasonic abnormalities characterized by poor outcomes, whereas seven cases with multiple cavity effusions that resolved or remitted prior to birth showed normal development during the 3-4 years of follow-up.

CONCLUSIONS

In South China, Bart's hydrops fetalis and chromosomal abnormalities are the most common genetic etiologies of NIHF. Generalized skin edema and accompanying ultrasonic abnormalities are predictive of adverse outcomes, highlighting the need for intensive monitoring and better pregnancy management of NIHF patients.

The lymphatic vascular system: much more than just a sewer

Almost 400 years after the (re)discovery of the lymphatic vascular system (LVS) by Gaspare Aselli (Asellius G. De lactibus, sive lacteis venis, quarto vasorum mesaraicorum genere, novo invento Gasparis Asellii Cremo. Dissertatio. (MDCXXIIX), Milan; 1628.), structure, function, development and evolution of this so-called 'second' vascular system are still enigmatic. Interest in the LVS was low because it was (and is) hardly visible, and its diseases are not as life-threatening as those of the blood vascular system. It is not uncommon for patients with lymphedema to be told that yes, they can live with it. Usually, the functions of the LVS are discussed in terms of fluid homeostasis, uptake of chylomicrons from the gut, and immune cell circulation. However, the broad molecular equipment of lymphatic endothelial cells suggests that they possess many more functions, which are also reflected in the pathophysiology of the system. With some specific exceptions, lymphatics develop in all organs. Although basic structure and function are the same regardless their position in the body wall or the internal organs, there are important site-specific characteristics. We discuss common structure and function of lymphatics; and point to important functions for hyaluronan turn-over, salt balance, coagulation, extracellular matrix production, adipose tissue development and potential appetite regulation, and the influence of hypoxia on the regulation of these functions. Differences with respect to the embryonic origin and molecular equipment between somatic and splanchnic lymphatics are discussed with a side-view on the phylogeny of the LVS. The functions of the lymphatic vasculature are much broader than generally thought, and lymphatic research will have many interesting and surprising aspects to offer in the future.

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.