Postmortem Genetic Testing for Cardiac Ion Channelopathies in Stillbirths

A Pilot Study of Ultrasound Assessment of Umbilical Cord and Placental Vascular Flow for Cord Accident Stillbirth Prevention

OBJECTIVE

Our objective was to determine the feasibility and interobserver reliability of umbilical cord and placental arteriolar flow assessment in low-risk pregnancies near term.

METHODS

This was a prospective pilot study in low-risk pregnancies at 36 weeks with anterior placentas. We excluded any with an indication for antenatal testing or delivery before 39 weeks. Each participant underwent two ultrasounds by different examiners, which included arterial and venous velocimetry at three cord sites (fetal, free loop, and placental) in addition to maternal and fetal placental arterioles. The interobserver reliability was quantified using the Pearson correlation coefficient with that of standard clinical parameters serving as a benchmark for interpretation.

RESULTS

Among 53 participants scanned at 356/7-371/7 weeks, the mean examination duration was 20.5 ± 4.2 minutes. Ascertainment success was high for measures at the free loop, placental cord insertion, and fetal placental arterioles (range 90.6%-99.1%) and was lower at the fetal cord insertion and maternal spiral arterioles (range 47.2%-87.7%). Interobserver reliability estimates for free-loop systolic/diastolic and pulsatility index ranged from 0.38 to 0.44. Interobserver reliability for experimental parameters varied by measurement site, and all were poor at the fetal insertion and in placental arterioles. Parameters had significant variation across cord sites (range 4.3%-21.7%).

CONCLUSION

In our cohort, flow assessments of the free loop, placental insertion, and placental arterioles are feasible, but interrater reliability varies by measurement type and cord site. Future studies are needed to establish feasibility and reliability in nonanterior placentation and to assess clinical relevance.

Further exploration of cardiac channelopathy and cardiomyopathy genes in stillbirth

OBJECTIVE

To explore genetic variation including whole genome copy number variation and sequence analysis of 98 genes associated with pediatric or adult cardiomyopathies, cardiac channelopathies, and sudden death in an unexplained intrauterine fetal death cohort.

METHODS

The study population included 55 stillbirth cases that remained unexplained after thorough postmortem examination, excluding maternal, fetal, and placental causes of stillbirth. Molecular karyotyping was performed in 55 cases and the trio exome sequencing approach was applied in 19 cases.

RESULTS

The analysis revealed six rare variants with predicted effects on protein function in six genes (CASQ2, DSC2, KCNE1, LDB3, MYH6, and SCN5A) previously reported in cases of stillbirth or severe early onset pediatric cardiac related phenotypes. When applying strict American College of Genetics and Genomics classification guidelines, these are still variants of uncertain significance.

CONCLUSIONS

Several potentially stillbirth-related genetic variants were detected in our cohort, adding to the growing literature on cardiac phenotype gene variation in stillbirth. However, the mechanisms of action, gene-gene interaction, and contribution of the uterine environment are still to be deciphered. In order to advance our knowledge of the genetics of unexplained fetal death, there is an evident need for international collaboration and field standardization.

Genomics of stillbirth

Stillbirth, defined as fetal death at 20 weeks gestation or later, is a devastating pregnancy outcome affecting 1 in 175 pregnancies in the United States. Although efforts to understand the etiology of stillbirth have expanded, 25 % of cases remain unexplained and some cases previously thought to be explained may have additional unknown causative factors. Determining an etiology for stillbirth is important for clinical management and for grieving families to obtain closure, to find meaning, and to understand recurrence risks. However, the evaluation of stillbirth is not completed uniformly despite American College of Obstetrics and Gynecology (ACOG) guidelines and stillbirth data is frequently incomplete due to lack of genomic analysis, fetal autopsy, and placental pathology. Karyotype and chromosomal microarray have been the gold standard in genetic analysis in perinatal medicine for many years, but next generation sequencing holds promise towards improving diagnostic yields and providing clarity for both clinicians and patients.

Sodium Channel Gene Variants in Fetuses with Abnormal Sonographic Findings: Expanding the Prenatal Phenotypic Spectrum of Sodium Channelopathies

Voltage-gated sodium channels (VGSCs) are responsible for the initiation and propagation of action potentials in the brain and muscle. Pathogenic variants in genes encoding VGSCs have been associated with severe disorders including epileptic encephalopathies and congenital myopathies. In this study, we identified pathogenic variants in genes encoding the α subunit of VGSCs in the fetuses of two unrelated families with the use of trio-based whole exome sequencing, as part of a larger cohort study. Sanger sequencing was performed for variant confirmation as well as parental phasing. The fetus of the first family carried a known de novo heterozygous missense variant in the SCN2A gene (NM_001040143.2:c.751G>A p.(Val251Ile)) and presented intrauterine growth retardation, hand clenching and ventriculomegaly. Neonatally, the proband also exhibited refractory epilepsy, spasms and MRI abnormalities. The fetus of the second family was a compound heterozygote for two parentally inherited novel missense variants in the SCN4A gene (NM_000334.4:c.4340T>C, p.(Phe1447Ser), NM_000334.4:c.3798G>C, p.(Glu1266Asp)) and presented a severe prenatal phenotype including talipes, fetal hypokinesia, hypoplastic lungs, polyhydramnios, ear abnormalities and others. Both probands died soon after birth. In a subsequent pregnancy of the latter family, the fetus was also a compound heterozygote for the same parentally inherited variants. This pregnancy was terminated due to multiple ultrasound abnormalities similar to the first pregnancy. Our results suggest a potentially crucial role of the VGSC gene family in fetal development and early lethality.

The genetic approach to stillbirth: A »systematic review«

Unexplained stillbirth is defined as a stillbirth with no known cause after the exclusion of common causes, including obstetric complications, infections, placental insufficiency or abruption, umbilical cord complications, and congenital abnormalities with or without known genetic cause. More than 60% of stillbirth cases remain unexplained. The aim of this systematic review was to investigate the known genetic causes of unexplained stillbirth cases and to evaluate the current position and future directions for the use of genetic and genomic testing in expanding the knowledge in this field. A systematic search through several databases was performed using the keywords genetics and stillbirths in humans. Different methods to detect various types of causal genetic aberrations have been used in the past decades, from standard karyotyping to novel methods such as chromosomal microarray analysis and next generation sequencing technologies. Apart from common chromosomal aneuploidies, a promising hypothesis about genetic causes included genes related to cardiomyopathies and channelopathies. However, these were tested in the research settings, since molecular karyotyping is currently the standard approach in the routine evaluation of genetic causes of stillbirth. Hereby, we provide evidence that expanding knowledge using novel genetic and genomic testing might uncover new genetic causes of unexplained stillbirth.

Cardiac ion channels associated with unexplained stillbirth - an immunohistochemical study

OBJECTIVES

Despite the use of post-mortem investigations, approximately 20% of stillbirths remain unexplained. Cardiac ion channelopathies have been identified as a cause of death in Sudden Infant Death Syndrome (SIDS) and could be associated with unexplained stillbirths. This study aimed to understand if the expression or localisation of cardiac ion channels associated with channelopathies were altered in cases of unexplained stillbirths.

METHODS

A case control study was conducted using formalin-fixed cardiac tissue from 20 cases of unexplained stillbirth and a control group of 20 cases of stillbirths from intrapartum hypoxia. 4 µm tissue sections were stained using haematoxylin and eosin, Masson's trichrome (MT) and Elastic van Gieson (EVG). Immunohistochemistry (IHC) was performed using antibodies against CACNA1G, KCNJ2, KCNQ1, KCNH2 and KCNE1. The cardiac conduction system in samples stained with MT and EVG could not be identified. Therefore, the levels of immunoperoxidase staining were quantified using QuPath software.

RESULTS

The nuclear-cytoplasmic ratio of sections stained with haematoxylin and eosin was higher for the hypoxia group (hypoxia median 0.13 vs. 0.04 unexplained, p < 0.001). CACNA1G (unexplained median 0.26 vs. hypoxia 0.30, p=0.009) and KCNJ2 (unexplained median 0.35 vs. hypoxia 0.41, p=0.001) had lower staining intensity in the unexplained stillbirth group. There were no statistically significant differences in the staining intensity of KCNQ1, KCNH2 and KCNE1.

CONCLUSIONS

Two ion channels associated with channelopathies demonstrated lower levels of expression in cases of unexplained stillbirth. Further genetic studies using human tissue should be performed to understand the association between channelopathies and otherwise unexplained stillbirths.

Clinical Characteristics, Genetic Findings and Arrhythmic Outcomes of Patients with Catecholaminergic Polymorphic Ventricular Tachycardia from China: A Systematic Review

INTRODUCTION

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare inherited cardiac ion channelopathy. The present study aims to examine the clinical characteristics, genetic basis, and arrhythmic outcomes of CPVT patients from China to elucidate the difference between CPVT patients in Asia and Western countries.

METHODS

PubMed and Embase were systematically searched for case reports or series reporting on CPVT patients from China until 19 February 2022 using the keyword: "Catecholaminergic Polymorphic Ventricular Tachycardia" or "CPVT", with the location limited to: "China" or "Hong Kong" or "Macau" in Embase, with no language or publication-type restriction. Articles that did not state a definite diagnosis of CPVT and articles with duplicate cases found in larger cohorts were excluded. All the included publications in this review were critically appraised based on the Joanna Briggs Institute Critical Appraisal Checklist. Clinical characteristics, genetic findings, and the primary outcome of spontaneous ventricular tachycardia/ventricular fibrillation (VT/VF) were analyzed.

RESULTS

A total of 58 unique cases from 15 studies (median presentation age: 8 (5.0-11.8) years old) were included. All patients, except one, presented at or before 19 years of age. There were 56 patients (96.6%) who were initially symptomatic. Premature ventricular complexes (PVCs) were present in 44 out of 51 patients (86.3%) and VT in 52 out of 58 patients (89.7%). Genetic tests were performed on 54 patients (93.1%) with a yield of 87%. RyR2, CASQ2, TERCL, and SCN10A mutations were found in 35 (71.4%), 12 (24.5%), 1 (0.02%) patient, and 1 patient (0.02%), respectively. There were 54 patients who were treated with beta-blockers, 8 received flecainide, 5 received amiodarone, 2 received verapamil and 2 received propafenone. Sympathectomy (n = 10), implantable cardioverter-defibrillator implantation (n = 8) and ablation (n = 1) were performed. On follow-up, 13 patients developed VT/VF.

CONCLUSION

This was the first systematic review of CPVT patients from China. Most patients had symptoms on initial presentation, with syncope as the presenting complaint. RyR2 mutation accounts for more than half of the CPVT cases, followed by CASQ2, TERCL and SCN10A mutations.

Pitfalls of International Classification of Diseases - Perinatal mortality in analysing stillbirths

OBJECTIVES

This study aimed to evaluate the trend of stillbirth from 2009 to 2018. The causes of stillbirth were classified using the International Classification of Diseases - Perinatal Mortality (ICD-PM).

STUDY DESIGN AND METHODS

A retrospective chart review was performed on 135 stillbirths from 2009 to 2018 in a tertiary university teaching hospital. The annual stillbirth rate was calculated, and the trend was evaluated. The cause of death was reclassified using ICD-PM.

RESULTS

The stillbirth rate was 3.70 per 1000 total births, and it remained stable over the studied period (P = 0.238). Most of the stillbirth (97.8%) were antepartum deaths. The proportion of unexplained stillbirth was reduced from 57% to 18.5% after reclassified by ICD-PM coding. Another major cause of antepartum stillbirths was disorders related to fetal growth, which consisted of mothers with medical and surgical conditions (11%, n = 15, ICD-PM code A5, M4) or mothers with complications of placenta, cord and membranes (8.9%, n = 12, ICD-PM code A5, M1).

CONCLUSION

The use of ICD-PM was useful in reducing the proportion of unexplained stillbirths. ICD-PM has the advantages of coding related to the timing of stillbirth and associated maternal conditions. Pitfalls including the unclear use of the code A3-'antepartum hypoxia,' guidance on coding of well-controlled maternal medical conditions and placental pathology and the importance of subcategorisation need to be addressed.

Recurrent Pregnancy Loss and Concealed Long-QT Syndrome

Background

Recurrent pregnancy loss affects 1% to 2% of couples attempting childbirth. A large fraction of all cases remains idiopathic, which warrants research into monogenic causes of this distressing disorder.

Methods and Results

We investigated a nonconsanguineous Estonian family who had experienced 5 live births, intersected by 3 early pregnancy losses, and 6 fetal deaths, 3 of which occurred during the second trimester. No fetal malformations were described at the autopsies performed in 3 of 6 cases of fetal death. Parental and fetal chromosomal abnormalities (including submicroscopic) and maternal risk factors were excluded. Material for genetic testing was available from 4 miscarried cases (gestational weeks 11, 14, 17, and 18). Exome sequencing in 3 pregnancy losses and the mother identified no rare variants explicitly shared by the miscarried conceptuses. However, the mother and 2 pregnancy losses carried a heterozygous nonsynonymous variant, resulting in p.Val173Asp (rs199472695) in the ion channel gene KCNQ1. It is expressed not only in heart, where mutations cause type 1 long‐QT syndrome, but also in other tissues, including uterus. The p.Val173Asp variant has been previously identified in a patient with type 1 long‐QT syndrome, but not reported in the Genome Aggregation Database. With heterologous expression in CHO cells, our in vitro electrophysiologic studies indicated that the mutant slowly activating voltage‐gated K+ channel (I_Ks) is dysfunctional. It showed reduced total activating and deactivating currents (P<0.01), with dramatically positive shift of voltage dependence of activation by ≈10 mV (P<0.05).

Conclusions

The current study uncovered concealed maternal type 1 long‐QT syndrome as a potential novel cause behind recurrent fetal loss.

Genetic variants in TRPM7 associated with unexplained stillbirth modify ion channel function

Stillbirth is the loss of a fetus after 22 weeks of gestation, of which almost half go completely unexplained despite post-mortem. We recently sequenced 35 arrhythmia-associated genes from 70 unexplained stillbirth cases. Our hypothesis was that deleterious mutations in channelopathy genes may have a functional effect in utero that may be pro-arrhythmic in the developing fetus. We observed four heterozygous, nonsynonymous variants in transient receptor potential melastatin 7 (TRPM7), a ubiquitously expressed ion channel known to regulate cardiac development and repolarization in mice.

We used site-directed mutagenesis and single-cell patch-clamp to analyze the functional effect of the four stillbirth mutants on TRPM7 ion channel function in heterologous cells. We also used cardiomyocytes derived from human pluripotent stem cells to model the contribution of TRPM7 to action potential morphology.

Our results show that two TRPM7 variants, p.G179V and p.T860M, lead to a marked reduction in ion channel conductance. This observation was underpinned by a lack of measurable TRPM7 protein expression, which in the case of p.T860M was due to rapid proteasomal degradation. We also report that human hiPSC-derived cardiomyocytes possess measurable TRPM7 currents; however, siRNA knockdown did not directly affect action potential morphology.

TRPM7 variants found in the unexplained stillbirth population adversely affect ion channel function and this may precipitate fatal arrhythmia in utero.

Cardio-pathogenic variants in unexplained intrauterine fetal death: a retrospective pilot study

To describe the prevalence and spectrum of cardio-pathogenic variants in singleton fetuses after unexplained intrauterine fetal death (IUFD). DNA from post-mortem fibroblastic tissue samples of 16 fetuses after unexplained IUFD was retrieved at two tertiary university hospitals for clinical exome sequencing with subsequent filtering of 122 cardio-specific genes to elucidate underlying cardio-pathogenic variants. In total, we included 12 (75%) male and four (25%) female fetuses who were stillborn at a median gestational age of 34⁺⁶ (23⁺²–40⁺⁵) weeks. In two (12.5%) fetuses no cardio-pathogenic variants were found. In 14 (87.5%) fetuses, overall 33 variants were detected in 22 cardio-specific genes, involving 14 (63.63%) genes associated with cardiomyopathy, six (27.27%) arrhythmogenic susceptibility genes and two (9.09%) arrhythmia and cardiomyopathy associated genes. Among the 33 variants, five (15.2%) were classified as likely benign according to the American College of Medical Genetics and Genomics; 28 (84.8%) variants were considered as variants of uncertain significance. Compared to a cohort of explained IUFDs, the cases with and without fetal variants in cardiac genes differed not significantly regarding maternal age, previous history of stillbirth, time of stillbirth or fetal sex. Unexplained stillbirth may be caused by cardio-genetic pathologies, yet a high number of variants of uncertain significance merit a more detailed post-mortem examination including family segregation analysis.

Genetic innovations and our understanding of stillbirth

Stillbirth after 20 weeks gestation happens in 1 in 200 pregnancies and occurs more commonly than neonatal loss and sudden infant death syndrome (SIDs) combined. The stillbirth rate is several times greater in low as opposed to high-resource countries. However, among high-resource countries, although a lower overall stillbirth rate exists, there has been little change for several decades. Molecular genetic technologies are emerging as important contributors to our understanding of stillbirth. Initially, genetic etiologies included alterations in chromosome number or structure such as aneuploidy and microduplications and deletions. More recently, next-generation sequencing analysis in two genetic conditions, Smith Lemli Optiz Syndrome (SLOs) and the channelopathy disorders (such as long QT syndrome (LQTS)) provide examples into the association of pathogenic gene variants with stillbirth. Although these specific conditions individually account for only a small number of stillbirths, investigating these disorders provides a new and innovative approach for further understanding genetic contributors to adverse pregnancy outcomes. Our knowledge of the role of genetic disease as an etiology for stillbirth is elementary. Genomic interrogation of maternal-fetal genotypes, gene-gene, and genotype-environment interaction is lacking in stillbirth research. At the DNA sequence level, further investigation of variants of unknown significance is an opportunity for exploration of biologic pathways of importance to pregnancy loss. This review concentrates on SLO as an example of a single gene disorder with a high carrier but low affected liveborn proband rate. The channelopathy disorders are included as initial examples of genetic conditions with variable presentation including an association with sudden infant death syndrome. Highlighted are the challenges when numerous genes and variants are involved, and the task of assigning pathogenicity. The advantages and limitations of genetic evaluations are presented and avenues for further research considered.

Feasibility of Non-invasive Fetal Electrocardiographic Interval Measurement in the Outpatient Clinical Setting

Non-invasive fetal electrocardiography (ECG) is a promising method for evaluating fetal cardiac electrical activity. Despite advances in fetal ECG technology, its ability to provide reliable, interpretable results in a typical outpatient fetal cardiology setting remains unclear. We sought to determine the feasibility of measuring standard ECG intervals in an outpatient fetal cardiology practice using an abdominal fetal ECG device that employs blind source separation with reference, an innovative signal-processing technique for fetal ECG extraction. Women scheduled for clinically indicated outpatient fetal echocardiogram underwent 10 min of fetal ECG acquisition from the maternal abdomen using specialized gel electrodes. A bedside laptop computer performed fetal ECG extraction, allowing real-time visualization of fetal and maternal ECG signals. Offline post-processing of 1 min of recorded data yielded fetal P-wave duration, PR interval, QRS duration, RR interval, QT interval, and QTc. Fifty-five fetuses were studied with gestational age 18-37 weeks, including 13 with abnormal fetal echocardiogram findings and three sets of twins. Interpretable results were obtained in 91% of fetuses, including 85% during the vernix period and 100% of twin fetuses. PR interval and RR interval of 18-24 week gestation fetuses were significantly shorter than those with gestational age 25-31 and 32-37 weeks. Of the six fetuses with abnormal rhythms on fetal echocardiogram, fetal ECG tracing was interpretable in five and matched the rhythm noted on fetal echocardiogram. Abdominal fetal ECG acquisition is feasible for arrhythmia detection and ECG interval calculation in a routine clinical setting.