Whole genome sequencing in transposition of the great arteries and associations with clinically relevant heart, brain and laterality genes

In-Depth Genomic Analysis: The New Challenge in Congenital Heart Disease

The use of next-generation sequencing has provided new insights into the causes and mechanisms of congenital heart disease (CHD). Examinations of the whole exome sequence have detected detrimental gene variations modifying single or contiguous nucleotides, which are characterised as pathogenic based on statistical assessments of families and correlations with congenital heart disease, elevated expression during heart development, and reductions in harmful protein-coding mutations in the general population. Patients with CHD and extracardiac abnormalities are enriched for gene classes meeting these criteria, supporting a common set of pathways in the organogenesis of CHDs. Single-cell transcriptomics data have revealed the expression of genes associated with CHD in specific cell types, and emerging evidence suggests that genetic mutations disrupt multicellular genes essential for cardiogenesis. Metrics and units are being tracked in whole-genome sequencing studies.

Novel Loss of Function Variants in CENPF Including a Large Intragenic Deletion in Patients with Strømme Syndrome

Strømme syndrome is an ultra-rare primary ciliopathy with clinical variability. The syndrome is caused by bi-allelic variants in CENPF, a protein with key roles in both chromosomal segregation and ciliogenesis. We report three unrelated patients with Strømme syndrome and, using high-throughput sequencing approaches, we identified novel pathogenic variants in CENPF, including one structural variant, giving a genetic diagnosis to the patients. Patient 1 was a premature baby who died at 26 days with congenital malformations affecting many organs including the brain, eyes, and intestine. She was homozygous for a donor splice variant in CENPF, NM_016343.3:c.1068+1G>A, causing skipping of exon 7, resulting in a frameshift. Patient 2 was a female with intestinal atresia, microcephaly, and a Peters anomaly. She had normal developmental milestones at the age of 7 years. She is compound heterozygous for CENPF NM_016343.3:c.5920dup and c.8991del, both frameshift. Patient 3 was a male with anomalies of the brain, eye, intestine, and kidneys. He was compound heterozygous for CENPF p.(Glu298Ter), and a 5323 bp deletion covering exon 1. CENPF exon 1 is flanked by repetitive sequences that may represent a site of a recurrent structural variation, which should be a focus in patients with Strømme syndrome of unknown etiology.

Understanding laterality disorders and the left-right organizer: Insights from zebrafish

Vital internal organs display a left-right (LR) asymmetric arrangement that is established during embryonic development. Disruption of this LR asymmetry-or laterality-can result in congenital organ malformations. Situs inversus totalis (SIT) is a complete concordant reversal of internal organs that results in a low occurrence of clinical consequences. Situs ambiguous, which gives rise to Heterotaxy syndrome (HTX), is characterized by discordant development and arrangement of organs that is associated with a wide range of birth defects. The leading cause of health problems in HTX patients is a congenital heart malformation. Mutations identified in patients with laterality disorders implicate motile cilia in establishing LR asymmetry. However, the cellular and molecular mechanisms underlying SIT and HTX are not fully understood. In several vertebrates, including mouse, frog and zebrafish, motile cilia located in a "left-right organizer" (LRO) trigger conserved signaling pathways that guide asymmetric organ development. Perturbation of LRO formation and/or function in animal models recapitulates organ malformations observed in SIT and HTX patients. This provides an opportunity to use these models to investigate the embryological origins of laterality disorders. The zebrafish embryo has emerged as an important model for investigating the earliest steps of LRO development. Here, we discuss clinical characteristics of human laterality disorders, and highlight experimental results from zebrafish that provide insights into LRO biology and advance our understanding of human laterality disorders.

Insights into the genetic architecture underlying complex, critical congenital heart disease

Congenital heart disease (CHD) has a multifactorial aetiology, raising the possibility of an underlying genetic burden, predisposing to disease but also variable expression, including variation in disease severity, and incomplete penetrance. Using whole genome sequencing (WGS), the findings of this study, indicate that complex, critical CHD is distinct from other types of disease due to increased genetic burden in common variation, specifically among established CHD genes. Additionally, these findings highlight associations with regulatory genes and environmental "stressors" in the final presentation of disease.

Clustering of Genetic Anomalies of Cilia Outer Dynein Arm and Central Apparatus in Patients with Transposition of the Great Arteries

Transposition of the great arteries (TGA) is a congenital heart defect with a complex pathogenesis that has not been fully elucidated. In this study, we performed whole-exome sequencing (WES) in isolated TGA-diagnosed patients and analyzed genes of motile and non-motile cilia ciliogenesis and ciliary trafficking, as well as genes previously associated with this heart malformation. Deleterious missense and splicing variants of genes DNAH9, DNAH11, and ODAD4 of cilia outer dynein arm and central apparatus, HYDIN, were found in our TGA patients. Remarkable, there is a clustering of deleterious genetic variants in cilia genes, suggesting it could be an oligogenic disease. Our data evidence the genetic diversity and etiological complexity of TGA and point out that population allele determination and genetic aggregation studies are required to improve genetic counseling.

Molecular genetic mechanisms of congenital heart disease

Congenital heart disease (CHD) affects ~1% of all live births, but a definitive etiology is identified in only ~50%. The causes include chromosomal aneuploidies and copy-number variations, pathogenic variation in single genes, and exposure to environmental factors. High-throughput sequencing of large CHD patient cohorts and continued expansion of the complex molecular regulation of cardiac morphogenesis has uncovered numerous disease-causing genes, but the previously held monogenic model for CHD etiology does not sufficiently explain the heterogeneity and incomplete penetrance of CHD phenotypes. Here, we provide a summary of well-known genetic contributors to CHD and discuss emerging concepts supporting complex genetic mechanisms that may provide explanations for cases that currently lack a molecular diagnosis.

A Rare Case of Polysplenia Syndrome Associated with Severe Cardiac Malformations and Congenital Alveolar Dysplasia in a One-Month-Old Infant: A Complete Macroscopic and Histopathologic Study

Polysplenia syndrome represents a type of left atrial isomerism characterized by multiple small spleens, often associated with cardiac malformations and with situs ambiguus of the abdominal organs. The case presented is of a one-month-old male infant, weighing approximately 3000 g, born at the County Clinical Emergency Hospital of Sibiu, who was hospitalized from birth until death. The patient suffered cardio-respiratory arrest due to severe hypoxia and septicemia on the background of a series of complex cardiac malformations associated with congenital abdominal organ anomalies. Examination of the body revealed a common atrium with complete atrioventricular canal defect, left ventricular hypertrophy, right ventricle hypoplasia, truncus arteriosus, superior vena cava duplication, bilobation of the lungs, situs ambiguous of the abdominal organs with right-sided stomach, a midline liver, gall bladder agenesis, multiple right-sided spleens and complete inversion of the intestines and pancreas. Histopathology concluded that the patient suffered cardiac lesions consistent with infantile lactic acidosis, as well as pulmonary modifications suggesting congenital alveolar dysplasia and altered hepatic architecture compatible with fibrosis.