A novel mutation in two Hmong families broadens the range of STRA6-related malformations to include contractures and camptodactyly

The etiology of congenital diaphragmatic hernia: the retinoid hypothesis 20 years later

Congenital diaphragmatic hernia (CDH) is a severe birth defect and a major cause of neonatal respiratory distress. Impacting ~2-3 in 10,000 births, CDH is associated with a high mortality rate, and long-term morbidity in survivors. Despite the significant impact of CDH, its etiology remains incompletely understood. In 2003, Greer et al. proposed the Retinoid Hypothesis, stating that the underlying cause of abnormal diaphragm development in CDH was related to altered retinoid signaling. In this review, we provide a comprehensive update to the Retinoid Hypothesis, discussing work published in support of this hypothesis from the past 20 years. This includes reviewing teratogenic and genetic models of CDH, lessons from the human genetics of CDH and epidemiological studies, as well as current gaps in the literature and important areas for future research. The Retinoid Hypothesis is one of the leading hypotheses to explain the etiology of CDH, as we continue to better understand the role of retinoid signaling in diaphragm development, we hope that this information can be used to improve CDH outcomes. IMPACT: This review provides a comprehensive update on the Retinoid Hypothesis, which links abnormal retinoic acid signaling to the etiology of congenital diaphragmatic hernia. The Retinoid Hypothesis was formulated in 2003. Twenty years later, we extensively review the literature in support of this hypothesis from both animal models and humans.

Perinatal palliative care for family with prenatal diagnosis of Matthew-Wood syndrome

Matthew-Wood syndrome (MWS) is a rare autosomal recessive disorder caused by pathogenic variants of the STRA6 gene. Several studies in the available literature comprise patients with pathogenic variants of gene STRA6 with various phenotypic expressions: from lethal forms of MWS to non-lethal anophthalmia. These reports mainly describe new pathogenic variants and phenotypic expression but do not describe medical or paramedical care for the affected families. In our case report, we describe the second case of MWS in the same family and the benefits of including the patient's family in the perinatal palliative care program. The first pregnancy was terminated with a cesarean section; the boy was intubated in the delivery room and died soon after. The mother was not allowed to say farewell or keep any remembrances of her child. In the second pregnancy, the family was involved in the perinatal palliative care program, and all paramedical aspects, crucial from the parent's perspective, were planned and implemented. Palliative perinatal care enables complex care for the pregnant woman and her family. The possibility of palliative perinatal care is significant in decision-making in families with a high risk of lethal disease in subsequent pregnancies.

Evaluating High-Confidence Genes in Conotruncal Cardiac Defects by Gene Burden Analyses

Background In nonsyndromic conotruncal cardiac defects, the use of next-generation sequencing for clinical diagnosis is increasingly adopted, but gene-disease associations in research are only partially translated to diagnostic panels, suggesting a need for evidence-based consensus. Methods and Results In an exome data set of 245 patients with conotruncal cardiac defects, we performed burden analysis on a high-confidence congenital heart disease gene list (n=132) with rare (<0.01%) and ultrarare (absent in the Genome Aggregation Database) protein-altering variants. Overall, we confirmed an excess of rare variants compared with ethnicity-matched controls and identified 2 known genes (GATA6, NOTCH1) and 4 candidate genes supported by the literature (ANKRD11, DOCK6, NPHP4, and STRA6). Ultrarare variant analysis was performed in combination with 3 other published studies (n=1451) and identified 3 genes (FLT4, NOTCH1, TBX1) to be significant, whereas a subgroup analysis involving 391 Chinese subjects identified only GATA6 as significant. Conclusions We suggest that these significant genes in our rare and ultrarare burden analyses warrant prioritization for clinical testing implied for rare inherited and de novo variants. Additionally, associations on ClinVar for these genes were predominantly variants of uncertain significance. Therefore, a more stringent assessment of gene-disease associations in a larger and ethnically diverse cohort is required to be prudent for future curation of conotruncal cardiac defect genes.

Biallelic hypomorphic variants in ALDH1A2 cause a novel lethal human multiple congenital anomaly syndrome encompassing diaphragmatic, pulmonary, and cardiovascular defects

This study shows a causal association between ALDH1A2 variants and a novel, severe multiple congenital anomaly syndrome in humans that is neonatally lethal due to associated pulmonary hypoplasia and respiratory failure. In two families, exome sequencing identified compound heterozygous missense variants in ALDH1A2. ALDH1A2 is involved in the conversion of retinol (vitamin A) into retinoic acid (RA), which is an essential regulator of diaphragm and cardiovascular formation during embryogenesis. Reduced RA causes cardiovascular, diaphragmatic, and associated pulmonary defects in several animal models, matching the phenotype observed in our patients. In silico protein modeling showed probable impairment of ALDH1A2 for three of the four substitutions. In vitro studies show a reduction of RA. Few pathogenic variants in genes encoding components of the retinoic signaling pathway have been described to date, likely due to embryonic lethality. Thus, this study contributes significantly to knowledge of the role of this pathway in human diaphragm and cardiovascular development and disease. Some clinical features in our patients are also observed in Fryns syndrome (MIM# 229850), syndromic microphthalmia 9 (MIM# 601186), and DiGeorge syndrome (MIM# 188400). Patients with similar clinical features who are genetically undiagnosed should be tested for recessive ALDH1A2-deficient malformation syndrome.

Genetic Basis of Human Congenital Heart Disease

Congenital heart disease (CHD) is the most common major congenital anomaly with an incidence of ∼1% of live births and is a significant cause of birth defect-related mortality. The genetic mechanisms underlying the development of CHD are complex and remain incompletely understood. Known genetic causes include all classes of genetic variation including chromosomal aneuploidies, copy number variants, and rare and common single-nucleotide variants, which can be either de novo or inherited. Among patients with CHD, ∼8%-12% have a chromosomal abnormality or aneuploidy, between 3% and 25% have a copy number variation, and 3%-5% have a single-gene defect in an established CHD gene with higher likelihood of identifying a genetic cause in patients with nonisolated CHD. These genetic variants disrupt or alter genes that play an important role in normal cardiac development and in some cases have pleiotropic effects on other organs. This work reviews some of the most common genetic causes of CHD as well as what is currently known about the underlying mechanisms.

Expanding the phenotype of STRA6-related disorder to include left ventricular non-compaction

Background

Syndromic microphthalmia‐9 (MCOPS9) is a rare autosomal recessive disorder caused by mutations in STRA6, an important regulator of vitamin A and retinoic acid metabolism. This disorder is characterized by bilateral clinical anophthalmia, pulmonary hypoplasia/aplasia, cardiac malformations, and diaphragmatic defects. The clinical characteristics of this disorder have not been fully determined because of the rarity of clinical reports.

Methods

A comprehensive genotyping examination including copy number variation sequencing (CNV‐Seq) and whole‐exome sequencing (WES) was applied to a fetus of Han Chinese with bilateral anophthalmia, bilateral pulmonary agenesis, interrupted aortic arch type A, and left ventricular non‐compaction (LVNC).

Results

No aneuploidy or pathogenic CNV were identified by CNV‐seq. WES analysis revealed a previously reported homozygous splice site (NM_022369.4:c.113+3_113+4del) in the STRA6 gene. This variant was confirmed by Sanger sequencing. The diagnosis of MCOPS9 was confirmed given the identification of the STRA6 mutation and the association of bilateral anophthalmia, pulmonary agenesis, and cardiac malformations.

Conclusion

This case adds to the phenotypic spectrum of MCOPS9, supporting the association with LVNC, and the presence of interruption of aortic arch further demonstrates the variability of the cardiac malformations.

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

Genetics of anophthalmia and microphthalmia. Part 2: Syndromes associated with anophthalmia-microphthalmia

As new genes for A/M are identified in the genomic era, the number of syndromes associated with A/M has greatly expanded. In this review, we provide a brief synopsis of the clinical presentation and molecular genetic etiology of previously characterized pathways involved in A/M, including the Sex-determining region Y-box 2 (SOX2), Orthodenticle Homeobox 2 (OTX2) and Paired box protein-6 (PAX6) genes, and the Stimulated by retinoic acid gene 6 homolog (STRA6), Aldehyde Dehydrogenase 1 Family Member A3 (ALDH1A3), and RA Receptor Beta (RARβ) genes that are involved in retinoic acid synthesis. Less common genetic causes of A/M, including genes involved in BMP signaling [Bone Morphogenetic Protein 4 (BMP4), Bone Morphogenetic Protein 7 (BMP7) and SPARC-related modular calcium-binding protein 1 (SMOC1)], genes involved in the mitochondrial respiratory chain complex [Holocytochrome c-type synthase (HCCS), Cytochrome C Oxidase Subunit 7B (COX7B), and NADH:Ubiquinone Oxidoreductase subunit B11 (NDUFB11)], the BCL-6 corepressor gene (BCOR), Yes-Associated Protein 1 (YAP1) and Transcription Factor AP-2 Alpha (TFAP2α), are more briefly discussed. We also review several recently described genes and pathways associated with A/M, including Smoothened (SMO) that is involved in Sonic hedgehog (SHH) signaling, Structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) and Solute carrier family 25 member 24 (SLC25A24), emphasizing phenotype-genotype correlations and shared pathways where relevant.

Enzymatic Metabolism of Vitamin A in Developing Vertebrate Embryos

Embryonic development is orchestrated by a small number of signaling pathways, one of which is the retinoic acid (RA) signaling pathway. Vitamin A is essential for vertebrate embryonic development because it is the molecular precursor of the essential signaling molecule RA. The level and distribution of RA signaling within a developing embryo must be tightly regulated; too much, or too little, or abnormal distribution, all disrupt embryonic development. Precise regulation of RA signaling during embryogenesis is achieved by proteins involved in vitamin A metabolism, retinoid transport, nuclear signaling, and RA catabolism. The reversible first step in conversion of the precursor vitamin A to the active retinoid RA is mediated by retinol dehydrogenase 10 (RDH10) and dehydrogenase/reductase (SDR family) member 3 (DHRS3), two related membrane-bound proteins that functionally activate each other to mediate the interconversion of retinol and retinal. Alcohol dehydrogenase (ADH) enzymes do not contribute to RA production under normal conditions during embryogenesis. Genes involved in vitamin A metabolism and RA catabolism are expressed in tissue-specific patterns and are subject to feedback regulation. Mutations in genes encoding these proteins disrupt morphogenesis of many systems in a developing embryo. Together these observations demonstrate the importance of vitamin A metabolism in regulating RA signaling during embryonic development in vertebrates.