Cdon mutation and fetal ethanol exposure synergize to produce midline signaling defects and holoprosencephaly spectrum disorders in mice

Bone morphogenetic protein signaling pathway- Ethanol interactions disrupt palate formation independent of gata3

Fetal Alcohol Spectrum Disorders (FASD) describes a wide array of neurological defects and craniofacial malformations, associated with ethanol teratogenicity. While there is growing evidence for a genetic component to FASD, little is known of the genes underlying these ethanol-induced defects. Along with timing and dosage, genetic predispositions may help explain the variability within FASD. From a screen for gene-ethanol interactions, we found that mutants for Bmp signaling components are ethanol-sensitive leading to defects in the zebrafish palate. Loss of Bmp signaling results in reductions in gata3 expression in the maxillary domain of the neural crest in the 1st pharyngeal arch, leading to palate defects while upregulation of human GATA3 rescues these defects. Here, we show that ethanol-treated Bmp mutants exhibit misshaped and/or broken trabeculae. Surprisingly, up regulation of GATA3 does not rescue ethanol-induced palate defects and gata3 expression was not altered in ethanol-treated Bmp mutants or dorsomorphin-treated larvae. Timing of ethanol sensitivity shows that Bmp mutants are ethanol sensitive from 10 to 18 hours post-fertilization (hpf), prior to Bmp's regulation of gata3 in palate formation. This is consistent with our previous work with dorsomorphin-dependent knock down of Bmp signaling from 10 to 18 hpf disrupting endoderm formation and subsequent jaw development. Overall, this suggests that ethanol disrupts Bmp-dependent palate development independent of and earlier than the role of gata3 in palate formation by disrupting epithelial development. Ultimately, these data demonstrate that zebrafish is a useful model to identify and characterize gene-ethanol interactions and this work will directly inform our understanding of FASD.

Efcab7 deletion sensitizes mice to the teratogenic effects of gastrulation-stage alcohol exposure

Alcohol exposure during the gastrulation stage of development can disrupt Sonic hedgehog (Shh) signaling and cause eye, craniofacial, and brain defects. One of the genes that regulates Shh signaling is Efcab7, which encodes a protein that facilitates the actions of Smoothened (Smo), a critical component of the Shh pathway. Previous work from our lab has demonstrated that Efcab7 is differentially expressed between two sub-strains of C57BL/6 mice that differ in their sensitivity to gastrulation-stage alcohol exposure. The more alcohol-sensitive C57BL/6 J mice express lower levels of Efcab7 during gastrulation than do the less alcohol-sensitive C57BL/6NHsd mice. The current study examined whether partial or full Efcab7 deletions render mice more sensitive to gastrulation-stage alcohol exposure and affect the sensitivity to other modulators of Shh signaling that cause craniofacial malformations. Efcab7+/- dams were mated with Efcab7+/- sires to produce Efcab7+/+, Efcab7+/-, and Efcab7-/- fetuses. On gestational day 7 (GD 7), they received either alcohol (two doses of 2.9 g/kg, i.p., given 4 hours apart), the Smo antagonist vismodegib (40 mg/kg, or vehicle, p.o.), the Smo agonist SAG (20 mg/kg) or the appropriate vehicles. GD 17 fetuses were collected and examined for ocular and craniofacial dysmorphology. As compared to Efcab7+/+ fetuses, Efcab7-/- fetuses exposed to alcohol or vismodegib treatment had more severe ocular and craniofacial malformations. In contrast, Efcab7-/- fetuses had less severe malformations induced by SAG. These results confirm that Efcab7 can modify responses to Shh agonists and antagonists and further identify Efcab7 as a gene important for the sensitivity to gastrulation-stage alcohol exposure.

Exome Sequencing Has a High Diagnostic Rate in Sporadic Congenital Hypopituitarism and Reveals Novel Candidate Genes

CONTEXT

The pituitary gland is key for childhood growth, puberty, and metabolism. Pituitary dysfunction is associated with a spectrum of phenotypes, from mild to severe. Congenital hypopituitarism (CH) is the most commonly reported pediatric endocrine dysfunction, with an incidence of 1:4000, yet low rates of genetic diagnosis have been reported.

OBJECTIVE

We aimed to unveil the genetic etiology of CH in a large cohort of patients from Argentina.

METHODS

We performed whole exome sequencing of 137 unrelated cases of CH, the largest cohort examined with this method to date.

RESULTS

Of the 137 cases, 19.1% and 16% carried pathogenic or likely pathogenic variants in known and new genes, respectively, while 28.2% carried variants of uncertain significance. This high yield was achieved through the integration of broad gene panels (genes described in animal models and/or other disorders), an unbiased candidate gene screen with a new bioinformatics pipeline (including genes with high loss-of-function intolerance), and analysis of copy number variants. Three novel findings emerged. First, the most prevalent affected gene encodes the cell adhesion factor ROBO1. Affected children had a spectrum of phenotypes, consistent with a role beyond pituitary stalk interruption syndrome. Second, we found that CHD7 mutations also produce a phenotypic spectrum, not always associated with full CHARGE syndrome. Third, we add new evidence of pathogenicity in the genes PIBF1 and TBC1D32, and report 13 novel candidate genes associated with CH (eg, PTPN6, ARID5B).

CONCLUSION

Overall, these results provide an unprecedented insight into the diverse genetic etiology of hypopituitarism.

Bone Morphogenetic Protein signaling pathway - ethanol interactions disrupt palate formation independent of gata3

Fetal Alcohol Spectrum Disorders (FASD) describes a wide array of neurological defects and craniofacial malformations, associated with ethanol teratogenicity. While there is growing evidence for a genetic component to FASD, little is known of the genes underlying these ethanol-induced defects. Along with timing and dosage, genetic predispositions may help explain the variability within FASD. From a screen for gene-ethanol interactions, we found that mutants for Bmp signaling components are ethanol-sensitive leading to defects in the zebrafish palate. Loss of Bmp signaling results in reductions in gata3 expression in the maxillary domain of the neural crest in the 1st pharyngeal arch, leading to palate defects while upregulation of human GATA3 rescues these defects. Here, we show that ethanol-treated Bmp mutants exhibit misshaped and/or broken trabeculae. Surprisingly, up regulation of GATA3 does not rescue ethanol-induced palate defects and gata3 expression was not altered in ethanol-treated Bmp mutants or dorsomorphin-treated larvae. Timing of ethanol sensitivity shows that Bmp mutants are ethanol sensitive from 10-18 hours post-fertilization (hpf), prior to Bmp's regulation of gata3 in palate formation. This is consistent with our previous work with dorsomorphin-dependent knock down of Bmp signaling from 10-18 hpf disrupting endoderm formation and subsequent jaw development. Overall, this suggests that ethanol disrupts Bmp-dependent palate development independent of and earlier than the role of gata3 in palate formation by disrupting epithelial development. Ultimately, these data demonstrate that zebrafish is a useful model to identify and characterize gene-ethanol interactions and this work will directly inform our understanding of FASD.

Highlights

Bmp pathway mutants are ethanol sensitive resulting in palate defects. Ethanol disrupts Bmp-dependent palate development independent of gata3 . Timing of ethanol sensitivity suggests ethanol disrupts Bmp-dependent epithelial morphogenesis.

Mutations in the Bone Morphogenetic Protein signaling pathway sensitize zebrafish and humans to ethanol-induced jaw malformations

Fetal Alcohol Spectrum Disorders (FASD) describe ethanol-induced developmental defects including craniofacial malformations. While ethanol-sensitive genetic mutations contribute to facial malformations, the impacted cellular mechanisms remain unknown. Bmp signaling is a key regulator of epithelial morphogenesis driving facial development, providing a possible ethanol-sensitive mechanism. We found that zebrafish mutants for Bmp signaling components are ethanol-sensitive and affect anterior pharyngeal endoderm shape and gene expression, indicating ethanol-induced malformations of the anterior pharyngeal endoderm cause facial malformations. Integrating FASD patient data, we provide the first evidence that variants in the human Bmp receptor gene BMPR1B associate with ethanol-related differences in jaw volume. Our results show that ethanol exposure disrupts proper morphogenesis of, and tissue interactions between, facial epithelia that mirror overall viscerocranial shape changes and are predictive for Bmp-ethanol associations in human jaw development. Our data provide a mechanistic paradigm linking ethanol to disrupted epithelial cell behaviors that underlie facial defects in FASD.

Summary Statement

In this study, we apply a unique combination of zebrafish-based approaches and human genetic and facial dysmorphology analyses to resolve the cellular mechanisms driven by the ethanol-sensitive Bmp pathway.

CDON Mutation Related to Nose Deformity with Variable Expression in Holoprosencephaly in an Iranian Family: A Case Report

Holoprosencephaly, a complicated brain abnormality arising from incomplete prosencephalon cleavage, affects both the forebrain and the face. Holoprosencephaly Type 11, with variable expression or partial penetrance, is caused by CDON pathogenic variants associated with the disrupted Sonic Hedgehog (SHH)-pathway. Herein, we aimed to describe a family with genetic nose problems. After counselling and drawing pedigree in Farhud's Genetic Clinic, Tehran, Iran in 2021, DNA extraction of a proband and a few members of his family (patient and control) was conducted. Whole exome sequencing was utilized for detecting the gene and its variant in the proband with a nose deformity. The results were confirmed with Sanger sequencing. This variant was checked in other members by Sanger sequencing. Analysis of the Exome data showed a heterozygous splicing variant in the CDON gene (NM_016952; c.3276+1G>T) in the proband who had a nose deformity and then the results were confirmed with Sanger sequencing. Such a variant was observed in Proband's brother with a nose deformity and was not observed in Proband's cousin with no abnormal phenotype. Recent investigations, in an Iranian family, with a heterozygous splicing CDON mutation as a human candidate gene are discussed for the first time in relation to the likely pathogenesis of facial deformities, particularly nose deformity, in Holoprosencephaly.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

Combined exposure to alcohol and cannabis during development: Mechanisms and outcomes

Exposure to substances of abuse during pregnancy can have long-lasting effects on offspring. Alcohol is one of the most widely used substances of abuse that leads to the most severe consequences. Recent studies in the United States, Canada, and the United Kingdom showed that between 1% and 7% of all children exhibit signs and symptoms of fetal alcohol spectrum disorder (FASD). Despite preventive campaigns, the rate of children with FASD has not decreased during recent decades. Alcohol consumption often accompanies exposure to such drugs as tobacco, cocaine, opioids, and cannabis. These interactions can be synergistic and exacerbate the deleterious consequences of developmental alcohol exposure. The present review focuses on interactions between alcohol and cannabis exposure and the potential consequences of these interactions.

Embryonic Ethanol but Not Cannabinoid Exposure Affects Zebrafish Cardiac Development via Agrin and Sonic Hedgehog Interaction

Recent studies demonstrate the adverse effects of cannabinoids on development, including via pathways shared with ethanol exposure. Our laboratory has shown that both the nervous system and cardiac development are dependent on agrin modulation of sonic hedgehog (shh) and fibroblast growth factor (Fgf) signaling pathways. As both ethanol and cannabinoids impact these signaling molecules, we examined their role on zebrafish heart development. Zebrafish embryos were exposed to a range of ethanol and/or cannabinoid receptor 1 and 2 agonist concentrations in the absence or presence of morpholino oligonucleotides that disrupt agrin or shh expression. In situ hybridization was employed to analyze cardiac marker gene expression. Exposure to cannabinoid receptor agonists disrupted midbrain-hindbrain boundary development, but had no effect on heart development, as assessed by the presence of cardiac edema or the altered expression of cardiac marker genes. In contrast, exposure to 1.5% ethanol induced cardiac edema and the altered expression of cardiac marker genes. Combined exposure to agrin or shh morpholino and 0.5% ethanol disrupted the cmlc2 gene expression pattern, with the restoration of the normal expression following shh mRNA overexpression. These studies provide evidence that signaling pathways critical to heart development are sensitive to ethanol exposure, but not cannabinoids, during early zebrafish embryogenesis.

Holoprosencephaly: Review of Embryology, Clinical Phenotypes, Etiology and Management

Holoprosencephaly (HPE) is the most common malformation of the prosencephalon in humans. It is characterized by a continuum of structural brain anomalies resulting from the failure of midline cleavage of the prosencephalon. The three classic subtypes of HPE are alobar, semilobar and lobar, although a few additional categories have been added to this original classification. The severity of the clinical phenotype is broad and usually mirrors the radiologic and associated facial features. The etiology of HPE includes both environmental and genetic factors. Disruption of sonic hedgehog (SHH) signaling is the main pathophysiologic mechanism underlying HPE. Aneuploidies, chromosomal copy number variants and monogenic disorders are identified in a large proportion of HPE patients. Despite the high postnatal mortality and the invariable presence of developmental delay, recent advances in diagnostic methods and improvements in patient management over the years have helped to increase survival rates. In this review, we provide an overview of the current knowledge related to HPE, and discuss the classification, clinical features, genetic and environmental etiologies and management.

High-throughput detection of craniofacial defects in fluorescent zebrafish

Losses and malformations of cranial neural crest cell (cNCC) derivatives are a hallmark of several common brain and face malformations. Nevertheless, the etiology of these cNCC defects remains unknown for many cases, suggesting a complex basis involving interactions between genetic and/or environmental factors. However, the sheer number of possible factors (thousands of genes and hundreds of thousands of toxicants) has hindered identification of specific interactions. Here, we develop a high-throughput analysis that will enable faster identification of multifactorial interactions in the genesis of craniofacial defects. Zebrafish embryos expressing a fluorescent marker of cNCCs (fli1:EGFP) were exposed to a pathway inhibitor standard or environmental toxicant, and resulting changes in fluorescence were measured in high-throughput using a fluorescent microplate reader to approximate cNCC losses. Embryos exposed to the environmental Hedgehog pathway inhibitor piperonyl butoxide (PBO), a Hedgehog pathway inhibitor standard, or alcohol (ethanol) exhibited reduced fli1:EGFP fluorescence at one day post fertilization, which corresponded with craniofacial defects at five days post fertilization. Combining PBO and alcohol in a co-exposure paradigm synergistically reduced fluorescence, demonstrating a multifactorial interaction. Using pathway reporter transgenics, we show that the plate reader assay is sensitive at detecting alterations in Hedgehog signaling, a critical regulator of craniofacial development. We go on to demonstrate that this technique readily detects defects in other important cell types, namely neurons. Together, these findings demonstrate this novel in vivo platform can predict developmental abnormalities and multifactorial interactions in high-throughput.

Gene-environment interactions in birth defect etiology: Challenges and opportunities

Birth defects are relatively common congenital outcomes that significantly impact affected individuals, their families, and communities. Effective development and deployment of prevention and therapeutic strategies for these conditions requires sufficient understanding of etiology, including underlying genetic and environmental causes. Tremendous progress has been made in defining the genetic basis of familial and syndromic forms of birth defects. However, the majority of birth defect cases are considered nonsyndromic and thought to result from multifactorial gene-environment interactions. While substantial advances have been made in elucidating the genetic landscape of these etiologically complex conditions, significant biological and technical constraints have stymied progress toward a refined knowledge of environmental risk factors. Defining specific gene-environment interactions in birth defect etiology is even more challenging. However, progress has been made, including demonstration of critical proofs of concept and development of new conceptual and technical approaches for resolving complex gene-environment interactions. In this review, we discuss current views of multifactorial birth defect etiology, comparing them with other diseases that also involve gene-environment interactions, including primary immunodeficiency and cancer. We describe how various model systems have illuminated mechanisms of multifactorial etiology and these models' individual strengths and weaknesses. Finally, suggestions for areas of future emphasis are proposed.

The role of genes and environment in the etiology of congenital diaphragmatic hernias

Structural birth defects are a common cause of abnormalities in newborns. While there are cases of structural birth defects arising due to monogenic defects or environmental exposures, many birth defects are likely caused by a complex interaction between genes and the environment. A structural birth defect with complex etiology is congenital diaphragmatic hernias (CDH), a common and often lethal disruption in diaphragm development. Mutations in more than 150 genes have been implicated in CDH pathogenesis. Although there is generally less evidence for a role for environmental factors in the etiology of CDH, deficiencies in maternal vitamin A and its derivative embryonic retinoic acid are strongly associated with CDH. However, the incomplete penetrance of CDH-implicated genes and environmental factors such as vitamin A deficiency suggest that interactions between genes and environment may be necessary to cause CDH. In this review, we examine the genetic and environmental factors implicated in diaphragm and CDH development. In addition, we evaluate the potential for gene-environment interactions in CDH etiology, focusing on the potential interactions between the CDH-implicated gene, Gata4, and maternal vitamin A deficiency.

The pro-apoptotic Bax gene modifies susceptibility to craniofacial dysmorphology following gastrulation-stage alcohol exposure

BACKGROUND

During early development, alcohol exposure causes apoptotic cell death in discrete regions of the embryo which are associated with distinctive patterns of later-life abnormalities. In gastrulation, which occurs during the third week of human pregnancy, alcohol targets the ectoderm, the precursor of the eyes, face, and brain. This midline tissue loss leads to the craniofacial dysmorphologies, such as microphthalmia and a smooth philtrum, which define fetal alcohol syndrome (FAS). An important regulator of alcohol-induced cell death is the pro-apoptotic protein Bax. The current study determines if mice lacking the Bax gene are less susceptible to the pathogenic effects of gastrulation-stage alcohol exposure.

METHODS

Male and female Bax^+/- mice mated to produce embryos with full (^-/- ) or partial (^+/- ) Bax deletions, or Bax^+/+ wild-type controls. On Gestational Day 7 (GD 7), embryos received two alcohol (2.9 g/kg, 4 hr apart), or control exposures. A subset of embryos was collected 12 hr later and examined for the presence of apoptotic cell death, while others were examined on GD 17 for the presence of FAS-like facial features.

RESULTS

Full Bax deletion reduced embryonic apoptotic cell death and the incidence of fetal eye and face malformations, indicating that Bax normally facilitates the development of alcohol-induced defects. An RNA-seq analysis of GD 7 Bax^+/+ and Bax^-/- embryos revealed 63 differentially expressed genes, some of which may interact with the Bax deletion to further protect against apoptosis.

CONCLUSIONS

Overall, these experiments identify that Bax is a primary teratogenic mechanism of gastrulation-stage alcohol exposure.

Gene-alcohol interactions in birth defects

Most human birth defects are thought to result from complex interactions between combinations of genetic and environmental factors. This is true even for conditions that, at face value, may appear simple and straightforward, like fetal alcohol spectrum disorders (FASD). FASD describe the full range of structural and neurological disruptions that result from prenatal alcohol exposure. While FASD require alcohol exposure, evidence from human and animal model studies demonstrate that additional genetic and/or environmental factors can influence the embryo's susceptibility to alcohol. Only a limited number of alcohol interactions in birth defects have been identified, with many sensitizing genetic and environmental factors likely yet to be identified. Because of this, while unsatisfying, there is no definitively "safe" dose of alcohol for all pregnancies. Determining these other factors, as well as mechanistically characterizing known interactions, is critical for better understanding and preventing FASD and requires combined scrutiny of human and model organism studies.

Ethanol Effects on Early Developmental Stages Studied Using the Zebrafish

Fetal alcohol spectrum disorder (FASD) results from prenatal ethanol exposure. The zebrafish (Danio rerio) is an outstanding in vivo FASD model. Early development produced the three germ layers and embryonic axes patterning. A critical pluripotency transcriptional gene circuit of sox2, pou5f1 (oct4; recently renamed pou5f3), and nanog maintain potency and self-renewal. Ethanol affects sox2 expression, which functions with pou5f1 to control target gene transcription. Various genes, like elf3, may interact and regulate sox2, and elf3 knockdown affects early development. Downstream of the pluripotency transcriptional circuit, developmental signaling activities regulate morphogenetic cell movements and lineage specification. These activities are also affected by ethanol exposure. Hedgehog signaling is a critical developmental signaling pathway that controls numerous developmental events, including neural axis specification. Sonic hedgehog activities are affected by embryonic ethanol exposure. Activation of sonic hedgehog expression is controlled by TGF-ß family members, Nodal and Bmp, during dorsoventral (DV) embryonic axis establishment. Ethanol may perturb TGF-ß family receptors and signaling activities, including the sonic hedgehog pathway. Significantly, experiments show that activation of sonic hedgehog signaling rescues some embryonic ethanol exposure effects. More research is needed to understand how ethanol affects early developmental signaling and morphogenesis.

Analysis of Gene-Environment Interactions Related to Developmental Disorders

Various genetic and environmental factors are associated with developmental disorders (DDs). It has been suggested that interaction between genetic and environmental factors (G × E) is involved in the etiology of DDs. There are two major approaches to analyze the interaction: genome-wide and candidate gene-based approaches. In this mini-review, we demonstrate how these approaches can be applied to reveal the G × E related to DDs focusing on zebrafish and mouse models. We also discuss novel approaches to analyze the G × E associated with DDs.

Differential regulation of cranial and cardiac neural crest by serum response factor and its cofactors

Serum response factor (SRF) is an essential transcription factor that influences many cellular processes including cell proliferation, migration, and differentiation. SRF directly regulates and is required for immediate early gene (IEG) and actin cytoskeleton-related gene expression. SRF coordinates these competing transcription programs through discrete sets of cofactors, the ternary complex factors (TCFs) and myocardin-related transcription factors (MRTFs). The relative contribution of these two programs to in vivo SRF activity and mutant phenotypes is not fully understood. To study how SRF utilizes its cofactors during development, we generated a knock-in SrfaI allele in mice harboring point mutations that disrupt SRF-MRTF-DNA complex formation but leave SRF-TCF activity unaffected. Homozygous SrfaI/aI mutants die at E10.5 with notable cardiovascular phenotypes, and neural crest conditional mutants succumb at birth to defects of the cardiac outflow tract but display none of the craniofacial phenotypes associated with complete loss of SRF in that lineage. Our studies further support an important role for MRTF mediating SRF function in cardiac neural crest and suggest new mechanisms by which SRF regulates transcription during development.

Pharmacological activation of the Sonic hedgehog pathway with a Smoothened small molecule agonist ameliorates the severity of alcohol-induced morphological and behavioral birth defects in a zebrafish model of fetal alcohol spectrum disorder

Ethanol exposure during the early stages of embryonic development can lead to a range of morphological and behavioral differences termed fetal alcohol spectrum disorders (FASDs). In a zebrafish model, we have shown that acute ethanol exposure at 8-10 hr postfertilization (hpf), a critical time of development, produces birth defects similar to those clinically characterized in FASD. Dysregulation of the Sonic hedgehog (Shh) pathway has been implicated as a molecular basis for many of the birth defects caused by prenatal alcohol exposure. We observed in zebrafish embryos that shh expression was significantly decreased by ethanol exposure at 8-10 hpf, while smo expression was much less affected. Treatment of zebrafish embryos with SAG or purmorphamine, small molecule Smoothened agonists that activate Shh signaling, ameliorated the severity of ethanol-induced developmental malformations including altered eye size and midline brain development. Furthermore, this rescue effect of Smo activation was dose dependent and occurred primarily when treatment was given after ethanol exposure. Markers of Shh signaling (gli1/2) and eye development (pax6a) were restored in embryos treated with SAG post-ethanol exposure. Since embryonic ethanol exposure has been shown to produce later-life neurobehavioral impairments, juvenile zebrafish were examined in the novel tank diving test. Our results further demonstrated that in zebrafish embryos exposed to ethanol, SAG treatment was able to mitigate long-term neurodevelopmental impairments related to anxiety and risk-taking behavior. Our results indicate that pharmacological activation of the Shh pathway at specific developmental timing markedly diminishes the severity of alcohol-induced birth defects.

Concepts in Multifactorial Etiology of Developmental Disorders: Gene-Gene and Gene-Environment Interactions in Holoprosencephaly

Many common developmental disorders are thought to arise from a complex set of genetic and environmental risk factors. These factors interact with each other to affect the strength and duration of key developmental signaling pathways, thereby increasing the possibility that they fail to achieve the thresholds required for normal embryonic patterning. One such disorder, holoprosencephaly (HPE), serves as a useful model system in understanding various forms of multifactorial etiology. Genomic analysis of HPE cases, epidemiology, and mechanistic studies of animal models have illuminated multiple potential ways that risk factors interact to produce adverse developmental outcomes. Among these are: 1) interactions between driver and modifier genes; 2) oligogenic inheritance, wherein each parent provides predisposing variants in one or multiple distinct loci; 3) interactions between genetic susceptibilities and environmental risk factors that may be insufficient on their own; and 4) interactions of multiple genetic variants with multiple non-genetic risk factors. These studies combine to provide concepts that illuminate HPE and are also applicable to additional disorders with complex etiology, including neural tube defects, congenital heart defects, and oro-facial clefting.

Prenatal alcohol exposure disrupts Sonic hedgehog pathway and primary cilia genes in the mouse neural tube

Neurulation-stage alcohol exposure (NAE; embryonic day [E] 8-10) is associated with midline craniofacial and CNS defects that likely arise from disruption of morphogen pathways, such as Sonic hedgehog (Shh). Notably, midline anomalies are also a hallmark of genetic ciliopathies such as Joubert syndrome. We tested whether NAE alters Shh pathway signaling and the number and function of primary cilia, organelles critical for Shh pathway transduction. Female C57BL/6 J mice were administered two doses of alcohol (2.9 g/kg/dose) or vehicle on E9. Embryos were collected 6, 12, or 24 h later, and changes to Shh, cell cycle genes, and primary cilia were measured in the rostroventral neural tube (RVNT). Within the first 24 h post-NAE, reductions in Shh pathway and cell cycle gene expression and the ratio of Gli3 forms in the full-length activator state were observed. RVNT volume and cell layer width were reduced at 12 h. In addition, altered expression of multiple cilia-related genes was observed at 6 h post-NAE. As a further test of cilia gene-ethanol interaction, mice heterozygous for Kif3a exhibited perturbed behavior during adolescence following NAE compared to vehicle-treated mice, and Kif3a heterozygosity exacerbated the hyperactive effects of NAE on exploratory activity. These data demonstrate that NAE downregulates the Shh pathway in a region of the neural tube that gives rise to alcohol-sensitive brain structures and identifies disruption of primary cilia function, or a "transient ciliopathy", as a possible cellular mechanism of prenatal alcohol pathogenesis.

Δ9-Tetrahydrocannabinol inhibits Hedgehog-dependent patterning during development

Many developmental disorders are thought to arise from an interaction between genetic and environmental risk factors. The Hedgehog (HH) signaling pathway regulates myriad developmental processes, and pathway inhibition is associated with birth defects, including holoprosencephaly (HPE). Cannabinoids are HH pathway inhibitors, but little is known of their effects on HH-dependent processes in mammalian embryos, and their mechanism of action is unclear. We report that the psychoactive cannabinoid Δ9-tetrahydrocannabinol (THC) induces two hallmark HH loss-of-function phenotypes (HPE and ventral neural tube patterning defects) in Cdon mutant mice, which have a subthreshold deficit in HH signaling. THC therefore acts as a 'conditional teratogen', dependent on a complementary but insufficient genetic insult. In vitro findings indicate that THC is a direct inhibitor of the essential HH signal transducer smoothened. The canonical THC receptor, cannabinoid receptor-type 1, is not required for THC to inhibit HH signaling. Cannabis consumption during pregnancy may contribute to a combination of risk factors underlying specific developmental disorders. These findings therefore have significant public health relevance.

Evidence That the Etiology of Congenital Hypopituitarism Has a Major Genetic Component but Is Infrequently Monogenic

Purpose

Congenital hypopituitarism usually occurs sporadically. In most patients, the etiology remains unknown.

Methods

We studied 13 children with sporadic congenital hypopituitarism. Children with non-endocrine, non-familial idiopathic short stature (NFSS) (n = 19) served as a control group. Exome sequencing was performed in probands and both unaffected parents. A burden testing approach was used to compare the number of candidate variants in the two groups.

Results

First, we assessed the frequency of rare, predicted-pathogenic variants in 42 genes previously reported to be associated with pituitary gland development. The average number of variants per individual was greater in probands with congenital hypopituitarism than those with NFSS (1.1 vs. 0.21, mean variants/proband, P = 0.03). The number of probands with at least 1 variant in a pituitary-associated gene was greater in congenital hypopituitarism than in NFSS (62% vs. 21%, P = 0.03). Second, we assessed the frequency of rare, predicted-pathogenic variants in the exome (to capture undiscovered causes) that were inherited in a fashion that could explain the sporadic occurrence of the proband's condition with a monogenic etiology (de novo mutation, autosomal recessive, or X-linked recessive) with complete penetrance. There were fewer monogenic candidates in the probands with congenital hypopituitarism than those with NFSS (1.3 vs. 2.5 candidate variants/proband, P = 0.024). We did not find any candidate variants (0 of 13 probands) in genes previously reported to explain the phenotype in congenital hypopituitarism, unlike NFSS (8 of 19 probands, P = 0.01).

Conclusion

Our findings provide evidence that the etiology of sporadic congenital hypopituitarism has a major genetic component but may be infrequently monogenic with full penetrance, suggesting a more complex etiology.

CDON gene contributes to pituitary stalk interruption syndrome associated with unilateral facial and abducens nerve palsy

The relationship between congenital defects of the brain and facial anomalies was proven. The Hedgehog signaling pathway plays a fundamental role in normal craniofacial development in humans. Mutations in the sonic hedgehog (SHH) signaling gene CDON have been recently reported in patients with holoprosencephaly and with pituitary stalk interruption syndrome (PSIS). This study’s aim was an elucidation of an 18-year-old patient presenting PSIS, multiple pituitary hormone deficiency, and congenital unilateral facial and abducens nerve palsy. Additionally, bilateral sensorineural hearing loss, dominating at the right site, was diagnosed. From the second year of life, growth deceleration was observed, and from the age of eight, anterior pituitary hormone deficiencies were gradually confirmed and substituted. At the MRI, characteristic triad for PSIS (anterior pituitary hypoplasia, interrupted pituitary stalk and ectopic posterior lobe) was diagnosed. We performed a comprehensive genomic screening, including microarrays for structural rearrangements and whole-exome sequencing for a monogenic defect. A novel heterozygous missense variant in the CDON gene (c.1814G > T; p.Gly605Val) was identified. The variant was inherited from the mother, who, besides short stature, did not show any disease symptoms. The variant was absent in control databases and 100 healthy subjects originating from the same population. We report a novel variant in the CDON gene associated with PSIS and congenital cranial nerve palsy. The variant revealed autosomal dominant inheritance with incomplete penetrance in concordance with previous studies reporting CDON defects.

Exposure to ethanol leads to midfacial hypoplasia in a zebrafish model of FASD via indirect interactions with the Shh pathway

Background

Gene-environment interactions are likely to underlie most human birth defects. The most common known environmental contributor to birth defects is prenatal alcohol exposure. Fetal alcohol spectrum disorders (FASD) describe the full range of defects that result from prenatal alcohol exposure. Gene-ethanol interactions underlie susceptibility to FASD, but we lack a mechanistic understanding of these interactions. Here, we leverage the genetic tractability of zebrafish to address this problem.

Results

We first show that vangl2, a member of the Wnt/planar cell polarity (Wnt/PCP) pathway that mediates convergent extension movements, strongly interacts with ethanol during late blastula and early gastrula stages. Embryos mutant or heterozygous for vangl2 are sensitized to ethanol-induced midfacial hypoplasia. We performed single-embryo RNA-seq during early embryonic stages to assess individual variation in the transcriptional response to ethanol and determine the mechanism of the vangl2-ethanol interaction. To identify the pathway(s) that are disrupted by ethanol, we used these global changes in gene expression to identify small molecules that mimic the effects of ethanol via the Library of Integrated Network-based Cellular Signatures (LINCS L1000) dataset. Surprisingly, this dataset predicted that the Sonic Hedgehog (Shh) pathway inhibitor, cyclopamine, would mimic the effects of ethanol, despite ethanol not altering the expression levels of direct targets of Shh signaling. Indeed, we found that ethanol and cyclopamine strongly, but indirectly, interact to disrupt midfacial development. Ethanol also interacts with another Wnt/PCP pathway member, gpc4, and a chemical inhibitor of the Wnt/PCP pathway, blebbistatin, phenocopies the effect of ethanol. By characterizing membrane protrusions, we demonstrate that ethanol synergistically interacts with the loss of vangl2 to disrupt cell polarity required for convergent extension movements.

Conclusions

Our results show that the midfacial defects in ethanol-exposed vangl2 mutants are likely due to an indirect interaction between ethanol and the Shh pathway. Vangl2 functions as part of a signaling pathway that regulates coordinated cell movements during midfacial development. Ethanol exposure alters the position of a critical source of Shh signaling that separates the developing eye field into bilateral eyes, allowing the expansion of the midface. Collectively, our results shed light on the mechanism by which the most common teratogen can disrupt development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01062-9.

Transcriptomic analyses of gastrulation-stage mouse embryos with differential susceptibility to alcohol

Genetics are a known contributor to differences in alcohol sensitivity in humans with fetal alcohol spectrum disorders (FASDs) and in animal models. Our study profiled gene expression in gastrulation-stage embryos from two commonly used, genetically similar mouse substrains, C57BL/6J (6J) and C57BL/6NHsd (6N), that differ in alcohol sensitivity. First, we established normal gene expression patterns at three finely resolved time points during gastrulation and developed a web-based interactive tool. Baseline transcriptional differences across strains were associated with immune signaling. Second, we examined the gene networks impacted by alcohol in each strain. Alcohol caused a more pronounced transcriptional effect in the 6J versus 6N mice, matching the increased susceptibility of the 6J mice. The 6J strain exhibited dysregulation of pathways related to cell death, proliferation, morphogenic signaling and craniofacial defects, while the 6N strain showed enrichment of hypoxia and cellular metabolism pathways. These datasets provide insight into the changing transcriptional landscape across mouse gastrulation, establish a valuable resource that enables the discovery of candidate genes that may modify alcohol susceptibility that can be validated in humans, and identify novel pathogenic mechanisms of alcohol. This article has an associated First Person interview with the first author of the paper.

Neural crest-specific deletion of Bmp7 leads to midfacial hypoplasia, nasal airway obstruction, and disordered breathing modelling Obstructive Sleep Apnea

Pediatric obstructive sleep apnea (OSA), a relatively common sleep-related breathing disorder (SRBD) affecting approximately 1-5% of children, is often caused by anatomical obstruction and/or collapse of the nasal and/or pharyngeal airways. The resulting sleep disruption and intermittent hypoxia lead to various systemic morbidities. Predicting the development of OSA from craniofacial features alone is currently not possible and a controversy remains if upper airway obstruction facilitates reduced midfacial growth or vice-versa. Currently, there is no rodent model that recapitulates both the development of craniofacial abnormalities and upper airway obstruction to address these questions. Here, we describe that mice with a neural crest-specific deletion of Bmp7 (Bmp7ncko) present with shorter, more acute angled cranial base, midfacial hypoplasia, nasal septum deviation, turbinate swelling and branching defects, and nasal airway obstruction. Interestingly, several of these craniofacial features develop after birth during periods of rapid midfacial growth and precede the development of an upper airway obstruction. We identified that in this rodent model, no single feature appeared to predict upper airway obstruction, but the sum of those features resulted in a reduced breathing frequency, apneas and overall reduced oxygen consumption. Metabolomics analysis of serum from peripheral blood identified increased levels of hydroxyproline, a metabolite upregulated under hypoxic conditions. As this model recapitulates many features observed in OSA, it offers unique opportunities for studying how upper airway obstruction affects breathing physiology and leads to systemic morbidities.

Pituitary stalk interruption syndrome

Pituitary stalk interruption syndrome (PSIS) is a distinct developmental defect of the pituitary gland identified by magnetic resonance imaging and characterized by a thin, interrupted, attenuated or absent pituitary stalk, hypoplasia or aplasia of the adenohypophysis, and an ectopic posterior pituitary. The precise etiology of PSIS still remains elusive or incompletely confirmed in most cases. Adverse perinatal events, including breech delivery and hypoxia, were initially proposed as the underlying mechanism affecting the hypothalamic-pituitary axis. Nevertheless, recent findings have uncovered a wide variety of PSIS-associated molecular defects in genes involved in pituitary development, holoprosencephaly (HPE), neural development, and other important cellular processes such as cilia function. The application of whole exome sequencing (WES) in relatively large cohorts has identified an expanded pool of potential candidate genes, mostly related to the Wnt, Notch, and sonic hedgehog signaling pathways that regulate pituitary growth and development during embryogenesis. Importantly, WES has revealed coexisting pathogenic variants in a significant number of patients; therefore, pointing to a multigenic origin and inheritance pattern of PSIS. The disorder is characterized by inter- and intrafamilial variability and incomplete or variable penetrance. Overall, PSIS is currently viewed as a mild form of an expanded HPE spectrum. The wide and complex clinical manifestations include evolving pituitary hormone deficiencies (with variable timing of onset and progression) and extrapituitary malformations. Severe and life-threatening symptomatology is observed in a subset of patients with complete pituitary hormone deficiency during the neonatal period. Nevertheless, most patients are referred later in childhood for growth retardation. Prompt and appropriate hormone substitution therapy constitutes the cornerstone of treatment. Further studies are needed to uncover the etiopathogenesis of PSIS.

Developmental Genes and Malformations in the Hypothalamus

The hypothalamus is a heterogeneous rostral forebrain region that regulates physiological processes essential for survival, energy metabolism, and reproduction, mainly mediated by the pituitary gland. In the updated prosomeric model, the hypothalamus represents the rostralmost forebrain, composed of two segmental regions (terminal and peduncular hypothalamus), which extend respectively into the non-evaginated preoptic telencephalon and the evaginated pallio-subpallial telencephalon. Complex genetic cascades of transcription factors and signaling molecules rule their development. Alterations of some of these molecular mechanisms acting during forebrain development are associated with more or less severe hypothalamic and pituitary dysfunctions, which may be associated with brain malformations such as holoprosencephaly or septo-optic dysplasia. Studies on transgenic mice with mutated genes encoding critical transcription factors implicated in hypothalamic-pituitary development are contributing to understanding the high clinical complexity of these pathologies. In this review article, we will analyze first the complex molecular genoarchitecture of the hypothalamus resulting from the activity of previous morphogenetic signaling centers and secondly some malformations related to alterations in genes implicated in the development of the hypothalamus.

Compound heterozygous splicing CDON variants result in isolated ocular coloboma

Ocular coloboma is caused by failure of optic fissure closure during development and recognized as part of the microphthalmia, anophthalmia, and coloboma (MAC) spectrum. While many genes are known to cause colobomatous microphthalmia, relatively few have been reported in coloboma with normal eye size. Genetic analysis including trio exome sequencing and Sanger sequencing was undertaken in a family with two siblings affected with bilateral coloboma of the iris, retina, and choroid. Pathogenic variants in MAC genes were excluded. Trio analysis identified compound heterozygous donor splice site variants in CDON, a cell-surface receptor known to function in the Sonic Hedgehog pathway, c.928 + 1G > A and c.2650 + 1G > T, in both affected individuals. Heterozygous missense and truncating CDON variants are associated with dominant holoprosencephaly (HPE) with incomplete penetrance and Cdon-/- mice display variable HPE and coloboma. A homozygous nonsense allele of uncertain significance was recently identified in a consanguineous patient with coloboma and a second molecular diagnosis. We report the first compound heterozygous variants in CDON as a cause of isolated coloboma. CDON is the first HPE gene identified to cause recessive coloboma. Given the phenotypic overlap, further examination of HPE genes in coloboma is indicated.

Identifying environmental risk factors and gene-environment interactions in holoprosencephaly

BACKGROUND

Holoprosencephaly is the most common malformation of the forebrain (1 in 250 embryos) with severe consequences for fetal and child development. This study evaluates nongenetic factors associated with holoprosencephaly risk, severity, and gene-environment interactions.

METHODS

For this retrospective case control study, we developed an online questionnaire focusing on exposures to common and rare toxins/toxicants before and during pregnancy, nutritional factors, maternal health history, and demographic factors. Patients with holoprosencephaly were primarily ascertained from our ongoing genetic and clinical studies of holoprosencephaly. Controls included children with Williams-Beuren syndrome (WBS) ascertained through online advertisements in a WBD support group and fliers.

RESULTS

Difference in odds of exposures between cases and controls as well as within cases with varying holoprosencephaly severity were studied. Cases included children born with holoprosencephaly (n = 92) and the control group consisted of children with WBS (n = 56). Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02), higher alcohol consumption (adjusted odds ratio [aOR], 1.73; 95% CI, 0.88-15.71), and exposure to consumer products such as aerosols or sprays including hair sprays (aOR, 2.46; 95% CI, 0.89-7.19). Significant gene-environment interactions were identified including for consumption of cheese (p < .05) and espresso drinks (p = .03).

CONCLUSION

The study identifies modifiable risk factors and gene-environment interactions that should be considered in future prevention of holoprosencephaly. Studies with larger HPE cohorts will be needed to confirm these findings.

Multifactorial Genetic and Environmental Hedgehog Pathway Disruption Sensitizes Embryos to Alcohol-Induced Craniofacial Defects

BACKGROUND

Prenatal alcohol exposure (PAE) is perhaps the most common environmental cause of human birth defects. These exposures cause a range of structural and neurological defects, including facial dysmorphologies, collectively known as fetal alcohol spectrum disorders (FASD). While PAE causes FASD, phenotypic outcomes vary widely. It is thought that multifactorial genetic and environmental interactions modify the effects of PAE. However, little is known of the nature of these modifiers. Disruption of the Hedgehog (Hh) signaling pathway has been suggested as a modifier of ethanol teratogenicity. In addition to regulating the morphogenesis of craniofacial tissues commonly disrupted in FASD, a core member of the Hh pathway, Smoothened, is susceptible to modulation by structurally diverse chemicals. These include environmentally prevalent teratogens like piperonyl butoxide (PBO), a synergist found in thousands of pesticide formulations.

METHODS

Here, we characterize multifactorial genetic and environmental interactions using a zebrafish model of craniofacial development.

RESULTS

We show that loss of a single allele of shha sensitized embryos to both alcohol- and PBO-induced facial defects. Co-exposure of PBO and alcohol synergized to cause more frequent and severe defects. The effects of this co-exposure were even more profound in the genetically susceptible shha heterozygotes.

CONCLUSIONS

Together, these findings shed light on the multifactorial basis of alcohol-induced craniofacial defects. In addition to further implicating genetic disruption of the Hh pathway in alcohol teratogenicity, our findings suggest that co-exposure to environmental chemicals that perturb Hh signaling may be important variables in FASD and related craniofacial disorders.

Cdon mutation and fetal alcohol converge on Nodal signaling in a mouse model of holoprosencephaly

Holoprosencephaly (HPE), a defect in midline patterning of the forebrain and midface, arises ~1 in 250 conceptions. It is associated with predisposing mutations in the Nodal and Hedgehog (HH) pathways, with penetrance and expressivity graded by genetic and environmental modifiers, via poorly understood mechanisms. CDON is a multifunctional co-receptor, including for the HH pathway. In mice, Cdon mutation synergizes with fetal alcohol exposure, producing HPE phenotypes closely resembling those seen in humans. We report here that, unexpectedly, Nodal signaling is a major point of synergistic interaction between Cdon mutation and fetal alcohol. Window-of-sensitivity, genetic, and in vitro findings are consistent with a model whereby brief exposure of Cdon mutant embryos to ethanol during gastrulation transiently and partially inhibits Nodal pathway activity, with consequent effects on midline patterning. These results illuminate mechanisms of gene-environment interaction in a multifactorial model of a common birth defect.

Identification of novel candidate pathogenic genes in pituitary stalk interruption syndrome by whole-exome sequencing

Pituitary stalk interruption syndrome (PSIS) is a type of congenital malformation of the anterior pituitary, which leads to isolated growth hormone deficiency or multiple hypothalamic-pituitary deficiencies. Many genetic factors have been explored, but they only account for a minority of the genetic aetiology. To identify novel PSIS pathogenic genes, we conducted whole-exome sequencing with 59 sporadic PSIS patients, followed by filtering gene panels involved in pituitary development, holoprosencephaly and midline abnormality. A total of 81 heterozygous variants, distributed among 59 genes, were identified in 50 patients, with 31 patients carrying polygenic variants. Fourteen of the 59 pathogenic genes clustered to the Hedgehog pathway. Of them, PTCH1 and PTCH2, inhibitors of Hedgehog signalling, showed the most frequent heterozygous mutations (22%, seven missense and one frameshift mutations were identified in 13 patients). Moreover, five novel heterozygous null variants in genes including PTCH2 (p.S391fs, combined with p.L104P), Hedgehog acyltransferase (p.R280X, de novo), MAPK3 (p.H50fs), EGR4 (p.G22fs, combined with LHX4 p.S263N) and SPG11 (p.Q1624X), which lead to truncated proteins, were identified. In conclusion, genetic mutations in the Hedgehog signalling pathway might underlie the complex polygenic background of PSIS, and the findings of our study could extend the understanding of PSIS pathogenic genes.

Gene-environment interactions: aligning birth defects research with complex etiology

Developmental biologists rely on genetics-based approaches to understand the origins of congenital abnormalities. Recent advancements in genomics have made it easier than ever to investigate the relationship between genes and disease. However, nonsyndromic birth defects often exhibit non-Mendelian inheritance, incomplete penetrance or variable expressivity. The discordance between genotype and phenotype indicates that extrinsic factors frequently impact the severity of genetic disorders and vice versa. Overlooking gene-environment interactions in birth defect etiology limits our ability to identify and eliminate avoidable risks. We present mouse models of sonic hedgehog signaling and craniofacial malformations to illustrate both the importance of and current challenges in resolving gene-environment interactions in birth defects. We then prescribe approaches for overcoming these challenges, including use of genetically tractable and environmentally responsive in vitro systems. Combining emerging technologies with molecular genetics and traditional animal models promises to advance our understanding of birth defect etiology and improve the identification and protection of vulnerable populations.

Ethanol and Cannabinoids Regulate Zebrafish GABAergic Neuron Development and Behavior in a Sonic Hedgehog and Fibroblast Growth Factor-Dependent Mechanism

BACKGROUND

Ethanol (EtOH) has diverse effects on nervous system development, which includes development and survival of GABAergic neurons in a sonic hedgehog (Shh) and fibroblast growth factor (Fgf)-dependent mechanism. Cannabinoids also function as inhibitors of Shh signaling, raising the possibility that EtOH and cannabinoids may interact to broadly disrupt neuronal function during brain development.

METHODS

Zebrafish embryos were exposed to a range of EtOH and/or cannabinoid receptor 1 (CB1R) agonist concentrations at specific developmental stages, in the absence or presence of morpholino oligonucleotides that disrupt shh expression. In situ hybridization was employed to analyze glutamic acid decarboxylase (gad1) gene expression as a marker of GABAergic neuron differentiation, and zebrafish behavior was analyzed using the novel tank diving test as a measure of risk-taking behavior.

RESULTS

Combined acute subthreshold EtOH and CB1R agonist exposure results in a marked reduction in gad1 mRNA expression in zebrafish forebrain. Consistent with the EtOH and cannabinoid effects on Shh signaling, fgf8 mRNA overexpression rescues the EtOH- and cannabinoid-induced decrease in gad1 gene expression and also prevents the changes in behavior induced by EtOH and cannabinoids.

CONCLUSIONS

These studies provide evidence that forebrain GABAergic neuron development and zebrafish risk-taking behavior are sensitive to both EtOH and cannabinoid exposure in a Shh- and Fgf-dependent mechanism, and provide additional evidence that a signaling pathway involving Shh and Fgf crosstalk is a critical target of EtOH and cannabinoids in FASD.

Quantification of Ethanol Levels in Zebrafish Embryos Using Head Space Gas Chromatography

Fetal Alcohol Spectrum Disorders (FASD) describe a highly variable continuum of ethanol-induced developmental defects, including facial dysmorphologies and neurological impairments. With a complex pathology, FASD affects approximately 1 in 100 children born in the United States each year. Due to the highly variable nature of FASD, animal models have proven critical in our current mechanistic understanding of ethanol-induced development defects. An increasing number of laboratories has focused on using zebrafish to examine ethanol-induced developmental defects. Zebrafish produce large numbers of externally fertilized, genetically tractable, translucent embryos. This allows researchers to precisely control timing and dosage of ethanol exposure in multiple genetic contexts and quantify the impact of embryonic ethanol exposure through live imaging techniques. This, combined with the high degree of conservation of both genetics and development with humans, has proven zebrafish to be a powerful model in which to study the mechanistic basis of ethanol teratogenicity. However, ethanol exposure regimens have varied between different zebrafish studies, which has confounded the interpretation of zebrafish data across these studies. Here is a protocol to quantify ethanol concentrations in zebrafish embryos using head space gas chromatography.

Caracterización de la exposición prenatal de un grupo de niños de 0 a 5 años con cardiopatía congénita atendidos en Cali, Colombia. La importancia del ácido fólico

Introducción. Con una prevalencia estimada de 4 a 9 casos por cada 1 000 nacimientos, las cardiopatías congénitas (CC) tienen gran impacto en la morbimortalidad pediátrica. La variabilidad de prevalencia se ha atribuido a diferencias regionales en cuanto a factores genéticos, ambientales, entre otros.Objetivo. Obtener datos sobre variables de exposición prenatales de pacientes con CC atendidos en Cali, Colombia.Materiales y métodos. Se aplicó una encuesta a las madres de 30 pacientes de 0 a 5 años con CC atendidos en 2 clínicas de alta complejidad (tercer y cuarto nivel) de Cali. La encuesta estaba orientada a múltiples variables de exposición y la información recolectada fue digitalizada en una base de datos en el programa Microsoft Excel para hacer un análisis estadístico descriptivo.Resultados. Se evidenciaron varias exposiciones potencialmente asociadas a CC, tales como índice de masa corporal alterado, administración inadecuada de suplementos de ácido fólico y exposición a vitamina A, rayos X, alcohol y cigarrillo.Conclusión. El consumo insuficiente o inoportuno de ácido fólico podría facilitar la generación de efectos teratogénicos de sustancias oxidantes. Por lo tanto, se debe educar a las mujeres de Cali sobre la importancia de una ingesta adecuada de ácido fólico y sobre los riesgos de la exposición a agentes teratogénicos durante el embarazo para reducir las tasas de incidencia de CC en esta ciudad.

Animal models of gene-alcohol interactions

Most birth defects arise from complex interactions between multiple genetic and environmental factors. However, our current understanding of how these interactions and their contributions affect birth defects remains incomplete. Human studies are limited in their ability to identify the fundamental causes of birth defects due to ethical and practical limitations. Animal models provide a great number of resources not available to human studies and they have been critical in advancing our understanding of birth defects and the complex interactions that underlie them. In this review, we discuss the use of animal models in the context of gene-environment interactions that underlie birth defects. We focus on alcohol which is the most common environmental factor associated with birth defects. Prenatal alcohol exposure leads to a wide range of cognitive impairments and structural deficits broadly termed fetal alcohol spectrum disorders (FASD). We discuss the broad impact of prenatal alcohol exposure on the developing embryo and elaborate on the current state of gene-alcohol interactions. Additionally, we discuss how animal models have informed our understanding of the genetics of FASD. Ultimately, these topics will provide insight into the use of animal models in understanding gene-environment interactions and their subsequent impact on birth defects.

Cannabinoids Exacerbate Alcohol Teratogenesis by a CB1-Hedgehog Interaction

We tested whether cannabinoids (CBs) potentiate alcohol-induced birth defects in mice and zebrafish, and explored the underlying pathogenic mechanisms on Sonic Hedgehog (Shh) signaling. The CBs, Δ⁹-THC, cannabidiol, HU-210, and CP 55,940 caused alcohol-like effects on craniofacial and brain development, phenocopying Shh mutations. Combined exposure to even low doses of alcohol with THC, HU-210, or CP 55,940 caused a greater incidence of birth defects, particularly of the eyes, than did either treatment alone. Consistent with the hypothesis that these defects are caused by deficient Shh, we found that CBs reduced Shh signaling by inhibiting Smoothened (Smo), while Shh mRNA or a CB1 receptor antagonist attenuated CB-induced birth defects. Proximity ligation experiments identified novel CB1-Smo heteromers, suggesting allosteric CB1-Smo interactions. In addition to raising concerns about the safety of cannabinoid and alcohol exposure during early embryonic development, this study establishes a novel link between two distinct signaling pathways and has widespread implications for development, as well as diseases such as addiction and cancer.

Update on new GH-IGF axis genetic defects

The somatotropic axis is the main hormonal regulator of growth. Growth hormone (GH), also known as somatotropin, and insulin-like growth factor 1 (IGF-1) are the key components of the somatotropic axis. This axis has been studied for a long time and the knowledge of how some molecules could promote or impair hormones production and action has been growing over the last decade. The enhancement of large-scale sequencing techniques has expanded the spectrum of known genes and several other candidate genes that could affect the GH-IGF1-bone pathway. To date, defects in more than forty genes were associated with an impairment of the somatotropic axis. These defects can affect from the secretion of GH to the bioavailability and action of IGF-1. Affected patients present a large heterogeneous group of conditions associated with growth retardation. In this review, we focus on the description of the GH-IGF axis genetic defects reported in the last decade. Arch Endocrinol Metab. 2019;63(6):608-17.

Holoprosencephaly from conception to adulthood

Holoprosencephaly (HPE) consists of a spectrum of malformations related to incomplete separation of the prosencephalon. There is a wide clinical variability depending on the HPE subtype seen on imaging. Early postnatal lethality is common, however a significant fraction of newborns diagnosed with HPE will survive into childhood and even adulthood. Here we will review the clinical management of HPE during different ages from the prenatal period to adulthood.

A forebrain undivided: Unleashing model organisms to solve the mysteries of holoprosencephaly

Evolutionary conservation and experimental tractability have made animal model systems invaluable tools in our quest to understand human embryogenesis, both normal and abnormal. Standard genetic approaches, particularly useful in understanding monogenic diseases, are no longer sufficient as research attention shifts toward multifactorial outcomes. Here, we examine this progression through the lens of holoprosencephaly (HPE), a common human malformation involving incomplete forebrain division, and a classic example of an etiologically complex outcome. We relate the basic underpinning of HPE pathogenesis to critical cell-cell interactions and signaling molecules discovered through embryological and genetic approaches in multiple model organisms, and discuss the role of the mouse model in functional examination of HPE-linked genes. We then outline the most critical remaining gaps to understanding human HPE, including the conundrum of incomplete penetrance/expressivity and the role of gene-environment interactions. To tackle these challenges, we outline a strategy that leverages new and emerging technologies in multiple model systems to solve the puzzle of HPE.

Oxidative stress and DNA damage in the mechanism of fetal alcohol spectrum disorders

This review covers molecular mechanisms involving oxidative stress and DNA damage that may contribute to morphological and functional developmental disorders in animal models resulting from exposure to alcohol (ethanol, EtOH) in utero or in embryo culture. Components covered include: (a) a brief overview of EtOH metabolism and embryopathic mechanisms other than oxidative stress; (b) mechanisms within the embryo and fetal brain by which EtOH increases the formation of reactive oxygen species (ROS); (c) critical embryonic/fetal antioxidative enzymes and substrates that detoxify ROS; (d) mechanisms by which ROS can alter development, including ROS-mediated signal transduction and oxidative DNA damage, the latter of which leads to pathogenic genetic (mutations) and epigenetic changes; (e) pathways of DNA repair that mitigate the pathogenic effects of DNA damage; (f) related indirect mechanisms by which EtOH enhances risk, for example by enhancing the degradation of some DNA repair proteins; and, (g) embryonic/fetal pathways like NRF2 that regulate the levels of many of the above components. Particular attention is paid to studies in which chemical and/or genetic manipulation of the above mechanisms has been shown to alter the ability of EtOH to adversely affect development. Alterations in the above components are also discussed in terms of: (a) individual embryonic and fetal determinants of risk and (b) potential risk biomarkers and mitigating strategies. FASD risk is likely increased in progeny which/who are biochemically predisposed via genetic and/or environmental mechanisms, including enhanced pathways for ROS formation and/or deficient pathways for ROS detoxification or DNA repair.

Hedgehog Signaling and Embryonic Craniofacial Disorders

Since its initial discovery in a Drosophila mutagenesis screen, the Hedgehog pathway has been revealed to be instrumental in the proper development of the vertebrate face. Vertebrates possess three hedgehog paralogs: Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). Of the three, Shh has the broadest range of functions both in the face and elsewhere in the embryo, while Ihh and Dhh play more limited roles. The Hedgehog pathway is instrumental from the period of prechordal plate formation early in the embryo, until the fusion of the lip and secondary palate, which complete the major patterning events of the face. Disruption of Hedgehog signaling results in an array of developmental disorders in the face, ranging from minor alterations in the distance between the eyes to more serious conditions such as severe clefting of the lip and palate. Despite its critical role, Hedgehog signaling seems to be disrupted through a number of mechanisms that may either be direct, as in mutation of a downstream target of the Hedgehog ligand, or indirect, such as mutation in a ciliary protein that is otherwise seemingly unrelated to the Hedgehog pathway. A number of teratogens such as alcohol, statins and steroidal alkaloids also disrupt key aspects of Hedgehog signal transduction, leading to developmental defects that are similar, if not identical, to those of Hedgehog pathway mutations. The aim of this review is to highlight the variety of roles that Hedgehog signaling plays in developmental disorders of the vertebrate face.

Case report: a novel mutation in ZIC2 in an infant with microcephaly, holoprosencephaly, and arachnoid cyst

RATIONALE

Holoprosencephaly (HPE) is a severe congenital brain malformation resulting from failed or incomplete forebrain division in early pregnancy.

PATIENT CONCERNS

In this study, we reported a 9-month old infant girl with mild microcephaly, semilobor HPE, and arachnoid cyst.

DIAGNOSES

Potential genetic defects were screened directly using trio-case whole exome sequencing (WES) rather than traditional karyotype, microarray, and Sanger sequencing of select genes.

OUTCOMES

A previous unpublished de novo missense mutation (c.1069C >G, p.H357D) in the 3rd zinc finger domain (ZFD3) of the ZIC2 gene was identified in the affected individual, but not in the parents. Sanger sequencing using specific primers verified the mutation. Extensive bioinformatics analysis confirmed the pathogenicity of this extremely rare mutation. Phenotype-genotype analysis revealed significant correlation between the 3rd zinc-finger domain with semilobor HPE.

LESSONS

These findings expanded the spectrum of the ZIC2 gene mutations and associated clinical manifestations, which is the first identification of a mutated ZIC2 gene in a Han infant girl with mild microcephaly, semilobor HPE, and arachnoid cyst.

Ethanol and cannabinoids interact to alter behavior in a zebrafish fetal alcohol spectrum disorder model

BACKGROUND

Recent work suggests that endocannabinoids (eCBs) may signal through the sonic hedgehog signaling pathway. We therefore hypothesized that combined ethanol and eCB exposure during defined stages of zebrafish embryogenesis will produce deficits comparable to human fetal alcohol spectrum disorder (FASD).

METHODS

Zebrafish embryos were exposed to ethanol or cannabinoid agonists alone or in combination at defined developmental stages and assessed for changes in brain morphology or expression of marker genes such as pax6a. Juvenile fish were then assessed for risk-taking/anxiety-like behavior using the novel tank dive test.

RESULTS

Either chronic or acute exposure to high doses of the CB1R agonist ACEA resulted in FASD phenotypes. However, acute subthreshold doses of CB1R agonist alone, or combined with 0.5% ethanol, did not induce morphological phenotypes, but did induce dysmorphogenesis when combined with acute 1% ethanol. Phenotypes were rescued using the CB1R antagonist SR141716A. In addition, JZL195, a dual inhibitor of FAAH and MAGL, two degradative enzymes for eCBs, induced FASD phenotypes in the presence of subthreshold ethanol, confirming the activation of common signaling pathways by ethanol and eCBs. We next analyzed the effects of ethanol and CB1R agonist on juvenile zebrafish behavior and show that ACEA or ethanol alone did not alter behavior, but combined ACEA and ethanol increased risk-taking behavior.

CONCLUSIONS

These studies demonstrate that pathological and behavioral phenotypes associated with FASD are induced by exposure to CB1R agonists and suggest that combined exposure to lower levels of alcohol and marijuana may be capable of inducing FASD-like morphological and behavioral impairments.

The oculoauriculofrontonasal syndrome: Further clinical characterization and additional evidence suggesting a nontraditional mode of inheritance

The oculoauriculofrontonasal syndrome (OAFNS) is a rare disorder characterized by the association of frontonasal dysplasia (widely spaced eyes, facial cleft, and nose abnormalities) and oculo-auriculo-vertebral spectrum (OAVS)-associated features, such as preauricular ear tags, ear dysplasia, mandibular asymmetry, epibulbar dermoids, eyelid coloboma, and costovertebral anomalies. The etiology is unknown so far. This work aimed to identify molecular bases for the OAFNS. Among a cohort of 130 patients with frontonasal dysplasia, accurate phenotyping identified 18 individuals with OAFNS. We describe their clinical spectrum, including the report of new features (micro/anophtalmia, cataract, thyroid agenesis, polymicrogyria, olfactory bulb hypoplasia, and mandibular cleft), and emphasize the high frequency of nasal polyps in OAFNS (56%). We report the negative results of ALX1, ALX3, and ALX4 genes sequencing and next-generation sequencing strategy performed on blood-derived DNA from respectively, four and four individuals. Exome sequencing was performed in four individuals, genome sequencing in one patient with negative exome sequencing result. Based on the data from this series and the literature, diverse hypotheses can be raised regarding the etiology of OAFNS: mosaic mutation, epigenetic anomaly, oligogenism, or nongenetic cause. In conclusion, this series represents further clinical delineation work of the rare OAFNS, and paves the way toward the identification of the causing mechanism.

Choanal atresia and stenosis: Development and diseases of the nasal cavity

Proper craniofacial development in vertebrates depends on growth and fusion of the facial processes during embryogenesis. Failure of any step in this process could lead to craniofacial anomalies such as facial clefting, which has been well studied with regard to its molecular etiology and cellular pathogenesis. Nasal cavity invagination is also a critical event in proper craniofacial development, and is required for the formation of a functional nasal cavity and airway. The nasal cavity must connect the nasopharynx with the primitive choanae to complete an airway from the nostril to the nasopharynx. In contrast to orofacial clefts, defects in nasal cavity and airway formation, such as choanal atresia (CA), in which the connection between the nasal airway and nasopharynx is physically blocked, have largely been understudied. This is also true for a narrowed connection between the nasal cavity and the nasopharynx, which is known as choanal stenosis (CS). CA occurs in approximately 1 in 5,000 live births, and can present in isolation but typically arises as part of a syndrome. Despite the fact that CA and CS usually require immediate intervention, and substantially affect the quality of life of affected individuals, the etiology and pathogenesis of CA and CS have remained elusive. In this review I focus on the process of nasal cavity development with respect to forming a functional airway and discuss the cellular behavior and molecular networks governing this process. Additionally, the etiology of human CA is discussed using examples of disorders which involve CA or CS. This article is categorized under: Signaling Pathways > Cell Fate Signaling Comparative Development and Evolution > Model Systems Birth Defects > Craniofacial and Nervous System Anomalies.