Mutations in two nonhomologous genes in a head-to-head configuration cause Ellis-van Creveld syndrome

Variant characterisation and clinical profile in a large cohort of patients with Ellis-van Creveld syndrome and a family with Weyers acrofacial dysostosis

BACKGROUND

Ellis-van Creveld syndrome (EvC) is a recessive disorder characterised by acromesomelic limb shortening, postaxial polydactyly, nail-teeth dysplasia and congenital cardiac defects, primarily caused by pathogenic variants in EVC or EVC2. Weyers acrofacial dysostosis (WAD) is an ultra-rare dominant condition allelic to EvC. The present work aimed to enhance current knowledge on the clinical manifestations of EvC and WAD and broaden their mutational spectrum.

METHODS

We conducted molecular studies in 46 individuals from 43 unrelated families with a preliminary clinical diagnosis of EvC and 3 affected individuals from a family with WAD and retrospectively analysed clinical data. The deleterious effect of selected variants of uncertain significance was evaluated by cellular assays.

MAIN RESULTS

We identified pathogenic variants in EVC/EVC2 in affected individuals from 41 of the 43 families with EvC. Patients from each of the two remaining families were found with a homozygous splicing variant in WDR35 and a de novo heterozygous frameshift variant in GLI3, respectively. The phenotype of these patients showed a remarkable overlap with EvC. A novel EVC2 C-terminal truncating variant was identified in the family with WAD. Deep phenotyping of the cohort recapitulated 'classical EvC findings' in the literature and highlighted findings previously undescribed or rarely described as part of EvC.

CONCLUSIONS

This study presents the largest cohort of living patients with EvC to date, contributing to better understanding of the full clinical spectrum of EvC. We also provide comprehensive information on the EVC/EVC2 mutational landscape and add GLI3 to the list of genes associated with EvC-like phenotypes.

The oligodontia phenotype in a X-linked hypohidrotic ectodermal dysplasia patient with a novel EVC2 variant

Objectives

To analyse the pathogenic genes in a patient with hypohidrotic ectodermal dysplasia (HED) and explore the relationship between pathogenic genes and the oligodontia phenotype.

Methods

Clinical data and peripheral blood were collected from a patient with HED. Pathogenic genes were analysed by whole-exon sequencing (WES) and verified by Singer sequencing. The secondary and tertiary structures of the variant proteins were predicted to analyse their toxicity.

Results

The patient exhibited a severe oligodontia phenotype, wherein only two deciduous canines were left in the upper jaw. WES revealed a hemizygous EDA variant c.466C > T p.(Arg156Cys) and a novel heterozygous EVC2 variant c.1772T > C p.(Leu591Ser). Prediction of the secondary and tertiary structures of the EDA variant p.(Arg156Cys) and EVC2 variant p.(Leu591Ser) indicated impaired function of both molecules.

Conclusion

The patient demonstrated a more severe oligodontia phenotype when compared with the other patients caused by the EDA variant c.466C > T. Since Evc2 is a positive regulator of the Sonic Hedgehog (Shh) signal pathway, we speculated that the EVC2 variant p.(Leu591Ser) may play a synergistic role in the oligodontia phenotype of HED, thereby exacerbating the oligodontia phenotype. Knowledge of oligodontia caused by multiple gene variants is of great significance for understanding individual differences in oligodontia phenotypes.

ClinGen guidance for use of the PP1/BS4 co-segregation and PP4 phenotype specificity criteria for sequence variant pathogenicity classification

The 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology variant classification publication established a standard employed internationally to guide laboratories in variant assessment. Those recommendations included both pathogenic (PP1) and benign (BS4) criteria for evaluating the inheritance patterns of variants, but details of how to apply those criteria at appropriate evidence levels were sparse. Several publications have since attempted to provide additional guidance, but anecdotally, this issue is still challenging. Additionally, it is not clear that those prior efforts fully distinguished disease-gene identification considerations from variant pathogenicity considerations nor did they address autosomal-recessive and X-linked inheritance. Here, we have taken a mixed inductive and deductive approach to this problem using real diseases as examples. We have developed a practical heuristic for genetic co-segregation evidence and have also determined that the specific phenotype criterion (PP4) is inseparably coupled to the co-segregation criterion. We have also determined that negative evidence at one locus constitutes positive evidence for other loci for disorders with locus heterogeneity. Finally, we provide a points-based system for evaluating phenotype and co-segregation as evidence types to support or refute a locus and show how that can be integrated into the Bayesian framework now used for variant classification and consistent with the 2015 guidelines.

Human Genetics of Ventricular Septal Defect

Ventricular septal defects (VSDs) are recognized as one of the commonest congenital heart diseases (CHD), accounting for up to 40% of all cardiac malformations, and occur as isolated CHDs as well as together with other cardiac and extracardiac congenital malformations in individual patients and families. The genetic etiology of VSD is complex and extraordinarily heterogeneous. Chromosomal abnormalities such as aneuploidy and structural variations as well as rare point mutations in various genes have been reported to be associated with this cardiac defect. This includes both well-defined syndromes with known genetic cause (e.g., DiGeorge syndrome and Holt-Oram syndrome) and so far undefined syndromic forms characterized by unspecific symptoms. Mutations in genes encoding cardiac transcription factors (e.g., NKX2-5 and GATA4) and signaling molecules (e.g., CFC1) have been most frequently found in VSD cases. Moreover, new high-resolution methods such as comparative genomic hybridization enabled the discovery of a high number of different copy number variations, leading to gain or loss of chromosomal regions often containing multiple genes, in patients with VSD. In this chapter, we will describe the broad genetic heterogeneity observed in VSD patients considering recent advances in this field.

Prenatal whole exome sequencing identified two rare compound heterozygous variants in EVC2 causing Ellis-van Creveld syndrome

BACKGROUND

Pathogenic mutations in EVC or EVC2 gene can lead to Ellis-van Creveld (EvC) syndrome, which is a rare autosomal recessive skeletal dysplasia disorder. This study aimed to determine pathogenic gene variations associated with EvC syndrome in fetuses showing ultrasound anomalies.

METHODS

A 32-year-old pregnant woman from Quanzhou, China was investigated. In her pregnancy examination, the fetus exhibited multiple fetal malformations, including a narrow thorax, short limbs, postaxial polydactyly, cardiac malformations, and separation of double renal pelvis. Karyotype, chromosomal microarray analysis and whole exome sequencing were performed for prenatal genetic etiology analysis.

RESULTS

Chromosome abnormalities and copy number variants were not observed in the fetus using karyotype and chromosomal microarray analysis. Using whole exome sequencing, two compound heterozygous variants NM_147127.5:c.[2484G>A(p.Trp828Ter)];[871-2_894del] in EVC2 gene were identified in the fetus as pathogenic variants inherited from parents.

CONCLUSIONS

The study is the first to identify two rare compound variants in EVC2 gene in a Chinese family using whole exome sequencing. The application of whole-exome sequencing would be helpful in fetal etiological diagnosis with ultrasound anomalies.

EVC-EVC2 complex stability and ciliary targeting are regulated by modification with ubiquitin and SUMO

Ellis van Creveld syndrome and Weyers acrofacial dysostosis are two rare genetic diseases affecting skeletal development. They are both ciliopathies, as they are due to malfunction of primary cilia, microtubule-based plasma membrane protrusions that function as cellular antennae and are required for Hedgehog signaling, a key pathway during skeletal morphogenesis. These ciliopathies are caused by mutations affecting the EVC-EVC2 complex, a transmembrane protein heterodimer that regulates Hedgehog signaling from inside primary cilia. Despite the importance of this complex, the mechanisms underlying its stability, targeting and function are poorly understood. To address this, we characterized the endogenous EVC protein interactome in control and Evc-null cells. This proteomic screen confirmed EVC's main known interactors (EVC2, IQCE, EFCAB7), while revealing new ones, including USP7, a deubiquitinating enzyme involved in Hedgehog signaling. We therefore looked at EVC-EVC2 complex ubiquitination. Such ubiquitination exists but is independent of USP7 (and of USP48, also involved in Hh signaling). We did find, however, that monoubiquitination of EVC-EVC2 cytosolic tails greatly reduces their protein levels. On the other hand, modification of EVC-EVC2 cytosolic tails with the small ubiquitin-related modifier SUMO3 has a different effect, enhancing complex accumulation at the EvC zone, immediately distal to the ciliary transition zone, possibly via increased binding to the EFCAB7-IQCE complex. Lastly, we find that EvC zone targeting of EVC-EVC2 depends on two separate EFCAB7-binding motifs within EVC2's Weyers-deleted peptide. Only one of these motifs had been characterized previously, so we have mapped the second herein. Altogether, our data shed light on EVC-EVC2 complex regulatory mechanisms, with implications for ciliopathies.

Identification of Compound Heterozygous EVC2 Gene Variants in Two Mexican Families with Ellis-van Creveld Syndrome

BACKGROUND

Ellis-van Creveld syndrome (EvCS) is an autosomal recessive ciliopathy with a disproportionate short stature, polydactyly, dystrophic nails, oral defects, and cardiac anomalies. It is caused by pathogenic variants in the EVC or EVC2 genes. To obtain further insight into the genetics of EvCS, we identified the genetic defect for the EVC2 gene in two Mexican patients.

METHODS

Two Mexican families were enrolled in this study. Exome sequencing was applied in the probands to screen potential genetic variant(s), and then Sanger sequencing was used to identify the variant in the parents. Finally, a prediction of the three-dimensional structure of the mutant proteins was made.

RESULTS

One patient has a compound heterozygous EVC2 mutation: a novel heterozygous variant c.519_519 + 1delinsT inherited from her mother, and a heterozygous variant c.2161delC (p.L721fs) inherited from her father. The second patient has a previously reported compound heterozygous EVC2 mutation: nonsense mutation c.645G > A (p.W215*) in exon 5 inherited from her mother, and c.273dup (p.K92fs) in exon 2 inherited from her father. In both cases, the diagnostic was Ellis-van Creveld syndrome. Three-dimensional modeling of the EVC2 protein showed that truncated proteins are produced in both patients due to the generation of premature stop codons.

CONCLUSION

The identified novel heterozygous EVC2 variants, c.2161delC and c.519_519 + 1delinsT, were responsible for the Ellis-van Creveld syndrome in one of the Mexican patients. In the second Mexican patient, we identified a compound heterozygous variant, c.645G > A and c.273dup, responsible for EvCS. The findings in this study extend the EVC2 mutation spectrum and may provide new insights into the EVC2 causation and diagnosis with implications for genetic counseling and clinical management.

Ellis-Van Creveld Syndrome: Clinical and Molecular Analysis of 50 Individuals

BACKGROUND

Ellis-Van Creveld (EVC) syndrome is one of the entities belonging to the skeletal ciliopathies short rib-polydactyly subgroup. Major signs are ectodermal dysplasia, chondrodysplasia, polydactyly and congenital cardiopathy, with a high degree of variability in phenotypes ranging from lethal to mild clinical presentations. The EVC and EVC2 genes are the major genes causative of EVC syndrome. However, an increased number of genes involved in the ciliopathy complex have been identified in EVC syndrome, leading to a better understanding of its physiopathology, namely, WDR35, GLI1, DYNC2LI1, PRKACA, PRKACB and SMO. They all code for proteins located in the primary cilia, playing a key role in signal transduction of the Hedgehog pathways.

METHODS

The aim of this study was the analysis of 50 clinically identified EVC cases from 45 families to further define the phenotype and molecular bases of EVC.

RESULTS

Our detection rate in the cohort of 45 families was of 91.11%, with variants identified in EVC/EVC2 (77.8%), DYNC2H1 (6.7%), DYNC2LI1 (2.2%), SMO (2.2%) or PRKACB (2.2%). No distinctive feature was remarkable of a specific genotype-phenotype correlation. Interestingly, we identified a high proportion of heterozygous deletions in EVC/EVC2 of variable sizes (26.92%), mostly inherited from the mother, and probably resulting from recombinations involving Alu sequences.

CONCLUSION

We confirmed that EVC and EVC2 are the major genes involved in the EVC phenotype and highlighted the high prevalence of previously unreported CNVs (Copy Number Variation).

Clinical variability in DYNC2H1-related skeletal ciliopathies includes Ellis-van Creveld syndrome

Deleterious variants of DYNC2H1 gene are associated with a wide spectrum of skeletal ciliopathies (SC). We used targeted parallel sequencing to analyze 25 molecularly unsolved families with different SCs. Deleterious DYNC2H1 variants were found in six sporadic patients and two monozygotic (MZ) twins. Clinical diagnoses included short rib-polydactyly type 3 in two cases, and asphyxiating thoracic dystrophy (ATD) in one case. Remarkably, clinical diagnosis fitted with EvC, mixed ATD/EvC and short rib-polydactyly/EvC phenotypes in three sporadic patients and the MZ twins. EvC/EvC-like features always occurred in compound heterozygotes sharing a previously unreported splice site change (c.6140-5A>G) or compound heterozygotes for two missense variants. These results expand the DYNC2H1 mutational repertoire and its clinical spectrum, suggesting that EvC may be occasionally caused by DYNC2H1 variants presumably acting as hypomorphic alleles.

The missing link between genetic association and regulatory function

The genetic basis of most traits is highly polygenic and dominated by non-coding alleles. It is widely assumed that such alleles exert small regulatory effects on the expression of cis-linked genes. However, despite the availability of gene expression and epigenomic datasets, few variant-to-gene links have emerged. It is unclear whether these sparse results are due to limitations in available data and methods, or to deficiencies in the underlying assumed model. To better distinguish between these possibilities, we identified 220 gene-trait pairs in which protein-coding variants influence a complex trait or its Mendelian cognate. Despite the presence of expression quantitative trait loci near most GWAS associations, by applying a gene-based approach we found limited evidence that the baseline expression of trait-related genes explains GWAS associations, whether using colocalization methods (8% of genes implicated), transcription-wide association (2% of genes implicated), or a combination of regulatory annotations and distance (4% of genes implicated). These results contradict the hypothesis that most complex trait-associated variants coincide with homeostatic expression QTLs, suggesting that better models are needed. The field must confront this deficit and pursue this 'missing regulation.'

NSD1 mutations deregulate transcription and DNA methylation of bivalent developmental genes in Sotos syndrome

Sotos syndrome (SS), the most common overgrowth with intellectual disability (OGID) disorder, is caused by inactivating germline mutations of NSD1, which encodes a histone H3 lysine 36 methyltransferase. To understand how NSD1 inactivation deregulates transcription and DNA methylation (DNAm), and to explore how these abnormalities affect human development, we profiled transcription and DNAm in SS patients and healthy control individuals. We identified a transcriptional signature that distinguishes individuals with SS from controls and was also deregulated in NSD1-mutated cancers. Most abnormally expressed genes displayed reduced expression in SS; these downregulated genes consisted mostly of bivalent genes and were enriched for regulators of development and neural synapse function. DNA hypomethylation was strongly enriched within promoters of transcriptionally deregulated genes: overexpressed genes displayed hypomethylation at their transcription start sites while underexpressed genes featured hypomethylation at polycomb binding sites within their promoter CpG island shores. SS patients featured accelerated molecular aging at the levels of both transcription and DNAm. Overall, these findings indicate that NSD1-deposited H3K36 methylation regulates transcription by directing promoter DNA methylation, partially by repressing polycomb repressive complex 2 (PRC2) activity. These findings could explain the phenotypic similarity of SS to OGID disorders that are caused by mutations in PRC2 complex-encoding genes.

Novel large deletion involving EVC and EVC2 in Ellis-van Creveld syndrome

Ellis-van Creveld syndrome is an autosomal recessive skeletal dysplasia that is characterized by thoracic hypoplasia, polydactyly, oral abnormalities, and congenital heart disease. It is caused by pathogenic variants in the EVC or EVC2 genes. We report a case of a newborn with a compound heterozygous variant comprising NM_147127.5: c.1991dup:[p.Lys665Glufs*10] in the EVC2 gene and a novel large deletion involving exon 1 in EVC and exons 1-7 in EVC2.

First case reported of COVID-19 infection in an adult patient with Ellis-van Creveld syndrome

Ellis-van Creveld syndrome (EVC) is a rare autosomal recessive disorder, the features of the syndrome are: chondral and ectodermal dysplasia characterized by short ribs, polydactyly, growth retardation resulting in dwarfism, teeth and craniofacial abnormalities and heart defects (mostly endocardial cushions and atrial septal defects).

We describe the first case reported of COVID-19 infection in a 24-years-old girl, diagnosed with EVC syndrome. The patient suffered only from a mild illness, she remained stable with normal saturation without need of neither respiratory support nor specific therapy and she was rapidly discharged.

This case appraises the pathophysiological interplay between different specific prognostic variable in a syndromic patient with congenital heart disease and COVID-19. In patients with congenital heart disease, comorbidities related to syndromic picture may affect the clinical course of COVID-19 infection regardless of the anatomic complexity.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Molecular Bases of Human Malformation Syndromes Involving the SHH Pathway: GLIA/R Balance and Cardinal Phenotypes

Human hereditary malformation syndromes are caused by mutations in the genes of the signal transduction molecules involved in fetal development. Among them, the Sonic hedgehog (SHH) signaling pathway is the most important, and many syndromes result from its disruption. In this review, we summarize the molecular mechanisms and role in embryonic morphogenesis of the SHH pathway, then classify the phenotype of each malformation syndrome associated with mutations of major molecules in the pathway. The output of the SHH pathway is shown as GLI activity, which is generated by SHH in a concentration-dependent manner, i.e., the sum of activating form of GLI (GLIA) and repressive form of GLI (GLIR). Which gene is mutated and whether the mutation is loss-of-function or gain-of-function determine in which concentration range of SHH the imbalance occurs. In human malformation syndromes, too much or too little GLI activity produces symmetric phenotypes affecting brain size, craniofacial (midface) dysmorphism, and orientation of polydactyly with respect to the axis of the limb. The symptoms of each syndrome can be explained by the GLIA/R balance model.

Genetics of congenital heart disease: a narrative review of recent advances and clinical implications

Congenital heart disease (CHD) is the most common human birth defect and remains a leading cause of mortality in childhood. Although advances in clinical management have improved the survival of children with CHD, adult survivors commonly experience cardiac and non-cardiac comorbidities, which affect quality of life and prognosis. Therefore, the elucidation of genetic etiologies of CHD not only has important clinical implications for genetic counseling of patients and families but may also impact clinical outcomes by identifying at-risk patients. Recent advancements in genetic technologies, including massively parallel sequencing, have allowed for the discovery of new genetic etiologies for CHD. Although variant prioritization and interpretation of pathogenicity remain challenges in the field of CHD genomics, advances in single-cell genomics and functional genomics using cellular and animal models of CHD have the potential to provide novel insights into the underlying mechanisms of CHD and its associated morbidities. In this review, we provide an updated summary of the established genetic contributors to CHD and discuss recent advances in our understanding of the genetic architecture of CHD along with current challenges with the interpretation of genetic variation. Furthermore, we highlight the clinical implications of genetic findings to predict and potentially improve clinical outcomes in patients with CHD.

Cardiac Defects and Genetic Syndromes: Old Uncertainties and New Insights

Recent advances in understanding the genetic causes and anatomic subtypes of cardiac defects have revealed new links between genetic etiology, pathogenetic mechanisms and cardiac phenotypes. Although the same genetic background can result in different cardiac phenotypes, and similar phenotypes can be caused by different genetic causes, researchers’ effort to identify specific genotype–phenotype correlations remains crucial. In this review, we report on recent advances in the cardiac pathogenesis of three genetic diseases: Down syndrome, del22q11.2 deletion syndrome and Ellis–Van Creveld syndrome. In these conditions, the frequent and specific association with congenital heart defects and the recent characterization of the underlying molecular events contributing to pathogenesis provide significant examples of genotype–phenotype correlations. Defining these correlations is expected to improve diagnosis and patient stratification, and it has relevant implications for patient management and potential therapeutic options.

Late survival in Ellis-van Creveld syndrome with common single atrium

Ellis-van Creveld (EVC) syndrome is a relatively rare chondroectodermal dysplasia considered mainly as a generalised disorder of the maturation of endochondral ossification. Congenital heart disease occurs in approximately half of the patients with EVC syndrome, 60% of which is a common atrium. Common atrium is a rare variety of interatrial communication characterised by absence or virtual absence of the atrial septum. Patients with this syndrome rarely survive to an old age. We report a case of EVC who presented for the first time at 60 years of age, as survival to an advanced age is exceptional in case of EVC.

Estimation of the carrier frequencies and proportions of potential patients by detecting causative gene variants associated with autosomal recessive bone dysplasia using a whole-genome reference panel of Japanese individuals

Bone dysplasias are a group of rare hereditary diseases, with up to 436 disease types. Perinatal diagnosis is clinically important for adequate personalized management and counseling. There are no reports focused on pathogenic variants of bone dysplasias in the general population. In this study, we focused on autosomal recessive bone dysplasias. We identified pathogenic variants using whole-genome reference panel data from 3552 Japanese individuals. For the first time, we were able to estimate the carrier frequencies and the proportions of potential patients. For autosomal recessive bone dysplasias, we detected 198 pathogenic variants of 54 causative genes. We estimated the variant carrier frequencies and the proportions of potential patients with variants associated with four clinically important bone dysplasias: osteogenesis imperfecta (OI), hypophosphatasia (HPP), asphyxiating thoracic dysplasia (ATD), and Ellis–van Creveld syndrome (EvC). The proportions of potential patients with OI, ATD, and EvC based on pathogenic variants classified as “pathogenic” and “likely pathogenic” by InterVar were closer to the reported incidence rates in Japanese subjects. Furthermore, the proportions of potential patients with HPP variants classified as “pathogenic” and “likely pathogenic” in InterVar and “pathogenic” in ClinVar were closer to the reported incidence rates. For bone dysplasia, the findings of this study will provide a better understanding of the variant types and frequencies in the Japanese general population, and should be useful for clinical diagnosis, genetic counseling, and personalized medicine.

A bioinformatics approach helps estimate carrier frequency of a rare inherited bone disease which causes abnormalities in skeletal shape and structure. Autosomal recessive bone dysplasias affect bone and cartilage development and result from inheriting two mutated genes, one from each parent. Junichi Sugawara, Tohoku University, Sendai, Japan, and colleagues used mutation databases and a bioinformatics tool for variant interpretation to detect 198 pathogenic variants in 54 genes associated with autosomal recessive bone dysplasia in a whole-genome reference panel of 3,552 general Japanese individuals (3.5KJPNv2). They then estimated the frequency of people in the sample carrying bone dysplasia mutations and the expected proportion in whom the disorder could manifest, which compared well with reported incidence rates in the general population. These findings could prove useful for calculating the risk of bone dysplasia in the future children of carrier parents.

Germline and Mosaic Variants in PRKACA and PRKACB Cause a Multiple Congenital Malformation Syndrome

PRKACA and PRKACB code for two catalytic subunits (Cα and Cβ) of cAMP-dependent protein kinase (PKA), a pleiotropic holoenzyme that regulates numerous fundamental biological processes such as metabolism, development, memory, and immune response. We report seven unrelated individuals presenting with a multiple congenital malformation syndrome in whom we identified heterozygous germline or mosaic missense variants in PRKACA or PRKACB. Three affected individuals were found with the same PRKACA variant, and the other four had different PRKACB mutations. In most cases, the mutations arose de novo, and two individuals had offspring with the same condition. Nearly all affected individuals and their affected offspring shared an atrioventricular septal defect or a common atrium along with postaxial polydactyly. Additional features included skeletal abnormalities and ectodermal defects of variable severity in five individuals, cognitive deficit in two individuals, and various unusual tumors in one individual. We investigated the structural and functional consequences of the variants identified in PRKACA and PRKACB through the use of several computational and experimental approaches, and we found that they lead to PKA holoenzymes which are more sensitive to activation by cAMP than are the wild-type proteins. Furthermore, expression of PRKACA or PRKACB variants detected in the affected individuals inhibited hedgehog signaling in NIH 3T3 fibroblasts, thereby providing an underlying mechanism for the developmental defects observed in these cases. Our findings highlight the importance of both Cα and Cβ subunits of PKA during human development.

Common atrium/atrioventricular canal defect and postaxial polydactyly: A mild clinical subtype of Ellis-van Creveld syndrome caused by hypomorphic mutations in the EVC gene

Clinical expression of Ellis-van Creveld syndrome (EvC) is variable and mild phenotypes have been described, including patients with mostly cardiac and limb involvement. Whether these cases are part of the EvC phenotypic spectrum or separate conditions is disputed. Herein, we describe a family with vertical transmission of atrioventricular canal defect (AVCD), common atrium, and postaxial polydactyly. Targeted sequencing of EVC, EVC2, WDR35, DYNC2LI1, and DYNC2H1 identified different compound heterozygosity in EVC genotypes in the two affected members, consisting of a nonsense (p.Arg622Ter) and a missense (p.Arg663Pro) variant in the father, and the same nonsense variant and a noncanonical splice-site in-frame change (c.1316-7A>G) in the daughter. Complementary DNA sequencing, immunoblot, and immunofluorescence experiments using patient-derived fibroblasts and Evc^-/- mouse embryonic fibroblasts showed that p.Arg622Ter is a loss-of-function mutation, whereas p.Arg663Pro and the splice-site change c.1316-7A>G are hypomorphic variants resulting in proteins that retain, in part, the ability to complex with EVC2. Our molecular and functional data demonstrate that at least in some cases the condition characterized as "common atrium/AVCD with postaxial polydactyly" is a mild form of EvC due to hypomorphic EVC mutations, further supporting the occurrence of genotype-phenotype correlations in this 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.

Sox21 Regulates Anapc10 Expression and Determines the Fate of Ectodermal Organ

The transcription factor Sox21 is expressed in the epithelium of developing teeth. The present study aimed to determine the role of Sox21 in tooth development. We found that disruption of Sox21 caused severe enamel hypoplasia, regional osteoporosis, and ectopic hair formation in the gingiva in Sox21 knockout incisors. Differentiation markers were lost in ameloblasts, which formed hair follicles expressing hair keratins. Molecular analysis and chromatin immunoprecipitation sequencing indicated that Sox21 regulated Anapc10, which recognizes substrates for ubiquitination-mediated degradation, and determined dental-epithelial versus hair follicle cell fate. Disruption of either Sox21 or Anapc10 induced Smad3 expression, accelerated TGF-β1-induced promotion of epithelial-to-mesenchymal transition (EMT), and resulted in E-cadherin degradation via Skp2. We conclude that Sox21 disruption in the dental epithelium leads to the formation of a unique microenvironment promoting hair formation and that Sox21 controls dental epithelial differentiation and enamel formation by inhibiting EMT via Anapc10.

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Sox21 was induced by Shh in dental epithelial cells

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Sox21 deficiency in dental epithelium caused differentiation into hair cells

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Sox21 deficiency did not cause differentiation into mature ameloblasts

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Anapc10 induced by Sox21 bound to Fzr1 and regulated EMT via Skp2

Bi-allelic Variations of SMO in Humans Cause a Broad Spectrum of Developmental Anomalies Due to Abnormal Hedgehog Signaling

The evolutionarily conserved hedgehog (Hh) pathway is essential for organogenesis and plays critical roles in postnatal tissue maintenance and renewal. A unique feature of the vertebrate Hh pathway is that signal transduction requires the primary cilium (PC) where major pathway components are dynamically enriched. These factors include smoothened (SMO) and patched, which constitute the core reception system for sonic hedgehog (SHH) as well as GLI transcription factors, the key mediators of the pathway. Here, we report bi-allelic loss-of-function variations in SMO in seven individuals from five independent families; these variations cause a wide phenotypic spectrum of developmental anomalies affecting the brain (hypothalamic hamartoma and microcephaly), heart (atrioventricular septal defect), skeleton (postaxial polydactyly, narrow chest, and shortening of long bones), and enteric nervous system (aganglionosis). Cells derived from affected individuals showed normal ciliogenesis but severely altered Hh-signal transduction as a result of either altered PC trafficking or abnormal activation of the pathway downstream of SMO. In addition, Hh-independent GLI2 accumulation at the PC tip in cells from the affected individuals suggests a potential function of SMO in regulating basal ciliary trafficking of GLI2 when the pathway is off. Thus, loss of SMO function results in abnormal PC dynamics of key components of the Hh signaling pathway and leads to a large continuum of malformations in humans.

Ellis-van Creveld syndrome: Report of a case and recurrent variant

BACKGROUND

Ellis-van Creveld syndrome (EvCS) is a rare autosomal recessive skeletal dysplasia that is characterized by short stature, short limbs, short ribs, polydactyly and structural heart defect. Despite locus heterogeneity, in the majority of the cases, the disorder segregates with mutations in the EVC and EVC2 genes, notably mutations with truncating protein as a final sequence. In the present study, we report the prenatal findings and genetic analysis of a terminated pregnancy affected by severe thoracic and skeletal dysplasia.

METHODS

After detailed physical and clinical examination, whole exome sequencing (WES) was performed and the variant was confirmed by Sanger sequencing.

RESULTS

One homozygote variant in EVC2 gene was identified in the fetus (NM_147127, c.942G>A, p.W314X). The EVC2 gene is strongly associated with EvCS, which is consistent with the sonographic findings of the fetus.

CONCLUSIONS

The homozygous p.W314X mutation found in this family was recently reported to be segregated in a consanguineous family originating from Pakistan. The occurrence of the p.W314X mutation in two unrelated families (Iranian and Pakistani) may be the result of an old founder effect or arose because of a mutational hotspot and is supporting evidence for the pathogenicity of this variant. Because skeletal dysplasia belongs to a broad spectrum of syndromes and therefore exhibits considerable background locus and allelic heterogeneity, our report highlights the need for appropriate genetic counseling and supports the feasibility of WES to determine an accurate diagnosis, as well as precise recurrence risk prediction.

Genetic Basis for Congenital Heart Disease: Revisited: A Scientific Statement From the American Heart Association

This review provides an updated summary of the state of our knowledge of the genetic contributions to the pathogenesis of congenital heart disease. Since 2007, when the initial American Heart Association scientific statement on the genetic basis of congenital heart disease was published, new genomic techniques have become widely available that have dramatically changed our understanding of the causes of congenital heart disease and, clinically, have allowed more accurate definition of the pathogeneses of congenital heart disease in patients of all ages and even prenatally. Information is presented on new molecular testing techniques and their application to congenital heart disease, both isolated and associated with other congenital anomalies or syndromes. Recent advances in the understanding of copy number variants, syndromes, RASopathies, and heterotaxy/ciliopathies are provided. Insights into new research with congenital heart disease models, including genetically manipulated animals such as mice, chicks, and zebrafish, as well as human induced pluripotent stem cell-based approaches are provided to allow an understanding of how future research breakthroughs for congenital heart disease are likely to happen. It is anticipated that this review will provide a large range of health care-related personnel, including pediatric cardiologists, pediatricians, adult cardiologists, thoracic surgeons, obstetricians, geneticists, genetic counselors, and other related clinicians, timely information on the genetic aspects of congenital heart disease. The objective is to provide a comprehensive basis for interdisciplinary care for those with congenital heart disease.

A severe form of Ellis-van Creveld syndrome caused by novel mutations in EVC2

Ellis-van Creveld syndrome (EvC MIM. #225500) is an autosomal recessive skeletal dysplasia characterised by thoracic hypoplasia, cardiac anomalies, acromesomelic limb shortening, and postaxial polydactyly. Affected individuals commonly manifest with cardiorespiratory failure as neonates but generally survive neonatal difficulties. We report here on affected Japanese sibs with a lethal phenotype of EvC caused by novel compound heterozygous mutations of EVC2, c.871-3 C > G and c.1991dupA.

A Ciliary Protein EVC2/LIMBIN Plays a Critical Role in the Skull Base for Mid-Facial Development

Ellis-van Creveld (EvC) syndrome is an autosomal recessive chondrodysplastic disorder. Affected patients present a wide spectrum of symptoms including short stature, postaxial polydactyly, and dental abnormalities. We previously disrupted Evc2, one of the causative genes for EvC syndrome, in mice using a neural crest-specific, Cre-mediated approach (i.e., P0-Cre, referred to as Evc2 P0 mutants). Despite the fact that P0-Cre predominantly targets the mid-facial region, we reported that many mid-facial defects identified in Evc2 global mutants are not present in Evc2 P0 mutants at postnatal day 8 (P8). In the current study, we used multiple Cre lines (P0-Cre and Wnt1-Cre, respectively), to specifically delete Evc2 in neural crest-derived tissues and compared the resulting mid-facial defects at multiple time points (P8 and P28, respectively). While both Cre lines indistinguishably targeted the mid-facial region, they differentially targeted the anterior portion of the skull base. By comprehensively analyzing the shapes of conditional mutant skulls, we detected differentially affected mid-facial defects in Evc2 P0 mutants and Evc2 Wnt1 mutants. Micro-CT analysis of the skull base further revealed that the Evc2 mutation leads to a differentially affected skull base, caused by premature closure of the intersphenoid synchondrosis (presphenoidal synchondrosis), which limited the elongation of the anterior skull base during the postnatal development of the skull. Given the importance of the skull base in mid-facial bone development, our results suggest that loss of function of Evc2 within the skull base secondarily leads to many aspects of the mid-facial defects developed by the EvC syndrome.

GLI1 inactivation is associated with developmental phenotypes overlapping with Ellis-van Creveld syndrome

GLI1, GLI2 and GLI3 form a family of transcription factors which regulate development by mediating the action of Hedgehog (Hh) morphogens. Accordingly, inactivating variants in GLI2 and GLI3 are found in several developmental disorders. In contrast, loss-of-function mutations in GLI1 have remained elusive, maintaining enigmatic the role of this gene in the human embryo. We describe eight patients from three independent families having biallelic truncating variants in GLI1 and developmental defects overlapping with Ellis-van Creveld syndrome (EvC), a disease caused by diminished Hh signaling. Two families had mutations in the last exon of the gene and a third family was identified with an N-terminal stop gain variant predicted to be degraded by the NMD-pathway. Analysis of fibroblasts from one of the patients with homozygous C-terminal truncation of GLI1 demonstrated that the corresponding mutant GLI1 protein is fabricated by patient cells and becomes upregulated in response to Hh signaling. However, the transcriptional activity of the truncated GLI1 factor was found to be severely impaired by cell culture and in vivo assays, indicating that the balance between GLI repressors and activators is altered in affected subjects. Consistent with this, reduced expression of the GLI target PTCH1 was observed in patient fibroblasts after chemical induction of the Hh pathway. We conclude that GLI1 inactivation is associated with a phenotypic spectrum extending from isolated postaxial polydactyly to an EvC-like condition.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Sending mixed signals: Cilia-dependent signaling during development and disease

Molecular signals are the guiding force of development, imparting direction upon cells to divide, migrate, differentiate, etc. The mechanisms by which a cell can receive and transduce these signals into measurable actions remains a 'black box' in developmental biology. Primary cilia are ubiquitous, microtubule-based organelles that dynamically extend from a cell to receive and process molecular and mechanical signaling cues. In the last decade, this organelle has become increasingly intriguing to the research community due to its ability to act as a cellular antenna, receive and transduce molecular stimuli, and initiate a cellular response. In this review, we discuss the structure of primary cilia, emphasizing how the ciliary components contribute to the transduction of signaling pathways. Furthermore, we address how the cilium integrates these signals and conveys them into cellular processes such as proliferation, migration and tissue patterning. Gaining a deeper understanding of the mechanisms used by primary cilia to receive and integrate molecular signals is essential, as it opens the door for the identification of therapeutic targets within the cilium that could alleviate pathological conditions brought on by aberrant molecular signaling.

Biallelic mutations in DYNC2LI1 are a rare cause of Ellis-van Creveld syndrome

Ellis-van Creveld syndrome (EvC) is a chondral and ectodermal dysplasia caused by biallelic mutations in the EVC, EVC2 and WDR35 genes. A proportion of cases with clinical diagnosis of EvC, however, do not carry mutations in these genes. To identify the genetic cause of EvC in a cohort of mutation-negative patients, exome sequencing was undertaken in a family with 3 affected members, and mutation scanning of a panel of clinically and functionally relevant genes was performed in 24 additional subjects with features fitting/overlapping EvC. Compound heterozygosity for the c.2T>C (p.Met1?) and c.662C>T (p.Thr221Ile) variants in DYNC2LI1, which encodes a component of the intraflagellar transport-related dynein-2 complex previously found mutated in other short-rib thoracic dysplasias, was identified in the 3 affected members of the first family. Targeted resequencing detected compound heterozygosity for the same missense variant and a truncating change (p.Val141*) in 2 siblings with EvC from a second family, while a newborn with a more severe phenotype carried 2 DYNC2LI1 truncating variants. Our findings indicate that DYNC2LI1 mutations are associated with a wider clinical spectrum than previously appreciated, including EvC, with the severity of the phenotype likely depending on the extent of defective DYNC2LI1 function.

Phenotypic Variation in Patients with Homozygous c.1678G>T Mutation in EVC Gene: Report of Two Mexican Families with Ellis-van Creveld Syndrome

Case series

Patient: —

Final Diagnosis: Ellis van Creveld syndrome

Symptoms: Conical teeth • polydactyly • short stature

Medication: —

Clinical Procedure: —

Specialty: Pediatrics and Neonatology

Dual Diagnosis of Ellis-van Creveld Syndrome and Hearing Loss in a Consanguineous Family

Multilocus analysis of rare or genetically heterogeneous diseases is a distinct advantage of next-generation sequencing (NGS) over conventional single-gene investigations. Recent studies have begun to uncover an under-recognized prevalence of dual molecular diagnoses in patients with a "blended" phenotype that is the result of 2 clinical diagnoses involving 2 separate genetic loci. This blended phenotype could be mistakenly interpreted as a novel clinical extension of a single-gene disorder. In this study, we ascertained a proband from a large consanguineous Iranian family who manifests postlingual, progressive, moderate hearing loss in addition to suspected Ellis-van Creveld syndrome phenotype. NGS with a customized skeletal dysplasia panel containing over 370 genes and subsequent bioinformatics analysis disclosed 2 homozygous mutations in EVC2 (c.2653C>T; p.Arg885*) and COL11A2 (c.966dup; p.Thr323Hisfs*19), respectively. This study highlights a dual molecular diagnosis in a patient with a blending of 2 distinct phenotypes and illustrates the advantage and importance of this staple technology to facilitate rapid and comprehensive genetic dissection of a heterogeneous phenotype. The differentiation between phenotypic expansion of a genetic disorder and a blended phenotype that is due to more than one distinct genetic aberration is essential in order to reduce the diagnostic odyssey endured by patients.

The Role of Ellis-Van Creveld 2(EVC2) in Mice During Cranial Bone Development

EvC syndrome is a type of autosomal-recessive chondrodysplasia. Previous case studies in patients suggest abnormal craniofacial development, in addition to dwarfism and tooth abnormalities. To investigate how craniofacial development is affected in EvC patients, surface models were generated from micro-CT scans of control mice, Evc2 global mutant mice and Evc2 neural crest-specific mutant mice. The anatomic landmarks were placed on the surface model to assess the morphological abnormalities in the Evc2 mutants. Through analyzing the linear and angular measurements between landmarks, we identified a smaller overall skull, shorter nasal bone, shorter frontal bone, and shorter cranial base in the Evc2 global mutants. By comparing neural crest-specific Evc2 mutants with control mice, we demonstrated that the abnormalities within the mid-facial regions are not accounted for by the Evc2 mutation within these regions. Additionally, we also identified disproportionate length to width ratios in the Evc2 mutants at all levels from anterior to posterior of the skull. Overall, this study demonstrates a more comprehensive analysis on the craniofacial morphological abnormalities in EvC syndrome and provides the developmental insight to appreciate the impact of Evc2 mutation within the neural crest cells on multiple aspects of skull deformities. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:46-55, 2018. © 2017 Wiley Periodicals, Inc.

Role of Primary Cilia in Odontogenesis

Primary cilium is a solitary organelle that emanates from the surface of most postmitotic mammalian cells and serves as a sensory organelle, transmitting the mechanical and chemical cues to the cell. Primary cilia are key coordinators of various signaling pathways during development and maintenance of tissue homeostasis. The emerging evidence implicates primary cilia function in tooth development. Primary cilia are located in the dental epithelium and mesenchyme at early stages of tooth development and later during cell differentiation and production of hard tissues. The cilia are present when interactions between both the epithelium and mesenchyme are required for normal morphogenesis. As the primary cilium coordinates several signaling pathways essential for odontogenesis, ciliary defects can interrupt the latter process. Genetic or experimental alterations of cilia function lead to various developmental defects, including supernumerary or missing teeth, enamel and dentin hypoplasia, or teeth crowding. Moreover, dental phenotypes are observed in ciliopathies, including Bardet-Biedl syndrome, Ellis-van Creveld syndrome, Weyers acrofacial dysostosis, cranioectodermal dysplasia, and oral-facial-digital syndrome, altogether demonstrating that primary cilia play a critical role in regulation of both the early odontogenesis and later differentiation of hard tissue-producing cells. Here, we summarize the current evidence for the localization of primary cilia in dental tissues and the impact of disrupted cilia signaling on tooth development in ciliopathies.

Primary Cilia and Mammalian Hedgehog Signaling

It has been a decade since it was discovered that primary cilia have an essential role in Hedgehog (Hh) signaling in mammals. This discovery came from screens in the mouse that identified a set of genes that are required for both normal Hh signaling and for the formation of primary cilia. Since then, dozens of mouse mutations have been identified that disrupt cilia in a variety of ways and have complex effects on Hedgehog signaling. Here, we summarize the genetic and developmental studies used to deduce how Hedgehog signal transduction is linked to cilia and the complex effects that perturbation of cilia structure can have on Hh signaling. We conclude by describing the current status of our understanding of the cell-type-specific regulation of ciliogenesis and how that determines the ability of cells to respond to Hedgehog ligands.

Mutations in IFT-A satellite core component genes IFT43 and IFT121 produce short rib polydactyly syndrome with distinctive campomelia

Background

Skeletal ciliopathies comprise a spectrum of ciliary malfunction disorders that have a profound effect on the skeleton. Most common among these disorders is short rib polydactyly syndrome (SRPS), a recessively inherited perinatal lethal condition characterized by a long narrow chest, markedly shortened long bones, polydactyly and, often, multi-organ system involvement. SRPS shows extensive locus heterogeneity with mutations in genes encoding proteins that participate in cilia formation and/or function.

Results

Herein we describe mutations in IFT43, a satellite member of the retrograde IFT-A complex, that produce a form of SRPS with unusual bending of the ribs and appendicular bones. These newly described IFT43 mutations disrupted cilia formation, produced abnormalities in cartilage growth plate architecture thus contributing to altered endochondral ossification. We further show that the IFT43 SRPS phenotype is similar to SRPS resulting from mutations in the gene encoding IFT121 (WDR35), a direct interactor with IFT43.

Conclusions

This study defines a new IFT43-associated phenotype, identifying an additional locus for SRPS. The data demonstrate that IFT43 is essential for ciliogenesis and that the mutations disrupted the orderly proliferation and differentiation of growth plate chondrocytes, resulting in a severe effect on endochondral ossification and mineralization. Phenotypic similarities with SRPS cases resulting from mutations in the gene encoding the IFT43 direct interacting protein IFT121 suggests that similar mechanisms may be disrupted by defects in these two IFT-A satellite interactors.

Electronic supplementary material

The online version of this article (doi:10.1186/s13630-017-0051-y) contains supplementary material, which is available to authorized users.

Loss of Function of Evc2 in Dental Mesenchyme Leads to Hypomorphic Enamel

Ellis-van Creveld (EvC) syndrome is an autosomal-recessive skeletal dysplasia, characterized by short stature and postaxial polydactyly. A series of dental abnormalities, including hypomorphic enamel formation, has been reported in patients with EvC. Despite previous studies that attempted to uncover the mechanism leading to abnormal tooth development, little is known regarding how hypomorphic enamel is formed in patients with EvC. In the current study, using Evc2/ Limbin mutant mice we recently generated, we analyzed enamel formation in the mouse incisor. Consistent with symptoms in human patients, we observed that Evc2 mutant mice had smaller incisors with enamel hypoplasia. Histologic observations coupled with ameloblast marker analyses suggested that Evc2 mutant preameloblasts were capable of differentiating to secretory ameloblasts; this process, however, was apparently delayed, due to delayed odontoblast differentiation, mediated by a limited number of dental mesenchymal stem cells in Evc2 mutant mice. This concept was further supported by the observation that dental mesenchymal-specific deletion of Evc2 phenocopied the tooth abnormalities in Evc2 mutants. Overall, our findings suggest that mutations in Evc2 affect dental mesenchymal stem cell homeostasis, which further leads to hypomorphic enamel formation.

Elevated Fibroblast Growth Factor Signaling Is Critical for the Pathogenesis of the Dwarfism in Evc2/Limbin Mutant Mice

Ellis-van Creveld (EvC) syndrome is a skeletal dysplasia, characterized by short limbs, postaxial polydactyly, and dental abnormalities. EvC syndrome is also categorized as a ciliopathy because of ciliary localization of proteins encoded by the two causative genes, EVC and EVC2 (aka LIMBIN). While recent studies demonstrated important roles for EVC/EVC2 in Hedgehog signaling, there is still little known about the pathophysiological mechanisms underlying the skeletal dysplasia features of EvC patients, and in particular why limb development is affected, but not other aspects of organogenesis that also require Hedgehog signaling. In this report, we comprehensively analyze limb skeletogenesis in Evc2 mutant mice and in cell and tissue cultures derived from these mice. Both in vivo and in vitro data demonstrate elevated Fibroblast Growth Factor (FGF) signaling in Evc2 mutant growth plates, in addition to compromised but not abrogated Hedgehog-PTHrP feedback loop. Elevation of FGF signaling, mainly due to increased Fgf18 expression upon inactivation of Evc2 in the perichondrium, critically contributes to the pathogenesis of limb dwarfism. The limb dwarfism phenotype is partially rescued by inactivation of one allele of Fgf18 in the Evc2 mutant mice. Taken together, our data uncover a novel pathogenic mechanism to understand limb dwarfism in patients with Ellis-van Creveld syndrome.

Ellis-van Creveld syndrome in adulthood: extending the clinical spectrum

Ellis-van Creveld (EvC) syndrome is a rare autosomal recessive malformation disorder. Cardiac defects are observed in about 50% of EvC cases. Surgical data is lacking on the prognosis and life expectancy of EvC patients. Herein, we report the case of a 38-year-old man with EvC syndrome who underwent two surgical corrections for cardiac anomalies. This report supplements the available information on the clinical course of EvC syndrome in older patients.

Ellis-Van Creveld syndrome in siblings: A rare case report

Ellis-Van Creveld syndrome or chondroectodermal dysplasia is a rare autosomal recessive disorder presenting several skeletal manifestations and congenital heart malformations. Ellis-Van Creveld syndrome comprises of a tetrad of clinical manifestations of chondrodysplasia, polydactyly, ectodermal dysplasia, and cardiac defects. Here, we are presenting a very rare case of Ellis-Van Creveld syndrome in siblings.

Destabilization of the IFT-B cilia core complex due to mutations in IFT81 causes a Spectrum of Short-Rib Polydactyly Syndrome

Short-rib polydactyly syndromes (SRPS) and Asphyxiating thoracic dystrophy (ATD) or Jeune Syndrome are recessively inherited skeletal ciliopathies characterized by profound skeletal abnormalities and are frequently associated with polydactyly and multiorgan system involvement. SRPS are produced by mutations in genes that participate in the formation and function of primary cilia and usually result from disruption of retrograde intraflagellar (IFT) transport of the cilium. Herein we describe a new spectrum of SRPS caused by mutations in the gene IFT81, a key component of the IFT-B complex essential for anterograde transport. In mutant chondrocytes, the mutations led to low levels of IFT81 and mutant cells produced elongated cilia, had altered hedgehog signaling, had increased post-translation modification of tubulin, and showed evidence of destabilization of additional anterograde transport complex components. These findings demonstrate the importance of IFT81 in the skeleton, its role in the anterograde transport complex, and expand the number of loci associated with SRPS.

Cilia gene mutations cause atrioventricular septal defects by multiple mechanisms

Atrioventricular septal defects (AVSDs) are a common severe form of congenital heart disease (CHD). In this study we identified deleterious non-synonymous mutations in two cilia genes, Dnah11 and Mks1, in independent N-ethyl-N-nitrosourea-induced mouse mutant lines with heritable recessive AVSDs by whole-exome sequencing. Cilia are required for left/right body axis determination and second heart field (SHF) Hedgehog (Hh) signaling, and we find that cilia mutations affect these requirements differentially. Dnah11^avc4 did not disrupt SHF Hh signaling and caused AVSDs only concurrently with heterotaxy, a left/right axis abnormality. In contrast, Mks1^avc6 disrupted SHF Hh signaling and caused AVSDs without heterotaxy. We performed unbiased whole-genome SHF transcriptional profiling and found that cilia motility genes were not expressed in the SHF whereas cilia structural and signaling genes were highly expressed. SHF cilia gene expression predicted the phenotypic concordance between AVSDs and heterotaxy in mice and humans with cilia gene mutations. A two-step model of cilia action accurately predicted the AVSD/heterotaxyu phenotypic expression pattern caused by cilia gene mutations. We speculate that cilia gene mutations contribute to both syndromic and non-syndromic AVSDs in humans and provide a model that predicts the phenotypic consequences of specific cilia gene mutations.

Oral and craniofacial manifestations of Ellis-van Creveld syndrome: Case series

PURPOSE

The objective of this case series was to determine the oral, dental and craniofacial features of patients with EvC syndrome.

MATERIAL AND METHODS

Eight patients with EvC syndrome were enrolled. A complete family history, pedigree analysis, detailed medical history were collected. Findings of clinical examination, including craniofacial and orodental manifestations, and radiological investigations were thoroughly studied.

RESULTS

All eight patients had characteristic face, hypertrophic frenulum, conical and peg-shaped teeth, hypodontia of deciduous and/or permanent teeth and also skeletal dysplasia, small chest, short stature and hypoplastic nails. Additionally dysmorphic filtrum, serrated appearance of gingiva, diastema, enamel hypoplasia, microdontia, taurodontism, single rooted permanent molar, delayed eruption and high caries rate were observed with varying degrees. Cephalometric evaluation revealed skeletal Class III growth pattern in four subjects and Class II growth pattern in one subject.

CONCLUSION

Evaluation of craniofacial and orodental anomalies of EvC syndrome is required for accurate differential diagnosis from other congenital syndromes.

Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as a Model for Heart Development and Congenital Heart Disease

Congenital heart disease (CHD) remains a significant health problem, with a growing population of survivors with chronic disease. Despite intense efforts to understand the genetic basis of CHD in humans, the etiology of most CHD is unknown. Furthermore, new models of CHD are required to better understand the development of CHD and to explore novel therapies for this patient population. In this review, we highlight the role that human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes can serve to enhance our understanding of the development, pathophysiology and potential therapeutic targets for CHD. We highlight the use of hiPSC-derived cardiomyocytes to model gene regulatory interactions, cell-cell interactions and tissue interactions contributing to CHD. We further emphasize the importance of using hiPSC-derived cardiomyocytes as personalized research models. The use of hiPSCs presents an unprecedented opportunity to generate disease-specific cellular models, investigate the underlying molecular mechanisms of disease and uncover new therapeutic targets for CHD.

Expression of Evc2 in craniofacial tissues and craniofacial bone defects in Evc2 knockout mouse

OBJECTIVE

Our objectives were to determine the expression of EVC2 in craniofacial tissues and investigate the effect of Evc2 deficiency on craniofacial bones using Evc2 knockout (KO) mouse model.

DESIGN

Evc2 KO mice were generated by introducing a premature stop codon followed by the Internal Ribosomal Entry Site fused to β-galactosidase (LacZ). Samples from wild-type (WT), heterozygous (Het) and homozygous Evc2 KO mice were prepared. LacZ staining and immunohistochemistry (IHC) with anti-β-galactosidase, anti-EVC2 and anti-SOX9 antibodies were performed. The craniofacial bones were stained with alcian blue and alizarin red.

RESULTS

The LacZ activity in KO was mainly observed in the anterior parts of viscerocranium. The Evc2-expressing cells were identified in many cartilageous regions by IHC with anti-β-galactosidase antibody in KO and Het embryos. The endogenous EVC2 protein was observed in these areas in WT embryos. Double labeling with anti-SOX9 antibody showed that these cells were mainly chondrocytes. At adult stages, the expression of EVC2 was found in chondrocytes of nasal bones and spheno-occipital synchondrosis, and osteocytes and endothelial-like cells of the premaxilla and mandible. The skeletal double staining demonstrated that craniofacial bones, where the expression of EVC2 was observed, in KO had the morphological defects as compared to WT.

CONCLUSION

To our knowledge, our study was the first to identify the types of Evc2-expressing cells in craniofacial tissues. Consistent with the expression pattern, abnormal craniofacial bone morphology was found in the Evc2 KO mice, suggesting that EVC2 may be important during craniofacial growth and development.

Ellis Van Creveld2 is Required for Postnatal Craniofacial Bone Development

Ellis-van Creveld (EvC) syndrome is a genetic disorder with mutations in either EVC or EVC2 gene. Previous case studies reported that EvC patients underwent orthodontic treatment, suggesting the presence of craniofacial bone phenotypes. To investigate whether a mutation in EVC2 gene causes a craniofacial bone phenotype, Evc2 knockout (KO) mice were generated and cephalometric analysis was performed. The heads of wild type (WT), heterozygous (Het) and homozygous Evc2 KO mice (1-, 3-, and 6-week-old) were prepared and cephalometric analysis based on the selected reference points on lateral X-ray radiographs was performed. The linear and angular bone measurements were then calculated, compared between WT, Het and KO and statistically analyzed at each time point. Our data showed that length of craniofacial bones in KO was significantly lowered by ∼20% to that of WT and Het, the growth of certain bones, including nasal bone, palatal length, and premaxilla was more affected in KO, and the reduction in these bone length was more significantly enhanced at later postnatal time points (3 and 6 weeks) than early time point (1 week). Furthermore, bone-to-bone relationship to cranial base and cranial vault in KO was remarkably changed, i.e. cranial vault and nasal bone were depressed and premaxilla and mandible were developed in a more ventral direction. Our study was the first to show the cause-effect relationship between Evc2 deficiency and craniofacial defects in EvC syndrome, demonstrating that Evc2 is required for craniofacial bone development and its deficiency leads to specific facial bone growth defect. Anat Rec, 299:1110-1120, 2016. © 2016 Wiley Periodicals, Inc.

Hedgehog receptor function during craniofacial development

The Hedgehog signalling pathway plays a fundamental role in orchestrating normal craniofacial development in vertebrates. In particular, Sonic hedgehog (Shh) is produced in three key domains during the early formation of the head; neuroectoderm of the ventral forebrain, facial ectoderm and the pharyngeal endoderm; with signal transduction evident in both ectodermal and mesenchymal tissue compartments. Shh signalling from the prechordal plate and ventral midline of the diencephalon is required for appropriate division of the eyefield and forebrain, with mutation in a number of pathway components associated with Holoprosencephaly, a clinically heterogeneous developmental defect characterized by a failure of the early forebrain vesicle to divide into distinct halves. In addition, signalling from the pharyngeal endoderm and facial ectoderm plays an essential role during development of the face, influencing cranial neural crest cells that migrate into the early facial processes. In recent years, the complexity of Shh signalling has been highlighted by the identification of multiple novel proteins that are involved in regulating both the release and reception of this protein. Here, we review the contributions of Shh signalling during early craniofacial development, focusing on Hedgehog receptor function and describing the consequences of disruption for inherited anomalies of this region in both mouse models and human populations.