Craniofacial Phenotype Research Articles

The etiology, clinical features, and treatment options of hemifacial microsomia.

The second most frequent craniomaxillofacial congenital deformity is hemifacial microsomia (HFM). Patients often accompany short mandible, ear dysplasia, facial nerve, and soft tissue dysplasia. The etiology of HFM is not fully understood. To organize the possible up-to-date information on the etiology, craniofacial phenotypes, and therapeutic alternatives in order to fully comprehend the HFM. Reviewing the potential causes, exploring the clinical features of HFM and summarizing the available treatment options. Vascular malformation, Meckel's cartilage abnormalities, and cranial neural crest cells (CNCCs) abnormalities are three potential etiology hypotheses. The commonly used clinical classification for HFM is OMENS, OMENS-plus, and SAT. Other craniofacial anomalies, like dental defects, and zygomatic deformities, are still not precisely documented in the classification. Patients with moderate phenotypes may not need any treatment from infancy through adulthood. However, patients with severe HFM require to undergo multiple surgeries to address facial asymmetries, such as mandibular distraction osteogenesis (MDO), autologous costochondral rib graft (CCG), orthodontic and orthognathic treatment, and facial soft tissue reconstruction. It is anticipated that etiology research will examine the pathogenic mechanism of HFM. A precise treatment for HFM may be possible with thoroughly documented phenotypes and a pathogenic diagnosis.

Role of craniofacial phenotypes in the response to oral appliance therapy for obstructive sleep apnea.

Mandibular advancement device (MAD) is a good alternative for patients with obstructive sleep apnea (OSA). However, the treatment response varies among individuals. This study aimed to explore the role of craniofacial features in the response to MADs to improve prognostication and patient selection. The retrospective trial contained 42 males aged 41.5±9.0 years, and with an apnea-hypopnea index (AHI) of 21.5±13.8 events/h. According to the mandibular plane angle, participants were divided into three groups: low angle (n=13), average angle (n=14), and high angle (n=15). Under monitor of home sleep testing, adjustable MADs were used to titrate the mandible forward from 0 mm with an increment of 0.5 mm every day. The polysomnography outcomes, mandibular protrusion amounts, changes in upper airway MRI measurements, and nasal resistance were compared among three groups. The normalization rate (AHI < 5 /h) was 92.3%, 57.1%, and 46.7% respectively in the low, average, and high angle groups (p=0.027). The effective protrusion where AHI was reduced by half was 20 (11.3~37.5) %, 31.3 (23.6~50) %, and 50 (36.9~64.9) % of the maximal mandibular protrusion, in the low, average, and high angle groups (p=0.004). Multivariate logistic regression revealed that increased gonion angle (OR=0.878) and baseline AHI(OR=0.868) can reduce the probability of normalization. The high mandibular plane angle might be an unfavorable factor to MAD treatment and more protrusion was needed to achieve a 50% reduction in AHI. Vertical craniofacial pattern (gonion angle) and baseline AHI constituted the model for predicting the effect of MADs.

Predicting Modifiers of Genotype-Phenotype Correlations in Craniofacial Development.

Most human birth defects are phenotypically variable even when they share a common genetic basis. Our understanding of the mechanisms of this variation is limited, but they are thought to be due to complex gene-environment interactions. Loss of the transcription factor Gata3 associates with the highly variable human birth defects HDR syndrome and microsomia, and can lead to disruption of the neural crest-derived facial skeleton. We have demonstrated that zebrafish gata3 mutants model the variability seen in humans, with genetic background and candidate pathways modifying the resulting phenotype. In this study, we sought to use an unbiased bioinformatic approach to identify environmental modifiers of gata3 mutant craniofacial phenotypes. The LINCs L1000 dataset identifies chemicals that generate differential gene expression that either positively or negatively correlates with an input gene list. These chemicals are predicted to worsen or lessen the mutant phenotype, respectively. We performed RNA-seq on neural crest cells isolated from zebrafish across control, Gata3 loss-of-function, and Gata3 rescue groups. Differential expression analyses revealed 551 potential targets of gata3. We queried the LINCs database with the 100 most upregulated and 100 most downregulated genes. We tested the top eight available chemicals predicted to worsen the mutant phenotype and the top eight predicted to lessen the phenotype. Of these, we found that vinblastine, a microtubule inhibitor, and clofibric acid, a PPAR-alpha agonist, did indeed worsen the gata3 phenotype. The Topoisomerase II and RNA-pol II inhibitors daunorubicin and triptolide, respectively, lessened the phenotype. GO analysis identified Wnt signaling and RNA polymerase function as being enriched in our RNA-seq data, consistent with the mechanism of action of some of the chemicals. Our study illustrates multiple potential pathways for Gata3 function, and demonstrates a systematic, unbiased process to identify modifiers of genotype-phenotype correlations.

Embryonic alcohol exposure disrupts the ubiquitin-proteasome system.

Ethanol (EtOH) is a commonly encountered teratogen that can disrupt organ development and lead to fetal alcohol spectrum disorders (FASDs); many mechanisms of developmental toxicity are unknown. Here, we used transcriptomic analysis in an established zebrafish model of embryonic alcohol exposure (EAE) to identify the ubiquitin-proteasome system (UPS) as a critical target of EtOH during development. Surprisingly, EAE alters 20S, 19S, and 11S proteasome gene expression and increases ubiquitylated protein load. EtOH and its metabolite acetaldehyde decrease proteasomal peptidase activity in a cell type-specific manner. Proteasome 20S subunit β 1 (psmb1hi2939Tg) and proteasome 26S subunit, ATPase 6 (psmc6hi3593Tg), genetic KOs define the developmental impact of decreased proteasome function. Importantly, loss of psmb1 or psmc6 results in widespread developmental abnormalities resembling EAE phenotypes, including growth restriction, abnormal craniofacial structure, neurodevelopmental defects, and failed hepatopancreas maturation. Furthermore, pharmacologic inhibition of chymotrypsin-like proteasome activity potentiates the teratogenic effects of EAE on craniofacial structure, the nervous system, and the endoderm. Our studies identify the proteasome as a target of EtOH exposure and signify that UPS disruptions contribute to craniofacial, neurological, and endodermal phenotypes in FASDs.

Craniofacial and cardiac defects in chd7 zebrafish mutants mimic CHARGE syndrome.

Congenital heart defects occur in almost 80% of patients with CHARGE syndrome, a sporadically occurring disease causing craniofacial and other abnormalities due to mutations in the CHD7 gene. Animal models have been generated to mimic CHARGE syndrome; however, heart defects are not extensively described in zebrafish disease models of CHARGE using morpholino injections or genetic mutants. Here, we describe the co-occurrence of craniofacial abnormalities and heart defects in zebrafish chd7 mutants. These mutant phenotypes are enhanced in the maternal zygotic mutant background. In the chd7 mutant fish, we found shortened craniofacial cartilages and extra cartilage formation. Furthermore, the length of the ventral aorta is altered in chd7 mutants. Many CHARGE patients have aortic arch anomalies. It should be noted that the aberrant branching of the first branchial arch artery is observed for the first time in chd7 fish mutants. To understand the cellular mechanism of CHARGE syndrome, neural crest cells (NCCs), that contribute to craniofacial and cardiovascular tissues, are examined using sox10:Cre lineage tracing. In contrast to its function in cranial NCCs, we found that the cardiac NCC-derived mural cells along the ventral aorta and aortic arch arteries are not affected in chd7 mutant fish. The chd7 fish mutants we generated recapitulate some of the craniofacial and cardiovascular phenotypes found in CHARGE patients and can be used to further determine the roles of CHD7.

Craniofacial phenotyping by photogrammetry in Chinese prepubertal children with obstructive sleep apnea.

This study aimed to examine the craniofacial phenotype of Chinese prepubertal children with and without obstructive sleep apnea (OSA) using a quantitative photographic analysis technique and to develop a prediction model for OSA diagnosis based on the photogrammetric data. Potential ethnic differences in the association between OSA and photogrammetric data between Chinese and Caucasian children were also examined. This was a cross-sectional study. Chinese children aged 5-12 years old, suspected to have OSA were recruited from our sleep clinic. Frontal and side photos were taken for craniofacial phenotyping by photogrammetry. Polysomnography was performed and participants were divided into three groups: non-OSA (obstructive apnea hypopnea index (OAHI) < 1/h), mild OSA (OAHI between 1/h and 5/h), and moderate-to-severe (MS) OSA (OAHI ≥ 5/h). Prediction models were built from 70% of training data using logistic regression and evaluated on the remaining 30% of test data for receiver operating characteristic (ROC) curve construction. This study included 90 participants (mean age: 8.2 ± 1.6 years, 67 males). Non-OSA, mild OSA, and MS OSA groups included 32, 31, and 27 participants, respectively. There were significant trends for an increasing maxillary-mandibular relationship angle (p = .002) and a decreasing anterior mandibular height to whole face length ratio (p < .001) with increasing OSA severity. A prediction model built with clinical measurements and the two photogrammetric features yielded an area under the ROC curve (AUC) of 0.81 (95% C.I.: 0.64-0.96). Craniofacial features obtained by photogrammetry are significantly different between OSA groups in prepubertal children. Increased maxillary-mandibular relationship angle is an OSA feature found in both Asian and Caucasian children.

Bi-allelic CAMSAP1 variants cause a clinically recognizable neuronal migration disorder

Non-centrosomal microtubules are essential cytoskeletal filaments that are important for neurite formation, axonal transport, and neuronal migration. They require stabilization by microtubule minus-end-targeting proteins including the CAMSAP family of molecules. Using exome sequencing on samples from five unrelated families, we show that bi-allelic CAMSAP1 loss-of-function variants cause a clinically recognizable, syndromic neuronal migration disorder. The cardinal clinical features of the syndrome include a characteristic craniofacial appearance, primary microcephaly, severe neurodevelopmental delay, cortical visual impairment, and seizures. The neuroradiological phenotype comprises a highly recognizable combination of classic lissencephaly with a posterior more severe than anterior gradient similar to PAFAH1B1(LIS1)-related lissencephaly and severe hypoplasia or absence of the corpus callosum; dysplasia of the basal ganglia, hippocampus, and midbrain; and cerebellar hypodysplasia, similar to the tubulinopathies, a group of monogenic tubulin-associated disorders of cortical dysgenesis. Neural cell rosette lineages derived from affected individuals displayed findings consistent with these phenotypes, including abnormal morphology, decreased cell proliferation, and neuronal differentiation. Camsap1-null mice displayed increased perinatal mortality, and RNAScope studies identified high expression levels in the brain throughout neurogenesis and in facial structures, consistent with the mouse and human neurodevelopmental and craniofacial phenotypes. Together our findings confirm a fundamental role of CAMSAP1 in neuronal migration and brain development and define bi-allelic variants as a cause of a clinically distinct neurodevelopmental disorder in humans and mice.

Variable paralog expression underlies phenotype variation.

Human faces are variable; we look different from one another. Craniofacial disorders further increase facial variation. To understand craniofacial variation and how it can be buffered, we analyzed the zebrafish mef2ca mutant. When this transcription factor encoding gene is mutated, zebrafish develop dramatically variable craniofacial phenotypes. Years of selective breeding for low and high penetrance of mutant phenotypes produced strains that are either resilient or sensitive to the mef2ca mutation. Here, we compared gene expression between these strains, which revealed that selective breeding enriched for high and low mef2ca paralog expression in the low- and high-penetrance strains, respectively. We found that mef2ca paralog expression is variable in unselected wild-type zebrafish, motivating the hypothesis that heritable variation in paralog expression underlies mutant phenotype severity and variation. In support, mutagenizing the mef2ca paralogs, mef2aa, mef2b, mef2cb, and mef2d demonstrated modular buffering by paralogs. Specifically, some paralogs buffer severity while others buffer variability. We present a novel, mechanistic model for phenotypic variation where variable, vestigial paralog expression buffers development. These studies are a major step forward in understanding the mechanisms of facial variation, including how some genetically resilient individuals can overcome a deleterious mutation.

Early enzyme replacement therapy prevents dental and craniofacial abnormalities in a mouse model of mucopolysaccharidosis type VI.

Mucopolysaccharidosis VI (MPS VI) is a hereditary lysosomal storage disease caused by the absence of the enzyme arylsulfatase B (ARSB). Craniofacial defects are common in MPS VI patients and manifest as abnormalities of the facial bones, teeth, and temporomandibular joints. Although enzyme replacement therapy (ERT) is the treatment of choice for MPS VI, the effects on the craniofacial and dental structures are still poorly understood. In this study, we used an Arsb-deficient mouse model (Arsb m/m ) that mimics MPS VI to investigate the effects of ERT on dental and craniofacial structures and compared these results with clinical and radiological observations from three MPS VI patients. Using micro-computed tomography, we found that the craniofacial phenotype of the Arsb m/m mice was characterized by bone exostoses at the insertion points of the masseter muscles and an overall increased volume of the jaw bone. An early start of ERT (at 4 weeks of age for 20 weeks) resulted in a moderate improvement of these jaw anomalies, while a late start of ERT (at 12 weeks of age for 12 weeks) showed no effect on the craniofacial skeleton. While teeth typically developed in Arsb m/m mice, we observed a pronounced loss of tooth-bearing alveolar bone. This alveolar bone loss, which has not been described before in MPS VI, was also observed in one of the MPS VI patients. Interestingly, only an early start of ERT led to a complete normalization of the alveolar bone in Arsb m/m mice. The temporomandibular joints in Arsb m/m mice were deformed and had a porous articular surface. Histological analysis revealed a loss of physiological cartilage layering, which was also reflected in an altered proteoglycan content in the cartilage of Arsb m/m mice. These abnormalities could only be partially corrected by an early start of ERT. In conclusion, our results show that an early start of ERT in Arsb m/m mice achieves the best therapeutic effects for tooth, bone, and temporomandibular joint development. As the MPS VI mouse model in this study resembles the clinical findings in MPS VI patients, our results suggest enzyme replacement therapy should be started as early as possible.

Mechanical loading of cranial joints minimizes the craniofacial phenotype in Crouzon syndrome

Children with syndromic forms of craniosynostosis undergo a plethora of surgical interventions to resolve the clinical features caused by the premature fusion of cranial sutures. While surgical correction is reliable, the need for repeated rounds of invasive treatment puts a heavy burden on the child and their family. This study explores a non-surgical alternative using mechanical loading of the cranial joints to prevent or delay craniofacial phenotypes associated with Crouzon syndrome. We treated Crouzon syndrome mice before the onset of craniosynostosis by cyclical mechanical loading of cranial joints using a custom designed set-up. Cranial loading applied to the frontal bone partially restores normal skull morphology, significantly reducing the typical brachycephalic appearance. This is underpinned by the delayed closure of the coronal suture and of the intersphenoidal synchondrosis. This study provides a novel treatment alternative for syndromic craniosynostosis which has the potential to be an important step towards replacing, reducing or refining the surgical treatment of all craniosynostosis patients.

Mosaic Evolution of Craniofacial Morphologies in Ghost Electric Fishes (Gymnotiformes: Apteronotidae)

Ghost electric knifefishes (Gymnotiformes: Apteronotidae) are a dominant component of the species diversity and biomass of large lowland rivers in Greater Amazonia, including 77 species that exhibit diverse craniofacial morphologies associated with trophic and secondary sexual traits. Here we use open-source computed micro-tomography (µCT) scans to generate 3D reconstructions for a majority of apteronotid species and almost all valid genera, and geometric morphometric and phylogenetic analyses to explore patterns of skull evolution. As with most vertebrates, principal component 1 (PC1) summarizes variance from brachycephalic to dolichocephalic morphologies, previously described as heterocephaly, and PC2 summarizes variance from recurved (upturned) to decurved (downturned) snout morphologies, described here as heterorhynchy. Phylomorphospace and traitogram analyses found instances of both convergent and divergent evolution along both of the first two PC axes, as well as a preponderance of clades characterized by morphological stasis or phylogenetic conservatism. Certain phenotypic combinations predominate among species and clades, including elongated-downturned snouts and foreshortened-upturned snouts, while other phenotypic combinations are not observed, including elongated-upturned snouts and foreshortened-downturned snouts. These results highlight the power of 3D geometric morphometrics in the study of craniofacial evolution and indicate developmental or functional constraints in the evolution of craniofacial phenotypes in an ecologically dominant clade of riverine Amazonian fishes.

0771 Artificial Intelligence Based Mask Fit Algorithm Application in the Pittsburgh Veteran Population

Abstract Introduction Positive airway pressure (PAP) therapy has been used for obstructive sleep apnea (OSA) since 1980 and remains the treatment of choice for moderate to severe OSA. Proper mask fitting for patient comfort is essential to continued success on PAP therapy, as early adherence rates are strong predictors of future use. Mask selection continues to be challenging given the significant heterogeneity in craniofacial phenotypes and the rapidly growing mask options. Artificial intelligence software has combined survey data and digital photography to algorithmically predict PAP masks for best fit. This study aimed to describe mask failure rates in the Pittsburgh Veteran population with OSA following mask selection utilizing this specialized software. Methods Retrospective chart review was performed on 124 patients who underwent mask fitting with AI software May through November 2021. The primary outcome was to determine the rate of mask success within 1-3 months of fitting as defined by absence of mask switching. Mask switch was identified when patients underwent re-evaluation for new mask selection either by the AI software or had evidence of new mask selection from supply orders. Results Of the 124 patients who underwent evaluation with AI mask fit software, 96% were male with an average AHI 35/hr, BMI 34 and average age of 58 years. Of the 65 patients who were new to PAP therapy, 14 patients required refitting, yielding an initial mask acceptance rate of 78%. Of the 59 patients established on PAP, 8 required subsequent mask switches, yielding a refit mask acceptance rate of 86%. Overall mask acceptance rate after first exposure to fitting software across both groups was 82%. Conclusion AI software appears to result in successful mask fitting in a high proportion of VA patients. Higher mask acceptance rate was noted in the refit group, suggesting a particular use-case for this software. Most importantly, this software allows for remote mask fitting. This is ideal given recent telehealth growth and can save time and visits, leading to expedited therapy and increased access. Support (If Any)

Craniofacial Phenotypes and Genetics of DiGeorge Syndrome.

The 22q11.2 deletion is one of the most common genetic microdeletions, affecting approximately 1 in 4000 live births in humans. A 1.5 to 2.5 Mb hemizygous deletion of chromosome 22q11.2 causes DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS). DGS/VCFS are associated with prevalent cardiac malformations, thymic and parathyroid hypoplasia, and craniofacial defects. Patients with DGS/VCFS manifest craniofacial anomalies involving the cranium, cranial base, jaws, pharyngeal muscles, ear-nose-throat, palate, teeth, and cervical spine. Most craniofacial phenotypes of DGS/VCFS are caused by proximal 1.5 Mb microdeletions, resulting in a hemizygosity of coding genes, microRNAs, and long noncoding RNAs. TBX1, located on chromosome 22q11.21, encodes a T-box transcription factor and is a candidate gene for DGS/VCFS. TBX1 regulates the fate of progenitor cells in the cranial and pharyngeal apparatus during embryogenesis. Tbx1-null mice exhibit the most clinical features of DGS/VCFS, including craniofacial phenotypes. Despite the frequency of DGS/VCFS, there has been a limited review of the craniofacial phenotypes of DGC/VCFS. This review focuses on these phenotypes and summarizes the current understanding of the genetic factors that impact DGS/VCFS-related phenotypes. We also review DGS/VCFS mouse models that have been designed to better understand the pathogenic processes of DGS/VCFS.

Craniofacial morphology of a new mouse model of Down syndrome

Down syndrome (DS) is a complex condition caused by triplication of human chromosome 21 (Hsa21). Several mouse models have been developed to study the genotypic and phenotypic outcomes of DS. The most extensively studied and used in DS research is Ts65Dn. More recently, the TcMAC21 ‐ a transchromosomic mouse strain with comparable gene dosage to Hsa21 ‐ was developed, and represents a more complete genetic mouse model of DS than Ts65Dn. While Ts65Dn has been the focus of several studies, relatively little is known about the craniofacial phenotype of TcMAC21 mice relative to the other DS mouse models. Here we conducted a quantitative study of the cranial morphology of TcMAC21 and Ts65Dn mice and their respective unaffected littermates. Comparative data comprised of three‐dimensional cranial measurements taken from micro‐computed tomography scans of the mouse models used in the study. Our results show that TcMAC21 exhibit similar patterns of craniofacial change to Ts65Dn, but are less severe in their DS‐related cranial manifestations than Ts65Dn. TcMAC21 also do not present with the broadening and general ‘globularity’ of the cranium, particularly the face, as seen in Ts65Dn. Since Ts65Dn and TcMAC21 carry similarly large but not the same numbers of genes at dosage imbalance, our findings reveal the complexity of potential gene interaction in the production of craniofacial phenotypes.

Facial dysmorphologies in genetic disorders: exploring the ancestry component in a Colombian population

Currently there are more than 10,000 rare diseases that affect about 7% of the world's population. Up to 40% of rare genetic disorders present craniofacial dysmorphologies, which can vary from subtle facial anomalies to severe malformations. Visual assessment of facial dysmorphology is commonly used for clinical diagnosis, patient management and treatment monitoring. However, qualitative descriptions are usually vague and quantitative approaches using craniofacial phenotypes for the diagnosis of rare diseases are based on North American and European populations, disregarding the influence of population ancestry on facial variation, as in Latin‐America. In this study, we assessed facial dysmorphologies associated to three different genetic disorders (Down (DS), Morquio (MS) and Noonan syndrome (NS)) in a Latin‐American population from Cali (Colombia). We recorded the coordinates of 18 facial landmarks in 2D images from 34 pediatric patients (19 DS, 8 MS, 6 NS) and 75 controls and quantified facial differences between patients and control groups using Euclidean Distance Matrix Analysis (EDMA).Comparisons between control and syndromic phenotypes indicated that individuals diagnosed with DS and MS presented the largest percentage of dysmorphologies, with respectively 56.2% and 54.9% of significantly different facial traits. In NS, the percentage decreased to 12.4%. Each syndrome presented a characteristic facial pattern. In DS, all facial structures were affected, with a 6% increase of relative distance between the eyes and a 7‐10% reduction in facial height. The eyes and nose were most affected in MS, but not the mouth, with higher hypertelorism and facial reduction than in DS (9% and 8‐17%). In NS, facial differences were more subtle and affected mainly the eyes and mouth, reducing the relative distance between them from 1 to 4% in patients as compared to controls. Our study provides a precise quantitative comparison of facial dysmorphologies in three genetic disorders that in the future can be compared with other world‐wide populations to test whether facial traits associated to disease are altered by different evolutionary and adaptive histories of human populations.

A Recurrent FAM83H Mutation in an Extended Colombian Family and Variable Craniofacial Phenotypes.

Amelogenesis imperfecta (AI) is a collection of rare genetic disorders affecting the quantity and/or quality of the tooth enamel. AI can be classified into three major types according to the clinical phenotype: hypoplastic, hypocalcified, and hypomatured. Among them, the hypocalcified type shows the weakest physical properties, leaving rough and discolored enamel surfaces after tooth eruption. To date, mutations in the FAM83H gene are responsible for the autosomal-dominant hypocalcified AI. In this study, we recruited a four-generation Colombian family with hypocalcified AI and identified a recurrent nonsense mutation in the FAM83H gene (NM_198488.5:c.1289C>A, p.(Ser430 *)) by candidate gene sequencing. Cephalometric analyses revealed the anterior open bite that occurred in the proband is not correlated with the AI in this family.

Chondroitin/dermatan sulfate glycosyltransferase genes are essential for craniofacial development.

Chondroitin/dermatan sulfate (CS/DS) proteoglycans are indispensable for animal development and homeostasis but the large number of enzymes involved in their biosynthesis have made CS/DS function a challenging problem to study genetically. In our study, we generated loss-of-function alleles in zebrafish genes encoding CS/DS biosynthetic enzymes and characterized the effect on development in single and double mutants. Homozygous mutants in chsy1, csgalnact1a, csgalnat2, chpfa, ust and chst7, respectively, develop to adults. However, csgalnact1a-/- fish develop distinct craniofacial defects while the chsy1-/- skeletal phenotype is milder and the remaining mutants display no gross morphological abnormalities. These results suggest a high redundancy for the CS/DS biosynthetic enzymes and to further reduce CS/DS biosynthesis we combined mutant alleles. The craniofacial phenotype is further enhanced in csgalnact1a-/-;chsy1-/- adults and csgalnact1a-/-;csgalnact2-/- larvae. While csgalnact1a-/-;csgalnact2-/- was the most affected allele combination in our study, CS/DS is still not completely abolished. Transcriptome analysis of chsy1-/-, csgalnact1a-/- and csgalnact1a-/-;csgalnact2-/- larvae revealed that the expression had changed in a similar way in the three mutant lines but no differential expression was found in any of fifty GAG biosynthesis enzymes identified. Thus, zebrafish larvae do not increase transcription of GAG biosynthesis genes as a consequence of decreased CS/DS biosynthesis. The new zebrafish lines develop phenotypes similar to clinical characteristics of several human congenital disorders making the mutants potentially useful to study disease mechanisms and treatment.

A recessive variant in SIM2 in a child with complex craniofacial anomalies and global developmental delay

Rare deletions and duplications on the long arm of Chromosome 21 have previously been reported in many patients with craniofacial and developmental phenotypes. However, this Down Syndrome Critical Region (DSCR) contains multiple genes, making identifying a single causative gene difficult. Here, we report a case of a boy with bicoronal craniosynostosis, facial dysmorphism, developmental delay, and intellectual impairment who was found by whole genome sequencing to have a homozygous missense mutation in the Single-Minded Homolog 2 (SIM2) gene (c.461 A > G, p.Tyr154Cys) within the DSCR. SIM2 encodes an essential bHLH and PAS domain transcription factor expressed during fetal brain development and acts as a master regulator of neurogenesis. This variant is globally very rare, segregates in the family, and is predicted to be highly deleterious by in silico analysis, 3D molecular modeling of protein structure, and functional analysis of zebrafish models. Zebrafish expressing the human SIM2p.Y154C variant displayed a progressed microcephaly-like phenotype and head shape abnormalities. When combined with careful phenotyping of the patient vis-à-vis previously reported cases harboring structural variants in this critical 21q22 region, the data support a pathogenic role of SIM2 in this complex syndrome and demonstrates the utility of next-generation sequencing in prioritizing genes in contiguous deletions/duplications syndromes and diagnosing microarray-negative patients in the craniofacial clinic.

Computational anatomy and geometric shape analysis enables analysis of complex craniofacial phenotypes in zebrafish.

ABSTRACTDue to the complexity of fish skulls, previous attempts to classify craniofacial phenotypes have relied on qualitative features or sparce 2D landmarks. In this work we aim to identify previously unknown 3D craniofacial phenotypes with a semiautomated pipeline in adult zebrafish mutants. We first estimate a synthetic ‘normative’ zebrafish template using MicroCT scans from a sample pool of wild-type animals using the Advanced Normalization Tools (ANTs). We apply a computational anatomy (CA) approach to quantify the phenotype of zebrafish with disruptions in bmp1a, a gene implicated in later skeletal development and whose human ortholog when disrupted is associated with Osteogenesis Imperfecta. Compared to controls, the bmp1a fish have larger otoliths, larger normalized centroid sizes, and exhibit shape differences concentrated around the operculum, anterior frontal, and posterior parietal bones. Moreover, bmp1a fish differ in the degree of asymmetry. Our CA approach offers a potential pipeline for high-throughput screening of complex fish craniofacial shape to discover novel phenotypes for which traditional landmarks are too sparce to detect. The current pipeline successfully identifies areas of variation in zebrafish mutants, which are an important model system for testing genome to phenome relationships in the study of development, evolution, and human diseases. This article has an associated First Person interview with the first author of the paper.

First person – Kelly Diamond

ABSTRACTFirst Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Kelly Diamond is first author on ‘ Computational anatomy and geometric shape analysis enables analysis of complex craniofacial phenotypes in zebrafish’, published in BiO. Kelly is a postdoc in the lab of Dr Murat Maga at the Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, USA, investigating which combination of factors contribute to organismal morphology.