Isolated sagittal and coronal craniosynostosis associated with TWIST box mutations

Systematic Review of Nonsyndromic Craniosynostosis: Genomic Alterations and Impacted Signaling Pathways

BACKGROUND

Genetic research in nonsyndromic craniosynostosis remains limited compared with syndromic craniosynostosis. This systematic review aimed to comprehensively summarize the genetic literature of nonsyndromic craniosynostosis and highlight key signaling pathways.

METHODS

The authors performed a systematic literature search of PubMed, Ovid, and Google Scholar databases from inception until December of 2021 using search terms related to nonsyndromic craniosynostosis and genetics. Two reviewers screened titles and abstract for relevance, and three reviewers independently extracted study characteristics and genetic data. Gene networks were constructed using Search Tool for Retrieval of Interacting Genes/Proteins (version 11) analysis.

RESULTS

Thirty-three articles published between 2001 and 2020 met inclusion criteria. Studies were further classified into candidate gene screening and variant identification studies ( n = 16), genetic expression studies ( n = 13), and common and rare variant association studies ( n = 4). Most studies were good quality. Using our curated list of 116 genes extracted from the studies, two main networks were constructed.

CONCLUSIONS

This systematic review concerns the genetics of nonsyndromic craniosynostosis, with network construction revealing TGF-β/BMP, Wnt, and NF-κB/RANKL as important signaling pathways. Future studies should focus on rare rather than common variants to examine the missing heritability in this defect and, going forward, adopt a standard definition.

Mechanisms of Regulation of the CHRDL1 Gene by the TWIST2 and ADD1/SREBP1c Transcription Factors

Setleis syndrome (SS) is a rare focal facial dermal dysplasia caused by recessive mutations in the basic helix-loop-helix (bHLH) transcription factor, TWIST2. Expression microarray analysis showed that the chordin-like 1 (CHRDL1) gene is up-regulated in dermal fibroblasts from three SS patients with the Q119X TWIST2 mutation.

METHODS

Putative TWIST binding sites were found in the upstream region of the CHRDL1 gene and examined by electrophoretic mobility shift (EMSA) and reporter gene assays.

RESULTS

EMSAs showed specific binding of TWIST1 and TWIST2 homodimers, as well as heterodimers with E12, to the more distal E-boxes. An adjoining E-box was bound by ADD1/SREBP1c. EMSA analysis suggested that TWIST2 and ADD1/SREBP1c could compete for binding. Luciferase (luc) reporter assays revealed that the CHRDL1 gene upstream region drives its expression and ADD1/SREBP1c increased it 2.6 times over basal levels. TWIST2, but not the TWIST2-Q119X mutant, blocked activation by ADD1/SREBP1c, but overexpression of TWIST2-Q119X increased luc gene expression. In addition, EMSA competition assays showed that TWIST2, but not TWIST1, competes with ADD1/SREBP1c for DNA binding to the same site.

CONCLUSIONS

Formation of an inactive complex between the TWIST2 Q119X and Q65X mutant proteins and ADD1/SREBP1c may prevent repressor binding and allow the binding of other regulators to activate CHRDL1 gene expression.

A Twist-Box domain of the C. elegans Twist homolog, HLH-8, plays a complex role in transcriptional regulation

TWIST1 is a basic helix-loop-helix (bHLH) transcription factor in humans that functions in mesoderm differentiation. TWIST1 primarily regulates genes as a transcriptional repressor often through TWIST-Box domain-mediated protein-protein interactions. The TWIST-Box also can function as an activation domain requiring 3 conserved, equidistant amino acids (LXXXFXXXR). Autosomal dominant mutations in TWIST1, including 2 reported in these conserved amino acids (F187L and R191M), lead to craniofacial defects in Saethre-Chotzen syndrome (SCS). Caenorhabditis elegans has a single TWIST1 homolog, HLH-8, that functions in the differentiation of the muscles responsible for egg laying and defecation. Null alleles in hlh-8 lead to severely egg-laying defective and constipated animals due to defects in the corresponding muscles. TWIST1 and HLH-8 share sequence identity in their bHLH regions; however, the domain responsible for the transcriptional activity of HLH-8 is unknown. Sequence alignment suggests that HLH-8 has a TWIST-Box LXXXFXXXR motif; however, its function also is unknown. CRISPR/Cas9 genome editing was utilized to generate a domain deletion and several missense mutations, including those analogous to SCS patients, in the 3 conserved HLH-8 amino acids to investigate their functional role. The TWIST-Box alleles did not phenocopy hlh-8 null mutants. The strongest phenotype detected was a retentive (Ret) phenotype with late-stage embryos in the hermaphrodite uterus. Further, GFP reporters of HLH-8 downstream target genes (arg-1::gfp and egl-15::gfp) revealed tissue-specific, target-specific, and allele-specific defects. Overall, the TWIST-Box in HLH-8 is partially required for the protein's transcriptional activity, and the conserved amino acids contribute unequally to the domain's function.

Clinical interest of molecular study in cases of isolated midline craniosynostosis

In some cases of infants with apparently isolated single-suture synostosis, an underlying variant can be found. We aimed to determine the molecular substratum in isolated sagittal and metopic craniosynostosis. To this end, we included all infants who presented isolated midline synostosis (sagittal or metopic) and had undergone surgery at the craniosynostosis national reference center of Lyon University Hospital. All infants were examined by a multidisciplinary team including neurosurgeons, clinical geneticists and neuropsychologist. Among 101 infants tested, 13 carried a total of 13 variants; that is, 12.9% of the infants carried a variant in genes known to be involved in craniosynostosis. Seven infants carried SMAD6 variants, 2 in FGFR2, 1 in TWIST1, one in FREM1, one in ALX4 and one in TCF12. All variants were detected at the heterozygous level in genes associated with autosomal dominant craniosynostosis. Also, neurodevelopmental testing showed especially delayed acquisition of language in children with than without variants in SMAD6. In conclusion, a high percentage of young children with isolated midline craniosynostosis, especially in isolated trigonocephaly, carried SMAD6 variants. The interpretation of the pathogenicity of the genes must take into account incomplete penetrance, usually observed in craniosynostosis. Our results highlight the interest of molecular analysis in the context of isolated sagittal and/or metopic craniosynostosis to enhance an understanding of the pathophysiology of midline craniosynostosis.

The current understanding of germline predisposition in non-syndromic sagittal craniosynostosis: a systematic review

PURPOSE

The objective of this literature review was to provide a comprehensive and up-to-date overview of the current understanding of the genetic etiology for non-syndromic sagittal craniosynostosis.

METHODS

Using the PubMed database and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), we systematically reviewed relevant records on germline genetics in children with non-syndromic sagittal craniosynostosis.

RESULTS

Two hundred two records were identified, of which 25 were included following title and abstract screening and subsequent full-text review. The 25 records in combination included 829 children with non-syndromic sagittal craniosynostosis. A likely pathogenic or pathogenic germline variant was reported for 9.8% of the 827 patients for whom germline genetic testing was performed. The reported variants were distributed across 50 different genes, with more than one variant detected in 13 genes.

CONCLUSION

Based on the existing literature, genetic predisposition is likely to play a role in at least 9% of children with non-syndromic sagittal craniosynostosis. Future studies will benefit from international consensus in terms of diagnostic nomenclature and a higher level of standardization across study methodologies and bioinformatic approaches.

TWIST1 interacts with β/δ-catenins during neural tube development and regulates fate transition in cranial neural crest cells

Cell fate determination is a necessary and tightly regulated process for producing different cell types and structures during development. Cranial neural crest cells (CNCCs) are unique to vertebrate embryos and emerge from the neural plate borders into multiple cell lineages that differentiate into bone, cartilage, neurons and glial cells. We have previously reported that Irf6 genetically interacts with Twist1 during CNCC-derived tissue formation. Here, we have investigated the mechanistic role of Twist1 and Irf6 at early stages of craniofacial development. Our data indicate that TWIST1 is expressed in endocytic vesicles at the apical surface and interacts with β/δ-catenins during neural tube closure, and Irf6 is involved in defining neural fold borders by restricting AP2α expression. Twist1 suppresses Irf6 and other epithelial genes in CNCCs during the epithelial-to-mesenchymal transition (EMT) process and cell migration. Conversely, a loss of Twist1 leads to a sustained expression of epithelial and cell adhesion markers in migratory CNCCs. Disruption of TWIST1 phosphorylation in vivo leads to epidermal blebbing, edema, neural tube defects and CNCC-derived structural abnormalities. Altogether, this study describes a previously uncharacterized function of mammalian Twist1 and Irf6 in the neural tube and CNCCs, and provides new target genes for Twist1 that are involved in cytoskeletal remodeling.

De novo ALX4 variant detected in child with non-syndromic craniosynostosis

Current understanding of the genetic factors contributing to the etiology of non-syndromic craniosynostosis (NSC) remains scarce. The present work investigated the presence of variants in ALX4, EFNA4, and TWIST1 genes in children with NSC to verify if variants within these genes may contribute to the occurrence of these abnormal phenotypes. A total of 101 children (aged 45.07±40.94 months) with NSC participated in this cross-sectional study. Parents and siblings of the probands were invited to participate. Medical and family history of craniosynostosis were documented. Biological samples were collected to obtain genomic DNA. Coding exons of human TWIST1, ALX4, and EFNA4 genes were amplified by polymerase chain reaction and Sanger sequenced. Five missense variants were identified in ALX4 in children with bilateral coronal, sagittal, and metopic synostosis. A de novo ALX4 variant, c.799G>A: p.Ala267Thr, was identified in a proband with sagittal synostosis. Three missense variants were identified in the EFNA4 gene in children with metopic and sagittal synostosis. A TWIST1 variant occurred in a child with unilateral coronal synostosis. Variants were predicted to be among the 0.1% (TWIST1, c.380C>A: p. Ala127Glu) and 1% (ALX4, c.769C>T: p.Arg257Cys, c.799G>A: p.Ala267Thr, c.929G>A: p.Gly310Asp; EFNA4, c.178C>T: p.His60Tyr, C.283A>G: p.Lys95Glu, c.349C>A: Pro117Thr) most deleterious variants in the human genome. With the exception of ALX4, c.799G>A: p.Ala267Thr, all other variants were present in at least one non-affected family member, suggesting incomplete penetrance. Thus, these variants may contribute to the development of craniosynostosis, and should not be discarded as potential candidate genes in the diagnosis of this condition.

Chiari 1 malformation and exome sequencing in 51 trios: the emerging role of rare missense variants in chromatin-remodeling genes

Type 1 Chiari malformation (C1M) is characterized by cerebellar tonsillar herniation of 3–5 mm or more, the frequency of which is presumably much higher than one in 1000 births, as previously believed. Its etiology remains undefined, although a genetic basis is strongly supported by C1M presence in numerous genetic syndromes associated with different genes. Whole-exome sequencing (WES) in 51 between isolated and syndromic pediatric cases and their relatives was performed after confirmation of the defect by brain magnetic resonance image (MRI). Moreover, in all the cases showing an inherited candidate variant, brain MRI was performed in both parents and not only in the carrier one to investigate whether the defect segregated with the variant. More than half of the variants were Missense and belonged to the same chromatin-remodeling genes whose protein truncation variants are associated with severe neurodevelopmental syndromes. In the remaining cases, variants have been detected in genes with a role in cranial bone sutures, microcephaly, neural tube defects, and RASopathy. This study shows that the frequency of C1M is widely underestimated, in fact many of the variants, in particular those in the chromatin-remodeling genes, were inherited from a parent with C1M, either asymptomatic or with mild symptoms. In addition, C1M is a Mendelian trait, in most cases inherited as dominant. Finally, we demonstrate that modifications of the genes that regulate chromatin architecture can cause localized anatomical alterations, with symptoms of varying degrees.

Gain-of-function variants and overexpression of RUNX2 in patients with nonsyndromic midline craniosynostosis

Craniosynostosis (CS), the premature fusion of one or more cranial sutures, is a relatively common congenital anomaly, occurring in 3-5 per 10,000 live births. Nonsyndromic CS (NCS) accounts for up to 80% of all CS cases, yet the genetic factors contributing to the disorder remain largely unknown. The RUNX2 gene, encoding a transcription factor critical for bone and skull development, is a well known CS candidate gene, as copy number variations of this gene locus have been found in patients with syndromic craniosynostosis. In the present study, we aimed to characterize RUNX2 to better understand its role in the genetic etiology and in the molecular mechanisms underlying midline suture ossification in NCS. We report four nonsynonymous variants, one intronic variant and one 18 bp in-frame deletion in RUNX2 not found in our study control population. Significant difference in allele frequency (AF) for the deletion variant RUNX2 p.Ala84-Ala89del (ClinVar 257,095; dbSNP rs11498192) was observed in our sagittal NCS cohort when compared to the general population (P = 1.28 × 10^-6), suggesting a possible role in the etiology of NCS. Dual-luciferase assays showed that three of four tested RUNX2 variants conferred a gain-of-function effect on RUNX2, further suggesting their putative pathogenicity in the tested NCS cases. Downregulation of RUNX2 expression was observed in prematurely ossified midline sutures. Metopic sites showed significant downregulation of promoter 1-specific isoforms compared to sagittal sites. Suture-derived mesenchymal stromal cells showed an increased expression of RUNX2 over matched unfused suture derived cells. This demonstrates that RUNX2, and particularly the distal promoter 1-isoform group, are overexpressed in the osteogenic precursors within the pathological suture sites.

An ENU-induced mutation in Twist1 transactivation domain causes hindlimb polydactyly with complete penetrance and dominant-negatively impairs E2A-dependent transcription

Twist1 encodes a basic helix-loop-helix transcription factor (TF), which forms homodimer or heterodimer with other TFs, like E2A, to regulate target genes' expression. Mutations in TWIST1 are associated with Saethre-Chotzen syndrome (SCS), a rare congenital disorder characterized with osteogenesis abnormalities. However, how dysfunction of TWIST1 leads to SCS is still largely unknown. Here, using an unbiased ENU-induced mutagenesis screening, we identified a novel Twist1 mutation and the mutant mouse phenocopies some features of SCS in a dominant manner. Physically, our mutation p.F191S lies at the edge of a predicted α-helix in Twist1 transactivation (TA) domain. Adjacent to F191, a consecutive three-residue (AFS) has been hit by 3 human and 2 mouse disease-associated mutations, including ours. Unlike previously reported mouse null and p.S192P alleles that lead to hindlimb polydactyly with incomplete penetrance but a severe craniofacial malformation, our p.F191S causes the polydactyly (84.2% bilateral and 15.8% unilateral) with complete penetrance but a mild craniofacial malformation. Consistent with the higher penetrance, p.F191S has stronger impairment on E2A-dependent transcription than p.S192P. Although human p.A186T and mouse p.S192P disease mutations are adjacent to ours, these three mutations function differently to impair the E2A-dependent transcription. Unlike p.A186T and p.S192S that disturb local protein conformation and unstabilize the mutant proteins, p.F191S keeps the mutant protein stable and its interaction with E2A entire. Therefore, we argue that p.F191S we identified acts in a dominant-negative manner to impair E2A-dependent transcription and to cause the biological consequences. In addition, the mutant mouse we provided here could be an additional and valuable model for better understanding the disease mechanisms underlying SCS caused by TWIST1 dysfunction.

Recent Advances in Craniosynostosis

Craniosynostosis is a pathologic craniofacial disorder and is defined as the premature fusion of one or more cranial (calvarial) sutures. Cranial sutures are fibrous joints consisting of nonossified mesenchymal cells that play an important role in the development of healthy craniofacial skeletons. Early fusion of these sutures results in incomplete brain development that may lead to complications of several severe medical conditions including seizures, brain damage, mental delay, complex deformities, strabismus, and visual and breathing problems. As a congenital disease, craniosynostosis has a heterogeneous origin that can be affected by genetic and epigenetic alterations, teratogens, and environmental factors and make the syndrome highly complex. To date, approximately 200 syndromes have been linked to craniosynostosis. In addition to being part of a syndrome, craniosynostosis can be nonsyndromic, formed without any additional anomalies. More than 50 nuclear genes that relate to craniosynostosis have been identified. Besides genetic factors, epigenetic factors like microRNAs and mechanical forces also play important roles in suture fusion. As craniosynostosis is a multifactorial disorder, evaluating the craniosynostosis syndrome requires and depends on all the information obtained from clinical findings, genetic analysis, epigenetic or environmental factors, or gene modulators. In this review, we will focus on embryologic and genetic studies, as well as epigenetic and environmental studies. We will discuss published studies and correlate the findings with unknown aspects of craniofacial disorders.

Animal models of craniosynostosis

BACKGROUND

Various animal models mimicking craniosynostosis have been developed, using mutant zebrafish and mouse. The aim of this paper is to review the different animal models for syndromic craniosynostosis and analyze what insights they have provided in our understanding of the pathophysiology of these conditions.

MATERIAL AND METHODS

The relevant literature for animal models of craniosynostosis was reviewed.

RESULTS

Although few studies on craniosynostosis using zebrafish were published, this model appears useful in studying the suture formation mechanisms conserved across vertebrates. Conversely, several mouse models have been generated for the most common syndromic craniosynostoses, associated with mutations in FGFR1, FGFR2, FGFR3 and TWIST genes and also in MSX2, EFFNA, GLI3, FREM1, FGF3/4 genes. The mouse models have also been used to test pharmacological treatments to restore craniofacial growth.

CONCLUSIONS

Several zebrafish and mouse models have been developed in recent decades. These animal models have been helpful for our understanding of normal and pathological craniofacial growth. Mouse models mimicking craniosynostoses can be easily used for the screening of drugs as therapeutic candidates.

Calvarial osteoblast gene expression in patients with craniosynostosis leads to novel polygenic mouse model

Craniosynostosis is the premature fusion of the sutures of the calvaria and is principally designated as being either syndromic (demonstrating characteristic extracranial malformations) or non-syndromic. While many forms of syndromic craniosynostosis are known to be caused by specific mutations, the genetic etiology of non-syndromic, single-suture craniosynostosis (SSC) is poorly understood. Based on the low recurrence rate (4-7%) and the fact that recurrent mutations have not been identified for most cases of SSC, we propose that some cases of isolated, single suture craniosynostosis may be polygenic. Previous work in our lab identified a disproportionately high number of rare and novel gain-of-function IGF1R variants in patients with SSC as compared to controls. Building upon this result, we used expression array data from calvarial osteoblasts isolated from infants with and without SSC to ascertain correlations between high IGF1 expression and expression of other osteogenic genes of interest. We identified a positive correlation between increased expression of IGF1 and RUNX2, a gene known to cause SSC with increased gene dosage. Subsequent phosphorylation assays revealed that osteoblast cell lines from cases with high IGF1 expression demonstrated inhibition of GSK3β, a serine/threonine kinase known to inhibit RUNX2, thus activating osteogenesis through the IRS1-mediated Akt pathway. With these findings, we have utilized established mouse strains to examine a novel model of polygenic inheritance (a phenotype influenced by more than one gene) of SSC. Compound heterozygous mice with selective disinhibition of RUNX2 and either overexpression of IGF1 or loss of function of GSK3β demonstrated an increase in the frequency and severity of synostosis as compared to mice with the RUNX2 disinhibition alone. These polygenic mouse models reinforce, in-vivo, that the combination of activation of the IGF1 pathway and disinhibition of the RUNX2 pathway leads to an increased risk of developing craniosynostosis and serves as a model of human SSC.

Nonsyndromic craniosynostosis: novel coding variants

BACKGROUND

Craniosynostosis (CS), the premature fusion of one or more neurocranial sutures, is associated with approximately 200 syndromes; however, about 65-85% of patients present with no additional major birth defects.

METHODS

We conducted targeted next-generation sequencing of 60 known syndromic and other candidate genes in patients with sagittal nonsyndromic CS (sNCS, n = 40) and coronal nonsyndromic CS (cNCS, n = 19).

RESULTS

We identified 18 previously published and 5 novel pathogenic variants, including three de novo variants. Novel variants included a paternally inherited c.2209C>G:p.(Leu737Val) variant in BBS9 of a patient with cNCS. Common variants in BBS9, a gene required for ciliogenesis during cranial suture development, have been associated with sNCS risk in a previous genome-wide association study. We also identified c.313G>T:p.(Glu105*) variant in EFNB1 and c.435G>C:p.(Lys145Asn) variant in TWIST1, both in patients with cNCS. Mutations in EFNB1 and TWIST1 have been linked to craniofrontonasal and Saethre-Chotzen syndrome, respectively; both present with coronal CS.

CONCLUSIONS

We provide additional evidence that variants in genes implicated in syndromic CS play a role in isolated CS, supporting their inclusion in genetic panels for screening patients with NCS. We also identified a novel BBS9 variant that further shows the potential involvement of BBS9 in the pathogenesis of CS.

Identification of sequence variants associated with severe microtia-astresia by targeted sequencing

Background

Microtia-atresia is characterized by abnormalities of the auricle (microtia) and aplasia or hypoplasia of the external auditory canal, often associated with middle ear abnormalities. To date, no causal genetic mutations or genes have been identified in microtia-atresia patients.

Methods

We designed a panel of 131 genes associated with external/middle or inner ear deformity. Targeted genomic capturing combined with next-generation sequencing (NGS) was utilized to screen for mutations in 40 severe microtia-atresia patients. Mutations detected by NGS were filtered and validated. And then mutations were divided into three categories—rare or novel variants, low-frequency variants and common variants—based on their frequency in the public database. The rare or novel mutations were prioritized by pathogenicity analysis. For the low-frequency variants and common variants, we used association studies to explore risk factors of severe microtia-atresia.

Results

Sixty-five rare heterozygous mutations of 42 genes were identified in 27 (67.5%) severe microtia-atresia patients. Association studies to determine genes that were potentially pathogenic found that PLEC, USH2A, FREM2, DCHS1, GLI3, POMT1 and GBA genes were significantly associated with severe microtia-atresia. Of these, DCHS1 was strongly suggested to cause severe microtia-atresia as it was identified by both low-frequency and common variants association studies. A rare mutation (c.481C > T, p.R161C) in DCHS1 identified in one individual may be deleterious and may cause severe microtia-atresia.

Conclusion

We identified several genes that were significantly associated with severe microtia-atresia. The findings provide new insights into genetic background of external ear deformities.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0475-x) contains supplementary material, which is available to authorized users.

Genetics of Nonsyndromic Craniosynostosis

Occurring once in every 2000 live births, craniosynostosis is one of the most frequent congenital anomalies encountered by the craniofacial surgeon. Syndromic craniosynostoses account for approximately 15 percent of cases and demonstrate Mendelian patterns of inheritance with well-established genetic causes; however, nonsyndromic craniosynostoses, which account for approximately 85 percent of cases, are genetically heterogeneous and largely unexplored. Nonsyndromic craniosynostosis is sporadic in more than 95 percent of affected families; thus, surgeons have suggested for decades that nonsyndromic craniosynostosis is likely a fluke occurrence. Contrary to this, recent studies have established that genetics underlie a substantial fraction of nonsyndromic craniosynostosis risk. Given the predominantly sporadic occurrence of disease, parents are often bewildered by the primary occurrence of nonsyndromic craniosynostosis or even recurrence in their own families and request genetic testing. Existing genetic testing panels are useful when the phenotype strongly resembles a known syndrome, wherein the risk of disease recurrence can be accurately predicted for future offspring of the parents and the future offspring of the affected child. The diagnostic utility of existing panels for nonsyndromic craniosynostosis, however, is extremely low, and these tests are quite costly. Recent genetic studies have identified several novel genes and pathways that cause nonsyndromic craniosynostosis, providing genetic evidence linking the causes of syndromic and nonsyndromic craniosynostoses, and allowing for genotype-based prediction of risk of recurrence in some nonsyndromic families. Based on analysis of exome sequence data from 384 families, the authors provide recommendations for a new genetic testing protocol for children with nonsyndromic craniosynostosis, which include testing nonsyndromic cases of sagittal, metopic, and coronal craniosynostosis.

Modification of the Melbourne Method for Total Calvarial Vault Remodeling

Background:

Sagittal synostosis is the most common form of single suture synostosis. It often results in characteristic calvarial deformities, including a long, narrow head, frontal bossing, a bullet-shaped occiput, and an anteriorly placed vertex. Several methods for correcting the phenotypic deformities have been described, each with their own advantages and challenges. In this study, we describe a modification of the Melbourne method of total calvarial remodeling for correcting scaphocephaly.

Methods:

We conducted a retrospective review of all consecutive patients who underwent total calvarial remodeling using a modified version of the Melbourne technique from 2011 to 2015. We evaluated clinical photographs, computed tomographic imaging, and cephalic indices both pre- and postoperatively to determine morphologic changes after operation.

Results:

A total of 9 patients underwent the modified Melbourne technique for calvarial vault remodeling during the study period. Intraoperative blood loss was 260 mL (range, 80–400 mL), and mean intraoperative transfusion was 232 mL (range, 0–360 mL). The average length of stay in the hospital was 3.9 days. The mean cephalic indices increased from 0.66 to 0.74 postoperatively (P < 0.01).

Conclusions:

A modified Melbourne method for calvarial vault reconstruction addresses the phenotypic aspects of severe scaphocephaly associated with isolated sagittal synostosis and maintains a homeotopic relationship across the calvaria. It is associated with shorter operative times, lower blood loss, and lower transfusion requirements.

BBS9 gene in nonsyndromic craniosynostosis: Role of the primary cilium in the aberrant ossification of the suture osteogenic niche

Nonsyndromic craniosynostosis (NCS) is the premature ossification of skull sutures, without associated clinical features. Mutations in several genes account for a small number of NCS patients; thus, the molecular etiopathogenesis of NCS remains largely unclear. Our study aimed at characterizing the molecular signaling implicated in the aberrant ossification of sutures in NCS patients. Comparative gene expression profiling of NCS patient sutures identified a fused suture-specific signature, including 17 genes involved in primary cilium signaling and assembly. Cells from fused sutures displayed a reduced potential to form primary cilia compared to cells from control patent sutures of the same patient. We identified specific upregulated splice variants of the Bardet Biedl syndrome-associated gene 9 (BBS9), which encodes a structural component of the ciliary BBSome complex. BBS9 expression increased during in vitro osteogenic differentiation of suture-derived mesenchymal cells of NCS patients. Also, Bbs9 expression increased during in vivo ossification of rat sutures. BBS9 functional knockdown affected the expression of primary cilia on patient suture cells and their osteogenic potential. Computational modeling of the upregulated protein isoforms (observed in patients) predicted that their binding affinity within the BBSome may be affected, providing a possible explanation for the aberrant suture ossification in NCS.

Genetic Analysis of Syndromic and Nonsyndromic Patients With Craniosynostosis Identifies Novel Mutations in the TWIST1 and EFNB1 Genes

INTRODUCTION

Craniosynostosis, the premature fusion of cranial sutures, is usually divided into 2 major categories: syndromic and nonsyndromic. Mutations in the FGFR1, FGFR2, FGFR3, TWIST1, and EFNB1 genes cause the common craniosynostosis syndromes Muenke, Crouzon and Crouzon with acanthosis nigricans, Apert, Pfeiffer, Saethre-Chotzen, and Craniofrontonasal. Overlapping features among craniosynostosis syndromes, phenotypic heterogeneity even within the same syndrome, especially in the case of Muenke syndrome, and inadequate clinical evaluation can lead to misdiagnosis, which molecular testing can help clarify.

OBJECTIVE

The aim of this study is to investigate the underlying genetic cause in 46 patients with syndromic or nonsyndromic craniosynostosis by direct sequencing and/or microdeletion/microduplication analysis of the FGFR1-3, TWIST1, and EFNB1 genes.

RESULTS

Genetic analysis identified 3 novel mutations, c.413T>C - p.(Leu138Pro) [p.(L138P)] in TWIST1, the previously reported c.373G>A - p.(Glu125Lys) [p.(E125K)], and c.717dupA - p.(Leu240IlefsTer79) [p.(L240fs)] mutation in EFNB1 gene as well as 6 previously known mutations and a heterozygous TWIST1 gene deletion. The 2 novel mutations within EFNB1 gene arose de novo, but the novel mutation p.(L138P) within TWIST1 gene was inherited from the patient's father, who was found to be mosaic for the mutation. To our knowledge, this is the first case of mosaicism described for TWIST1 gene.

CONCLUSIONS

The contribution of molecular genetic analysis to the diagnosis of patients with syndromic craniosynostosis was useful because some were originally misdiagnosed. Conversely, thorough clinical evaluation can guide molecular testing and result in a correct diagnosis.

Fibroblast Growth Factor Receptor 2 (FGFR2) Mutation Related Syndromic Craniosynostosis

Craniosynostosis results from the premature fusion of cranial sutures, with an incidence of 1 in 2,100-2,500 live births. The majority of cases are non-syndromic and involve single suture fusion, whereas syndromic cases often involve complex multiple suture fusion. The fibroblast growth factor receptor 2 (FGFR2) gene is perhaps the most extensively studied gene that is mutated in various craniosynostotic syndromes including Crouzon, Apert, Pfeiffer, Antley-Bixler, Beare-Stevenson cutis gyrata, Jackson-Weiss, Bent Bone Dysplasia, and Seathre-Chotzen-like syndromes. The majority of these mutations are missense mutations that result in constitutive activation of the receptor and downstream molecular pathways. Treatment involves a multidisciplinary approach with ultimate surgical fixation of the cranial deformity to prevent further sequelae. Understanding the molecular mechanisms has allowed for the investigation of different therapeutic agents that can potentially be used to prevent the disorders. Further research efforts are need to better understand screening and effective methods of early intervention and prevention. Herein, the authors provide a comprehensive update on FGFR2-related syndromic craniosynostosis.

Genetic advances in craniosynostosis

Craniosynostosis, the premature ossification of one or more skull sutures, is a clinically and genetically heterogeneous congenital anomaly affecting approximately one in 2,500 live births. In most cases, it occurs as an isolated congenital anomaly, that is, nonsyndromic craniosynostosis (NCS), the genetic, and environmental causes of which remain largely unknown. Recent data suggest that, at least some of the midline NCS cases may be explained by two loci inheritance. In approximately 25-30% of patients, craniosynostosis presents as a feature of a genetic syndrome due to chromosomal defects or mutations in genes within interconnected signaling pathways. The aim of this review is to provide a detailed and comprehensive update on the genetic and environmental factors associated with NCS, integrating the scientific findings achieved during the last decade. Focus on the neurodevelopmental, imaging, and treatment aspects of NCS is also provided.

Neosuture formation after endoscope-assisted craniosynostosis repair

OBJECTIVE The goal of this study was to identify the rate of neosuture formation in patients with craniosynostosis treated with endoscope-assisted strip craniectomy and investigate whether neosuture formation in sagittal craniosynostosis has an effect on postoperative calvarial shape. METHODS The authors retrospectively reviewed 166 cases of nonsyndromic craniosynostosis that underwent endoscope-assisted repair between 2006 and 2014. Preoperative and 1-year postoperative head CT scans were evaluated, and the rate of neosuture formation was calculated. Three-dimensional reconstructions of the CT data were used to measure cephalic index (CI) (ratio of head width and length) of patients with sagittal synostosis. Regression analysis was used to calculate significant differences between patients with and without neosuture accounting for age at surgery and preoperative CI. RESULTS Review of 96 patients revealed that some degree of neosuture development occurred in 23 patients (23.9%): 16 sagittal, 2 bilateral coronal, 4 unilateral coronal, and 1 lambdoid synostosis. Complete neosuture formation was seen in 14 of those 23 patients (9 of 16 sagittal, 1 of 2 bilateral coronal, 3 of 4 unilateral coronal, and 1 of 1 lambdoid). Mean pre- and postoperative CI in the complete sagittal neosuture group was 67.4% and 75.5%, respectively, and in the non-neosuture group was 69.8% and 74.4%, respectively. There was no statistically significant difference in the CI between the neosuture and fused suture groups preoperatively or 17 months postoperatively in patients with sagittal synostosis. CONCLUSIONS Neosuture development can occur after endoscope-assisted strip craniectomy and molding helmet therapy for patients with craniosynostosis. Although the authors did not detect a significant difference in calvarial shape postoperatively in the group with sagittal synostosis, the relevance of neosuture formation remains to be determined. Further studies are required to discover long-term outcomes comparing patients with and without neosuture formation.

Effects of thyroxine exposure on the Twist 1 +/- phenotype: A test of gene-environment interaction modeling for craniosynostosis

BACKGROUND

Craniosynostosis, the premature fusion of one or more of the cranial sutures, is estimated to occur in 1:1800 to 2500 births. Genetic murine models of craniosynostosis exist, but often imperfectly model human patients. Case, cohort, and surveillance studies have identified excess thyroid hormone as an agent that can either cause or exacerbate human cases of craniosynostosis.

METHODS

Here we investigate the influence of in utero and in vitro exogenous thyroid hormone exposure on a murine model of craniosynostosis, Twist 1 +/-.

RESULTS

By 15 days post-natal, there was evidence of coronal suture fusion in the Twist 1 +/- model, regardless of exposure. With the exception of craniofacial width, there were no significant effects of exposure; however, the Twist 1 +/- phenotype was significantly different from the wild-type control. Twist 1 +/- cranial suture cells did not respond to thyroxine treatment as measured by proliferation, osteogenic differentiation, and gene expression of osteogenic markers. However, treatment of these cells did result in modulation of thyroid associated gene expression.

CONCLUSION

Our findings suggest the phenotypic effects of the genetic mutation largely outweighed the effects of thyroxine exposure in the Twist 1 +/- model. These results highlight difficultly in experimentally modeling gene-environment interactions for craniosynostotic phenotypes. Birth Defects Research (Part A) 106:803-813, 2016. © 2016 Wiley Periodicals, Inc.

Mutation Screening of Candidate Genes in Patients with Nonsyndromic Sagittal Craniosynostosis

BACKGROUND

Craniosynostosis is a condition that includes the premature fusion of one or multiple cranial sutures. Among various craniosynostosis forms, sagittal nonsyndromic craniosynostosis is the most prevalent. Although different gene mutations have been identified in some craniosynostosis syndromes, the cause of sagittal nonsyndromic craniosynostosis remains largely unknown.

METHODS

To screen for candidate genes for sagittal nonsyndromic craniosynostosis, the authors sequenced DNA of 93 sagittal nonsyndromic craniosynostosis patients from a population-based study conducted in Iowa and New York states. FGFR1-3 mutational hotspots and the entire TWIST1, RAB23, and BMP2 coding regions were screened because of their known roles in human nonsyndromic or syndromic sagittal craniosynostosis, expression patterns, and/or animal model studies.

RESULTS

The authors identified two rare variants in their cohort. A FGFR1 insertion c.730_731insG, which led to a premature stop codon, was predicted to abolish the entire immunoglobulin-like III domain, including the ligand-binding region. A c.439C>G variant was observed in TWIST1 at its highly conserved loop domain in another patient. The patient's mother harbored the same variant and was reported with jaw abnormalities. These two variants were not detected in 116 alleles from unaffected controls or seen in the several databases; however, TWIST1 variant was found in a low frequency of 0.000831 percent in Exome Aggregation Consortium database.

CONCLUSIONS

The low mutation detection rate indicates that these genes account for only a small proportion of sagittal nonsyndromic craniosynostosis patients. The authors' results add to the perception that sagittal nonsyndromic craniosynostosis is a complex developmental defect with considerable genetic heterogeneity.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, II.

Deciphering the molecular mechanisms underlying the binding of the TWIST1/E12 complex to regulatory E-box sequences

The TWIST1 bHLH transcription factor controls embryonic development and cancer processes. Although molecular and genetic analyses have provided a wealth of data on the role of bHLH transcription factors, very little is known on the molecular mechanisms underlying their binding affinity to the E-box sequence of the promoter. Here, we used an in silico model of the TWIST1/E12 (TE) heterocomplex and performed molecular dynamics (MD) simulations of its binding to specific (TE-box) and modified E-box sequences. We focused on (i) active E-box and inactive E-box sequences, on (ii) modified active E-box sequences, as well as on (iii) two box sequences with modified adjacent bases the AT- and TA-boxes. Our in silico models were supported by functional in vitro binding assays. This exploration highlighted the predominant role of protein side-chain residues, close to the heart of the complex, at anchoring the dimer to DNA sequences, and unveiled a shift towards adjacent ((-1) and (-1*)) bases and conserved bases of modified E-box sequences. In conclusion, our study provides proof of the predictive value of these MD simulations, which may contribute to the characterization of specific inhibitors by docking approaches, and their use in pharmacological therapies by blocking the tumoral TWIST1/E12 function in cancers.

Insights into the development of molecular therapies for craniosynostosis

For the past 2 decades, clinical and basic science researchers have gained significant insights into the molecular and genetic pathways associated with common forms of craniosynostosis. This has led to invaluable information for families and physicians in their attempts to understand the heterogeneity of craniosynostosis. Genetic mutations have been identified in the fibroblast growth factor receptors (FGFRs) as well as in other targets, including TWIST1, BMP, and RUNX2. Greater understanding of these and other pathways has led to the development of innovative approaches for applying medical therapies to the treatment of craniosynostosis, in particular by maintaining suture patency. In this article, the authors discuss the molecular pathophysiological mechanisms underlying various forms of craniosynostosis. They also highlight recent developments in the field of molecular craniosynostosis research with the hope of identifying targets for medical therapies that might augment the results of surgical intervention.

Skull base development and craniosynostosis

Abnormal skull shape resulting in craniofacial deformity is a relatively common clinical finding, with deformity either positional (positional plagiocephaly) or related to premature ossification and fusion of the skull sutures (craniosynostosis). Growth restriction occurring at a stenosed suture is associated with exaggerated growth at the open sutures, resulting in fairly predictable craniofacial phenotypes in single-suture non-syndromic pathologies. Multi-suture syndromic subtypes are not so easy to understand without imaging. Imaging is performed to define the site and extent of craniosynostosis, to determine the presence or absence of underlying brain anomalies, and to evaluate both pre- and postoperative complications of craniosynostosis. Evidence for intracranial hypertension may be seen both pre- and postoperatively, associated with jugular foraminal stenosis, sinovenous occlusion, hydrocephalus and Chiari 1 malformations. Following clinical assessment, imaging evaluation may include radiographs, high-frequency US of the involved sutures, low-dose (20-30 mAs) CT with three-dimensional reformatted images, MRI and nuclear medicine brain imaging. Anomalous or vigorous collateral venous drainage may be mapped preoperatively with CT or MR venography or catheter angiography.

Clinical and genetic characteristics of craniosynostosis in Hungary

Craniosynostosis, the premature closure of cranial sutures, is a common craniofacial disorder with heterogeneous etiology and appearance. The purpose of this study was to investigate the clinical and molecular characteristics of craniosynostoses in Hungary, including the classification of patients and the genetic analysis of the syndromic forms. Between 2006 and 2012, 200 patients with craniosynostosis were studied. Classification was based on the suture(s) involved and the associated clinical features. In syndromic cases, genetic analyses, including mutational screening of the hotspot regions of the FGFR1, FGFR2, FGFR3, and TWIST1 genes, karyotyping and FISH study of TWIST1, were performed. The majority (88%) of all patients with craniosynostosis were nonsyndromic. The sagittal suture was most commonly involved, followed by the coronal, metopic, and lambdoid sutures. Male, twin gestation, and very low birth weight were risk factors for craniosynostosis. Syndromic craniosynostosis was detected in 24 patients. In 17 of these patients, Apert, Crouzon, Pfeiffer, Muenke, or Saethre-Chotzen syndromes were identified. In one patient, multiple-suture craniosynostosis was associated with achondroplasia. Clinical signs were not typical for any particular syndrome in six patients. Genetic abnormalities were detected in 18 syndromic patients and in 8 relatives. In addition to 10 different, known mutations in FGFR1,FGFR2 or FGFR3, one novel missense mutation, c.528C>G(p.Ser176Arg), was detected in the TWIST1 gene of a patient with Saethre-Chotzen syndrome. Our results indicate that detailed clinical assessment is of paramount importance in the classification of patients and allows indication of targeted molecular testing with the highest possible diagnostic yield.

Quantitative trait loci affecting the 3D skull shape and size in mouse and prioritization of candidate genes in-silico

We describe the first application of high-resolution 3D micro-computed tomography, together with 3D landmarks and geometric morphometrics, to map QTL responsible for variation in skull shape and size using a backcross between C57BL/6J and A/J inbred strains. Using 433 animals, 53 3D landmarks, and 882 SNPs from autosomes, we identified seven QTL responsible for the skull size (SCS.qtl) and 30 QTL responsible for the skull shape (SSH.qtl). Size, sex, and direction-of-cross were all significant factors and included in the analysis as covariates. All autosomes harbored at least one SSH.qtl, sometimes up to three. Effect sizes of SSH.qtl appeared to be small, rarely exceeding 1% of the overall shape variation. However, they account for significant amount of variation in some specific directions of the shape space. Many QTL have stronger effect on the neurocranium than expected from a random vector that will parcellate uniformly across the four cranial regions. On the contrary, most of QTL have an effect on the palate weaker than expected. Combined interval length of 30 SSH.qtl was about 315 MB and contained 2476 known protein coding genes. We used a bioinformatics approach to filter these candidate genes and identified 16 high-priority candidates that are likely to play a role in the craniofacial development and disorders. Thus, coupling the QTL mapping approach in model organisms with candidate gene enrichment approaches appears to be a feasible way to identify high-priority candidates genes related to the structure or tissue of interest.

An evolutionarily conserved DNA architecture determines target specificity of the TWIST family bHLH transcription factors

Basic helix-loop-helix (bHLH) transcription factors recognize the canonical E-box (CANNTG) to regulate gene transcription; however, given the prevalence of E-boxes in a genome, it has been puzzling how individual bHLH proteins selectively recognize E-box sequences on their targets. TWIST is a bHLH transcription factor that promotes epithelial-mesenchymal transition (EMT) during development and tumor metastasis. High-resolution mapping of TWIST occupancy in human and Drosophila genomes reveals that TWIST, but not other bHLH proteins, recognizes a unique double E-box motif with two E-boxes spaced preferentially by 5 nucleotides. Using molecular modeling and binding kinetic analyses, we found that the strict spatial configuration in the double E-box motif aligns two TWIST-E47 dimers on the same face of DNA, thus providing a high-affinity site for a highly stable intramolecular tetramer. Biochemical analyses showed that the WR domain of TWIST dimerizes to mediate tetramer formation, which is functionally required for TWIST-induced EMT. These results uncover a novel mechanism for a bHLH transcription factor to recognize a unique spatial configuration of E-boxes to achieve target specificity. The WR-WR domain interaction uncovered here sets an example of target gene specificity of a bHLH protein being controlled allosterically by a domain outside of the bHLH region.

Methylenetetrahydrofolate reductase C677T variant in Indian children with craniosynostosis: Its role in the pathogenesis, risk of craniosynostosis

BACKGROUND

677C to T allele in the 5, 10-methylenetetrahydrofolate reductase (MTHFR) gene has been implicated in the etiology of various syndromes and nonsyndromic diseases but till date no direct studies have been reported with craniosynostosis.

OBJECTIVES

The aim was to study the family-based association of MTHFR polymorphism in different categories of craniosynostosis patients.

MATERIALS AND METHODS

This was a cross-sectional study in which 30 patients classified as Apert syndrome, Pfeiffr syndrome and nonsyndromic craniosynostosis patients with their family were recruited. A sample of 3 ml intravenous blood was taken from patients and from their family members (father and mother) in ethylenediaminetetraacetic acid-anticoagulated vacutainer for the purpose of the study. Genomic DNA was extracted from peripheral blood lymphocytes by phenol chloroform extraction method. Primers for MTHFR gene were designed. The polymerase chain reaction was carried out. After successful amplification, a small aliquot (5 μl) of the MTHFR reaction mixture was treated with 1 units of Hinf I restriction enzyme (NEB). Results were obtained and compiled.

RESULTS

A total of 30 patients/participants with craniosynostosis of Indian descent and their parents formed the study group. The genotyping did not confirm an association between the MTHFR 677C to T polymorphism and between different categories of craniosynostosis. When comparing the offspring of mothers statistically significant differences were found.

CONCLUSION

C667T polymorphism of the MTHFR gene is unlikely to play a role in the pathogenesis of craniosynostosis though maternal MTHFR C677T polymorphism may be a genetic risk factor.

Closing the Gap: Genetic and Genomic Continuum from Syndromic to Nonsyndromic Craniosynostoses

Craniosynostosis, a condition that includes the premature fusion of one or multiple cranial sutures, is a relatively common birth defect in humans and the second most common craniofacial anomaly after orofacial clefts. There is a significant clinical variation among different sutural synostoses as well as significant variation within any given single-suture synostosis. Craniosynostosis can be isolated (i.e., nonsyndromic) or occurs as part of a genetic syndrome (e.g., Crouzon, Pfeiffer, Apert, Muenke, and Saethre-Chotzen syndromes). Approximately 85 % of all cases of craniosynostosis are nonsyndromic. Several recent genomic discoveries are elucidating the genetic basis for nonsyndromic cases and implicate the newly identified genes in signaling pathways previously found in syndromic craniosynostosis. Published epidemiologic and phenotypic studies clearly demonstrate that nonsyndromic craniosynostosis is a complex and heterogeneous condition supporting a strong genetic component accompanied by environmental factors that contribute to the pathogenetic network of this birth defect. Large population, rather than single-clinic or hospital-based studies is required with phenotypically homogeneous subsets of patients to further understand the complex genetic, maternal, environmental, and stochastic factors contributing to nonsyndromic craniosynostosis. Learning about these variables is a key in formulating the basis of multidisciplinary and lifelong care for patients with these conditions.

Unilateral coronal craniosynostosis and Down syndrome

There is no known correlation between Down syndrome and craniosynostosis. The authors report 2 infants with trisomy 21 and right unilateral coronal craniosynostosis. Both patients were clinically asymptomatic but displayed characteristic craniofacial features associated with each disorder. One patient underwent a bilateral fronto-orbital advancement and the other underwent an endoscopically assisted strip craniectomy with postoperative helmet therapy. Both patients demonstrated good cosmesis at follow-up.

Id1 Expression Level Determines the Differentiation of Human Dental Pulp Stem Cells

TWIST1 plays a crucial role in dentinogenesis, and its activity depends on both a dimerization partner selection and phosphorylation. Other factors, like Id proteins, can affect the availability of dimerization partners for TWIST1, subsequently leading to diverse biological outcomes. The purpose of this study was to evaluate an impact of Id1 expression on differentiation of dental pulp stem cells (DPSCs). The altered expression of Id1 was achieved by transfection of human DPSCs with lentiviral vectors either driving an entire sequence of Id1, hence leading to Id1 overexpression, or carrying the Id1 silencing sequence. We observed that both overexpression and silencing of Id1 modulated human DPSC differentiation. Id1 overexpression resulted in a prevailing formation of TWIST1 homodimer and increased expression of genes encoding dentin sialophosphoprotein and dentin matrix protein 1, which confirm an enhanced odontogenic differentiation of DPSCs. Concurrently, Id1 silencing produced an opposite effect, slowing DPSC differentiation. These results highlight Id1 as an important modulator of molecular events during DPSC commitment and differentiation, which should be considered in dental research on tissue engineering. Moreover, we assume that the balance between TWIST1 dimerization forms in DPSCs might function in a cell-type-specific manner.

Craniofacial shape variation in Twist1+/- mutant mice

Craniosynostosis (CS) is a relatively common birth defect resulting from the premature fusion of one or more cranial sutures. Human genetic studies have identified several genes in association with CS. One such gene that has been implicated in both syndromic (Saethre-Chotzen syndrome) and nonsyndromic forms of CS in humans is TWIST1. In this study, a heterozygous Twist1 knock out (Twist1(+/-) ) mouse model was used to study the craniofacial shape changes associated with the partial loss of function. A geometric morphometric approach was used to analyze landmark data derived from microcomputed tomography scans to compare craniofacial shape between 17 Twist1(+/-) mice and 26 of their Twist1(+/+) (wild type) littermate controls at 15 days of age. The results show that despite the purported wide variation in synostotic severity, Twist1(+/-) mice have a consistent pattern of craniofacial dysmorphology affecting all major regions of the skull. Similar to Saethre-Chotzen, the calvarium is acrocephalic and wide with an overall brachycephalic shape. Mutant mice also exhibited a shortened cranial base and a wider and shorted face, consistent with coronal CS associated phenotypes. The results suggest that these differences are at least partially the direct result of the Twist1 haploinsufficiency on the developing craniofacial skeleton. This study provides a quantitative phenotype complement to the developmental and molecular genetic research previously done on Twist1. These results can be used to generate further hypotheses about the effect of Twist1 and premature suture fusion on the entire craniofacial skeleton.

Genotype and clinical care correlations in craniosynostosis: findings from a cohort of 630 Australian and New Zealand patients

Craniosynostosis is one of the most common craniofacial disorders encountered in clinical genetics practice, with an overall incidence of 1 in 2,500. Between 30% and 70% of syndromic craniosynostoses are caused by mutations in hotspots in the fibroblast growth factor receptor (FGFR) genes or in the TWIST1 gene with the difference in detection rates likely to be related to different study populations within craniofacial centers. Here we present results from molecular testing of an Australia and New Zealand cohort of 630 individuals with a diagnosis of craniosynostosis. Data were obtained by Sanger sequencing of FGFR1, FGFR2, and FGFR3 hotspot exons and the TWIST1 gene, as well as copy number detection of TWIST1. Of the 630 probands, there were 231 who had one of 80 distinct mutations (36%). Among the 80 mutations, 17 novel sequence variants were detected in three of the four genes screened. In addition to the proband cohort there were 96 individuals who underwent predictive or prenatal testing as part of family studies. Dysmorphic features consistent with the known FGFR1-3/TWIST1-associated syndromes were predictive for mutation detection. We also show a statistically significant association between splice site mutations in FGFR2 and a clinical diagnosis of Pfeiffer syndrome, more severe clinical phenotypes associated with FGFR2 exon 10 versus exon 8 mutations, and more frequent surgical procedures in the presence of a pathogenic mutation. Targeting gene hot spot areas for mutation analysis is a useful strategy to maximize the success of molecular diagnosis for individuals with craniosynostosis.

Molecular Analysis of Twist1 and FGF Receptors in a Rabbit Model of Craniosynostosis: Likely Exclusion as the Loci of Origin

Craniosynostosis is the premature fusion of the cranial vault sutures. We have previously described a colony of rabbits with a heritable pattern of nonsyndromic, coronal suture synostosis; however, the underlying genetic defect remains unknown. We now report a molecular analysis to determine if four genes implicated in human craniosynostosis, TWIST1 and fibroblast growth factor receptors 1–3 (FGFR1–3), could be the loci of the causative mutation in this unique rabbit model. Single nucleotide polymorphisms (SNPs) were identified within the Twist1, FGFR1, and FGFR2 genes, and the allelic patterns of these silent mutations were examined in 22 craniosynostotic rabbits. SNP analysis of the Twist1, FGFR1, and FGFR2 genes indicated that none were the locus of origin of the craniosynostotic phenotype. In addition, no structural mutations were identified by direct sequence analysis of Twist1 and FGFR3 cDNAs. These data indicate that the causative locus for heritable craniosynostosis in this rabbit model is not within the Twist1, FGFR1, and FGFR2 genes. Although a locus in intronic or flanking sequences of FGFR3 remains possible, no direct structural mutation was identified for FGFR3.

MAPK/ERK Signaling Pathway Analysis in Primary Osteoblasts From Patients With Nonsyndromic Sagittal Craniosynostosis

OBJECTIVE

The MAPK/ERK signaling pathway has been implicated in several craniosynostosis syndromes and represents a plausible target for therapeutic management of craniosynostosis. The causes of sagittal nonsyndromic craniosynostosis (sNSC) have not been well understood and the role that MAPK/ERK signaling cascade plays in this condition warrants an investigation. We hypothesized that MAPK-signaling is misregulated in calvarial osteoblasts derived from patients with sNSC.

METHODS

In order to analyze if the MAPK/ERK pathway is perturbed in sNSC, we established primary calvarial osteoblast cell lines from patients undergoing surgery for correction of this congenital anomaly. Appropriate negative and positive control cell lines were used for comparison, and we examined the levels of phosphorylated ERK by immunoblotting.

RESULTS

Primary osteoblasts from patients with sNSC showed no difference in ERK1/2 phosphorylation with or without FGF2 stimulation as compared with control osteoblasts.

CONCLUSION

Under the described test conditions, we did not observe convincing evidence that MAPK/ERK signaling contributes to the development of sNSC.

A genome-wide association study identifies susceptibility loci for nonsyndromic sagittal craniosynostosis near BMP2 and within BBS9

Sagittal craniosynostosis is the most common form of craniosynostosis, affecting approximately one in 5,000 newborns. We conducted, to our knowledge, the first genome-wide association study for nonsyndromic sagittal craniosynostosis (sNSC) using 130 non-Hispanic case-parent trios of European ancestry (NHW). We found robust associations in a 120-kb region downstream of BMP2 flanked by rs1884302 (P = 1.13 × 10(-14), odds ratio (OR) = 4.58) and rs6140226 (P = 3.40 × 10(-11), OR = 0.24) and within a 167-kb region of BBS9 between rs10262453 (P = 1.61 × 10(-10), OR = 0.19) and rs17724206 (P = 1.50 × 10(-8), OR = 0.22). We replicated the associations to both loci (rs1884302, P = 4.39 × 10(-31) and rs10262453, P = 3.50 × 10(-14)) in an independent NHW population of 172 unrelated probands with sNSC and 548 controls. Both BMP2 and BBS9 are genes with roles in skeletal development that warrant functional studies to further understand the etiology of sNSC.

Frank-ter Haar syndrome associated with sagittal craniosynostosis and raised intracranial pressure

BACKGROUND

Frank-ter Haar syndrome is a rare disorder associated with skeletal, cardiac, ocular and craniofacial features including hypertelorism and brachycephaly. The most common underlying genetic defect in Frank-ter Haar syndrome appears to be a mutation in the SH3PXD2B gene on chromosome 5q35.1. Craniosynostosis, or premature fusion of the calvarial sutures, has not previously been described in Frank-ter Haar syndrome.

CASE PRESENTATION

We present a family of three affected siblings born to consanguineous parents with clinical features in keeping with a diagnosis of Frank-ter Haar syndrome. All three siblings have a novel mutation caused by the deletion of exon 13 of the SH3PXD2B gene. Two of the three siblings also have non-scaphocephalic sagittal synostosis associated with raised intracranial pressure.

CONCLUSION

The clinical features of craniosynostosis and raised intracranial pressure in this family with a confirmed diagnosis of Frank-ter Haar syndrome expand the clinical spectrum of the disease. The abnormal cranial proportions in a mouse model of the disease suggests that the association is not coincidental. The possibility of craniosynostosis should be considered in individuals with a suspected diagnosis of Frank-ter Haar syndrome.

Multicenter study of neurodevelopment in 3-year-old children with and without single-suture craniosynostosis

OBJECTIVE

To evaluate the hypothesis that 3-year-old children with single-suture craniosynostosis would receive lower neurodevelopmental scores than a comparable group of children born with patent sutures.

DESIGN

Longitudinal comparison study.

SETTING

Five tertiary care craniofacial centers.

PARTICIPANTS

Patients with craniosynostosis (cases) and a comparison group of children without craniosynostosis(controls). Patients diagnosed with single-suture craniosynostosis from 2002 to 2006 were eligible as cases.Controls were frequency-matched to cases on age, sex, race, socioeconomic status, and study site.

MAIN EXPOSURE

Craniosynostosis.

MAIN OUTCOME MEASURES

We administered the Bayley Scales of Infant Development, Second Edition, mental and motor development indices and the Preschool Language Scales, Third Edition, receptive and expressive communication scales. Children were evaluated at baseline (before surgery in cases and at a similar age in controls)and at 18 and 36 months of age. We compared the groups' performances at 36 months by fitting adjusted linear and logistic regression models. We also estimated adjusted associations between age at surgery and neurodevelopmental scores.

RESULTS

Adjusted mean case deficits ranged from 3 to 6 points (P≤ .008 for all comparisons). Compared with controls, the odds of cases being delayed ranged from 1.5 to 2.0, depending on the neurodevelopmental scale (P values ranged from .03 to .09). Cases' ages at craniosynostosis repair were not strongly related to neurodevelopmental performance.

CONCLUSIONS

In this large, carefully controlled, multicenter study, we observed consistently lower mean neurodevelopmental scores in children with single-suture craniosynostosis compared with controls. These results provide further support for neurodevelopmental screening in young children with single-suture craniosynostosis.

Atypical scaphocephaly: a review

BACKGROUND AND PURPOSE

Sagittal craniosynostosis (SCS) is common and easily recognized and corrected surgically. However, rare cases of SCS are more complex: these associate closure of the metopic or delayed closure of the coronal suture, uni- or bilaterally.

MATERIAL AND METHODS

We reviewed the available literature on atypical sagittal craniosynostosis (ASCS). We also reviewed retrospectively our series of SCS treated since 1980 and selected cases with simultaneous closure of the metopic (leptocephaly) or delayed closure of other sutures (plagiocephaly, oxycephaly, or Crouzon syndrome).

RESULTS

ASCS is rare, representing <10 % of SCS. In our series, among 447 cases of SCS followed for a mean duration of 63.7 months, we identified 22 cases of ASCS: 6 with leptocephaly, 9 with non-syndromic oxycephaly, 4 with Crouzon syndrome, and 3 with plagiocephaly. Fourteen patients required a second operation, either planned initially (severe leptocephaly) or because of brain compression. The actuarial incidence of ASCS requiring reoperation was 5.3 % of SCS at 10 years. After a mean follow-up of 113 months, morphological results in ASCS were grade 1 (no defect) in 5, grade 2 (mild defect) in 2, grade 3 (minor reoperation) in 3, and grade 4 (major reoperation) in 12; one patient had visual impairment, and two had learning difficulties.

CONCLUSIONS

ACSC can be detected initially or occur with a delay in apparently standard SCS. Leptocephaly is a specific entity. Because of the implications on the management and risk for the patient, preoperative evaluation of patients with SCS with CT scanner and prolonged follow-up are necessary.

Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications

BACKGROUND

Non syndromic craniosynostoses are the most frequent craniofacial malformations worldwide. They represent a wide and heterogeneous group of entities, in which the dysmorphism may occur in a single (simple forms) or in multiple sutures (complex forms). Simple forms present a higher birth prevalence and are classified according to the involved suture and to the corresponding abnormal cranial shape: scaphocephaly (SC; sagittal suture), trigonocephaly (TC; metopic suture), anterior plagiocephaly (unilateral coronal suture), posterior plagiocephaly (unilateral lambdoid suture). They occur commonly as sporadic forms, although a familiar recurrence is sometimes observed, suggesting a mendelian inheritance. The genetic causes of simple craniosynostosis are still largely unknown, as mutations in common craniosynostosis-associated genes and structural chromosomal aberrations have been rarely found in these cases.

AIMS

This review is intended to dissect comprehensively the state-of-the art on the genetic etiology of single suture craniosynostoses, in the attempt to categorize all known disease-associated genes and chromosomal aberrations. Possible genotype/phenotype correlations are discussed as useful clues towards the definition of optimized clinical management flowcharts.