Enlarged parietal foramina caused by mutations in the homeobox genes ALX4 and MSX2: from genotype to phenotype

Bilateral Foramina Parietalia Permagna - A Calvarial Defect Caused by Haploinsufficiency of the Msh Homeobox 2 Gene: A Case Report and Current Literature Review

Foramina parietalia permagna (FPP) is a rare anatomical defect that affects the parietal bones of the human skull. FPP is characterized by symmetric perforations on either side of the skull, which are caused by insufficient ossification during embryogenesis. These openings are typically abnormally large and can range from a few millimeters to several centimeters in diameter. Enlarged foramina are often discovered incidentally during anatomical or radiological examinations and in most cases left untreated unless symptoms develop. Although this calvarial defect is usually asymptomatic, it may be accompanied by neurological or vascular conditions that can have clinical significance in certain cases. FPP is an inherited disorder and arises due to mutations in either Msh homeobox 2 (MSX2) or aristaless-like homeobox 4 (ALX4) genes. In almost all cases, one parent is affected. Clinical findings and diagnostic imaging typically contribute to determine the diagnosis.

Integrative analysis of transcriptome dynamics during human craniofacial development identifies candidate disease genes

Craniofacial disorders arise in early pregnancy and are one of the most common congenital defects. To fully understand how craniofacial disorders arise, it is essential to characterize gene expression during the patterning of the craniofacial region. To address this, we performed bulk and single-cell RNA-seq on human craniofacial tissue from 4-8 weeks post conception. Comparisons to dozens of other human tissues revealed 239 genes most strongly expressed during craniofacial development. Craniofacial-biased developmental enhancers were enriched +/- 400 kb surrounding these craniofacial-biased genes. Gene co-expression analysis revealed that regulatory hubs are enriched for known disease causing genes and are resistant to mutation in the normal healthy population. Combining transcriptomic and epigenomic data we identified 539 genes likely to contribute to craniofacial disorders. While most have not been previously implicated in craniofacial disorders, we demonstrate this set of genes has increased levels of de novo mutations in orofacial clefting patients warranting further study.

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.

Transcriptomic Signatures of Single-Suture Craniosynostosis Phenotypes

Craniosynostosis is a birth defect where calvarial sutures close prematurely, as part of a genetic syndrome or independently, with unknown cause. This study aimed to identify differences in gene expression in primary calvarial cell lines derived from patients with four phenotypes of single-suture craniosynostosis, compared to controls. Calvarial bone samples (N = 388 cases/85 controls) were collected from clinical sites during reconstructive skull surgery. Primary cell lines were then derived from the tissue and used for RNA sequencing. Linear models were fit to estimate covariate adjusted associations between gene expression and four phenotypes of single-suture craniosynostosis (lambdoid, metopic, sagittal, and coronal), compared to controls. Sex-stratified analysis was also performed for each phenotype. Differentially expressed genes (DEGs) included 72 genes associated with coronal, 90 genes associated with sagittal, 103 genes associated with metopic, and 33 genes associated with lambdoid craniosynostosis. The sex-stratified analysis revealed more DEGs in males (98) than females (4). There were 16 DEGs that were homeobox (HOX) genes. Three TFs (SUZ12, EZH2, AR) significantly regulated expression of DEGs in one or more phenotypes. Pathway analysis identified four KEGG pathways associated with at least one phenotype of craniosynostosis. Together, this work suggests unique molecular mechanisms related to craniosynostosis phenotype and fetal sex.

Dissection of mendelian predisposition and complex genetic architecture of craniovertebral junction malformation

The craniovertebral junction (CVJ) is an anatomically complex region of the axial skeleton that provides protection of the brainstem and the upper cervical spinal cord. Structural malformation of the CVJ gives rise to life-threatening neurological deficits, such as quadriplegia and dyspnea. Unfortunately, genetic studies on human subjects with CVJ malformation are limited and the pathogenesis remains largely elusive. In this study, we recruited 93 individuals with CVJ malformation and performed exome sequencing. Manual interpretation of the data identified three pathogenic variants in genes associated with Mendelian diseases, including CSNK2A1, MSX2, and DDX3X. In addition, the contribution of copy number variations (CNVs) to CVJ malformation was investigated and three pathogenic CNVs were identified in three affected individuals. To further dissect the complex mutational architecture of CVJ malformation, we performed a gene-based rare variant association analysis utilizing 4371 in-house exomes as control. Rare variants in LGI4 (carrier rate = 3.26%, p = 3.3 × 10^-5) and BEST1 (carrier rate = 5.43%, p = 5.77 × 10^-6) were identified to be associated with CVJ malformation. Furthermore, gene set analyses revealed that extracellular matrix- and RHO GTPase-associated biological pathways were found to be involved in the etiology of CVJ malformation. Overall, we comprehensively dissected the genetic underpinnings of CVJ malformation and identified several novel disease-associated genes and biological pathways.

Craniolacunia and the Development of the Fetal Calvaria: An Autopsy Series With Clinical and Histological Analysis

BACKGROUND

Craniolacunia, also known as lückenschädel, is a congenital abnormality of the calvaria featuring well-circumscribed areas of marked thinning, interspersed with more-normal bone. It is most commonly associated with myelomeningocele and/or Chiari 2 malformation.

METHODS

Records, photographs, and histologic sections were reviewed from 13 autopsy cases with craniolacunia. To investigate normal calvarial development, 23 parietal bone samples from fetuses/infants of 16-42 weeks gestation were examined.

RESULTS

Parietal bone development had reproducible morphologic stages. Bone thickness increased with gestational age, while osteoblast numbers decreased. Craniolacunia was mainly seen in neonates. Five patients had Chiari 2 malformation, 1 had hydrocephalus, and 2 had other structural CNS abnormalities. One had trisomy 18. Four had no congenital abnormalities. Two sustained intrapartum skull fractures. Histologic sections were available in 5 cases. Lacunae in term infants had architecture similar to normal calvaria at 16-20 weeks. Adjacent bone had age appropriate architecture but increased osteoblast numbers.

CONCLUSIONS

This is the largest autopsy series of craniolacunia and first systematic histologic analysis of craniolacunia and the developing fetal calvaria. Decreased cerebrospinal fluid pressure, due to myelomeningocele or other structural abnormality, may promote craniolacunia development. The risk of intrapartum fracture through lacunae emphasizes the continued clinical relevance of this diagnosis.

Retroperitoneal liposarcoma and craniosynostosis: possible genomic relationship, case report, and literature review

Based on a case report, this review explores the genomic landscape for patients with liposarcomas and possible relationships with gene mutations related to craniosynostosis. We describe the case of a 40-year-old man, known for a surgical correction of craniosynostosis before the age of 1 year, who underwent a radical resection of a voluminous retroperitoneal liposarcoma; histopathological analysis revealed a low-grade well-differentiated, mostly sclerosing, liposarcoma. A genetic analysis searching for mutations in blood DNA was performed and did not detect any specific mutation. A literature review was also conducted. Several tumors related to syndromic and non-syndromic craniosynostosis are mentioned in the literature; no specific link with retroperitoneal liposarcoma is established but the FGFR3 mutation is detected in dedifferentiated liposarcomas. To date, no case has been reported in the literature demonstrating a genetic relationship between craniosynostosis and low-grade differentiated retroperitoneal liposarcoma. We conclude that further studies for gene complex mutations should be conducted to show a possible genetic relationship between retroperitoneal liposarcoma and craniosynostosis.

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.

Study of non-metric characters of the skull to determine the epigenetic variability in populations of the European wildcat (Felis silvestris silvestris) and domestic cats (Felis catus)

We studied the variability of non-metric cranial traits, mainly foramina, of European wildcats (Felis silvestris silvestris) and domestic cats (Felis catus) from Germany based on 28 non-metric traits in 211 skulls. The domestic cats were grouped together as a statistical population. The wildcats were divided into two populations: Harz and Hesse, which were further subdivided, based on traffic infrastructure, natural landscape, and in the Harz, on time period. Epigenetic variability, epigenetic distance and the fluctuating asymmetry were calculated to assess genetic variability, possible depressions and population stability. The epigenetic variability Iev of the wildcat groups ranged from 0.27 (Hesse II) to 0.40 (Harz I). The difference in Iev between all specimens from Harz and Hesse respectively was less (Iev = 0.37 Harz and 0.31 Hesse). Compared to other studies these values are not assumed to indicate genetic depression. The epigenetic distance between the wildcat samples is 0.0774 overall, and in each case higher between sub-groups of the Harz and Hesse than between groups within these regions, respectively. The significant epigenetic distance between Harz and Hesse might indicate—at least past formerly—restricted connectivity between these regions. The fluctuating asymmetry for wildcats in total is 11.74% and in the sub-groups it ranges from 8.47 to 16.14%. These values are below 20% are at the lower range known from populations of other mammal species. The use of fluctuating asymmetry had also been discussed critically in its usefulness to assess viability of populations.

Transcription Factors of the Alx Family: Evolutionarily Conserved Regulators of Deuterostome Skeletogenesis

Members of the alx gene family encode transcription factors that contain a highly conserved Paired-class, DNA-binding homeodomain, and a C-terminal OAR/Aristaless domain. Phylogenetic and comparative genomic studies have revealed complex patterns of alx gene duplications during deuterostome evolution. Remarkably, alx genes have been implicated in skeletogenesis in both echinoderms and vertebrates. In this review, we provide an overview of current knowledge concerning alx genes in deuterostomes. We highlight their evolutionarily conserved role in skeletogenesis and draw parallels and distinctions between the skeletogenic gene regulatory circuitries of diverse groups within the superphylum.

A Rare Congenital Cause of Epilepsy

Enlarged parietal foramina (PFM) are congenital calvarial defects characterized by bilateral parietal bone defects (>5 mm), occurring on each side of the sagittal suture along its posterior aspect. While often lacking underlying intracranial malformations, there has been increasing recognition of coexisting brain malformations in certain subtypes. We present a case of a 12-year-old girl presenting with new-onset grand mal seizure with developmental delay and a known family history of epilepsy. Brain MRI revealed large, bilateral parietal bone defects with underlying cortical malformation (polymicrogyria and ulegyria) and vascular abnormalities (persistent falcine sinus), related to PFM. This case report describes the genetic basis for recognized subtypes of PFM and the rare association of brain malformations associated with PFM due to mutations in the ALX4 homeobox gene.

Cranium Bifidum Occultum Associated with Hypertelorism Treated with Posterior Vault Reconstruction and Orbital Box Osteotomies: Case Report and Technical Note

Cranium bifidum occultum is a disorder of skull ossification presenting as an enlarged posterior fontanelle in the upper posterior angle of the parietal bone near the intersection of the sagittal and lambdoid sutures. The standard treatment for cranium bifidum occultum is observation. We present a case of a 5-year-old boy who presented with a 15 × 4.5 cm midline posterior cranial vault defect consistent with diagnosis of cranium bifidum occultum associated with orbital hypertelorism and a widened nose. The patient underwent posterior vault reconstruction for correction of cranium bifidum occultum defect followed by bifrontal craniotomy and orbital box osteotomies for correction of orbital hypertelorism and nasal deformity. To our knowledge, this is the first reported case describing surgical treatment for cranium bifidum occultum associated with orbital hypertelorism.

Foramina parietalia permagna: familial and radiological evaluation of two cases and review of literature

PURPOSE

Foramina parietalia permagna is a variable intramembranous ossification defect of the parietal bones. Foramina parietalia permagna have an autosomal dominant inheritance, and it is showed that mutations in chromosome 5 and 11 are causing this anomaly. Enlarged parietal foramina occurs extremely rare. They are usually asymptomatic, but occasional headache, vomiting, pain over unprotected cerebral cortex, and seizures may be experienced by the patients. In the literature, some associated congenital bony defects, soft tissue pathologies, underlying neuronal deficits, and vascular variations have been described.

METHODS

We report two cases of foramina parietal permagna with their pedigrees and genetic analysis.

RESULTS

In case 1, cytogenetic analysis revealed a mutation of the ALX4 gene and all of the members of the family diagnosed with FPP. MRI revealed inferior vermian cerebellar hypoplasia. Surgery was not considered. In case 2, cytogenetic analysis could not be obtained because of financial reasons. Cranial MRI revealed hypoplastic right transverse sinus and sigmoid sinus, with a persistent parafalcine sinus. Surgery was not considered.

CONCLUSION

Despite of its rarity, genetic background and some important associated anomalies make foramina parietalia permagna more than an uncommon insignificant genetic disorder.

Frontonasal Dysplasia: Towards an Understanding of Molecular and Developmental Aetiology

The complex anatomy of the skull and face arises from the requirement to support multiple sensory and structural functions. During embryonic development, the diverse component elements of the neuro- and viscerocranium must be generated independently and subsequently united in a manner that sustains and promotes the growth of the brain and sensory organs, while achieving a level of structural integrity necessary for the individual to become a free-living organism. While each of these individual craniofacial components is essential, the cranial and facial midline lies at a structural nexus that unites these disparately derived elements, fusing them into a whole. Defects of the craniofacial midline can have a profound impact on both form and function, manifesting in a diverse array of phenotypes and clinical entities that can be broadly defined as frontonasal dysplasias (FNDs). Recent advances in the identification of the genetic basis of FNDs along with the analysis of developmental mechanisms impacted by these mutations have dramatically altered our understanding of this complex group of conditions.

Chitayat syndrome: hyperphalangism, characteristic facies, hallux valgus and bronchomalacia results from a recurrent c.266A>G p.(Tyr89Cys) variant in the ERF gene

BACKGROUND

In 1993, Chitayat et al., reported a newborn with hyperphalangism, facial anomalies, and bronchomalacia. We identified three additional families with similar findings. Features include bilateral accessory phalanx resulting in shortened index fingers; hallux valgus; distinctive face; respiratory compromise.

OBJECTIVES

To identify the genetic aetiology of Chitayat syndrome and identify a unifying cause for this specific form of hyperphalangism.

METHODS

Through ongoing collaboration, we had collected patients with strikingly-similar phenotype. Trio-based exome sequencing was first performed in Patient 2 through Deciphering Developmental Disorders study. Proband-only exome sequencing had previously been independently performed in Patient 4. Following identification of a candidate gene variant in Patient 2, the same variant was subsequently confirmed from exome data in Patient 4. Sanger sequencing was used to validate this variant in Patients 1, 3; confirm paternal inheritance in Patient 5.

RESULTS

A recurrent, novel variant NM_006494.2:c.266A>G p.(Tyr89Cys) in ERF was identified in five affected individuals: de novo (patient 1, 2 and 3) and inherited from an affected father (patient 4 and 5). p.Tyr89Cys is an aromatic polar neutral to polar neutral amino acid substitution, at a highly conserved position and lies within the functionally important ETS-domain of the protein. The recurrent ERF c.266A>C p.(Tyr89Cys) variant causes Chitayat syndrome.

DISCUSSION

ERF variants have previously been associated with complex craniosynostosis. In contrast, none of the patients with the c.266A>G p.(Tyr89Cys) variant have craniosynostosis.

CONCLUSIONS

We report the molecular aetiology of Chitayat syndrome and discuss potential mechanisms for this distinctive phenotype associated with the p.Tyr89Cys substitution in ERF.

Enlarged parietal foramina: a rare forensic autopsy finding

Enlarged parietal foramina (EPF) are a quite rare developmental defect of the parietal bone which has to be distinguished from the normal small parietal foramina. We report a forensic case of an individual found in an advanced state of putrefaction in his own house with an undetermined cause of death. No evidence of trauma was observed, and the toxicological exam was negative. The victim was a 40-year-old man with a history of epilepsy. The large biparietal foramina, a rare anatomical variation and unusual autopsy finding, were observed at autopsy. The recognition of anatomical variations is important to avoid false interpretations and conclusions and has a significant potential as an identity factor, thus contributing to positive identification.

Spectrum of genes involved in a unique case of Potocki Schaffer syndrome with a large chromosome 11 deletion

Letter to the Editor.

Mild nasal clefting may be predictive for ALX4 heterozygotes

Heterozygous loss-of-function mutations in ALX4 are responsible for enlarged parietal foramina, whereas patients with biallelic ALX4 mutations display a phenotypic spectrum of clinical findings, from mild to severe alopecia, cranium bifidum, hypertelorism, microphthalmia, with alar clefting being the pivotal sign in all affecteds. We report on four affected individuals in a three-generation family, displaying a phenotypic spectrum ranging from mild nasal clefting and broad columella to subtle changes in nasal configuration in addition to parietal foramina, caused by a novel ALX4 mutation (c.646C>G, p.Arg216Gly). This is the second report of a family showing vertical transmission of a dominant ALX4 mutation with facial involvement in addition to parietal foramina, mimicking mild recessive ALX4 phenotype. We discuss possible pathological mechanisms that may have lead to phenotypic variation in the family and challenges in genetic counseling.

MSX2 Gene Duplication in a Patient with Eye Development Defects

BACKGROUND

MSX2 mutations are a very rare cause of craniosynostosis. Gain-of-function mutations may lead to the Boston-type craniosynostosis with limb defects and refraction errors, whereas loss-of-function mutations causes primary osseous defects such as enlarged parietal foramina.

MATERIALS AND METHODS

Herein we report the case of a child with bicoronal synostosis and cutaneous syndactylies, who presented iridal and chorioretinal colobomas. Due to the craniofacial features that were prominent in the clinical picture, the genes involved in craniosynostosis were explored.

RESULTS

The patient disclosed an intragenic duplication of the entire MSX2 gene whereas no mutation was identified in any major genes known to be involved in craniosynostosis.

CONCLUSION

This is the first report of an eye development defect due to an increase in the MSX2 copy number in a human being. The implication of this gene in eye development has already been shown in several animal models. Indeed, overexpression of the Msx2 gene in a mouse model resulted also in optic nerve aplasia and microphthalmia. This report expands the phenotypic spectrum of the MSX2 mutations impacting early ocular development knowledge.

Boston type craniosynostosis: report of a second mutation in MSX2

We describe a family that segregated an autosomal dominant form of craniosynostosis characterized by variable expression and limited extra-cranial features. Linkage analysis and genome sequencing were performed to identify the underlying genetic mutation. A c.443C>T missense mutation in MSX2, which predicts p.Pro148Leu was identified and segregated with the disease in all affected family members. One other family with autosomal dominant craniosynostosis (Boston type) has been reported to have a missense mutation in MSX2. These data confirm that missense mutations altering the proline at codon 148 of MSX2 cause dominantly inherited craniosynostosis.

Second family with the Boston-type craniosynostosis syndrome: novel mutation and expansion of the clinical spectrum

Craniosynostosis, caused by early fusion of one or more cranial sutures, can affect the coronal or lambdoid sutures, or include premature fusion of the sagittal (scaphocephaly) or metopic suture (trigonocephaly). Often occurring as isolated finding, their co-existence in a craniosynostosis syndrome is infrequent. We describe a four-generation family with variable expression of a craniosynostosis phenotype with scaphocephaly and a particularly severe trigonocephaly. Molecular analysis revealed a missense mutation in the MSX2-associated with the Boston-type craniosynostosis syndrome-affecting the same amino-acid residue as in the original Boston family. Besides unique features such as the cranial sutures involved, minor limb abnormalities and incomplete penetrance, our patients share with the original family autosomal dominant inheritance and the presence of multiple endocranial erosions on CT imaging. Though these findings appear to be important diagnostic clues for MSX2-related craniosynostosis, it is noteworthy that the first affected generation in this family presented merely with isolated sagittal or unicoronal craniosynostosis and cutaneous syndactyly. Molecular analysis of MSX2 should therefore be considered in patients with isolated scaphocephaly/unicoronal synostosis, especially in the presence of a family history for craniosynostosis or syndactyly.

Large parietal midline defect with unusual ridge-like structure at the rim and persistent falcine sinus

BACKGROUND

Midline cranial defects can be divided into lesions with intracranial tissue herniation (cranium bifidum cysticum) and lesions mainly with ossification failure (cranium bifidum occultum). Herniated cephaloceles mostly require surgical resection, while persisted parietal foramina might become smaller with age.

CLINICAL CASE

Here, we report a neonate with large symmetric midline skull defect at high parietal area. A mild bulging mass was noticed. Interestingly, unlike sac herniation, it was surrounded by bony ridges extended from the rim of the calvarial defect, which suggests aberrant ossification. Persistent falcine sinus was also detected. At the corrected age of 11 months, the size of the skull defect had decreased spontaneously, favoring the diagnosis of parietal bone ossification defect. Potential mechanisms resulting in the special appearance of skull bone were discussed.

CONCLUSION

Incomplete closing of the parietal foramina might be expected due to the aberrant ridge formation. We suggest protective measures for the calvarial defect.

Enlarged parietal foramina: a rare finding in a female Greek skull with unusual multiple Wormian bones and a rich parietal vascular network

Enlarged parietal foramina (>5 mm) is an extremely rare developmental defect of the parietal bone, which is distinguished from the normal small parietal foramina, as genes associated with this entity have been identified, suggesting that it is hereditary in nature. We describe a dry skull of a 35-year-old female, with enlarged parietal foramina symmetrically situated bilaterally, oval in shape, measuring 4.5 × 9.3 mm (right) and 4.9 × 9.2 mm (left) in size. The foramina coexisted with multiple Wormian bones in several sites of the skull. On the inner parietal bone surface, the anterior, posterior and lateral foramina's rims carried grooves, which were continuous with the middle meningeal vessels' branches, indicating that a rich vascular network existed around the foramina. These vascular grooves also notched the external table at the margin of the foramina, which suggests a potential communication between the meningeal and the scalp vessels. In addition, this vascular variation should be taken into consideration when performing surgical interventions in the area, because the large vascular supply to the foramina is a possible source of extensive bleeding. Moreover, the interaction of intracranial and extracranial veins and the fact that the blood flows in them in both directions, as they are valveless, could represent a possible pathway for infections to spread in the cranial cavity.

Enlarged parietal foramina: a review of genetics, prognosis, radiology, and treatment

INTRODUCTION

Enlarged parietal foramina are variable ossification defects in the parietal bones that present as symmetric radiolucencies on skull radiographs. In contrast to the normal small parietal foramina, enlarged parietal foramina are a hereditary condition and genes associated with it have been identified.

METHODS

A literature review was performed to discuss the many known findings related to enlarged parietal foramina.

CONCLUSIONS

Even though they remain asymptomatic in the majority of cases, they may be associated with other pathologies and occasionally become symptomatic. This article provides a comprehensive review of the current knowledge of enlarged parietal foramina.

An enlarged parietal foramen in the late archaic Xujiayao 11 neurocranium from Northern China, and rare anomalies among Pleistocene Homo

We report here a neurocranial abnormality previously undescribed in Pleistocene human fossils, an enlarged parietal foramen (EPF) in the early Late Pleistocene Xujiayao 11 parietal bones from the Xujiayao (Houjiayao) site, northern China. Xujiayao 11 is a pair of partial posteromedial parietal bones from an adult. It exhibits thick cranial vault bones, arachnoid granulations, a deviated posterior sagittal suture, and a unilateral (right) parietal lacuna with a posteriorly-directed and enlarged endocranial vascular sulcus. Differential diagnosis indicates that the perforation is a congenital defect, an enlarged parietal foramen, commonly associated with cerebral venous and cranial vault anomalies. It was not lethal given the individual’s age-at-death, but it may have been associated with secondary neurological deficiencies. The fossil constitutes the oldest evidence in human evolution of this very rare condition (a single enlarged parietal foramen). In combination with developmental and degenerative abnormalities in other Pleistocene human remains, it suggests demographic and survival patterns among Pleistocene Homo that led to an elevated frequency of conditions unknown or rare among recent humans.

Vertical transmission of a frontonasal phenotype caused by a novel ALX4 mutation

Frontonasal dysplasias (FND) comprise a spectrum of disorders caused by abnormal median facial development. Its etiology is still poorly understood but recently frontonasal dysplasia phenotypes were linked to loss-of-function mutations in the ALX homeobox gene family, which comprises the ALX1, ALX3, and ALX4 genes. All ALX-related frontonasal phenotypes till date had been compatible with an autosomal recessive mode of inheritance. In contrast, heterozygous loss-of-function mutations in ALX4 had been only associated with isolated symmetrical parietal ossification defects at the intersection of the sagittal and lambdoid sutures, known as enlarged parietal foramina. We report a family with vertical transmission from mother to son of mild frontonasal dysplasia phenotype caused by a novel ALX4 gene mutation (c.1080-1089_delGACCCGGTGCinsCTAAGATCTCAACAGAGATGGCAACT, p.Asp326fsX21).This is the first report of a frontonasal phenotype related to a heterozygous mutation in ALX4. This mutation is predicted to cause the loss of the aristaless domain in the C-terminal region of the protein and preserves the homeodomain. We speculate that a different mechanism, a dominant-negative effect, is responsible for the distinct phenotype in this family.

Defective neural crest migration revealed by a Zebrafish model of Alx1-related frontonasal dysplasia

Frontonasal dysplasia (FND) refers to a class of midline facial malformations caused by abnormal development of the facial primordia. The term encompasses a spectrum of severities but characteristic features include combinations of ocular hypertelorism, malformations of the nose and forehead and clefting of the facial midline. Several recent studies have drawn attention to the importance of Alx homeobox transcription factors during craniofacial development. Most notably, loss of Alx1 has devastating consequences resulting in severe orofacial clefting and extreme microphthalmia. In contrast, mutations of Alx3 or Alx4 cause milder forms of FND. Whilst Alx1, Alx3 and Alx4 are all known to be expressed in the facial mesenchyme of vertebrate embryos, little is known about the function of these proteins during development. Here, we report the establishment of a zebrafish model of Alx-related FND. Morpholino knock-down of zebrafish alx1 expression causes a profound craniofacial phenotype including loss of the facial cartilages and defective ocular development. We demonstrate for the first time that Alx1 plays a crucial role in regulating the migration of cranial neural crest (CNC) cells into the frontonasal primordia. Abnormal neural crest migration is coincident with aberrant expression of foxd3 and sox10, two genes previously suggested to play key roles during neural crest development, including migration, differentiation and the maintenance of progenitor cells. This novel function is specific to Alx1, and likely explains the marked clinical severity of Alx1 mutation within the spectrum of Alx-related FND.

ALX4 gain-of-function mutations in nonsyndromic craniosynostosis

Craniosynostosis is the early fusion of one or more sutures of the infant skull and is a common defect occurring in approximately 1 of every 2,500 live births. Nonsyndromic craniosynostosis (NSC) accounts for approximately 80% of all cases and is thought to have strong genetic determinants that are yet to be identified. ALX4 is a homeodomain transcription factor with known involvement in osteoblast regulation. By direct sequencing of the ALX4 coding region in sagittal or sagittal-suture-involved nonsyndromic craniosynostosis probands, we identified novel, nonsynonymous, familial variants in three of 203 individuals with NSC. Using dual-luciferase assay we show that two of these variants (V7F and K211E) confer a significant gain-of-function effect on ALX4. Our results suggest that ALX4 variants may have an impact on the genetic etiology of NSC.

Translocations disrupting PHF21A in the Potocki-Shaffer-syndrome region are associated with intellectual disability and craniofacial anomalies

Potocki-Shaffer syndrome (PSS) is a contiguous gene disorder due to the interstitial deletion of band p11.2 of chromosome 11 and is characterized by multiple exostoses, parietal foramina, intellectual disability (ID), and craniofacial anomalies (CFAs). Despite the identification of individual genes responsible for multiple exostoses and parietal foramina in PSS, the identity of the gene(s) associated with the ID and CFA phenotypes has remained elusive. Through characterization of independent subjects with balanced translocations and supportive comparative deletion mapping of PSS subjects, we have uncovered evidence that the ID and CFA phenotypes are both caused by haploinsufficiency of a single gene, PHF21A, at 11p11.2. PHF21A encodes a plant homeodomain finger protein whose murine and zebrafish orthologs are both expressed in a manner consistent with a function in neurofacial and craniofacial development, and suppression of the latter led to both craniofacial abnormalities and neuronal apoptosis. Along with lysine-specific demethylase 1 (LSD1), PHF21A, also known as BHC80, is a component of the BRAF-histone deacetylase complex that represses target-gene transcription. In lymphoblastoid cell lines from two translocation subjects in whom PHF21A was directly disrupted by the respective breakpoints, we observed derepression of the neuronal gene SCN3A and reduced LSD1 occupancy at the SCN3A promoter, supporting a direct functional consequence of PHF21A haploinsufficiency on transcriptional regulation. Our finding that disruption of PHF21A by translocations in the PSS region is associated with ID adds to the growing list of ID-associated genes that emphasize the critical role of transcriptional regulation and chromatin remodeling in normal brain development and cognitive function.

Mild nasal malformations and parietal foramina caused by homozygous ALX4 mutations

We report on a boy born to consanguineous parents, who had hypertelorism, a broad nasal bridge, ridge and tip, bifid nasal tip, cleft alae nasi, broad columella, unilateral preauricular tag, shallow labiogingival sulcus, and bilateral large parietal foramina. Cranial MRI revealed a kinked corpus body and small cerebellar vermis. Molecular analysis uncovered a homozygous c.673C > G (p.Q225E) mutation in ALX4 gene. We compare the relatively mild phenotype in the patient to the more marked phenotype described in other patients with homozygous ALX4 mutations, and to the phenotypes in patients with mutations in other ALX genes.

Prevalence and complications of single-gene and chromosomal disorders in craniosynostosis

OBJECTIVES

We describe the first cohort-based analysis of the impact of genetic disorders in craniosynostosis. We aimed to refine the understanding of prognoses and pathogenesis and to provide rational criteria for clinical genetic testing.

METHODS

We undertook targeted molecular genetic and cytogenetic testing for 326 children who required surgery because of craniosynostosis, were born in 1993-2002, presented to a single craniofacial unit, and were monitored until the end of 2007.

RESULTS

Eighty-four children (and 64 relatives) had pathologic genetic alterations (86% single-gene mutations and 14% chromosomal abnormalities). The FGFR3 P250R mutation was the single largest contributor (24%) to the genetic group. Genetic diagnoses accounted for 21% of all craniosynostosis cases and were associated with increased rates of many complications. Children with an initial clinical diagnosis of nonsyndromic craniosynostosis were more likely to have a causative mutation if the synostoses were unicoronal or bicoronal (10 of 48 cases) than if they were sagittal or metopic (0 of 55 cases; P = .0003). Repeat craniofacial surgery was required for 58% of children with single-gene mutations but only 17% of those with chromosomal abnormalities (P = .01).

CONCLUSIONS

Clinical genetic assessment is critical for the treatment of children with craniosynostosis. Genetic testing of nonsyndromic cases (at least for FGFR3 P250R and FGFR2 exons IIIa/c) should be targeted to patients with coronal or multisuture synostoses. Single-gene disorders that disrupt physiologic signaling in the cranial sutures often require reoperation, whereas chromosomal abnormalities follow a more-indolent course, which suggests a different, secondary origin of the associated craniosynostosis.

ALX4 dysfunction disrupts craniofacial and epidermal development

Genetic control of craniofacial morphogenesis requires a complex interaction of numerous genes encoding factors essential for patterning and differentiation. We present two Turkish families with a new autosomal recessive frontofacial dysostosis syndrome characterized by total alopecia, a large skull defect, coronal craniosynostosis, hypertelorism, severely depressed nasal bridge and ridge, bifid nasal tip, hypogonadism, callosal body agenesis and mental retardation. Using homozygosity mapping, we mapped the entity to chromosome 11p11.2-q12.3 and subsequently identified a homozygous c.793C-->T nonsense mutation in the human ortholog of the mouse aristaless-like homeobox 4 (ALX4) gene. This mutation is predicted to result in a premature stop codon (p.R265X) of ALX4 truncating 146 amino acids of the protein including a part of the highly conserved homeodomain and the C-terminal paired tail domain. Although the RNA is stable and not degraded by nonsense-mediated RNA decay, the mutant protein is likely to be non-functional. In a skin biopsy of an affected individual, we observed a hypomorphic interfollicular epidermis with reduced suprabasal layers associated with impaired interfollicular epidermal differentiation. Hair follicle-like structures were present but showed altered differentiation. Our data indicate that ALX4 plays a critical role both in craniofacial development as in skin and hair follicle development in human.

Pitfalls in the phylogenomic evaluation of human disease-causing mutations

A detailed sequence comparison of the MSX homeobox family sheds light on its evolution and identifies new conserved motifs. But in the absence of corroborative genetic data, phylogenomics alone can provide only limited insights into the pathogenicity of heterozygous missense substitutions in human genes.

Syndromes, disorders and maternal risk factors associated with neural tube defects (VII)

Neural tube defects (NTDs) may be associated with syndromes, disorders and maternal risk factors. This article provides a comprehensive review of the syndromes, disorders and maternal risk factors associated with NTDs, including DK phocomelia syndrome (von Voss-Cherstvoy syndrome), Siegel-Bartlet syndrome, fetal warfarin syndrome, craniotelencephalic dysplasia, Czeizel-Losonci syndrome, maternal cocaine abuse, Weissenbacher- Zweymller syndrome, parietal foramina (cranium bifidum), Apert syndrome, craniomicromelic syndrome, XXagonadism with multiple dysraphic lesions including omphalocele and NTDs, Fryns microphthalmia syndrome, Gershoni-Baruch syndrome, PHAVER syndrome, periconceptional vitamin B6 deficiency, and autosomal dominant Dandy-Walker malformation with occipital cephalocele. NTDs associated with these syndromes, disorders and maternal risk factors are a rare but important cause of NTDs. The recurrence risk and the preventive effect of maternal folic acid intake in NTDs associated with syndromes, disorders and maternal risk factors may be different from those of nonsyndromic multifactorial NTDs. Perinatal diagnosis of NTDs should alert doctors to the syndromes, disorders and maternal risk factors associated with NTDs, and prompt thorough etiologic investigation and genetic counseling.

Clinical dividends from the molecular genetic diagnosis of craniosynostosis

A dozen years have passed since the first genetic lesion was identified in a family with craniosynostosis, the premature fusion of the cranial sutures. Subsequently, mutations in the FGFR2, FGFR3, TWIST1, and EFNB1 genes have been shown to account for approximately 25% of craniosynostosis, whilst several additional genes make minor contributions. Using specific examples, we show how these discoveries have enabled refinement of information on diagnosis, recurrence risk, prognosis for mental development, and surgical planning. However, phenotypic variability can present a significant challenge to the clinical interpretation of molecular genetic tests. In particular, the difficulty of analyzing the complex interaction of genetic background and prenatal environment in determining clinical features, limits the value of identifying low penetrance mutations.

Msx2 -/- transgenic mice develop compound amelogenesis imperfecta, dentinogenesis imperfecta and periodental osteopetrosis

The physiological function of the transcription factor Msx2 in tooth and alveolar bone was analysed using a knock-in transgenic mouse line. In this mouse line, the beta-galactosidase gene was used to disrupt Msx2: thus, beta-galactosidase expression was driven by the Msx2 promoter, but Msx2 was not produced. This allowed to monitor Msx2 expression using a beta-galactosidase assay. Msx2 transgenic mice ubiquitously and continuously expressed the mutated Msx2-nlacZ gene in cells of the complex formed by tooth and alveolar bone. Msx2 -/- homozygous mice displayed a wide spectrum of alterations in tooth eruption and morphology as well as dental and periodontal defects from the first post-natal weeks up to 6 months. These defects culminated with the formation of an odontogenic tumour at the mandibular third molar site. This study suggests that bone resorption is a functional target of Msx2 in the alveolar compartment, since Msx2 was expressed in osteoclasts, with the highest expression levels found in the active sites of bone modelling associated with tooth eruption and root elongation. The RANK osteoclast differentiation pathway was affected in microdissected Msx2 -/- mouse alveolar bone (as inferred by RANK ligand mRNA levels) compared to basal bone and wild-type controls. Decreased alveolar osteoclast activity was observed in Msx2 -/- mice, similar to that seen in osteopetrosis, another condition in which osteoclast activity is impaired and odontogenic tumours form. These data suggest a pleiotropic role for Msx2 in oral bone growth from birth until adult homeostasis. RANK pathway appeared to be modulated by Msx2, in addition to the previously reported modulations of BMP4 and laminin5alpha3 in early tooth development. Non-overlapping Msx1 and Msx2 expression patterns suggested that these two homeogenes play non-redundant roles in skeletal growth, with Msx1 targeting basal bone and Msx2 targeting alveolar bone. This study provides a detailed analysis of the phenotype resulting from the Msx2 null mutation and identifies the impact of Msx1 and Msx2 on post-natal oral bone growth.

Developmental mechanisms and experimental models to understand forebrain malformative diseases

The development of the central nervous system can be divided into a number of phases, each of which can be subject of genetic or epigenetic alterations that may originate particular developmental disorders. In recent years, much progress has been made in elucidating the molecular and cellular mechanisms by which the vertebrate forebrain develops. Therefore, our understanding of major developmental brain disorders such as cortical malformations and neuronal migration disorders has significantly increased. In this review, we will describe the major stages in forebrain morphogenesis and regionalization, with special emphasis on developmental molecular mechanisms derailing telencephalic development with subsequent damage to cortical function. Because animal models, mainly mouse, have been fundamental for this progress, we will also describe some characteristic mouse models that have been capital to explore these molecular mechanisms of malformative diseases of the human brain. Although most of the genes involved in the regulation of basic developmental processes are conserved among vertebrates, the extrapolation of mouse data to corresponding gene expression and function in humans needs careful individual analysis in each functional system.