Genetic evaluation and application of posterior cranial fossa traits as endophenotypes for Chiari type I malformation

The Genetics of Chiari 1 Malformation

Chiari malformation type 1 (CM1) is a structural defect that involves the herniation of the cerebellar tonsils through the foramen magnum, causing mild to severe neurological symptoms. Little is known about the molecular and developmental mechanisms leading to its pathogenesis, prompting current efforts to elucidate genetic drivers. Inherited genetic disorders are reported in 2-3% of CM1 patients; however, CM1, including familial forms, is predominantly non-syndromic. Recent work has focused on identifying CM1-asscoiated variants through the study of both familial cases and de novo mutations using exome sequencing. This article aims to review the current understanding of the genetics of CM1. We discuss three broad classes of CM1 based on anatomy and link them with genetic lesions, including posterior fossa-linked, macrocephaly-linked, and connective tissue disorder-linked CM1. Although the genetics of CM1 are only beginning to be understood, we anticipate that additional studies with diverse patient populations, tissue types, and profiling technologies will reveal new insights in the coming years.

Anomalies of the Craniocervical Junction (Chiari Malformations)

Arnold Chiari malformations include a combination of posterior fossa, hindbrain, and cervical occipital junction abnormalities, sometimes associated with spinal cord abnormalities such as spina bifida, syringomyelia, and syringobulbia. The most frequent form is Chiari I syndrome but two other variants, progressively more severe, have been described. Chiari malformations are the result of defective development of posterior fossa and can be due to genetic mutations, skeletal malformations, and intrautero factors. Clinical manifestations depend on the compression of the nerve structures within the foramen magnum and the spinal canal and mainly consist in headache or neck pain, gait disturbances, sensory or motor abnormalities, and autonomic signs. However, a high number of cases of Chiari I is asymptomatic and the diagnosis is occasional. Diagnosis is performed through nuclear magnetic resonance imaging of the brain and cervical tract, although other investigations may support the diagnosis. First-line treatment for candidate patients is a surgical procedure that involves decompression of the posterior cranial fossa and the craniocervical junction, as well as correction of associated malformations with techniques that depend on the severity of the case. Anyhow, some symptomatic patients benefit from conservative medical treatment with nonsteroidal anti-inflammatory drugs.

Exploring pathogenesis, prevalence, and genetic associations in Chiari malformation type 1: a contemporary perspective

Chiari malformation type 1 (CM 1) entails a structural defect in the cerebellum, involving the herniation of cerebellar tonsils toward the foramen magnum. The symptomatic or asymptomatic nature of CM 1 is contingent upon the condition of malformation in the spinal cord. This review presents an updated perspective on the prevalence of CM 1, its pathogenesis, genetic associations, and treatment. CM 1 exhibits a higher prevalence in adult females than males. Despite the incomplete understanding of the exact cause of CM 1, recent research suggests the involvement of both genetic and environmental factors in its development. One of the reasons for the occurrence of CM 1 in individuals is the smaller posterior cranial fossa, which manifests as typical morphological features. Additionally, environmental factors can potentially interact with genetic factors, modifying the observable characteristics of the disease and affecting the symptoms, severity, and development of the condition. Notably, headaches, neck pain, dizziness, and neurological deficits may be exhibited by individuals with CM 1, highlighting the importance of early diagnosis. Magnetic resonance imaging (MRI) serves as an alternative diagnostic technique for monitoring the symptoms of CM 1. Multiple genetic factors are likely to contribute to a cascade of abnormalities in CM 1. Early studies provided evidence, including clustering within families, bone development, and co-segregation with known genetic syndromes, establishing CM 1's association with a genetic basis. Furthermore, surgery is the only available treatment option to alleviate symptoms or hinder the progression of damage to the central nervous system (CNS) in CM 1 cases.

Prenatal diagnosis of non-typical Chiari malformation type I associated with de novo Nuclear Factor I A gene mutation: a case report

BACKGROUND

Chiari malformation is one of the most common Central nervous system (CNS) abnormalities that can be detected in routine fetal scanning. Chiari malformation type I (CMI) is a congenital defect characterized by a displacement of the cerebellar tonsils through the foramen magnum. The etiology of CMI has not been well established and suggested having multifactorial contributions, especially genetic deletion. Clinical characteristics of this anomaly may express in different symptoms from neurological dysfunction and/or skeletal abnormalities in the later age, but it is rarely reported in pregnancy.

CASE PRESENTATION

We present a case in which the Chiari malformation type I was diagnosed with comorbidities of facial anomalies (flatting forehead and micrognathia) and muscular-skeletal dysmorphologies (clenched hands and clubfeet) at the 24+6 weeks of gestation in a 29-year-old Vietnamese pregnant woman. The couple refused an amniocentesis, and the pregnancy was followed up every 4 weeks until a spontaneous delivery occurred at 38 weeks. The newborn had a severe asphyxia and seizures at birth required to have an emergency resuscitation at delivery. He is currently being treated in the intensive neonatal care unit. He carries the novel heterozygous NFIA gene mutation confirmed after birth. No further postnatal malformation detected.

CONCLUSION

CMI may only represent with facial abnormalities and muscle-skeletal malformations at the early stage of pregnancy, which may also alert an adverse outcome. A novel heterozygous NFIA gene mutation identified after birth helps to confirm prenatal diagnosis of CMI and to provide an appropriate consultation.

Evaluation and Treatment of Patients with Small Posterior Cranial Fossa and Chiari Malformation, Types 0 and 1

The diagnosis of Chiari I malformation is straightforward in patients with typical signs and symptoms of Chiari I malformation and magnetic resonance imaging (MRI) confirming ≥5 mm of cerebellar tonsillar ectopia, with or without a syrinx. However, in many cases, Chiari I malformation is discovered incidentally on MRI to evaluate global headache, cervical radiculopathy, or other conditions. In those cases, the clinician must consider if cerebellar tonsillar ectopia is related to the presenting symptoms. Surgical decompression of the cerebellar tonsils and foramen magnum in patients with symptomatic Chiari I malformation effectively relieves suboccipital headache, reduces syrinx distension, and arrests syringomyelia progression. Neurosurgeons must avoid operative treatments decompressing incidental tonsillar ectopia, not causing symptoms. Such procedures unnecessarily place patients at risk of operative complications and tissue injuries related to surgical exploration. This chapter reviews the typical signs and symptoms of Chiari I malformation and its variant, Chiari 0 malformation, which has <5 mm of cerebellar tonsillar ectopia and is often associated with syringomyelia. Chiari I and Chiari 0 malformations are associated with incomplete occipital bone development, reduced volume and height of the posterior fossa, tonsillar ectopia, and compression of the neural elements and cerebrospinal fluid (CSF) pathways at the foramen magnum. Linear, angular, cross-sectional area, and volume measurements of the posterior fossa, craniocervical junction, and upper cervical spine identify morphometric abnormalities in Chiari I and Chiari 0 malformation patients. Chiari 0 patients respond like Chiari I patients to foramen magnum decompression and should not be excluded from surgical treatment because their tonsillar ectopia is <5 mm. The authors recommend the adoption of diagnostic criteria for Chiari 0 malformation without syringomyelia. This chapter provides updated information and guidance to the physicians managing Chiari I and Chiari 0 malformation patients and neuroscientists interested in Chiari malformations.

Human genetics and molecular genomics of Chiari malformation type 1

Chiari malformation type 1 (CM1) is the most common structural brain disorder involving the craniocervical junction, characterized by caudal displacement of the cerebellar tonsils below the foramen magnum into the spinal canal. Despite the heterogeneity of CM1, its poorly understood patho-etiology has led to a 'one-size-fits-all' surgical approach, with predictably high rates of morbidity and treatment failure. In this review we present multiplex CM1 families, associated Mendelian syndromes, and candidate genes from recent whole exome sequencing (WES) and other genetic studies that suggest a significant genetic contribution from inherited and de novo germline variants impacting transcription regulation, craniovertebral osteogenesis, and embryonic developmental signaling. We suggest that more extensive WES may identify clinically relevant, genetically defined CM1 subtypes distinguished by unique neuroradiographic and neurophysiological endophenotypes.

A Critical Update of the Classification of Chiari and Chiari-like Malformations

Chiari malformations are a group of craniovertebral junction anomalies characterized by the herniation of cerebellar tonsils below the foramen magnum, often accompanied by brainstem descent. The existing classification systems for Chiari malformations have expanded from the original four categories to nine, leading to debates about the need for a more descriptive and etiopathogenic terminology. This review aims to examine the various classification approaches employed and proposes a simplified scheme to differentiate between different types of tonsillar herniations. Furthermore, it explores the most appropriate terminology for acquired herniation of cerebellar tonsils and other secondary Chiari-like malformations. Recent advances in magnetic resonance imaging (MRI) have revealed a higher prevalence and incidence of Chiari malformation Type 1 (CM1) and identified similar cerebellar herniations in individuals unrelated to the classic phenotypes described by Chiari. As we reassess the existing classifications, it becomes crucial to establish a terminology that accurately reflects the diverse presentations and underlying causes of these conditions. This paper contributes to the ongoing discussion by offering insights into the evolving understanding of Chiari malformations and proposing a simplified classification and terminology system to enhance diagnosis and management.

A likely HOXC4 predisposition variant for Chiari malformations

OBJECTIVE

Inherited variants predisposing patients to type 1 or 1.5 Chiari malformation (CM) have been hypothesized but have proven difficult to confirm. The authors used a unique high-risk pedigree population resource and approach to identify rare candidate variants that likely predispose individuals to CM and protein structure prediction tools to identify pathogenicity mechanisms.

METHODS

By using the Utah Population Database, the authors identified pedigrees with significantly increased numbers of members with CM diagnosis. From a separate DNA biorepository of 451 samples from CM patients and families, 32 CM patients belonging to 1 or more of 24 high-risk Chiari pedigrees were identified. Two high-risk pedigrees had 3 CM-affected relatives, and 22 pedigrees had 2 CM-affected relatives. To identify rare candidate predisposition gene variants, whole-exome sequence data from these 32 CM patients belonging to 24 CM-affected related pairs from high-risk pedigrees were analyzed. The I-TASSER package for protein structure prediction was used to predict the structures of both the wild-type and mutant proteins found here.

RESULTS

Sequence analysis of the 24 affected relative pairs identified 38 rare candidate Chiari predisposition gene variants that were shared by at least 1 CM-affected pair from a high-risk pedigree. The authors found a candidate variant in HOXC4 that was shared by 2 CM-affected patients in 2 independent pedigrees. All 4 of these CM cases, 2 in each pedigree, exhibited a specific craniocervical bony phenotype defined by a clivoaxial angle less than 125°. The protein structure prediction results suggested that the mutation considered here may reduce the binding affinity of HOXC4 to DNA.

CONCLUSIONS

Analysis of unique and powerful Utah genetic resources allowed identification of 38 strong candidate CM predisposition gene variants. These variants should be pursued in independent populations. One of the candidates, a rare HOXC4 variant, was identified in 2 high-risk CM pedigrees, with this variant possibly predisposing patients to a Chiari phenotype with craniocervical kyphosis.

A Case of Anesthetic Management of Arnold-Chiari Malformation I: A Contest to Anesthesiologists

Arnold-Chiari malformation is a very uncommon array of deformities in the posterior part of the cranium and hindbrain caused due to abnormal extension of the posterior brain into the spinal canal. Chiari malformation is further divided into subtypes 1, 2, and 3. The latter two are more common in pediatric forms and present at birth. The severity of symptoms depends upon the extent of herniation of the hindbrain due to herniation of the cerebellum through the foramen of the cranium. Also, there have been instances of absence of cerebellum. Multiple associated disorders like hydrocephalus due to increased intracranial pressure, then encephalocele, syrinx, or spinal deformity in the form of scoliosis have been presented in many cases. All these factors thus become a challenge to anesthesiologists for such patients. Hence evidence-based knowledge along with multidisciplinary, well-planned approach is required for its management.

Relationship between phenotypic features in Loeys-Dietz syndrome and the presence of intracranial aneurysms

OBJECTIVE

Loeys-Dietz syndrome (LDS) is a rare autosomal dominant condition characterized by aneurysms of the aorta, aortic branches, and intracranial arteries; skeletal and cutaneous abnormalities; and craniofacial malformations. Previous authors have reported that higher craniofacial severity index (CFI) scores, which indicate more severe craniofacial abnormalities, correlate with the severity of aortic aneurysm pathology. However, the association between syndromic features and the formation of intracranial aneurysms in LDS patients has yet to be determined. In this study, the authors evaluate the incidence of phenotypic abnormalities, craniofacial features, and Chiari malformation type I (CM-I) in a large LDS cohort and explore possible risk factors for the development of intracranial aneurysms.

METHODS

This was a retrospective cohort study of all patients with LDS who had been seen at the Marfan Syndrome and Aortopathy Center at Washington University School of Medicine in St. Louis in 2010–2022. Medical records were reviewed to obtain demographic, clinical, and radiographic data. The prevalence of craniofacial, skeletal, and cutaneous pathologies was determined. Bivariate logistic regression was performed to identify possible risk factors for the formation of an intracranial aneurysm.

RESULTS

Eighty-one patients with complete medical records and intracranial vascular imaging were included in the analysis, and 18 patients (22.2%) had at least 1 intracranial aneurysm. Patients frequently demonstrated the thin or translucent skin, doughy skin texture, hypertelorism, uvular abnormalities, and joint hypermobility typical of LDS. CM-I was common, occurring in 7.4% of the patients. Importantly, the patients with intracranial aneurysms were more likely to have CM-I (22.2%) than those without intracranial aneurysms (3.2%). The mean CFI score in the cohort with available data was 1.81, with higher means in the patients with the TGFBR1 or TGFBR2 disease-causing variants (2.05 and 3.30, respectively) and lower in the patients with the SMAD3, TGFB2, or TGFB3 pathogenic variants (CFI < 1). No significant CFI difference was observed in patients with or without intracranial aneurysms (2.06 vs 1.74, p = 0.61).

CONCLUSIONS

CM-I, and not the CFI, is significantly associated with the presence of intracranial aneurysms in patients with LDS. Surveillance for intracranial aneurysms is essential in all patients with LDS and should not be limited to those with severe phenotypes. Long-term monitoring studies will be necessary to determine whether a correlation between craniofacial abnormalities and adverse outcomes from intracranial aneurysms (growth, intervention, or rupture) exists.

The Small Posterior Cranial Fossa Syndrome and Chiari Malformation Type 0

Patients showing typical Chiari malformation type 1 (CM1) signs and symptoms frequently undergo cranial and cervical MRI. In some patients, MRI documents >5 mm of cerebellar tonsillar herniation (TH) and the diagnosis of CM1. Patients with 3−5 mm TH have “borderline” CM1. Patients with less than 3 mm of TH and an associated cervical syrinx are diagnosed with Chiari “zero” malformation (CM0). However, patients reporting CM1 symptoms are usually not diagnosed with CM if MRI shows less than 3−5 mm of TH and no syrinx. Recent MRI morphometric analysis of the posterior fossa and upper cervical spine detected anatomical abnormalities in and around the foramen magnum (FM) that explain these patients’ symptoms. The abnormalities include a reduced size of the posterior fossa, FM, and upper cervical spinal canal and extension of the cerebellar tonsils around the medulla rather than inferior to the foramen magnum, as in CM1. These morphometric findings lead some neurologists and neurosurgeons to diagnose CM0 in patients with typical CM1 signs and symptoms, with or without cervical syringes. This article reviews recent findings and controversies about CM0 diagnosis and updates current thinking about the clinical and radiological relationship between CM0, borderline CM1, and CM1.

On the association between Chiari malformation type 1, bone mineral density and bone related genes

Background

Chiari malformation type 1 (C1M) is a neurological disease characterized by herniation of the cerebellar tonsils below the foramen magnum. Cranial bone constriction is suspected to be its main cause. To date, genes related to bone development (e.g. DKK1 or COL1A2) have been associated with C1M, while some bone diseases (e.g. Paget) have been found to cosegregate with C1M. Nevertheless, the association between bone mineral density (BMD) and C1M has not been investigated, yet. Here, we systematically investigate the association between C1M and BMD, and between bone related genes and C1M.

Methods

We have recruited a small cohort of C1M patients (12 unrelated patients) in whom we have performed targeted sequencing of an in-house bone-related gene panel and BMD determination through non-invasive DXA.

Results

In the search for association between the bone related genes and C1M we have found variants in more than one C1M patient in WNT16, CRTAP, MYO7A and NOTCH2. These genes have been either associated with craniofacial development in different ways, or previously associated with C1M (MYO7A). Regarding the potential link between BMD and C1M, we have found three osteoporotic patients and one patient who had high BMD, very close to the HBM phenotype values, although most patients had normal BMD.

Conclusions

Variants in bone related genes have been repeatedly found in some C1M cases. The relationship of bone genes with C1M deserves further study, to get a clearer estimate of their contribution to its etiology. No direct correlation between BMD and C1M was observed.

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We used an in-house bone gene panel to investigate a small cohort of C1M patients.

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Variants in WNT16, CRTAP, MYO7A and NOTCH2 were found in more than one C1M patient.

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No clear relationship was found between C1M and BMD in this small C1M cohort.

Is there a morphometric cause of Chiari malformation type I? Analysis of existing literature

Although many etiologies have been proposed for Chiari malformation type I (CM-I), there currently is no singular known cause of CM-I pathogenesis. Advances in imaging have greatly progressed the study of CM-I. This study reviews the literature to determine if an anatomical cause for CM-I could be proposed from morphometric studies in adult CM-I patients. After conducting a literature search using relevant search terms, two authors screened abstracts for relevance. Full-length articles of primary morphometric studies published in peer-reviewed journals were included. Detailed information regarding methodology and symptomatology, craniocervical instability, syringomyelia, operative effects, and genetics were extracted. Forty-six studies met inclusion criteria, averaging 93.2 CM-I patients and 41.4 healthy controls in size. To obtain measurements, 40 studies utilized MRI and 10 utilized CT imaging, whereas 41 analyzed parameters within the posterior fossa and 20 analyzed parameters of the craniovertebral junction. The most commonly measured parameters included clivus length (n = 30), tonsillar position or descent (n = 28), McRae line length (n = 26), and supraocciput length (n = 26). While certain structural anomalies including reduced clivus length have been implicated in CM-I, there is a lack of consensus on how several other morphometric parameters may or may not contribute to its development. Heterogeneity in presentation with respect to the extent of tonsillar descent suggests alternate methods utilizing morphometric measurements that may help to identify CM-I patients and may benefit future research to better understand underlying pathophysiology and sequelae such as syringomyelia.

Rare functional genetic variants in COL7A1, COL6A5, COL1A2 and COL5A2 frequently occur in Chiari Malformation Type 1

Chiari Malformation Type 1 (CM-1) is characterized by herniation of the cerebellar tonsils below the foramen magnum and the presence of headaches and other neurologic symptoms. Cranial bone constriction is suspected to be the most common biologic mechanism leading to CM-1. However, other mechanisms may also contribute, particularly in the presence of connective tissue disorders (CTDs), such as Ehlers Danlos Syndrome (EDS). Accumulating data suggest CM-1 with connective tissue disorders (CTD+) may have a different patho-mechanism and different genetic risk factors than CM-1 without CTDs (CTD-). To identify CM-1 genetic risk variants, we performed whole exome sequencing on a single large, multiplex family from Spain and targeted sequencing on a cohort of 186 unrelated adult, Caucasian females with CM-1. Targeted sequencing captured the coding regions of 21 CM-1 and EDS candidate genes, including two genes identified in the Spanish family. Using gene burden analysis, we compared the frequency of rare, functional variants detected in CM-1 cases versus publically available ethnically-matched controls from gnomAD. A secondary analysis compared the presence of rare variants in these genes between CTD+ and CTD- CM-1 cases. In the Spanish family, rare variants co-segregated with CM-1 in COL6A5, ADGRB3 and DST. A variant in COL7A1 was present in affected and unaffected family members. In the targeted sequencing analysis, rare variants in six genes (COL7A1, COL5A2, COL6A5, COL1A2, VEGFB, FLT1) were significantly more frequent in CM-1 cases compared to public controls. In total, 47% of CM-1 cases presented with rare variants in at least one of the four significant collagen genes and 10% of cases harbored variants in multiple significant collagen genes. Moreover, 26% of CM-1 cases presented with rare variants in the COL6A5 gene. We also identified two genes (COL7A1, COL3A1) for which the burden of rare variants differed significantly between CTD+ and CTD- CM-1 cases. A higher percentage of CTD+ patients had variants in COL7A1 compared to CTD+ patients, while CTD+ patients had fewer rare variants in COL3A1 than did CTD- patients. In summary, rare variants in several collagen genes are particularly frequent in CM-1 cases and those in COL6A5 co-segregated with CM-1 in a Spanish multiplex family. COL6A5 has been previously associated with musculoskeletal phenotypes, but this is the first association with CM-1. Our findings underscore the contribution of rare genetic variants in collagen genes to CM-1, and suggest that CM-1 in the presence and absence of CTD symptoms is driven by different genes.

Rare and de novo coding variants in chromodomain genes in Chiari I malformation

Chiari I malformation (CM1), the displacement of the cerebellum through the foramen magnum into the spinal canal, is one of the most common pediatric neurological conditions. Individuals with CM1 can present with neurological symptoms, including severe headaches and sensory or motor deficits, often as a consequence of brainstem compression or syringomyelia (SM). We conducted whole-exome sequencing (WES) on 668 CM1 probands and 232 family members and performed gene-burden and de novo enrichment analyses. A significant enrichment of rare and de novo non-synonymous variants in chromodomain (CHD) genes was observed among individuals with CM1 (combined p = 2.4 × 10-10), including 3 de novo loss-of-function variants in CHD8 (LOF enrichment p = 1.9 × 10-10) and a significant burden of rare transmitted variants in CHD3 (p = 1.8 × 10-6). Overall, individuals with CM1 were found to have significantly increased head circumference (p = 2.6 × 10-9), with many harboring CHD rare variants having macrocephaly. Finally, haploinsufficiency for chd8 in zebrafish led to macrocephaly and posterior hindbrain displacement reminiscent of CM1. These results implicate chromodomain genes and excessive brain growth in CM1 pathogenesis.

Functional and morphological changes in hypoplasic posterior fossa

BACKGROUND

The knowledge of the development and the anatomy of the posterior cranial fossa (PCF) is crucial to define the occurrence and the prognosis of diseases where the surface and/or the volume of PCF is reduced, as several forms of craniosynostosis or Chiari type I malformation (CIM). To understand the functional and morphological changes resulting from such a hypoplasia is mandatory for their correct management. The purpose of this article is to review the pertinent literature to provide an update on this topic.

METHODS

The related and most recent literature addressing the issue of the changes in hypoplasic PCF has been reviewed with particular interest in the studies focusing on the PCF characteristics in craniosynostosis, CIM, and achondroplasia.

RESULTS AND CONCLUSIONS

In craniosynostoses, namely, the syndromic ones, PCF shows different degrees of hypoplasia, according to the different pattern and timing of early suture fusion. Several factors concur to PCF hypoplasia and contribute to the resulting problems (CIM, hydrocephalus), as the fusion of the major and minor sutures of the lambdoid arch, the involvement of the basal synchondroses, and the occlusion of the jugular foramina. The combination of these factors explains the variety of the clinical and radiological phenotypes. In primary CIM, the matter is complicated by the evidence that, in spite of impaired PCF 2D measurements and theories on the mesodermal defect, the PCF volumetry is often comparable to healthy subjects. CIM is revealed by the overcrowding of the foramen magnum that is the result of a cranio-cerebral disproportion (altered PCF brain volume/PCF total volume). Sometimes, this disproportion is evident and can be demonstrated (basilar invagination, real PCF hypoplasia); sometimes, it is not. Some recent genetic observations would suggest that CIM is the result of an excessive growth of the neural tissue rather than a reduced growth of PCF bones. Finally, in achondroplasia, both macrocephaly and reduced 2D and 3D values of PCF occur. Some aspects of this disease remain partially obscure, as the rare incidence of hydrocephalus and syringomyelia and the common occurrence of asymptomatic upper cervical spinal cord damage. On the other hand, the low rate of CIM could be explained on the basis of the reduced area of the foramen magnum, which would prevent the hindbrain herniation.

Family History in Chiari Malformation Type I: Presentation and Outcome

BACKGROUND

Some patients with Chiari malformation type I (CM-1) present with a positive family history of CM-1, the significance of which remains unknown. We aimed to study whether family history affects the clinical presentation characteristics and surgical outcome of adult patients with CM-1.

METHODS

A database of adult patients with CM-1 presenting between January 1, 2006 and December 31, 2018 was used. Presenting characteristics were compared between patients with and without a family history (first, second, or third degree) of CM-1. Among surgically treated patients, perioperative and long-term outcomes, with favorable outcome defined as a Chiari Outcome Scale score ≥14, were compared between patients with and without CM-1 family history. All patients completed at least 6 months of postoperative follow-up.

RESULTS

The database consisted of 233 adult patients with CM-1, 14 of whom (6%) had a positive family history. Presenting characteristics were comparable between patients with and without a positive family history. A total of 150 patients underwent suboccipital decompression, 12 of whom (8%) had a positive family history. After a mean follow-up of 1.9 years, patients with a family history of CM-1 were significantly less likely to achieve a favorable outcome (odds ratio, 0.22; 95% confidence interval, 0.06-0.78; P = 0.019) while controlling for several covariates. Post hoc analysis showed that the difference was most significant when looking at pain symptoms.

CONCLUSIONS

Presentation characteristics are comparable between patients with and without a family history of CM-1. Patients with a positive family history may be less likely to respond favorably to suboccipital decompression.

Epidemiology of Symptomatic Chiari Malformation in Tatarstan: Regional and Ethnic Differences in Prevalence

BACKGROUND

Epidemiology can assess the effect of Chiari I malformation (CM1) on the neurological health of a population and evaluate factors influencing CM1 development.

OBJECTIVE

To analyze the regional and ethnic differences in the prevalence of CM1.

METHODS

The population of the Republic of Tatarstan (RT) in the Russian Federation was evaluated for patients with CM1 symptoms over an 11-yr period. Typical symptoms of CM1 were found in 868 patients. Data from neurological examination and magnetic resonance imaging (MRI) measurement of posterior cranial fossa structures were analyzed.

RESULTS

MRI evidence of CM1, defined as cerebellar tonsils lying at least 5 mm inferior to the foramen magnum, was found in 67% of symptomatic patients. Another 33% of symptomatic patients had 2 to 4 mm of tonsillar ectopia, which we defined as "borderline Chiari malformation type 1 (bCM1)." The period prevalence in the entire RT for symptomatic CM1 was 20:100 000; for bCM1 was 10:100 000; and for CM1 and bCM1 together was 30:100 000. Prevalence of patients with CM1 symptoms was greater in the northern than southern districts of Tatarstan, due to a high prevalence (413:100 000) of CM1 in the Baltasy region in one of the northern districts.

CONCLUSION

One-third of patients with typical symptoms of CM1 had less than 5 mm of tonsillar ectopia (bCM1). Assessments of the health impact of CM1-type symptoms on a patient population should include the bCM1 patient group. A regional disease cluster of patients with Chiari malformation was found in Baltasy district of RT and needs further study.

Chiari malformation type I: what information from the genetics?

PURPOSE

Chiari malformation type I (CMI), a rare disorder of the craniocerebral junction with an estimated incidence of 1 in 1280, is characterized by the downward herniation of the cerebellar tonsils of at least 5 mm through the foramen magnum, resulting in significant neurologic morbidity. Classical CMI is thought to be caused by an underdeveloped occipital bone, resulting in a posterior cranial fossa which is too small to accommodate the normal-sized cerebellum. In this review, we dissect the lines of evidence supporting a genetic contribution for this disorder.

METHODS

We present the results of two types of approaches: animal models and human studies encompassing different study designs such as whole genome linkage analysis, case-control association studies, and expression studies. The update of the literature also includes the most recent findings emerged by whole exome sequencing strategy.

RESULTS

Despite evidence for a genetic component, no major genes have been identified and the genetics of CMI is still very much unknown. One major challenge is the variability of clinical presentation within CMI patient population that reflects an underlying genetic heterogeneity.

CONCLUSIONS

The identification of the genes that contribute to the etiology of CMI will provide an important step to the understanding of the underlying pathology. The finding of a predisposing gene may lead to the development of simple and accurate diagnostic tests for better prognosis, counseling, and clinical management of patients and their relatives.

Small posterior fossa in Chiari I malformation affected families is significantly linked to 1q43-44 and 12q23-24.11 using whole exome sequencing

The posterior fossa of the cranium contains the cerebellum and brainstem. Processes that reduce the volume of the posterior fossa squeeze the cerebellum and brainstem caudally, resulting in Chiari I malformation (CM1). CM1 causes neck pain, balance issues, decreased motor skills and headaches in those affected. We have posterior fossa measurements and whole exome sequence data on individuals from 7 extended families from Russia that have a family history of CM1. We performed parametric linkage analyses using an autosomal dominant inheritance model with a disease allele frequency of 0.01 and a penetrance of 0.8 for carriers and 0.0 for non-carriers. Variant-based two-point linkage analysis and gene-based linkage analysis was performed. Our results found a genome-wide significant signal on chromosome 1q43-44 (max HLOD = 3.3) in the variant-based analysis and 12q23 (max HLOD = 4.2) in the gene-based analysis. In both cases, the signal was driven by a single (different) family that contained a long, linked haplotype across the region in question. Using functional annotation, we were able to identify several rare nonsynonymous variants that were enriched in each family. The best candidate genes were rs765865412:G>A in MYBPC1 for the 12q haplotype and rs61749963:A>G in COX20 for the 1q haplotype. Good candidate variants in the 1q haplotype were also identified in CEP170 and AKT. Further laboratory work is planned to verify the causality of these genes.

Unexpected phenotype in a patient with two chromosomal deletions involving 6pter and 22q11

The 6p terminal deletions are rare and usually early diagnosed because of their association with eye and cranio-facial anomalies, particularly as part of Axenfeld-Rieger syndrome in relation with the haploinsufficiency of FOXC1 gene. Deletions in the 22q11 region are frequent, highly correlated with DiGeorge syndrome also named CATCH22, and may be associated with many clinical features of various severities. We report a 31-year-old man with an unbalanced 45,XY,der(6)t(6;22)(p25;q11.2),-22 karyotype leading to monosomies in both 6p25 and 22q11 regions, confirmed by FISH and array-CGH. The length of the deletions was respectively 770 Kb for 6pter and 2.9 Mb for 22q11. This karyotype was discovered at adult age following problems of fertility. The chromosomal formula was unexpected, regarding the patient's medical history and clinical features. This case makes a great example of the difficulties to correlate genotype and phenotype, and furthermore demonstrates the complexity of genetic counselling even in a case with two different chromosomal unbalances.

Cerebellar tonsil ectopia measurement in type I Chiari malformation patients show poor inter-operator reliability

Background

Type 1 Chiari malformation (CM-I) has been historically defined by cerebellar tonsillar position (TP) greater than 3–5 mm below the foramen magnum (FM). Often, the radiographic findings are highly variable, which may influence the clinical course and patient outcome. In this study, we evaluate the inter-operator reliability (reproducibility) of MRI-based measurement of TP in CM-I patients and healthy controls.

Methods

Thirty-three T2-weighted MRI sets were obtained for 23 CM-I patients (11 symptomatic and 12 asymptomatic) and 10 healthy controls. TP inferior to the FM was measured in the mid-sagittal plane by seven expert operators with reference to McRae’s line. Overall agreement between the operators was quantified by intraclass correlation coefficient (ICC).

Results

The mean and standard deviation of cerebellar TP measurements for asymptomatic (CM-Ia) and symptomatic (CM-Is) patients in mid-sagittal plane was 6.38 ± 2.19 and 9.57 ± 2.63 mm, respectively. TP measurements for healthy controls was 0.48 ± 2.88 mm. The average range of TP measurements for all data sets analyzed was 7.7 mm. Overall operator agreement for TP measurements was relatively high with an ICC of 0.83.

Conclusion

The results demonstrated a large average range (7.7 mm) of measurements among the seven expert operators and support that, if economically feasible, two radiologists should make independent measurements before radiologic diagnosis of CM-I and surgery is contemplated. In the future, an objective diagnostic parameter for CM-I that utilizes automated algorithms and results in smaller inter-operator variation may improve patient selection.

Population-based description of familial clustering of Chiari malformation Type I

OBJECTIVE

A population-based genealogical resource with linked medical data was used to define the observed familial clustering of Chiari malformation Type I (CM-I).

METHODS

All patients with CM-I were identified from the 2 largest health care providers in Utah; those patients with linked genealogical data were used to test hypotheses regarding familial clustering. Relative risks (RRs) in first-, second-, and third-degree relatives were estimated using internal cohort-specific CM-I rates; the Genealogical Index of Familiality (GIF) test was used to test for an excess of relationships between all patients with CM-I compared with the expected distribution of relationships for matched control sets randomly selected from the resource. Pedigrees with significantly more patients with CM-I than expected (p < 0.05) based on internal rates were identified.

RESULTS

A total of 2871 patients with CM-I with at least 3 generations of genealogical data were identified. Significantly increased RRs were observed for first- and third-degree relatives (RR 4.54, p < 0.001, and RR 1.36, p < 0.001, respectively); the RR for second-degree relatives was elevated, but not significantly (RR 1.20, p = 0.13). Significant excess pairwise relatedness was observed among the patients with CM-I (p < 0.001), and borderline significant excess pairwise relatedness was observed when all relationships closer than first cousins were ignored (p = 0.051). Multiple extended high-risk CM-I pedigrees with closely and distantly related members were identified.

CONCLUSIONS

This population-based description of the familial clustering of 2871 patients with CM-I provided strong evidence for a genetic contribution to a predisposition to CM-I.

Chiari 1 deformity in children: etiopathogenesis and radiologic diagnosis

The metamerically associated normal hindbrain and normal posterior fossa are programmed to grow together in such a way that the tonsils are located above the foramen magnum and surrounded by the cerebrospinal fluid (CSF) of the cisterna magna. This allows the pulsating CSF to move freely up and down across the craniovertebral junction (CVJ). A developmental mismatch between the rates of growth of the neural tissue and of the bony posterior fossa may result in the cerebellar tonsils being dislocated across the foramen magnum. The cause of this may be, rarely, an overgrowth of the cerebellum. More commonly, it is due to an insufficient development of the posterior fossa, possibly associated with a malformation of the craniocervical joint. When it is not due to a remediable cause, such a herniation is called a Chiari 1 deformity. This definition is anatomic (descent of the tonsils below the plane of the foramen magnum) and not clinical: many patients with the deformity are and will remain asymptomatic. Most authors consider that a descent of 5 mm or more is clinically significant but other factors, such as the diameter of the foramen magnum and the degree of tapering of the upper cervical "funnel," are likely to be as important. Morphologic markers of severity on magnetic resonance imaging are, beside the degree of descent, the peg-like deformity of the tonsils, the obstruction of the surrounding CSF spaces (at the craniocervical junction and in the whole posterior fossa), a compression of the cord, an abnormal signal of the cord, and a syringomyelia, typically cervicothoracic. The syringomyelia is assumed to be explained by the "Venturi effect" that is associated with the increased velocity of the CSF across the restricted CSF spaces. Radiologically, the etiopathogenic assessment should address the size and morphology of the posterior fossa, and the functional status of the craniocervical flexion joint. The posterior fossa is best evaluated on sagittal cuts by the posterior fossa pentagon proportionality associated with the line of Chamberlain, and on coronal cuts, by showing a possible shallowness of the posterior fossa. The functional status of the craniocervical joint is altered in case of a proatlantal hypoplasia, as this condition results in a cranial shift of the joint that brings the tip of the dens and of the flexion axis in front of the medulla, that is, in a situation of osteoneural conflict. Less commonly, similar conflicts may also occur when an abnormal craniocervical segmentation results in an instability of the joint.

Exome sequencing of two Italian pedigrees with non-isolated Chiari malformation type I reveals candidate genes for cranio-facial development

Chiari malformation type I (CMI) is a congenital abnormality of the cranio-cerebral junction with an estimated incidence of 1 in 1280. CMI is characterized by underdevelopment of the occipital bone and posterior fossa (PF) and consequent cerebellar tonsil herniation. The presence for a genetic basis to CMI is supported by many lines of evidence. The cellular and molecular mechanisms leading to CM1 are poorly understood. The occipital bone formation is dependent on complex interactions between genes and molecules with pathologies resulting from disruption of this delicate process. Whole-exome sequencing of affected and not affected individuals from two Italian families with non-isolated CMI was undertaken. Single-nucleotide and short insertion-deletion variants were prioritized using KGGSeq knowledge-based platform. We identified three heterozygous missense variants: DKK1 c.121G>A (p.(A41T)) in the first family, and the LRP4 c.2552C>G (p.(T851R)) and BMP1 c.941G>A (p.(R314H)) in the second family. The variants were located at highly conserved residues, segregated with the disease, but they were not observed in 100 unaffected in-house controls. DKK1 encodes for a potent soluble WNT inhibitor that binds to LRP5 and LRP6, and is itself regulated by bone morphogenetic proteins (BMPs). DKK1 is required for embryonic head development and patterning. LRP4 is a novel osteoblast expressed receptor for DKK1 and a WNT and BMP 4 pathways integrator. Screening of DKK1 in a cohort of 65 CMI sporadic patients identified another missense variant, the c.359G>T (p.(R120L)), in two unrelated patients. These findings implicated the WNT signaling in the correct development of the cranial mesenchyme originating the PF.

Neurologic involvement in patients with atypical Chediak-Higashi disease

OBJECTIVE

To delineate the developmental and progressive neurodegenerative features in 9 young adults with the atypical form of Chediak-Higashi disease (CHD) enrolled in a natural history study.

METHODS

Patients with atypical clinical features, but diagnostically confirmed CHD by standard evaluation of blood smears and molecular genotyping, underwent complete neurologic evaluation, MRI of the brain, electrophysiologic examination, and neuropsychological testing. Fibroblasts were collected to investigate the cellular phenotype and correlation with the clinical presentation.

RESULTS

In 9 mildly affected patients with CHD, we documented learning and behavioral difficulties along with developmental structural abnormalities of the cerebellum and posterior fossa, which are apparent early in childhood. A range of progressive neurologic problems emerge in early adulthood, including cerebellar deficits, polyneuropathies, spasticity, cognitive decline, and parkinsonism.

CONCLUSIONS

Patients with undiagnosed atypical CHD manifesting some of these wide-ranging yet nonspecific neurologic complaints may reside in general and specialty neurology clinics. The absence of the typical bleeding or infectious diathesis in mildly affected patients with CHD renders them difficult to diagnose. Identification of these individuals is important not only for close surveillance of potential CHD-related systemic complications but also for a full understanding of the natural history of CHD and the potential role of the disease-causing protein, LYST, to the pathophysiology of other neurodevelopmental and neurodegenerative disorders.

Cephalometric oropharynx and oral cavity analysis in Chiari malformation Type I: a retrospective case-control study

OBJECTIVE Traditionally, Chiari malformation Type I has been related to downward herniation of the cerebellar tonsils as a consequence of an underdeveloped posterior cranial fossa. Although the common symptoms of Chiari malformation Type I are occipital headaches, cervical pain, dizziness, paresthesia, and sensory loss, patients often report symptoms related to pharyngeal dysfunction such as choking, regurgitation, dysphagia, aspiration, chronic cough, and sleep disorders. In addition, tracheal intubation is often difficult in these patients. The purpose of this study was to analyze the morphological features of the oropharynx and oral cavity in patients with Chiari malformation Type I to help identify underlying anatomical anomalies leading to these debilitating symptoms. METHODS Seventy-six adult patients with symptomatic Chiari malformation Type I with cerebellar tonsillar descent greater than 5 mm below the foramen magnum and a small posterior cranial fossa and 49 sex-matched controls were selected to perform a retrospective case-control MRI-based morphometric study in a tertiary hospital. Eleven linear and areal parameters of the oropharyngeal cavity on midsagittal T1-weighted MRI were measured and the average values between patients and control cohorts were compared. Correlations between variables showing or approaching statistical significance in these structures and posterior cranial fossa measurements related with the occipital bone were sought. RESULTS Significant differences were detected for several oropharynx and oral cavity measures in the patient cohort, primarily involving the length and thickness of the soft palate (p = 9.5E-05 and p = 3.0E-03, respectively). A statistically significant (p < 0.01) moderate correlation between some of these variables and posterior cranial fossa parameters was observed. CONCLUSIONS The existence of structural oropharyngeal and oral cavity anomalies in patients with Chiari malformation Type I was confirmed, which may contribute to the frequent occurrence of respiratory and deglutitory complications and sleep disorders in this syndrome.

Neurologic involvement in patients with atypical Chediak-Higashi disease

OBJECTIVE

To delineate the developmental and progressive neurodegenerative features in 9 young adults with the atypical form of Chediak-Higashi disease (CHD) enrolled in a natural history study.

METHODS

Patients with atypical clinical features, but diagnostically confirmed CHD by standard evaluation of blood smears and molecular genotyping, underwent complete neurologic evaluation, MRI of the brain, electrophysiologic examination, and neuropsychological testing. Fibroblasts were collected to investigate the cellular phenotype and correlation with the clinical presentation.

RESULTS

In 9 mildly affected patients with CHD, we documented learning and behavioral difficulties along with developmental structural abnormalities of the cerebellum and posterior fossa, which are apparent early in childhood. A range of progressive neurologic problems emerge in early adulthood, including cerebellar deficits, polyneuropathies, spasticity, cognitive decline, and parkinsonism.

CONCLUSIONS

Patients with undiagnosed atypical CHD manifesting some of these wide-ranging yet nonspecific neurologic complaints may reside in general and specialty neurology clinics. The absence of the typical bleeding or infectious diathesis in mildly affected patients with CHD renders them difficult to diagnose. Identification of these individuals is important not only for close surveillance of potential CHD-related systemic complications but also for a full understanding of the natural history of CHD and the potential role of the disease-causing protein, LYST, to the pathophysiology of other neurodevelopmental and neurodegenerative disorders.

Joint eQTL assessment of whole blood and dura mater tissue from individuals with Chiari type I malformation

BACKGROUND

Expression quantitative trait loci (eQTL) play an important role in the regulation of gene expression. Gene expression levels and eQTLs are expected to vary from tissue to tissue, and therefore multi-tissue analyses are necessary to fully understand complex genetic conditions in humans. Dura mater tissue likely interacts with cranial bone growth and thus may play a role in the etiology of Chiari Type I Malformation (CMI) and related conditions, but it is often inaccessible and its gene expression has not been well studied. A genetic basis to CMI has been established; however, the specific genetic risk factors are not well characterized.

RESULTS

We present an assessment of eQTLs for whole blood and dura mater tissue from individuals with CMI. A joint-tissue analysis identified 239 eQTLs in either dura or blood, with 79% of these eQTLs shared by both tissues. Several identified eQTLs were novel and these implicate genes involved in bone development (IPO8, XYLT1, and PRKAR1A), and ribosomal pathways related to marrow and bone dysfunction, as potential candidates in the development of CMI.

CONCLUSIONS

Despite strong overall heterogeneity in expression levels between blood and dura, the majority of cis-eQTLs are shared by both tissues. The power to detect shared eQTLs was improved by using an integrative statistical approach. The identified tissue-specific and shared eQTLs provide new insight into the genetic basis for CMI and related conditions.

Identification of Chiari Type I Malformation subtypes using whole genome expression profiles and cranial base morphometrics

Background

Chiari Type I Malformation (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum at the base of the skull, resulting in significant neurologic morbidity. As CMI patients display a high degree of clinical variability and multiple mechanisms have been proposed for tonsillar herniation, it is hypothesized that this heterogeneous disorder is due to multiple genetic and environmental factors. The purpose of the present study was to gain a better understanding of what factors contribute to this heterogeneity by using an unsupervised statistical approach to define disease subtypes within a case-only pediatric population.

Methods

A collection of forty-four pediatric CMI patients were ascertained to identify disease subtypes using whole genome expression profiles generated from patient blood and dura mater tissue samples, and radiological data consisting of posterior fossa (PF) morphometrics. Sparse k-means clustering and an extension to accommodate multiple data sources were used to cluster patients into more homogeneous groups using biological and radiological data both individually and collectively.

Results

All clustering analyses resulted in the significant identification of patient classes, with the pure biological classes derived from patient blood and dura mater samples demonstrating the strongest evidence. Those patient classes were further characterized by identifying enriched biological pathways, as well as correlated cranial base morphological and clinical traits.

Conclusions

Our results implicate several strong biological candidates warranting further investigation from the dura expression analysis and also identified a blood gene expression profile corresponding to a global down-regulation in protein synthesis.