Clinical and Functional Characterization of a Missense ELF2 Variant in a CANVAS Family

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS): a family with five affected sibs from Turkey

BACKGROUND

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS), a relatively common cause of late-onset progressive ataxia, is a genetic disease characterised by biallelic pentanucleotide AAGGG repeat expansion in intron 2 of the replication factor complex subunit 1 gene. Herein, we describe the first molecularly confirmed CANVAS family with five affected siblings from Turkey.

CASE PRESENTATION

The family comprised seven siblings born from healthy non-consanguineous parents. CANVAS phenotype was present in five of them; two were healthy and asymptomatic. Chronic cough was the first symptom reported in all five siblings, followed by the development of sensory symptoms, oscillopsia and imbalance. Clinical head impulse test (HIT) was positive in all cases and video HIT performed on three patients revealed very low vestibulo-ocular reflex gains bilaterally. Magnetic resonance imaging and nerve conduction studies revealed cerebellar atrophy and sensory neuronopathy, respectively. RP-PCR confirmed the homozygous presence of the AAGGG repeat expansion in all five cases.

CONCLUSION

Genetic screening for CANVAS should be considered in all patients with late-onset ataxia, sensory disturbances and vestibular involvement, especially in the presence of chronic cough.

Schizophrenia endothelial cells exhibit higher permeability and altered angiogenesis patterns in patient-derived organoids

Schizophrenia (SCZ) is a complex neurodevelopmental disorder characterized by the manifestation of psychiatric symptoms in early adulthood. While many research avenues into the origins of SCZ during brain development have been explored, the contribution of endothelial/vascular dysfunction to the disease remains largely elusive. To model the neuropathology of SCZ during early critical periods of brain development, we utilized patient-derived induced pluripotent stem cells (iPSCs) to generate 3D cerebral organoids and define cell-specific signatures of disease. Single-cell RNA sequencing revealed that while SCZ organoids were similar in their macromolecular diversity to organoids generated from healthy controls (CTRL), SCZ organoids exhibited a higher percentage of endothelial cells when normalized to total cell numbers. Additionally, when compared to CTRL, differential gene expression analysis revealed a significant enrichment in genes that function in vessel formation, vascular regulation, and inflammatory response in SCZ endothelial cells. In line with these findings, data from 23 donors demonstrated that PECAM1+ microvascular vessel-like structures were increased in length and number in SCZ organoids in comparison to CTRL organoids. Furthermore, we report that patient-derived endothelial cells displayed higher paracellular permeability, implicating elevated vascular activity. Collectively, our data identified altered gene expression patterns, vessel-like structural changes, and enhanced permeability of endothelial cells in patient-derived models of SCZ. Hence, brain microvascular cells could play a role in the etiology of SCZ by modulating the permeability of the developing blood brain barrier (BBB).

Primary open-angle glaucoma risk prediction with ABCA1 and LOC102723944 variants and their genotype-phenotype correlations in southern Chinese population

Glaucoma is a leading cause of irreversible visual impairment and blindness worldwide. Previous genome-wide association studies have identified caveolin-1 (CAV1), ATP-binding cassette A1 (ABCA1), and forkhead box C1 (FOXC1) loci associated with primary open angle glaucoma (POAG), a major subtype of glaucoma. This study aimed to fine map the association pattern of FOXC1 locus with POAG and determine the correlations of FOXC1, ABCA1, and CAV1 variants with ocular and lipidemic parameters in southern Chinese population. In total, 1291 unrelated Han Chinese subjects were recruited, including 301 high-tension glaucoma (HTG), 126 normal-tension glaucoma (NTG), and 864 control subjects. Twelve variants in FOXC1 locus, and two variants in ABCA1 and CAV1 genes, were genotyped by TaqMan assays. Genetic risk score and genotype-phenotype correlation analyses were conducted. In the FOXC1 locus, LOC102723944 rs6596830, rather than previously reported rs2745572, showed significant association with POAG (P = 8.61 × 10-4, odds ratio (OR) = 0.75) and HTG (P = 3.68 × 10-3, OR = 0.75). ABCA1 rs2487032 was also significantly associated with POAG (P = 3.00 × 10-5, OR = 0.70) and HTG (P = 2.08 × 10-4, OR = 0.70). Joint analysis showed that carriers of homozygous non-protective alleles of ABCA1 rs2487032 and LOC102723944 rs6596830 had 2.99-fold higher risk of POAG (P = 1.27 × 10-3) when compared to those carrying homozygous non-risk alleles. Patients with POAG carrying ABCA1 rs2487032 G allele had higher HDL cholesterol, and those with LOC102723944 rs6596830 A allele had lower LDL. This study revealed individual and joint association of ABCA1 and LOC102723944 variants with POAG in southern Chinese population. Subjects carrying non-protective alleles had increased risk to POAG, and corresponding genotypes would affect the lipid profiles.

Whole-Genome and Long-Read Sequencing Identify a Novel Mechanism in RFC1 Resulting in CANVAS Syndrome

Objectives

Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS) results from biallelic intronic pentanucleotide repeats in RFC1. We describe an adult male proband with progressive imbalance, cerebellar atrophy, somatosensory neuronopathy, and absence of peripheral vestibular function for whom clinical testing demonstrated a heterozygous RFC1 expansion consistent with an unaffected carrier.

Methods

We performed whole-genome sequencing (WGS) on peripheral blood DNA samples from the proband and his unaffected mother. We performed DNA long-read sequencing and synthesized complementary DNA from RNA using peripheral blood from the proband.

Results

WGS confirmed the maternally inherited RFC1 expansion and identified a rare, nonsense RFC1 variant: c.C1147T; p.R383X in the proband but not the maternal DNA sample. RFC1 variants were confirmed in trans with long-read sequencing. Functional studies demonstrated the absence of complementary DNA (cDNA) transcript from the c.C1147T; p.R383X variant supporting nonsense-mediated decay of this transcript.

Discussion

We report an adult with CANVAS due to compound heterozygous pathogenic RFC1 variants: the pathogenic intronic pentanucleotide expansion confirmed in trans with a nonsense variant. This report represents a novel molecular mechanism for CANVAS. Sequencing for RFC1 should be considered for adults meeting clinical criteria for the CANVAS phenotype if only a heterozygous pathogenic RFC1 expansion is identified.

Bilateral vestibulopathy: the causes, diagnosis, and treatments

PURPOSE OF REVIEW

The current review covers recent advances in bilateral vestibulopathy (BVP) in terms of its etiology, diagnosis, and treatments.

RECENT FINDINGS

The etiology of BVP depends on its clinical course and associated findings, and genetic abnormalities are increasingly recognized in isolated as well as complicated form of BVP. Recent developments in evaluation of the vestibular function have greatly enhanced the detection of BVP, and introduction of the consensus diagnostic criteria by Barany Society has facilitated research on BVP. Vestibular prosthesis may improve vestibular function, posture, gait and quality of life in patients with BVP and would expand the therapeutic options for BVP in near future.

SUMMARY

Genetics is expanding its role in identifying the causes of BVP of hitherto unknown etiology. The detection and investigation of BVP have been greatly enhanced by introduction of consensus diagnostic criteria and recent developments in methodology evaluating the vestibular function. Vestibular prothesis appears promising in managing BVP.

VIDEO ABSTRACT

http://links.lww.com/CONR/A59.

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS): from clinical diagnosis towards genetic testing

The cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a late-onset and recessively inherited ataxia. For many years, CANVAS has been diagnosed based on the clinical phenotype. Only recently, a large biallelic pentanucleotide repeat expansion in the replication factor C subunit 1 (RFC1) gene has been identified as the underlying genetic cause for the large majority of CANVAS cases. Subsequently, other phenotypes such as ataxia with chronic cough, incomplete CANVAS and MSA-C-like phenotypes have been associated with biallelic RFC1 repeat expansions. Because of this heterogeneity it has been suggested to change the name of the disease to "RFC1 disease". Chronic cough is characteristic and can precede neurological symptoms by years or decades. In the neurological examination signs of cerebellar, sensory, and vestibular ataxia are frequently observed. Nerve conduction studies usually show absent or markedly reduced sensory nerve action potentials. On brain MRI cerebellar degeneration and spinal cord alterations are common. In later disease stages more widespread neurodegeneration with additional involvement of the brainstem and basal ganglia is possible. As yet, the exact incidence of RFC1-associated neurological diseases remains uncertain although first studies suggest that RFC1-related ataxia is common. Moreover, the pathophysiological mechanisms caused by the large biallelic pentanucleotide repeat expansions in RFC1 remain elusive. Future molecular and genetic research as well as natural history studies are highly desirable to pave the way towards personalized treatment approaches.

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (canvas): an important cause of late-onset ataxia with unique clinical features

Cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) is a late-onset, slowly progressive disorder characterized by cerebellar ataxia, sensory neuropathy and bilateral vestibulopathy. Recently, a biallelic intronic AAGGG repeat expansion, (AAGGG)_exp, in the Replication Factor C1 (RFC1) gene was identified as the cause of this disorder. In this study, we describe the phenotypic features of five patients from five different families diagnosed as CANVAS. The mean age at onset was 49.00 ± 9.05 years (between 34 and 56 years) and the most frequent presenting symptom in CANVAS was gait ataxia, followed by sensory disturbances. Persistent coughing was prominent in three patients, and it preceded the onset of ataxia and sensory symptoms in two patients. Parental consanguinity was present in three patients. Two patients showed symptoms or signs suggesting autonomic involvement. Sural nerve biopsy revealed axonal neuropathy in two patients. The mean age at onset was 49.00 ± 9.05 years (between 34 and 56 years) and the most frequent presenting symptom in CANVAS was gait ataxia, followed by sensory disturbances. Persistent coughing was prominent in three patients, and it preceded the onset of ataxia and sensory symptoms in two patients. Parental consanguinity was present in three patients. Two patients showed symptoms or signs suggesting autonomic involvement. Sural nerve biopsy revealed axonal neuropathy in two patients. Our study describes clinical findings, histopathological features and diagnostic clues of CANVAS from Turkey, a country with a high consanguineous marriage rate. Repeat expansion in the RFC1 gene should be considered in all cases with late-onset ataxia, especially when sensory disturbances, vestibular involvement and persistent coughing coexist.

Anaesthesia techniques and advanced monitoring in CANVAS patients - Implications for postoperative morbidity and patient recovery: A case report

Introduction

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a rare multisystem neurodegenerative disorder. We describe our perioperative evaluation and care of a patient with CANVAS undergoing a pancreaticoduodenectomy for an ampullary adenocarcinoma, with a focus on perioperative risk stratification and optimisation, intraoperative advanced haemodynamic monitoring and the postoperative care.

Case presentation

A 69-year-old female with CANVAS presented with asymptomatic obstructive jaundice, icterus and abdominal pain. She had limited mobility and deconditioning due to severe generalised neuropathy. Computed tomography confirmed a resectable periampullary tumour. Her Duke Activity Status Index was 8.25 points and Edmonton Frailty Scale score was 11, confirming moderate frailty. However, the Charlson Comorbidity Index was five, indicative of a 21% estimated 10-year survival. Further risk stratification including respiratory function testing, echocardiography and cardiopulmonary exercise testing was conducted. The patient proceeded with surgery after multidisciplinary discussions with her treating medical teams.

Discussion

CANVAS is a rare and challenging condition requiring careful perioperative planning and management. There is no effective treatment for CANVAS. The management approach focuses on mitigating symptoms and improving quality of life. Given that no specific guidelines for managing these patients in the perioperative period have been provided, this report highlights several critical medical issues and implications that should be considered for the successful management of these patients. We demonstrate the role of specific anaesthesia techniques and advanced haemodynamic monitoring in both preventing postoperative morbidity and optimising patient recovery.

Conclusion

CANVAS is a rare and challenging condition in anaesthesia requiring careful perioperative planning and management.

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CANVAS is a rare multisystem neurological disorder

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There is no effective treatment for CANVAS

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Perioperative management for patients with CANVAS is complex

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Perioperative risk stratification requires multidisciplinary involvement

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CANVAS patients can present with unique anaesthesia challenges

Update on Cerebellar Ataxia with Neuropathy and Bilateral Vestibular Areflexia Syndrome (CANVAS)

The syndrome of cerebellar ataxia with neuropathy and bilateral vestibular areflexia (CANVAS) has emerged progressively during the last 30 years. It was first outlined by the neurootology/neurophysiology community in the vestibular areflexic patients, through the description of patients slowly developing late-onset cerebellar ataxia and bilateral vestibulopathy. The characteristic deficit of visuo-vestibulo-ocular reflex (VVOR) due to the impaired slow stabilizing eye movements was put forward and a specific disease subtending this syndrome was suggested. The association to a peripheral sensory axonal neuropathy was described later on, with neuropathological studies demonstrating that both sensory neuropathy and vestibular areflexia were diffuse ganglionopathy. Clinical and electrophysiological criteria of CANVAS were then proposed in 2016. Besides the classical triad, frequent chronic cough, signs of dysautonomia and neurogenic pains were frequently observed. From the beginning of published cohorts, sporadic as well as familial cases were reported, the last suggestive of an autosomal recessive mode of transmission. The genetic disorder was discovered in 2019, under the form of abnormal biallelic expansion in the replication factor C subunit 1 (RFC1) in a population of late-onset ataxia. This pathological expansion was found in 100% of the familial form and 92% of sporadic ones when the triad was complete. But using the genetic criteria, the phenotype of CANVAS seems to expand, for exemple including patients with isolated neuronopathy. We propose here to review the clinical, electrophysiological, anatomical, genetic aspect of CANVAS in light of the recent discovery of the genetic aetiology, and discuss differential diagnosis, neuropathology and physiopathology.

Clinical spectrum of the pentanucleotide repeat expansion in the RFC1 gene in ataxia syndromes

OBJECTIVE

To determine the clinical significance of an intronic biallelic pentanucleotide repeat expansion in the gene encoding replication factor C subunit 1 (RFC1) in patients with late-onset cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS), in patients with other ataxias, and in healthy controls by comprehensive genetic analyses.

METHODS

In this case-control study, we included 457 individuals comprising 26 patients with complete or incomplete CANVAS, 70 patients with late-onset cerebellar ataxia, 208 healthy controls, and 153 individuals from 39 multigenerational families without ataxia to determine repeat stability. All 96 patients were screened for the repeat expansion by duplex PCR. To further characterize the repeat type and lengths, we used fragment length analysis, repeat-primed PCR, Sanger sequencing, and Southern blotting. Expression of RFC1 and the neighboring gene WDR19 were determined by quantitative PCR.

RESULTS

Massive biallelic pentanucleotide expansions were found in 15/17 patients with complete CANVAS (88%), in 2/9 patients with incomplete CANVAS (22%), in 4/70 patients with unspecified, late-onset cerebellar ataxia (6%), but not in controls. In patients, the expansion comprised 800-1,000 mostly AAGGG repeats. Nonmassively expanded repeat numbers were in the range of 7-137 repeats and relatively stable during transmission. Expression of RFC1 and WDR19 were unchanged and RFC1 intron retention was not found.

CONCLUSIONS

A biallelic pentanucleotide repeat expansion is a frequent cause of CANVAS and found in a considerable number of patients with an incomplete clinical presentation or other forms of cerebellar ataxia. The mechanism by which the repeat expansions are causing disease remains unclear and warrants further investigations.

Contributions to the study of spinocerebellar ataxia type 38 (SCA38)

OBJECTIVE

To report clinical and ancillary findings in a kindred with spinocerebellar ataxia 38 (SCA38).

PATIENTS AND METHODS

Five family members spanning two generations developed gait ataxia and intermittent diplopia. On examination, a cerebellar syndrome accompanied by downbeat nystagmus and a saccadic head impulse test (HIT) were found.

RESULTS

Whole-exome sequencing demonstrated a heterozygous variant in ELOVL5, c.779A > G (p.Tyr260Cys), in four tested patients. Intermittent concomitant esotropia and hypertropia caused transient diplopia in one individual each. Saccadic HIT responses were found in four subjects. Sensorineural hypoacusis was present in every case. Electrophysiological studies demonstrated a sensory neuronopathy in patients from the first generation, with prolonged disease duration. Baseline serum docosahexaenoic acid (DHA) percent was diminished in four individuals. Oral 26-week dietary DHA supplementation, 650 mg/day, raised serum DHA percent and induced a statistically significant reduction in Scale for the Assessment and Rating of Ataxia (SARA) total scores, and in stance and heel-shin slide item scores.

CONCLUSION

The mentioned ELOVL5 variant segregated with disease in this kindred. Downbeat nystagmus, intermittent heterotropia causing transient diplopia, vestibular impairment demonstrated by abnormal HIT, and sensory neuronopathy were part of the clinical picture in this series. DHA supplementation raised serum DHA percent in cases with diminished levels, and induced a clinical amelioration and a statistically significant reduction in SARA scores in the study group. Further studies are needed to investigate the role of these findings in SCA38, and to determine the response to prolonged DHA supplementation.

Is Cerebellar Ataxia, Neuropathy, and Vestibular Areflexia Syndrome (CANVAS) a Vestibular Ganglionopathy?

OBJECTIVES

CANVAS is an acronym for cerebellar ataxia, neuropathy and vestibular areflexia syndrome. Limited autopsy data has suggested that CANVAS is caused by a focal dorsal root ganglionopathy that damages Scarpa's (vestibular) ganglion, but spares the Spiral (hearing) ganglion. If the vestibular areflexia of CANVAS is in fact due to ganglionopathy, then there should be global reduction of all vestibular responses.

MATERIALS AND METHODS

With this hypothesis in mind, a retrospective review of 5 subjects who met the clinical criteria for CANVAS was performed. Recent advances in vestibular testing have made it possible to quantify responses from all 5 vestibular end organs in the inner ear. Results of the Video head impulse test (VHIT), video oculography, caloric test and vestibular evoked myogenic potential (VEMP) were examined to determine if all 5 end organs are nonfunctional in CANVAS.

RESULTS

Severe reduction of function of the six semicircular canals and ocular VEMPs were observed. Only the cervical VEMPs were present and reproducible, consistent with either partial sparing of the inferior vestibular ganglia, specific embryologic resistance of the saccule to the degeneration or a mechanism for cervical VEMPs that does not require an intact vestibular ganglion.

CONCLUSION

Our results suggest that Scarpa´s ganglia dysfunction could be the mechanism for loss of semicircular canal and utricular function in CANVAS patients, but the preservation of the cervical VEMP response is unexplained.

[Neuro-otology: at the borders of ear and brain]

Vertigo and dizziness are frequent chief complaints in clinical practice. Symptoms may originate from otological, neurological, medical and psychiatric etiologies, which poses an interdisciplinary challenge. Systematic analysis of case history and clinical examination generally allow classification into peripheral-, central- or non-vestibular disorders. The most important criteria for differentiation are the timeline, quality of symptoms, modulating factors and accompanying symptoms. As concerns the clinical examination, the following tests are relevant: head impulse test, test for spontaneous nystagmus, positional nystagmus, central ocular motor signs and the Romberg test. However, neuro-otological disorders with combined peripheral and central vestibular pathology do exist. Occlusion of the anterior inferior cerebellar artery results in ischemia of the labyrinth and cerebellum and therefore causes acute vestibular syndrome and unilateral hearing loss. Repetitive attacks of vertigo or dizziness which are accompanied by ear symptoms and headaches may be due to an overlap syndrome of Menière's disease and vestibular migraine. In this case patients often have to be treated with a dual prophylactic medication to control symptoms. In case of chronic dizziness and instability of gait a subsample of patients may suffer from CANVAS, which is a combination of bilateral vestibulopathy, a cerebellar syndrome and polyneuropathy. Chronic dizziness with signs of peripheral and central vestibular dysfunction can also originate from tumors of the cerebellopontine angle with compression of central structures. In conclusion, the diagnostic algorithm in the workup of patients with vertigo and dizziness should always include tests for peripheral and central vestibular and ocular motor function.

Bioinformatics-Based Identification of Expanded Repeats: A Non-reference Intronic Pentamer Expansion in RFC1 Causes CANVAS

Genomic technologies such as next-generation sequencing (NGS) are revolutionizing molecular diagnostics and clinical medicine. However, these approaches have proven inefficient at identifying pathogenic repeat expansions. Here, we apply a collection of bioinformatics tools that can be utilized to identify either known or novel expanded repeat sequences in NGS data. We performed genetic studies of a cohort of 35 individuals from 22 families with a clinical diagnosis of cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS). Analysis of whole-genome sequence (WGS) data with five independent algorithms identified a recessively inherited intronic repeat expansion [(AAGGG)exp] in the gene encoding Replication Factor C1 (RFC1). This motif, not reported in the reference sequence, localized to an Alu element and replaced the reference (AAAAG)11 short tandem repeat. Genetic analyses confirmed the pathogenic expansion in 18 of 22 CANVAS-affected families and identified a core ancestral haplotype, estimated to have arisen in Europe more than twenty-five thousand years ago. WGS of the four RFC1-negative CANVAS-affected families identified plausible variants in three, with genomic re-diagnosis of SCA3, spastic ataxia of the Charlevoix-Saguenay type, and SCA45. This study identified the genetic basis of CANVAS and demonstrated that these improved bioinformatics tools increase the diagnostic utility of WGS to determine the genetic basis of a heterogeneous group of clinically overlapping neurogenetic disorders.

Genetic contribution to vestibular diseases

Growing evidence supports the contribution of allelic variation to vestibular disorders. Heritability attributed to rare allelic variants is found in familial vestibular syndromes such as enlarged vestibular aqueduct syndrome or familial Meniere disease. However, the involvement of common allelic variants as key regulators of physiological processes in common and rare vestibular diseases is starting to be deciphered, including motion sickness or sporadic Meniere disease. The genetic contribution to most of the vestibular disorders is still largely unknown. This review will outline the role of common and rare variants in human genome to episodic vestibular syndromes, progressive vestibular syndrome, and hereditary sensorineural hearing loss associated with vestibular phenotype. Future genomic studies and network analyses of omic data will clarify the pathway towards a personalized stratification of treatments.