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.

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We propose staged diagnostic criteria based on the identified pathology in CANVAS. We envisage that these criteria will aid the clinician in diagnosing CANVAS and the researcher in further elucidating this complex disorder.

The association of bilateral vestibulopathy with cerebellar ataxia was first reported in 1991 and delineated as a distinct syndrome with a characteristic and measurable clinical sign--an absent visually enhanced vestibulo-ocular reflex--in 2004. We reviewed 27 patients with this syndrome and show that a non-length-dependent sensory deficit with absent sensory nerve action potentials is an integral component of this syndrome, which we now call "cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome" (CANVAS). All patients had brain MRI and 22/27 had evidence of cerebellar atrophy involving anterior and dorsal vermis, as well as the hemispheric crus I. Brain and temporal bone pathology in one patient showed marked loss of Purkinje cells and of vestibular, trigeminal, and facial ganglion cells, but not of spiral ganglion cells. There are two sets of sibling pairs, suggesting CANVAS is a late-onset recessive disorder. The characteristic clinical sign-the visual vestibulo-ocular reflex deficit-can be demonstrated and measured clinically using video-oculography.

Objective: The syndrome of cerebellar ataxia with bilateral vestibulopathy was delineated in 2004. Sensory neuropathy was mentioned in 3 of the 4 patients described. We aimed to characterize and estimate the frequency of neuropathy in this condition, and determine its typical MRI features. Methods:Retrospective review of 18 subjects (including 4 from the original description) who met the criteria for bilateral vestibulopathy with cerebellar ataxia. Results:The reported age at onset range was 39-71 years, and symptom duration was 3-38 years. The syndrome was identified in one sibling pair, suggesting that this may be a late-onset recessive disorder, although the other 16 cases were apparently sporadic. All 18 had sensory neuropathy with absent sensory nerve action potentials, although this was not apparent clinically in 2, and the presence of neuropathy was not a selection criterion. In 5, the loss of pinprick sensation was virtually global, mimicking a neuronopathy. However, findings in the other 11 with clinically manifest neuropathy suggested a length-dependent neuropathy. MRI scans showed cerebellar atrophy in 16, involving anterior and dorsal vermis, and hemispheric crus I, while 2 were normal. The inferior vermis and brainstem were spared.

Objective: To elucidate the neuropathology in cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS), a novel cerebellar ataxia comprised of the triad of cerebellar impairment, bilateral vestibular hypofunction, and a peripheral sensory deficit.Method: Brain and spinal neuropathology in 2 patients with CANVAS, together with brain and otopathology in another patient with CANVAS, were examined postmortem.Results: Spinal cord pathology demonstrated a marked dorsal root ganglionopathy with secondary tract degeneration. Cerebellar pathology showed loss of Purkinje cells, predominantly in the vermis. Conclusion:The likely underlying sensory pathology in CANVAS is loss of neurons from the dorsal root and V, VII, and VIII cranial nerve ganglia-in other words, it is a "neuronopathy" rather than a "neuropathy." Clinically, CANVAS is a differential diagnosis for both spinocerebellar ataxia type 3 (or Machado-Joseph disease) and Friedreich ataxia. In addition, there are 6 sets of sibling pairs, implying that CANVAS is likely to be a late-onset recessive or autosomal dominant with reduced penetrance disorder, and identification of the culprit gene is currently a target of investigation. An abnormal visually enhanced vestibulo-ocular reflex (VVOR) represents a compound impairment of the 3 key corrective oculomotor reflexes, namely, smooth pursuit, the vestibulo-ocular reflex (VOR), and the opticokinetic reflex. We refer the reader to our earlier work for details of the VVOR.1 While the initial description of a syndrome of cerebellar ataxia and bilateral vestibulopathy noted the presence of a peripheral neuropathy in 3 of the 4 index cases, we later showed that in 18 patients a peripheral nerve disease was an integral component of the syndrome we renamed cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS).2 At this time, we noted that a neuronopathy (ganglionopathy) could not be definitively excluded. Subsequently, temporal bone histopathology 1 revealed a vestibular, facial, and trigeminal sensory neuronopathy. In an effort to unify the underlying pathology in CANVAS, we speculated that the peripheral sensory deficit, invariably seen in this syndrome, was more likely to be a neuronopathy than a neuropathy. Our efforts at testing this hypothesis were initially limited by the difficulty in differentiating these 2 entities with conventional neurophysiologic protocols. On obtaining the first spinal cord postmortem samples in cases of diagnosed CANVAS, it appears that the peripheral sensory deficit in CANVAS may be due to a dorsal root ganglionopathy. We hope to develop neurophysiologic protocols that may be used to identify this pathology in the living patient.

BACKGROUND: Cerebellar Ataxia with Neuropathy and bilateral Vestibular Areflexia Syndrome (CANVAS) is a multi-system ataxia which results in cerebellar ataxia, a bilateral vestibulopathy and a somatosensory deficit. This sensory deficit has recently been shown to be a neuronopathy, with marked dorsal root ganglia neuronal loss. The characteristic oculomotor clinical sign is an abnormal visually enhanced vestibulo-ocular reflex. OBJECTIVE: To outline the expanding understanding of the pathology in this condition, as well as diagnostic and management issues encountered in clinical practice. METHODS: Retrospective data on 80 CANVAS patients is reviewed. RESULTS: In addition to the triad of cerebellar impairment, bilateral vestibulopathy and a somatosensory deficit, CANVAS patients may also present with orthostatic hypotension, a chronic cough and neuropathic pain. Management of falls risk and dysphagia is a major clinical priority. CONCLUSIONS: CANVAS is an increasingly recognised cause of late-onset ataxia and disequilibrium, and is likely to be a recessive disorder.

Background Cerebellar damage can often result in disabilities affecting the peripheral regions of the body. These include poor and inaccurate coordination, tremors and irregular movements that often manifest as disorders associated with balance, gait and speech. The severity assessment of Cerebellar ataxia (CA) is determined by expert opinion and is likely to be subjective in nature. This paper investigates automated versions of three commonly used tests: Finger to Nose test (FNT), test for upper limb Dysdiadochokinesia Test (DDK) and Heel to Shin Test (HST), in evaluating disability due to CA. Methods Limb movements associated with these tests are measured using Inertial Measurement Units (IMU) to capture the disability. Kinematic parameters such as acceleration, velocity and angle are considered in both time and frequency domain in three orthogonal axes to obtain relevant disability related information. The collective dominance in the data distributions of the underlying features were observed though the Principal Component Analysis (PCA). The dominant features were combined to substantiate the correlation with the expert clinical assessments through Linear Discriminant Analysis. Here, the Pearson correlation is used to examine the relationship between the objective assessments and the expert clinical scores while the performance was also verified by means of cross validation. Results The experimental results show that acceleration is a major feature in DDK and HST, whereas rotation is the main feature responsible for classification in FNT. Combining the features enhanced the correlations in each domain. The subject data was classified based on the severity information based on expert clinical scores. Conclusion For the predominantly translational movement in the upper limb FNT, the rotation captures disability and for the DDK test with predominantly rotational movements, the linear acceleration captures the disability but cannot be extended to the lower limb HST. The orthogonal direction manifestation of ataxia attributed to sensory measurements was determined for each test. Trial registration Human Research and Ethics Committee, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia (HREC Reference Number: 11/994H/16). Electronic supplementary material The online version of this article (10.1186/s12984-019-0490-3) contains supplementary material, which is available to authorized users.