Is the ataxia of Charlevoix–Saguenay a developmental disease?

An MRI evaluation of white matter involvement in paradigmatic forms of spastic ataxia: results from the multi-center PROSPAX study

BACKGROUND

Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) and Spastic Paraplegia Type 7 (SPG7) are paradigmatic spastic ataxias (SPAX) with suggested white matter (WM) involvement. Aim of this work was to thoroughly disentangle the degree of WM involvement in these conditions, evaluating both macrostructure and microstructure via the analysis of diffusion MRI (dMRI) data.

MATERIAL AND METHODS

In this multi-center prospective study, ARSACS and SPG7 patients and Healthy Controls (HC) were enrolled, all undergoing a standardized dMRI protocol and a clinimetrics evaluation including the Scale for the Assessment and Rating of Ataxia (SARA). Differences in terms of WM volume or global microstructural WM metrics were probed, as well as the possible occurrence of a spatially defined microstructural WM involvement via voxel-wise analyses, and its correlation with patients' clinical status.

RESULTS

Data of 37 ARSACS (M/F = 21/16; 33.4 ± 12.4 years), 37 SPG7 (M/F = 24/13; 55.7 ± 10.7 years), and 29 HC (M/F = 13/16; 42.1 ± 17.2 years) were analyzed. While in SPG7, only a mild mean microstructural damage was found compared to HC, ARSACS patients present a severe WM involvement, with a reduced global volume (p < 0.001), an alteration of all microstructural metrics (all with p < 0.001), without a spatially defined pattern of damage but with a prominent involvement of commissural fibers. Finally, in ARSACS, a correlation between microstructural damage and SARA scores was found (p = 0.004).

CONCLUSION

In ARSACS, but not SPG7 patients, we observed a complex and multi-faced involvement of brain WM, with a clinically meaningful widespread loss of axonal and dendritic integrity, secondary demyelination and, overall, a reduction in cellularity and volume.

Autosomal recessive cerebellar ataxias: a diagnostic classification approach according to ocular features

Autosomal recessive cerebellar ataxias (ARCAs) are a heterogeneous group of neurodegenerative disorders affecting primarily the cerebellum and/or its afferent tracts, often accompanied by damage of other neurological or extra-neurological systems. Due to the overlap of clinical presentation among ARCAs and the variety of hereditary, acquired, and reversible etiologies that can determine cerebellar dysfunction, the differential diagnosis is challenging, but also urgent considering the ongoing development of promising target therapies. The examination of afferent and efferent visual system may provide neurophysiological and structural information related to cerebellar dysfunction and neurodegeneration thus allowing a possible diagnostic classification approach according to ocular features. While optic coherence tomography (OCT) is applied for the parametrization of the optic nerve and macular area, the eye movements analysis relies on a wide range of eye-tracker devices and the application of machine-learning techniques. We discuss the results of clinical and eye-tracking oculomotor examination, the OCT findings and some advancing of computer science in ARCAs thus providing evidence sustaining the identification of robust eye parameters as possible markers of ARCAs.

Documenting manifestations and impacts of autosomal recessive spastic ataxia of Charlevoix-Saguenay to develop patient-reported outcome

BACKGROUND

Autosomal recessive cerebellar ataxias (ARCA) are a group of rare inherited disorders characterized by degeneration or abnormal development of the cerebellum. Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is one of the most prevalent in Europe.

OBJECTIVES

The aim of this study is to provide a better understanding of the manifestations and impacts of ARSACS.

METHODS

A systematic review of the literature was conducted, followed by a qualitative study using semistructured interviews and discussion groups to obtain the experience of people affected.

RESULTS

According to the PROMIS framework, the results show manifestations and impacts in three components of health: physical, mental, and social. Fatigue and struggles with balance and dexterity are the physical manifestations of the disease most often cited by participants. Negative affects such as frustration and depression are among the mental health impacts with some loss in cognitive abilities. Social health is the least documented component; nonetheless, people with the disease report significant impacts in terms of social relationships, activities and work.

CONCLUSIONS

These findings shed new light on the experience of people with recessive ataxia and identify key aspects to assess to improve their overall health.

Retinal Architecture in Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS): Insights into Disease Pathogenesis and Biomarkers

BACKGROUND

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) causes unique retinal abnormalities, which have not been systematically investigated.

OBJECTIVE

To deeply phenotype the retina in ARSACS in order to better understand its pathogenesis and identify potential biomarkers.

METHODS

We evaluated 29 patients with ARSACS, 66 with spinocerebellar ataxia (SCA), 38 with autosomal recessive cerebellar ataxia (ATX), 22 with hereditary spastic paraplegia (SPG), 21 cases of papilledema, and 20 healthy controls (total n = 196 subjects). Participants underwent visual acuity assessment, intraocular pressure measurement, fundoscopy, and macular and peripapillary optical coherence tomography (OCT). Macular layers thicknesses in ARSACS were compared with those of age-matched healthy controls. Ophthalmologists analyzed the scans for abnormal signs in the different patient groups. Linear regression analysis was conducted to look for associations between retinal changes and age, age at onset, disease duration, and Scale for the Assessment and Rating of Ataxia (SARA) scores in ARSACS.

RESULTS

Only patients with ARSACS exhibited peripapillary retinal striations (82%) on fundoscopy, and their OCT scans revealed foveal hypoplasia (100%), sawtooth appearance (89%), papillomacular fold (86%), and macular microcysts (18%). Average peripapillary retinal nerve fiber layer (pRNFL) was thicker in ARSACS than in SCA, ATX, SPG, and controls; a cut-off of 121 μm was 100% accurate in diagnosing ARSACS. All macular layers were thicker in ARSACS when compared to healthy controls. RNFL thickness in the inferior sector of the macula positively correlated with SARA scores.

CONCLUSIONS

Retinal abnormalities are highly specific for ARSACS, and suggest retinal hyperplasia due to abnormal retinal development. OCT may provide potential biomarkers for future clinical trials. © 2021 International Parkinson and Movement Disorder Society.

A clinical diagnostic algorithm for early onset cerebellar ataxia

Early onset cerebellar Ataxia (EOAc) comprises a large group of rare heterogeneous disorders. Determination of the underlying etiology can be difficult given the broad differential diagnosis and the complexity of the genotype-phenotype relationships. This may change the diagnostic work-up into a time-consuming, costly and not always rewarding task. In this overview, the Childhood Ataxia and Cerebellar Group of the European Pediatric Neurology Society (CACG-EPNS) presents a diagnostic algorithm for EOAc patients. In seven consecutive steps, the algorithm leads the clinician through the diagnostic process, including EOA identification, application of the Inventory of Non-Ataxic Signs (INAS), consideration of the family history, neuro-imaging, laboratory investigations, genetic testing by array CGH and Next Generation Sequencing (NGS). In children with EOAc, this algorithm is intended to contribute to the diagnostic process and to allow uniform data entry in EOAc databases.

Subtle Imaging Findings Aid the Diagnosis of Adolescent Hereditary Spastic Paraplegia and Ataxia

PURPOSE

Hereditary spastic paraplegia (HSP) and hereditary spastic ataxia (HSA) are a heterogeneous group of genetic disorders characterized by progressive lower limb spasticity resulting from pyramidal tract dysfunction. By identifying critical imaging findings within the clinical context of spasticity, radiologists are uniquely positioned to recommend specific genetic testing, and thus facilitate diagnosis.

METHODS

We present two examples of HSP and HSA that had gone clinically unrecognized for years, and in which magnetic resonance imaging played a critical role in the diagnosis.

RESULTS

Radiologists' awareness of HSP and HSA, combined with a critical review of the clinical history and characteristic imaging findings led to specific genetic testing and a definitive diagnosis.

CONCLUSION

Awareness of HSP and HSA among radiologists will expedite more accurate diagnosis, explanation of patient symptoms, recommendation for syndrome-specific treatment, and family planning considerations.

Retinal nerve fiber layer thickening in ARSACS carriers

PURPOSE

Two Caucasian Belgian families were diagnosed with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). The ophthalmological findings in both ARSACS disease and carriers are described.

METHODS

In addition to a complete ophthalmological assessment, in both patients and carriers, spectral-domain Optical Coherence Tomography scans of the peri-papillary retinal nerve fiber layer were performed.

RESULTS

Molecular analysis revealed a missense mutation which has not been reported before. Besides patients with ARSACS, who also presented additional ophthalmological abnormalities i.e. eye movement problems, ARSACS carriers demonstrated thickening of the retinal nerve fiber layer.

CONCLUSION

The most conspicuous ophthalmological feature of ARSACS is an increased thickness of the peri-papillary retinal nerve fiber layer. Retinal striation and thickening of the nerve fiber layer on spectral-domain Optical Coherence Tomography appeared also in carriers of the ARSACS-gene. Other ophthalmological features encountered, were gaze-evoked nystagmus and rebound nystagmus.

Novel SACS mutations associated with intellectual disability, epilepsy and widespread supratentorial abnormalities

We describe eight subjects from two consanguineous families segregating with autosomal recessive childhood onset spastic ataxia, peripheral neuropathy and intellectual disability. The degree of intellectual disability varied from mild to severe and all four affected individuals in one family developed aggressive behavior and epilepsy. Using exome sequencing, we identified two novel truncating mutations (c.2656C>T (p.Gln886*)) and (c.4756_4760delAATCA (p.Asn1586Tyrfs*3)) in the SACS gene responsible for autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). MRI revealed typical cerebellar and pontine changes associated with ARSACS as well as multiple supratentorial changes in both families as likely contributing factors to the cognitive symptoms. Intellectual disability and behavioral abnormalities have been reported in some cases of ARSACS but are not a part of the characteristic triad of symptoms that includes cerebellar ataxia, spasticity and peripheral neuropathy. Our combined findings bring further knowledge to the phenotypic spectrum, neurodegenerative changes and genetic variability associated with the SACS gene of clinical and diagnostic importance.

Keys to overcoming the challenge of diagnosing autosomal recessive spinocerebellar ataxia

INTRODUCTION

Autosomal recessive spinocerebellar ataxia refers to a large group of diseases affecting the cerebellum and/or its connections, although they may also involve other regions of the nervous system. These diseases are accompanied by a wide range of systemic manifestations (cardiopathies, endocrinopathies, skeletal deformities, and skin abnormalities).

DEVELOPMENT

This study reviews current knowledge of the most common forms of autosomal recessive spinocerebellar ataxia in order to provide tips that may facilitate diagnosis.

CONCLUSIONS

A thorough assessment of clinical phenotype (pure cerebellar or cerebellar-plus syndrome, with or without systemic manifestations), laboratory tests (vitamin E, acanthocytosis, albumin, cholesterol, phytanic acid, lactic acid, creatine kinase, cholestanol, coenzyme Q10, alpha-fetoprotein, copper, ceruloplasmin, chitotriosidase), nerve conduction studies (presence and type of neuropathy), and an magnetic resonance imaging study (presence of cerebellar atrophy, presence and location of signal alterations) may help establish a suspected diagnosis, which should be confirmed by detecting the underlying genetic mutation. A positive genetic test result is necessary to determine prognosis and provide adequate genetic counselling, and will also permit appropriate treatment of some entities (abetalipoproteinaemia, ataxia with vitamin E deficiency, Refsum disease, cerebrotendinous xanthomatosis, Niemann-Pick disease type C, Wilson disease). Without a genetic diagnosis, conducting basic research and therapeutic trials will not be possible.

Assessment of whole-brain white matter by DTI in autosomal recessive spastic ataxia of Charlevoix-Saguenay

BACKGROUND AND PURPOSE

Extension and characteristics of WM involvement other than the brain stem remain inadequately investigated in ARSACS. The aim of this study was to investigate whole-brain WM alterations in patients with ARSACS.

MATERIALS AND METHODS

Nine Turkish unrelated patients with ARSACS and 9 sex- and age-matched healthy control participants underwent neurologic examination, molecular studies, electrophysiologic studies, and DTI of the brain. TBSS was used for whole-brain voxelwise analysis of FA, AD, RD, mean diffusivity of WM. Tractographies for the CST and TPF were also computed.

RESULTS

Molecular studies revealed 8 novel mutations (3 nonsense, 4 missense, and 1 frameshift insertion) and a missense variation in the SACS gene. Thick TPF displaced and compressed the CST in the pons. The TPF had increased FA, decreased RD, and increased AD, which may be attributed to hypertrophy and/or hypermyelination. Widespread decreased FA and increased RD, suggesting demyelination, was found in the limbic, commissural, and projection fibers. In addition to demyelination, CST coursing cranial and caudal to the pons also showed a marked decrease in AD, suggesting axonal degeneration. Electrophysiologic studies revealed findings that concur with demyelination and axonal involvement.

CONCLUSIONS

In addition to developmental changes of the TPF and their effects on the CST in the brain stem, axonal degeneration mainly along the pyramidal tracts and widespread demyelination in WM also occur in patients with ARSACS. Widespread tissue damage may be associated with extensive loss of sacsin protein in the brain and may explain a wide range of progressive neurologic abnormalities in patients with ARSACS.

Autosomal recessive spastic ataxia of Charlevoix Saguenay (ARSACS): expanding the genetic, clinical and imaging spectrum

BACKGROUND

Mutations in SACS, leading to autosomal-recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), have been identified as a frequent cause of recessive early-onset ataxia around the world. Here we aimed to enlarge the spectrum of SACS mutations outside Quebec, to establish the pathogenicity of novel variants, and to expand the clinical and imaging phenotype.

METHODS

Sequencing of SACS in 22 patients with unexplained early-onset ataxia, assessment of novel SACS variants in 3.500 European control chromosomes and extensive phenotypic investigations of all SACS carriers.

RESULTS

We identified 11 index patients harbouring 17 novel SACS variants. 9/11 patients harboured two variants of at least probable pathogenicity which were not observed in controls and, in case of missense mutations, were located in highly conserved domains. These 9 patients accounted for at least 11% (9/83) in our series of unexplained early onset ataxia subjects. While most patients (7/9) showed the classical ARSACS triad, the presenting phenotype reached from pure neuropathy (leading to the initial diagnosis of Charcot-Marie-Tooth disease) in one subject to the absence of any signs of neuropathy in another. In contrast to its name "spastic ataxia", neither spasticity (absent in 2/9=22%) nor extensor plantar response (absent in 3/9=33%) nor cerebellar ataxia (absent in 1/9=11%) were obligate features. Autonomic features included urine urge incontinence and erectile dysfunction. Apart from the well-established MRI finding of pontine hypointensities, all patients (100%) showed hyperintensities of the lateral pons merging into the (thickened) middle cerebellar peduncles. In addition, 63% exhibited bilateral parietal cerebral atrophy, and 63% a short circumscribed thinning of the posterior midbody of the corpus callosum. In 2 further patients with differences in important clinical features, VUS class 3 variants (c.1373C>T [p.Thr458Ile] and c.2983 G>T [p.Val995Phe]) were identified. These variants were, however, also observed in controls, thus questioning their pathogenic relevance.

CONCLUSIONS

We here demonstrate that each feature of the classical ARSACS triad (cerebellar ataxia, spasticity and peripheral neuropathy) might be missing in ARSACS. Nevertheless, characteristic MRI features - which also extend to supratentorial regions and involve the cerebral cortex - will help to establish the diagnosis in most cases.

Supratentorial and pontine MRI abnormalities characterize recessive spastic ataxia of Charlevoix-Saguenay. A comprehensive study of an Italian series

BACKGROUND AND PURPOSE

The autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative disorder caused by mutations in the SACS gene. The disease, first described in Canadian families from Québec, is characterized by cerebellar ataxia, pyramidal tract involvement and peripheral neuropathy.

METHODS

Analysis of SACS gene allowed the identification of 14 patients with ARSACS from 13 unrelated Italian families. Clinical phenotype, gene mutations and magnetic resonance imaging (MRI) findings were analysed.

RESULTS

We found 16 novel SACS gene mutations, including a large in-frame deletion. The age at onset was in infancy, but one patient presented the first symptoms at age 32. Progression of the disease was variable, and increased muscle tone was mostly recognized in later stages. Structural MRI showed atrophy of the superior cerebellar vermis, a bulky pons exhibiting T2-hypointense stripes, identified as the corticospinal tract (CST), thinning of the corpus callosum and a rim of T2-hyperintensity around the thalami in 100% of cases. The presence of iron or other paramagnetic substances was excluded. Diffusion tensor imaging (DTI) revealed grossly over-represented transverse pontine fibres (TPF), which prevented reconstruction of the CST at this level (100% of cases). In all patients, significant microstructural alterations were found in the supratentorial white matter of forceps, cingulum and superior longitudinal fasciculus.

CONCLUSIONS

Our findings further enlarge the genetic spectrum of SACS mutations and widen the study of clinical phenotype. MRI characteristics indicate that pontine changes and supratentorial abnormalities are diagnostic. The over-representation of TPF on DTI suggests a developmental component in the pathogenesis of the disease.

Mitochondrial dysfunction and Purkinje cell loss in autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS)

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a childhood-onset neurological disease resulting from mutations in the SACS gene encoding sacsin, a 4,579-aa protein of unknown function. Originally identified as a founder disease in Québec, ARSACS is now recognized worldwide. Prominent features include pyramidal spasticity and cerebellar ataxia, but the underlying pathology and pathophysiological mechanisms are unknown. We have generated an animal model for ARSACS, sacsin knockout mice, that display age-dependent neurodegeneration of cerebellar Purkinje cells. To explore the pathophysiological basis for this observation, we examined the cell biological properties of sacsin. We show that sacsin localizes to mitochondria in non-neuronal cells and primary neurons and that it interacts with dynamin-related protein 1, which participates in mitochondrial fission. Fibroblasts from ARSACS patients show a hyperfused mitochondrial network, consistent with defects in mitochondrial fission. Sacsin knockdown leads to an overly interconnected and functionally impaired mitochondrial network, and mitochondria accumulate in the soma and proximal dendrites of sacsin knockdown neurons. Disruption of mitochondrial transport into dendrites has been shown to lead to abnormal dendritic morphology, and we observe striking alterations in the organization of dendritic fields in the cerebellum of knockout mice that precedes Purkinje cell death. Our data identifies mitochondrial dysfunction/mislocalization as the likely cellular basis for ARSACS and indicates a role for sacsin in regulation of mitochondrial dynamics.