A Novel Exon Duplication in the SACS Gene in Charlevoix-Saguenay Ataxia and a Summary of Polish Cases

Autosomal recessive spastic ataxia of Charlevoix-Saguenay caused by novel mutations in SACS gene: A report of two Chinese families

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a neurodegenerative disorder commonly diagnosed in infants and characterized by progressive cerebellar ataxia, spasticity, motor sensory neuropathy and axonal demyelination. ARSACS is caused by mutations in the SACS gene that lead to truncated or defective forms of the 520 kDa multidomain protein, sacsin. Sacsin function is exclusively studied on neuronal cells, where it regulates mitochondrial network organization and facilitates the normal polymerization of neuronal intermediate filaments (i.e., neurofilaments and vimentin). Here, we show that sacsin is also highly expressed in astrocytes, C6 rat glioma cells and N9 mouse microglia. Sacsin knockout in C6 cells (C6Sacs−/−) induced the accumulation of the glial intermediate filaments glial fibrillary acidic protein (GFAP), nestin and vimentin in the juxtanuclear area, and a concomitant depletion of mitochondria. C6Sacs−/− cells showed impaired responses to oxidative challenges (Rotenone) and inflammatory stimuli (Interleukin-6). GFAP aggregation is also associated with other neurodegenerative conditions diagnosed in infants, such as Alexander disease or Giant Axonal Neuropathy. Our results, and the similarities between these disorders, reinforce the possible connection between ARSACS and intermediate filament-associated diseases and point to a potential role of glia in ARSACS pathology.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative human disease characterized in part by ataxia and Purkinje cell loss in anterior cerebellar lobules. A knock-out mouse model has been developed that recapitulates several features of ARSACS. Using this ARSACS mouse model, we report changes in synaptic input and intrinsic firing in cerebellar Purkinje cells, as well as in their synaptic output in the deep cerebellar nuclei. Changes in firing are observed in anterior lobules that later exhibit Purkinje cell death, but not in posterior lobules that do not. Our results show that both synaptic and intrinsic alterations in Purkinje cell properties likely contribute to disease manifestation in ARSACS; these findings resemble pathophysiological changes reported in several other ataxias. Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative disease that includes a pronounced and progressive cerebellar dysfunction. ARSACS is caused by an autosomal recessive loss-of-function mutation in the Sacs gene that encodes the protein sacsin. To better understand the cerebellar pathophysiology in ARSACS, we studied synaptic and firing properties of Purkinje cells from a mouse model of ARSACS, Sacs-/- mice. We found that excitatory synaptic drive was reduced onto Sacs-/- Purkinje cells, and that Purkinje cell firing rate, but not regularity, was reduced at postnatal day (P)40, an age when ataxia symptoms were first reported. Firing rate deficits were limited to anterior lobules that later display Purkinje cell death, and were not observed in posterior lobules where Purkinje cells are not lost. Mild firing deficits were observed as early as P20, prior to the manifestation of motor deficits, suggesting that a critical level of cerebellar dysfunction is required for motor coordination to emerge. Finally, we observed a reduction in Purkinje cell innervation onto target neurons in the deep cerebellar nuclei (DCN) in Sacs-/- mice. Together, these findings suggest that multiple alterations in the cerebellar circuit including Purkinje cell input and output contribute to cerebellar-related disease onset in ARSACS.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS: MIM 270550) is a neurodegenerative disorder characterized by early-onset cerebellar ataxia with spasticity and peripheral neuropathy. This disorder, considered to be rare, was first described in the late seventies among French Canadians in the isolated Charlevoix-Saguenay region of Quebec. Nowadays, it is known that the disorder is not only limited to this region but occurs worldwide. Our objective was to identify cases of autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) in Dutch patients with recessive early-onset cerebellar ataxia by sequencing the complete SACS gene. In a Dutch cohort of 43 index patients with ataxia onset before age 25, we identified 16 index patients (total 23 patients) with mutations in the SACS gene. Nine of them had homozygous mutations, and seven of them had compound heterozygous mutations. Retrospectively, the phenotype of patients carrying mutations was remarkably uniform: cerebellar ataxia with onset before age 13 years, lower limb spasticity and sensorimotor axonal neuropathy, and cerebellar (vermis) atrophy on magnetic resonance imaging, consistent with the core ARSACS phenotype previously described. The high rate of mutations (37%) identified in this cohort of Dutch patients suggests that ARSACS is substantially more frequent than previously estimated. We predict that the availability of SACS mutation analysis as well as an increasing awareness of the characteristic ARSACS phenotype will lead to the diagnosis of many additional patients, possibly even at a younger age.

The phenotype of Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) was initially reported as early-onset limb ataxia, spastic paraparesis and sensorimotor neuropathy with dysarthria, retinal abnormalities, horizontal nystagmus, urinary dysfunction...

Background:A 38-year-old woman was diagnosed autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) with a novel pathogenic variant in the SACS gene presented with gradually progressive spastic ataxia since the age of 2 years; then, she became wheelchair-bound at the age of 28 years.Phenomenology:The patient presented a combination of cerebellar dysfunctions e.g., gaze-evoked nystagmus, scanning speech, finger dysmetria, and wide-based gait, lower limb spasticity, and typical funduscopic examination which was a hypermyelinated nerve fibers radiating from the optic disc.Educational value:At present, ARSACS is recognized as a rare, worldwide, inherited movement disorder in which we should to aware of a diagnosis of this disorder in the patient who is presented with FXN gene negative early-onset spastic ataxia.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) – A Polish family with novel SACS mutations

Charcot-Marie-Tooth disease (CMT) is among the most common group of inherited neuromuscular diseases. SACS mutations were demonstrated to cause autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). However, there have been few case reports regarding to NEFH and SACS gene mutation to CMT in Vietnamese patients, and the diagnosis of CMT and ARSACS in the clinical setting still overlapped. We report two patients presenting with sensorimotor neuropathy without cerebellar ataxia, spasticity and other neurological features, being diagnosed with intermediate form CMT by electrophysiological and clinical examination and neuroimaging. By whole-exome sequencing panel of two affected members, and PCR Sanger on NEFH and SACS genes to confirm the presence of selected variants on their parents, we identified a novel missense variant NEFH c.1925C>T (inherited from the mother) in an autosomal dominant heterozygous state, and two recessive SACS variants (SACS c.13174C>T, causing missense variant, and SACS c.11343del, causing frameshift variant) (inherited one from the mother and another from the father) in these two patients. Clinical and electrophysiological findings on these patients did not match classical ARSACS. To the best of our knowledge, this is the first case report of two affected siblings diagnosed with CMT carrying both a novel NEFH variant and biallelic SACS variants. We concluded that this novel NEFH variant is likely benign, and biallelic SACS mutation (c.13174C>T and c.11343del) is likely pathogenic for intermediate form CMT. This study is also expected to emphasize the current knowledge of intermediate form CMT, ARSACS, and the phenotypic spectrum of NEFH-related and SACS-related disorders. We expect to give a new understanding of CMT; however, further research should be conducted to provide a more thorough knowledge of the pathogenesis of CMT in the future.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is characterized by triad of progressive cerebellar ataxia, progressive spasticity, and axonal/demyelinating peripheral neuropathy. Other manifestations include dysarthria, weakness in lower extremities and distal muscle wasting, foot deformities, retinal striation, prolapse of the mitral valve and rarely intellectual disability, hearing loss, and myoclonic epilepsy. We describe a patient who developed peripheral sensorimotor neuropathy in the absence of spasticity on initial presentation. He had nerve root enhancement on magnetic resonance imaging (MRI) lumbar spine, and nerve conduction studies were suggestive of demyelinating polyneuropathy. Patient had mild cerebellar atrophy on MRI and some delay of motor milestones. Over the course of several months, he developed spasticity, and genetic analysis together with clinical presentation was consistent with ARSACS. He was noted to have a pathogenic mutation c.8108G>A (p. Arg2703His) inherited from mother and a variant of uncertain significance c.7216T>C (p. Ser2406Pro) inherited from his father in SACS gene. Atypical cases may present later in life or in absence of one of the classical features at the time of presentation, which may make diagnosis difficult. Our patient had such an atypical presentation of ARSACS. Young patients with neuropathy and concomitant cerebellar atrophy on MRI should raise suspicion for hereditary spastic ataxia syndrome. Follow-up examination can often reveal additional findings to aid the diagnosis.

Migraine patients often complain of repeated attacks of monocular visual disturbance including scintillations, scotomas, blindness and pupillary dysfunction. Temporary pupillary enlargement of the ipsilateral side during migraine attack, although rarely reported, is referred to as an Adie’s-like tonic pupil [1]. Adie’s tonic pupil is caused by denervation of the postganglionic parasympathetic pupillary nerves, with light-near dissociation, and cholinergic supersensitivity. Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is characterized by early-onset spastic ataxia, peripheral sensorimotor neuropathy, and pyramidal symptoms. ARSACS is caused by mutations in the SACS gene, which encodes the Sacsin expressed in various tissues including brain motor systems. Sacsin is believed to integrate the ubiquitin-proteasome system and Hsp70 chaperone machinery, which are important components of the cellular response associated with neurodegenerative diseases [2]. Here, we describe a patient suffering from chronic migraine without aura who developed cerebellar ataxia and unilateral mydriasis during acute migraine persisted after resolved headache. Presence of a SACS gene mutation is an expansion of the clinical phenotype associated with SACS mutations to ciliary ganglioplegic migraine. A 47-year-old female who suffers from long standing headache developed unsteady gait and poor coordination. With a diagnosis of migraine without aura based on the third edition of the International Classification of Headache Disorders (ICHD-III) criteria, she was prescribed preventive medicine with topiramate and onabotulinumtoxinA injection on occasion. Physical examination revealed a dilated pupil in the left eye without reflexive constriction to light or accommodation which persisted after resolution of migraine. Except for anisocoria, no other abnormal findings were identified. Remarkable reduction of the left pupil size was observed in response to 0.125% pilocarpine (Figure 1). The patient also showed mild nonataxic spastic paraplegia but without distal weakness or pyramidal signs. A family history of migraine headache and other neurological disorders was denied. Nerve conduction studies confirmed the mixed demyelinating and axonal character of polyneuropathy. Brain MRI with angiography did not reveal any abnormalities.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) was originally found among inhabitants of the Charlevoix-Saguenay region of northeastern Quebec in Canada. This disease is a neurodegenerative disorder characterized by early-onset spastic ataxia, dysarthria, nystagmus, distal muscle wasting, finger and foot deformities, and retinal hypermyelination. The principal neuropathology comprises atrophy of the upper vermis and the loss of Purkinje cells in the cerebellum. The SACS gene was originally reported to consist of a single gigantic exon spanning 12.8 kb with an 11.5-kb open reading frame (ORF), and to encode the protein sacsin. Recently, eight exons upstream from the original gigantic one, however, have been found, and the new ORF has elongated to 13.7 kb. To date, at least 28 mutations have been found in Quebec and non-Quebec patients including ones in Italy, Japan, Spain, Tunisia, and Turkey, and ARSACS thus shows a worldwide occurrence. Although most of the mutations reported have been in the gigantic exon, the genotype is now expanding upstream from this gigantic exon. Therefore, the new exons upstream of the gigantic one should be analyzed when a case is clinically compatible with ARSACS, even without any mutation in the gigantic exon. Although Quebec patients show a homogeneous phenotype, non-Quebec patients exhibit some atypical clinical features, as follows: slightly later onset than that in Quebec patients, absence of retinal hypermyelination, intellectual impairment, and lack of spasticity. Thus, since ARSACS shows the clinical diversity, the SACS gene should be analyzed not only in typical cases as Quebec patients but also in atypical cases as non-Quebec patients. As more SACS mutations are identified worldwide, the clinical spectrum of 'sacsinopathies' will expand, and a finer genotype-phenotype correlation study will become possible and shed light on the molecular mechanism underlying ARSACS.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is caused by pathogenic variants in the SACS gene and is characterized by ataxia, peripheral neuropathy, pyramidal impairment and episodic conditions such as epilepsy. Paroxysmal kinesigenic dyskinesia (PKD) had not been previously described in ARSACS. We analyzed clinical manifestations and performed whole-exome sequencing (WES) in two independent patients with ARSACS and PKD. Both patients' parents were unaffected. Genetic data were filtered for potential pathogenic variants, searching for de novo mutations suggestive of a dominant disease model or homozygous and compound heterozygous variants of a recessive model. Potential mutations that existed in both patients were generated and subjected to Sanger sequencing. The WES results of 163 PKD patients without additional symptoms from previous experiments were also reviewed. Novel compound heterozygous mutations in the SACS gene were identified in Patient 1 (p.P3007S and p.H3392fs), and a novel homozygous truncating mutation (p.W1376X) was identified in Patient 2. In both patients, each mutant allele was inherited from one of his or her unaffected parents. All 3 mutations were absent in 196 ethnic-matched control chromosomes or in data from the 1000 Genomes Project. No pathogenic variants associated with paroxysmal diseases, especially PKD and episodic ataxia, were identified. In PKD patients without additional symptoms, no homozygous or compound heterozygous variants in the SACS gene were detected. This study expands the clinical phenotype of ARSACS and suggests the inclusion of SACS screening in patients with PKD plus ARSACS.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a rare progressive neurodegenerative disease caused by either homozygous or compound heterozygous mutations in the SACS gene. The original ARSACS cases found in Quebec showed very homogenous phenotypes characterized by cerebellar ataxia, spasticity, and polyneuropathy. However, many cases with atypical phenotypes have been found in other regions and ethnic groups. We herein present a Japanese patient with atypical ARSACS who showed cerebellar ataxia and polyneuropathy, but no spasticity. She carried novel compound heterozygous mutations (p.Lys4326Glu and p.Leu1412Lysfs*16) in the SACS gene. The brain MRI findings were useful for making a diagnosis of ARSACS.

A 24-year-old Chilean man with slowly progressive ataxia since age 2 presented with spastic ataxia, hyperreflexia, pes cavus, axonal polyneuropathy, incomplete right-bundle branch block on ECG, and impaired glucose tolerance test, suggesting Friedreich ataxia (figure; video at [Neurology.org][1]). However, the combination of hyperreflexia and cerebellar (rather than cervical cord) atrophy with T2-weighted linear hypointensity in the pons on brain MRI suggested autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). Biallelic mutations were found (c.4492C>T p.[R1498X] and c.2388dupA p.[L797Ifs*4]) in the SACS gene (NCBI sequence NM_001278055). ARSACS is the second most common cause of autosomal recessive spastic ataxia syndrome ( SACS mutations account for 37% of Friedreich-negative cases)1 and should be considered in any population with suggestive MRI abnormalities.2 [1]: http://neurology.org/lookup/doi/10.1212/WNL.0000000000004556

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), classically presenting as a triad of early-onset cerebellar ataxia, lower extremity spasticity and peripheral neuropathy, is caused by mutations in SACS gene which encodes the protein sacsin. To provide new insight into the occurrence of SACS mutations in South India. Patients with three cardinal features of ARSACS-peripheral neuropathy, cerebellar ataxia, and pyramidal tract signs were included. Nine patients were clinically identified and genetically evaluated. Mutation screening of SACS by targeted sequencing of 40 recessive ataxia genes panel by next-generation sequencing was conducted. Additional investigations included magnetic resonance imaging (MRI), fundoscopy, optical coherence tomography (OCT) and nerve conduction studies (NCS). Functional disability was assessed by the Spinocerebellar Degeneration Functional Score. Two hundred and fifteen cerebellar ataxia patients were screened, and 9 patients with cerebellar ataxia with spasticity, peripheral neuropathy and MRI brain characteristics, consistent with a clinical diagnosis of ARSACS were identified, of which 7 patients were identified to have mutation in the SACS gene and are detailed hereafter. Age of presentation ranged from 20 to 55years (29.8 ± 11.9) with a mean disease duration of 12.7years (SD-7.65, range 5-22years). All except one had onset of symptoms in the form of an ataxic gait noticed before 20years of age. Additional features were subnormal intelligence (4/7), slow and hypometric saccades (1/7), seizures (1/7), kyphoscoliosis (1/7) and dysmorphic facies (1/7). SDFS was 3 in 5/7 patients signifying moderate disability with independent ambulation. MRI showed cerebellar atrophy with predominant atrophy of the superior vermis (7/7), horizontal linear T2 hypointensities in the pons(7/7), hyperintensities where lateral pons merges with the middle cerebellar peduncle (MCP) (7/7) well seen in fluid-attenuated inversion recovery (FLAIR) images, thickening of MCP (3/7), symmetric lateral thalamic hyperintensities (6/7), posterior fossa arachnoid cyst (4/7),thinning of posterior mid-body of corpus callosum (7/7), marginal mineralisation of the basal ganglia (7/7), bilateral parietal atrophy (7/7) and thinning of corticospinal tract on diffusion tensor imaging (DTI) (7/7). We identified pathogenic homozygous frameshift mutations in the SACS gene in six patients (including two siblings), while one patient had a heterozygous pathogenic deletion. This is the largest series of genetically confirmed ARSACS patients from India highlighting the clinical, ophthalmological, imaging and genetic features of this cohort.