SACS variants are a relevant cause of autosomal recessive hereditary motor and sensory neuropathy

Exploring the evidence for mitochondrial dysfunction and genetic abnormalities in the etiopathogenesis of tropical ataxic neuropathy

Tropical ataxic neuropathy (TAN) is characterised by ataxic polyneuropathy, degeneration of the posterior columns and pyramidal tracts, optic atrophy, and sensorineural hearing loss. It has been attributed to nutritional/toxic etiologies, but evidence for the same has been equivocal. TAN shares common clinical features with inherited neuropathies and mitochondrial disorders, it may be hypothesised that genetic abnormalities may underlie the pathophysiology of TAN. This study aimed to establish evidence for mitochondrial dysfunction by adopting an integrated biochemical and multipronged genetic analysis. Patients (n = 65) with chronic progressive ataxic neuropathy with involvement of visual and/or auditory pathways underwent deep phenotyping, genetic studies including mitochondrial DNA (mtDNA) deletion analysis, mtDNA and clinical exome sequencing (CES), and respiratory chain complex (RCC) assay. The phenotypic characteristics included dysfunction of visual (n = 14), auditory (n = 12) and visual + auditory pathways (n = 29). Reduced RCC activity was present in 13 patients. Mitochondrial DNA deletions were noted in five patients. Sequencing of mtDNA (n = 45) identified a homoplasmic variant (MT-ND6) and a heteroplasmic variant (MT-COI) in one patient each. CES (n = 45) revealed 55 variants in nuclear genes that are associated with neuropathy (n = 27), deafness (n = 7), ataxia (n = 4), and mitochondrial phenotypes (n = 5) in 36 patients. This study provides preliminary evidence that TAN is associated with a spectrum of genetic abnormalities, including those associated with mitochondrial dysfunction, which is in contradistinction from the prevailing hypothesis that TAN is related to dietary toxins. Analysing the functional relevance of these genetic variants may improve the understanding of the pathogenesis of TAN.

Neuropathy in ARSACS is demyelinating but without typical nerve enlargement in nerve ultrasound

BACKGROUND

To specify peripheral nerve affection in autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) by correlating high-resolution nerve ultrasound and nerve conduction studies.

METHODS

We assessed a cohort of 11 ARSACS patients with standardized nerve conduction studies and high-resolution ultrasound of peripheral nerves and compared nerve ultrasound findings to a healthy control group matched for age, sex, size and weight.

RESULTS

Mean age of patients was 39.0 (± 14.1) years and disease duration at assessment 30.6 (± 12.5) years. All patients presented with a spasticity, ataxia and peripheral neuropathy. Neuropathy appeared to be primarily demyelinating in 9/11 cases and was not classifiable in 2/11 cases due to not evocable potentials. Nerve ultrasound revealed a normal ultrasound pattern sum score (UPSS) in each ARSACS patient and no significant nerve enlargement compared to the control group.

CONCLUSIONS

Peripheral neuropathy in ARSACS showed primarily demyelinating rather than axonal characteristics and presented without nerve enlargement. As demyelinating neuropathies do commonly present enlarged nerves we recommend further genetic testing of the SACS gene in patients who present with this combination of demyelinating neuropathy without nerve enlargement. ARSACS cases that initially presented only with neuropathy without spasticity or ataxia and therefore were misdiagnosed as Charcot-Marie-Tooth disease are supporting this suggestion.

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.

A genetic correlation and bivariate genome-wide association study of grip strength and depression

Grip strength is an important biomarker reflecting muscle strength, and depression is a psychiatric disorder all over the world. Several studies found a significant inverse association between grip strength and depression, and there is also evidence for common physiological mechanisms between them. We used twin data from Qingdao, China to calculate genetic correlations, and we performed a bivariate GWAS to explore potential SNPs, genes, and pathways in common between grip strength and depression. 139 pairs of Dizygotic twins were used for bivariate GWAS. VEAGSE2 and PASCAL software were used for gene-based analysis and pathway enrichment analysis, respectively. And the resulting SNPs were subjected to eQTL analysis and pleiotropy analysis. The genetic correlation coefficient between grip strength and depression was -0.41 (-0.96, -0.15). In SNP-based analysis, 7 SNPs exceeded the genome-wide significance level (P<5×10-8) and a total of 336 SNPs reached the level of suggestive significance (P<1×10-5). Gene-based analysis and pathway-based analysis identified genes and pathways related to muscle strength and the nervous system. The results of eQTL analysis were mainly enriched in tissues such as the brain, thyroid, and skeletal muscle. Pleiotropy analysis shows that 9 of the 15 top SNPs were associated with both grip strength and depression. In conclusion, this bivariate GWAS identified potentially common pleiotropic SNPs, genes, and pathways in grip strength and depression.

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.

Phenotypical spectrum of SACS variants: Neuromuscular perspective of a complex neurodegenerative disorder

OBJECTIVES

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is caused by the SACS gene variants. Main clinical features include early-onset and progressive cerebellar ataxia, spasticity, sensorimotor polyneuropathy. However, the phenotypic spectrum expanded with the increased availability of next-generation sequencing methods.

MATERIALS AND METHODS

Herein, we describe the clinical features of nine patients from seven unrelated families with SACS variants from the cohort of the Neuromuscular Disorders Unit of the Neurology Department of the Istanbul University, Istanbul Faculty of Medicine.

RESULTS

Seven patients were male. Seven patients in our cohort had disease onset in the first decade of life. Eight patients were born to consanguineous marriages. Distal weakness in the lower limbs was a prominent feature in all of our patients. Seven patients had ataxia, and six patients had spasticity. Interestingly, one patient showed an isolated Charcot-Marie-Tooth-like phenotype. Five patients showed sensorimotor demyelinating polyneuropathy in the nerve conduction studies. Linear pontine hypointensity was the most frequent cranial magnetic resonance imaging (MRI) abnormality. Two patients with a later disease onset had a homozygous c.11542_11544delATT (p.Ile3848del) variant. The rest of the identified variants were scattered throughout the SACS gene.

CONCLUSIONS

Atypical clinical features in our patients highlight that the phenotypic spectrum of ARSACS can be observed in a wide range.

Genetics of Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) and Role of Sacsin in Neurodegeneration

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative disease that was originally discovered in the population from the Charlevoix-Saguenay-Lac-Saint-Jean (CSLSJ) region in Quebec. Although the disease progression of ARSACS may start in early childhood, cases with later onset have also been observed. Spasticity and ataxia could be common phenotypes, and retinal optic nerve hypermyelination is detected in the majority of patients. Other symptoms, such as pes cavus, ataxia and limb deformities, are also frequently observed in affected individuals. More than 200 mutations have been discovered in the SACS gene around the world. Besides French Canadians, SACS genetics have been extensively studied in Tunisia or Japan. Recently, emerging studies discovered SACS mutations in several other countries. SACS mutations could be associated with pathogenicity either in the homozygous or compound heterozygous stages. Sacsin has been confirmed to be involved in chaperon activities, controlling the microtubule balance or cell migration. Additionally, sacsin may also play a crucial role in regulating the mitochondrial functions. Through these mechanisms, it may share common mechanisms with other neurodegenerative diseases. Further studies are needed to define the exact functions of sacsin. This review introduces the genetic mutations discovered in the SACS gene and discusses its pathomechanisms and its possible involvement in other neurodegenerative diseases.

Genetic spectrum and clinical features in a cohort of Chinese patients with autosomal recessive cerebellar ataxias

Background

Although many causative genes have been uncovered in recent years, genetic diagnosis is still missing for approximately 50% of autosomal recessive cerebellar ataxia (ARCA) patients. Few studies have been performed to determine the genetic spectrum and clinical profile of ARCA patients in the Chinese population.

Methods

Fifty-four Chinese index patients with unexplained autosomal recessive or sporadic ataxia were investigated by whole-exome sequencing (WES) and copy number variation (CNV) calling with ExomeDepth. Likely causal CNV predictions were validated by CNVseq.

Results

Thirty-eight mutations including 29 novel ones were identified in 25 out of the 54 patients, providing a 46.3% positive molecular diagnostic rate. Ten different genes were involved, of which four most common genes were SACS, SYNE1, ADCK3 and SETX, which accounted for 76.0% (19/25) of the positive cases. The de novo microdeletion in SACS was reported for the first time in China and the uniparental disomy of ADCK3 was reported for the first time worldwide. Clinical features of the patients carrying SACS, SYNE1 and ADCK3 mutations were summarized.

Conclusions

Our results expand the genetic spectrum and clinical profiles of ARCA patients, demonstrate the high efficiency and reliability of WES combined with CNV analysis in the diagnosis of suspected ARCA, and emphasize the importance of complete bioinformatics analysis of WES data for accurate diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00264-z.

The Intersection Between Cerebellar Ataxia and Neuropathy: a Proposed Classification and a Diagnostic Approach

Neuropathy is a common associated feature of different types of genetic or sporadic cerebellar ataxias. The pattern of peripheral nerve involvement and its associated clinical features can be an invaluable aspect for narrowing the etiologic diagnosis in the investigation of cerebellar ataxias. In this review, we discuss the differential diagnosis of the intersection between peripheral nerve and cerebellar involvement, and classify them in accordance with the predominant features. Genetics, clinical features, neuroimaging, and neurophysiologic characteristics are discussed. Furthermore, a diagnostic approach for cerebellar ataxia with neuropathy is proposed according to the different clinical characteristics. This is an Educational and Descriptive review with the aim of medical education for the approach to the patients with cerebellar ataxia and neuropathy. The diagnostic approach to the patient with cerebellar ataxia with neuropathy requires a detailed medical history, phenotyping, characterization of disease progression and family history. Neuroimaging features and the neurophysiological findings play pivotal roles in defining the diagnosis. Establishing an organized classification method for the disorders based on the clinical features may be very helpful, and could be divided as those with predominant cerebellar features, predominant neuropathic feature, or conditions with both cerebellar ataxia and neuropathy. Second, determining the mode of inheritance is critical on cerebellar ataxias: autosomal dominant and recessive cerebellar ataxias, mitochondrial or sporadic types. Third, one must carefully assess neurophysiologic findings in order to better characterize the predominant pattern of involvement: damage location, mechanism of lesion (axonal or demyelinating), motor, sensory or sensory motor compromise, large or small fibers, and autonomic system abnormalities.

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 rare hereditary disease characterized by cerebellar ataxia, pyramidal signs in lower limbs, and sensorimotor neuropathy. The disease is caused by bi-allelic mutations of the SACS gene encoding the sacsin protein. Over 200 mutations have been reported worldwide. Here, we report two unrelated Chinese ARSACS patients with novel mutations revealed by whole-exome sequencing (WES). One 36-year-old female patient exhibited classical ARSACS characteristics including cerebellar ataxia, pyramidal tract signs in the lower limbs and sensorimotor neuropathy, while the other 9-year-old male showed cerebellar ataxia and peripheral neuropathy. WES identified a compound heterozygous variant in the SACS gene (c.5692 G > T, p.E1898X; c.12673-12677 del TATCA, p.Y4225D fs*6) in the female patient and another compound heterozygous variant (c.1773C > A, p.S578X; c.8088-8089 in. CA, p.M2697Q fs*43) in the male patient. All of these novel mutations were predicted to be loss-of-function which affect the expression of the two important C-terminal domains (DnaJ and HEPN). These findings add new insights into the mutational and clinical spectrum of ARSACS.

A Proposed Diagnostic Algorithm for Inborn Errors of Metabolism Presenting With Movements Disorders

Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.

Charcot-Marie-Tooth disease and related disorders: an evolving landscape

PURPOSE OF REVIEW

Charcot-Marie-Tooth (CMT) disease and related disorders are the commonest group of inherited neuromuscular diseases and represent a heterogeneous group of disorders. This review will cover recent advances in genetic diagnosis and the evolving genetic and phenotype landscape of this disease group. We will review recent evidence of the increasingly recognized phenotypic overlap with other neurodegenerative conditions including hereditary spastic paraplegia, hereditary ataxias and mitochondrial diseases and highlight the importance of deep phenotyping to inform genetic diagnosis and prognosis.

RECENT FINDINGS

Through whole exome sequencing and multicentre collaboration new genes are being identified as causal for CMT expanding the genetic heterogeneity of this condition. In addition, an increasing number of variants have been identified in genes known to cause complex inherited diseases in which the peripheral neuropathy is part of the disorder and may be the presenting feature. The recent discovery of a repeat expansion in the RFC1 gene in cerebellar ataxia, neuropathy, vestibular areflexia syndrome highlights the prevalence of late-onset recessive conditions which have historically been considered to cause early-onset disease.

SUMMARY

CMT is an evolving field with considerable phenotypic and genetic heterogeneity and deep phenotyping remains a cornerstone in contemporary CMT diagnostics.

[Spastic ataxia of Charlevoix-Saguenay: the first Russian case report and literature review]

Spastic ataxia of Charlevoix-Saguenay (ARSACS) is a rare autosomal recessive neurodegenerative disease related to SACS gene and characterized by cerebellar, pyramidal and some other signs. The disease was delineated in Quebec, where it cumulates due to founder effect and has similar phenotype with very early onset. ARSACS in other populations is more variable. The first Russian case of ARSACS in a 37-year-old woman, an only patient in a Lak (one of Dagestan ethnicities) family, is presented. Along with main typical features, she had atypical late disease onset (in 32 years) and moderate cognitive decline. MPS-panel 'hereditary paraplegias' detected an earlier reported homo- or hemizygous mutation c.72276C>T (p.Arg2426Stop) in SACS exon 10.

Childhood-onset autosomal recessive ataxias: a cross-sectional study from Turkey

Autosomal recessive ataxias (ARAs) are a heterogeneous group of inherited neurodegenerative disorders that affect the cerebellum, the spinocerebellar tract, and/or the sensory tracts of the spinal cord. This study is aimed at establishing molecular classification and phenotypic correlation of childhood-onset ARAs in Southeast Anatolia of Turkey. Sixty-five children (aged 0 to 18) from 40 unrelated families who were analyzed through hereditary ataxia NGS panel between the years of 2015-2018 were selected for the study. Seventeen different, clinically significant ARA-related pathogenic variants were detected in 33 of 40 families (82.5%), 12 of which were noted to be unreported variants. Among these 33 families, 24 had ATM-related (72.72%), four had SACS-related (12.12%), three had COQ8A-related (9.09%), and two had APTX-related (6.06%) pathogenic variants. The c.3576G>A (p.K1192=) was the most common homozygous pathogenic ATM variant (33.33%) that was associated with milder phenotype of ataxia telangiectasia (AT) with the onset of age of 3. Patients with SACS variants demonstrated developmental delay and progressive ataxia before the age of 3. Slowly progressive ataxia and intellectual disability were the common clinical manifestations of the patients with homozygous c.1396delG (p. E466Rfs*11) pathogenic variant in COQ8A. Homozygous APTX c.689T>G (p.V230G) pathogenic variant was identified in two patients who had chief complaint of ataxic gait onset after puberty. The most common types of ARAs in this region are AT- and Charlevoix-Saguenay-type spastic ataxia. ATM gene analysis should be performed foremost on children presenting early-onset ataxia from Southeastern Anatolia. If there is a concomitant peripheral neuron involvement, SACS gene analysis should be preferred. This valuable data will be a guide for the first step molecular diagnostic approach before requesting the NGS panel for ARA.

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.