Machado-Joseph disease presenting as motor neuron disease

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.

Rescue of ATXN3 neuronal toxicity in Caenorhabditiselegans by chemical modification of endoplasmic reticulum stress

Polyglutamine expansion diseases are a group of hereditary neurodegenerative disorders that develop when a CAG repeat in the causative genes is unstably expanded above a certain threshold. The expansion of trinucleotide CAG repeats causes hereditary adult-onset neurodegenerative disorders, such as Huntington's disease, dentatorubral–pallidoluysian atrophy, spinobulbar muscular atrophy and multiple forms of spinocerebellar ataxia (SCA). The most common dominantly inherited SCA is the type 3 (SCA3), also known as Machado–Joseph disease (MJD), which is an autosomal dominant, progressive neurological disorder. The gene causatively associated with MJD is ATXN3. Recent studies have shown that this gene modulates endoplasmic reticulum (ER) stress. We generated transgenic Caenorhabditiselegans strains expressing human ATXN3 genes in motoneurons, and animals expressing mutant ATXN3-CAG89 alleles showed decreased lifespan, impaired movement, and rates of neurodegeneration greater than wild-type ATXN3-CAG10 controls. We tested three neuroprotective compounds (Methylene Blue, guanabenz and salubrinal) believed to modulate ER stress and observed that these molecules rescued ATXN3-CAG89 phenotypes. Furthermore, these compounds required specific branches of the ER unfolded protein response (UPR^ER), reduced global ER and oxidative stress, and polyglutamine aggregation. We introduce new C. elegans models for MJD based on the expression of full-length ATXN3 in a limited number of neurons. Using these models, we discovered that chemical modulation of the UPR^ER reduced neurodegeneration and warrants investigation in mammalian models of MJD.

Summary: We introduce a novel C. elegans model for Machado–Joseph disease for use in preclinical drug discovery and identified guanabenz as a potent neuroprotective molecule.

Pattern of Peripheral Nerve Involvement in Spinocerebellar Ataxia Type 2: a Neurophysiological Assessment

Peripheral neuropathy is frequent in spinocerebellar ataxia type 2 (SCA2), but the pattern and characteristics of nerve involvement are still an unsettled issue. This study aimed to evaluate the prevalence, extent, and distribution of nerve involvement in SCA2 patients through neurophysiological studies. Thirty-one SCA2 patients and 20 control subjects were enrolled in this study. All subjects were prospectively evaluated through electromyography, including nerve conduction, needle electromyography in proximal and distal muscles of the upper and lower limbs, and sural radial amplitude ratio (SRAR). We aimed to differentiate distal axonopathy from diffuse nerve commitment, characterizing neuronopathy. Nerve involvement was observed in 83.6 % (26 individuals) of SCA2 patients. Among these, 19 had diffuse sensory abnormalities on nerve conduction predominantly on the upper limbs, with diffuse chronic denervation on needle electromyography and elevated SRAR values. Four individuals had only diffuse sensory involvement, and 2 had only motor involvement on needle evaluation and normal nerve conduction. These were interpreted as neuronopathy due to the diffuse distribution of the involvement. One individual had distal sensory axonopathy, with lower limb predominance. In this study, we found neuronopathy as the main pattern of nerve involvement in SCA2 patients and that motor involvement is a frequent feature. This information brings new insights into the understanding of the pathophysiology of nerve involvement in SCA2 and sets some key points about the phenotype, which is relevant to guide the genetic/molecular diagnosis.

Motor cortical dysfunction develops in spinocerebellar ataxia type 3

OBJECTIVE

Spinocerebellar ataxia type 3 (SCA3) is an inherited neurodegenerative disorder characterized by cerebellar ataxia and variable expression of clinical features beyond the cerebellum. To gain further insights into disease pathophysiology, the present study explored motor cortex function in SCA3 to determine whether cortical dysfunction was present and if this contributed to the development of clinical manifestations.

METHODS

Clinical phenotyping and longitudinal assessments were combined with central (threshold-tracking transcranial magnetic stimulation) and peripheral (nerve excitability) techniques in 11 genetically characterized SCA3 patients.

RESULTS

Short-interval intracortical inhibition was significantly reduced in presymptomatic and symptomatic SCA3 patients (-1.3±1.4%) compared to healthy controls (10.3±0.7%, P<0.0005), with changes evident prior to clinical onset of ataxia and related to worsening severity (R=-0.78, P<0.005). Central motor conduction time was also significantly prolonged in presymptomatic and symptomatic SCA3 patients (7.5±0.4ms) compared to healthy controls (5.3±0.2ms, P<0.0005) and related to clinical severity (R=0.81, P<0.005). Markers of peripheral motor neurodegeneration and excitability did not correlate with cortical hyperexcitability or ataxia.

CONCLUSIONS

Simultaneous investigation of clinical status, and central and peripheral nerve function has identified progressive cortical dysfunction in SCA3 patients related to the development of ataxia.

SIGNIFICANCE

These findings suggest alteration in cortical activity is associated with SCA3 pathogenesis and neurodegeneration.

Spinocerebellar ataxia: relationship between phenotype and genotype - a review

Spinocerebellar ataxia (SCA) comprises a large group of heterogeneous neurodegenerative disorders inherited in an autosomal dominant fashion. It is characterized by progressive cerebellar ataxia with oculomotor dysfunction, dysarthria, pyramidal signs, extrapyramidal signs, pigmentary retinopathy, peripheral neuropathy, cognitive impairment and other symptoms. It is classified according to the clinical manifestations or genetic nosology. To date, 40 SCAs have been characterized, and include SCA1-40. The pathogenic genes of 28 SCAs were identified. In recent years, with the widespread clinical use of next-generation sequencing, the genes underlying SCAs, and the mutants as well as the affected phenotypes were identified. These advances elucidated the phenotype-genotype relationship in SCAs. We reviewed the recent clinical advances, genetic features and phenotype-genotype correlations involving each SCA and its differentiation. The heterogeneity of the disease and the genetic diagnosis might be attributed to the regional distribution and clinical characteristics. Therefore, recognition of the phenotype-genotype relationship facilitates genetic testing, prognosis and monitoring of symptoms.

Spinocerebellar ataxia type 3: subphenotypes in a cohort of Brazilian patients

Spinocerebellar ataxia type 3 (SCA3) involves cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems with strong phenotypic heterogeneity, that lead us to classify the disorder into different clinical subtypes according to the predominantly affected motor systems.

METHOD

The series comprises 167 SCA3 patients belonging to 68 pedigrees, studied from 1989-2013. These patients were categorized into seven different subphenotypes.

RESULTS

SCA3 cases were clustered according to the predominant clinical features. Three most common forms were subphenotype 2, characterized by ataxia and pyramidal symptom was observed in 67.5%, subphenotype 3 with ataxia and peripheral signs in 13.3%, and subphenotype 6 with pure cerebellar syndrome in 7.2%.

CONCLUSION

Our study was the first to systematically classify SCA3 into seven subphenotypes. This classification may be particularly useful for determination of a more specific and direct phenotype/genotype correlation in future studies.

Pattern of peripheral nerve involvement in Machado-Joseph disease: neuronopathy or distal axonopathy? A clinical and neurophysiological evaluation

OBJECTIVE

Neuropathy is a well-recognized feature in spinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD), but the pattern of neuropathy is still a matter of debate. This study aimed to evaluate peripheral nerve involvement in MJD patients. Neurophysiological and clinical data were analyzed to distinguish neuronopathy from length-dependent distal axonopathy.

METHODS

In the present study we evaluated 26 patients with clinical and molecular-proven MJD and investigated their peripheral nerve involvement. Neurophysiological and clinical data were compared and correlated aiming to distinguish neuronopathy from distal axonopathy.

RESULTS

The neurophysiological evaluation showed that 42.3% of the patients had polyneuropathy. Among these patients, 81.8% presented neuronopathy.

CONCLUSION

We concluded that neuronopathy is the most common form of peripheral nerve involvement in MJD patients.

The modulation of Amyotrophic Lateral Sclerosis risk by ataxin-2 intermediate polyglutamine expansions is a specific effect

Full expansions of the polyglutamine domain (polyQ≥34) within the polysome-associated protein ataxin-2 (ATXN2) are the cause of a multi-system neurodegenerative disorder, which usually presents as a Spino-Cerebellar Ataxia and is therefore known as SCA2, but may rarely manifest as Levodopa-responsive Parkinson syndrome or as motor neuron disease. Intermediate expansions (27≤polyQ≤33) were reported to modify the risk of Amyotrophic Lateral Sclerosis (ALS). We have now tested the reproducibility and the specificity of this observation. In 559 independent ALS patients from Central Europe, the association of ATXN2 expansions (30≤polyQ≤35) with ALS was highly significant. The study of 1490 patients with Parkinson's disease (PD) showed an enrichment of ATXN2 alleles 27/28 in a subgroup with familial cases, but the overall risk of sporadic PD was unchanged. No association was found between polyQ expansions in Ataxin-3 (ATXN3) and ALS risk. These data indicate a specific interaction between ATXN2 expansions and the causes of ALS, possibly through altered RNA-processing as a common pathogenic factor.

Neocortical atrophy in Machado-Joseph disease: a longitudinal neuroimaging study

BACKGROUND/PURPOSE

Previous imaging studies in the Machado-Joseph disease (MJD/SCA3) have mostly concentrated on the cerebellum and brainstem. Our goal was to perform a whole brain longitudinal evaluation.

METHODS

We included 45 patients and 51 controls, who underwent two brain magnetic resonance imaging and magnetic resonance spectroscopy (mean interval of 12.5 ± 1.5 months). We used voxel-based morphometry (VBM) and the MarsBar analysis toolbox to extract grey matter density (GMD) values from regions of interest. We used a linear regression model and a general linear model to correlate GMD with clinical markers, and paired t-test for the longitudinal evaluation.

RESULTS

We observed decreased GMD (P < .01) at frontal, parietal, temporal and occipital lobes, subcortical grey matter, cerebellum, and brainstem. White matter atrophy was restricted to the cerebellum. Age, CAG, and disease duration predicted GMD in different areas, but age and CAG were the most important predictors. The longitudinal analysis failed to demonstrate changes. Changes in regions other than the cerebellum appeared to contribute significantly to the final International Cooperative Ataxia Rating Scale score.

CONCLUSION

We confirmed cortical involvement in MJD/SCA3. The most important factors in predicting GMD were age and CAG. The lack of progression of atrophy may indicate floor effect and/or short duration of follow-up.

Rare association of motor neuron disease and spinocerebellar ataxia type 2 (SCA2): a new case and review of the literature

We report a rare association of spinocerebellar ataxia and motor neuron disease (MND) in a woman with genetically confirmed SCA2 who subsequently developed a rapidly progressive and fatal form of MND. Considering the rarity of these two neurological conditions, it is interesting to note that the concomitant occurrence of SCA mutations and MND have been previously observed in three cases: in one patient affected by SCA6 and two other cases with SCA2.