Clinical features and molecular mechanisms of spinal and bulbar muscular atrophy (SBMA)

One case of spinal bulbar muscular atrophy misdiagnosed as polymyositis: Case report

RATIONALE

Spinal bulbar muscular atrophy (SBMA) is a rare X-linked recessive motor neuron degenerative disease. Due to the lack of specificity in its early clinical manifestations, SBMA is easily misdiagnosed. Herein, we present a case in which SBMA was misdiagnosed as polymyositis.

PATIENT CONCERNS

A 58-year-old patient began to develop symptoms of limb weakness 20 years ago and was admitted to the Second Hospital of Hebei Medical University 10 years ago without special treatment. Two years ago, the above symptoms worsened and he was admitted to Peking Union Medical College Hospital. The patient was misdiagnosed as polymyositis. According to the gene mutation characteristics of SBMA, the patient was diagnosed with SBMA.

DIAGNOSES

The result of the Kennedy gene test was positive, and the patient was diagnosed with Kennedy disease.

INTERVENTIONS

After the diagnosis of SBMA, the patient was given symptomatic treatment to alleviate the condition.

OUTCOMES

Conservative treatment after discharge was requested. It is recommended that patients avoid bucking to prevent complications.

LESSONS

This is a case of milder SBMA being misdiagnosed as polymyositis. For patients with weak limbs, the possibility of SBMA should be considered.

Comprehensive analyses of brain cell communications based on multiple scRNA-seq and snRNA-seq datasets for revealing novel mechanism in neurodegenerative diseases

AIMS

Complex cellular communications between glial cells and neurons are critical for brain normal function and disorders, and single-cell level RNA-sequencing datasets display more advantages for analyzing cell communications. Therefore, it is necessary to systematically explore brain cell communications when considering factors such as sex and brain region.

METHODS

We extracted a total of 1,039,459 cells derived from 28 brain single-cell RNA-sequencing (scRNA-seq) or single-nucleus RNA-sequencing (snRNA-seq) datasets from the GEO database, including 12 human and 16 mouse datasets. These datasets were further divided into 71 new sub-datasets when considering disease, sex, and region conditions. In the meanwhile, we integrated four methods to evaluate ligand-receptor interaction score among six major brain cell types (microglia, neuron, astrocyte, oligodendrocyte, OPC, and endothelial cell).

RESULTS

For Alzheimer's disease (AD), disease-specific ligand-receptor pairs when compared with normal sub-datasets, such as SEMA4A-NRP1, were identified. Furthermore, we explored the sex- and region-specific cell communications and identified that WNT5A-ROR1 among microglia cells displayed close communications in male, and SPP1-ITGAV displayed close communications in the meninges region from microglia to neurons. Furthermore, based on the AD-specific cell communications, we constructed a model for AD early prediction and confirmed the predictive performance using multiple independent datasets. Finally, we developed an online platform for researchers to explore brain condition-specific cell communications.

CONCLUSION

This research provided a comprehensive study to explore brain cell communications, which could reveal novel biological mechanisms involved in normal brain function and neurodegenerative diseases such as AD.

Myoglobin: a new biomarker for spinal and bulbar muscular atrophy?

OBJECTIVES

There is a primary muscular affection in spinal and bulbar muscular atrophy (SBMA). Myoglobin (Myo) is mainly distributed in the myocardium and skeletal muscle. The purpose of the study was to explore the significance of serum Myo detection in the diagnosis and clinical evaluation of SBMA.

MATERIALS AND METHODS

In this study, serum creatine kinase (CK), Myo, and Troponin T (cTNT) levels were assessed in 80 patients with SBMA and were compared with those of 60 patients with amyotrophic lateral sclerosis (ALS). All measurement data were analyzed using the t-test and enumeration data using the χ2-test.

RESULTS

The rate of abnormal Myo levels in the SBMA group was 100%, however, none of the patients with ALS had an abnormal Myo level. There was no overlap between the two groups. The Myo levels in patients with SBMA were correlated with the course of the disease. Further, their CK level was significantly elevated compared with that in patients with ALS, however, there was an overlap between the two groups. The serum cTNT level in patients with SBMA was not significantly different from that in patients with ALS.

CONCLUSION

Myo, as a simple, inexpensive, and readily available biochemical indicator, is likely to be used for the differentiation between SBMA and ALS, and used as a new biomarker for the clinical evaluation of SBMA.

The Role of Sex and Sex Hormones in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a wide class of disorders of the central nervous system (CNS) with unknown etiology. Several factors were hypothesized to be involved in the pathogenesis of these diseases, including genetic and environmental factors. Many of these diseases show a sex prevalence and sex steroids were shown to have a role in the progression of specific forms of neurodegeneration. Estrogens were reported to be neuroprotective through their action on cognate nuclear and membrane receptors, while adverse effects of male hormones have been described on neuronal cells, although some data also suggest neuroprotective activities. The response of the CNS to sex steroids is a complex and integrated process that depends on (i) the type and amount of the cognate steroid receptor and (ii) the target cell type-either neurons, glia, or microglia. Moreover, the levels of sex steroids in the CNS fluctuate due to gonadal activities and to local metabolism and synthesis. Importantly, biochemical processes involved in the pathogenesis of NDs are increasingly being recognized as different between the two sexes and as influenced by sex steroids. The aim of this review is to present current state-of-the-art understanding on the potential role of sex steroids and their receptors on the onset and progression of major neurodegenerative disorders, namely, Alzheimer's disease, Parkinson's diseases, amyotrophic lateral sclerosis, and the peculiar motoneuron disease spinal and bulbar muscular atrophy, in which hormonal therapy is potentially useful as disease modifier.

Central nervous system abnormalities in spinal and bulbar muscular atrophy (Kennedy's disease)

Spinal and bulbar (bulbospinal) muscular atrophy (BSMA, SBMA, Kennedy's disease) is a progressive motor neuron disease with rare involvement of structures other than the lower motor neuron, such as the endocrine system and the central nervous system (CNS). Aim of the review was to study type and frequency of clinical, imaging, and functional (CNS) abnormalities in SBMA patients. The most frequent clinical CNS manifestations in SBMA are postural or kinetic tremor predominantly of the hands and mild cognitive impairment. The most frequent instrumental CNS abnormality in SBMA patients are white matter lesions, visible on voxel-based morphometry, magnetic resonance spectroscopy, or diffusion tensor imaging. Single patients with enlarged pituitary volume, or diminished somato-sensory representation in the cortex have been also reported. Seizures, epilepsy, ataxia, spasticity, dystonia, or migraine have not been found in SBMA patients. Only supportive treatment is available for CNS manifestations in SBMA. It is concluded that the most frequent CNS abnormalities in SBMA are tremor, cognitive impairment, and white matter lesions on new imaging modalities. CNS involvement in SBMA should not be neglected as a phenotypic manifestation of SBMA and, apart from cognitive involvement, may help to differentiate clinically SBMA from other types of motor neuron disease.

Allele-selective suppression of mutant genes in polyglutamine diseases

Polyglutamine (polyQ) diseases are heritable dominant neurological disorders, caused by abnormal CAG tri-nucleotide expansion in the coding sequence of affected genes. Extension of CAG repeats results in the production of aberrant gene products that are deleterious to neurons, such as transcripts with a CAG stem-loop secondary structure, and proteins containing a long stretch of polyQ residues. Thus, determining methods for the prevention or elimination of these mutant gene products from neuronal cells and translating this knowledge to clinical application are currently important goals in the fields of neurology and neurogenetics. Recently, several studies have revealed intriguing findings related to the allele-selective regulation of CAG-expanded genes, and have proposed novel designs to selectively diminish the mutant polyQ proteins. In this review, we focus on the genes, genetically engineered proteins, and oligonucleotides that show potential to modulate the expression of mutant genes. We also discuss their respective molecular functions at the levels of transcription, translation, and post-translation.

Brain MR diffusion tensor imaging in Kennedy's disease

INTRODUCTION

Kennedy's disease (KD) is a progressive degenerative disorder affecting lower motor neurons. We investigated the correlation between disease severity and whole brain white matter microstructure, including upper motor neuron tracts, by using diffusion-tensor imaging (DTI) in eight patients with KD in whom disease severity was evaluated using the Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS).

METHODS

From DTI acquisitions we obtained maps of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (L1) and radial diffusivities (L2, L3). We then employed tract-based spatial statistics (TBSS) to investigate within-patient correlations of DTI invariants with ALSFRS and disease duration (DD).

RESULTS

We found a significant correlation between low ALSFRS and 1) low FA values in association commissural and projection fibers, and 2) high L3 values in commissural tracts and fronto-parietal white matter. Additionally, we found a significant association between longer DD and 1) low FA in the genu and body of corpus callosum, association fibers and midbrain and 2) high L1 in projection and association tracts.

CONCLUSIONS

The associations between clinical variables and white matter microstructural changes in areas thought to be spared by the disease process support the hypothesis of a multisystem involvement in the complex pathogenic mechanisms responsible for the clinical disability of these patients.

Fast and accurate semi-automated segmentation method of spinal cord MR images at 3T applied to the construction of a cervical spinal cord template

Objective

To design a fast and accurate semi-automated segmentation method for spinal cord 3T MR images and to construct a template of the cervical spinal cord.

Materials and Methods

A semi-automated double threshold-based method (DTbM) was proposed enabling both cross-sectional and volumetric measures from 3D T₂-weighted turbo spin echo MR scans of the spinal cord at 3T. Eighty-two healthy subjects, 10 patients with amyotrophic lateral sclerosis, 10 with spinal muscular atrophy and 10 with spinal cord injuries were studied. DTbM was compared with active surface method (ASM), threshold-based method (TbM) and manual outlining (ground truth). Accuracy of segmentations was scored visually by a radiologist in cervical and thoracic cord regions. Accuracy was also quantified at the cervical and thoracic levels as well as at C2 vertebral level. To construct a cervical template from healthy subjects’ images (n=59), a standardization pipeline was designed leading to well-centered straight spinal cord images and accurate probability tissue map.

Results

Visual scoring showed better performance for DTbM than for ASM. Mean Dice similarity coefficient (DSC) was 95.71% for DTbM and 90.78% for ASM at the cervical level and 94.27% for DTbM and 89.93% for ASM at the thoracic level. Finally, at C2 vertebral level, mean DSC was 97.98% for DTbM compared with 98.02% for TbM and 96.76% for ASM. DTbM showed similar accuracy compared with TbM, but with the advantage of limited manual interaction.

Conclusion

A semi-automated segmentation method with limited manual intervention was introduced and validated on 3T images, enabling the construction of a cervical spinal cord template.

Influence of CAG Repeat Polymorphism on the Targets of Testosterone Action

In the last decade, ample evidence has demonstrated the growing importance of androgen receptor (AR) CAG repeat polymorphism in andrology. This genetic parameter is able to condition the peripheral effects of testosterone and therefore to influence male sexual function and fertility, cardiovascular risk, body composition, bone metabolism, the risk of prostate and testicular cancer, the psychiatric status, and the onset of neurodegenerative disorders. In this review, we extensively discuss the literature data and identify a role for AR CAG repeat polymorphism in conditioning the systemic testosterone effects. In particular, our main purpose was to provide an updated text able to shed light on the many and often contradictory findings reporting an influence of CAG repeat polymorphism on the targets of testosterone action.

Sleep disorders in spinal and bulbar muscular atrophy (Kennedy's disease): a controlled polysomnographic and self-reported questionnaires study

No data are available regarding the occurrence of sleep disorders in spinal and bulbar muscular atrophy (SBMA). We investigated the sleep-wake cycle in SBMA patients compared with healthy subjects. Nine SBMA outpatients and nine age-matched and sex-matched healthy controls were evaluated. Subjective quality of sleep was assessed by means of the Pittsburgh Sleep Quality Index (PSQI). The Epworth Sleepiness Scale was used in order to evaluate excessive daytime sleepiness. All participants underwent a 48-h polysomnography followed by the multiple sleep latency test. Time in bed, total sleep time and sleep efficiency were significantly lower in SBMA than controls. Furthermore, the apnea-hypopnea index (AHI) was significantly higher in SBMA than controls. Obstructive sleep apnea (OSA: AHI >5/h) was evident in 6/9 patients (66.6 %). REM sleep without atonia was evident in three patients also affected by OSA and higher AHI in REM; 2/9 (22.2 %) SBMA patients showed periodic limb movements in sleep. The global PSQI score was higher in SBMA versus controls. Sleep quality in SBMA is poorer than in controls. OSA is the most common sleep disorder in SBMA. The sleep impairment could be induced both by OSA or/and the neurodegenerative processes involving crucial areas regulating the sleep-wake cycle.

Clearance of the mutant androgen receptor in motoneuronal models of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is an X-linked motoneuron disease caused by an abnormal expansion of a tandem CAG repeat in exon 1 of the androgen receptor (AR) gene that results in an abnormally long polyglutamine tract (polyQ) in the AR protein. As a result, the mutant AR (ARpolyQ) misfolds, forming cytoplasmic and nuclear aggregates in the affected neurons. Neurotoxicity only appears to be associated with the formation of nuclear aggregates. Thus, improved ARpolyQ cytoplasmic clearance, which indirectly decreases ARpolyQ nuclear accumulation, has beneficial effects on affected motoneurons. In addition, increased ARpolyQ clearance contributes to maintenance of motoneuron proteostasis and viability, preventing the blockage of the proteasome and autophagy pathways that might play a role in the neuropathy in SBMA. The expression of heat shock protein B8 (HspB8), a member of the small heat shock protein family, is highly induced in surviving motoneurons of patients affected by motoneuron diseases, where it seems to participate in the stress response aimed at cell protection. We report here that HspB8 facilitates the autophagic removal of misfolded aggregating species of ARpolyQ. In addition, though HspB8 does not influence p62 and LC3 (two key autophagic molecules) expression, it does prevent p62 bodies formation, and restores the normal autophagic flux in these cells. Interestingly, trehalose, a well-known autophagy stimulator, induces HspB8 expression, suggesting that HspB8 might act as one of the molecular mediators of the proautophagic activity of trehalose. Collectively, these data support the hypothesis that treatments aimed at restoring a normal autophagic flux that result in the more efficient clearance of mutant ARpolyQ might produce beneficial effects in SBMA patients.

Mechanisms mediating spinal and bulbar muscular atrophy: investigations into polyglutamine-expanded androgen receptor function and dysfunction

Spinal and bulbar muscular atrophy (SBMA, Kennedy’s disease), a late-onset neuromuscular disorder, is caused by expansion of the polymorphic polyglutamine tract in the androgen receptor (AR). The AR is a ligand-activated transcription factor, but plays roles in other cellular pathways. In SBMA, selective motor neuron degeneration occurs in the brainstem and spinal cord, thus the causes of neuronal dysfunction have been studied. However, pathogenic pathways in muscles may also be involved. Cultured cells, fly and mouse models are used to study the molecular mechanisms leading to SBMA. Both the structure of the polyglutamine-expanded AR (polyQ AR) and its interactions with other proteins are altered relative to the normal AR. The ligand-dependent translocation of the polyQ AR to the nucleus appears to be critical, as are interdomain interactions. The polyQ AR, or fragments thereof, can form nuclear inclusions, but their pathogenic or protective nature is unclear. Other data suggests soluble polyQ AR oligomers can be harmful. Post-translational modifications such as phosphorylation, acetylation, and ubiquitination influence AR function and modulate the deleterious effects of the polyQ AR. Transcriptional dysregulation is highly likely to be a factor in SBMA; deregulation of non-genomic AR signaling may also be involved. Studies on polyQ AR-protein degradation suggest inhibition of the ubiquitin proteasome system and changes to autophagic pathways may be relevant. Mitochondrial function and axonal transport may also be affected by the polyQ AR. Androgens, acting through the AR, can be neurotrophic and are important in muscle development; hence both loss of normal AR functions and gain of novel harmful functions by the polyQ AR can contribute to neurodegeneration and muscular atrophy. Thus investigations into polyQ AR function have shown that multiple complex mechanisms lead to the initiation and progression of SBMA.

New routes to therapy for spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a genetically inherited neuromuscular disorder characterized by loss of lower motor neurons in the brainstem and spinal cord and skeletal muscle fasciculation, weakness, and atrophy. SBMA is caused by expansion of a polyglutamine (polyQ) tract in the gene coding for the androgen receptor (AR). PolyQ expansions cause at least eight other neurological disorders, which are collectively known as polyQ diseases. SBMA is unique in the family of polyQ diseases in that the disease manifests fully in male individuals only. The sex specificity of SBMA is the result of the interaction between mutant AR and its natural ligand, testosterone. Here, we will discuss emerging therapeutic perspectives for SBMA in light of recent findings regarding disease pathogenesis.

Small-molecule hormones: molecular mechanisms of action

Small-molecule hormones play crucial roles in the development and in the maintenance of an adult mammalian organism. On the molecular level, they regulate a plethora of biological pathways. Part of their actions depends on their transcription-regulating properties, exerted by highly specific nuclear receptors which are hormone-dependent transcription factors. Nuclear hormone receptors interact with coactivators, corepressors, basal transcription factors, and other transcription factors in order to modulate the activity of target genes in a manner that is dependent on tissue, age and developmental and pathophysiological states. The biological effect of this mechanism becomes apparent not earlier than 30-60 minutes after hormonal stimulus. In addition, small-molecule hormones modify the function of the cell by a number of nongenomic mechanisms, involving interaction with proteins localized in the plasma membrane, in the cytoplasm, as well as with proteins localized in other cellular membranes and in nonnuclear cellular compartments. The identity of such proteins is still under investigation; however, it seems that extranuclear fractions of nuclear hormone receptors commonly serve this function. A direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated. In these mechanisms, the reaction to hormonal stimulus appears within seconds or minutes.

CUG-BP, Elav-like family (CELF)-mediated alternative splicing regulation in the brain during health and disease

Alternative splicing is an important mechanism for generating transcript and protein diversity. In the brain, alternative splicing is particularly prevalent, and alternative splicing factors are highly enriched. These include the six members of the CUG-BP, Elav-like family (CELF). This review summarizes what is known about the expression of different CELF proteins in the nervous system and the evidence that they are important in neural development and function. The involvement of CELF proteins in the pathogenesis of a number of neurodegenerative disorders, including myotonic dystrophy, spinocerebellar ataxia, fragile X syndrome, spinal muscular atrophy, and spinal and bulbar muscular atrophy is discussed. Finally, the known targets of CELF-mediated alternative splicing regulation in the nervous system and the functional consequences of these splicing events are reviewed. This article is part of a Special Issue entitled "RNA and splicing regulation in neurodegeneration."

Androgen receptor polyglutamine repeat number: models of selection and disease susceptibility

Variation in polyglutamine repeat number in the androgen receptor (AR CAGn) is negatively correlated with the transcription of androgen-responsive genes and is associated with susceptibility to an extensive list of human disease. Only a small portion of the heritability for many of these diseases is explained by conventional SNP-based genome-wide association studies, and the forces shaping AR CAGn among humans remains largely unexplored. Here, we propose evolutionary models for understanding selection at the AR CAG locus, namely balancing selection, sexual conflict, accumulation-selection, and antagonistic pleiotropy. We evaluate these models by examining AR CAGn-linked susceptibility to eight extensively studied diseases representing the diverse physiological roles of androgens, and consider the costs of these diseases by their frequency and fitness effects. Five diseases could contribute to the distribution of AR CAGn observed among contemporary human populations. With support for disease susceptibilities associated with long and short AR CAGn, balancing selection provides a useful model for studying selection at this locus. Gender-specific differences AR CAGn health effects also support this locus as a candidate for sexual conflict over repeat number. Accompanied by the accumulation of AR CAGn in humans, these models help explain the distribution of repeat number in contemporary human populations.

[Motor neuron diseases]

Motor neuron diseases (MND) are a group of neurodegenerative disorders which are present in clinical, prognostic and genetic diversity. The most common MND are amyotrophic lateral sclerosis (ALS), proximal spinal muscular atrophy (SMA) and various forms of hereditary and sporadic lower motor neuron syndromes including hereditary motor neuropathies (HMN). Familial and "sporadic" forms of ALS and lower motor neuron syndromes are known. The essential pathogenic findings in MND have emerged from molecular biological examinations of the hereditary forms of MND. In ALS, one consistent neuropathological feature is intraneuronal protein inclusions which arise from TDP-43, FUS, SOD1 or ataxin-2 aggregations. TDP-43, FUS, SOD1 and ataxin-2 are multifunctional DNA/RNA-binding proteins which are involved in transcription regulation. SMA and HMN are associated with different genes whose gene products may also be involved in RNA processing. A disturbance in the regulation of RNA possibly represents an overlapping pathophysiological characteristic in MND. The elucidation of common pathways in the cascade of motor neuron degeneration is an essential point of departure for molecular genetically defined treatment strategies both in ALS and in hereditary and sporadic lower motor neuron syndromes.

Neurotoxic properties of the anabolic androgenic steroids nandrolone and methandrostenolone in primary neuronal cultures

Anabolic-androgenic steroid (AAS) abuse is associated with multiple neurobehavioral disturbances. The sites of action and the neurobiological sequels of AAS abuse are unclear at present. We investigated whether two different AASs, nandrolone and methandrostenolone, could affect neuronal survival in culture. The endogenous androgenic steroid testosterone was used for comparison. Both testosterone and nandrolone were neurotoxic at micromolar concentrations, and their effects were prevented by blockade of androgen receptors (ARs) with flutamide. Neuronal toxicity developed only over a 48-hr exposure to the steroids. The cell-impermeable analogues testosterone-BSA and nandrolone-BSA, which preferentially target membrane-associated ARs, were also neurotoxic in a time-dependent and flutamide-sensitive manner. Testosterone-BSA and nandrolone-BSA were more potent than their parent compounds, suggesting that membrane-associated ARs were the relevant sites for the neurotoxic actions of the steroids. Unlike testosterone and nandrolone, toxicity by methandrostenolone and methandrostenolone-BSA was insensitive to flutamide, but it was prevented by the glucocorticoid receptor (GR) antagonist RU-486. Methandrostenolone-BSA was more potent than the parent compound, suggesting that its toxicity relied on the preferential activation of putative membrane-associated GRs. Consistently with the evidence that membrane-associated GRs can mediate rapid effects, a brief challenge with methandrostenolone-BSA was able to promote neuronal toxicity. Activation of putative membrane steroid receptors by nontoxic (nanomolar) concentrations of either nandrolone-BSA or methandrostenolone-BSA became sufficient to increase neuronal susceptibility to the apoptotic stimulus provided by β-amyloid (the main culprit of AD). We speculate that AAS abuse might facilitate the onset or progression of neurodegenerative diseases not usually linked to drug abuse.

Tremor in X-linked recessive spinal and bulbar muscular atrophy (Kennedy's disease)

OBJECTIVE

To study tremor in patients with X-linked recessive spinobulbar muscular atrophy or Kennedy's disease.

METHODS

Ten patients (from 7 families) with a genetic diagnosis of Kennedy's disease were screened for the presence of tremor using a standardized clinical protocol and followed up at a neurology outpatient clinic. All index patients were genotyped and showed an expanded allele in the androgen receptor gene.

RESULTS

Mean patient age was 37.6 years and mean number of CAG repeats 47 (44-53). Tremor was present in 8 (80%) patients and was predominantly postural hand tremor. Alcohol responsiveness was detected in 7 (88%) patients with tremor, who all responded well to treatment with a β-blocker (propranolol).

CONCLUSION

Tremor is a common feature in patients with Kennedy's disease and has characteristics similar to those of essential tremor.