Analysis of inconsistencies in terminology of spinal and bulbar muscular atrophy and its effect on retrieval of research

Motor neuron diseases (MNDs) are neurodegenerative disorders characterized by upper and/or lower MN loss. MNDs include amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and spinal and bulbar muscular atrophy (SBMA). Despite variability in onset, progression, and genetics, they share a common skeletal muscle involvement, suggesting that it could be a primary site for MND pathogenesis. Due to the key role of muscle-specific microRNAs (myomiRs) in skeletal muscle development, by real-time PCR we investigated the expression of miR-206, miR-133a, miR-133b, and miR-1, and their target genes, in G93A-SOD1 ALS, Δ7SMA, and KI-SBMA mouse muscle during disease progression. Further, we analyzed their expression in serum of SOD1-mutated ALS, SMA, and SBMA patients, to demonstrate myomiR role as noninvasive biomarkers. Our data showed a dysregulation of myomiRs and their targets, in ALS, SMA, and SBMA mice, revealing a common pathogenic feature associated with muscle impairment. A similar myomiR signature was observed in patients’ sera. In particular, an up-regulation of miR-206 was identified in both mouse muscle and serum of human patients. Our overall findings highlight the role of myomiRs as promising biomarkers in ALS, SMA, and SBMA. Further investigations are needed to explore the potential of myomiRs as therapeutic targets for MND treatment.

Polyglutamine expansion within the androgen receptor (AR) causes spinal and bulbar muscular atrophy (SBMA) and is associated with misfolded and aggregated species of the mutant AR. We showed previously that nuclear localization of the mutant AR was necessary but not sufficient for SBMA. Here we show that an interdomain interaction of the AR that is central to its function within the nucleus is required for AR aggregation and toxicity. Ligands that prevent the interaction between the amino-terminal FXXLF motif and carboxyl-terminal AF-2 domain (N/C interaction) prevented toxicity and AR aggregation in an SBMA cell model and rescued primary SBMA motor neurons from 5α-dihydrotestosterone-induced toxicity. Moreover, genetic mutation of the FXXLF motif prevented AR aggregation and 5α-dihydrotestosterone toxicity. Finally, selective androgen receptor modulators, which prevent the N/C interaction, ameliorated AR aggregation and toxicity while maintaining AR function, highlighting a novel therapeutic strategy to prevent the SBMA phenotype while retaining AR transcriptional function.

The neurodegenerative disorder spinal and bulbar muscular atrophy or Kennedy disease is caused by a CAG trinucleotide repeat expansion within the androgen receptor (AR) gene. The resulting expanded polyglutamine tract in the N-terminal region of the receptor renders AR prone to ligand-dependent misfolding and formation of oligomers and aggregates that are linked to neuronal toxicity. How AR misfolding is influenced by post-translational modifications, however, is poorly understood. AR is a target of SUMOylation, and this modification inhibits AR activity in a promoter context-dependent manner. SUMOylation is up-regulated in response to multiple forms of cellular stress and may therefore play an important cytoprotective role. Consistent with this view, we find that gratuitous enhancement of overall SUMOylation significantly reduced the formation of polyglutamine-expanded AR aggregates without affecting the levels of the receptor. Remarkably, this effect requires SUMOylation of AR itself because it depends on intact AR SUMOylation sites. Functional analyses, however, indicate that the protective effects of enhanced AR SUMOylation are not due to alterations in AR transcriptional activity because a branched protein structure in the appropriate context of the N-terminal region of AR is necessary to antagonize aggregation but not for inhibiting AR transactivation. Remarkably, small ubiquitin-like modifier (SUMO) attenuates AR aggregation through a unique mechanism that does not depend on critical features essential for its interaction with canonical SUMO binding motifs. Our findings therefore reveal a novel function of SUMOylation and suggest that approaches that enhance AR SUMOylation may be of clinical use in polyglutamine expansion diseases.

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.

ObjectiveThe ‘split hand’ sign refers to preferential wasting of the thenar and first dorsal interosseous muscles with relatively sparing of the hypothenar muscles in amyotrophic lateral sclerosis (ALS) and both...

Spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis 4 (ALS4) are two forms of motor neuron disease characterized by clinically slow disease progression. Based on the current limited human studies, the contribution of central nervous neurodegeneration to these diseases and the rate of clinical progression is unclear. Neuronal proteins glial fibrillary acidic protein (GFAP), neurofilament light (NfL) chain, or Total-tau measured in either cerebrospinal fluid or blood could serve as sensitive markers of neurodegeneration. We studied 56 adult participants (32 SBMA, 7 ALS4, and 17 controls) who were enrolled at the National Institutes of Health, of whom 22 (10 SBMA, 7 ALS4, and 5 controls) underwent paired CSF and serum sampling, and of whom 6 participants were assessed longitudinally up to 24 months from initial visit. An additional 7 controls completed CSF sampling only. CSF GFAP, NfL chain, and Total-tau correlated with corresponding levels in serum (r = 0.74, r = 0.47, and r = 0.70, respectively). CSF GFAP was increased in patients with SBMA (median, 8840 pg/mL, interquartile range (IQR) 5780-10489) as compared to controls (median, 5315 pg/mL, IQR 1822-6657; P = 0.029) but not compared with ALS4 (median, 5015 pg/mL, IQR 3172-9803; P = 0.31). Patients with SBMA had increased concentrations of CSF NfL chain (median, 719 pg/mL, IQR 483-773) as compared to ALS4 (median, 307 pg/mL, IQR 187-629; P = 0.034) or controls (median, 395 pg/mL, IQR 307-497; P = 0.024). In contrast, serum concentrations of either biomarker did not differ significantly between SBMA, ALS4, or controls. Higher CSF GFAP and NfL chain levels were associated with lower SBMA Functional Rating Scale scores (r = -0.49 and r = -0.42, respectively). Over the course of 24 months, the average change in SBMA Functional Rating Scale was -0.83 points, while the changes in CSF GFAP and NfL chain were progressive (increased 1.4-fold and 1.3-fold, respectively). Our data suggest that SBMA patients have increased concentrations of CSF GFAP and NfL chain as compared to ALS4 and controls, and higher levels of these biomarkers are associated with disease severity. Importantly, these results indicate that SBMA is associated with progressive neurodegeneration and that either CSF GFAP or NfL chain may be useful for patient stratification and monitoring treatment effects in clinical trials.

Ultrasonography (US) is a noninvasive and patient-friendly tool for the evaluation of peripheral nerves. In motor neuron diseases, amyotrophic lateral sclerosis (ALS) has been reported to show the atrophy of peripheral nerves on US. However, the US findings are still unclear in spinal and bulbar muscular atrophy (SBMA), an adult-onset lower motor neuron disease caused by an abnormal CAG repeat expansion in the androgen receptor gene. We prospectively recruited and evaluated 11 patients with genetically confirmed SBMA and 9 patients with ALS diagnosed according to the revised El Escorial ALS criteria or the Awaji electrodiagnostic criteria. The C5-C7 cervical nerve roots and the median and ulnar nerves were evaluated ultrasonographically. The cross-sectional areas (CSAs) of the C6 and C7 nerve roots, the median nerve in the upper arm and forearm, and the ulnar nerve in the upper arm were smaller in patients with SBMA than those in patients with ALS (p < 0.05), whereas the CSAs of the C5 nerve root and the ulnar nerve in the forearm were not smaller. US showed that the peripheral nerves in patients with SBMA were thinner than those in patients with ALS despite similar degrees of weakness and motor neuron loss. Possible causes include additional sensory nerve involvement and longer disease duration in patients with SBMA than those in patients with ALS.

Spinal and bulbar muscular atrophy (SBMA) is an adult-onset hereditary neurodegenerative disease caused by the expansions of CAG repeats in the androgen receptor (AR) gene. Androgen-dependent nuclear accumulation of pathogenic AR protein causes degeneration of lower motor neurons, leading to progressive muscle weakness and atrophy. While the successful induction of SBMA-like pathology has been achieved in mouse models, mechanisms underlying motor neuron vulnerability remain unclear. In the present study, we performed a transcriptome-based screening for genes expressed exclusively in motor neurons and dysregulated in the spinal cord of SBMA mice. We found upregulation of Mid1 encoding a microtubule-associated RNA binding protein which facilitates the translation of CAG-expanded mRNAs. Based on the finding that lower motor neurons begin expressing Mid1 during embryonic stages, we developed an organotypic slice culture system of the spinal cord obtained from SBMA mouse fetuses to study the pathogenic role of Mid1 in SBMA motor neurons. Impairment of axonal regeneration arose in the spinal cord culture in SBMA mice in an androgen-dependent manner, but not in mice with non-CAG-expanded AR, and was either exacerbated or ameliorated by Mid1 overexpression or knockdown, respectively. Hence, an early Mid1 expression confers vulnerability to motor neurons, at least by inducing axonogenesis defects, in SBMA.

Troponin T in spinal and bulbar muscular atrophy (SBMA)

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by expansions of a polyglutamine (polyQ) tract in the androgen receptor (AR) gene. SBMA is associated with the progressive loss of lower motor neurons, together with muscle weakness and atrophy. PolyQ-AR is converted to a toxic species upon binding to its natural ligands, testosterone, and dihydrotestosterone (DHT). Our previous patch-clamp studies on a motor neuron-derived cell model of SBMA showed alterations in voltage-gated ion currents. Here, we identified and characterized chloride currents most likely belonging to the chloride channel-2 (ClC-2) subfamily, which showed significantly increased amplitudes in the SBMA cells. The treatment with the pituitary adenylyl cyclase-activating polypeptide (PACAP), a neuropeptide with a proven protective effect in a mouse model of SBMA, recovered chloride channel current alterations in SBMA cells. These observations suggest that the CIC-2 currents are affected in SBMA, an alteration that may contribute and potentially determine the pathophysiology of the disease.

T38. Altered axonal excitability in spinal and bulbar muscular atrophy

The aim of this study was to characterize the respiratory function profile of subjects with spinal and bulbar muscular atrophy (SBMA), and to explore the underlying pathological mechanism by comparing the clinical and biochemical indices of this disease with those of amyotrophic lateral sclerosis (ALS). We enrolled male subjects with SBMA (n = 40) and ALS (n = 25) along with 15 healthy control subjects, and assessed their respiratory function, motor function, and muscle strength. Predicted values of peak expiratory flow (%PEF) and forced vital capacity were decreased in subjects with SBMA compared with controls. In SBMA, both values were strongly correlated with the trunk subscores of the motor function tests and showed deterioration relative to disease duration. Compared with activities of daily living (ADL)-matched ALS subjects, %PEF, tongue pressure, and grip power were substantially decreased in subjects with SBMA. Both immunofluorescence and RT-PCR demonstrated a selective decrease in the expression levels of the genes encoding the myosin heavy chains specific to fast-twitch fibers in SBMA subjects. The mRNA levels of peroxisome proliferator-activated receptor gamma coactivator 1-alpha and peroxisome proliferator-activated receptor delta were up-regulated in SBMA compared with ALS and controls. In conclusion, %PEF is a disease-specific respiratory marker for the severity and progression of SBMA. Explosive muscle strength, including %PEF, was selectively affected in subjects with SBMA and was associated with activation of the mitochondrial biogenesis-related molecular pathway in skeletal muscles.

Dear Editor,Spinal and bulbar muscular atrophy (SBMA) is a rare, progressive neurodegenerative disorder caused by CAG-repeat expansion in the androgen receptor (AR) gene.SBMA is characterized by hand tremor, bulbar weakness, fatigability, and slowly progressive limb weakness. 1Botulinum toxin (BoNT) is widely administered in various conditions, and it acts by inhibiting acetylcholine release at the neuromuscular junction (NMJ).We report this case to highlight the potential for an exaggerated response to BoNT in SBMA patients, which is possibly due to NMJ dysfunction.A 47-year-old male with no underlying disease received a 100-unit injection of BoNT into his bilateral masseter and temporalis at a dental clinic for head tremor.One day later he developed jaw drop, which required manual assistance to close his mouth.After 9 months he visited our clinic due to no improvement in his chewing difficulty.A neurological examination showed significant jaw-closing weakness but preserved jaw-opening strength.Additionally, subtle perioral fasciculation, tongue atrophy, dysarthria, and postural hand tremors were observed.Bilateral masseter atrophy was suspected, but limb muscle atrophy was not observed.Also, limb tone, muscle power, sensation, and tendon reflexes were all normal.Nerve conduction studies revealed low action-potential amplitudes in sensory nerves while motor nerve conduction remained normal.Needle electromyography demonstrated positive sharp waves (2+) in the genioglossus, as well as polyphasic and giant motor-unit action potentials with amplitudes up to 20 mV in the cervical, thoracic, and lumbar segments.Repetitive nerve stimulation (RNS) of right orbicularis oculi, abductor digiti quinti (ADQ), and flexor carpi ulnaris (FCU) at low frequency (5 Hz) induced response decrements of 26.1%, 10.8%, and 13.7%, respectively (Fig. 1A).However, high frequency (30 Hz) RNS of ADQ and FCU induced no incremental responses (Fig. 1B).Antibodies against the acetylcholine receptor (AChR) and muscle-specific kinase were all negative.The creatine kinase level was 85 IU/L (normal range 22-198 IU/L).MRI showed diffusely increased T1weighted signals in his tongue muscles (Fig. 1C).Genetic testing identified 49 CAG repeats in the AR gene, confirming the diagnosis of SBMA.The patient had no family history of SBMA.His score on the SBMA Functional Rating Scale was 51, with deficits only on the bulbar-related subscales.The symptoms did not improve significantly during a 1-year follow-up.SBMA is caused by the toxic effects of mutant AR protein that lead to the degeneration of anterior horn cells in the spinal cord, motor units, and dorsal root ganglia.Additionally, direct toxic effects on skeletal muscles contribute to the primary myopathic features.Moreover, recent studies have highlighted the involvement of the NMJ in SBMA, such as a lack of AChR colocalization 2 and smaller NMJ. 3 Consistent with these findings, clinical cases have demonstrated decremental responses to RNS 4 and responsiveness to acetylcholinesterase inhibi-

Exonic trinucleotide repeats and expression of androgen receptor gene in spinal cord from X-linked spinal and bulbar muscular atrophy

Pathogenesis, animal models and therapeutics in Spinal and bulbar muscular atrophy (SBMA)