Spinal and Bulbar Muscular Atrophy Overview

Genetic Basis of Motor Neuron Diseases: Insights, Clinical Management, and Future Directions

Motor neuron diseases (MNDs) are a heterogeneous group of neurodegenerative disorders characterized by the progressive loss of motor neurons, resulting in debilitating physical decline. Advances in genetics have revolutionized the understanding of MNDs, elucidating critical genes such as SOD1, TARDBP, FUS, and C9orf72, which are implicated in their pathogenesis. Despite these breakthroughs, significant gaps persist in understanding the interplay between genetic and environmental factors, the role of rare variants, and epigenetic contributions. This review synthesizes current knowledge on the genetic landscape of MNDs, highlights challenges in linking genotype to phenotype, and discusses the promise of precision medicine approaches. Emphasis is placed on emerging strategies, such as gene therapy and targeted molecular interventions, offering hope for personalized treatments. Addressing these challenges is imperative to harness the full potential of genomics for improving outcomes in MNDs.

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.

Using genetic testing to diagnose Kennedy's disease: a case report and literature review

Theoretical basis: Kennedy's disease (KD) is also known as spinal bulbar muscular dystrophy. Because the symptoms of KD are similar to most neuromuscular diseases, it is difficult to make a rapid clinical diagnosis. Patient case: We report the case of a 50-year-old man who was diagnosed with "lumbar disc herniation" five years ago because of progressive proximal limb weakness. After his initial diagnosis, his condition worsened gradually, and a muscle biopsy was performed 3 years ago, and he was then diagnosed with "motor neuron disease", but he had no such family history. His physical examination showed female breast development, erectile dysfunction, a weakness of the quadriceps femoris, a bilateral tendon reflex, and atrophy of the tongue muscle. One year ago, it was found that his blood sugar had increased, and when oral hypoglycemic drugs were given, his blood glucose control was not ideal. At the same time, it was found that his creatine kinase continued to increase significantly. He was admitted to the hospital again because of the aggravation of his walking difficulties. Diagnosis: A laboratory examination showed elevated creatine kinase, an impaired glucose tolerance, and abnormal lactate values. The diagnosis was confirmed using a genetic analysis, which showed a repeated amplification of CAG in the androgen receptor gene. Intervention measures and results: After this diagnosis, the patient had a good prognosis after receiving symptomatic treatment. Lesson: Genetic testing is the key to the diagnosis of KD. Clinicians should make a differential diagnosis, an early diagnosis, and provide treatment as soon as possible according to the patient's clinical manifestations and laboratory examination.

Metabolic alterations in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a rare, X-linked neuromuscular disease characterised by lower motor neurons degeneration, slowly progressive myopathy and multisystem involvement. SBMA is caused by trinucleotide repeat expansion in the first exon of the androgen receptor (AR) gene on chromosome X that encodes a polyglutamine (polyQ) tract in the AR protein. Disease onset occurs between 30-60 years of age with easy fatigability, muscle cramps, and weakness in the limbs. In addition to neuromuscular involvement, in SBMA phenotype, many non-neural manifestations are present. Recently, some studies have reported a high prevalence of metabolic and liver disorders in patients with SBMA. Particularly, fatty liver and insulin resistance (IR) have been found in many SBMA patients. The alteration of AR function and the androgen insensitivity can be involved in both fatty liver and IR. In turn, IR and liver alterations can influence neuromuscular damage through different mechanisms. These data lead to consider SBMA as a metabolic as well as a neuromuscular disease. The mechanism of metabolic alterations, their link with the neuromuscular damage, the effects on the course of disease and their treatment will have to be yet fully clarified.

Src inhibition attenuates polyglutamine-mediated neuromuscular degeneration in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by an expanded CAG repeat in the androgen receptor (AR) gene. Here, we perform a comprehensive analysis of signaling pathways in a mouse model of SBMA (AR-97Q mice) utilizing a phosphoprotein assay. We measure the levels of 17 phosphorylated proteins in spinal cord and skeletal muscle of AR-97Q mice at three stages. The level of phosphorylated Src (p-Src) is markedly increased in the spinal cords and skeletal muscles of AR-97Q mice prior to the onset. Intraperitoneal administration of a Src kinase inhibitor improves the behavioral and histopathological phenotypes of the transgenic mice. We identify p130Cas as an effector molecule of Src and show that the phosphorylated p130Cas is elevated in murine and cellular models of SBMA. These results suggest that Src kinase inhibition is a potential therapy for SBMA.

Expression of Human Endogenous Retrovirus-K in Spinal and Bulbar Muscular Atrophy

Background: Spinal and Bulbar Muscular Atrophy (SBMA) is caused by the extension of the polyglutamine tract within the androgen receptor (AR) gene, and results in a multisystem presentation, including the degeneration of lower motor neurons. The androgen receptor (AR) is known to modulate the expression of endogenous retrovirus-K (ERVK), a pathogenic viral genomic symbiont. Since ERVK is associated with motor neuron disease, such as Amyotrophic Lateral Sclerosis (ALS), we sought to determine if patients with SBMA exhibit evidence of ERVK reactivation. Results: Data from a pilot study demonstrate that peripheral blood mononuclear cell (PBMC) samples from controls and patients with SBMA were examined ex vivo for the expression of ERVK viral transcripts and proteins. No differences in ERVK RNA expression was observed between the clinical groups. In contrast, enhancement of processed ERVK Gag and integrase proteins were observed in SBMA-derived PBMC as compared to healthy control specimens. Increased ERVK protein maturation co-occurred with elevation in the expression of the pro-inflammatory transcription factor IRF1 in SBMA. Conclusions: Our findings indicate that ERVK viral protein maturation in SBMA is an unrecognized biomarker and facet of the disease. We discuss how our current understanding of ERVK-driven pathology may tie into key aspects of multi-system dysfunction in SBMA, with a focus on inflammation, proteinopathy, as well as DNA damage and repair.

DNA methylation inhibitor attenuates polyglutamine-induced neurodegeneration by regulating Hes5

Spinal and bulbar muscular atrophy (SBMA) is a polyglutamine-mediated neuromuscular disease caused by a CAG repeat expansion in the androgen receptor (AR) gene. While transcriptional dysregulation is known to play a critical role in the pathogenesis of SBMA, the underlying molecular pathomechanisms remain unclear. DNA methylation is a fundamental epigenetic modification that silences the transcription of various genes that have a CpG-rich promoter. Here, we showed that DNA methyltransferase 1 (Dnmt1) is highly expressed in the spinal motor neurons of an SBMA mouse model and in patients with SBMA. Both genetic Dnmt1 depletion and treatment with RG108, a DNA methylation inhibitor, ameliorated the viability of SBMA model cells. Furthermore, a continuous intracerebroventricular injection of RG108 mitigated the phenotype of SBMA mice. DNA methylation array analysis identified hairy and enhancer of split 5 (Hes5) as having a CpG island with hyper-methylation in the promoter region, and the Hes5 expression was strongly silenced in SBMA. Moreover, Hes5 over-expression rescued the SBMA cells possibly by inducing Smad2 phosphorylation. Our findings suggest DNA hyper-methylation underlies the neurodegeneration in SBMA.

X-linked spinal and bulbar muscular atrophy (Kennedy's disease): the first case described in the Brazilian Amazon

The X-linked spinal and bulbar muscular atrophy (Kennedy’s disease) is a rare X-linked, recessive, lower motor neuron disease, characterized by weakness, atrophy, and fasciculations of the appendicular and bulbar muscle. The disease is caused by an expansion of the CAG repetition in the androgen receptor gene. Patients with Kennedy’s disease have more than 39 CAG repetitions. We report a case of 57-year-old man, resident of Monte Dourado (PA, Brazil) who complained of brachiocrural paresis evolving for 3 years along with fasciculations and tremors of extremities. In addition, he also developed dysarthria, dysphagia, and sexual dysfunction. The patient clinical picture included gait impairment, global hyporeflexia, proximal muscle atrophy of upper limbs, deviation of the uvula to right during phonation and tongue atrophy with fasciculations. The patient reported that about 30 years ago he had undergone gynecomastia surgery. His electroneuromyography suggested spinal muscular atrophy, and nuclear magnetic resonance imaging showed tapering of the cervical and thoracic spinal cord. Patient’s creatine kinase level was elevated. In view of the findings, an exam was requested to investigate Kennedy’s disease. The exam identified 46 CAG repetitions in the androgen receptor gene, which confirmed the diagnostic suspicion. This was the first case of Kennedy’s disease diagnosed and described in the Brazilian Amazon. To our knowledge only other four papers were published on this disease in Brazilian patients. A brief review is also provided on etiopathogenic, clinical and diagnostic aspects.

Peripheral sensitivity to steroids revisited

Resistance to steroid hormones presents a serious problem with respect to their mass use in therapy. It may be caused genetically by mutation of genes involved in hormonal signaling, not only steroid receptors, but also other players in the signaling cascade as co-regulators and other nuclear factors, mediating the hormone-born signal. Another possibility is acquired resistance which may develop under long-term steroid treatment, of which a particular case is down regulation of the receptors. In the review recent knowledge is summarized on the mechanism of main steroid hormone action, pointing to already proven or potential sites causing steroid resistance. We have attempted to address following questions: 1) What does stay behind differences among patients as to their response to the (anti)steroid treatment? 2) Why do various tissues/cells respond differently to the same steroid hormone though they contain the same receptors? 3) Are such differences genetically dependent? The main attention was devoted to glucocorticoids as the most frequently used steroid therapeutics. Further, androgen insensitivity is discussed with a particular attention to acquired resistance to androgen deprivation therapy of prostate cancer. Finally the potential causes are outlined of breast and related cancer(s) resistance to antiestrogen therapy.

The metabolic and endocrine characteristics in spinal and bulbar muscular atrophy

OBJECTIVE

Spinal and bulbar muscular atrophy (SBMA) is caused by an abnormal expansion of the CAG repeat in the androgen receptor gene. This study aimed to systematically phenotype a German SBMA cohort (n = 80) based on laboratory markers for neuromuscular, metabolic, and endocrine status, and thus provide a basis for the selection of biomarkers for future therapeutic trials.

METHODS

We assessed a panel of 28 laboratory parameters. The clinical course and blood biomarkers were correlated with disease duration and CAG repeat length. A subset of 11 patients was evaluated with body fat MRI.

RESULTS

Almost all patients reported muscle weakness (99%), followed by dysphagia (77%), tremor (76%), and gynecomastia (75%) as major complaints. Creatine kinase was the most consistently elevated (94%) serum marker, which, however, did not relate with either the disease duration or the CAG repeat length. Paresis duration and CAG repeat length correlated with dehydroepiandrosterone sulfate after correction for body mass index and age. The androgen insensitivity index was elevated in nearly half of the participants (48%).

CONCLUSIONS

Metabolic alterations in glucose homeostasis (diabetes) and fat metabolism (combined hyperlipidemia), and sex hormone abnormalities (androgen insensitivity) could be observed among SBMA patients without association with the neuromuscular phenotype. Dehydroepiandrosterone sulfate was the only biomarker that correlated strongly with both weakness duration and the CAG repeat length after adjusting for age and BMI, indicating its potential as a biomarker for both disease severity and duration and, therefore, its possible use as a reliable outcome measure in future therapeutic studies.

RBD and Neurodegenerative Diseases

Rapid eye movement (REM) sleep behavior disorder (RBD) is a sleep disorder characterized by enacting one's dreams during the REM sleep, with most of the dreams being violent or aggressive, so that patients often come to see the doctor complaining hurting themselves or bed partners during sleep. Prevalence of RBD, based on population, is 0.38-2.01 %, but much higher in patients with neurodegenerative diseases, especially synucleinopathies. RBD may herald the emergence of synucleinopathies by decades, such that it may be used as an effective early marker of neurodegenerative diseases. Pharmaceutical treatment of RBD includes clonazepam, melatonin, pramipexole, and some newly reported medications. In this review, we summarized the clinical and PSG features of RBD, the pathophysiology and the therapy of it, focusing on the correlation between neurodegenerative diseases and RBD, in order to emphasize the significance of RBD as an early marker of neurodegenerative diseases.

Introduction to the Special Issue on Spinal and Bulbar Muscular Atrophy

This special issue is dedicated to spinal and bulbar muscular atrophy (SBMA) and is based on the conference sponsored by the European Neuromuscular Centre (ENMC) held in March 2015. SBMA, also known as Kennedy's disease, is a neurodegenerative disease caused by an expansion of a repeat of the trinucleotide CAG encoding glutamine in the gene encoding androgen receptor (AR). Expansion of polyglutamine in the AR results in selective lower motor neuron degeneration and skeletal muscle atrophy. SBMA belongs to the family of polyglutamine diseases, which also includes Huntington's disease, dentatorubral-pallidoluysian atrophy, and spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, and 17. Within the family of polyglutamine diseases, SBMA is unique in its gender-specificity, with full disease manifestation restricted to males. Since the disease is ligand (androgen)-dependent, SBMA manifests primarily in males which have high levels of circulating androgens in the serum; females are usually asymptomatic. Indeed, the polyglutamine-expanded AR is converted to a neurotoxic species upon binding to androgens. The mechanisms through which androgen binding triggers the disease are under investigation. Although several therapeutic strategies have been proposed to date, there is currently no effective therapy to arrest or delay disease progression in patients.