Late adult-onset of X-linked myopathy with excessive autophagy

Identification of a Novel Intronic Mutation in VMA21 Associated with a Classical Form of X-Linked Myopathy with Autophagy

Introduction   VMA21 -related myopathy is one of the rare forms of slowly progressive myopathy observed in males. Till now, there have been only a handful of reports, mainly from Europe and America, and two reports from India. Method  Here, we describe a case of genetically confirmed VMA21 -associated myopathy with clinical, histopathological, and imaging features with a list of known VMA21 mutations. Results  A 29-year-old man had the onset of symptoms at 18 years of age with features of proximal lower limb weakness. Muscle magnetic resonance imaging showed the preferential involvement of vasti and adductor magnus. A biopsy of the left quadriceps femoris showed features of autophagic vacuolar myopathy with vacuoles containing granular eosinophilic materials. In targeted next-generation sequencing, hemizygous mutation in the 3' splice site of intron 2 of the VMA21 gene (c.164-7 T > A) was identified and confirmed the diagnosis of X-linked myopathy with excessive autophagy. Conclusion  This report expands the phenotypic and genotypic profile of VMA21 -related myopathy, with a yet unreported mutation in India.

Phenotype variability and natural history of X-linked myopathy with excessive autophagy

OBJECTIVE

X-linked myopathy with excessive autophagy (XMEA) linked to the VMA21 gene leads to autophagy failure with progressive vacuolation and atrophy of skeletal muscles. Current knowledge of this rare disease is limited. Our objective was to define the clinical, radiological, and natural history of XMEA.

METHODS

We conducted a retrospective study collecting clinical, genetic, muscle imaging, and biopsy data of XMEA patients followed in France and reviewed the literature for additional cases.

RESULTS

Eighteen males had genetically confirmed XMEA in France, carrying four different VMA21 variants. Mean age at disease onset was 9.4 ± 9.9 (range 1-40) years. In 14/18 patients (77.8%), onset occurred during childhood (< 15 years); however in four patients, the disease started in adulthood. Patients had anterior and medial compartment thigh muscle weakness, distal contractures (56.3%), elevated CK levels (1287.9 ± 757.8 U/l) and autophagic vacuoles with sarcolemmal features on muscle histopathology. Muscle MRI (n = 10) showed a characteristic pattern of lower limb muscle involvement. In 11 patients, outcome measures were available for an average follow-up period of 10.6 ± 9.8 years and six of them show disease progression. Mean change of functional outcomes was 0.5 ± 1.2 points for Brooke and 2.2 ± 2.5 points for Vignos score, 7/16 patients (43.8%) needed a walking aid and 3/16 (18.8%) were wheelchair-bound (median age of 40 years old, range 39-48). The variant c.164-7 T > G was associated with a later onset of symptoms. Respiratory insufficiency was common (57.1%) but cardiac involvement rare (12.5%).

INTERPRETATION

XMEA has variable age of onset, but a characteristic clinical, histopathological, and muscle imaging presentation, guiding the diagnosis. Although slowly, motor disability progresses with time, and relevant genotype-phenotype correlations will help design future clinical trials.

Complement and MHC patterns can provide the diagnostic framework for inflammatory neuromuscular diseases

Histopathological analysis stands as the gold standard for the identification and differentiation of inflammatory neuromuscular diseases. These disorders continue to constitute a diagnostic challenge due to their clinical heterogeneity, rarity and overlapping features. To establish standardized protocols for the diagnosis of inflammatory neuromuscular diseases, the development of cost-effective and widely applicable tools is crucial, especially in settings constrained by limited resources. The focus of this review is to emphasize the diagnostic value of major histocompatibility complex (MHC) and complement patterns in the immunohistochemical analysis of these diseases. We explore the immunological background of MHC and complement signatures that characterize inflammatory features, with a specific focus on idiopathic inflammatory myopathies. With this approach, we aim to provide a diagnostic algorithm that may improve and simplify the diagnostic workup based on a limited panel of stainings. Our approach acknowledges the current limitations in the field of inflammatory neuromuscular diseases, particularly the scarcity of large-scale, prospective studies that validate the diagnostic potential of these markers. Further efforts are needed to establish a consensus on the diagnostic protocol to effectively distinguish these diseases.

Severe congenital X-linked myopathy with excessive autophagy secondary to an apparently synonymous but pathogenic novel variant

X-linked myopathy with excessive autophagy is a rare inherited disease characterized by aberrant accumulation of autophagic vacuoles in skeletal muscle. Affected males usually show a slow progression and the heart is characteristically spared. We present four male patients from the same family with an extremely aggressive form of this disease, requiring permanent mechanical ventilation from birth. Ambulation was never achieved. Three died, one in the first hour of life, one at 7 years and one at 17 years, the last death being a consequence of heart failure. Muscle biopsy showed pathognomonic features of the disease in the 4 affected males. Genetic study found a novel synonymous variant in VMA21, c.294C>T (Gly98=). Genotyping was consistent with co-segregation with the phenotype in an X-linked recessive manner. An alteration of the normal splice pattern was confirmed by transcriptome analysis, proving that the apparently synonymous variant was the cause of this extremely severe phenotype.

Novel Intronic Mutation in VMA21 Causing Severe Phenotype of X-Linked Myopathy with Excessive Autophagy-Case Report

X-linked Myopathy with Excessive Autophagy (XMEA) is a rare autophagic vacuolar myopathy caused by mutations in the Vacuolar ATPase assembly factor VMA21 gene; onset usually occurs during childhood and rarely occurs during adulthood. We described a 22-year-old patient with XMEA, whose onset was declared at 11 through gait disorder. He had severe four-limb proximal weakness and amyotrophy, and his proximal muscle MRC score was between 2 and 3/5 in four limbs; creatine kinase levels were elevated (1385 IU/L), and electroneuromyography and muscle MRI were suggestive of myopathy. Muscle biopsy showed abnormalities typical of autophagic vacuolar myopathy. We detected a hemizygous, unreported, intronic, single-nucleotide substitution c.164-20T>A (NM_001017980.4) in intron 2 of the VMA21 gene. Fibroblasts derived from this patient displayed a reduced level of VMA21 transcripts (at 40% of normal) and protein, suggesting a pathogenicity related to an alteration of the splicing efficiency associated with an intron retention. This patient with XMEA displayed a severe phenotype (rapid weakness of upper and lower limbs) due to a new intronic variant of VMA21, related to an alteration in the splicing efficiency associated with intron retention, suggesting that phenotype severity is closely related to the residual expression of the VMA21 protein.

X-linked Myopathy with Excessive Autophagy - A Rare Cause of Vacuolar Myopathy in Children

X-linked myopathy with excessive autophagy (XMEA) is a rare, recently characterized type of autophagic vacuolar myopathy caused by mutations in the VMA21 gene. It is characterized by slowly progressive weakness restricted to proximal limb muscles and generally has a favorable outcome. The characteristic histological and ultrastructural features distinguish this entity from other mimics, notably Danon disease. XMEA is an under recognized disease and should be considered in the differentials of slowly progressive myopathy in children. Awareness of this rare entity is also important for the pathologists in order to distinguish it from other causes of vacuolar myopathy in view of its favourable prognosis. We report the first genetically confirmed case of XMEA from India in an 8-year-old boy which was diagnosed based on the characteristic light microscopic and ultrastructural findings on muscle biopsy and subsequently confirmed by mutation analysis. The differential diagnostic considerations are also discussed.

X-linked myopathy with excessive autophagy: First report of an Israeli family presenting with late onset lower limb girdle weakness

X-linked myopathy with excessive autophagy (XMEA) is a rare disorder characterized by slow progressive muscle weakness and distinctive pathology of excessive autophagic vacuoles on muscle biopsy. Here we report on five patients, in a single family, with proximal lower limb weakness. The proband, a 25-year-old man, presented with 5 years of progressive lower limbs proximal muscle weakness. His maternal grandfather and three of his maternal male cousins had similar clinical findings and were initially suspected to have Becker muscular dystrophy. Muscle biopsy in two affected family members demonstrated autophagic myopathy, and guided the genetic investigations to the identification of a pathogenic mutation, c.272G > C in the VMA21 gene, known to cause XMEA [1]. To the best of our knowledge this is the first identified Israeli Jewish family afflicted by XMEA.

The Role of Autophagy in Skeletal Muscle Diseases

Skeletal muscle is the most abundant type of tissue in human body, being involved in diverse activities and maintaining a finely tuned metabolic balance. Autophagy, characterized by the autophagosome–lysosome system with the involvement of evolutionarily conserved autophagy-related genes, is an important catabolic process and plays an essential role in energy generation and consumption, as well as substance turnover processes in skeletal muscles. Autophagy in skeletal muscles is finely tuned under the tight regulation of diverse signaling pathways, and the autophagy pathway has cross-talk with other pathways to form feedback loops under physiological conditions and metabolic stress. Altered autophagy activity characterized by either increased formation of autophagosomes or inhibition of lysosome-autophagosome fusion can lead to pathological cascades, and mutations in autophagy genes and deregulation of autophagy pathways have been identified as one of the major causes for a variety of skeleton muscle disorders. The advancement of multi-omics techniques enables further understanding of the molecular and biochemical mechanisms underlying the role of autophagy in skeletal muscle disorders, which may yield novel therapeutic targets for these disorders.

Mutations in the V-ATPase Assembly Factor VMA21 Cause a Congenital Disorder of Glycosylation With Autophagic Liver Disease

BACKGROUND AND AIMS

Vacuolar H+-ATP complex (V-ATPase) is a multisubunit protein complex required for acidification of intracellular compartments. At least five different factors are known to be essential for its assembly in the endoplasmic reticulum (ER). Genetic defects in four of these V-ATPase assembly factors show overlapping clinical features, including steatotic liver disease and mild hypercholesterolemia. An exception is the assembly factor vacuolar ATPase assembly integral membrane protein (VMA21), whose X-linked mutations lead to autophagic myopathy.

APPROACH AND RESULTS

Here, we report pathogenic variants in VMA21 in male patients with abnormal protein glycosylation that result in mild cholestasis, chronic elevation of aminotransferases, elevation of (low-density lipoprotein) cholesterol and steatosis in hepatocytes. We also show that the VMA21 variants lead to V-ATPase misassembly and dysfunction. As a consequence, lysosomal acidification and degradation of phagocytosed materials are impaired, causing lipid droplet (LD) accumulation in autolysosomes. Moreover, VMA21 deficiency triggers ER stress and sequestration of unesterified cholesterol in lysosomes, thereby activating the sterol response element-binding protein-mediated cholesterol synthesis pathways.

CONCLUSIONS

Together, our data suggest that impaired lipophagy, ER stress, and increased cholesterol synthesis lead to LD accumulation and hepatic steatosis. V-ATPase assembly defects are thus a form of hereditary liver disease with implications for the pathogenesis of nonalcoholic fatty liver disease.

Altered in vitro muscle differentiation in X-linked myopathy with excessive autophagy

X-linked myopathy with excessive autophagy (XMEA) is a genetic disease associated with weakness of the proximal muscles. It is caused by mutations in the VMA21 gene, coding for a chaperone that functions in the vacuolar ATPase (v-ATPase) assembly. Mutations associated with lower content of assembled v-ATPases lead to an increase in lysosomal pH, culminating in partial blockage of macroautophagy, with accumulation of vacuoles of undigested content. Here, we studied a 5-year-old boy affected by XMEA, caused by a small indel in the VMA21 gene. Detection of sarcoplasmic Lc3 (also known as MAP1LC3B)-positive vacuoles in his muscle biopsy confirmed an autophagy defect. To understand how autophagy is regulated in XMEA myogenesis, we used patient-derived muscle cells to evaluate autophagy during in vitro muscle differentiation. An increase in lysosomal pH was observed in the patient's cells, compatible with predicted functional defect of his mutation. Additionally, there was an increase in autophagic flux in XMEA myotubes. Interestingly, we observed that differentiation of XMEA myoblasts was altered, with increased myotube formation observed through a higher fusion index, which was not dependent on lysosomal acidification. Moreover, no variation in the expression of myogenic factors nor the presence of regenerating fibers in the patient's muscle were observed. Myoblast fusion is a tightly regulated process; therefore, the uncontrolled fusion of XMEA myoblasts might generate cells that are not as functional as normal muscle cells. Our data provide new evidence on the reason for predominant muscle involvement in the context of the XMEA phenotype.

This article has an associated First Person interview with the first author of the paper.

Summary: Here, we show that in X-linked myopathy with excessive autophagy there is increased fusion of myoblasts, which is not caused by the primary lysosomal acidification defect.

X-Linked Myopathy with Excessive Autophagy; A Case Report

X-linked myopathy with excessive autophagy (XMEA) is a rare, slowly progressive muscle disease characterized by membrane-bound sarcoplasmic vacuoles distinct from other forms of myopathies with vacuoles. We report this rare condition in a 5-year-old boy with proximal muscle weakness and morphological evidence of autophagic vacuoles.

"Get the Balance Right": Pathological Significance of Autophagy Perturbation in Neuromuscular Disorders

Recent research has revealed that autophagy, a major catabolic process in cells, is dysregulated in several neuromuscular diseases and contributes to the muscle wasting caused by non-muscle disorders (e.g. cancer cachexia) or during aging (i.e. sarcopenia). From there, the idea arose to interfere with autophagy or manipulate its regulatory signalling to help restore muscle homeostasis and attenuate disease progression. The major difficulty for the development of therapeutic strategies is to restore a balanced autophagic flux, due to the dynamic nature of autophagy. Thus, it is essential to better understand the mechanisms and identify the signalling pathways at play in the control of autophagy in skeletal muscle. A comprehensive analysis of the autophagic flux and of the causes of its dysregulation is required to assess the pathogenic role of autophagy in diseased muscle. Furthermore, it is essential that experiments distinguish between primary dysregulation of autophagy (prior to disease onset) and impairments as a consequence of the pathology. Of note, in most muscle disorders, autophagy perturbation is not caused by genetic modification of an autophagy-related protein, but rather through indirect alteration of regulatory signalling or lysosomal function. In this review, we will present the mechanisms involved in autophagy, and those ensuring its tight regulation in skeletal muscle. We will then discuss as to how autophagy dysregulation contributes to the pathogenesis of neuromuscular disorders and possible ways to interfere with this process to limit disease progression.

Muscle magnetic resonance imaging abnormalities in X-linked myopathy with excessive autophagy

INTRODUCTION

X-linked myopathy with excessive autophagy (XMEA) is an X-linked recessive myopathy due to recently reported mutations in the VMA21 gene.

METHODS

Four men from 2 separate families were studied. The clinical presentation, genetic data, muscle biopsy, and muscle MRI were analyzed.

RESULTS

A known VMA21 mutation, c.163+4A>G, and a new mutation, c.163+3A>G, respectively, were found in the 2 families. The clinical course was characterized by onset in childhood and progressive muscle weakness with a limb-girdle pattern. Muscle biopsy revealed a mild myopathy with an increased number of giant autophagic vacuoles. Whole-body muscle MRI showed that pelvic girdle and proximal thighs were the most and earliest affected territories, with sparing of rectus femoris muscles. Muscle changes essentially consisted of degenerative fatty replacement.

CONCLUSIONS

This study highlights a distinctive MRI pattern of muscle involvement, which can be helpful for diagnosis of XMEA, even before muscle biopsy or genetic analysis.

X-linked myopathy with excessive autophagy: a failure of self-eating

Autophagic vacuolar myopathies (AVMs) are a group of disorders united by shared histopathological features on muscle biopsy that include the aberrant accumulation of autophagic vacuoles. The classic conditions that compose the AVMs include Pompe Disease, Danon Disease and X-linked myopathy with excessive autophagy (XMEA). Other disorders, including acquired myopathies like chloroquine toxicity, also have features of an autophagic myopathy. This review is focused on XMEA, a myopathy with onset of slowly progressive proximal weakness and elevated serum creatine kinase (2× to 20× normal) typically in the first decade of life. However, both late-adult onset and severe, sometimes lethal, neonatal cases also occur. Skeletal muscle pathology is characterized by numerous cytoplasmic autophagic vacuoles, complex muscle fiber splitting with internalization of capillaries, and complement C5b-9 deposition within vacuoles and along the sarcolemma. The autophagic vacuoles have sarcolemmal features. Mutations in the VMA21 gene at Xq28 cause XMEA by reducing the activity of lysosomal hydrolases. The VMA21 protein regulates the assembly of the V-ATPase required to acidify the lysosome. Increased lysosomal pH and poor degradation of cellular debris may secondarily induce autophagy, the net effect being accumulation of autophagolysosomes. The relationship of XMEA to other lysosomal disorders of muscle and potential therapeutic interventions for XMEA are discussed.

Molecular regulation of autophagy and its implications for metabolic diseases

PURPOSE OF REVIEW

Autophagy is an evolutionarily conserved cellular programme for the turnover of organelles, proteins, and other macromolecules, involving the lysosomal degradation pathway. Emerging evidence suggests that autophagy can play a central role in human metabolism as well as impact diverse cellular processes including organelle homeostasis, cell death and proliferation, lipid and glycogen metabolism, and the regulation of inflammation and immune responses. The purpose of this review is to examine recent evidence for the role of autophagy in cellular metabolism, and its relevance to select human diseases that involve disorders of metabolism.

RECENT FINDINGS

Recent studies suggest that autophagy may play multiple roles in metabolic diseases, including diabetes and its complications, metabolic syndrome and obesity, myopathies and other inborn errors of metabolism, as well as other diseases that may involve altered mitochondrial function.

SUMMARY

Strategies aimed at modulating autophagy may lead to therapies for diseases in which altered cellular and tissue metabolism play a key role.