Brain of miyoshi myopathy/dysferlinopathy patients presents with structural and metabolic anomalies

Miyoshi myopathy/dysferlinopathy (MMD) is a rare muscle disease caused by DYSF gene mutations. Apart from skeletal muscles, DYSF is also expressed in the brain. However, the impact of MMD-causing DYSF variants on brain structure and function remains unexplored. To investigate this, we utilized magnetic resonance (MR) modalities (MR volumetry and 31P MR spectroscopy) in a family with seven children, four of whom have the illness. The MMD siblings showed distinct differences from healthy controls: (1) a significant (p < 0.001) right-sided volume asymmetry (+ 232 mm3) of the inferior lateral ventricles; and (2) a significant (p < 0.001) decrease in [Mg2+], along with a modified energy metabolism profile and altered membrane turnover in the hippocampus and motor and premotor cortices. The patients' [Mg2+], energy metabolism, and membrane turnover measures returned to those of healthy relatives after a month of 400 mg/day magnesium supplementation. This work is the first to describe anatomical and functional abnormalities characteristic of neurodegeneration in the MMD brain. Therefore, we call for further examination of brain functions in larger cohorts of MMD patients and testing of magnesium supplementation, which has proven to be an effective corrective approach in our study.

Missense variants in ANO4 cause sporadic encephalopathic or familial epilepsy with evidence for a dominant-negative effect

Anoctamins are a family of Ca2+-activated proteins that may act as ion channels and/or phospholipid scramblases with limited understanding of function and disease association. Here, we identified five de novo and two inherited missense variants in ANO4 (alias TMEM16D) as a cause of fever-sensitive developmental and epileptic or epileptic encephalopathy (DEE/EE) and generalized epilepsy with febrile seizures plus (GEFS+) or temporal lobe epilepsy. In silico modeling of the ANO4 structure predicted that all identified variants lead to destabilization of the ANO4 structure. Four variants are localized close to the Ca2+ binding sites of ANO4, suggesting impaired protein function. Variant mapping to the protein topology suggests a preliminary genotype-phenotype correlation. Moreover, the observation of a heterozygous ANO4 deletion in a healthy individual suggests a dysfunctional protein as disease mechanism rather than haploinsufficiency. To test this hypothesis, we examined mutant ANO4 functional properties in a heterologous expression system by patch-clamp recordings, immunocytochemistry, and surface expression of annexin A5 as a measure of phosphatidylserine scramblase activity. All ANO4 variants showed severe loss of ion channel function and DEE/EE associated variants presented mild loss of surface expression due to impaired plasma membrane trafficking. Increased levels of Ca2+-independent annexin A5 at the cell surface suggested an increased apoptosis rate in DEE-mutant expressing cells, but no changes in Ca2+-dependent scramblase activity were observed. Co-transfection with ANO4 wild-type suggested a dominant-negative effect. In summary, we expand the genetic base for both encephalopathic sporadic and inherited fever-sensitive epilepsies and link germline variants in ANO4 to a hereditary disease.

Patterns of Clinical Progression Among Patients With Autosomal Recessive Limb-Girdle Muscular Dystrophy: A Systematic Review

OBJECTIVES

As the clinical course of autosomal recessive limb-girdle muscular dystrophy (LGMDR) is highly variable, this study characterized the frequency of loss of ambulation (LOA) among patients by subtype (LGMDR1, LGMDR2, LGMDR3-6, LGMDR9, LGMDR12) and progression to cardiac and respiratory involvement among those with and without LOA.

METHODS

Systematic literature review.

RESULTS

From 2929 abstracts screened, 418 patients were identified with ambulatory status data (LOA: 265 [63.4%]). Cardiac and/or respiratory function was reported for 142 patients (34.0%; all with LOA). Among these, respiratory involvement was most frequent in LGMDR3-6 (74.1%; mean [SD] age 23.9 [11.0] years) and cardiac in LGMDR9 (73.3%; mean [SD] age 23.7 [17.7] years). Involvement was less common in patients without LOA except in LGMDR9 (71.4% respiratory and 52.4% cardiac).

CONCLUSIONS

This study described the co-occurrence of LOA, cardiac, and respiratory involvement in LGMDR and provides greater understanding of the clinical progression of LGMDR.

Evaluation of myotonometry for myotonia, muscle stiffness and elasticity in neuromuscular disorders

Neuromuscular disorders show extremely varied expressions of different symptoms and the involvement of muscles. Non-invasively, myotonia and muscle stiffness are challenging to measure objectively. Our study aims to test myotonia, elasticity, and stiffness in various neuromuscular diseases and to provide reference values for different neuromuscular disease groups using a novel handheld non-invasive myometer device MyotonPRO®. We conducted a monocentric blinded cross-sectional study in patients with a set of distinct neuromuscular diseases (NCT04411732, date of registration June 2, 2020). Fifty-two patients in five groups and 21 healthy subjects were enrolled. We evaluated motor function (6-min walk test, handheld dynamometry, Medical Research Council (MRC) Scale) and used ultrasound imaging to assess muscle tissue (Heckmatt scale). We measured muscle stiffness, frequency, decrement, creep, or relaxation using myotonometry with the device MyotonPRO®. Statistically, all values were calculated using the t test and Mann-Whitney U test. No differences were found in comparing the results of myotonometry between healthy and diseased probands. Furthermore, we did not find significant results in all five disease groups regarding myotonometry correlating with muscle strength or ultrasound imaging results. In summary, the myometer MyotonPRO® could not identify significant differences between healthy individuals and neuromuscular patients in our patient collective. Additionally, this device could not distinguish between the five different groups of disorders displaying increased stiffness or decreased muscle tone due to muscle atrophy. In contrast, classic standard muscle tests could clearly decipher healthy controls and neuromuscular patients.

Anoctamin 5 (ANO5) Muscle Disorders: A Narrative Review

Anoctaminopathy-5 refers to a group of hereditary skeletal muscle or bone disorders due to mutations in the anoctamin 5 (ANO5)-encoding gene, ANO5. ANO5 is a 913-amino acid protein of the anoctamin family that functions predominantly in phospholipid scrambling and plays a key role in the sarcolemmal repairing process. Monoallelic mutations in ANO5 give rise to an autosomal dominant skeletal dysplastic syndrome (gnathodiaphyseal dysplasia or GDD), while its biallelic mutations underlie a continuum of four autosomal recessive muscle phenotypes: (1). limb–girdle muscular dystrophy type R12 (LGMDR12); (2). Miyoshi distal myopathy type 3 (MMD3); (3). metabolic myopathy-like (pseudometabolic) phenotype; (4). asymptomatic hyperCKemia. ANO5 muscle disorders are rare, but their prevalence is relatively high in northern European populations because of the founder mutation c.191dupA. Weakness is generally asymmetric and begins in proximal muscles in LGMDR12 and in distal muscles in MMD3. Patients with the pseudometabolic or asymptomatic hyperCKemia phenotype have no weakness, but conversion to the LGMDR12 or MMD3 phenotype may occur as the disease progresses. There is no clear genotype–phenotype correlation. Muscle biopsy displays a broad spectrum of pathology, ranging from normal to severe dystrophic changes. Intramuscular interstitial amyloid deposits are observed in approximately half of the patients. Symptomatic and supportive strategies remain the mainstay of treatment. The recent development of animal models of ANO5 muscle diseases could help achieve a better understanding of their underlying pathomechanisms and provide an invaluable resource for therapeutic discovery.

Progression to Loss of Ambulation Among Patients with Autosomal Recessive Limb-girdle Muscular Dystrophy: A Systematic Review

Background

The impact of age at autosomal recessive limb girdle muscular dystrophy (LGMDR) onset on progression to loss of ambulation (LOA) has not been well established, particularly by subtype.

Objectives:

To describe the characteristics of patients with adult-, late childhood-, and early childhood-onset LGMDR by subtype and characterize the frequency and timing of LOA.

Methods:

A systematic review was conducted in MEDLINE, Embase and the Cochrane library. Frequency and timing of LOA in patients with LGMDR1, LGMDR2/Miyoshi myopathy (MM), LGMDR3-6, LGMDR9, and LGMDR12 were synthesized from published data.

Results:

In 195 studies, 695 (43.4%) patients had adult-, 532 (33.2%) had late childhood-, and 376 (23.5%) had early childhood-onset of disease across subtypes among those with a reported age at onset (n = 1,603); distribution of age at onset varied between subtypes. Among patients with LOA (n = 228), adult-onset disease was uncommon in LGMDR3-6 (14%) and frequent in LGMDR2/MM (42%); LGMDR3-6 cases with LOA primarily had early childhood-onset (74%). Mean (standard deviation [SD]) time to LOA varied between subtypes and was shortest for patients with early childhood-onset LGMDR9 (12.0 [4.9] years, n = 19) and LGMDR3-6 (12.3 [10.7], n = 56) and longest for those with late childhood-onset LGMDR2/MM (21.4 [11.5], n = 36).

Conclusions:

This review illustrated that patients with early childhood-onset disease tend to have faster progression to LOA than those with late childhood- or adult-onset disease, particularly in LGMDR9. These findings provide a greater understanding of progression to LOA by LGMDR subtype, which may help inform clinical trial design and provide a basis for natural history studies.

Unraveling the Molecular Basis of the Dystrophic Process in Limb-Girdle Muscular Dystrophy LGMD-R12 by Differential Gene Expression Profiles in Diseased and Healthy Muscles

Limb-girdle muscular dystrophy R12 (LGMD-R12) is caused by two mutations in anoctamin-5 (ANO5). Our aim was to identify genes and pathways that underlie LGMD-R12 and explain differences in the molecular predisposition and susceptibility between three thigh muscles that are severely (semimembranosus), moderately (vastus lateralis) or mildly (rectus femoris) affected in this disease. We performed transcriptomics on these three muscles in 16 male LGMD-R12 patients and 15 age-matched male controls. Our results showed that LGMD-R12 dystrophic muscle is associated with the expression of genes indicative of fibroblast and adipocyte replacement, such as fibroadipogenic progenitors and immune cell infiltration, while muscle protein synthesis and metabolism were downregulated. Muscle degeneration was associated with an increase in genes involved in muscle injury and inflammation, and muscle repair/regeneration. Baseline differences between muscles in healthy individuals indicated that muscles that are the most affected by LGMD-R12 have the lowest expression of transcription factor networks involved in muscle (re)generation and satellite stem cell activation. Instead, they show relative high levels of fetal/embryonic myosins, all together indicating that muscles differ in their baseline regenerative potential. To conclude, we profiled the gene expression landscape in LGMD-R12, identified baseline differences in expression levels between differently affected muscles and characterized disease-associated changes.

Novel Variants of ANO5 in Two Patients With Limb Girdle Muscular Dystrophy: Case Report

Here we report on two unrelated adult patients presenting with Limb girdle muscular dystrophy who were found to have novel variants in ANO5. Both patients had prominent weakness of their proximal lower limbs with mild weakness of elbow flexion and markedly elevated creatine kinase. Next generation sequencing using a custom-designed neuromuscular panel was performed in both patients. In one patient, 336 genes were targeted for casual variants and in the other patient (using a later panel design), 464 genes were targeted. One patient was homozygous for a novel splice variant [c.294+5G>A; p.(Ala98Ins4^*)] in ANO5. Another patient was compound heterozygous for two variants in ANO5; a common frameshift variant [c.191dupA; p.(Asn64fs)] and a novel missense variant [c.952G>C; p.(Ala318Pro)]. These findings support the utility of next generation sequencing in the diagnosis of patients presenting with a Limb girdle muscular dystrophy phenotype and extends the genotypic spectrum of ANO5 disease.

Sex differences in the involvement of skeletal and cardiac muscles in myopathic Ano5-/- mice

Limb-girdle muscular dystrophy R12 (LGMD-R12) is caused by recessive mutations in the Anoctamin-5 gene (ANO5, TMEM16E). Although ANO5 myopathy is not X-chromosome linked, we performed a meta-analysis of the research literature and found that three-quarters of patients with LGMD-R12 are males. Females are less likely to present with moderate to severe skeletal muscle and/or cardiac pathology. Because these sex differences could be explained in several ways, we compared males and females in a mouse model of LGMD-R12. This model recapitulates the sex differences in human LGMD-R12. Only male Ano5-/- mice had elevated serum creatine kinase after exercise and exhibited defective membrane repair after laser injury. In contrast, by these measures, female Ano5-/- mice were indistinguishable from wild type. Despite these differences, both male and female Ano5-/- mice exhibited exercise intolerance. Although exercise intolerance of male mice can be explained by skeletal muscle dysfunction, echocardiography revealed that Ano5-/- female mice had features of cardiomyopathy that may be responsible for their exercise intolerance. These findings heighten concerns that mutations of ANO5 in humans may be linked to cardiac disease.

Muscle biopsy and MRI findings in ANO5-related myopathy

INTRODUCTION/AIMS

Mutations in the anoctamin 5 (ANO5) gene are a common cause of muscular dystrophy. We aimed to investigate whether inflammatory changes in muscle are present in patients with ANO5 myopathy when assessed by muscle biopsy and muscle magnetic resonance imaging (MRI).

METHODS

Adults with pathogenic variations in ANO5 known to cause muscular dystrophy were included in our study. Muscle biopsies of pelvic and lower extremity muscles were reviewed retrospectively. Muscle MR short-tau inversion recovery (STIR) images of a subset of these patients were obtained prospectively.

RESULTS

Muscle biopsies from 24 patients were reviewed. MR STIR images were performed in 17 of these patients. We found inflammatory changes in muscle biopsies of three patients and MRI revealed hyperintense signals on STIR images in 14 of 17 patients.

DISCUSSION

In this study, we found that muscle edema is very common in patients with ANO5 myopathy and that some patients have inflammatory changes in muscle biopsies. Further studies are needed to determine whether the STIR+ lesions reflect inflammation.

Phenotypic Spectrum of Myopathies with Recessive Anoctamin-5 Mutations

BACKGROUND

Biallelic variants in Anoctamin 5 (ANO5) gene are causative of limb-girdle muscular dystrophy (LGMD) R12 anoctamin5-related, non-dysferlin Miyoshi-like distal myopathy (MMD3), and asymptomatic hyperCKemia.

OBJECTIVE

To describe clinic, histologic, genetic and imaging features, of ANO5 mutated patients.

METHODS

Five patients, four from France (P1, P2, P3 and P4) and one from Mexico (P5), from four families were included. P1 and P2, belonging to group 1, had normal muscle strength; Group 2, P3, P4 and P5, presented with muscular weakness. Muscle strength was measured by manual muscle testing, Medical Research Council (MRC) grades 1/5 to 5/5. Laboratory exams included serum CK levels, nerve conduction studies (NCS)/needle electromyography (EMG), pulmonary function tests, EKG and cardiac ultrasound. ANO5 molecular screening was performed with different approaches.

RESULTS

Group 1 patients showed myalgias with hyperCKemia or isolated hyperCKemia. Group 2 patients presented with limb-girdle or proximo-distal muscular weakness. Serum CK levels ranged from 897 to 5000 UI/L. Muscle biopsy analysis in P4 and P5 showed subsarcolemmal mitochondrial aggregates. Electron microscopy confirmed mitochondrial proliferation and revealed discontinuity of the sarcolemmal membrane. Muscle MRI showed asymmetrical fibro-fatty substitution predominant in the lower limbs.P1 and P2 were compound heterozygous for c.191dupA (p.Asn64Lysfs*15) and c.1898 + G>A; P3 was homozygous for the c.692G>T. (p.Gly231Val); P4 harbored a novel biallelic homozygous exons 1-7 ANO5 gene deletion, and P5 was homozygous for a c.172 C > T (p.(Arg 58 Trp)) ANO5 pathogenic variant.

CONCLUSIONS

Our cohort confirms the wide clinical variability and enlarge the genetic spectrum of ANO5-related myopathies.

[Calcium-activated chloride channels: structure, properties, role in physiological and pathological processes]

Ca2+-activated chloride channels (CaCC) are a class of intracellular calcium activated chloride channels that mediate numerous physiological functions. In 2008, the molecular structure of CaCC was determined. CaCC are formed by the protein known as anoctamine 1 (ANO1 or TMEM16A). CaCC mediates the secretion of Cl- in secretory epithelia, such as the airways, salivary glands, intestines, renal tubules, and sweat glands. The presence of CaCC has also been recognized in the vascular muscles, smooth muscles of the respiratory tract, which control vascular tone and hypersensitivity of the respiratory tract. TMEM16A is activated in many cancers; it is believed that TMEM16A is involved in carcinogenesis. TMEM16A is also involved in cancer cells proliferation. The role of TMEM16A in the mechanisms of hypertension, asthma, cystic fibrosis, nociception, and dysfunction of the gastrointestinal tract has been determined. In addition to TMEM16A, its isoforms are involved in other physiological and pathophysiological processes. TMEM16B (or ANO2) is involved in the sense of smell, while ANO6 works like scramblase, and its mutation causes a rare bleeding disorder, known as Scott syndrome. ANO5 is associated with muscle and bone diseases. TMEM16A interacts with various cellular signaling pathways including: epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPK), calmodulin (CaM) kinases, transforming growth factor TGF-β. The review summarizes existing information on known natural and synthetic compounds that can block/modulate CaCC currents and their effect on some pathologies in which CaCC is involved.

Neuromuscular amyloidosis: Unmasking the master of disguise

Amyloidosis refers to an etiologically heterogeneous group of protein misfolding diseases, pathologically characterized by extracellular amyloid fibrils producing congophillic amorphous deposits in organs and tissues, which may lead to severe organ dysfunction and mortality. Clinical presentations vary and are often nonspecific, depending on what organs or tissues are affected. In systemic amyloidosis, the peripheral nervous system is commonly affected, whereas the skeletal muscles are only rarely involved. Immunoglobulin light chain (AL) amyloidosis and hereditary transthyretin (ATTRv) amyloidosis are the most frequent types of systemic amyloidosis involving the neuromuscular system. Localized amyloidosis can occur in skeletal muscle, so-called isolated amyloid myopathy. Amyloid neuropathy typically involves small myelinated and unmyelinated sensory and autonomic nerve fibers early in the course of the disease, followed by large myelinated fiber sensory and motor deficits. The relentlessly progressive nature with motor, painful sensory and severe autonomic dysfunction, profound weight loss, and systemic features are distinct characteristics of amyloid neuropathy. Amyloid myopathy presentation differs between systemic amyloidosis and isolated amyloid myopathy. Long-standing symptoms, distal predominant myopathy, markedly elevated creatine kinase level, and lack of peripheral neuropathy or systemic features are highly suggestive of isolated amyloid myopathy. In ATTR and AL amyloidosis, early treatment correlates with favorable outcomes. Therefore, awareness of these disorders and active screening for amyloidosis in patients with neuropathy or myopathy are crucial in detecting these patients in the everyday practice of neuromuscular medicine. Herein, we review the clinical manifestations of neuromuscular amyloidosis and provide a diagnostic approach to this disorder.

Cardiac MRI identifies valvular and myocardial disease in a subset of ANO5-related muscular dystrophy patients

Patients with bi-allelic loss-of-function mutations in the gene ANO5 most commonly present with muscular dystrophy. In some studies, patients with ANO5-related dystrophy (ANO5-RD) had evidence of mild cardiac abnormalities; however, cardiac magnetic resonance imaging (MRI) has not been used for myocardial characterization. Ten patients with genetically confirmed ANO5-RD were enrolled in a phenotyping study to better characterize cardiac involvement. Evaluations included medical history, neurological examination and cardiac evaluations (electrocardiogram, echocardiogram and cardiac MRI). All patients were clinically asymptomatic from a cardiac perspective. Muscle MRI was consistent with previous studies of ANO5-RD with increased T1 signal in the posterior and medial compartments of the upper leg and the posterior compartment of the lower leg. Cardiac studies using echocardiography and cardiac MRI revealed dilation of the aortic root and thickening of the aortic valve without significant stenosis in 3/10 patients. There was evidence of abnormal late gadolinium enhancement (LGE) on cardiac MRI in 2/10 patients. In ANO5-RD, the development of cardiac fibrosis, edema or inflammation as demonstrated by LGE has not yet been reported. Cardiac MRI can characterize cardiac tissue and may detect subtle changes before they appear on echocardiography, with potential prognostic implications.

Limb Girdle Muscular Dystrophies

The limb girdle muscular dystrophies (LGMDs) are genetic muscle diseases with primary skeletal muscle involvement in persons with the ability to walk independently at some point in the disease course. They usually have increased creatine kinase levels along with patterns of fatty and fibrous deposition on muscle imaging and/or dystrophic features on muscle biopsy. Distinctive clinical features provide valuable diagnostic clues to the diagnosis and sometimes treatment of these disorders. The advent of gene and cell-based therapies; gene replacement, editing, and modulation; along with stem cell and small molecule therapies may significantly ameliorate clinical severity in the LGMDs.

The Genetic Mutation of ANO5 in Rabbits Recapitulates Human Cardiomyopathy

The limb girdle muscular dystrophy type 2L (LGMD2L) is caused by mutations of the ANO5 gene in humans which encodes a 913 amino-acid integral membrane protein. Although cardiomyopathy has been reported in patients with an ANO5 mutation, the ANO5 mutant mice did not recapitulate this phenotype in previous studies. This study demonstrated that the ANO5−/− rabbits recapitulated the typical signs of cardiomyopathy with decreased ejection fraction (EF) and fraction shortening (FS) with increased interstitial fibrosis. This ANO5−/− rabbit model would promote basic research to comprehend the pathogenesis and mechanism of ANO5-related cardiomyopathy.

Anoctamin 5 (ANO5) muscular dystrophy-three different phenotypes and a new histological pattern

OBJECTIVE

Anoctamin 5 (ANO5) is a putative intracellular calcium-activated chloride channel. Recessive mutations in ANO5 may present from asymptomatic hyperCKemia and exercise-induced myalgia to proximal and/or distal muscle weakness. Here we describe the clinical, pathological, and molecular findings of three unrelated patients with ANO5-related muscular dystrophy.

METHODS

In this retrospective study, we analyzed our database which includes 1700 muscle biopsies performed for diagnostic purposes from October 2004 to February 2019. Patients were attended by two myology experts, who performed and analyzed the muscle biopsies. Muscle biopsies were frozen in cooled isopenthane, cryostat sectioned, and routinely stained and reacted (minimum 16 stainings). A custom panel, including 115 genes (Nextera Rapid Capture, Illumina) and whole-exome sequencing analysis, was used for next-generation sequencing in cases without a definite pathological diagnosis.

RESULTS

Three patients were diagnosed with ANO5-related muscular dystrophy, with all presenting the common exon 5 mutation c.191dup plus a compound heterozygous missense mutation. They showed three different phenotypes (distal myopathy, LGMD2L, and asymptomatic hyperCKemia). Curiously, all three muscle biopsies showed different patterns, but numerous ragged-red fibers with little endomysial inflammation and partial invasion cell by T lymphocytes were observed in one.

CONCLUSION

ANO5-related muscular dystrophy is a heterogeneous disease with different clinical phenotypes as well as different histological patterns, which may even mimic a mitochondrial myopathy. The results of this study provide further knowledge of the clinical, histological, and pathological features related to ANO5 mutations.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

As a group, the limb-girdle muscular dystrophies (LGMDs) are the fourth most prevalent genetic muscle disease, yet they are still not well known or understood. This article defines and describes LGMDs, delineates a diagnostic strategy, and discusses treatment of the LGMDs.

RECENT FINDINGS

In 2018, the definition of the LGMDs was further refined, and a new nomenclature was proposed. Diagnosis of the LGMDs was long guided by the distinctive clinical characteristics of each particular subtype but now integrates use of genetics-with next-generation sequencing panels, exomes, and full genome analysis-early in the diagnostic assessment. Appreciation of the phenotypic diversity of each LGMD subtype continues to expand. This emphasizes the need for precision genetic diagnostics to better understand each subtype and formulate appropriate management for individual patients. Of significant relevance, the explosion of research into therapeutic options accentuates the need for accurate diagnosis, comprehensive disease characterization, and description of the natural histories of the LGMDs to move the field forward and to mitigate disease impact on patients with LGMD.

SUMMARY

The LGMDs are genetic muscle diseases that superficially appear similar to one another but have important differences in rates of progression and concomitant comorbidities. Definitive diagnoses are crucial to guide management and treatment now and in the future. As targeted treatments emerge, it will be important for clinicians to understand the nomenclature, diagnosis, clinical manifestations, and treatments of the LGMDs.

Cardiac Phenotypes in Hereditary Muscle Disorders: JACC State-of-the-Art Review

Hereditary muscular diseases commonly involve the heart. Cardiac manifestations encompass a spectrum of phenotypes, including both cardiomyopathies and rhythm disorders. Common biomarkers suggesting cardiomuscular diseases include increased circulating creatine kinase and/or lactic acid levels or disease-specific metabolic indicators. Cardiac and extra-cardiac traits, imaging tests, family studies, and genetic testing provide precise diagnoses. Cardiac phenotypes are mainly dilated and hypokinetic in dystrophinopathies, Emery-Dreifuss muscular dystrophies, and limb girdle muscular dystrophies; hypertrophic in Friedreich ataxia, mitochondrial diseases, glycogen storage diseases, and fatty acid oxidation disorders; and restrictive in myofibrillar myopathies. Left ventricular noncompaction is variably associated with the different myopathies. Conduction defects and arrhythmias constitute a major phenotype in myotonic dystrophies and skeletal muscle channelopathies. Although the actual cardiac management is rarely based on the cause, the cardiac phenotypes need precise characterization because they are often the only or the predominant manifestations and the prognostic determinants of many hereditary muscle disorders.

Clinical and molecular findings in a cohort of ANO5-related myopathy

OBJECTIVE

ANO5-related myopathy is an important cause of limb-girdle muscular dystrophy (LGMD) and hyperCKemia. The main descriptions have emerged from European cohorts, and the burden of the disease worldwide is unclear. We provide a detailed characterization of a large Brazilian cohort of ANO5 patients.

METHODS

A national cross-sectional study was conducted to describe clinical, histopathological, radiological, and molecular features of patients carrying recessive variants in ANO5. Correlation of clinical and genetic characteristics with different phenotypes was studied.

RESULTS

Thirty-seven patients from 34 nonrelated families with recessive mutations of ANO5 were identified. The most common phenotype was LGMD, observed in 25 (67.5%) patients, followed by pseudometabolic presentation in 7 (18.9%) patients, isolated asymptomatic hyperCKemia in 4 (10.8%) patients, and distal myopathy in a single patient. Nine patients presented axial involvement, including one patient with isolated axial weakness. The most affected muscles according to MRI were the semimembranosus and gastrocnemius, but paraspinal and abdominal muscles, when studied, were involved in most patients. Fourteen variants in ANO5 were identified, and the c.191dupA was present in 19 (56%) families. Sex, years of disease, and the presence of loss-of-function variants were not associated with specific phenotypes.

INTERPRETATION

We present the largest series of anoctaminopathy outside Europe. The most common European founder mutation c.191dupA was very frequent in our population. Gender, disease duration, and genotype did not determine the phenotype.

Identification of a novel ANO5 missense mutation in a Chinese family with familial florid osseous dysplasia

Familial florid osseous dysplasia (FFOD) is an autosomal dominant disorder of connective tissue, characterized by lobulated cementum-like masses scattered throughout the jaws and the alveolar process. This study aimed to identify the genetic etiology of a three-generation Chinese family affected with FFOD. A novel missense mutation p.C356W in anoctamin 5 (ANO5) gene was successfully identified as the pathogenic mutation by whole-exome sequencing (WES). The p.C356W mutation is located in the first loop between the first and second transmembrane domain of ANO5 protein. Sequence alignment of ANO5 protein among many different species revealed that this position is highly conserved. The p.C356W mutation may damage the predicted protein stability of ANO5 by altering the structure of several extracellular loops of ANO5 and affecting the formation of the disulfide bond, thereby disrupting the correct folding of ANO5 protein. Thus, the amino acid at position 356 appears to play a key role in the protein structural stability and function of ANO5 protein. Our results may also provide new insights into the cause and diagnosis of FFOD and may have implications for genetic counseling and clinical management.

Role of anoctamin 5, a gene associated with gnathodiaphyseal dysplasia, in osteoblast and osteoclast differentiation

Anoctamin 5 (Ano5) mutations are responsible for gnathodiaphyseal dysplasia, a rare skeletal syndrome. Despite the close linkage of Ano5 to bone remodeling, the molecular mechanisms underlying the role of Ano5 in bone remodeling remain unknown. In this study, we investigated whether Ano5 regulates osteoblast or osteoclast differentiation to maintain normal bone remodeling. Downregulation of Ano5 expression did not affect osteoblast differentiation and mineralization, while ectopic expression of Ano5 significantly enhanced receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation. Furthermore, Ano5-mediated Akt phosphorylation resulted in nuclear factor of activated T-cells c1 (NFATc1) activation, indicating that Ano5 regulates osteoclast differentiation through activation of the Akt-NFATc1 signaling pathway. Thus, our results suggest a possibility that Ano5 is involved in bone remodeling through regulating the function of osteoclasts rather than that of osteoblasts.

The unfolding spectrum of inherited distal myopathies

Distal myopathies are a group of rare muscle diseases characterized by distal weakness at onset. Although acquired myopathies can occasionally present with distal weakness, the majority of distal myopathies have a genetic etiology. Their age of onset varies from early-childhood to late-adulthood while the predominant muscle weakness can affect calf, ankle dorsiflexor, or distal upper limb muscles. A spectrum of muscle pathological changes, varying from nonspecific myopathic changes to rimmed vacuoles to myofibrillar pathology to nuclei centralization, have been noted. Likewise, the underlying molecular defect is heterogeneous. In addition, there is emerging evidence that distal myopathies can result from defective proteins encoded by genes causative of neurogenic disorders, be manifestation of multisystem proteinopathies or the result of the altered interplay between different genes. In this review, we provide an overview on the clinical, electrophysiological, pathological, and molecular aspects of distal myopathies, focusing on the most recent developments in the field. Muscle Nerve 59:283-294, 2019.

First familial limb-girdle muscular dystrophy 2L in China: Clinical, imaging, pathological, and genetic features

Limb-girdle muscular dystrophy 2L (LGMD2L) is mainly characterized by late adult onset, atrophy of proximal muscles, chronic progressive and asymmetric weakness, accompanied by increased creatine kinase (CK) levels, dystrophic pathological changes and electromyography showing myogenic damage. To date, familial LGMD2L was reported in European countries and had not been reported in China.A careful investigation of the clinical manifestations, muscle performance imaging, biopsy, and target next-generation sequencing (NGS) technology was utilized to identify pathogenic genetic variants in a 4-generation pedigree that includes 6 affected individuals.The results revealed mild-to-moderate hypertrophy of bilateral gastrocnemii and slight weakness and atrophy in the proximal muscles of the lower limbs, with obviously increased serum creatine kinase levels. The symptoms were more serious in the male proband but were also observed in females. Obvious and symmetric atrophy and fat infiltration of posterior segments of the thigh was evident in muscle magnetic resonance imaging (MRI). The pathological changes included a small amount of atrophic and hypertrophic fibers, scattered necrotizing fibers, a small number of increased nuclei, inward migration, mild proliferation of interstitial connective tissue, and no inflammatory cell infiltration. The pathogenic allele was a c.220C > T mutation in the anoctamin 5 (ANO5) gene.The LGMD2L family was characterized by mild chronic myopathy and bilateral gastrocnemius hypertrophy with obviously increased CK levels. Pathological changes included atrophy of fibers with interstitial connective tissues hyperplasia. The pathogenic allele was a c.220C> T mutation in the ANO5 gene.

A novel ANO5 splicing variant in a LGMD2L patient leads to production of a truncated aggregation-prone Ano5 peptide

Mutations in ANO5 cause several human diseases including gnathodiaphyseal dysplasia 1 (GDD1), limb-girdle muscular dystrophy 2L (LGMD2L), and Miyoshi myopathy 3 (MMD3). Previous work showed that complete genetic disruption of Ano5 in mice did not recapitulate human muscular dystrophy, while residual expression of mutant Ano5 in a gene trapped mouse developed muscular dystrophy with defective membrane repair. This suggests that truncated Ano5 expression may be pathogenic. Here, we screened a panel of commercial anti-Ano5 antibodies using a recombinant adenovirus expressing human Ano5 with FLAG and YFP at the N- and C-terminus, respectively. The monoclonal antibody (mAb) N421A/85 was found to specifically detect human Ano5 by immunoblotting and immunofluorescence staining. The antigen epitope was mapped to a region of 28 residues within the N-terminus. Immunofluorescence staining of muscle cryosections from healthy control subjects showed that Ano5 is localized at the sarcoplasmic reticulum. The muscle biopsy from a LGMD2L patient homozygous for the c.191dupA mutation showed no Ano5 signal, confirming the specificity of the N421A/85 antibody. Surprisingly, strong Ano5 signal was detected in a patient with compound heterozygous mutations (c.191dupA and a novel splice donor site variant c.363 + 4A > G at the exon 6-intron 6 junction). Interestingly, insertion of the mutant intron 6, but not the wild-type intron 6, into human ANO5 cDNA resulted in a major transcript that carried the first 158-bp of intron 6. Transfection of the construct encoding the first 121 amino acids into C2C12 cells resulted in protein aggregate formation, suggesting that aggregate-forming Ano5 peptide may contribute to the pathogenesis of muscular dystrophy.

Untangling the complexity of limb-girdle muscular dystrophies

The limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous, autosomal inherited muscular dystrophies with a childhood to adult onset, manifesting with hip- and shoulder-girdle muscle weakness. When the term LGMD was first conceptualized in 1954, it was thought to be a single entity. Currently, there are 8 autosomal dominant (LGMD1A-1H) and 26 autosomal recessive (LGMD2A-2Z) variants according to the Online Mendelian Inheritance in Man database. In addition, there are other genetically identified muscular dystrophies with an LGMD phenotype not yet classified as LGMD. This highlights the entanglement of LGMDs, which represents an area in continuous expansion. Herein we aim to simplify the complexity of LGMDs by subgrouping them on the basis of the underlying defective protein and impaired function. Muscle Nerve 58: 167-177, 2018.

Characterization of isolated amyloid myopathy

BACKGROUND AND PURPOSE

Amyloid myopathy frequently occurs in the setting of systemic amyloidosis and less commonly in isolation (isolated amyloid myopathy). Anoctaminopathy-5 and dysferlinopathy were recently recognized as causes of isolated amyloid myopathy. The present study aimed to characterize the isolated amyloid myopathy and to compare it with amyloid myopathy associated with systemic amyloidosis.

METHODS

We searched the Muscle Laboratory database to identify patients with pathologically confirmed amyloid myopathy seen in neurology clinics between January 1998 and September 2016. Patients with monoclonal gammopathy, peripheral neuropathy, organomegaly or symptoms or pathologic evidence of amyloid deposition outside skeletal muscle were classified as having systemic amyloidosis-associated myopathy.

RESULTS

Fifty-two patients were identified, including 14 with isolated amyloid myopathy (eight anoctaminopathy-5, two dysferlinopathy and four genetically unknown) and 38 with systemic amyloidosis (32 immunoglobulin light-chain amyloidosis, four familial amyloid polyneuropathy and two senile systemic amyloidosis). Compared with patients with systemic amyloidosis, patients with isolated amyloid myopathy had a younger age of onset (median, 41.5 vs. 65 years), no dysphagia (0% vs. 26%) or weight loss (0% vs. 26%), but more frequent calf atrophy (57% vs. 0%), small collections of inflammatory cells on muscle biopsy (43% vs. 0%) and asymptomatic hyperCKemia at onset (21% vs. 0%). All patients with isolated amyloid myopathy had creatine kinase (CK) values >2.5 times the upper limit of normal.

CONCLUSIONS

Isolated amyloid myopathy accounts for 27% of patients with amyloid myopathy, mostly due to anoctaminopathy-5. There are various clinical and laboratory parameters that can help to differentiate isolated amyloid myopathy from systemic amyloidosis.

Molecular, biophysical, and pharmacological properties of calcium-activated chloride channels

Calcium-activated chloride channels (CaCCs) are a family of anionic transmembrane ion channels. They are mainly responsible for the movement of Cl^- and other anions across the biological membranes, and they are widely expressed in different tissues. Since the Cl^- flow into or out of the cell plays a crucial role in hyperpolarizing or depolarizing the cells, respectively, the impact of intracellular Ca²⁺ concentration on these channels is attracting a lot of attentions. After summarizing the molecular, biophysical, and pharmacological properties of CaCCs, the role of CaCCs in normal cellular functions will be discussed, and I will emphasize how dysregulation of CaCCs in pathological conditions can account for different diseases. A better understanding of CaCCs and a pivotal regulatory role of Ca²⁺ can shed more light on the therapeutic strategies for different neurological disorders that arise from chloride dysregulation, such as asthma, cystic fibrosis, and neuropathic pain.

Hyperckemia and myalgia are common presentations of anoctamin-5-related myopathy in French patients

INTRODUCTION

Patients with anoctamin-5 (ANO5) mutations may present not only with limb-girdle muscular dystrophy type 2L or adult-onset Miyoshi-type myopathy but also with asymptomatic hyperCKemia, exercise intolerance, or rhabdomyolysis.

MATERIALS AND METHODS

Data from 38 patients in France with ANO5 mutations with and without muscle weakness on first examination were compared.

RESULTS

Twenty patients presented without muscle weakness. Median age at symptom onset or discovery of hyperCKemia was 23 years. Creatine kinase levels ranged from 200 to 40,000 U/L. Electromyography showed a myopathic pattern in 5 patients, and muscle imaging showed involvement of posterior calf muscles in 10 patients. Mild cardiac involvement was observed in 2 patients. Sixteen patients remain free of weakness after a median follow-up period of 5 years.

DISCUSSION

Asymptomatic, sometimes mild hyperCKemia or exercise intolerance is a presentation of ANO5-related myopathy and may remain isolated or precede muscle weakness by many years. Muscle Nerve 56: 1096-1100, 2017.

Whole exome sequencing links dental tumor to an autosomal-dominant mutation in ANO5 gene associated with gnathodiaphyseal dysplasia and muscle dystrophies

Tumors of the jaws may represent different human disorders and frequently associate with pathologic bone fractures. In this report, we analyzed two affected siblings from a family of Russian origin, with a history of dental tumors of the jaws, in correspondence to original clinical diagnosis of cementoma consistent with gigantiform cementoma (GC, OMIM: 137575). Whole exome sequencing revealed the heterozygous missense mutation c.1067G > A (p.Cys356Tyr) in ANO5 gene in these patients. To date, autosomal-dominant mutations have been described in the ANO5 gene for gnathodiaphyseal dysplasia (GDD, OMIM: 166260), and multiple recessive mutations have been described in the gene for muscle dystrophies (OMIM: 613319, 611307); the same amino acid (Cys) at the position 356 is mutated in GDD. These genetic data and similar clinical phenotypes demonstrate that the GC and GDD likely represent the same type of bone pathology. Our data illustrate the significance of mutations in single amino-acid position for particular bone tissue pathology. Modifying role of genetic variations in another gene on the severity of the monogenic trait pathology is also suggested. Finally, we propose the model explaining the tissue-specific manifestation of clinically distant bone and muscle diseases linked to mutations in one gene.

Defective membrane fusion and repair in Anoctamin5-deficient muscular dystrophy

Limb-girdle muscular dystrophies are a genetically diverse group of diseases characterized by chronic muscle wasting and weakness. Recessive mutations in ANO5 (TMEM16E) have been directly linked to several clinical phenotypes including limb-girdle muscular dystrophy type 2L and Miyoshi myopathy type 3, although the pathogenic mechanism has remained elusive. ANO5 is a member of the Anoctamin/TMEM16 superfamily that encodes both ion channels and regulators of membrane phospholipid scrambling. The phenotypic overlap of ANO5 myopathies with dysferlin-associated muscular dystrophies has inspired the hypothesis that ANO5, like dysferlin, may be involved in the repair of muscle membranes following injury. Here we show that Ano5-deficient mice have reduced capacity to repair the sarcolemma following laser-induced damage, exhibit delayed regeneration after cardiotoxin injury and suffer from defective myoblast fusion necessary for the proper repair and regeneration of multinucleated myotubes. Together, these data suggest that ANO5 plays an important role in sarcolemmal membrane dynamics. Genbank Mouse Genome Informatics accession no. 3576659.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Common and rare variants associating with serum levels of creatine kinase and lactate dehydrogenase

Creatine kinase (CK) and lactate dehydrogenase (LDH) are widely used markers of tissue damage. To search for sequence variants influencing serum levels of CK and LDH, 28.3 million sequence variants identified through whole-genome sequencing of 2,636 Icelanders were imputed into 63,159 and 98,585 people with CK and LDH measurements, respectively. Here we describe 13 variants associating with serum CK and 16 with LDH levels, including four that associate with both. Among those, 15 are non-synonymous variants and 12 have a minor allele frequency below 5%. We report sequence variants in genes encoding the enzymes being measured (CKM and LDHA), as well as in genes linked to muscular (ANO5) and immune/inflammatory function (CD163/CD163L1, CSF1, CFH, HLA-DQB1, LILRB5, NINJ1 and STAB1). A number of the genes are linked to the mononuclear/phagocyte system and clearance of enzymes from the serum. This highlights the variety in the sources of normal diversity in serum levels of enzymes.

Genetic disruption of Ano5 in mice does not recapitulate human ANO5-deficient muscular dystrophy

BACKGROUND

Anoctamin 5 (ANO5) is a member of a conserved gene family (TMEM16), which codes for proteins predicted to have eight transmembrane domains and putative Ca(2+)-activated chloride channel (CaCC) activity. It was recently reported that mutations in this gene result in the development of limb girdle muscular dystrophy type 2L (LGMD2L), Miyoshi myopathy type 3 (MMD3), or gnathodiaphyseal dysplasia 1 (GDD1). Currently, there is a lack of animal models for the study of the physiological function of Ano5 and the disease pathology in its absence.

RESULTS

Here, we report the generation and characterization of the first Ano5-knockout (KO) mice. Our data demonstrate that the KO mice did not present overt skeletal or cardiac muscle pathology at rest conditions from birth up to 18 months of age. There were no significant differences in force production or force deficit following repeated eccentric contractions between wild type (WT) and KO mice. Although cardiac hypertrophy developed similarly in both KO and WT mice after daily isoproterenol (ISO, 100 mg/kg) treatment via intraperitoneal injection for 2 weeks, they were functionally indiscernible. However, microarray analysis identified the genes involved in lipid metabolism, and complement pathways were altered in the KO skeletal muscle.

CONCLUSIONS

Taken together, these data provide the evidence to show that genetic ablation of Ano5 in C57BL/6J mice does not cause overt pathology in skeletal and cardiac muscles, but Ano5 deficiency may lead to altered lipid metabolism and inflammation signaling.

Clinical and genetic features of anoctaminopathy in Saudi Arabia

Objectives:

Characterization of the phenotypic, pathological, radiological, and genetic findings in 2 Saudi Arabian families with anoctaminopathies, and limb girdle muscular dystrophy type 2L (LGMD2L).

Methods:

Over a 2-year period from December 2010 to January 2013, the clinical presentations were analyzed and all genes responsible for limb girdle muscular dystrophy (LGMD) were screened in families seen at King Faisal Specialist Hospital and Research Centre, a tertiary care hospital in Riyadh, Saudi Arabia. Out of 66 families with LGMD, we identified 2 families (3.1%) with anoctaminopathy, ANO5 muscular dystrophy.

Results:

In the first case, a man presented with asymmetrical calves’ muscles weakness and atrophy, which was first noted at age 39. The creatinine kinase (CK) level was >20x normal, muscle biopsy showed necrotizing myopathic changes, and an MRI of the legs showed fatty-tissue replacement to muscle tissue with volume loss involving the gastrocnemius and soleus muscles in an asymmetrical fashion. Minimal disease progression was noted over 18 years of follow up. Exercise induced recurrent rhabdomyolysis was noted over the last 2 years. A novel ANO5 gene mutation (Arg58Trp) was found. In the second family, a male presented at the age of 41 with asymptomatic hyperCkemia and intermittent dyspnea. Over 10 years follow up, he became disabled with muscle cramps, rhabdomyolysis, myoglobinurea, and difficulty ambulating. Muscle biopsy showed necrotizing myopathy and perivascular and interstitial amyloid deposit in skeletal muscle. A homozygous deletion of 11.9 Kb encompassing exon 13 to exon 17 was found in the ANO5 gene. Full cardiac investigations were normal in both patients.

Conclusion:

The prevalence of LGMD2L is approximately 3.1% in a Saudi Arabian native LGMD cohort. Slowly progressive, late onset, and asymmetrical weakness was the salient features in these 2 families. The genetic findings were novel and will add to the spectrum of ANO5 known mutations.

Next generation sequencing on patients with LGMD and nonspecific myopathies: Findings associated with ANO5 mutations

We studied 786 undiagnosed patients with LGMD or nonspecific myopathic features to investigate the role of ANO5 mutations in limb-girdle muscular dystrophies (LGMDs) and in nonspecific myopathies using the next generation sequencing (NGS) approach. In 160 LGMD patients, we first sequenced hotspot exons 5 and 20 and then sequenced the remaining part of the coding region. Another 626 patients, recruited using broader inclusion criteria, were directly analyzed by targeted NGS. By combining NGS and Sanger sequencing, we identified 33/786 (4%) patients carrying putative pathogenic changes in both alleles and 23 ANO5 heterozygotes (3%). The phenotypic spectrum is broader than expected, from hyperCKemia to myopathies, with lack of genotype/phenotype correlations. In particular, this is currently the largest screening of the ANO5 gene. The large number of heterozygotes for damaging mutations suggests that anoctaminopathies should be frequent and often nonpenetrant. We propose the multiple genetic testing by targeted NGS as a first step to analyze patients with nonspecific myopathic presentations. This represents a straightforward approach to overcome the difficulties of clinical heterogeneity of ANO5 patients, and to test, at the same time, many other genes involved in neuromuscular disorders.