Persistent asymptomatic or mild symptomatic hyperCKemia due to mutations in ANO5: the mildest end of the anoctaminopathies spectrum

MRI for the diagnosis of limb girdle muscular dystrophies

PURPOSE OF REVIEW

In the last 30 years, there have many publications describing the pattern of muscle involvement of different neuromuscular diseases leading to an increase in the information available for diagnosis. A high degree of expertise is needed to remember all the patterns described. Some attempts to use artificial intelligence or analysing muscle MRIs have been developed. We review the main patterns of involvement in limb girdle muscular dystrophies (LGMDs) and summarize the strategies for using artificial intelligence tools in this field.

RECENT FINDINGS

The most frequent LGMDs have a widely described pattern of muscle involvement; however, for those rarer diseases, there is still not too much information available. patients. Most of the articles still include only pelvic and lower limbs muscles, which provide an incomplete picture of the diseases. AI tools have efficiently demonstrated to predict diagnosis of a limited number of disease with high accuracy.

SUMMARY

Muscle MRI continues being a useful tool supporting the diagnosis of patients with LGMD and other neuromuscular diseases. However, the huge variety of patterns described makes their use in clinics a complicated task. Artificial intelligence tools are helping in that regard and there are already some accessible machine learning algorithms that can be used by the global medical community.

Variants in DTNA cause a mild, dominantly inherited muscular dystrophy

DTNA encodes α-dystrobrevin, a component of the macromolecular dystrophin-glycoprotein complex (DGC) that binds to dystrophin/utrophin and α-syntrophin. Mice lacking α-dystrobrevin have a muscular dystrophy phenotype, but variants in DTNA have not previously been associated with human skeletal muscle disease. We present 12 individuals from four unrelated families with two different monoallelic DTNA variants affecting the coiled-coil domain of α-dystrobrevin. The five affected individuals from family A harbor a c.1585G > A; p.Glu529Lys variant, while the recurrent c.1567_1587del; p.Gln523_Glu529del DTNA variant was identified in the other three families (family B: four affected individuals, family C: one affected individual, and family D: two affected individuals). Myalgia and exercise intolerance, with variable ages of onset, were reported in 10 of 12 affected individuals. Proximal lower limb weakness with onset in the first decade of life was noted in three individuals. Persistent elevations of serum creatine kinase (CK) levels were detected in 11 of 12 affected individuals, 1 of whom had an episode of rhabdomyolysis at 20 years of age. Autism spectrum disorder or learning disabilities were reported in four individuals with the c.1567_1587 deletion. Muscle biopsies in eight affected individuals showed mixed myopathic and dystrophic findings, characterized by fiber size variability, internalized nuclei, and slightly increased extracellular connective tissue and inflammation. Immunofluorescence analysis of biopsies from five affected individuals showed reduced α-dystrobrevin immunoreactivity and variably reduced immunoreactivity of other DGC proteins: dystrophin, α, β, δ and γ-sarcoglycans, and α and β-dystroglycans. The DTNA deletion disrupted an interaction between α-dystrobrevin and syntrophin. Specific variants in the coiled-coil domain of DTNA cause skeletal muscle disease with variable penetrance. Affected individuals show a spectrum of clinical manifestations, with severity ranging from hyperCKemia, myalgias, and exercise intolerance to childhood-onset proximal muscle weakness. Our findings expand the molecular etiologies of both muscular dystrophy and paucisymptomatic hyperCKemia, to now include monoallelic DTNA variants as a novel cause of skeletal muscle disease in humans.

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.

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.

An integrated approach to the evaluation of patients with asymptomatic or minimally symptomatic hyperCKemia

Introduction/Aims

Currently, there are no straightforward guidelines for the clinical and diagnostic management of hyperCKemia, a frequent and nonspecific presentation in muscle diseases. Therefore, we aimed to describe our diagnostic workflow for evaluating patients with this condition.

Methods

We selected 83 asymptomatic or minimally symptomatic patients with persistent hyperCKemia for participation in this Italian multicenter study. Patients with facial involvement and distal or congenital myopathies were excluded, as were patients with suspected inflammatory myopathies or predominant respiratory or cardiac involvement. All patients underwent a neurological examination and nerve conduction and electromyography studies. The first step of the investigation included a screening for Pompe disease. We then evaluated the patients for myotonic dystrophy type II–related CCTG expansion and excluded patients with copy number variations in the DMD gene. Subsequently, the undiagnosed patients were investigated using a target gene panel that included 20 genes associated with isolated hyperCKemia.

Results

Using this approach, we established a definitive diagnosis in one third of the patients. The detection rate was higher in patients with severe hyperCKemia and abnormal electromyographic findings.

Discussion

We have described our diagnostic workflow for isolated hyperCKemia, which is based on electrodiagnostic data, biochemical screening, and first‐line genetic investigations, followed by successive targeted sequencing panels. Both clinical signs and electromyographic abnormalities are associated with increased diagnostic yields.

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.

Diagnostic muscle biopsies in the era of genetics: the added value of myopathology in a selection of limb-girdle muscular dystrophy patients

In the second most common dystrophy associated with predominant pelvic and shoulder girdle muscle weakness termed Limb-Girdle Muscular Dystrophy (LGMD), genetic complexity, large phenotypic variability, and clinical overlap can result in extensive diagnostic delays in certain individuals. In view of the large strides genetics has taken in this day and age, we address the question if muscle biopsies can still provide diagnostic evidence of substance for these patients. We reviewed and reanalyzed muscle biopsy characteristics in a cohort of LGMD patient pairs in which gene variants were picked up in CAPN3, FKRP, TTN, and ANO5, using histochemical-immunohistochemical-and immunofluorescent staining, and western blotting. We found that not the nature and severity of inflammatory changes, but the changed properties of the dystrophin complex were the most valuable assets to differentiate LGMD from myositis. Proteomic evaluation brought both primary and secondary deficiencies to light, which could be equally revealing for diagnosis. Though a muscle biopsy might, at present, not always be strictly necessary anymore, it still represents an irrefutable asset when the genetic diagnosis is complicated.

Panorama of the distal myopathies

Distal myopathies are genetic primary muscle disorders with a prominent weakness at onset in hands and/or feet. The age of onset (from early childhood to adulthood), the distribution of muscle weakness (upper versus lower limbs) and the histological findings (ranging from nonspecific myopathic changes to myofibrillar disarrays and rimmed vacuoles) are extremely variable. However, despite being characterized by a wide clinical and genetic heterogeneity, the distal myopathies are a category of muscular dystrophies: genetic diseases with progressive loss of muscle fibers. Myopathic congenital arthrogryposis is also a form of distal myopathy usually caused by focal amyoplasia. Massive parallel sequencing has further expanded the long list of genes associated with a distal myopathy, and contributed identifying as distal myopathy-causative rare variants in genes more often related with other skeletal or cardiac muscle diseases. Currently, almost 20 genes (ACTN2, CAV3, CRYAB, DNAJB6, DNM2, FLNC, HNRNPA1, HSPB8, KHLH9, LDB3, MATR3, MB, MYOT, PLIN4, TIA1, VCP, NOTCH2NLC, LRP12, GIPS1) have been associated with an autosomal dominant form of distal myopathy. Pathogenic changes in four genes (ADSSL, ANO5, DYSF, GNE) cause an autosomal recessive form; and disease-causing variants in five genes (DES, MYH7, NEB, RYR1 and TTN) result either in a dominant or in a recessive distal myopathy. Finally, a digenic mechanism, underlying a Welander-like form of distal myopathy, has been recently elucidated. Rare pathogenic mutations in SQSTM1, previously identified with a bone disease (Paget disease), unexpectedly cause a distal myopathy when combined with a common polymorphism in TIA1. The present review aims at describing the genetic basis of distal myopathy and at summarizing the clinical features of the different forms described so far.

What is in the Myopathy Literature?

This update begins with muscle manifestations of coronavirus 2019. They may include myalgias and elevations in serum creatine kinase. It is unknown whether there is direct muscle invasion and how often the critically ill have muscle sequelae. Regarding autoimmune myopathies, a retrospective study of statin-induced necrotizing myopathy is covered. A relatively large proportion of patients had normal strength at presentation. Examples of dermatomyositis associated with immune checkpoint inhibitors are provided including one with cytokine storm. A report of juvenile dermatomyositis with severe abdominal complications is noteworthy. Two articles address unusual associations with inclusion body myositis, namely, spinocerebellar ataxias and granuloma myositis. In the category of muscular dystrophies, a relatively large single center study of the outcome of scapulothoracic arthrodesis for facioscapulohumeral muscular dystrophy is discussed and a article on anoctaminopathies with pauci- or asymptomatic hyperCKemia.