High cardiovascular morbidity and mortality in myofibrillar myopathies due to DES gene mutations: a 10-year longitudinal study

Unexpected Genetic Twists in Patients with Cardiac Devices

Objective: To assess the frequency and types of genetic mutations in patients with arrhythmias who underwent cardiac device implantation. Methods: Retrospective observational study, including 38 patients with different arrhythmias and cardiac arrest as a first cardiac event. Treatment modalities encompass pacemakers, transvenous defibrillators, loop recorders, subcutaneous defibrillators, and cardiac resynchronization therapy. All patients underwent genetic testing, using commercially available panels (106-174 genes). Outcome measures include mortality, arrhythmia recurrence, and device-related complications. Results: Clinical parameters revealed a family history of sudden cardiac death in 19 patients (50%), who were predominantly male (58%) and had a mean age of 44.5 years and a mean left ventricle ejection fraction of 40.3%. Genetic testing identified mutations in various genes, predominantly TMEM43 (11%). In two patients (3%) with arrhythmogenic cardiomyopathy, complete subcutaneous defibrillator extraction with de novo transvenous implantable cardioverter-defibrillator implantation was needed. The absence of multiple associations among severe gene mutations was crucial for cardiac resynchronization therapy response. Mortality in this group was around 3% in titin dilated cardiomyopathy patients. Conclusions: Integration of genetic testing into the decision-making process for patients with electronic devices represents a paradigm shift in personalized medicine. By identifying genetic markers associated with arrhythmia susceptibility, heart failure etiology, and cardiac resynchronization therapy response, clinicians can tailor device choices to optimize patient outcomes.

Viral myocarditis in combination with genetic cardiomyopathy as a cause of sudden death. An autopsy series

Sudden cardiac death (SCD) is a major public health issue worldwide. In the young (< 40 years of age), genetic cardiomyopathies and viral myocarditis, sometimes in combination, are the most frequent, but underestimated, causes of SCD. Molecular autopsy is essential for prevention. Several studies have shown an association between genetic cardiomyopathies and viral myocarditis, which is probably underestimated due to insufficient post-mortem investigations. We report on four autopsy cases illustrating the pathogenesis of these combined pathologies. In two cases, a genetic hypertrophic cardiomyopathy was diagnosed in combination with Herpes Virus Type 6 (HHV6) and/or Parvovirus-B19 (PVB19) in the heart. In the third case, autopsy revealed a dilated cardiomyopathy and virological analyses revealed acute myocarditis caused by three viruses: PVB19, HHV6 and Epstein-Barr virus. Genetic analyses revealed a mutation in the gene coding for desmin. The fourth case illustrated a channelopathy and a PVB19/HHV6 coinfection. Our four cases illustrate the highly probable deleterious role of cardiotropic viruses in the occurrence of SCD in subjects with genetic cardiomyopathies. We discuss the pathogenetic link between viral myocarditis and genetic cardiomyopathy. Molecular autopsy is essential in prevention of these SCD, and a close collaboration between cardiologists, pathologists, microbiologists and geneticians is mandatory.

Pathophysiological mechanisms of cardiomyopathies induced by desmin gene variants located in the C-Terminus of segment 2B

Desmin, the most abundant intermediate filament in cardiomyocytes, plays a key role in maintaining cardiomyocyte structure by interconnecting intracellular organelles, and facilitating cardiomyocyte interactions with the extracellular matrix and neighboring cardiomyocytes. As a consequence, mutations in the desmin gene (DES) can lead to desminopathies, a group of diseases characterized by variable and often severe cardiomyopathies along with skeletal muscle disorders. The basic desmin intermediate filament structure is composed of four segments separated by linkers that further assemble into dimers, tetramers and eventually unit-length filaments that compact radially to give the final form of the filament. Each step in this process is critical for proper filament formation and allow specific interactions within the cell. Mutations within the desmin gene can disrupt filament formation, as seen by aggregate formation, and thus have severe cardiac and skeletal outcomes, depending on the locus of the mutation. The focus of this review is to outline the cardiac molecular consequences of mutations located in the C-terminal part of segment 2B. This region is crucial for ensuring proper desmin filament formation and is a known hotspot for mutations that significantly impact cardiac function.

Generation of human induced pluripotent stem cell lines from five patients with Myofibrillar myopathy carrying different heterozygous mutations in the DES gene

Myofibrillar myopathy (MFM) is a rare genetic disorder characterized by muscular dystrophy that is often associated with cardiac disease. This disease is caused by mutations in several genes, among them DES (encoding desmin) is the most frequently affected. Peripheral blood mononuclear cells from 5 different MFM patients with different DES mutations were reprogrammed into induced pluripotent stem cells (IPSC) using non-integrative vectors. For each patient, one IPSC clone was selected and demonstrated pluripotency hallmarks without genomic abnormalities. SNP profiles were identical to the cells of origin and all the clones have the capacity to differentiate into all three germ layers.

Understanding Arrhythmogenic Cardiomyopathy: Advances through the Use of Human Pluripotent Stem Cell Models

Cardiomyopathies (CMPs) represent a significant healthcare burden and are a major cause of heart failure leading to premature death. Several CMPs are now recognized to have a strong genetic basis, including arrhythmogenic cardiomyopathy (ACM), which predisposes patients to arrhythmic episodes. Variants in one of the five genes (PKP2, JUP, DSC2, DSG2, and DSP) encoding proteins of the desmosome are known to cause a subset of ACM, which we classify as desmosome-related ACM (dACM). Phenotypically, this disease may lead to sudden cardiac death in young athletes and, during late stages, is often accompanied by myocardial fibrofatty infiltrates. While the pathogenicity of the desmosome genes has been well established through animal studies and limited supplies of primary human cells, these systems have drawbacks that limit their utility and relevance to understanding human disease. Human induced pluripotent stem cells (hiPSCs) have emerged as a powerful tool for modeling ACM in vitro that can overcome these challenges, as they represent a reproducible and scalable source of cardiomyocytes (CMs) that recapitulate patient phenotypes. In this review, we provide an overview of dACM, summarize findings in other model systems linking desmosome proteins with this disease, and provide an up-to-date summary of the work that has been conducted in hiPSC-cardiomyocyte (hiPSC-CM) models of dACM. In the context of the hiPSC-CM model system, we highlight novel findings that have contributed to our understanding of disease and enumerate the limitations, prospects, and directions for research to consider towards future progress.

Deep Characterization of a Greek Patient with Desmin-Related Myofibrillar Myopathy and Cardiomyopathy

Desmin is a class III intermediate filament protein highly expressed in cardiac, smooth and striated muscle. Autosomal dominant or recessive mutations in the desmin gene (DES) result in a variety of diseases, including cardiomyopathies and myofibrillar myopathy, collectively called desminopathies. Here we describe the clinical, histological and radiological features of a Greek patient with a myofibrillar myopathy and cardiomyopathy linked to the c.734A>G,p.(Glu245Gly) heterozygous variant in the DES gene. Moreover, through ribonucleic acid sequencing analysis in skeletal muscle we show that this variant provokes a defect in exon 3 splicing and thus should be considered clearly pathogenic.

Phenotypic variability within the desminopathies: A case series of three patients

The DES gene encodes desmin, a key intermediate filament of skeletal, cardiac and smooth muscle. Pathogenic DES variants produce a range of skeletal and cardiac muscle disorders collectively known as the desminopathies. We report three desminopathy cases which highlight the phenotypic heterogeneity of this disorder and discuss various factors that may contribute to the clinical differences seen between patients with different desmin variants and also between family members with the same variant.

Bi-Allelic DES Gene Variants Causing Autosomal Recessive Myofibrillar Myopathies Affecting Both Skeletal Muscles and Cardiac Function

Mutations in the human desmin gene (DES) may cause both autosomal dominant and recessive cardiomyopathies leading to heart failure, arrhythmias and atrio-ventricular blocks, or progressive myopathies. Cardiac conduction disorders, arrhythmias and cardiomyopathies usually associated with progressive myopathy are the main manifestations of autosomal dominant desminopathies, due to mono-allelic pathogenic variants. The recessive forms, due to bi-allelic variants, are very rare and exhibit variable phenotypes in which premature sudden cardiac death could also occur in the first or second decade of life. We describe a further case of autosomal recessive desminopathy in an Italian boy born of consanguineous parents, who developed progressive myopathy at age 12, and dilated cardiomyopathy four years later and died of intractable heart failure at age 17. Next Generation Sequencing (NGS) analysis identified the homozygous loss-of-function variant c.634C>T; p.Arg212*, which was likely inherited from both parents. Furthermore, we performed a comparison of clinical and genetic results observed in our patient with those of cases so far reported in the literature.

Genetic Testing as a Guide for Treatment in Dilated Cardiomyopathies

PURPOSE OF REVIEW

Dilated cardiomyopathy (DCM) is one of the most prevalent primary cardiomyopathies and may be caused by genetic and non-genetic etiologies. DCM may also be the final common pathway of other cardiomyopathies such as hypertrophic, arrhythmogenic, or non-compaction cardiomyopathy. We review the main DCM genetic substrates, specific genotype-phenotype aspects, the role of genetic testing in risk stratification, and advances regarding genotype-based precision medicine.

RECENT FINDINGS

Performing a comprehensive genetic study could have a diagnostic yield up to 40% in DCM, and it is considered a cost-effective approach nowadays. The detection of a specific underlying genetic substrate explaining the disease can have important consequences for clinical management, especially for familial cascade screening, optimizing medical treatment, and improving the arrhythmic risk stratification. The identification of the genetic substrate underlying dilated cardiomyopathy makes possible the genotype-phenotype correlation analysis and a better understanding of the natural history of this disease. Nowadays, there are many promising targeting-gene therapies in different developing phases.

Desmin variants: Trigger for cardiac arrhythmias?

Desmin (DES) is a classical type III intermediate filament protein encoded by the DES gene. Desmin is abundantly expressed in cardiac, skeletal, and smooth muscle cells. In these cells, desmin interconnects several protein-protein complexes that cover cell-cell contact, intracellular organelles such as mitochondria and the nucleus, and the cytoskeletal network. The extra- and intracellular localization of the desmin network reveals its crucial role in maintaining the structural and mechanical integrity of cells. In the heart, desmin is present in specific structures of the cardiac conduction system including the sinoatrial node, atrioventricular node, and His-Purkinje system. Genetic variations and loss of desmin drive a variety of conditions, so-called desminopathies, which include desmin-related cardiomyopathy, conduction system-related atrial and ventricular arrhythmias, and sudden cardiac death. The severe cardiac disease outcomes emphasize the clinical need to understand the molecular and cellular role of desmin driving desminopathies. As the role of desmin in cardiomyopathies has been discussed thoroughly, the current review is focused on the role of desmin impairment as a trigger for cardiac arrhythmias. Here, the molecular and cellular mechanisms of desmin to underlie a healthy cardiac conduction system and how impaired desmin triggers cardiac arrhythmias, including atrial fibrillation, are discussed. Furthermore, an overview of available (genetic) desmin model systems for experimental cardiac arrhythmia studies is provided. Finally, potential implications for future clinical treatments of cardiac arrhythmias directed at desmin are highlighted.

Diagnosis and Management of Rare Cardiomyopathies in Adult and Paediatric Patients. A Position Paper of the Italian Society of Cardiology (SIC) and Italian Society of Paediatric Cardiology (SICP)

Cardiomyopathies (CMPs) are myocardial diseases in which the heart muscle is structurally and functionally abnormal in the absence of coronary artery disease, hypertension, valvular disease and congenital heart disease sufficient to cause the observed myocardial abnormality. Thought for a long time to be rare diseases, it is now clear that most of the CMPs can be easily observed in clinical practice. However, there is a group of specific heart muscle diseases that are rare in nature whose clinical/echocardiographic phenotypes resemble those of the four classical morphological subgroups of hypertrophic, dilated, restrictive, arrhythmogenic CMPs. These rare CMPs, often but not solely diagnosed in infants and paediatric patients, should be more properly labelled as specific CMPs. Emerging consensus exists that these conditions require tailored investigation and management. Indeed, an appropriate understanding of these conditions is mandatory for early treatment and counselling. At present, however, the multisystemic and heterogeneous presentation of these entities is a challenge for clinicians, and time delay in diagnosis is a significant concern. The aim of this paper is to define practical recommendations for diagnosis and management of the rare CMPs in paediatric or adult age. A modified Delphi method was adopted to grade the recommendations proposed by each member of the writing committee.

A Case Report of a Rare Heterozygous Variant in the Desmin Gene Associated With Hypertrophic Cardiomyopathy and Complete Atrioventricular Block

Hypertrophic cardiomyopathy (HCM) is the primary cause of sudden cardiac death in children and adolescents. Patients with HCM frequently have ventricular tachycardia and ventricular fibrillation, although complete atrioventricular block (CAVB) is very rare. We report a case of HCM with CAVB in an 8-year-old girl who underwent transvenous implantable cardioverter-defibrillator placement after resuscitation. In this patient, we identified a de novo heterozygous missense variant, Arg406Trp (c.1216C > T), in the desmin (DES) gene. Pathogenic variants in the DES gene result in cardiomyopathy, conduction disorders, and skeletal muscle weakness. This recently identified variant may cause HCM with CAVB.

The Desmin Mutation DES-c.735G>C Causes Severe Restrictive Cardiomyopathy by Inducing In-Frame Skipping of Exon-3

Currently, little is known about the genetic background of restrictive cardiomyopathy (RCM). Herein, we screened an index patient with RCM in combination with atrial fibrillation using a next generation sequencing (NGS) approach and identified the heterozygous mutation DES-c.735G>C. As DES-c.735G>C affects the last base pair of exon-3, it is unknown whether putative missense or splice site mutations are caused. Therefore, we applied nanopore amplicon sequencing revealing the expression of a transcript without exon-3 in the explanted myocardial tissue of the index patient. Western blot analysis verified this finding at the protein level. In addition, we performed cell culture experiments revealing an abnormal cytoplasmic aggregation of the truncated desmin form (p.D214-E245del) but not of the missense variant (p.E245D). In conclusion, we show that DES-c.735G>C causes a splicing defect leading to exon-3 skipping of the DES gene. DES-c.735G>C can be classified as a pathogenic mutation associated with RCM and atrial fibrillation. In the future, this finding might have relevance for the genetic understanding of similar cases.

Expanding Spectrum of Desmin-Related Myopathy, Long-term Follow-up, and Cardiac Transplantation

OBJECTIVE

We aimed to determine the genetic and clinical phenotypes of desmin-related myopathy patients and long-term outcomes after cardiac transplant.

METHODS

Retrospective review of cardiac and neurological manifestations of genetically confirmed desmin-related myopathy patients (Jan 1^st, 1999-Jan 1^st, 2020).

RESULTS

Twenty-five patients in 20 different families were recognized. Median age at onset of symptoms was 20 years (range: 4-50), median follow-up time of 36 months (range: 1-156). Twelve patients initially presented with skeletal muscle involvement and 13 with cardiac disease. Sixteen patients had both cardiac and skeletal muscle involvement. Clinically muscle weakness distribution was distal (n=11), proximal (n=4) or both (n=7) of 22 patients. Skeletal muscle biopsy from patients with missense and splice site variants (n=12) showed abnormal fibers containing amorphous material in Gomori trichrome stained sections. Patients with cardiac involvement had atrioventricular conduction abnormalities or cardiomyopathy. The most common ECG abnormality was complete AV block in 11 patients all of whom required a permanent pacemaker at a median age of 25 years (range: 16-48). Sudden cardiac death resulting in implantable cardioverter defibrillator (ICD) shocks or resuscitation were reported in 3 patients, a total of 5 patients had ICDs. Orthotopic cardiac transplantation was performed in 3 patients at 20, 35 and 39 years of age.

CONCLUSIONS

Pathogenic variants in desmin can lead to varied neurological and cardiac phenotypes beginning at a young age. Two-thirds of the patients have both neurologic and cardiac symptoms usually starting in the third decade. Heart transplant was tolerated with improved cardiac function and quality of life.

Skeletal and Cardiac Muscle Disorders Caused by Mutations in Genes Encoding Intermediate Filament Proteins

Intermediate filaments are major components of the cytoskeleton. Desmin and synemin, cytoplasmic intermediate filament proteins and A-type lamins, nuclear intermediate filament proteins, play key roles in skeletal and cardiac muscle. Desmin, encoded by the DES gene (OMIM *125660) and A-type lamins by the LMNA gene (OMIM *150330), have been involved in striated muscle disorders. Diseases include desmin-related myopathy and cardiomyopathy (desminopathy), which can be manifested with dilated, restrictive, hypertrophic, arrhythmogenic, or even left ventricular non-compaction cardiomyopathy, Emery–Dreifuss Muscular Dystrophy (EDMD2 and EDMD3, due to LMNA mutations), LMNA-related congenital Muscular Dystrophy (L-CMD) and LMNA-linked dilated cardiomyopathy with conduction system defects (CMD1A). Recently, mutations in synemin (SYNM gene, OMIM *606087) have been linked to cardiomyopathy. This review will summarize clinical and molecular aspects of desmin-, lamin- and synemin-related striated muscle disorders with focus on LMNA and DES-associated clinical entities and will suggest pathogenetic hypotheses based on the interplay of desmin and lamin A/C. In healthy muscle, such interplay is responsible for the involvement of this network in mechanosignaling, nuclear positioning and mitochondrial homeostasis, while in disease it is disturbed, leading to myocyte death and activation of inflammation and the associated secretome alterations.

Pediatric Restrictive Cardiomyopathies

Restrictive cardiomyopathy (RCM) is the least frequent phenotype among pediatric heart muscle diseases, representing only 2.5-3% of all cardiomyopathies diagnosed during childhood. Pediatric RCM has a poor prognosis, high incidence of pulmonary hypertension (PH), thromboembolic events, and sudden death, is less amenable to medical or surgical treatment with high mortality rates. In this scenario, heart transplantation remains the only successful therapeutic option. Despite a shared hemodynamic profile, characterized by severe diastolic dysfunction and restrictive ventricular filling, with normal ventricle ejection fraction and wall thickness, RCM recognizes a broad etiological spectrum, consisting of genetic/familial and acquired causes, each of which has a distinct pathophysiology and natural course. Hence, the aim of this review is to cover the causes, clinical presentation, diagnostic evaluation, treatment, and prognosis of pediatric RCM.

Dual Functional States of R406W-Desmin Assembly Complexes Cause Cardiomyopathy With Severe Intercalated Disc Derangement in Humans and in Knock-In Mice

BACKGROUND

Mutations in the human desmin gene cause myopathies and cardiomyopathies. This study aimed to elucidate molecular mechanisms initiated by the heterozygous R406W-desmin mutation in the development of a severe and early-onset cardiac phenotype.

METHODS

We report an adolescent patient who underwent cardiac transplantation as a result of restrictive cardiomyopathy caused by a heterozygous R406W-desmin mutation. Sections of the explanted heart were analyzed with antibodies specific to 406W-desmin and to intercalated disc proteins. Effects of the R406W mutation on the molecular properties of desmin were addressed by cell transfection and in vitro assembly experiments. To prove the genuine deleterious effect of the mutation on heart tissue, we further generated and analyzed R405W-desmin knock-in mice harboring the orthologous form of the human R406W-desmin.

RESULTS

Microscopic analysis of the explanted heart revealed desmin aggregates and the absence of desmin filaments at intercalated discs. Structural changes within intercalated discs were revealed by the abnormal organization of desmoplakin, plectin, N-cadherin, and connexin-43. Next-generation sequencing confirmed the DES variant c.1216C>T (p.R406W) as the sole disease-causing mutation. Cell transfection studies disclosed a dual behavior of R406W-desmin with both its integration into the endogenous intermediate filament system and segregation into protein aggregates. In vitro, R406W-desmin formed unusually thick filaments that organized into complex filament aggregates and fibrillar sheets. In contrast, assembly of equimolar mixtures of mutant and wild-type desmin generated chimeric filaments of seemingly normal morphology but with occasional prominent irregularities. Heterozygous and homozygous R405W-desmin knock-in mice develop both a myopathy and a cardiomyopathy. In particular, the main histopathologic results from the patient are recapitulated in the hearts from R405W-desmin knock-in mice of both genotypes. Moreover, whereas heterozygous knock-in mice have a normal life span, homozygous animals die at 3 months of age because of a smooth muscle-related gastrointestinal phenotype.

CONCLUSIONS

We demonstrate that R406W-desmin provokes its severe cardiotoxic potential by a novel pathomechanism, where the concurrent dual functional states of mutant desmin assembly complexes underlie the uncoupling of desmin filaments from intercalated discs and their structural disorganization.

Desmin-related myopathy characterized by non-compaction cardiomyopathy, cardiac conduction defect, and coronary artery dissection

Desmin‐related myopathy (DRM) is a rare heritable cardiac and skeletal muscle disease caused by mutations in the desmin gene (DES). DRM is generally characterized by skeletal muscle weakness, conduction disturbance, and dilated cardiomyopathy. However, the clinical cardiac phenotypes of DRM are not yet fully understood. Herein, we report the first case of DRM with the de novo missense DES mutation, R454W, that is characterized by left ventricular non‐compaction cardiomyopathy, progressive cardiac conduction defect, spontaneous coronary artery dissection, and no skeletal muscle weakness. Our case findings suggest that clinicians should genetically test patients who have cardiomyopathy, progressive cardiac conduction defect, and coronary artery dissection, even if the patient has neither family history of DRM nor skeletal muscle symptoms.

TRPV2 channel as a possible drug target for the treatment of heart failure

Heart transplantation is currently the only viable option available for the treatment of severe heart failure conditions such as dilated cardiomyopathy. Hence, novel drugs for treating such conditions need to be developed urgently. Recent studies suggest that Ca²⁺ overload is involved in the onset and progression of dilated cardiomyopathy, and thus heart failure. The expression and activation of the Ca²⁺ permeable channel, transient receptor potential vanilloid 2 (TRPV2) channel have been found to play an essential role in sustained intracellular Ca²⁺ concentration increase, leading to heart failure. However, since there have been no TRPV2-specific inhibitors available until recently, the effect of TRPV2 inhibition on the pathology has not been clearly elucidated. Recent reports show that inhibiting TRPV2 activity effectively improves cardiac function, suppressing myocardial fibrosis and ameliorating the prognosis in animal models of cardiomyopathy with heart failure. In addition to that, inflammation is reported to be involved in the development of heart failure. Here, we review the recent findings on TRPV2 in cardiomyocytes and immune cells involved in the development of heart failure and discuss the current progress of drug development for the treatment of heart failure via targeting TRPV2.

A different background of arrhythmia in siblings with a positive family history of sudden death at young age

We present two symptomatic sisters who had a positive family history of sudden death. None of them had structural heart disease. In the 25‐year‐old proband, complex ventricular arrhythmia, cardiac conduction system disease, and skeletal muscle weakness were found. Genetic examination showed a pathogenic intronic variant in the desmin gene in the proband only. In the elder sister with palpitations, complex ventricular arrhythmia (>46 000 ectopic beats) was removed by radiofrequency ablation. This family case shows that complex ventricular arrhythmia may have different background within one family, genetic examinations should be performed in a person with broadest spectrum of symptoms.

A novel phenotype with splicing mutation identified in a Chinese family with desminopathy

BACKGROUND

Desminopathy, a hereditary myofibrillar myopathy, mainly results from the desmin gene (DES) mutations. Desminopathy involves various phenotypes, mainly including different cardiomyopathies, skeletal myopathy, and arrhythmia. Combined with genotype, it helps us precisely diagnose and treat for desminopathy.

METHODS

Sanger sequencing was used to characterize DES variation, and then a minigene assay was used to verify the effect of splice-site mutation on pre-mRNA splicing. Phenotypes were analyzed based on clinical characteristics associated with desminopathy.

RESULTS

A splicing mutation (c.735+1G>T) in DES was detected in the proband. A minigene assay revealed skipping of the whole exon 3 and transcription of abnormal pre-mRNA lacking 32 codons. Another affected family member who carried the identical mutation, was identified with a novel phenotype of desminopathy, non-compaction of ventricular myocardium. There were 2 different phenotypes varied in cardiomyopathy and skeletal myopathy among the 2 patients, but no significant correlation between genotype and phenotype was identified.

CONCLUSIONS

We reported a novel phenotype with a splicing mutation in DES, enlarging the spectrum of phenotype in desminopathy. Molecular studies of desminopathy should promote our understanding of its pathogenesis and provide a precise molecular diagnosis of this disorder, facilitating clinical prevention and treatment at an early stage.

Molecular insights into cardiomyopathies associated with desmin (DES) mutations

Increasing usage of next-generation sequencing techniques pushed during the last decade cardiogenetic diagnostics leading to the identification of a huge number of genetic variants in about 170 genes associated with cardiomyopathies, channelopathies, or syndromes with cardiac involvement. Because of the biochemical and cellular complexity, it is challenging to understand the clinical meaning or even the relevant pathomechanisms of the majority of genetic sequence variants. However, detailed knowledge about the associated molecular pathomechanism is essential for the development of efficient therapeutic strategies in future and genetic counseling. Mutations in DES, encoding the muscle-specific intermediate filament protein desmin, have been identified in different kinds of cardiac and skeletal myopathies. Here, we review the functions of desmin in health and disease with a focus on cardiomyopathies. In addition, we will summarize the genetic and clinical literature about DES mutations and will explain relevant cell and animal models. Moreover, we discuss upcoming perspectives and consequences of novel experimental approaches like genome editing technology, which might open a novel research field contributing to the development of efficient and mutation-specific treatment options.

Myofibrillar Myopathies: New Perspectives from Animal Models to Potential Therapeutic Approaches

Myofibrillar myopathies (MFMs) are muscular disorders involving proteins that play a role in the structure, maintenance processes and protein quality control mechanisms closely related to the Z-disc in the muscular fibers. MFMs share common histological characteristics including progressive disorganization of the interfibrillar network and protein aggregation. Currently no treatment is available. In this review, we describe first clinical symptoms associated with mutations of the six genes (DES, CRYAB, MYOT, ZASP, FLNC and BAG3) primary involved in MFM and defining the origin of this pathology. As mechanisms determining the aetiology of the disease remain unclear yet, several research teams have developed animal models from invertebrates to mammalians species. Thus we describe here these different models that often recapitulate human clinical symptoms. Therefore they are very useful for deeper studies to understand early molecular and progressive mechanisms determining the pathology. Finally in the last part, we emphasize on the potential therapeutic approaches for MFM that could be conducted in the future. In conclusion, this review offers a link from patients to future therapy through the use of MFMs animal models.

Functional characterization of a GFAP variant of uncertain significance in an Alexander disease case within the setting of an individualized medicine clinic

A de novo GFAP variant, p.R376W, was identified in a child presenting with hypotonia, developmental delay, and abnormal brain MRI. Following the 2015 ACMG variant classification guidelines and the functional studies showing protein aggregate formation in vitro, p.R376W should be classified as a pathogenic variant, causative for Alexander disease.

Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Afford New Opportunities in Inherited Cardiovascular Disease Modeling

Fundamental studies of molecular and cellular mechanisms of cardiovascular disease pathogenesis are required to create more effective and safer methods of their therapy. The studies can be carried out only when model systems that fully recapitulate pathological phenotype seen in patients are used. Application of laboratory animals for cardiovascular disease modeling is limited because of physiological differences with humans. Since discovery of induced pluripotency generating induced pluripotent stem cells has become a breakthrough technology in human disease modeling. In this review, we discuss a progress that has been made in modeling inherited arrhythmias and cardiomyopathies, studying molecular mechanisms of the diseases, and searching for and testing drug compounds using patient-specific induced pluripotent stem cell-derived cardiomyocytes.

Unusual multisystemic involvement and a novel BAG3 mutation revealed by NGS screening in a large cohort of myofibrillar myopathies

Background

Myofibrillar myopathies (MFM) are a group of phenotypically and genetically heterogeneous neuromuscular disorders, which are characterized by protein aggregations in muscle fibres and can be associated with multisystemic involvement.

Methods

We screened a large cohort of 38 index patients with MFM for mutations in the nine thus far known causative genes using Sanger and next generation sequencing (NGS). We studied the clinical and histopathological characteristics in 38 index patients and five additional relatives (n = 43) and particularly focused on the associated multisystemic symptoms.

Results

We identified 14 heterozygous mutations (diagnostic yield of 37%), among them the novel p.Pro209Gln mutation in the BAG3 gene, which was associated with onset in adulthood, a mild phenotype and an axonal sensorimotor polyneuropathy, in the absence of giant axons at the nerve biopsy. We revealed several novel clinical phenotypes and unusual multisystemic presentations with previously described mutations: hearing impairment with a FLNC mutation, dysphonia with a mutation in DES and the first patient with a FLNC mutation presenting respiratory insufficiency as the initial symptom. Moreover, we described for the first time respiratory insufficiency occurring in a patient with the p.Gly154Ser mutation in CRYAB. Interestingly, we detected a polyneuropathy in 28% of the MFM patients, including a BAG3 and a MYOT case, and hearing impairment in 13%, including one patient with a FLNC mutation and two with mutations in the DES gene. In four index patients with a mutation in one of the MFM genes, typical histological findings were only identified at the ultrastructural level (29%).

Conclusions

We conclude that extraskeletal symptoms frequently occur in MFM, particularly cardiac and respiratory involvement, polyneuropathy and/or deafness. BAG3 mutations should be considered even in cases with a mild phenotype or an adult onset. We identified a genetic defect in one of the known genes in less than half of the MFM patients, indicating that more causative genes are still to be found. Next generation sequencing techniques should be helpful in achieving this aim.

Myofibrillar myopathies: new developments

PURPOSE OF REVIEW

Myofibrillar myopathies (MFMs) are a heterogeneous group of skeletal and cardiac muscle diseases. In this review, we highlight recent discoveries of new genes and disease mechanisms involved in this group of disorders.

RECENT FINDINGS

The advent of next-generation sequencing technology, laser microdissection and mass spectrometry-based proteomics has facilitated the discovery of new MFM causative genes and pathomechanisms. New mutations have also been discovered in 'older' genes, helping to find a classification niche for MFM-linked disorders showing variant phenotypes. Cell transfection experiments using primary cultured myoblasts and newer animal models provide insights into the pathogenesis of MFMs.

SUMMARY

An increasing number of genes are involved in the causation of variant subtypes of MFM. The application of modern technologies in combination with classical histopathological and ultrastructural studies is helping to establish the molecular diagnosis and reach a better understanding of the pathogenic mechanisms of each MFM subtype, thus putting an emphasis on the development of specific means for prevention and therapy of these incapacitating and frequently fatal diseases.

Distal myopathies

The distal myopathies are a heterogeneous group of genetic disorders defined by a predominant distal weakness at onset or throughout the evolution of the disease and by pathological data supporting a myopathic process. The number of genes associated with distal myopathies continues to increase. Fourteen distinct distal myopathies are currently defined by their gene and causative mutations, compared to just five entities delineated on clinical grounds two decades ago. The known proteins affected in the distal myopathies are of many types and include a significant number of sarcomeric proteins. The useful indicators for clinicians to direct towards a correct molecular diagnosis are the mode of inheritance, the age at onset, the pattern of muscle involvement, the serum creatine kinase level and the muscle pathology findings. This review gives an overview of the clinical and genetic characteristics of the currently identified distal myopathies with emphasis on some recent findings.

Compound heterozygosity of predicted loss-of-function DES variants in a family with recessive desminopathy

Background

Variants in the desmin gene (DES) are associated with desminopathy; a myofibrillar myopathy mainly characterized by muscle weakness, conduction block, and dilated cardiomyopathy. To date, only ~50 disease-associated variants have been described, and the majority of these lead to dominant-negative effects. However, the complete genotypic spectrum of desminopathy is not well established.

Case presentation

Next-generation sequencing was performed on 51 cardiac disease genes in a proband with profound skeletal myopathy, dilated cardiomyopathy, and respiratory dysfunction. Our analyses revealed compound heterozygous DES variants, both of which are predicted to lead to a loss-of-function. Consistent with recessive inheritance, each variant was identified in an unaffected parent.

Conclusions

This case report serves to broaden the variant spectrum of desminopathies and provides insight into the molecular mechanisms of desminopathy, supporting distinct dominant-negative and loss-of-function etiologies.

Patient-specific induced-pluripotent stem cells-derived cardiomyocytes recapitulate the pathogenic phenotypes of dilated cardiomyopathy due to a novel DES mutation identified by whole exome sequencing

In this paper, we report a novel heterozygous mutation of A285V codon conversion on exon 4 of the desmin (DES), using whole exome sequencing (WES) in an isolated proband with documented dilated cardiomyopathy (DCM). This mutation is predicted to cause three-dimensional structure changes of DES. Immunohistological and electron microscopy studies demonstrated diffuse abnormal DES aggregations in DCM-induced-pluripotent stem cell (iPSC)-derived cardiomyocytes, and control-iPSC-derived cardiomyocytes transduced with A285V-DES. DCM-iPSC-derived cardiomyocytes also exhibited functional abnormalities in vitro. This is the first demonstration that patient-specific iPSC-derived cardiomyocytes can be used to provide histological and functional confirmation of a suspected genetic basis for DCM identified by WES.

Desminopathies: pathology and mechanisms

The intermediate filament protein desmin is an essential component of the extra-sarcomeric cytoskeleton in muscle cells. This three-dimensional filamentous framework exerts central roles in the structural and functional alignment and anchorage of myofibrils, the positioning of cell organelles and signaling events. Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive, and sporadic myopathies and/or cardiomyopathies with marked phenotypic variability. The disease onset ranges from childhood to late adulthood. The clinical course is progressive and no specific treatment is currently available for this severely disabling disease. The muscle pathology is characterized by desmin-positive protein aggregates and degenerative changes of the myofibrillar apparatus. The molecular pathophysiology of desminopathies is a complex, multilevel issue. In addition to direct effects on the formation and maintenance of the extra-sarcomeric intermediate filament network, mutant desmin affects essential protein interactions, cell signaling cascades, mitochondrial functions, and protein quality control mechanisms. This review summarizes the currently available data on the epidemiology, clinical phenotypes, myopathology, and genetics of desminopathies. In addition, this work provides an overview on the expression, filament formation processes, biomechanical properties, post-translational modifications, interaction partners, subcellular localization, and functions of wild-type and mutant desmin as well as desmin-related cell and animal models.