X-linked Dilated Cardiomyopathy Research Articles

The Development of Robust Antibodies to Sarcospan, a Dystrophin- and Integrin-Associated Protein, for Basic and Translational Research.

Sarcospan (SSPN) is a 25-kDa transmembrane protein that is broadly expressed at the cell surface of many tissues, including, but not limited to, the myofibers from skeletal and smooth muscles, cardiomyocytes, adipocytes, kidney epithelial cells, and neurons. SSPN is a core component of the dystrophin-glycoprotein complex (DGC) that links the intracellular actin cytoskeleton with the extracellular matrix. It is also associated with integrin α7β1, the predominant integrin expressed in skeletal muscle. As a tetraspanin-like protein with four transmembrane spanning domains, SSPN functions as a scaffold to facilitate protein-protein interactions at the cell membrane. Duchenne muscular dystrophy, Becker muscular dystrophy, and X-linked dilated cardiomyopathy are caused by the loss of dystrophin at the muscle cell surface and a concomitant loss of the entire DGC, including SSPN. SSPN overexpression ameliorates Duchenne muscular dystrophy in the mdx murine model, which supports SSPN being a viable therapeutic target. Other rescue studies support SSPN as a biomarker for the proper assembly and membrane expression of the DGC. Highly specific and robust antibodies to SSPN are needed for basic research on the molecular mechanisms of SSPN rescue, pre-clinical studies, and biomarker evaluations in human samples. The development of SSPN antibodies is challenged by the presence of its four transmembrane domains and limited antigenic epitopes. To address the significant barrier presented by limited commercially available antibodies, we aimed to generate a panel of robust SSPN-specific antibodies that can serve as a resource for the research community. We created antibodies to three SSPN protein epitopes, including the intracellular N- and C-termini as well as the large extracellular loop (LEL) between transmembrane domains 3 and 4. We developed a panel of rabbit antibodies (poly- and monoclonal) against an N-terminal peptide fragment of SSPN. We used several assays to show that the rabbit antibodies recognize mouse SSPN with a high functional affinity and specificity. We developed mouse monoclonal antibodies against the C-terminal peptide and the large extracellular loop of human SSPN. These antibodies are superior to commercially available antibodies and outperform them in various applications, including immunoblotting, indirect immunofluorescence analysis, immunoprecipitation, and an ELISA. These newly developed antibodies will significantly improve the quality and ease of SSPN detection for basic and translational research.

Chinese guidelines on the diagnosis of dystrophinopathy

Dystrophinopathy refers to a group of X-linked recessive myopathies that primarily affect skeletal and/or cardiac muscle caused by pathogenic variants in the dystrophin-encoding DMD gene, including Duchenne muscular dystrophy, Becker muscular dystrophy, and X-linked dilated cardiomyopathy. The broad and complex spectrum of pathogenic DMD variants complicates the diagnosis and clinical classification in some patients. The precise genetic diagnosis is of great significance for the clinical diagnosis and treatment, multidisciplinary management, genetic counseling, prenatal diagnosis, and selection of gene therapy in dystrophinopathy. The present guideline is primarily based on the research advances in dystrophinopathy. Meanwhile, the foreign and domestic clinical guidelines or consensus for dystrophinopathy were referenced to put forward 18 recommendations and reach a consensus on the clinical manifestations, genetic basis, clinical diagnosis and classification, genetic diagnosis, and clinical genetic counseling of dystrophinopathy. This guideline aims to standardize and optimize the diagnostic process and reduce the diagnostic difficulty of patients with dystrophinopathy. In addition, this guideline provides some practical reference for clinicians and government staff.

DMD deletions underlining mild dystrophinopathies: literature review highlights phenotype-related mutation clusters and provides insights about genetic mechanisms and prognosis.

DMD gene pathogenic variations cause a spectrum of phenotypes, ranging from severe Duchenne muscular dystrophy, the Becker milder cases, the intermediate or very mild muscle phenotypes invariably characterized by high CK, and the ultrarare fully-asymptomatic cases. Besides these phenotypes, X-linked dilated cardiomyopathy is also caused by DMD mutations. Males carrying DMD deletions with absent or very mild phenotypes have been sparsely described. We performed a horizon scan on public datasets to enroll males with the above phenotypes and carrying DMD deletions to delineate myopathic genotype-phenotype relationships. We inventoried 81 males, who were divided into the following clinical categorization: fully-asymptomatic males aged >43 years (A, N = 22); isolated hyperCKemia (CK, N = 35); and mild weakness (any age) with or without high CK (WCK, N = 24). In all cases, deleted intervals were exons 2 to 55, and no downstream exons were ever involved, apart from an exon 78 deletion in a WCK patient. All deletions were in-frame apart from the known exception to the rule of exon 2 and exon 78. We correlated the mild phenotypes (A and CK) to deleted exons, intronic breakpoints, exon-exon junctions, 3' isoforms rule, and protein epitopes, and we found that some genetic profiles are exclusively/mainly occurring in A/CK phenotypes, suggesting they are compatible with a quasi-normal muscular performance. We discussed diverse pathogenic mechanisms that may contribute to mild dystrophinopathic phenotypes, and we tried to address some "critical" genetic configurations or exon content needed to preserve a semi-functional DMD gene.

Drug-refractory Heart Failure in Female Carrier of Duchenne Muscular Dystrophy: A Case of X-linked Dilated Cardiomyopathy.

A 56-year-old woman was referred to our hospital for the further evaluation of drug-refractory heart failure with a reduced ejection fraction. A family history interview revealed that men in her family had died of Duchenne muscular dystrophy (DMD), whereas she had no skeletal muscle disorder. Myocardial histopathology revealed a reduced dystrophin expression in the cardiomyocyte membrane, and a dystrophin (DMD) gene analysis identified a duplication in exon 8-9 on Xp21, suggesting that she had a cardiac-specific phenotype of dystrophinopathy, i.e. X-linked dilated cardiomyopathy (XLDCM). In conclusion, careful family history interviews and an investigation of dystrophinopathy are required to detect XLDCM in women.

Clinical, muscle imaging, and genetic characteristics of dystrophinopathies with deep-intronic DMD variants.

Phenotypic heterogeneity within or between families with a same deep-intronic splice-altering variant in the DMD gene has never been systematically analyzed. This study aimed to determine the phenotypic and genetic characteristics of patients with deep-intronic DMD variants. Of 1338 male patients with a suspected dystrophinopathy, 38 were confirmed to have atypical pathogenic DMD variants via our comprehensive genetic testing approach. Of the 38 patients, 30 patients from 22 unrelated families with deep-intronic DMD variants underwent a detailed clinical and imaging assessment. Nineteen different deep-intronic DMD variants were identified in the 30 patients, including 15 with Duchenne muscular dystrophy (DMD), 14 with Becker muscular dystrophy (BMD), and one with X-linked dilated cardiomyopathy. Of the 19 variants, 15 were single-nucleotide variants, 2 were structural variants (SVs), and 2 were pure-intronic large-scale SVs causing aberrant inclusion of other protein-coding genes sequences into the mature DMD transcripts. The trefoil with single fruit sign was observed in 18 patients and the concentric fatty infiltration pattern was observed in 2 patients. Remarkable phenotypic heterogeneity was observed not only in skeletal but also cardiac muscle involvement in 2 families harboring a same deep-intronic variant. Different skeletal muscle involvement between families with a same variant was observed in 4 families. High inter-individual phenotypic heterogeneity was observed within two BMD families and one DMD family. Our study first highlights the variable phenotypic expressivity of deep-intronic DMD variants and demonstrates a new class of deep-intronic DMD variants, i.e., pure-intronic SVs involving other protein-coding genes.

A Novel Variant and a Missense Variant Identified in the DKC1 Gene in Three Chinese Familieswith Dyskeratosis Congenita.

PurposeDyskeratosis congenita (DC) is an inherited telomere biology disorder characterized clinically by mucocutaneous triad of reticulate hyperpigmentation, nail changes and oral leukoplakia. Bone marrow failure, pulmonary fibrosis and malignancies are the mainly life-threatening causes. There are X-linked recessive, autosomal dominant and autosomal recessive patterns of DC. DKC1 is the most common pathogenic mutation gene responsible for X-linked DC, and it encodes a protein, dyskerin, which is a component of telomerase holoenzyme complex essential for telomere maintenance. Patients with DC have very short telomeres, but the precise pathogenic mechanism remains unclear. This study aimed to identify the causative mutations in the DKC1 gene in three Chinese families with the X-linked form of DC.Patients and MethodsThree Chinese families with DC were included in this study. Whole exome sequencing and Sanger sequencing were performed to clarify the mutation of DKC1 gene. Measurement of relative telomere length through qPCR. Predictions of protein structure and function were performed using bioinformatics tools, including I-TASSER, Polyphen-2 and SIFT.ResultsThere were four males with DC and a female carrier in three Chinese pedigrees. The novel mutation c.92A>C (p. Q31P) and the missense mutation c.1058C>T (p. A353V) in DKC1 were identified. Both mutations locally changed the structure of dyskerin. Variant Q31P and A353V were predicted to have “deleterious” and “natural” effects on the function of dyskerin, respectively.ConclusionThe novel variant and missense variant detected in the DKC1 gene improve our understanding of DC and broaden the mutation spectrum of the DKC1 gene.

Generation of genomic-integration-free human induced pluripotent stem cells and the derived cardiomyocytes of X-linked dilated cardiomyopathy from DMD gene mutation

We derived an integration-free induced pluripotent stem cell (iPSC) line from the peripheral blood mononuclear cells (PBMCs) of a 23-year-old male patient. This patient carries a 5' splice site point mutation in intron 1 (c.31+1G>A) of the dystrophin gene, a mutation associated with X-linked dilated cardiomyopathy (XLDCM). Sendai virus was used to reprogram the PBMCs and deliver OCT3/4, SOX2, c-MYC, and KLF4 factors. The iPSC line (HKUi002-A) generated preserved the mutation, expressed common pluripotency markers, differentiated into three germ layers in vivo, and exhibited a normal karyotype. Further differentiation into cardiomyocytes enables the study of the disease mechanisms of XLDCM.

DMD – ANIMAL MODELS & PRECLINICAL TREATMENT: P.204 Patient-derived induced pluripotent stem cells differentiated cardiomyocytes as platform for disease modelling For X-linked dilated cardiomyopathy

X-linked dilated cardiomyopathy (XLDCM) is a serious condition caused by abnormalities in the DMD gene (dystrophin gene). The affected patients did not have major skeletal weakness but presented with early signs of heart failure, and deteriorated quickly despite medical treatment resulting in early death. Currently there is no curative treatment and heart transplantation is often required. We study the pathomechanism of the DMD-associated XLDCM with mutation in the first exon-intron boundary, through examination of dystrophin isoforms expression and the functional characterization of the manifested cardiomyocytes generated from patient-derived induced pluripotent stem cells (IPSCs) compared to normal control.

Interventions for preventing and treating cardiac complications in Duchenne and Becker muscular dystrophy and X-linked dilated cardiomyopathy.

Interventions for preventing and treating cardiac complications in Duchenne and Becker muscular dystrophy and X-linked dilated cardiomyopathy.

DUCHENNE MUSCULAR DYSTROPHY - GENETICS: P.212Mutational spectrum of the DMD gene in pediatric patients from an Argentinian referral center

Dystrophinopathies are a group of X-linked recessive neuromuscular disorders caused by mutations in DMD gene, which include Duchenne muscular dystrophy (DMD), Becker muscular dystrophy, X-linked dilated cardiomyopathy and mild forms of the disease. Large deletions and duplications account for 70% of the mutations while small mutations are found in the remaining 30% of the patients. Molecular diagnosis is important since it has implications in disease prognosis, genetic counselling and treatment options. In this study, we describe the mutation spectrum in DMD gene in patients from a Paediatric Reference Hospital in Argentina. A total of 344 unrelated patients (336 males/8 females) were studied by MLPA technique. Sequencing of DMD gene by Sanger or next generation sequencing was performed in 66 patients with negative MLPA, clinical and muscle biopsy compatible with dystrophinopathies. Molecular diagnosis was achieved in 276 (80.23%) of the cases. Overall, large deletions were found in 178 (65%) of the patients with positive results, followed by point mutations (22%) and large duplications (11%). Six patients showed contiguous gene deletion (2%). Point mutations identified in 62 patients were distributed as follows: 28 nonsense mutations, 19 small out of frame deletions, 8 splice site mutations, 3 small out of frame duplications, 2 missense mutations, 1 in frame deletion and 1 insertion. Genotype-phenotype analysis revealed exceptions to the reading frame rule in 10.1% of the cases. The highest percentage of this exception was due to in frame mutations that result in DMD phenotype caused by mutations that encompassed the actin binding domain and part of the rod domain. In conclusion, the diagnostic algorithm used in the present study was accurate for the molecular diagnosis of dystrophinopathies; in addition, this study provides data about phenotype characteristics and genetic profile in paediatric patients in our country.

X-Linked Dilated Cardiomyopathy Presenting as Acute Rhabdomyolysis and Presumed Epstein-Barr Virus-Induced Viral Myocarditis: A Case Report

Patient: Male, 23Final Diagnosis: Primary X-linked dilated cardiomyopathySymptoms: RhabdomyolysisMedication: —Clinical Procedure: —Specialty: General and Intrenal MedicineObjective:Rare co-existance of disease or pathologyBackground:Rhabdomyolysis and primary dilated cardiomyopathies without skeletal muscle weakness are rare features of X-linked dystrophinopathies. We report a rare case of an X-linked dilated cardiomyopathy (XLDCM) presenting with acute rhabdomyolysis and myocarditis. We illustrate the confounding diagnostic influence of a reactivated, persistent EBV myocarditis as the presumed cause for this patient’s XLDCM.Case Report:A 23-year-old Australian man presented with acute rhabdomyolysis and elevated creatine kinase (CK) levels. He was managed conservatively with intravenous hydration and developed acute pulmonary edema. Cardiac MRI and transthoracic echocardiogram revealed a dilated cardiomyopathy and viral myocarditis. Extensive serological investigations identified reactivation of EBV, which was presumed to account for his viral myocarditis. The patient recovered and was discharged with down-trending CK levels. Follow-up transthoracic echocardiograms and cardiac MRI showed a persisting dilated cardiomyopathy. His CK continued to remain elevated and his EBV IgM serology remained positive. An inflammatory polymyositis with either a primary autoimmune pathophysiology or secondary to a chronic EBV infection was considered. Oral corticosteroids were trialed and reduced his CK significantly until therapy was ceased. Massively parallel sequencing eventually identified a two-exon deletion targeting Xp21 consistent with the diagnosis of a rare XLDCM.Conclusions:Rhabdomyolysis and co-existing primary dilated cardiomyopathies are rare diagnostic manifestations in a minority of X-linked dystrophinopathies. Chronic viral infections and their reactivation may complicate the diagnostic process and incorrectly attribute an inherited cardiomyopathy to an acquired infective etiology. EBV reactivation rarely induces myocarditis. Therefore, primary and unresolving dilated cardiomyopathy with persistently elevated CK must prompt consideration of an underlying dystrophinopathy.

A novel DMD splicing mutation found in a family responsible for X-linked dilated cardiomyopathy with hyper-CKemia.

This study was aimed to detect a new mutation responsible for X-linked dilated cardiomyopathy with hyper-CKemia.We studied a proband who presented with cardiac symptoms with hyper-CKemia, but no clinical skeletal involvement in physical examination, laboratory tests, electromyography, echocardiography, and magnetic resonance imaging (MRI) of cardiac muscles. Muscle biopsy for histopathology and immunohistochemistry for accessing sarcolemma changes. The next-generation sequencing and bioinformatics analysis were performed on the patient and Sanger sequencing was confirmed on the other 6 unaffected families.The clinic investigations illustrated a dilated cardiomyopathy. Histopathology and immunohistochemistry showed dystrophic changes and an obvious reduction of dystrophin-N and δ-sarcoglycan, respectively. One hemizygous splicing pathogenic mutation c.31 + 1G > C of exon 1 in the DMD gene (chrX33229398, NM_00 4006) was finally identified in the patient and his nephew, but it was carried in his mother and sister.A novel small mutation was identified at the first exon-intron boundary splicing site by next-generation sequencing and bioinformatics analysis.

Cardiac Involvement in Duchenne Muscular Dystrophy and Related Dystrophinopathies.

Dystrophinopathies include Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy (XLCM), and facioscapulohumeral muscular dystrophy (FSHD). DMD/BMD are X-linked recessive disorders, related to the synthesis of dystrophin. Most of DMD after the third decade of their age develop cardiomyopathy that remains silent, due to relative physical inactivity. Cardiac disease in female carriers presents with hypertrophy, arrhythmias or dilated cardiomyopathy, clinically overt by increasing age.In ECG, DMD presents increased R/S ratio in the right precordial leads, deep Q waves in the lateral leads, conduction abnormalities, and arrhythmias. Echocardiography, although widely available and inexpensive, is highly depended on the acoustic window and operator's experience. Tissue Doppler can be used to identify early changes of cardiomyopathy and detect progressive cardiac damage. CMR, a noninvasive, nonradiating technique, by evaluation of cardiac volumes, mass, ejection fraction, inflammation, and fibrosis, is ideal for early diagnosis. Subepicardial fibrosis in the inferolateral wall is the typical CMR lesion in DMD/BMD.Early initiation of angiotensin converting enzyme inhibitors (ACEI) treatment, such as perindopril, was associated with lower mortality in DMD with normal LV ejection fraction at study entry. Other studies documented that a beta-blocker (BB), in addition to ACEI, improves LV systolic function in MD. These encouraging results recommend initiation of ACEI and/or BB early after diagnosis of the muscular dystrophy, especially in DMD.

Dystrophic Cardiomyopathy: Complex Pathobiological Processes to Generate Clinical Phenotype

Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and X-linked dilated cardiomyopathy (XL-DCM) consist of a unique clinical entity, the dystrophinopathies, which are due to variable mutations in the dystrophin gene. Dilated cardiomyopathy (DCM) is a common complication of dystrophinopathies, but the onset, progression, and severity of heart disease differ among these subgroups. Extensive molecular genetic studies have been conducted to assess genotype-phenotype correlation in DMD, BMD, and XL-DCM to understand the underlying mechanisms of these diseases, but the results are not always conclusive, suggesting the involvement of complex multi-layers of pathological processes that generate the final clinical phenotype. Dystrophin protein is a part of dystrophin-glycoprotein complex (DGC) that is localized in skeletal muscles, myocardium, smooth muscles, and neuronal tissues. Diversity of cardiac phenotype in dystrophinopathies suggests multiple layers of pathogenetic mechanisms in forming dystrophic cardiomyopathy. In this review article, we review the complex molecular interactions involving the pathogenesis of dystrophic cardiomyopathy, including primary gene mutations and loss of structural integrity, secondary cellular responses, and certain epigenetic and other factors that modulate gene expressions. Involvement of epigenetic gene regulation appears to lead to specific cardiac phenotypes in dystrophic hearts.

X-linked Dilated Cardiomyopathy with Mutation in the 5′ Splice Site Intron 1 of Dystrophin Gene with Utrophin Upregulation

AbstractWe report a teenage boy presented with dilated cardiomyopathy (DCM) with no initial skeletal involvement and initial normal creatine kinases. One year after the heart transplantation, he had exercise-induced transient muscle weakness with elevated creatine kinases (CKs). Muscle biopsy showed normal structures and normal dystrophin immunohistochemical labeling, but utrophin, which is an autosomal homologue of dystrophin, was overexpressed at sarcolemma. Sanger sequencing confirmed a heterozygous c.31 + 1G > A, 5′ splice site point mutation at the first intron of dystrophin gene. A review of previous reports of patients with different point mutations in the same region, the first exon–intron boundary that involved the muscle promotor to exon 1, confirmed a high correlation of cardiospecific phenotype sparing the muscles with this specific site of mutations. The confirmation of upregulation of brain and Purkinje isoforms of dystrophin protein in the skeletal muscles but not in the heart in past studies help to explain the skeletal sparing presentation. X-linked DCM (XLDCM) is an important cause of isolated cardiomyopathy. Routine immunohistochemical staining study including dystrophin in cardiac muscle biopsy, and dystrophin and utrophin labelling on skeletal muscle biopsy for patients with subsequent muscle symptoms or raised creatine kinases, help in the early diagnosis of the XLDCM. Future experimental study to determine the aberrant pre-mRNA splicing of this specific splice site mutation involving exon 1 and intron 1 will help to understand better the underlying complex mechanism of the splicing regulation.

Heart transplantation in patients with dystrophinopathic cardiomyopathy: Review of the literature and personal series.

Cardiomyopathy associated with dystrophinopathies [Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy (XL-dCM) and cardiomyopathy of Duchenne/Becker (DMD/BMD) carriers] is an increasing recognized manifestation of these neuromuscular disorders and notably contributes to their morbidity and mortality. Dystrophinopathic cardiomyopathy (DCM) is the result of the dystrophin protein deficiency at the myocardium level, parallel to the deficiency occurring at the skeletal muscle level. It begins as a "presymptomatic" stage in the first decade of life and evolves in a stepwise manner toward pictures of overt cardiomyopathy (hypertrophic stage, arrhythmogenic stage and dilated cardiomyopathy). The final stage caused by the extensive loss of cardiomyocytes results in an irreversible cardiac failure, characterized by frequent episodes of acute congestive heart failure (CHF), despite a correct pharmacological treatment. The picture of a severe dilated cardiomyopathy with intractable heart failure is typical of BMD, XL-dCM and cardiomyopathy of DMD/BMD carriers, while it is less frequently observed in patients with DMD. Heart transplantation (HT) is the only curative therapy for patients with dystrophinopathic end-stage heart failure who remain symptomatic despite an optimal medical therapy. However, no definitive figures exist in literature concerning the number of patients with DCM transplanted, and their outcome. This overview is to summarize the clinical outcomes so far published on the topic, to report the personal series of dystrophinopathic patients receiving heart transplantation and finally to provide evidence that heart transplantation is a safe and effective treatment for selected patients with end-stage DCM.

AB046. X-linked dilated cardiomyopathy: the dystrophinopathy in a Thai family

Background Idiopathic dilated cardiomyopathy generally presents with congestive heart failure secondary to an increase in ventricular size and impairment of ventricular function. It is one of the leading causes of cardiovascular morbidity and mortality. Most cases have been considered to be sporadic, but recent studies have demonstrated that up to 20% of cases may be inherited, suggesting a strong genetic component for this group of diseases. Inheritance patterns vary and may be X-linked, autosomal dominant, or autosomal recessive. Dystrophin gene defect is one of the known causes of the X-linked dilated cardiomyopathy (XLDCM).

X-Linked Dilated Cardiomyopathy: A Cardiospecific Phenotype of Dystrophinopathy.

X-linked dilated cardiomyopathy (XLDCM) is a distinct phenotype of dystrophinopathy characterized by preferential cardiac involvement without any overt skeletal myopathy. XLDCM is caused by mutations of the Duchenne muscular dystrophy (DMD) gene and results in lethal heart failure in individuals between 10 and 20 years. Patients with Becker muscular dystrophy, an allelic disorder, have a milder phenotype of skeletal muscle involvement compared to Duchenne muscular dystrophy (DMD) and sometimes present with dilated cardiomyopathy. The precise relationship between mutations in the DMD gene and cardiomyopathy remain unclear. However, some hypothetical mechanisms are being considered to be associated with the presence of some several dystrophin isoforms, certain reported mutations, and an unknown dystrophin-related pathophysiological mechanism. Recent therapy for Duchenne muscular dystrophy, the severe dystrophinopathy phenotype, appears promising, but the presence of XLDCM highlights the importance of focusing on cardiomyopathy while elucidating the pathomechanism and developing treatment.

Missense mutation Lys18Asn in dystrophin that triggers X-linked dilated cardiomyopathy decreases protein stability, increases protein unfolding, and perturbs protein structure, but does not affect protein function.

Genetic mutations in a vital muscle protein dystrophin trigger X-linked dilated cardiomyopathy (XLDCM). However, disease mechanisms at the fundamental protein level are not understood. Such molecular knowledge is essential for developing therapies for XLDCM. Our main objective is to understand the effect of disease-causing mutations on the structure and function of dystrophin. This study is on a missense mutation K18N. The K18N mutation occurs in the N-terminal actin binding domain (N-ABD). We created and expressed the wild-type (WT) N-ABD and its K18N mutant, and purified to homogeneity. Reversible folding experiments demonstrated that both mutant and WT did not aggregate upon refolding. Mutation did not affect the protein's overall secondary structure, as indicated by no changes in circular dichroism of the protein. However, the mutant is thermodynamically less stable than the WT (denaturant melts), and unfolds faster than the WT (stopped-flow kinetics). Despite having global secondary structure similar to that of the WT, mutant showed significant local structural changes at many amino acids when compared with the WT (heteronuclear NMR experiments). These structural changes indicate that the effect of mutation is propagated over long distances in the protein structure. Contrary to these structural and stability changes, the mutant had no significant effect on the actin-binding function as evident from co-sedimentation and depolymerization assays. These results summarize that the K18N mutation decreases thermodynamic stability, accelerates unfolding, perturbs protein structure, but does not affect the function. Therefore, K18N is a stability defect rather than a functional defect. Decrease in stability and increase in unfolding decrease the net population of dystrophin molecules available for function, which might trigger XLDCM. Consistently, XLDCM patients have decreased levels of dystrophin in cardiac muscle.

G.P.142: A new EMD gene missense mutation in exon 1 leads to absence of emerin and is responsible for X-linked dilated cardiomyopathy with conduction defects and arrhythmias and almost elusive skeletal muscle features

Mutations in the EMD gene, encoding emerin, lead to X-linked Emery-Dreifuss muscular dystrophy (EDMD). Although always associated with EDMD, an almost exclusive cardiac involvement was found in exceptional patients carrying EMD gene mutations. We here report 2 brothers belonging to a family where 9 affected male subjects developed dilated cardiomyopathy (DCM) with conduction defects and arrhythmias. The oldest brother of 53years developed DCM since 49years and requiring implantable cardioverter defibrillator (ICD) implantation. He subsequently developed atrio-ventricular and ventricular conduction defects as well as ventricular arrhythmias at 52years that required ICD upgrading and additional pacemaker implantation. His youngest brother aged 45years was also affected. The family history showed several affected members: a third brother who died after cardiac transplantation at 38years, a fourth brother who died suddenly at 50years, two maternal uncles and cousins died in their 5th or 6th decades among them 2 were diagnosed as arrhythmogenic right ventricular dysplasia. An X-linked mode of inheritance was therefore suspected and DMD gene analysis did not show any exonic deletion or duplication or exon 1 point mutation. Further neurological assessment of the oldest brother showed neither muscle weakness nor joint contractures whereas hands and legs were slightly hypotrophic. CPK were at normal level and needle electromyography examination showed normal pattern. Deltoid muscle biopsy was normal as were protein immunohistochemical studies including dystrophin, desmin, myotilin and caveolin 3 while emerin staining was totally absent. Subsequent EMD gene analysis revealed a new missense mutation in exon 1 (c.65C>T, p.Pro22Leu). In addition to the 2 previously reported families with a close emerin mutation (p.delK37) and an exclusive cardiac disease, our family further indicates that emerin protein is crucial for correct cardiac function.