Apical left ventricular aneurysm without atrio-ventricular block due to a lamin A/C gene mutation

The LMNA p.R541C mutation causes dilated cardiomyopathy in human and mice

Dilated cardiomyopathy (DCM) is a major cause of heart failure. LMNA variants contribute to 6-10% DCM cases, but the underlying mechanisms remain incompletely understood. Here, we reported two patients carrying the LMNA c.1621C > T/ p.R541C variant and generated a knock-in mouse model (Lmna^RC) to study the role of this variant in DCM pathogenesis. We found Lmna^RC/RC mice exhibited ventricular dilation and reduced systolic functions at 6 months after birth. The Lmna^RC/RC cardiomyocytes increased in size but no nuclear morphology defects were detected. Transcriptomic and microscopic analyses revealed suppressed gene expression and perturbed ultrastructure in Lmna^RC/RC mitochondria. These defects were associated with increased heterochromatin structures and epigenetic markers including H3K9me2/3. Together, these data implied that the LMNA c.1621C > T/ p.R541C variant enhanced heterochromatic gene suppression and disrupted mitochondria functions as a cause of DCM.

Clinical and Genomic Evaluation of 207 Genetic Myopathies in the Indian Subcontinent

Objective: Inherited myopathies comprise more than 200 different individually rare disease-subtypes, but when combined together they have a high prevalence of 1 in 6,000 individuals across the world. Our goal was to determine for the first time the clinical- and gene-variant spectrum of genetic myopathies in a substantial cohort study of the Indian subcontinent.

Methods: In this cohort study, we performed the first large clinical exome sequencing (ES) study with phenotype correlation on 207 clinically well-characterized inherited myopathy-suspected patients from the Indian subcontinent with diverse ethnicities.

Results: Clinical-correlation driven definitive molecular diagnosis was established in 49% (101 cases; 95% CI, 42–56%) of patients with the major contributing pathogenicity in either of three genes, GNE (28%; GNE-myopathy), DYSF (25%; Dysferlinopathy), and CAPN3 (19%; Calpainopathy). We identified 65 variant alleles comprising 37 unique variants in these three major genes. Seventy-eight percent of the DYSF patients were homozygous for the detected pathogenic variant, suggesting the need for carrier-testing for autosomal-recessive disorders like Dysferlinopathy that are common in India. We describe the observed clinical spectrum of myopathies including uncommon and rare subtypes in India: Sarcoglycanopathies (SGCA/B/D/G), Collagenopathy (COL6A1/2/3), Anoctaminopathy (ANO5), telethoninopathy (TCAP), Pompe-disease (GAA), Myoadenylate-deaminase-deficiency-myopathy (AMPD1), myotilinopathy (MYOT), laminopathy (LMNA), HSP40-proteinopathy (DNAJB6), Emery-Dreifuss-muscular-dystrophy (EMD), Filaminopathy (FLNC), TRIM32-proteinopathy (TRIM32), POMT1-proteinopathy (POMT1), and Merosin-deficiency-congenital-muscular-dystrophy-type-1 (LAMA2). Thirteen patients harbored pathogenic variants in >1 gene and had unusual clinical features suggesting a possible role of synergistic-heterozygosity/digenic-contribution to disease presentation and progression.

Conclusions: Application of clinically correlated ES to myopathy diagnosis has improved our understanding of the clinical and genetic spectrum of different subtypes and their overlaps in Indian patients. This, in turn, will enhance the global gene-variant-disease databases by including data from developing countries/continents for more efficient clinically driven molecular diagnostics.

Genotype-phenotype correlation of LMNA variants involving the Arg541 residue: a case report with multimodality imaging and literature review

We present a case of atypical LMNA cardiomyopathy associated with the pathogenic variant p.Arg541Ser. The patient had early-onset severe ventricular arrhythmias but atrioventricular conduction was normal. Segmental motion abnormalities and a large transmural scar, mainly apical and lateral, were found at cardiac magnetic resonance, corresponding to areas of severe wall thinning at computed tomography and of low voltages at electroanatomic mapping. Ventricular tachycardia ablation was successful in controlling ventricular arrhythmias. Few other cases described patients with pathogenic variants in the Arg541 residue, and they displayed similar atypical features, suggesting a genotype-phenotype correlation which may have specific prognostic and therapeutic implications.

Case series: LMNA-related dilated cardiomyopathy presents with reginal wall akinesis and transmural late gadolinium enhancement

Patients with LMNA mutation‐related heart disease are characterized by conduction abnormalities, ventricular tachyarrhythmias, and high risk of sudden cardiac death with mildly impaired systolic function, often without chamber dilation. Here, we presented three unrelated cases with LMNA mutation exhibited unusual cardiac phenotype of marked LV dilation, significant reduced ejection fraction with reginal wall akinesis, and transmural enhancement with a predilection of lateral wall on cardiovascular magnetic resonance (CMR). These three patients were found to have confirmed pathological LMNA mutations (c.1621C > T, p.R541C and c.1621G > A, p.R541H) at the same location (p.R541) in the tail region of lamin A/C.

Can Circulating Cardiac Biomarkers Be Helpful in the Assessment of LMNA Mutation Carriers?

Mutations in the lamin A/C gene are variably phenotypically expressed; however, it is unclear whether circulating cardiac biomarkers are helpful in the detection and risk assessment of cardiolaminopathies. We sought to assess (1) clinical characteristics including serum biomarkers: high sensitivity troponin T (hsTnT) and N-terminal prohormone brain natriuretic peptide (NT-proBNP) in clinically stable cardiolaminopathy patients, and (2) outcome among pathogenic/likely pathogenic lamin A/C gene (LMNA) mutation carriers. Our single-centre cohort included 53 patients from 21 families. Clinical, laboratory, follow-up data were analysed. Median follow-up was 1522 days. The earliest abnormality, emerging in the second and third decades of life, was elevated hsTnT (in 12% and in 27% of patients, respectively), followed by the presence of atrioventricular block, heart failure, and malignant ventricular arrhythmia (MVA). In patients with missense vs. other mutations, we found no difference in MVA occurrence and, surprisingly, worse transplant-free survival. Increased levels of both hsTnT and NT-proBNP were strongly associated with MVA occurrence (HR > 13, p ≤ 0.02 in both) in univariable analysis. In multivariable analysis, NT-proBNP level > 150 pg/mL was the only independent indicator of MVA. We conclude that assessment of circulating cardiac biomarkers may help in the detection and risk assessment of cardiolaminopathies.

Cardiomyopathy in Children: Classification and Diagnosis: A Scientific Statement From the American Heart Association

In this scientific statement from the American Heart Association, experts in the field of cardiomyopathy (heart muscle disease) in children address 2 issues: the most current understanding of the causes of cardiomyopathy in children and the optimal approaches to diagnosis cardiomyopathy in children. Cardiomyopathies result in some of the worst pediatric cardiology outcomes; nearly 40% of children who present with symptomatic cardiomyopathy undergo a heart transplantation or die within the first 2 years after diagnosis. The percentage of children with cardiomyopathy who underwent a heart transplantation has not declined over the past 10 years, and cardiomyopathy remains the leading cause of transplantation for children >1 year of age. Studies from the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry have shown that causes are established in very few children with cardiomyopathy, yet genetic causes are likely to be present in most. The incidence of pediatric cardiomyopathy is ≈1 per 100 000 children. This is comparable to the incidence of such childhood cancers as lymphoma, Wilms tumor, and neuroblastoma. However, the published research and scientific conferences focused on pediatric cardiomyopathy are sparcer than for those cancers. The aim of the statement is to focus on the diagnosis and classification of cardiomyopathy. We anticipate that this report will help shape the future research priorities in this set of diseases to achieve earlier diagnosis, improved clinical outcomes, and better quality of life for these children and their families.

Risk stratification in laminopathies and Emery Dreifuss muscular dystrophy

Laminopathies are genetic disorders due to gene mutation encoding for proteins of the nuclear envelope. Patients are at risk of conduction defect, arrhythmia, sudden death and heart failure. The authors summarize predictive factors for cardiac events reported in the literature in this group of disease.

The expression of Lamin A mutant R321X leads to endoplasmic reticulum stress with aberrant Ca2+ handling

Mutations in the Lamin A/C gene (LMNA), which encodes A‐type nuclear Lamins, represent the most frequent genetic cause of dilated cardiomyopathy (DCM). This study is focused on a LMNA nonsense mutation (R321X) identified in several members of an Italian family that produces a truncated protein isoform, which co‐segregates with a severe form of cardiomyopathy with poor prognosis. However, no molecular mechanisms other than nonsense mediated decay of the messenger and possible haploinsufficiency were proposed to explain DCM. Aim of this study was to gain more insights into the disease‐causing mechanisms induced by the expression of R321X at cellular level. We detected the expression of R321X by Western blotting from whole lysate of a mutation carrier heart biopsy. When expressed in HEK293 cells, GFP‐ (or mCherry)‐tagged R321X mislocalized in the endoplasmic reticulum (ER) inducing the PERK‐CHOP axis of the ER stress response. Of note, confocal microscopy showed phosphorylation of PERK in sections of the mutation carrier heart biopsy. ER mislocalization of mCherry‐R321X also induced impaired ER Ca²⁺ handling, reduced capacitative Ca²⁺ entry at the plasma membrane and abnormal nuclear Ca²⁺ dynamics. In addition, expression of R321X by itself increased the apoptosis rate. In conclusion, R321X is the first LMNA mutant identified to date, which mislocalizes into the ER affecting cellular homeostasis mechanisms not strictly related to nuclear functions.

What Should the Cardiologist know about Lamin Disease?

Lamins are intermediate filament proteins able to polymerise and form an organised meshwork underlying the inner nuclear membrane in most differentiated somatic cells. Mutations in the LMNA gene, which encodes the two major lamin A and C isoforms, cause a diverse range of diseases, called laminopathies, including dilated cardiomyopathy, associated with a poor prognosis and high rate of sudden death due to conduction defect and early ventricular arrhythmia. Identification of mutations in LMNA gene in clinical practice is rapidly increasing, as well as comprehensive cardiac and genetic family screening. As a consequence, cardiologists are more and more frequently faced to difficult questions regarding optimal management of patients and relatives, especially timing for prophylactic cardioverter defibrillator. This review focuses on recent data useful for the clinician, as well as therapeutic perspectives both in human and animal models.

Clinical and functional characterization of a novel mutation in lamin a/c gene in a multigenerational family with arrhythmogenic cardiac laminopathy

Mutations in the lamin A/C gene (LMNA) were associated with dilated cardiomyopathy (DCM) and, recently, were related to severe forms of arrhythmogenic right ventricular cardiomyopathy (ARVC). Both genetic and phenotypic overlap between DCM and ARVC was observed; molecular pathomechanisms leading to the cardiac phenotypes caused by LMNA mutations are not yet fully elucidated. This study involved a large Italian family, spanning 4 generations, with arrhythmogenic cardiomyopathy of different phenotypes, including ARVC, DCM, system conduction defects, ventricular arrhythmias, and sudden cardiac death. Mutation screening of LMNA and ARVC-related genes PKP2, DSP, DSG2, DSC2, JUP, and CTNNA3 was performed. We identified a novel heterozygous mutation (c.418_438dup) in LMNA gene exon 2, occurring in a highly conserved protein domain across several species. This newly identified variant was not found in 250 ethnically-matched control subjects. Genotype-phenotype correlation studies suggested a co-segregation of the LMNA mutation with the disease phenotype and an incomplete and age-related penetrance. Based on clinical, pedigree, and molecular genetic data, this mutation was considered likely disease-causing. To clarify its potential pathophysiologic impact, functional characterization of this LMNA mutant was performed in cultured cardiomyocytes expressing EGFP-tagged wild-type and mutated LMNA constructs, and indicated an increased nuclear envelope fragility, leading to stress-induced apoptosis as the main pathogenetic mechanism. This study further expands the role of the LMNA gene in the pathogenesis of cardiac laminopathies, suggesting that LMNA should be included in mutation screening of patients with suspected arrhythmogenic cardiomyopathy, particularly when they have ECG evidence for conduction defects. The combination of clinical, genetic, and functional data contribute insights into the pathogenesis of this form of life-threatening arrhythmogenic cardiac laminopathy.

A novel mutation in lamin a/c causing familial dilated cardiomyopathy associated with sudden cardiac death

BACKGROUND

Dilated cardiomyopathy (DCM), a cardiac heterogeneous pathology characterized by left ventricular or biventricular dilatation, is a leading cause of heart failure and heart transplantation. The genetic origin of DCM remains unknown in most cases, but >50 genes have been associated with DCM. We sought to identify the genetic implication and perform a genetic analysis in a Spanish family affected by DCM and sudden cardiac death.

METHODS AND RESULTS

Clinical assessment and genetic screening were performed in the index case as well as family members. Of all relatives clinically assessed, nine patients showed clinical symptoms related to the pathology. Genetic screening identified 20 family members who carried a novel mutation in LMNA (c.871 G>A, p.E291K). Family segregation analysis indicated that all clinically affected patients carried this novel mutation. Clinical assessment of genetic carriers showed that electrical dysfunction was present previous to mechanical and structural abnormalities.

CONCLUSIONS

Our results report a novel pathogenic mutation associated with DCM, supporting the benefits of comprehensive genetic studies of families affected by this pathology.

'State-of-the-heart' of cardiac laminopathies

PURPOSE OF REVIEW

LMNA gene encodes the nuclear A-type lamins. LMNA mutations are associated with more than 10 clinical entities and represent one of the first causes of inherited dilated cardiomyopathy. LMNA-dilated cardiomyopathy is associated with conduction disease (DCM-CD) and is a severe and aggressive form of DCM. However, pathogenesis remains largely unknown and no specific treatment is currently available for the patients. In this review, we present recent discoveries that improve the understanding of the cardiac pathophysiological roles of A-type lamins and shed light on potential therapeutic targets.

RECENT FINDINGS

In the last decade, many efforts have been made to elucidate how mutations in A-type lamins, ubiquitous proteins, lead to DCM-CD. No clear genotype/phenotype correlations have been found to help in elucidating those mechanisms. Analysis of several mouse models has helped in deciphering critical pathomechanisms. Among those, Mitogen-activated protein kinases (MAPK) and Akt/mTOR appear to be key early-activated signaling pathways in LMNA DCM-CD in both humans and mice. Inhibition of these signaling pathways has shown encouraging beneficial effects upon cardiac evolution of DCM-CD.

SUMMARY

These recent findings suggest that targeting MAPK and Akt/mTOR pathways with potent and specific compounds represents a promising intervention for the treatment of LMNA DCM-CD.

Genetic and clinical characteristics of skeletal and cardiac muscle in patients with lamin A/C gene mutations

Alterations of the lamin A/C (LMNA) gene are associated with different clinical entities, including disorders that affect skeletal and cardiac muscle, peripheral nerves, metabolism, bones, and disorders that cause premature aging. In this article we review the clinical and genetic characteristics of cardiac and skeletal muscle diseases related to alterations in the LMNA gene. There is no single explanation of how LMNA gene alterations may cause these disorders; however, important goals have been achieved in understanding the pathogenic effects of LMNA gene mutations on cardiac and skeletal muscle.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a progressive muscle-wasting disorder defined by early contractures of the Achilles tendon, spine, and elbows. EDMD is also distinctive for its association with defects of the cardiac conduction system that can result in sudden death. It can be inherited in an X-linked, autosomal dominant, or autosomal recessive fashion and is caused by mutations in proteins of the nuclear membrane. Mutations in the EMD gene, which encodes emerin, a transmembrane protein found at the inner nuclear membrane, are responsible for X-linked EDMD. The most common etiology of autosomal dominant EDMD is an LMNA gene mutation; LMNA encodes the intermediate filament protein lamins A and C, which constitute the major scaffolding protein of the inner nuclear membrane. Murine models of LMNA gene mutations have helped to identify different mechanisms of disease. Loss of LMNA function leads to nuclear fragility as well as other defects, such as abnormal nuclear function. Additional genes encoding nuclear membrane proteins such as SYNE1 and SYNE2 have also been implicated in EDMD, and in some cases their importance for cardiac and muscle function has been supported by animal modeling.

Left ventricular aneurysm in patients with idiopathic dilated cardiomyopathy: clinical analysis of six cases

Background. Left ventricular aneurysm (LVA) in patients with idiopathic dilated cardiomyopathy (IDCM) is rarely reported, and the incidence, pathogenesis and clinical features of LVA in IDCM are poorly understood.Methods. The diagnosis of IDCM with LVA formation was made in six patients between January 2003 and September 2008. Left ventriculography, coronary angiography, echocardiogram and electrocardiogram were performed in all patients. The hospital records of these patients with IDCM in our hospital and related literature were reviewed.Results. LVA was located at the posterobasal wall in five patients and at the anterolateral wall in one patient. Two patients had abnormal Q waves and no patients had sustained ST-segment elevation on electrocardiogram. No significant coronary stenosis or mural thrombi was detected in these patients. All patients had severe ventricular arrhythmia, such as frequent multifocal ventricular premature contractions and ventricular tachycardia.Conclusion. IDCM could be a rare cause of LVA. The LVA in IDCM was mainly located at the posterobasal wall. It was seldom accompanied by abnormal Q waves and sustained ST-segment elevation. The pathogenesis of LVA in IDCM seems to be less likely to be related to coronary emboli. Ventricular arrhythmia occurred frequently in these patients. (Neth Heart J 2009;17:475-80.).

Adult stem cell maintenance and tissue regeneration in the ageing context: the role for A-type lamins as intrinsic modulators of ageing in adult stem cells and their niches

Adult stem cells have been identified in most mammalian tissues of the adult body and are known to support the continuous repair and regeneration of tissues. A generalized decline in tissue regenerative responses associated with age is believed to result from a depletion and/or a loss of function of adult stem cells, which itself may be a driving cause of many age-related disease pathologies. Here we review the striking similarities between tissue phenotypes seen in many degenerative conditions associated with old age and those reported in age-related nuclear envelope disorders caused by mutations in the LMNA gene. The concept is beginning to emerge that nuclear filament proteins, A-type lamins, may act as signalling receptors in the nucleus required for receiving and/or transducing upstream cytosolic signals in a number of pathways central to adult stem cell maintenance as well as adaptive responses to stress. We propose that during ageing and in diseases caused by lamin A mutations, dysfunction of the A-type lamin stress-resistant signalling network in adult stem cells, their progenitors and/or stem cell niches leads to a loss of protection against growth-related stress. This in turn triggers an inappropriate activation or a complete failure of self-renewal pathways with the consequent initiation of stress-induced senescence. As such, A-type lamins should be regarded as intrinsic modulators of ageing within adult stem cells and their niches that are essential for survival to old age.

Long-term outcome and risk stratification in dilated cardiolaminopathies

OBJECTIVES

The aim of this study was to analyze the long-term follow-up of dilated cardiolaminopathies.

BACKGROUND

Lamin A/C (LMNA) gene mutations cause a variety of phenotypes. In the cardiology setting, patients diagnosed with idiopathic dilated cardiomyopathy (DCM) plus atrioventricular block (AVB) constitute the majority of reported cases.

METHODS

Longitudinal retrospective observational studies were conducted with 27 consecutive families in which LMNA gene defects were identified in the probands, all sharing the DCM phenotype.

RESULTS

Of the 164 family members, 94 had LMNA gene mutations. Sixty of 94 (64%) were phenotypically affected whereas 34 were only genotypically affected, including 5 with pre-clinical signs. Of the 60 patients, 40 had DCM with AVB, 12 had DCM with ventricular tachycardia/fibrillation, 6 had DCM with AVB and Emery-Dreifuss muscular dystrophy type 2 (EDMD2), and 2 had AVB plus EDMD2. During a median of 57 months (interquartile range 36 to 107 months), we observed 49 events in 43 DCM patients (6 had a later event, excluded from the analysis). The events were related to heart failure (15 heart transplants, 1 death from end-stage heart failure) and ventricular arrhythmias (15 sudden cardiac deaths and 12 appropriate implantable cardioverter-defibrillator interventions). By multivariable analysis, New York Heart Association functional class III to IV and highly dynamic competitive sports for >or=10 years were independent predictors of total events. By a bivariable Cox model, splice site mutations and competitive sport predicted sudden cardiac death.

CONCLUSIONS

Dilated cardiomyopathies caused by LMNA gene defects are highly penetrant, adult onset, malignant diseases characterized by a high rate of heart failure and life-threatening arrhythmias, predicted by New York Heart Association functional class, competitive sport activity, and type of mutation.

Genetic heterogeneity of left-ventricular noncompaction cardiomyopathy

Isolated noncompaction of the ventricular myocardium (INVM) sometimes referred to as spongy myocardium is a rare, congenital and also acquired cardiomyopathy. It appears to divide the presentation into neonatal, childhood and adult forms of which spongy myocardium and systolic dysfunction is the commonality. The disorder is characterized by a left ventricular hypertrophy with deep trabeculations, and with diminished systolic function, with or without associated left ventricular dilation. In half or more of the cases, the right ventricle is also affected. The sporadic type, however, in some patients, may be due to chromosomal abnormalities and the occurrence of familial incidence. Isolated noncompaction of the left ventricular myocardium in the majority of adult patients is an autosomal dominant disorder. The familial and X-linked disorders have been described by various authors. We here describe the genetic background of this disorder: some of the most mutated genes that are responsible for the disease are (G4.5 (tafazzin gene): alpha-dystrobrevin gene (DTNA); FKBP-12 gene; lamin A/C gene; Cypher/ZASP (LIM, LDB3) gene); and some genotype-phenotype correlations (Becker muscular dystrophy, Emery-Dreifuss muscular dystrophy or Barth syndrome) based on the literature review.

Left ventricular aneurysm in a patient with mucopolysaccharidosis type VI (Maroteaux–Lamy syndrome): clinical and pathological correlation

A 22-year-old man was diagnosed with mucopolysaccharidosis type VI, also known as Maroteaux-Lamy syndrome, which is a known cause of cardiac valvular disease. He presented with exercise intolerance and was diagnosed with a large, apical, left ventricular aneurysm (LV aneurysm) and subsequently underwent left ventricular aneurysmectomy with improvement in clinical status. Previous echocardiograms revealed that the LV aneurysm was new and is, therefore, likely acquired rather than congenital. Pathology confirmed a true aneurysm, replacement fibrosis, and PAS-positive material in cardiomyocytes. Subsequent echocardiography revealed progression of valvular heart disease with moderate stenosis of the aortic and mitral valves. We propose that altered metabolism of glycosaminoglycans in the extracellular matrix may have contributed to the development of the LV aneurysm in this patient.

Nuclear Lamins: Laminopathies and Their Role in Premature Ageing

It has been demonstrated that nuclear lamins are important proteins in maintaining cellular as well as nuclear integrity, and in maintaining chromatin organization in the nucleus. Moreover, there is growing evidence that lamins play a prominent role in transcriptional control. The family of laminopathies is a fast-growing group of diseases caused by abnormalities in the structure or processing of the lamin A/C ( LMNA) gene. Mutations or incorrect processing cause more than a dozen different inherited diseases, ranging from striated muscular diseases, via fat- and peripheral nerve cell diseases, to progeria. This broad spectrum of diseases can only be explained if the responsible A-type lamin proteins perform multiple functions in normal cells. This review gives an overview of current knowledge on lamin structure and function and all known diseases associated with LMNA abnormalities. Based on the knowledge of the different functions of A-type lamins and associated proteins, explanations for the observed phenotypes are postulated. It is concluded that lamins seem to be key players in, among others, controlling the process of cellular ageing, since disturbance in lamin protein structure gives rise to several forms of premature ageing.

In vivo and in vitro examination of the functional significances of novel lamin gene mutations in heart failure patients

CONTEXT

Lamin A/C (LMNA) gene variations have been reported in more than one third of genotyped families with dilated cardiomyopathy (DCM). However, the relationship between LMNA mutation and the development of DCM is poorly understood.

METHODS AND RESULTS

We found that end stage DCM patients carrying LMNA mutations displayed either dramatic ultrastructural changes of the cardiomyocyte nucleus (D192G) or nonspecific changes (R541S). Overexpression of the D192G lamin C dramatically increased the size of intranuclear speckles and reduced their number. This phenotype was only partially reversed by coexpression of the D192G and wild type lamin C. Moreover, the D192G mutation precludes insertion of lamin C into the nuclear envelope when co-transfected with the D192G lamin A. By contrast, the R541S phenotype was entirely reversed by coexpression of the R541S and wild type lamin C. As lamin speckle size is known to be correlated with regulation of transcription, we assessed the SUMO1 distribution pattern in the presence of mutated lamin C and showed that D192G lamin C expression totally disrupts the SUMO1 pattern.

CONCLUSION

Our in vivo and in vitro results question the relationship of causality between LMNA mutations and the development of heart failure in some DCM patients and therefore, the reliability of genetic counselling. However, LMNA mutations producing speckles result not only in nuclear envelope structural damage, but may also lead to the dysregulation of cellular functions controlled by sumoylation, such as transcription, chromosome organisation, and nuclear trafficking.

Mutation Glu82Lys in lamin A/C gene is associated with cardiomyopathy and conduction defect

Dilated cardiomyopathy is a form of heart muscle disease characterized by impaired systolic function and ventricular dilation. The mutations in lamin A/C gene have been linked to dilated cardiomyopathy. We screened genetic mutations in a large Chinese family of 50 members including members with dilated cardiomyopathy and found a Glu82Lys substitution mutation in the rod domain of the lamin A/C protein in eight family members, three of them have been diagnosed as dilated cardiomyopathy, one presented with heart dilation. The pathogenic mechanism of lamin A/C gene defect is poorly understood. Glu82Lys mutated lamin A/C and wild type protein was transfected into HEK293 cells. The mutated protein was not properly localized at the inner nuclear membrane and the emerin protein, which interacts with lamin A/C, was also aberrantly distributed. The nuclear membrane structure was disrupted and heterochromatin was aggregated aberrantly in the nucleus of the HEK293 cells stably transfected with mutated lamin A/C gene as determined by transmission electron microscopy.

Lamin A/C and cardiac diseases

PURPOSE OF REVIEW

In this review, we will outline the most recent and significant findings on the role of the lamin A/C in cardiac diseases.

RECENT FINDINGS

Mutations in the lamin A/C gene (LMNA) are associated with numerous diseases involving the heart, skeletal muscles, bones, adipose and nervous tissues. LMNA is one of the most prevalent genes in dilated cardiomyopathy in which it is associated with a high risk of dysrhythmias, sudden death and heart failure. Lamins A and C interact with several proteins reflecting their multiple functions, some of which are likely still unknown. No abnormalities specific to dilated cardiomyopathy are emerging from investigations of striated muscles biopsies or fibroblasts from LMNA mutation carriers. An early diagnosis of the disease is difficult. Both animal and cellular models tend to confirm that lamins A and C play a key role in maintaining the nuclear architecture as well as in regulating transcription.

SUMMARY

The cardiac phenotype associated to LMNA mutations is now much clearer, but the molecular mechanisms underlying cellular and tissue specific phenotypes are still puzzling. Systematic mutation screenings and cardioverter-defibrillator implantation have been recommended in patients with cardiac symptoms.

Nuclear envelope, nuclear lamina, and inherited disease

The nuclear envelope is composed of the nuclear membranes, nuclear lamina, and nuclear pore complexes. In recent years, mutations in nuclear-envelope proteins have been shown to cause a surprisingly wide array of inherited diseases. While the mutant proteins are generally expressed in most or all differentiated somatic cells, many mutations cause fairly tissue-specific disorders. Perhaps the most dramatic case is that of mutations in A-type lamins, intermediate filament proteins associated with the inner nuclear membrane. Different mutations in the same lamin proteins have been shown to cause striated muscle diseases, partial lipodystrophy syndromes, a peripheral neuropathy, and disorders with features of severe premature aging. In this review, we summarize fundamental aspects of nuclear envelope structure and function, the inherited diseases caused by mutations in lamins and other nuclear envelope proteins, and possible pathogenic mechanisms.

Meta-analysis of clinical characteristics of 299 carriers of LMNA gene mutations: do lamin A/C mutations portend a high risk of sudden death?

This study evaluated common clinical characteristics of patients with lamin A/C gene mutations that cause either isolated dilated cardiomyopathy or dilated cardiomyopathy in association with skeletal muscular dystrophy. We pooled clinical data of all published carriers of lamin A/C gene mutations as cause of skeletal and/or cardiac muscle disease and reviewed ECG findings. Cardiac dysrhythmias were reported in 92% of patients after the age of 30 years; heart failure was reported in 64% after the age of 50. Sudden death was the most frequently reported mode of death (46%) in both the cardiac and the neuromuscular phenotype. Carriers of lamin A/C gene mutations often received a pacemaker (28%). However, this intervention did not alter the rate of sudden death. Review of the ECG findings typically showed a low amplitude P wave and prolongation of the PR interval with a narrow QRS complex. This meta-analysis suggests that cardiomyopathy due to lamin A/C gene mutations portends a high risk of sudden death, and that this risk does not differ between subjects with predominantly cardiac or neuromuscular disease. This implies then that all carriers of a lamin A/C gene mutation need to be carefully screened with particular emphasis also on tachyarrhythmias. Prospective studies are needed to evaluate risk stratification and proper treatment strategies.

Laminopathies: from the heart of the cell to the clinics

PURPOSE OF REVIEW

This review outlines recent advances in the clinical, genetic and molecular aspects of laminopathies, an expanding group of disorders caused by mutations of the lamin A/C gene.

RECENT FINDINGS

Mutations in lamin A/C were originally described in skeletal and cardiac muscle disorders. It has subsequently been shown that partial lipodystrophy syndromes with or without developmental abnormalities and premature ageing are also associated with lamin A/C alterations. Concomitantly, peripheral nerve involvement with autosomal recessive and dominant inheritance is adding to the picture. The clinical heterogeneity of laminopathies ranges from intrafamilial variability to the description of overlapping phenotypes. A large variability in clinical presentation and the course of cardiomyopathy occurs, including sudden death despite pacemaker implant and embolic stroke in young patients. Similarly, premature ageing syndromes encompass classic and atypical forms of varying severity with the involvement of diverse tissues. In addition, an association of myopathic and neuropathic phenotypes is now emerging.

SUMMARY

Advances in molecular genetics of apparently unrelated disorders, involving muscle, heart, nerve, fat, bone, liver, skin tissues and premature ageing, have enriched our knowledge of the diverse phenotypes associated with lamin A/C mutations. Nevertheless, the understanding of pathogenetic mechanisms still remains speculative. More basic and clinical research is needed in order to identify genes concurring in determining the lamin A/C phenotypes and to envisage proper treatment strategies.