A gene defect that causes conduction system disease and dilated cardiomyopathy maps to chromosome 1p1-1q1

Nuclear envelope lamin-related dilated cardiomyopathy: a case series including histopathology

Background

Lamin A/C gene (LMNA) mutations cause myocardial fibrosis manifesting as arrhythmogenic, non-compaction, or dilated cardiomyopathies. Fibro-fatty replacement largely involves the conduction system and conduction disease commonly occurs prior to contractile dysfunction.

Case summary

Two young, unrelated Caucasian males, aged 34 and 25, were referred to our centre for treatment of advanced heart failure. Both patients had a family history of heart failure and sudden cardiac death among their first-degree relatives and were diagnosed with Lamin A/C mutations, but they had not been screened prior to disease onset. Although the initial phenotypes were dilated cardiomyopathy and left ventricular non-compaction cardiomyopathy, both patients' disease progressed rapidly to include ventricular arrhythmias, severe global left ventricular hypokinesis, and dependence on outpatient milrinone to complete activities of daily living. Both patients received heart transplantation within 2 years of initial disease onset. The surgical pathology of the explanted hearts revealed characteristic findings of fibro-fatty degeneration of the conduction system, and using light microscopy, they were found to have nuclear membrane thinning, bubbling, and convolution throughout all areas sampled.

Discussion

Lamin A/C-related cardiomyopathy is associated with sudden cardiac death early in the disease course, warranting early consideration of implantable cardioverter defibrillator implantation, and rapid progression to end-stage cardiomyopathy refractory to standard medical therapies, necessitating early referral to an advanced heart failure centre. We report a newly observed and recorded finding of morphologic nuclear alterations in late-stage disease using high-power light microscopy. These alterations underscore the pathophysiology of Lamin A/C-related cardiomyopathy and provide a basis for future research into disease-specific therapies.

A very long-term observation of a family with dilated cardiomyopathy and overlapping phenotype from lamin A/C mutation

AIMS

We aim to describe one of the longest longitudinal follow-ups reported so far (>22 years), concerning a whole family affected by a missense lamin A/C mutation (Arg60Gly), which manifested as an overlapping phenotype with cardiac and extracardiac involvement over time.

METHODS

Starting from the family history, two generations of that family were prospectively observed, from 1997 until 2020. At baseline, four individuals with dilated cardiomyopathy and cardiac conduction defects showed the same mutation. This was also found in three young individuals, phenotypically unaffected at baseline assessment.

RESULTS

The prolonged clinical and laboratory evaluation has shown the evolution of an overlapping phenotype in which cardiac alterations have been associated with lipodystrophy and neurological manifestations. In the first observed generation, the prognosis was negatively affected by the progression of heart failure and lipodystrophy, whereas in the second generation the first phenotypic manifestations became evident after the 2nd decade. Cardiac magnetic resonance played a relevant role in the early detection of cardiac alteration. Right bundle branch block was another sign of initial phenotypical expression.

CONCLUSION

In lamin A/C gene mutation carriers, a strict, multidisciplinary follow-up allows the opportunity to monitor the progress of the disease and to intervene precociously with the best available treatments.

Closing the 'phenotype gap' in precision medicine: improving what we measure to understand complex disease mechanisms

The central concept underlying precision medicine is a mechanistic understanding of each disease and its response to therapy sufficient to direct a specific intervention. To execute on this vision requires parsing incompletely defined disease syndromes into discrete mechanistic subsets and developing interventions to precisely address each of these etiologically distinct entities. This will require substantial adjustment of traditional paradigms which have tended to aggregate high-level phenotypes with very different etiologies. In the current environment, where diagnoses are not mechanistic, drug development has become so expensive that it is now impractical to imagine the cost-effective creation of new interventions for many prevalent chronic conditions. The vision of precision medicine also argues for a much more seamless integration of research and development with clinical care, where shared taxonomies will enable every clinical interaction to inform our collective understanding of disease mechanisms and drug responses. Ideally, this would be executed in ways that drive real-time and real-world discovery, innovation, translation, and implementation. Only in oncology, where at least some of the biology is accessible through surgical excision of the diseased tissue or liquid biopsy, has "co-clinical" modeling proven feasible. In most common germline disorders, while genetics often reveal the causal mutations, there still remain substantial barriers to efficient disease modeling. Aggregation of similar disorders under single diagnostic labels has directly contributed to the paucity of etiologic and mechanistic understanding by directly reducing the resolution of any subsequent studies. Existing clinical phenotypes are typically anatomic, physiologic, or histologic, and result in a substantial mismatch in information content between the phenomes in humans or in animal 'models' and the variation in the genome. This lack of one-to-one mapping of discrete mechanisms between disease and animal models causes a failure of translation and is one form of 'phenotype gap.' In this review, we will focus on the origins of the phenotyping deficit and approaches that may be considered to bridge the gap, creating shared taxonomies between human diseases and relevant models, using cardiovascular examples.

Skeletal myopathy in a family with lamin A/C cardiac disease

BACKGROUND

The objective of this study was to evaluate patients with known hereditary cardiac conduction and myocardial disease (HCCMD) caused by a lamin A/C gene mutation for skeletal muscle involvement using magnetic resonance imaging (MRI) computed tomography (CT).

METHODS

Twenty-one patients with the diagnosis of HCCMD were available for study. Of these 21, 11 had MRI scans of the lower legs. The 11 that had an MRI were compared to a control group of 17 healthy controls. In ten patients in whom MRI was contraindicated, CT was used for lower leg imaging and the gastrocnemius muscle was compared to an unaffected muscle.

RESULTS

In patients with severe cardiac involvement defined as conduction system disease requiring pacemaker implant and CT instead of MRI, there was a significant difference in the composition of the unaffected muscle versus the gastrocnemius muscle, P<0.05. In the patients who underwent MRI, there was no statistical significance between the normal population and the study population. However, many study patients' images showed dramatic changes in the gastrocnemius muscle where there was definite replacement of muscle tissue by fibrofatty tissue.

CONCLUSIONS

Our results showed that patients with HCCMD can also present with skeletal muscle problems. The degree of skeletal muscle involvement is greater in HCCMD patients requiring implantable cardiac devices.

Genetic Counseling and Screening Issues in Familial Dilated Cardiomyopathy

Idiopathic dilated cardiomyopathy (IDC), a treatable condition characterized by left ventricular dilatation and systolic dysfunction of unknown cause, has only recently been recognized to have genetic etiologies. Although familial dilated cardiomyopathy (FDC) was thought to be infrequent, it is now believed that 30-50% of cases of IDC may be familial. Echocardiographic and electrocardiographic (ECG) screening of first-degree relatives of individuals with IDC and FDC is indicated because detection and treatment are possible prior to the onset of advanced, symptomatic disease. However, such screening often creates uncertainty and anxiety surrounding the significance of the results. Furthermore, FDC demonstrates incomplete penetrance, variable expression, and significant locus and allelic heterogeneity, making genetic counseling complex. The provision of genetic counseling for IDC and FDC will require collaboration between cardiologists and genetics professionals, and may also improve the recognition of FDC, the availability of support services, and overall outcomes for patients and families.

Disruption of the lamin A and matrin-3 interaction by myopathic LMNA mutations

The nuclear face of the nuclear membrane is enriched with the intermediate filament protein lamin A. Mutations in LMNA, the gene encoding lamin A, lead to a diverse set of inherited conditions including myopathies that affect both the heart and skeletal muscle. To gain insight about lamin A protein interactions, binding proteins associated with the tail of lamin A were characterized. Of 130 nuclear proteins found associated with the lamin A tail, 17 (13%) were previously described lamin A binding partners. One protein not previously linked to lamin A, matrin-3, was selected for further study, because like LMNA mutations, matrin-3 has also been implicated in inherited myopathy. Matrin-3 binds RNA and DNA and is a nucleoplasmic protein originally identified from the insoluble nuclear fraction, referred to as the nuclear matrix. Anti-matrin-3 antibodies were found to co-immunoprecipitate lamin A, and the lamin-A binding domain was mapped to the carboxy-terminal half of matrin-3. Three-dimensional mapping of the lamin A-matrin-3 interface showed that the LMNA truncating mutation Δ303, which lacks the matrin-3 binding domain, was associated with an increased distance between lamin A and matrin-3. LMNA mutant cells are known to have altered biophysical properties and the matrin-3-lamin A interface is positioned to contribute to these defects.

Cell junctions in the specialized conduction system of the heart

Anchoring cell junctions are integral in maintaining electro-mechanical coupling of ventricular working cardiomyocytes; however, their role in cardiomyocytes of the cardiac conduction system (CCS) remains less clear. Recent studies in genetic mouse models and humans highlight the appearance of these cell junctions alongside gap junctions in the CCS and also show that defects in these structures and their components are associated with conduction impairments in the CCS. Here we outline current evidence supporting an integral relationship between anchoring and gap junctions in the CCS. Specifically we focus on (1) molecular and ultrastructural evidence for cell-cell junctions in specialized cardiomyocytes of the CCS, (2) genetic mouse models specifically targeting cell-cell junction components in the heart which exhibit CCS conduction defects and (3) human clinical studies from patients with cell-cell junction-based diseases that exhibit CCS electrophysiological defects.

Genetics of sudden cardiac death in children and young athletes

Sudden cardiac death is a rare but socially devastating event. The most common causes of sudden cardiac death are congenital electrical disorders and structural heart diseases. The majority of these diseases have an incomplete penetrance and variable expression; therefore, patients may be unaware of their illness. In several cases, physical activity can be the trigger for sudden cardiac death as first symptom. Our purpose is to review the causes of sudden cardiac death in sportive children and young adults and its genetic background. Symptomatic individuals often receive an implantable cardioverter-defibrillator, the preventive treatment for sudden cardiac death in most of cases due to channelopathies, which can become a challenging option in young and active patients. The identification of one of these diseases in asymptomatic patients has similarly a great impact on their everyday life, especially on their ability to undertake competitive physical activities, and the requirement of prophylactic treatment. We review main causes of sudden cardiac death in relation to its genetics and diagnostic work-up

Homozygosity mapping and exome sequencing reveal GATAD1 mutation in autosomal recessive dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder that typically exhibits autosomal dominant inheritance. Genomic strategies enable discovery of novel, unsuspected molecular underpinnings of familial DCM. We performed genome-wide mapping and exome sequencing in a unique family wherein DCM segregated as an autosomal recessive (AR) trait.

METHODS AND RESULTS

Echocardiography in 17 adult descendants of first cousins revealed DCM in 2 female siblings and idiopathic left ventricular enlargement in their brother. Genotyping and linkage analysis mapped an AR DCM locus to chromosome arm 7q21, which was validated and refined by high-density homozygosity mapping. Exome sequencing of the affected sisters was then used as a complementary strategy for mutation discovery. An iterative bioinformatics process was used to filter >40,000 genetic variants, revealing a single shared homozygous missense mutation localized to the 7q21 critical region. The mutation, absent in HapMap, 1000 Genomes, and 474 ethnically matched controls, altered a conserved residue of GATAD1, encoding GATA zinc finger domain-containing protein 1. Thirteen relatives were heterozygous mutation carriers with no evidence of myocardial disease, even at advanced ages. Immunohistochemistry demonstrated nuclear localization of GATAD1 in left ventricular myocytes, yet subcellular expression and nuclear morphology were aberrant in the proband.

CONCLUSIONS

Linkage analysis and exome sequencing were used as synergistic genomic strategies to identify GATAD1 as a gene for AR DCM. GATAD1 binds to a histone modification site that regulates gene expression. Consistent with murine DCM caused by genetic disruption of histone deacetylases, the data implicate an inherited basis for epigenetic dysregulation in human heart failure.

Heritable cardiac conduction and myocardial disease: from the clinic to the basic science laboratory and back to the clinic

A close collaboration between the physicians-scientists of the Division of Cardiology, The Ohio State University and the basic scientists of the Department of Genetics, Harvard Medical School was essential to define the multiple phenotypic expressions and the genetic abnormalities in the heritable conduction and myocardial disease in a family from central Ohio (Family OSU). The Family OSU presents evidence of sequential hierarchical progression through multiple cardiac phenotypes (sinus bradycardia, atrioventricular conduction defects requiring pacemaker, supraventricular arrhythmias including atrial fibrillation, heart failure, and sudden cardiac death) on a decade-to-decade basis. In this setting, each phenotype may be mistakenly considered as a specific diagnosis by physicians working without a pedigree or long-term follow-up. Genetic analysis, however, confirms lamin A/C mutation. The role of the physician-scientist and the basic scientist for the study of heritable disorders is equally important but different. Only the physician-scientist, however, who is in constant contact with the patient understands the complexity of the disease. The physician-scientist with an interest in a particular disease can guide the basic scientist to define molecular mechanisms of that disease and by extension learn important lessons for other diseases.

Beyond membrane channelopathies: alternative mechanisms underlying complex human disease

Over the past fifteen years, our understanding of the molecular mechanisms underlying human disease has flourished in large part due to the discovery of gene mutations linked with membrane ion channels and transporters. In fact, ion channel defects ("channelopathies" - the focus of this review series) have been associated with a spectrum of serious human disease phenotypes including cystic fibrosis, cardiac arrhythmia, diabetes, skeletal muscle defects, and neurological disorders. However, we now know that human disease, particularly excitable cell disease, may be caused by defects in non-ion channel polypeptides including in cellular components residing well beneath the plasma membrane. For example, over the past few years, a new class of potentially fatal cardiac arrhythmias has been linked with cytoplasmic proteins that include sub-membrane adapters such as ankyrin-B (ANK2), ankyrin-G (ANK3), and alpha-1 syntrophin, membrane coat proteins including caveolin-3 (CAV3), signaling platforms including yotiao (AKAP9), and cardiac enzymes (GPD1L). The focus of this review is to detail the exciting role of lamins, yet another class of gene products that have provided elegant new insight into human disease.

Genetics of Dilated Cardiomyopathy: Risk of Conduction Defects and Sudden Cardiac Death

Dilated cardiomyopathy is familial in at least 40--60% of cases and causal mutations have been identified in more than 40 different genes. Mutations in lamin A/C (LMNA) and desmosomal components appear associated with increased risk of sudden cardiac death, the latter in the context of left-dominant arrhythmogenic cardiomyopathy. Specific clinical features may be valuable in identifying patients with these mutations. Routine sequencing of all the genes implicated in dilated cardiomyopathy may not be cost-effective at present. Targeted mutation screening of LMNA and desmosomal components is recommended and may facilitate prognostication and management.

Genetic basis of ventricular arrhythmias

Sudden cardiac death caused by malignant ventricular arrhythmias is the most important cause of death in the industrialized world. Most of these lethal arrhythmias occur in the setting of ischemic heart disease. A significant number of sudden deaths, especially in young individuals, are caused by inherited ventricular arrhythmic disorders, however. Genetically induced ventricular arrhythmias can be divided in two subgroups: the primary electrical disorders or channelopathies, and the secondary arrhythmogenic cardiomyopathies. This article focuses on the genetic background of these electrical disorders and the current knowledge of genotype-phenotype interactions.

Lamin A/C gene mutations in familial cardiomyopathy with advanced atrioventricular block and arrhythmia

Lamin A and C proteins, encoded by the lamin A/C gene (LMNA), are inner nuclear membrane proteins predominantly expressed in terminally differentiated cells. Mutations in LMNA can cause various forms of cardiomyopathy with arrhythmia in an autosomal dominant manner. We collected and evaluated the clinical characteristics of unclassified familial cardiomyopathy with advanced AV block and sporadic cases with advanced AV block. Mutation in LMNA was directly screened using the cycle sequencing method in 5 probands of the familial cardiomyopathy and 60 sporadic cases with advanced AV block. In four of the five familial cases (80%), we identified four distinct mutations: two protein-truncation mutations, R225X and 815_818delinsCCAGAC, and two missense mutations, Y259H and R166P. No sporadic cases carried LMNA mutation. Left ventricular end-diastolic diameter (LVEDD) was slightly enlarged in LMNA mutant carriers (123.5 +/- 9.5%) as well as in non-carriers (125.1 +/- 13.3%), while left ventricular fractional shortening (LVFS) was preserved in LMNA mutant carriers (32.3 +/- 4.8%) and non-carriers (37.6 +/- 6.8%). In LMNA mutation carriers, the average age at onset of advanced AV block is significantly lower than that in non-carriers (43.7 +/- 9.5 vs. 65.3 +/- 13 yr., p < 0.01). Ventricular tachycardia, sudden death, and poor prognosis were observed in LMNA mutation carriers. LMNA mutation could cause familial cardiomyopathy with insignificant LV remodeling, early-age onset of advanced AV block, and lethal ventricular arrhythmia. Screening of LMNA mutation might be beneficial for risk stratification and clinical management of this type of unclassified familial cardiomyopathy.

Cardiovascular translational medicine (IV): The genetic basis of malignant arrhythmias and cardiomyopathies

The remarkable advances that have taken place in biomedicine over the past 50 years have resulted in dramatic improvements in the prevention, diagnosis and treatment of many diseases. Although cardiology has adopted these advances at a relatively slow pace, today it is fully immersed in this revolution and has become one of the most innovative medical specialties. Research is continuing to give rise to new developments in genetics and molecular biology that lead, almost daily, to innovative ways of preventing, diagnosing and treating the most severe forms of heart disease. Consequently, it is essential that clinical cardiologists have some basic knowledge of genetics and molecular biology as these disciplines are having an increasing influence on clinical practice.

Mouse models of congenital cardiovascular disease

Congenital heart defects occur in nearly 1% of human live births and many are lethal if not surgically repaired. In addition, the genetic contribution to congenital or acquired cardiovascular diseases that are silent at birth, but progress to cause significant disease in later life is being increasingly appreciated. Heart development and structure are highly conserved between mouse and human. The discoveries that are being made in this model system are highly relevant to understanding the pathogenesis of human heart defects whether they occus in isolation, or in the context of a syndrome. Many of the genes required for cardiovascular development were discovered fortuitously when early lethality or structural defects were observed in mouse mutants generated for other purposes, and relevant genes continue to be defined in this manner. Candidate genes for this process are being identified by their roles other species, or by their expression in pertinent tissues in mice. In this review, I will briefly summarize heart development as currently understood in the mouse, and then discuss how complementary studies in mouse and human have identified genes and pathways that are critical for normal cardiovascular development, and for maintaining the structure and function of this organ system throughout life.

Loss of Mdm4 results in p53-dependent dilated cardiomyopathy

BACKGROUND

Although several loci for familial dilated cardiomyopathy (DCM) have been mapped, the origin of a large percentage of DCM remains unclear. Mdm2, a p53-negative regulator, protects cardiomyocytes from ischemic and reperfusion-induced cell death. Mdm4, a homolog of Mdm2, inhibits p53 activity in numerous cell types. It is unknown whether Mdm4 plays a role in the inhibition of p53 in fully differentiated tissues such as adult cardiomyocytes and whether this role is associated with DCM.

METHODS AND RESULTS

The conditional knockout of Mdm4 in the heart by use of cardiomyocyte-specific Cre (alphaMyHC-Cre) allele does not result in any developmental defects. With time, however, mice with deletion of Mdm4 in the adult heart developed DCM and had a median survival of 234 days. More interestingly, the onset of DCM occurs significantly earlier in male mice than in female mice, which mimics human DCM disease. DCM in Mdm4 mutant mice was caused by loss of cardiomyocytes by apoptosis, and it was p53-dose dependent.

CONCLUSION

Activity of p53 was inhibited by Mdm4 even in the fully differentiated cardiomyocyte. Elevated apoptosis mediated by the p53 pathway in cardiomyocytes may be a mechanism for DCM.

Familial inflammatory dilated cardiomyopathy

BACKGROUND

Systematic family screening has recently identified dilated cardiomyopathy as an inherited disorder in up to 30% of cases. Mutations in genes encoding proteins responsible for myocardial architecture have been identified, but additional pathophysiological mechanisms including inflammatory reactions have been proposed.

AIMS

Identification and characterization of familial DCM, where at least one affected family member fulfils the criteria for inflammatory DCM may lead to a better understanding of the aetiology and pathogenesis of (inflammatory) DCM.

METHODS AND RESULTS

Ten families were examined. In six families, clinical characteristics and mode of inheritance were compatible with pure fDCM, fDCM with conduction defect and autosomal recessive fDCM. In four families, (auto-)immune features were diagnosed in affected and non-affected family members.

CONCLUSIONS

Familial DCM with an inflammatory component was identified as a specific subgroup of familial DCM. In most cases, the inflammatory process seems to modify, i.e. aggravate, the "classic, cytoskeletopathic" familial DCM, but in some, especially when taking clinical and genetic aspects into account, inflammatory (auto-)immune features can be addressed as the leading pathogenetic principle. Further elucidation of these families may provide a better insight into pathophysiologic processes and may aid in the development of specific therapeutic strategies.

What makes the heart fail? New insights from defective genes

Dilated cardiomyopathy (DCM) is an idiopathic, genetically heterogeneous disorder characterized by heart failure and arrhythmia. Over the past decade, the molecular basis for DCM has been partially uncovered by discovery of mutation in genes encoding cystoskeletal, sarcomeric, nuclear membrane, and sarcoplasmic reticulum proteins. These findings have implicated pathogenic mechanisms whereby structural integrity, contractile force dynamics, and calcium regulation within the cardiac myocyte are perturbed. Recognition of dilated and hypertrophic cardiomyopathies as allelic disorders has provided the opportunity to identify genotype-phenotype relationships and to gain new insight into pathways leading to cardiac failure and hypertrophy.

CONCLUSION

Collectively, family-based studies of DCM provide the rationale for clinical screening in first-degree relatives, regardless of family history or age of the index case.

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.

Laminopathies: multisystem dystrophy syndromes

Laminopathies are a heterogeneous group of genetic disorders due to abnormalities in type A lamins and can manifest varied clinical features affecting many organs including the skeletal and cardiac muscle, adipose tissue, nervous system, cutaneous tissue, and bone. Mutations in the gene encoding lamins A and C (LMNA) cause primary laminopathies, including various types of lipodystrophies, muscular dystrophies and progeroid syndromes, mandibuloacral dysplasia, dilated cardiomyopathies, and restrictive dermopathy. The secondary laminopathies are due to mutations in ZMPSTE24 gene which encodes for a zinc metalloproteinase involved in processing of prelamin A into mature lamin A and cause mandibuloacral dysplasia and restrictive dermopathy. Skin fibroblast cells from many patients with laminopathies show a range of abnormal nuclear morphology including bleb formation, honeycombing, and presence of multi-lobulated nuclei. The mechanisms by which mutations in LMNA gene cause multisystem dystrophy are an active area of current investigation. Further studies are needed to understand the underlying mechanisms of marked pleiotropy in laminopathies.

William Osler: slow pulse, stokes-adams disease, and sudden death in families

In 1903, William Osler, then at Johns Hopkins University, published "On the So-Called Stokes-Adams Disease (Slow Pulse with Syncopal Attacks, etc.)" in The Lancet, classifying a syndrome in evolution. There are thinly disguised references to a brother and to himself in the article, suggesting that Osler was concerned about a family and personal predisposition. Osler's decision to move to Oxford was triggered in part by his personal concerns about cardiac disease. Then, in 1909, Osler contributed a chapter on Stokes-Adams disease to Allbutt and Rolleston's A System of Medicine, complemented by a brilliant pathologic section by the renowned anatomist-morphologist, Arthur Keith. Osler's original contributions involved his emphasis on the importance of family history, his careful clinical and natural history observations, and his recognition of the familial occurrence of bradycardia, Stokes-Adams disease, sudden death, and cardiomyopathy.

The genetic basis for cardiac remodeling

Cardiomyopathies are primary disorders of cardiac muscle associated with abnormalities of cardiac wall thickness, chamber size, contraction, relaxation, conduction, and rhythm. They are a major cause of morbidity and mortality at all ages and, like acquired forms of cardiovascular disease, often result in heart failure. Over the past two decades, molecular genetic studies of humans and analyses of model organisms have made remarkable progress in defining the pathogenesis of cardiomyopathies. Hypertrophic cardiomyopathy can result from mutations in 11 genes that encode sarcomere proteins, and dilated cardiomyopathy is caused by mutations at 25 chromosome loci where genes encoding contractile, cytoskeletal, and calcium regulatory proteins have been identified. Causes of cardiomyopathies associated with clinically important cardiac arrhythmias have also been discovered: Mutations in cardiac metabolic genes cause hypertrophy in association with ventricular pre-excitation and mutations causing arrhythmogenic right ventricular dysplasia were recently discovered in protein constituents of desmosomes. This considerable genetic heterogeneity suggests that there are multiple pathways that lead to changes in heart structure and function. Defects in myocyte force generation, force transmission, and calcium homeostasis have emerged as particularly critical signals driving these pathologies. Delineation of the cell and molecular events triggered by cardiomyopathy gene mutations provide new fundamental knowledge about myocyte biology and organ physiology that accounts for cardiac remodeling and defines mechanistic pathways that lead to heart failure.

Familial progressive sinoatrial and atrioventricular conduction disease of adult onset with sudden death, dilated cardiomyopathy, and brachydactyly. A new type of heart-hand syndrome?

We identified a family with 10 affected members in four generations suffering from adult-onset progressive sinoatrial and atrioventricular conduction disease, sudden death due to ventricular tachyarrhythmia, dilated cardiomyopathy, and a unique type of brachydactyly with mild hand involvement (short distal, middle, proximal phalanges and clinodactyly) and more severe foot involvement (short distal, proximal phalanges and metatarsal bones, short or absent middle phalanges, terminal symphalangism, duplication of the bases of the second metatarsals, extra ossicles, and syndactyly). The phenotype differences from other reported genetic abnormalities and linkage exclusion of Holt-Oram syndrome, ulnar-mammary syndrome, brachydactyly type B or Robinow syndrome, and cardiac conduction disease or Brugada syndrome loci suggest that we report on a new hereditary heart-hand syndrome.

Nuclear envelopathies--raising the nuclear veil

The nuclear envelope separates the chromosomes from cytoplasm in eukaryotic cells and consists of three main domains: inner and outer nuclear membranes and nuclear pore complexes. The inner nuclear membrane maintains close associations with the underlying chromatin and nuclear lamina. For many years, the nuclear envelope was thought to function mainly as an architectural stabilizer of the nucleus, participating in assembly and disassembly processes during mitosis. However, recent findings demonstrate that nuclear envelope proteins are involved in fundamental nuclear functions, such as gene transcription and DNA replication, and that inherited or de novo mutated proteins cause human diseases, termed "nuclear envelopathies." These findings emphasize the importance of understanding the functions of this cellular domain, in both physiologic and pathologic states. To date, mutations in the genes encoding the nuclear envelope proteins emerin, MAN1, lamin A/C, and lamin B receptor were found to cause nuclear envelopathies. The diseases that are caused by mutations in LMNA gene are collectively called "laminopathies." Nuclear envelopathies have diverse clinical phenotypes, ranging from cardiac and skeletal myopathies to partial lipodystrophy, peripheral neuropathy, and premature aging. This raises the question of how do such ubiquitously expressed proteins give rise to tissue-specific disease phenotypes. One possible explanation is the involvement of nuclear envelope proteins in the regulation of gene transcription, a novel mechanism that has been the focus of research in our lab in recent years. In this review, we describe recent discoveries in the field of nuclear envelopathies and discuss current proposed pathophysiological mechanisms underlying these diseases.

Lamin A/C truncation in dilated cardiomyopathy with conduction disease

BACKGROUND

Mutations in the gene encoding the nuclear membrane protein lamin A/C have been associated with at least 7 distinct diseases including autosomal dominant dilated cardiomyopathy with conduction system disease, autosomal dominant and recessive Emery Dreifuss Muscular Dystrophy, limb girdle muscular dystrophy type 1B, autosomal recessive type 2 Charcot Marie Tooth, mandibuloacral dysplasia, familial partial lipodystrophy and Hutchinson-Gilford progeria.

METHODS

We used mutation detection to evaluate the lamin A/C gene in a 45 year-old woman with familial dilated cardiomyopathy and conduction system disease whose family has been well characterized for this phenotype 1.

RESULTS

DNA from the proband was analyzed, and a novel 2 base-pair deletion c.908_909delCT in LMNA was identified.

CONCLUSIONS

Mutations in the gene encoding lamin A/C can lead to significant cardiac conduction system disease that can be successfully treated with pacemakers and/or defibrillators. Genetic screening can help assess risk for arrhythmia and need for device implantation.

Electronic medical devices: a primer for pathologists

CONTEXT

Electronic medical devices (EMDs) with downloadable memories, such as implantable cardiac pacemakers, defibrillators, drug pumps, insulin pumps, and glucose monitors, are now an integral part of routine medical practice in the United States, and functional organ replacements, such as the artificial heart, pancreas, and retina, will most likely become commonplace in the near future. Often, EMDs end up in the hands of the pathologist as a surgical specimen or at autopsy. No established guidelines for systematic examination and reporting or comprehensive reviews of EMDs currently exist for the pathologist.

OBJECTIVE

To provide pathologists with a general overview of EMDs, including a brief history; epidemiology; essential technical aspects, indications, contraindications, and complications of selected devices; potential applications in pathology; relevant government regulations; and suggested examination and reporting guidelines.

DATA SOURCES

Articles indexed on PubMed of the National Library of Medicine, various medical and history of medicine textbooks, US Food and Drug Administration publications and product information, and specifications provided by device manufacturers.

STUDY SELECTION

Studies were selected on the basis of relevance to the study objectives.

DATA EXTRACTION

Descriptive data were selected by the author.

DATA SYNTHESIS

Suggested examination and reporting guidelines for EMDs received as surgical specimens and retrieved at autopsy.

CONCLUSIONS

Electronic medical devices received as surgical specimens and retrieved at autopsy are increasing in number and level of sophistication. They should be systematically examined and reported, should have electronic memories downloaded when indicated, will help pathologists answer more questions with greater certainty, and should become an integral part of the formal knowledge base, research focus, training, and practice of pathology.

Clinical and epidemiological aspects of cardiomyopathies: a critical review of current knowledge

Five years after the second report of the WHO/ISFC Task Force on the definition and classification of cardiomyopathies (CM), a critical review of the matter appears well-timed. The need for a correct definition of myocardial diseases is emphasized by considering them the result of a 'direct' injury due to different known and unknown causes and not a consequence of ischemic disease or of pressure and/or volume overload. This is in order to eliminate terms like ischemic CM, valvular CM, and hypertensive CM, which are a source of confusion. The concept of myocardial injury is also reviewed. This should not only include the structural/organic macroscopic injury, but also the subcellular, ultrastructural, and molecular damage (mostly of genetic origin) of the contracting element proteins, of citosol, sarcolemma and cell membrane ion channels. As the myocardium is a complex structure, made of common fibers and of specific conduction tissue, injury may be clinically identified either by ventricular function impairment or by bioelectric function defects, i.e. tachyarrhythmias and/or bradyarrhythmias, which sometimes are the unique manifestation of the disease (arrhythmogenic CM, in the strict sense). On the basis of the morpho-functional alterations, CMs may be classified as dilated CM (which could be better identified as hypokinetic CM, referring to the functional aspect, because the morphologic aspect is not always present), hypertrophic CM, restrictive CM, and arrhythmogenic CM (including not only arrhythmogenic right ventricular CM, but also other forms, like the so-called arrhythmias of the 'apparently' healthy heart, due to 'occult' myocardial injury). Moreover, these forms may present in association, like mixed CM (dilated-arrhythmogenic, dilated-hypertrophic, etc.). From an etiologic point of view, it is advisable to maintain the distinction between specific CM, due to a known cause, and primary or idiopathic CM, including, together with sporadic forms of an unknown origin, familial forms of a genetic origin, depending on alterations of contractile or regulating functional proteins, when myocardial injury is the sole manifestation (idiopathic) of clinical picture. The most modern etiopathogenetic, pathophysiological, and clinical features of each form of CM are briefly described in order to suggest a complete definition of the disease and to state a clinical-epidemiological setting that encompasses the current knowledge.

New phenotype of familial dilated cardiomyopathy and conduction disorders

BACKGROUND

Familial dilated cardiomyopathy (FDCM) is attributed to defects in cytoskeletal proteins, and different patterns of inheritance and phenotypic expressions according to assorted-protein modifications have been identified to date. We describe a clinical family study with 24 individuals in 3 generations affected by dilated cardiomyopathy (DCM) and cardiac conduction abnormalities.

METHODS AND RESULTS

After a follow-up period of 25 +/- 14 months, DCM developed in 7 male adults, 6 with associated arterioventricular block (AVB); and 10 female and 7 male adults had several degrees of isolated AVB. This particular clinical expression, with a strong predominance of dilation of the heart developing in the male population and the vertical distribution of patients affected with AVB, is consistent with autosomal dominant inheritance involving both cardiac abnormalities.

CONCLUSIONS

The presence of isolated AVB or that associated with DCM in a large number of individuals in the same family, in which members of the male sex seems to be predominantly affected by cardiac dilatation, differs from other FDCMs that have been described previously. This FDCM has an autosomal dominant pattern of inheritance with variable phenotypic expressivity, in which AVB may constitute in itself the only manifestation of this entity. To date, we have been unable to identify the mechanism of inheritance, and we advance some theoretical considerations about possible mechanisms.

Molecular diagnosis of myocardial disease

Myocardial disorders are major causes of morbidity and mortality, including heart failure, sudden death and the need for heart transplantation. The two most common forms of myocardial disorders, dilated cardiomyopathy and hypertrophic cardiomyopathy are paradigms of left ventricular systolic dysfunction and diastolic dysfunction. The genetics of these disorders are increasingly understood with the sarcomere playing a central role in the development of HCM and the link between sarcomere and sarcolemma being key to the development of DCM. In this review, the genetics of the myocardial diseases will be described.

No variants in the cardiac actin gene in Finnish patients with dilated or hypertrophic cardiomyopathy

BACKGROUND

Dilated and hypertrophic cardiomyopathies are primary myocardial diseases that cause considerable morbidity and mortality. Although these cardiomyopathies are clinically heterogeneous, genetic factors play an important role in their etiology and pathogenesis. The defects in the cardiac actin (ACTC) gene can cause both cardiomyopathies. The aim of our study was to screen for variants in the ACTC gene in patients with dilated or hypertrophic cardiomyopathy from Eastern Finland.

MATERIALS AND METHODS

Altogether, 32 patients with dilated and 40 patients with hypertrophic cardiomyopathy were included in the study. Commonly approved diagnostic criteria were applied, and secondary cardiomyopathies were carefully excluded. All 6 exons of the ACTC gene were amplified with polymerase chain reaction and screened for variants with single-strand conformation polymorphism analysis.

RESULTS AND CONCLUSION

We did not find any new or previously reported variants. Our results indicate that defects in the ACTC gene do not explain dilated cardiomyopathy or hypertrophic cardiomyopathy in subjects from Eastern Finland and confirm earlier results that the ACTC gene does not play an important role in the genetics of dilated or hypertrophic cardiomyopathies.

Periodic rescreening is indicated for family members at risk of developing familial dilated cardiomyopathy

OBJECTIVES

This study evaluated the role of clinical rescreening of family members at risk for familial dilated cardiomyopathy (FDC).

BACKGROUND

Familial dilated cardiomyopathy is a genetic cardiomyopathy that usually is transmitted in an autosomal dominant pattern and may underlie from one-quarter to one-half of idiopathic dilated cardiomyopathy (IDC) diagnoses. Thus, FDC may present with advanced heart failure (HF) or sudden cardiac death (SCD). Because FDC may respond to medical intervention, we have previously recommended that screening of first-degree relatives (parents, siblings, children) of patients diagnosed with IDC be undertaken to rule out FDC, and that with a diagnosis of FDC in the kindred, unaffected but at-risk family members be rescreened every three to five years. METHODS; Follow-up screening (history, examination, electrocardiogram, echocardiography) of a large family with FDC was performed six years after initial screening. Of 68 family members who underwent rescreening, two (one with left ventricular enlargement only, one with a left bundle branch block) presented with advanced HF and SCD, respectively. Two additional subjects, asymptomatic at initial screening, were also affected with FDC at follow-up.

CONCLUSIONS

Considerable vigilance for disease presentation and progression is indicated in at-risk members of a kindred with FDC, especially those with incipient FDC.

From the sarcomere to the nucleus: role of genetics and signaling in structural heart disease

The identification of genetic mutations underlying familial structural heart disease has provided exciting new insights into how alterations in structural components of the cardiomyocyte lead to different forms of cardiomyopathy. Specifically, mutations in components of the sarcomere are frequently associated with hypertrophic cardiomyopathy, whereas mutations in cytoskeletal proteins lead to dilated cardiomyopathy. In addition, extrinsic stresses such as hypertension and valvular disease can produce myocardial remodeling that is very similar to that observed in genetic cardiomyopathy. For myocardial remodeling to occur, changes in gene expression must occur; therefore, changes in contractile function or wall stress must be communicated to the nucleus via signal transduction pathways. The identity of these signaling pathways has become a key question in molecular biology. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, G alpha(q) and downstream effectors, mitogen-activated protein kinase pathways, and the Ca(2+)-regulated phosphatase, calcineurin. In the past it has been difficult to discern which signaling molecules actually contributed to disease progression in vivo; however, the development of numerous transgenic and knockout mouse models of cardiomyopathy is now allowing the direct testing of stimulatory and inhibitory molecules in the mouse heart. From this work it has been possible to identify signaling molecules and pathways that are required for different aspects of disease progression in vivo. In particular, a number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocyte. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underly heart disease.

The failing heart

Cardiomyopathies are disorders affecting heart muscle that usually result in inadequate pumping of the heart. They are the most common cause of heart failure and each year kill more than 10,000 people in the United States. In recent years, there have been breakthroughs in understanding the molecular mechanisms involved in this group of conditions, with knowledge of the genetic basis for cardiomyopathies perhaps seeing the largest advance, enabling clinicians to devise improved diagnostic strategies and preparing the stage for new therapies.

Molecular Mechanisms of Inherited Cardiomyopathies

Cardiomyopathies are diseases of heart muscle that may result from a diverse array of conditions that damage the heart and other organs and impair myocardial function, including infection, ischemia, and toxins. However, they may also occur as primary diseases restricted to striated muscle. Over the past decade, the importance of inherited gene defects in the pathogenesis of primary cardiomyopathies has been recognized, with mutations in some 18 genes having been identified as causing hypertrophic cardiomyopathy (HCM) and/or dilated cardiomyopathy (DCM). Defining the role of these genes in cardiac function and the mechanisms by which mutations in these genes lead to hypertrophy, dilation, and contractile failure are major goals of ongoing research. Pathophysiological mechanisms that have been implicated in HCM and DCM include the following: defective force generation, due to mutations in sarcomeric protein genes; defective force transmission, due to mutations in cytoskeletal protein genes; myocardial energy deficits, due to mutations in ATP regulatory protein genes; and abnormal Ca2+ homeostasis, due to altered availability of Ca2+ and altered myofibrillar Ca2+ sensitivity. Improved understanding that will result from these studies should ultimately lead to new approaches for the diagnosis, prognostic stratification, and treatment of patients with heart failure.

[Genetically modified animal models in cardiovascular research]

It is a basic tenet of molecular and clinical medicine that specific protein complements underlie cell and organ function. Since cellular and ultimately organ function depend upon the polypeptides that are present, it is not surprising that when function is altered changes in the protein pools occur. In the heart, numerous examples of contractile protein changes correlate with functional alterations, both during normal development and during the development of numerous pathologies. Similarly, different congenital heart diseases are characterized by certain shifts in the motor proteins. To understand these relationships, and to establish models in which the pathogenic processes can be studied longitudinally, it is necessary to direct the heart to stably synthesize, in the absence of other peliotropic changes, the candidate protein. Subsequently, one can determine if the protein's presence causes the effects directly or indirectly with the goal being to define potential therapeutic targets. By affecting the heart's protein complement in a defined manner, one has the means to establish both mechanism and the function of the different mutated proteins of protein isoforms. Gene targeting and transgenesis in the mouse provides a means to modify the mammalian genome and the cardiac motor protein complement. By directing expression of an engineered protein to the heart, one is now able to effectively remodel the cardiac protein profile and study the consequences of a single genetic manipulation at the molecular, biochemical, cytological and physiologic levels, both under normal and stress stimuli.

A new locus for autosomal dominant dilated cardiomyopathy identified on chromosome 6q12-q16

Dilated cardiomyopathy (DCM) is a heart-muscle disease characterized by ventricular dilatation and impaired heart contraction and is heterogeneous both clinically and genetically. To date, 12 candidate disease loci have been described for autosomal dominant DCM. We report the identification of a new locus on chromosome 6q12-16 in a French family with 9 individuals affected by the pure form of autosomal dominant DCM. This locus was found by using a genomewide search after exclusion of all reported disease loci and genes for DCM. The maximum pairwise LOD score was 3.52 at recombination fraction 0.0 for markers D6S1644 and D6S1694. Haplotype construction delineated a region of 16.4 cM between markers D6S1627 and D6S1716. This locus does not overlap with two other disease loci that have been described in nonpure forms of DCM and have been mapped on 6q23-24 and 6q23. The phospholamban, malic enzyme 1-soluble, and laminin-alpha4 genes were excluded as candidate genes, using single-strand conformation polymorphism or linkage analysis.

Evidence for autosomal recessive inheritance of infantile dilated cardiomyopathy: studies from the Eastern Province of Saudi Arabia

Familial dilated cardiomyopathy is being increasingly recognized, but affected individuals <10 y are rarely identified. We describe the natural history of dilated cardiomyopathy and evaluate the mode of inheritance among infants of Arab descent from the Eastern Province of Saudi Arabia. We evaluated 55 consecutive cases of dilated cardiomyopathy in patients <10 y of age seen during a 5-y interval. Echocardiography was the primary diagnostic modality. The 55 cases represented 20% of the offspring of 41 families of Arab descent. In 19 families (46%), parents were first cousins; there was no obvious consanguinity in 22 families (54%). Age at presentation was <30 mo (95%) (range, 1 to 100 mo); males (38%) and females (62%) were affected. Patients died (25 patients, 46%), improved (15 patients, 27%), or recovered (15 patients, 27%). The left ventricular shortening fraction at diagnosis ranged from 5 to 28% and did not differ in those who died, improved, or recovered. Complex segregation analysis of the family data using the mixed model of inheritance showed that a model of recessive inheritance best fits the data. Recessively inherited dilated cardiomyopathy has been infrequently reported, perhaps because it may be difficult to recognize in other patient groups in which consanguineous marriage is uncommon and the number of children per family is small. In the setting of consanguineous marriage, homozygosity mapping should lead to identification of the gene(s) causing dilated cardiomyopathy in the families we studied.

Prospects for gene therapy for inherited cardiomyopathies

Over the last few years the genes responsible for a number of genetic diseases of the cardiovascular system have been identified. These have included X-linked and autosomal dominant dilated cardiomyopathy, and hypertrophic cardiomyopathy. Genetic heterogeneity has been described in both of these diseases but a commonality of function has been apparent: defects in cytoskeletal proteins cause dilated cardiomyopathy and mutations in sarcomeric proteins cause hypertrophic cardiomyopathy. This led us to develop a 'final common pathway' hypothesis as a framework for selecting candidate genes for mutation screening in families with these diseases. The characterization of gene mutations has led to the development of therapies specifically targeting the defective protein or the pathway in which it is involved. These have included the use of pharmaceutical agents to replace or to antagonize the mutated protein, and replacement of the defective gene with a functional one (gene therapy). While early studies using gene therapy vectors were promising, translating studies in animals to viable therapeutic options for humans has remained problematic. There have been many publications describing the use of vectors to transduce target cells for the correction of gene defects, including recombinant retroviruses, adenoviruses, and adeno-associated viruses, as well as non-viral vectors. In this review we will discuss the identification of gene defects associated with cardiomyopathies, and the potential of gene therapy for the treatment of these diseases, as well as addressing some concerns related to the use of adenovirus-based vectors, a virus known to be an etiologic agent of acquired dilated cardiomyopathy.

Haemochromatosis gene mutations in idiopathic dilated cardiomyopathy

BACKGROUND

Two common mutations of the haemochromatosis associated gene (HFE) (cys282tyr (C282Y) and his63asp (H63D)) have been implicated in haemochromatosis and as modulators in cardiovascular disease.

OBJECTIVE

To investigate the role of these mutations in the pathogenesis of idiopathic dilated cardiomyopathy.

DESIGN AND SETTING

Case-control and prospective cohort study of patients attending a cardiomyopathy unit in a tertiary referral cardiac centre.

METHODS

207 unrelated white patients with dilated cardiomyopathy, followed up for 259 patient years, and 200 controls were tested for HFE C282Y and H63D mutations by polymerase chain reaction and restriction digestion.

RESULTS

31/207 patients (15%) v 24/200 controls (12%) carried C282Y (adjusted odds ratio (OR) 1.2 (95% confidence interval 0.7 to 2.2)), 74/207 (36%) v 53/200 (27%) carried H63D (OR 1.6 (1.1 to 2.5)), and 10/207 (4.8%) v 4/200 (2%) were compound heterozygotes (OR 2.6 (0.8 to 8.5)). Four patients and six controls were H63D homozygous and one was C282Y homozygous. There was a progressive increase in mean serum iron ([Fe]) and transferrin saturations from patients with no mutation ([Fe] = 16.3 micromol/l, transferrin saturation = 23.7%) through H63D heterozygotes (17.5 micromol/l, 25.8%), C282Y heterozygotes (17.1 micromol/l, 26.6%), H63D homozygotes (20.0 micromol/l, 33.5%), compound heterozygotes (26.8 micromol/l, 41.7%), and C282Y homozygotes (34 micromol/l, 71%). At follow up (median 90 months) the rate of death or cardiac transplantation was 52/207 (25%). C282Y heterozygotes had less ventricular dilatation (mean (SD): 59.9 (1.7) mm v 64.9 (0.9) mm, p < 0.05), better fractional shortening (24 (1. 7)% v 18.8 (1.4)%, p < 0.01), and a trend towards improved survival without transplantation. [Fe] and transferrin saturation did not correlate with disease severity and were not associated with reduced survival.

CONCLUSIONS

The frequency of the H63D mutation is significantly increased in patients with idiopathic dilated cardiomyopathy. As H63D has a relatively minor effect on iron status, the mechanism of this association may be unrelated to iron metabolism.