Lamin A/C haploinsufficiency causes dilated cardiomyopathy and apoptosis-triggered cardiac conduction system disease

Mutations in the lamin A/C (LMNA) gene, which encodes nuclear membrane proteins, cause a variety of human conditions including dilated cardiomyopathy (DCM) with associated cardiac conduction system disease. To investigate mechanisms responsible for electrophysiologic and myocardial phenotypes caused by dominant human LMNA mutations, we performed longitudinal evaluations in heterozygous Lmna^+/− mice. Despite one normal allele, Lmna^+/− mice had 50% of normal cardiac lamin A/C levels and developed cardiac abnormalities. Conduction system function was normal in neonatal Lmna^+/− mice but, by 4 weeks of age, atrioventricular (AV) nodal myocytes had abnormally shaped nuclei and active apoptosis. Telemetric and in vivo electrophysiologic studies in 10-week-old Lmna^+/− mice showed AV conduction defects and both atrial and ventricular arrhythmias, analogous to those observed in humans with heterozygous LMNA mutations. Isolated myocytes from 12-month-old Lmna^+/− mice exhibited impaired contractility. In vivo cardiac studies of aged Lmna^+/− mice revealed DCM; in some mice this occurred without overt conduction system disease. However, neither histopathology nor serum CK levels indicated skeletal muscle pathology. These data demonstrate cardiac pathology due to heterozygous Lmna mutations reflecting a 50% reduction in lamin protein levels. Lamin haploinsufficiency caused early-onset programmed cell death of AV nodal myocytes and progressive electrophysiologic disease. While lamin haploinsufficiency was better tolerated by non-conducting myocytes, ultimately, these too succumbed to diminished lamin levels leading to dilated cardiomyopathy, which presumably arose independently from conduction system disease.     

A型核纤层蛋白基因突变与扩张型心肌病

A型核纤层蛋白决定细胞核的大小及形状,与细胞核的稳定性、染色质结构以及基因表达有关。A型核纤层蛋白基因突变是扩张型心肌病病因之一,目前已经发现许多与扩张型心肌病发病相关突变位点。A型核纤层蛋白基因突变引起心肌细胞核膜破坏,核纤层蛋白与其他核膜蛋白、染色质连接异常;进一步引起心肌细胞功能失常,影响转录、染色体的构成和细胞收缩功能,导致扩张型心肌病的发生。     

核纤层蛋白A/C基因 Glu82Lys突变与扩张型心肌病

目的 检测中国人家族性扩张型心肌病核纤层蛋白A/C(Lamin A/C)基因突变情况。方法对1个扩张型心肌病家系进行核纤层蛋白A/C、基因突变扫描,聚合酶链反应(PCR)扩增核纤层蛋白A/L’基因1～12号外显子,测序检测突变。对照为60例正常人及9例无明显家族史的扩张型心肌病伴传导阻滞病人。结果 该家系先证者第1号外显子PCR产物测序分析表明该患者核纤层蛋白A/C基因第82密码子位置发生G→A转换,使谷氨酸(Glu)变为赖氦酸(Lys)。该患者临床表现劳力性呼吸困难、心动过缓、胸闷、夜间不能平卧,超声示左心室扩大,心电图显示Ⅲ°房室传导阻滞,现已安装起搏器治疗。患者母亲及哥哥皆有相似临床症状且都已于40余岁心衰死亡,其家属有多人死于相同症状。结论 核纤层蛋白A/C基因Glu82Lys错义突变位于核纤层蛋白的杆状结陶域,有氨基酸的极性改变,该突变表型呈现症状重,发病早,预后差的临床特点,台并Ⅱ-Ⅲ°传导阻滞,提示该突变是致扩张型心肌病的恶性突变。     

Expanding the phenotype of sudden cardiac death-An unusual presentation of a family with a Lamin A/C mutation

Familial occurrence of sudden cardiac death (SCD) is related to a variety of clinical conditions, which can be delineated in up to 40% of families through a combination of cardiovascular examination and genetic studies. Patients with Lamin A/C gene mutations are at increased risk for SCD, but "laminopathies" are not included into clinical algorithms of SCD. Here we present a family with SCD in the absence of left ventricular dysfunction, related to a Lamin A/C mutation.     

Left Ventricular Noncompaction in a Family with Lamin A/C Gene Mutation

Left ventricular noncompaction is a rare type of cardiomyopathy, the genetics of which are poorly understood to date. Lamin A/C gene mutations have been associated with dilated cardiomyopathy and diseases of the conduction system, but rarely in left ventricular noncompaction cardiomyopathy. This report describes the cases of 4 family members with a lamin A/C gene mutation, 3 of whom had phenotypic expression of left ventricular noncompaction.     

Lamin A/C mutation is independently associated with an increased risk of arterial and venous thromboembolic complications

Background

Lamin A/C (LMNA) mutation carriers suffer from a variety of clinical phenotypes, including dilated cardiomyopathy (DCM). Although it has been suggested that carriers are at risk for thromboembolic complications, it is unknown whether this risk is higher than can be expected from the underlying cardiac abnormalities. The purpose of this study was to determine whether a LMNA mutation is associated with an increased risk of thromboembolic complications.

Methods

We compared a cohort of 76 LMNA mutation carriers with a cohort of 224 idiopathic DCM patients without a LMNA mutation, with respect to the prevalence of arterial and venous thromboembolic complications. Furthermore, we carried out a case–control study to explore whether a prothrombotic phenotype was present in LMNA mutation carriers without DCM or atrial tachyarrhythmias (n = 14) and compared this with mutation negative relatives (n = 13).

Results

The prevalence of thromboembolic complications was higher in the cohort of LMNA mutation carriers than in DCM patients (22 vs 11%; p < 0.05), after respectively mean follow-up of 42 ± 12 and 49 ± 12 years. After adjustment for possible confounders, including atrial tachyarrhythmias and left ventricular ejection fraction, LMNA mutation carriership was independently associated with an increased risk of thromboembolic complications (HR 4.8, 95% CI: 2.2–10.6). The results of the case–control study suggested a prothrombotic phenotype in LMNA mutation carriers, as reflected by an altered platelet function and increased thrombin generation.

Conclusions

LMNA mutation is independently associated with an increased risk of arterial and venous thromboembolic complications. Laboratory research in LMNA mutation carriers without severe cardiac abnormalities suggests a prothrombotic phenotype.     

Heart involvement in lamin A/C related diseases

The LMNA gene encodes lamins A and C, components of the nuclear envelope. Its mutations cause a wide range of diseases named laminopathies involving either specific tissues in isolated fashion (cardiac and skeletal muscles, peripheral nerve, adipose tissue) or several tissues in a generalized way (premature ageing syndromes and related disorders). The striated muscle laminopathies include a variety of well clinically characterized disorders where cardiac muscle involvement represents the common feature that coexists with or without skeletal muscle disease. The cardiac disease of LMNA mutated patients is classically defined by conduction system and rhythm disturbances occurring early in the course of the disease, followed by dilated cardiomyopathy and heart failure. These features are life threatening and often responsible of cardiac sudden death. When associated, the skeletal muscle involvement is characterized by muscle weakness and wasting of variable topography with or without early joint contractures and spinal rigidity. Specific management of the cardiac disease to includes antiarrhythmic drugs, cardiac devices such as implantable cardioverter for primary and secondary prevention of sudden death, and heart transplantation at the end stage of heart failure. A large number of LMNA mutations leading to striated muscle laminopathies have been reported without so far any clear and definite phenotype/genotype relation. Finally, among the diverse hypotheses for pathomechanisms of LMNA mutations, the structural hypothesis suggesting a defective role of lamins A/C in maintaining the structural integrity of the nuclear envelope in striated muscles under constant mechanical stress is highly attractive to link the LMNA mutations and the cardiac disease.     

Analysis of the Lamin A/C gene as a candidate for Type II diabetes susceptibility in Pima Indians

Abstract Aims/hypothesis. Lamin A/C (LMNA) is located within a region on chromosome 1 q that has been linked with Type II (non-insulin-dependent) diabetes mellitus in Pima Indians. Rare mutations in exon 8 of LMNA underlie Dunnigan-Type familial partial lipodystrophy, a disease characterized by regional adipocyte degeneration and frequently accompanied by insulin resistance, glucose intolerance, and diabetes. A more common variant in exon 10 (3408C/T) has recently been associated with obesity in non-diabetic aboriginal Canadian subjects. Because obesity is a strongly predisposing factor for Type II diabetes, we hypothesized that the LMNA 3408C/T variant could be associated with diabetes and body mass index in Pima Indians. Methods. To determine whether the LMNA 3408C/T variant contributes to Type II diabetes susceptibility, we genotyped the polymorphism in 1338 Pimas using allelic discrimination technology. The locus was screened for additional variants in 20 diabetic Pima Indians and non-diabetic Pima Indians using denaturing high performance liquid chromatography and dideoxy sequencing. Results. We found no evidence for association of 3408C/T with diabetes, body mass index, total cholesterol, HDL cholesterol, triglycerides, leptin concentrations, or indices of insulin sensitivity and secretion. Subsequent screening of the remaining LMNA exons and flanking sequences revealed only rare variants in intron 4 and the 3'UTR, showing no frequency differences between diabetic and non-diabetic Pima Indians. We reassessed the linkage with diabetes following adjustment for the LMNA 3408C/T variant; adjustment for the effects of LMNA did not substantially modify the evidence for linkage. Conclusion/interpretation. We conclude that the LMNA 3408C/T variant probably does not play a role in susceptibility to diabetes or obesity in Pima Indians. [Diabetologia (2001) 44: 779–782] Received: 28 December 2000 and in revised form: 19 February 2001     

Calpains and cardiac diseases

Calpains are a large family of cytosolic cysteine proteases composed of at least fourteen distinct isoforms. The family can be divided into two groups on the basis of distribution: ubiquitous and tissue-specific. Our current knowledge about calpains properties apply mainly to the ubiquitous isozymes, micro- and milli-calpain (classic calpains). These forms are activated after autolysis. Translocation and subsequent interactions with phospholipids of these enzymes increase their activity. Calpains are able to cleave a subset of substrates, as enzymes, structural and signalling proteins. Cardiac pathologies, such as heart failure, atrial fibrillation or clinical states particularly ischemia reperfusion, are associated with an increase of cytosolic calcium and in this regards, calpain activation has been evoked as one of the mediators leading to myocardial damage. Calpain activities have been shown to be increased in hearts experimentally subjected to ischemia reperfusion or during hypertrophy, but also in atrial tissue harvested from patients suffering from atrial fibrillations. These activities have been related to an increase of the proteolysis of different myocardial components, particularly, troponins, which are major regulators of the contraction of cardiomyocytes. Moreover, recent works have demonstrated that calpains are involved in the development of myocardial cell death by necrosis or apoptosis.     

原发性心脏离子通道病与心脏性猝死

在心脏离子通道病中有一部分原发性心电疾病,在无任何结构性心脏病变的情况下易导致心脏性猝死(sudden cardiac death,SCD),约占年轻SCD患者的30％,包括先天性长QT间期综合征、先天性短QT间期综合征、Brugada综合征、儿茶酚胺敏感性多形性室速.这些疾病往往外显率较低,且缺乏典型的临床表现,临床诊断面临较大的挑战.然而,SCD可能作为原发性心脏离子通道病的首发症状,因此早期诊断尤为重要.本文全面介绍了上述4种原发性心脏离子通道病的临床表现及诊断标准、遗传背景及病理生理学机制和治疗,以期为严重心律失常乃至SCD的防治提供线索.