Cardiogenetics, Volume 1, Issue 1 (July 2011) – 14 articles

MicroRNAs (miRNAs) are small RNAs that bind to mRNAs and regulate gene expression. MyoMirs are miRNAs implicated in cardiogenesis. Some MyoMirs have been found deregulated in hearts from patients with left ventricular hypertrophy (LVH). DNA variants at these miRNAs could contribute to the risk of developing hypertrophic cardiomyopathy (HCM). To test this hypothesis we used single strand conformation analysis and direct sequencing to search for DNA variants in the mir-208a, miR-208b, miR-133a-1, miR-133a-2, miR-133b, miR-1-1, and miR-1-2 genes in patients with HCM (n=245), LVH secondary to hypertension (n=120), and healthy controls (n=250). We found several nucleotide variants. Genotyping of patients and healthy controls showed significantly associations between a 133a-1 polymorphism and HCM and a 133b polymorphism and hypertensive- LVH. We concluded that rare variants in these mature miRNAs would be rarely found among HCM patients, but miR-133a-1 and 133b polymorphisms could contribute to the risk of developing cardiac hypertrophy. Full article

The SNTA1-encoded α1-syntrophin (SNTA1) missense mutation, p.A257G, causes long QT syndrome (LQTS) by pathogenic accentuation of Nav1.5’s sodium current (INa). Subsequently, we found p.A257G in combination with the SNTA1 polymorphism, p.P74L in 4 victims of sudden infant death syndrome (SIDS) as well as in 3 adult controls. We hypothesized that p.P74L-SNTA1 could functionally modify the pathogenic phenotype of p.A257G-SNTA1, thus explaining its occurrence in non-LQTS populations. The SNTA1 variants p.P74L, p.A257G, and the combination variant p.P74L/p.A257G were engineered using PCR-based overlapextension and were co-expressed heterologously with SCN5A in HEK293 cells. I_Na was recorded using the whole-cell method. Compared to wild-type (WT), the significant increase in peak I_Na and window current found with p.A257G was reversed by the intragenic variant p.P74L (p.P74L/p.A257G). These results report for the first time the intragenic rescue of an LQT-associated SNTA1 mutation when found in combination with the SNTA1 polymorphism p.P74L, suggesting an ever-increasing picture of complexity in terms of genetic risk stratification for arrhythmia. Full article

Idiopathic dilated cardiomyopathy (DCM) is a primary myocardial disorder characterized by ventricular chamber enlargement and systolic dysfunction. Twenty to fifty percent of idiopathic DCM cases are thought to have a genetic cause. Of more than 30 genes known to be associated with DCM, rare variants in the VCL and MYBPC3 genes have been reported in several cases of DCM. In this report, we describe a family with DCM and congenital abnormalities who carry a novel missense mutation in the VCL gene. More severely affected family members also possess a second missense variant in MYBPC3, raising the possibility that this variant may be a disease modifier. Intere - stingly, many of the affected individuals also have congenital defects, including two with bicuspid aortic valve with aortic regurgitation. We discuss the implications of the family history and genetic information on management of at-risk individuals with aortic regurgitation. Full article

Cardiomyopathies are diseases of the heart muscle leading to heart failure and/or an increased risk of arrhythmogenic sudden cardiac death. These disorders represent a major cause of morbidity and mortality in children. In childhood forms of cardiomyopathy, genetic etiologies are frequent, but non-genetic or acquired causes, such viral infection, also play a significant role. In the last twenty years, the genetic causes of cardiomyopathies have been increasingly identified and clinical correlations are beginning to be defined. Here we present an overview of the recent advances in our understanding of the genetics of cardiomyopathies in children and what is known about the pathophysiological mechanisms underlying these gene-related forms of disease. Full article

Atrioventricular canal defect (AVCD) is a common congenital heart defect (CHD), representing 7.4% of all cardiac malformations, considered secondary to an extracellular matrix anomaly. The AVCD is associated with extracardiac defects in about 75% of the cases. In this review we analyzed different syndromic AVCDs, in particular those associated with polydactyly disorders, which show remarkable genotype-phenotype correlations. Chromo - some imbalances more frequently associated with AVCD include Down syndrome, deletion 8p23 and deletion 3p25, while mendelian disorders include Noonan syndrome and related RASopathies, several polydactyly syndromes, CHARGE and 3C (cranio-cerebello-cardiac) syndrome. The complete form of AVCD is prevalent in patients with chromosomal imbalances. Additional cardiac defects are found in patients affected by chromosomal imbalances different from Down syndrome. Left-sided obstructive lesions are prevalently found in patients with RASopathies. Patients with deletion 8p23 often display AVCD with tetralogy of Fallot or with pulmonary valve stenosis. Tetralogy of Fallot is the only additional cardiac defect found in patients with Down syndrome and AVCD. On the other hand, the association of AVCD and tetralogy of Fallot is also quite characteristic of CHARGE and 3C syndromes. Heterotaxia defects, including common atrium and anomalous pulmonary venous return, occur in patients with AVCD associated with polydactyly syndromes (Ellis-van Creveld, short rib polydactyly, oral-facial-digital, Bardet-Biedl, and Smith-Lemli-Opitz syndromes). The initial clinical evidence of anatomic similarities between AVCD and heterotaxia in polydactyly syndromes was corroborated and explained by experimental studies in transgenic mice. These investigations have suggested the involvement of the Sonic Hedgehog pathway in syndromes with postaxial polydactyly and heterotaxia, and ciliary dysfunction was detected as pathomechanism for these disorders. Anatomic differences in AVCD in the different groups are probably due to different genetic causes. Full article

Dear E.G., this is an open letter on 22q11.2 deletion syndrome (DiGeorge syndrome). You are the mother of a beautiful 3 year old child. And you are one of the most active members of Aidel22, the Italian Association of 22q deletion syndrome patients and families. We would like to hear your story and learn from you. But before that, we asked some scholars in the field to help us understand what 22q11.2 deletion syndrome is [...] Full article

The inherited cardiovascular diseases, including cardiomyopathies, channelopaties and inherited diseases of the aorta are heterogeneous conditions with highly variable morphologic and functional features, clinical presentation, evolution and prognosis. Hundreds of mutations in different genes have been associated with each one of these entities and it is likely that this genetic heterogeneity is one of the main reasons for the variability in their clinical expression. Information from the genetic studies may help the clinicians to diagnose the diseases in early stages, to identify relatives at risk and those who do not require periodic follow up, and may also provide prognostic information. An appropriate and accurate interpretation of the genetic tests is required to get all the potential advantages of these studies. This interpretation is not simple and requires information, specialized knowledge and dedication to the task. The first step is to decide which the appropriate genetic test is. Negative results do not exclude the disease and in that situation we need to decide whether to continue the screening or not. When the genetic study identifies one or multiple genetic variants we will have to evaluate their frequency in the general population (polymorphisms vs. mutations) and their pathogenicity. To establish whether a given variant is associated with the disease we have to integrate both basic and clinical information. When a variant is considered potentially pathogenic we still have to evaluate whether this variant explains the phenotype of the patient and of his/her family (more than one mutation may be present). Finally, we have to analyse all the available information about the consequences of the identified mutations and to integrate this information with all the available clinical data of the patient and family. With this approach, genetic test becomes a very useful tool in the management of all the inherited cardiovascular diseases. Full article

Matrix metalloproteinase 9 (MMP9) is functionally implicated in the process of infarct healing. Several genetic variation of the MMP9 gene have been described, among which the MMP9 Arg668Gln polymorphism. In the present study, we assessed whether this polymorphism influences outcome after acute myocardial infarction (MI). One thousand forty-nine patients undergoing coronary angiography were genotyped for the MMP9 Arg668Gln polymorphism by TaqMan allelic discrimination assay. This population included 154 controls, 161 patients with non ST-elevation MI (NSTEMI), 504 patients with ST-elevation MI (STEMI), and 230 patients with angina. Frequency of the MMP9 Arg668Gln polymorphism in the global population was 25.1%, and was comparable between all groups. STEMI patients had higher creatine phosphokinase (CPK), troponin T (TnT) and MMP9 plasma levels and had lower ejection fraction (EF) than NSTEMI patients. However, the polymorphism was not associated with infarct severity as determined by peak CPK and TnT levels, nor with LV remodeling and outcome as assessed by 1-month EF and NYHA class, as well as 2- year mortality. In silico molecular modeling simulations predicted that the MMP9 polymorphism may decrease MMP9 activity, but this could not be verified by plasma determinations. This study investigated for the first time the association between the MMP9 Arg668Gln polymorphism and clinical outcome after acute MI. Our results indicate that the polymorphism does not seem to be associated with clinical outcome and in particular with the development of left ventricular dysfunction and heart failure. Full article

Phenotypic plasticity of mutations in LMNA, which encodes Lamin A/C, is unsurpassed by any other gene. Mutations in LMNA are responsible for least a dozen distinct phenotype sthat affect various mesenchymal organs and are collectively referred to as lamino - pathies or less frequently envelopathies. Cardiolaminopathies are a subset of lamino - pathies wherein involvement of the heart is the most prominent feature. The typical phenotype of cardiolaminopathies encompasses dilated cardiomyopathy (DCM) and conduction defects. LMNA is probably the most common causal gene for human DCM, being responsible up to 8% of all familial DCM. Several hundred mutations in the LMNA gene have already been described. The p.R644C mutation is the most commonly reported mutation in cardiolaminopathies. The phenotype in cardiolaminopathies is notable for a rapid progression of cardiac failure, conduction defects and arrhythmias, often necessitating implantation of a pacemaker and/or a defibrillator. The molecular pathogenesis of cardiolamino - pathies is poorly understood. Studies in animal models and cultured cells suggest involvement of the Mitogen-Activated Protein Kinase (MAPK) and transforming growth factor –β1 pathways. Comprehensive molecular genetics studies complemented with mechanistic studies are needed to delineate the mechanistic underpinnings of cardiolaminopathies, prerequisite for the ultimate cure of these potentially deadly disorders. Full article

Barth syndrome is an X-linked genetic condition featuring neutropenia, skeletal myopathy, and dilated cardiomyopathy in boys due to tafazzin (TAZ) mutations. Pure dilated cardiomyopathy without other features of Barth syndrome may also result from TAZ mutations and survival into adulthood has been described. Although TAZ testing is routinely included in dilated cardiomyopathy panels in adults, the prevalence of TAZ mutations in the adult population, including women who may be at risk to develop later onset disease due to TAZ mutations, has not been measured. We screened 292 families with dilated cardiomyopathy (209 male and 83 female probands) for TAZ mutations using denaturing high-performance liquid chromatography and sequence analysis. Putative mutations were evaluated based on standard criteria including screening available relatives and healthy controls and for effects on splicing efficiency in the case of one intronic variant. Two variants suspicious for being pathogenic were found in two unrelated families (c.387T>C, Phe128Ser and c.507C>T, Leu169Leu). The Phe128Ser variant had been previously reported as a pathogenic mutation; however we determined that this variant is instead a rare polymorphism restricted to African Americans. The Leu169Leu variant was detected in a male patient and altered RNA processing in our minigene assay supporting a pathogenic role. No mutations in female subjects were detected. Tafazzin mutations were rare in our population of adults with dilated cardiomyopathy and none were found in females. Our findings indicate that genetic testing for tafazzin should not be routinely performed in dilated cardiomyopathy as suggested by current guidelines. Furthermore, the Phe128Ser variant is not pathogenic, but likely represents a benign polymorphism in persons of African American ancestry. Full article

More than two decades have elapsed since the discovery that sarcomere gene defects cause familial hypertrophic cardiomyopathy (HCM). Since then, genetic testing in HCM has developed and expanded, and is now widely available as a potential clinical service in the Western countries. In the meantime, however, the cross-talk between geneticists and clinicians has developed slowly, and still remains unstandardized, with modalities of interaction and degree of mutual comprehension that vary wildly in various settings. In addition, clinicians often question the clinical utility of genetic testing in HCM patients and their families. The apparent lack of practical benefit, in the face of considerable costs, has long hindered large-scale diffusion of genetic testing, particularly in developing countries, and still accounts for understandable (but not always justifiable) resistance on the part of the physicians. However, such resistance is in contrast with considerable evidence supporting a role for molecular diagnosis in tailoring management for HCM patients. We here review several sound clinical reasons in favour of systematic genetic testing in HCM, ranging from identification of complex genotypes, heralding severe disease expression and outcome, to the added benefit of multidisciplinary genetic teamwork, enhancing awareness towards inheritable diseases in the cardiology community. We hope to show that to underestimate the clinical potential of genetic testing in HCM, and to defer its implementation until more advanced knowledge becomes available, is to lose an important opportunity for present improvement in care. Full article