Transcription factor MEF2A mutations in patients with coronary artery disease

Genetic polymorphisms that predict outcome and need for treatment in cardiovascular disease

PURPOSE OF REVIEW

Interest in the genetic determinants of complications of cardiovascular disease, and the resultant influence on management, has increased. We have therefore reviewed the literature in the last 12-16 months for studies documenting genetic risk of complications. The focus is on risk of complications or differences in management, rather than only susceptibility to cardiovascular disease itself.

RECENT FINDINGS

Polymorphisms in myocyte enhancer factor 2A, a transcription factor, tumor necrosis factor (ligand) superfamily, member 4, the OX40 ligand, and proprotein convertase subtilisin/kexin type 9, which affect low-density lipoprotein levels, have all been associated with an altered risk of coronary artery disease and myocardial infarction. A preliminary study of genotype-specific therapy of the 5-lipoxygenase pathway has shown benefit in the intermediate endpoint of reduction in inflammatory markers in patients at risk of myocardial infarction and stroke. Bleeding and renal complications after coronary artery bypass surgery have also been associated with genetic polymorphisms. A familial study confirms a genetic association with thoracic aortic aneurysms.

SUMMARY

A familial risk of cardiovascular disease is well known. The specific genotypes at risk are increasingly being discovered. The science has progressed to the point that genotype-specific interventions are increasingly feasible.

Myocyte enhancing factor-2A in Alzheimer's disease: Genetic analysis and association with MEF2A-polymorphisms

Polymorphisms at different genes have been proposed as determinants of the risk for developing late-onset Alzheimer's disease (LOAD). Among the several candidate genes are those that encode proteins involved in neuronal degeneration/survival. Studies of primary neuronal cultures supported that members of the myocyte enhancing factor-2 (MEF2) family of transcription factors have an anti-apoptotic effect, regulating the expression of proteins involved in neuronal survival and differentiation. We analysed the MEF2A gene in a total of 357 patients (mean age 72 years, range 60-97 years). Among others, a Pro279Leu in exon 8 and a polyglutamine (CAG) repeat polymorphisms in exon 12 were found. These variants were also genotyped in 495 healthy controls (>50 years old), and the frequencies were statistically compared. Eight patients were 279L (six P/L and two L/L), compared to only one control (2% vs. 0.2%; p=0.004, OR=11.32). There was a significantly higher frequency of 279L-carriers among APOE epsilon4+ (7/154=4.5%), compared to epsilon4- (1/203) (p=0.02). In conclusion, our work suggests that the variation at the MEF2A gene could be involved in the risk of developing LOAD. Because MEF2 has been related with neuronal survival, and the 279L allele has been related with a reduction in the transcriptional activation activity of MEF2A, the effect of this allele could be mediated through a down-regulation of antiapoptotic genes.

Challenges in the phenotypic characterisation of patients in genetic studies of coronary artery disease

Coronary artery disease and acute myocardial infarction are complex traits in which there has been recent research to identify the principal genes that engender susceptibility or provide protection. Although there has been exceptional progress in the technology, which now allows genotyping of hundreds of thousands of single-nucleotide polymorphisms in each individual, there remains a pattern of inconsistency in the studies performed to date, in part owing to the difficulties in defining cases and controls. In this paper, salient issues to facilitate research in this important field are reviewed.

Identification of atherosclerosis-modifying genes: pathogenic insights and therapeutic potential

Atherosclerosis is a common, complex trait, with genetic variation in many genes and the environment contributing to risk for this condition, which has multiple and highly variable phenotypic manifestations. Progress has been made in the identification of atherosclerosis-modifying genes in both human studies and through the use of animal models. In the future, it may be possible to administer a genetic test for variation in a handful of the most common atherosclerosis-modifier genes, and thus predict if a patient is likely to develop atherosclerosis and ischemic heart disease. These patients could then be treated aggressively to lower their low-density lipoprotein cholesterol levels and other risk factors, including counseling to make adjustments in their lifestyle. This review will summarize the methods and results thus far in the identification of atherosclerosis-modifier genes.

Genetic susceptibility to myocardial infarction and coronary artery disease

Atherosclerotic involvement in the coronary arteries, which can result in heart attack and sudden death, is a common disease and prototypic of a complex human trait. To understand its genomic basis, eight linkage studies of sibling pairs have been performed. Although there was limited inter-study concordance of important loci, two gene variants in the leukotriene pathway (ALOX5AP and LTA4) have emerged as susceptibility factors for myocardial infarction (MI). Genome-wide association studies have also been undertaken, and the pro-inflammatory cytokine lymphotoxin-alpha (LTA), and its key ligand galectin-2 (LGALS2) have been identified as genes implicated in predisposition for heart attack. By cueing into the genomic basis for low serum LDL cholesterol levels, much work has been done to advance the importance of the serine protease PCSK9, which modulates LDL receptor function. Lifelong lowered LDL cholesterol associated with PCSK9 point mutations in 2-3% of individuals have been shown to provide marked protection from coronary artery disease (CAD). Most of the success in this field has been with the phenotype of MI, which is considerably more restrictive than CAD. Four principal and interdependent processes--lipoprotein handling, endothelial integrity, arterial inflammation, and thrombosis--have been supported as important via the clustering of genes, thus far implicated in CAD susceptibility. Of note, connecting genes in a single pathway (leukotriene), of a protein and its ligand (LTAalpha) or from one disease to another [age-related macular degeneration (AMD); complement factor H (CFH)], or even three disease characterized by inflammation (MHC2) have now been reported. Although the population attributable risk for any of the genes identified to date is limited, such discovery is likely to be accelerated in the future.

LGALS2 functional variant rs7291467 is not associated with susceptibility to myocardial infarction in Caucasians

Myocardial infarction (MI) is currently among the leading causes of death in the developed world. A functional SNP (rs7291467) in galectin-2 (LGALS2), a protein involved in the LTA cascade, has been associated with susceptibility to MI in the Japanese population. We explored for the first time the hypothesis that the same SNP could be associated with the risk of MI in the British population. We conducted a case-control association study on a cohort of 752 British MI patients and 705 population controls. Power calculations showed that our resource had 98% of power to detect a significant association at OR of 1.57, and 80% power to detect an association with an OR of 1.35 (recessive model). Despite this, we found no significant association of allele frequency with risk of MI. Stratification for age, gender and other cardiovascular risk factors also failed to reveal an association of this polymorphism with MI.

Genetics and heritability of coronary artery disease and myocardial infarction

A positive family history is frequently reported by patients with coronary artery disease (CAD) or myocardial infarction. For risk stratification, it is crucial to distinguish between accidental reoccurrence of sporadic cases and cases with a true heritable component of the conditions. A familial predisposition is assumed when a myocardial infarction is diagnosed by a male first degree relative before the 55th year of life or a female first degree relative before the 65th year of life. The current manuscript reviews major studies from which a familial risk of CAD or myocardial infarction can be inferred. Moreover, a brief overview summarizes the current results of molecular genetic research on chromosomal loci and genes relevant for CAD and myocardial infarction.

Lack of MEF2A Delta7aa mutation in Irish families with early onset ischaemic heart disease, a family based study

BACKGROUND

Ischaemic heart disease (IHD) is a complex disease due to the combination of environmental and genetic factors. Mutations in the MEF2A gene have recently been reported in patients with IHD. In particular, a 21 base pair deletion (Delta7aa) in the MEF2A gene was identified in a family with an autosomal dominant pattern of inheritance of IHD. We investigated this region of the MEF2A gene using an Irish family-based study, where affected individuals had early-onset IHD.

METHODS

A total of 1494 individuals from 580 families were included (800 discordant sib-pairs and 64 parent-child trios). The Delta7aa region of the MEF2A gene was investigated based on amplicon size.

RESULTS

The Delta7aa mutation was not detected in any individual. Variation in the number of CAG (glutamate) and CCG (proline) residues was detected in a nearby region. However, this was not found to be associated with IHD.

CONCLUSION

The Delta7aa mutation was not detected in any individual within the study population and is unlikely to play a significant role in the development of IHD in Ireland. Using family-based tests of association the number of tri-nucleotide repeats in a nearby region of the MEF2A gene was not associated with IHD in our study group.

GATA2 is associated with familial early-onset coronary artery disease

The transcription factor GATA2 plays an essential role in the establishment and maintenance of adult hematopoiesis. It is expressed in hematopoietic stem cells, as well as the cells that make up the aortic vasculature, namely aortic endothelial cells and smooth muscle cells. We have shown that GATA2 expression is predictive of location within the thoracic aorta; location is suggested to be a surrogate for disease susceptibility. The GATA2 gene maps beneath the Chromosome 3q linkage peak from our family-based sample set (GENECARD) study of early-onset coronary artery disease. Given these observations, we investigated the relationship of several known and novel polymorphisms within GATA2 to coronary artery disease. We identified five single nucleotide polymorphisms that were significantly associated with early-onset coronary artery disease in GENECARD. These results were validated by identifying significant association of two of these single nucleotide polymorphisms in an independent case-control sample set that was phenotypically similar to the GENECARD families. These observations identify GATA2 as a novel susceptibility gene for coronary artery disease and suggest that the study of this transcription factor and its downstream targets may uncover a regulatory network important for coronary artery disease inheritance.

Coronary artery disease (CAD) is the most common form of heart disease in the Western world and is one of the leading causes of death in the United States. CAD is inherited and is a complex genetic disease because it results from changes to multiple genes acting in concert with one another and the environment. The authors locate CAD susceptibility genes by convergence of techniques and identify variation within a gene of interest in an early-onset CAD population. If a specific variant is found more often in affected individuals or families than in controls, this can suggest that this gene variant is associated with disease. The authors have identified a gene, GATA2, which is located in a genomic region suspected to contain genes for CAD and displays expression patterns predictive of location of disease within human donor aortas. They have identified several GATA2 variants that segregate with CAD in a family-based early-onset CAD population and have further validated two of these associations in a separate young case-control sample affected with CAD. These data imply that the transcription factor GATA2 may play a role in CAD susceptibility and suggest that the study of GATA2 targets may uncover a set of GATA2-regulated genes important to CAD inheritance.

Nonconventional genetic risk factors for cardiovascular disease

Despite numerous advances made in identifying the genes for rare mendelian forms of cardiovascular disease (CVD), relatively little is known about the common, complex forms at the genetic level. Moreover, most genes that have been associated with CVD, whether they are single gene forms or more common forms of the disease, have primarily been involved in biochemical pathways related to what are considered "conventional" risk factors. However, recent genetic studies have begun to identify genes and pathways associated with CVD that would not be considered to underlie conventional risk factors. In this review, we discuss the evidence for this latter notion based on recent linkage and association studies in humans. As an example, we also illustrate how a combination of mouse and human genetics led to identification of the 5-lipoxygenase pathway for CVD, with potentially important implications for its treatment and diagnosis. We conclude with a discussion of the prospects for identifying CVD genes in the future and for potentially developing more effective therapeutic strategies.

Genetic variants predisposing to cardiovascular disease

PURPOSE OF REVIEW

The goal of this review is to provide an update on the most recent and relevant findings in the area of genotype-phenotype associations as well as the relationships between genetic factors and cardiovascular disease risk markers and events. In addition, emphasis will be placed on the methodological problems associated with studying the genetics of complex disorders, specifically cardiovascular diseases.

RECENT FINDINGS

Genes associated with cardiovascular disease predisposition have been examined, including traditional cardiovascular disease candidate genes, such as ACE, AGT, eNOS, PON and MTHFR, new loci that have recently been added to the growing list of cardiovascular disease candidate genes (i.e. MEF2A, ALOX5, LTA, APOM, PDE4D), and genes that have been shown to be at the intersection of several age-related disorders through interaction with one another or with environmental factors (i.e. APOA5, APOE, PPARgamma, LPL and LIPC).

SUMMARY

During the last year, tremendous effort has been made in elucidating new genes associated with cardiovascular disease predisposition. For the most part, however, major breakthroughs have not been made, primarily due to the poor replication of results among studies, as a consequence of poor experimental design. Nevertheless, we have increased our understanding of the complexity of cardiovascular disease and the relevance of gene-environment interactions as the ultimate drivers of the individual predisposition to the disease. It is essential, therefore, that present and future genetic studies in this area take into consideration the inclusion of high-quality environmental data in the analytical process to test the clinical usefulness of a genetic marker as a risk predictor.

Genetic susceptibility to coronary artery disease: from promise to progress

Family history is an important independent risk factor for coronary artery disease (CAD), and identification of susceptibility genes for this common, complex disease is a vital goal. Although there has been considerable success in identifying genetic variants that influence well-known risk factors, such as cholesterol levels, progress in unearthing novel CAD genes has been slow. However, advances are now being made through the application of large-scale, systematic, genome-wide approaches. Recent findings particularly highlight the link between CAD and inflammation and immunity, and highlight the biological insights to be gained from a genetic understanding of the world's biggest killer.

Common genetic vulnerability to depressive symptoms and coronary artery disease: a review and development of candidate genes related to inflammation and serotonin

OBJECTIVE

Although it is well established that depressive symptoms are associated with recurrent cardiac events among cardiac patients and novel cardiac events among participants with no known coronary artery disease (CAD), the nature of this association remains unclear. In this regard, little attention has been paid to the possibility that common genetic vulnerability contributes to both depressive symptoms and CAD. In this paper, we review the existing evidence for common genetic contributions to depression and CAD, primarily using evidence from twin and family studies, followed by a review of two major pathophysiological mechanisms thought to underlie covariation between depressive symptoms and CAD: inflammation and serotonin. We conclude with an overview of select candidate genes within these pathways.

METHODS

Literature review.

RESULTS

In twin studies, both depression and CAD appear heritable. In the only twin study to consider depression and CAD jointly, the correlation across heritabilities was 0.42, suggesting that nearly 20% of variability in depressive symptoms and CAD was attributable to common genetic factors. In addition, although it is plausible that genetic variation related to inflammation and serotonin may be associated with both depression and CAD, genetic variation related to inflammation has been primary examined in relation to CAD, whereas genetic variation in the serotonin system has been primarily examined in relation to depression.

CONCLUSIONS

It appears that the covariation of depressive symptoms and CAD may be attributable, in part, to a common genetic vulnerability. Although several pathways may be involved, genes within the inflammation and serotonin pathways may serve as good candidates for the first steps in identifying genetic variation important for depression, CAD or both.

Advances in the genetic basis of coronary artery disease

Exciting advances have been made recently in genetic studies of coronary artery disease (CAD), myocardial infarction (MI), and ischemic stroke. One disease-causing gene for CAD and MI has been identified as MEF2A, which is located on chromosome 15q26.3 and encodes a transcriptional factor with a high level of expression in coronary endothelium. Approximately 1% to 2% of CAD patients may carry an MEF2A mutation. Four new susceptibility genes have been identified using genome-wide association studies or genome-wide linkage studies: LTA (encoding cytokine lymphotoxin-alpha) on 6p21.3 for MI; LGALS2 (encoding galectin-2, an LTA-interacting protein) on 22q12-q13 for MI; ALOX5AP (encoding 5-lipoxygenase activating protein involved in synthesizing potent pro-inflammatory leukotrienes) on 13q12-13 for MI and stroke; and PDE4D (encoding phosphodiesterase 4D) on 5q12 for ischemic stroke. These studies identify a new mechanism, the myocyte enhancer factor 2 (MEF2) signaling pathway of vascular endothelium, for the pathogenesis of CAD, and also confirm the role of inflammation in the disease process.

Requirements of myocyte-specific enhancer factor 2A in zebrafish cardiac contractility

Myocyte-specific enhancer factor 2A (MEF2A) regulates a broad range of fundamental cellular processes including cell division, differentiation and death. Here, we tested the hypothesis that MEF2A is required in cardiac contractility employing zebrafish as a model organism. MEF2A is highly expressed in heart as well as somites during zebrafish embryogenesis. Knock-down of MEF2A in zebrafish impaires the cardiac contractility and results in sarcomere assembly defects. Dysregulation of cardiac genes in MEF2A morphants suggests that sarcomere assembly disturbances account for the cardiac contractile deficiency. Our studies suggested that MEF2A is essential in cardiac contractility.

Identifying novel genes for atherosclerosis through mouse-human comparative genetics

Susceptibility to atherosclerosis is determined by both environmental and genetic factors. Its genetic determinants have been studied by use of quantitative-trait-locus (QTL) analysis. So far, 21 atherosclerosis QTLs have been identified in the mouse: 7 in a high-fat-diet model only, 9 in a sensitized model (apolipoprotein E- or LDL [low-density lipoprotein] receptor-deficient mice) only, and 5 in both models, suggesting that different gene sets operate in each model and that a subset operates in both. Among the 27 human atherosclerosis QTLs reported, 17 (63%) are located in regions homologous (concordant) to mouse QTLs, suggesting that these mouse and human atherosclerosis QTLs have the same underlying genes. Therefore, genes regulating human atherosclerosis will be found most efficiently by first finding their orthologs in concordant mouse QTLs. Novel mouse QTL genes will be found most efficiently by using a combination of the following strategies: identifying QTLs in new crosses performed with previously unused parental strains; inducing mutations in large-scale, high-throughput mutagenesis screens; and using new genomic and bioinformatics tools. Once QTL genes are identified in mice, they can be tested in human association studies for their relevance in human atherosclerotic disease.

Lack of MEF2A mutations in coronary artery disease

Mutations in MEF2A have been implicated in an autosomal dominant form of coronary artery disease (adCAD1). In this study we sought to determine whether severe mutations in MEF2A might also explain sporadic cases of coronary artery disease (CAD). To do this, we resequenced the coding sequence and splice sites of MEF2A in approximately 300 patients with premature CAD and failed to find causative mutations in the CAD cohort. However, we did identify the 21-bp MEF2A coding sequence deletion originally implicated in adCAD1 in 1 of 300 elderly control subjects without CAD. Further screening of approximately 1,500 additional individuals without CAD revealed 2 more subjects with the MEF2A 21-bp deletion. Genotyping of 19 family members of the 3 probands with the 21-bp deletion in MEF2A revealed that the mutation did not cosegregate with early CAD. These studies support that MEF2A mutations are not a common cause of CAD in white people and argue strongly against a role for the MEF2A 21-bp deletion in autosomal dominant CAD.

The Pro279Leu variant in the transcription factor MEF2A is associated with myocardial infarction

BACKGROUND

A myocyte enhancer factor 2A (MEF2A) mutation that segregated with coronary artery disease/myocardial infarction (CAD/MI) in a large family has recently been described. Missense mutations in sporadic coronary artery disease patients were also reported. These data suggest that mutations in exons 7 and 11 of MEF2A cause CAD/MI, though the association was refuted by another study.

OBJECTIVE

To analyse the genetic variation of exons 7 and 11 in a large cohort of Spanish CAD/MI patients and controls.

METHODS AND RESULTS

A rare polymorphism, P279L, was detected both in patients and controls. Carriers of the 279Leu allele had a threefold risk of suffering CAD/MI compared with controls (p = 0.009; odds ratio = 3.06 (95% confidence interval, 1.17 to 8.06)). In the controls the allele was found only in those under 50 years of age. Exon 11 showed a high degree of heterogeneity caused by a polyglutamine (CAG)n polymorphism, but no significant differences in genotype or allelic frequencies were found.

CONCLUSIONS

The 279Leu allele appears to be a genetic risk factor for CAD/MI in the population studied. This effect could be the result of a reduced transcriptional activity on MEF2A with 279Leu.

Molecular genetics of coronary artery disease

PURPOSE OF REVIEW

Coronary artery disease, including its most severe complication myocardial infarction, is the leading cause of death; however, its genetic studies lag behind other diseases. Many advances have recently been made, however, and these are reviewed here.

RECENT FINDINGS

Positional cloning based on genome-wide linkage analysis with large families identified the first non - lipid-related disease-causing gene, MEF2A (encoding a transcriptional factor), for coronary artery disease and myocardiaI infarction. The MEF2A mutations may account for up to 1.93% of the disease population; thus, genetic testing based on mutational analysis of MEF2A may soon be available for many coronary artery disease/myocardial infarction patients. Genome-wide association studies identified significant association for myocardiaI infarction with the LTA gene (encoding lymphotoxin-alpha), and a follow-up study found that an LTA-interacting gene, LGALS2 (encoding galectin-2), is also a susceptibility gene for myocardiaI infarction. Studies that employ genome-wide linkage scans with hundreds of small nuclear families have identified new susceptibility genes for coronary artery disease and myocardiaI infarction, including ALOX5AP (encoding 5-lipoxygenase-activating protein) associated with myocardial infarction and stroke and PDE4D (encoding phosphodiesterase 4D) for ischemic stroke.

SUMMARY

Genetic studies provide new insights into the pathogenesis of coronary artery disease and myocardial infarction. Future studies will focus on identification of new disease-causing genes and susceptibility genes, exploration of the molecular mechanisms by which mutations cause coronary artery disease/myocardiaI infarction, and gene-specific therapies for patients.

MEF2A sequence variants and coronary artery disease: a change of heart?

Rare mutations in MEF2A have been proposed as a cause of coronary artery disease (CAD) and myocardial infarction (MI). In this issue of the JCI, Pennacchio and colleagues report sequencing MEF2A in 300 patients with premature CAD and in controls. Only 1 CAD patient was found to carry a missense mutation not found in controls. The specific 21-bp deletion in MEF2A previously proposed as causal for CAD and/or MI was observed in unaffected individuals and did not segregate with CAD in families. These results do not support the hypothesis that mutations in MEF2A are a cause of CAD and/or MI but do illustrate general principles regarding the difficulty of connecting genetic variation to common diseases.

MEF2A sequence variants and coronary artery disease: a change of heart?

Rare mutations in MEF2A have been proposed as a cause of coronary artery disease (CAD) and myocardial infarction (MI). In this issue of the JCI, Pennacchio and colleagues report sequencing MEF2A in 300 patients with premature CAD and in controls. Only 1 CAD patient was found to carry a missense mutation not found in controls. The specific 21-bp deletion in MEF2A previously proposed as causal for CAD and/or MI was observed in unaffected individuals and did not segregate with CAD in families. These results do not support the hypothesis that mutations in MEF2A are a cause of CAD and/or MI but do illustrate general principles regarding the difficulty of connecting genetic variation to common diseases.

Assessment of MEF2A Mutations in Myocardial Infarction in Japanese Patients

BACKGROUND

Recently, a mutation in the human MEF2A gene was reported to be responsible for an autosomal dominant form of coronary artery disease, so the purpose of the present study was to assess the significance of MEF2A mutations in Japanese subjects with myocardial infarction (MI).

METHODS AND RESULTS

The study population consisted of 589 control subjects recruited from the Suita study and 379 subjects with MI. The promoter, all the exons, and 3'-UTR regions of MEF2A were sequenced in 190 subjects with myocardial infarction. We found 2 amino acid length polymorphisms, a 7-amino acid deletion polymorphism, and a nonsense mutation (R447X) in exon 12. The length and deletion polymorphisms did not confer susceptibility to MI. Although the nonsense mutation was detected in 1 subject with MI, and in none of the control subjects, the impact of this mutation does not appear to be great; the subject had the MI while in his 70 s, had 2 major risk factors, and no family history of ischemic heart disease.

CONCLUSION

MEF2A polymorphism does not contribute appreciably to MI in the Japanese population.