Comments for:
Abstract
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.
Authors
Li Weng, Nihan Kavaslar, Anna Ustaszewska, Heather Doelle, Wendy Schackwitz, Sybil Hébert, Jonathan C. Cohen, Ruth McPherson, Len A. Pennacchio
Miscues on the ”lack of MEF2A mutations” in coronary artery disease
Submitter: Eric Topol | TOPOLE@ccf.org
Cleveland Clinic Foundation
Published April 4, 2005
We would like to comment on the report by Weng et al. that claimed lack of MEF2A mutations in coronary artery disease (CAD) and the accompanying editorial by Altshuler and Hirschorn (1;2). They analyzed the exons and exon-intron boundaries of the MEF2A gene in 300 CAD patients and 300 elderly subjects by direct sequence analysis.
First, the new report actually found one patient with coronary artery disease who had a mutation (S360L) which is located in the critical transcriptional activation domain (3) and may affect the transactivation function of MEF2A. The mutation was not found in any control subject. Rather than following up its assessment experimentally, the investigators analyzed S360L quickly with computer software and claimed it to be benign, but computational analysis does not have any power to distinguish whether a variant is a disease-causing mutation or a polymorphism. The bias is quite apparent and the title of the report “lack of MEF2A mutations in coronary artery disease” is inaccurate and inappropriate. Taken together with our previous report of MEF2A mutations in sporadic cases of coronary artery disease (4), there are 5 of 507 individuals with CAD with MEF2A mutations and 0 of 491 in controls, which suggests a significant association between MEF2A mutations and CAD (P = 0.03 estimated by conservative Fisher exact test). The statistic analysis by Altshuler and Hirschorn appears to be incorrect, and inaccurately reported as P>0.2 (2).
Second, the phenotyping work in this new report for categorization of CAD is grossly inadequate. The investigators used resting echocardiograms in the 5 subjects they classified as “controls” with the 21 base pair deletion. This test does not provide any insight regarding the presence of significant coronary atherosclerosis. Coronary artery disease is frequently asymptomatic and its diagnosis relies on performance of a coronary angiogram. In all of our studies we have used the angiographic evidence of disease as critical criteria for classification as a “control” (4-6). Furthermore, it is impossible to classify young individuals to be “controls” and this was done in several individuals including the 45 year old controls of family 2 and 3, the 37 year old and 42 year old individuals in family 1 (III:5 and III:6). Virtually all of the “controls” in the report by Weng et al. (1) should have been properly defined as uncertain phenotype with respect to the presence or absence of coronary artery disease. It is quite unreasonable for any conclusions to be based about co-segregation of the 21 bp deletion of MEF2A to be made with such poor phenotypic characterization.
Of note, the proband of family 1 had a transient ischemic attack (1), raising the issue of atherosclerotic vascular disease, and only 2 other individuals in the family were old enough to be properly categorized--- only one of these had an exercise stress test and none had a coronary angiogram. Two individuals without the 21-bp deletion from the family are affected with CAD, but they may represent phencopies as CAD is very common (both parents of one affected, III:1, are normal, and the father of another affected, III:3, had stroke and died at 46 years of age). In sum, careful analysis of family data suggests that the available clinical data are insufficient to make any conclusions, and certainly does not support the author’s conclusion that the 21 bp deletion does not cosegregate with the disease and does not cause CAD.
Third, the authors mistakenly suggest that our 21 bp deletion in MEF2A was associated with premature CAD and myocardial infarction (MI) (5). This was not at all the case (5). The age-of-onset for the 21 bp deletion in the Wang et al. report ranges from 35 to 68 years for CAD and 40 to 80 years of age for MI (5). Reduced penetrance is well-known for many human diseases with autosomal dominant inheritance patterns including cardiovascular diseases like Brugada syndrome and long QT syndrome. The phenotypic expression of a mutation varies in different families as well as in different members of the same family. For example, 45% of mutation carriers can be silent carriers and incomplete penetrance in families can be as low as 12.5% for Brugada syndrome (7). The molecular mechanisms for reduced or incomplete penetrance are not clear. Modifier genes, environmental factors, gene-gene interactions, and gene-environment interactions may play a role. For a complex disease like CAD with involvement of numerous environmental factors, genetic factors and interactions among these factors, incomplete penetrance should not be unexpected, and may explain why the four individuals over 60 years of age and with the 21-bp deletion in the new report have not developed MI yet. The heterogeneity of European-American Caucasians (who are known to be highly heterogeneous) may also be a contributing factor.
It is interesting that the 21-bp deletion is present in 0.15% of elderly subjects (1). The action of this deletion may be analagous to a variant of the cardiac sodium channel gene SCN5A, S1103Y, which is more prevalent in African Americans (13.2%) than in other populations (8). S1103Y cosegregates with cardiac arrhythmia in some families, and is associated with arrhythmia in the African American population; but many carriers do not develop arrhythmias (8;9).
Consistent identification of mutations of MEF2A in CAD patients, but not in controls, is consistent with the hypothesis that MEF2A mutations are causative. In another 200 CAD patients, we have identified another potential mutation (T215A) (unpublished data). Continued identification of MEF2A mutations in CAD population by other independent research groups and studies with knockout/knockin mice with MEF2A mutations will provide further supportive evidence that MEF2A is a disease-causing gene for CAD and reveal how MEF2A defects lead to atherosclerosis.
In conclusion, identification of the 21 bp deletion of MEF2A in one large family (5), identification of multiple mutations in other CAD patients and families (1;4), and functional data demonstrating the deleterious effect of mutations on the function of the MEF2A protein (4;5) provide evidence that MEF2A is a disease-causing for CAD. The new report by Weng et al. (1) does not refute our findings. It advances the field by helping to establish the incidence of the 21 bp MEF2A deletion and pointing out the possibility of incomplete penetrance. But without proper phenotyping work and experimental biological assessment, it is a misleading report that unfortunately suggests a negative bias and premature dismissal of an important biologic underpinning of CAD.
References
1. Weng L, Kavaslar N, Ustaszewska A, Doelle H, Schackwitz W, Hebert S, Cohen JC, McPherson R, and Pennacchio LA 2005. Lack of MEF2A mutations in coronary artery disease. J Clin Invest 115:1016-1020.
2. Altshuler D, and Hirschhorn JN 2005. MEF2A sequence variants and coronary artery disease: a change of heart. J Clin Invest 115:831-833.
3. Yu,Y.T. 1996. Distinct domains of myocyte enhancer binding factor -2A determining nuclear localization and cell type-specific transcriptional activity. J. Biol. Chem. 271:24675-24683.
4. Bhagavatula,M.R., Fan,C., Shen,G.Q., Cassano,J., Plow,E.F., Topol,E.J., and Wang,Q. 2004. Transcription factor MEF2A mutations in patients with coronary artery disease. Hum Mol. Genet 13:3181-3188.
5. Wang,L., Fan,C., Topol,S.E., Topol,E.J., and Wang,Q. 2003. Mutation of MEF2A in an inherited disorder with features of coronary artery disease. Science 302:1578-1581.
6. Wang,Q., Rao,S., Shen,G.Q., Li,L., Moliterno,D.J., Newby,L.K., Rogers,W.J., Cannata,R., Zirzow,E., Elston,R.C. et al 2004. Premature Myocardial Infarction Novel Susceptibility Locus on Chromosome 1P34-36 Identified by Genomewide Linkage Analysis. Am. J Hum. Genet. 74:262-271.
7. Priori,S.G., Napolitano,C., Gasparini,M., Pappone,C., Della,B.P., Brignole,M., Giordano,U., Giovannini,T., Menozzi,C., Bloise,R. et al 2000. Clinical and genetic heterogeneity of right bundle branch block and ST- segment elevation syndrome : A prospective evaluation of 52 families. Circulation 102:2509-2515.
8. Splawski,I., Timothy,K., Tateyama M, Clancy,C.E., Malhotra A, Beggs,AH., Cappuccio FP, Sagnella GA, Kass R, and Keating,M. 2002. Variant of SCN5A sodium channel implicated in risk of cardaic arrhythmia. Science 297:1333-1336.
9. Chen,S., Chung,M.K., Martin,D., Rozich,R., Tchou,P.J., and Wang,Q. 2002. SNP S1103Y in the cardiac sodium channel gene SCN5A is associated with cardiac arrhythmias and sudden death in a white family. J. Med. Genet. 39:913-915.
Qing Wang, Shaoqi Rao, and Eric J. Topol The Cleveland Clinic Foundation Cleveland, OH 44195, USA
Nonstandard abbreviations used: CAD, coronary artery disease; MI, myocardial infarction.
Conflict of interest: The authors have declared that no conflict of interest exists.
Address correspondence to: Qing Wang or Eric J. Topol, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA. E-mail: wangq2@ccf.org or topole@ccf.org.
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