Gene Variations Don't Pan Out for Acute Coronary Syndromes

NEW HAVEN, Conn., April 10 -- A panel of 85 variants in 70 genes singled out as key predictors of heart disease risk factors failed to tell the tale, researchers reported here.

A case-control study of 1,461 participants did not verify findings from smaller studies that the 85 gene variations represent risk factors for acute coronary syndromes, said Thomas M. Morgan, M.D., of Yale, now at Washington University in St. Louis, and colleagues.

Of the variants tested, only one putative risk genotype was nominally statistically significant in a primary analysis, and only four additional genes were positive in a secondary analysis, the researchers reported in the April 11 issue of the Journal of the American Medical Association.

Neither number of associations was more frequent than expected by chance, given the number of comparisons, they said.

Until now, numerous candidate genes have been implicated as potential cardiovascular risk factors, but few, if any, have been "replicated en masse in large, well-characterized patient populations," Dr. Morgan said. Thus, he added, before use in clinical care, there has been a need for a comprehensive validation of these 85 susceptibility genotypes.

These findings, the investigators said, come at a critical juncture in complex disease genetics. Some cardiovascular gene variants included in this study can already be ordered clinically, for indications that explicitly include possible acute coronary syndrome risk.

"However," Dr. Morgan and colleagues wrote, "our findings suggest that such clinical genetic testing is premature and underscore the importance of robust replication studies of reported associations prior to their application to clinical care."

The study was launched with a systematic literature search of articles published before March 10, 2005, in which the researchers identified genetic variants previously reported as significant susceptibility factors for atherosclerosis or acute coronary syndromes, including unstable angina and myocardial infarction.

The analysis was restricted to white patients to reduce confounding from racial admixture. The researchers identified 811 patients seen from March 2001 through June 2003 with acute coronary syndrome at two Kansas City, Mo., university-affiliated hospitals.

From 2005 to 2006, the researchers genotyped these 811 patients along with 650 age- and sex-matched controls for 85 variants in 70 genes.

The researchers then attempted to replicate previously reported associations and also explored possible associations without prior

assumption of specific risk models, using the Sign test to search for weak associations.

Of 85 variants tested, only one putative-risk genotype (?455 promoter variant in ?-fibrinogen) was nominally statistically significant, with a frequency of 66% in cases versus 61% in controls (odds ratio 1.27; P= 0.03).

Only four additional genes were marginally positive in a secondary model-free analysis, but in each case the specific genetic risk model providing significance was different from that reported in the literature. Thus, the researchers said, the total number of replications and positive associations was not in excess of that expected by chance.

Finally, only 41 of 84 predefined risk variants were even marginally more frequent in cases than in controls (with one tie). This represented a 48.8% "win rate" (95% confidence interval, 38.1% to 59.5%) for the collective risk genotypes (P=0.91, Sign test).

Despite the findings of one variant in the primary analysis and of the four variants in the secondary analysis that met nominal statistical thresholds, the investigators wrote that there was an excess of a different variant than previously reported among cases in the primary analysis, which did not support replication.

The researchers said the study with its large sample and well-characterized patients "cannot support that this panel of gene variants contains bona fide acute coronary syndromes risk factors."

Possible explanations for the negative results of this study, the researchers wrote, included false-negative results in this study, false positive associations in previous studies, and the varied effects of risk variants in different genetic backgrounds.

However, the researchers said, false negative results in this study were an unlikely explanation, given the large size of the sample and that the study was powered to detect relatively modest relative risks.

Other caveats included the possibility that the effect of risk variants is different in other genetic backgrounds. If true, the lack of generalizability of these results will severely limit their clinical application, the researchers said.

However, they added, this also holds for the findings of earlier studies and supports the premise that it is premature to extrapolate the earlier findings to routine clinical care.

Regardless of the approach taken, the researchers said, it is clear that multiple, large, well-matched cohorts of cases and controls will be required to achieve valid progress in the genetic analysis of acute coronary syndromes and other complex human diseases.