Electrocardiography

We conducted a genetic association study with three stages as displayed in Figure 1. Stage 1 consisted of the Myocardial Infarction Genetics Consortium (MIGen), a collection of 2,967 cases of early-onset MI (in men ≤50 years old or women ≤60 years old) and 3,075 age- and sex-matched controls free of MI from six international sites: Boston and Seattle in the United States as well as Sweden, Finland, Spain, and Italy (Table 1). At each site, MI was diagnosed on the basis of autopsy evidence of fatal MI or a combination of chest pain, electrocardiographic evidence of MI, or elevation of one or more cardiac biomarkers (creatine kinase or cardiac troponin). The mean age at the time of MI was 41 years among male cases and 47 years among female cases.
We took forward SNPs into two stages of replication (Stages 2 and 3, Figure 1). 1441 SNPs were tested in Stage 2 based on two criteria: i) strength of statistical evidence in Stage 1 (1433 SNPs from loci with P < 10^-3 in Stage 1) or ii) belonging to one of eight reported loci from recent genome-wide association studies for coronary artery disease (a common SNP from each of 9p21.3, near CXCL12, SMAD3, MTHFD1L, MIA3, near CELSR2/PSRC1/SORT1, 2q36, and PCSK9)3 (link),7 (link).
Stage 2 consisted of in silico comparisons with four recently completed GWAS for MI consisting of a symmetric effective sample size of up to 3,942 cases of MI and 3,942 controls. These studies included the Wellcome Trust Case Control Consortium Coronary Heart Disease study3 (link), German MI Family Study I3 (link), PennCATH, and MedStar (Supplementary Table 1). In each Stage 2 study, the analysis was restricted to the phenotype of MI with an age of onset threshold of <66 years for men or women. Although this age cutoff is slightly less restrictive than that used in Stage 1, this cutoff is at or below the mean age of first MI in the US (65 years for men and 70 years for women).
Thirty-three SNPs were taken forward to Stage 3, which consisted of genotyping an additional 6 studies with a symmetric effective sample size of up to 5,469 cases of MI and 5,469 controls. These six studies included Acute MI Gene Study/Dortmund Health Study, Verona Heart Study29 (link), Mid-America Heart Institute Study30 (link), Irish Family Study31 (link), German MI Family Study II, and INTERHEART32 (link) (European ancestry and South Asian ancestry each analyzed separately) (Supplementary Table 2). Stage 3 was comprised of 25 SNPs with the best combined statistical evidence for MI from Stages 1 and 2 (P < 10^-5) and the eight previously-reported SNPs discussed above. In each Stage 3 study, the analysis was restricted to the phenotype of MI and in four of the six studies, an age of onset threshold was established at <66 years for men or women.