Cases and controls were recruited from the United Kingdom. Cases were considered eligible for the study if premature coronary artery disease was present. This was defined as myocardial infarction (MI), unstable or stable angina, or coronary revascularization that occurred before age 66. 80% of cases had a sibling with a history of MI or acute coronary syndrome before age 66. Controls were matched by age and gender and recruited from the same centers simultaneously. Controls were eligible for the study if they had no personal or sibling history of MI, unstable or stable angina, or coronary revascularization before the age of 66.