Abstract 5093: Genetically Elevated Lipoprotein(a) and Risk of Myocardial Infarction - a Positive Mendelian Randomization Study
Background: High levels of lipoprotein(a) (Lp(a)) associate with increased risk of myocardial infarction (MI). We tested whether this is a causal effect using a Mendelian randomization design.
Methods: We genotyped for the Lp(a) kringle IV type 2 (KIV-2) size polymorphism, which explains 21% of variation in plasma levels of Lp(a). We used a cohort study of the Danish general population, The Copenhagen City Heart Study, including 9867 individuals followed for up to 16 years during which time 599 developed MI, and a case-control study, The Copenhagen Ischemic Heart Disease Study, including 1118 MI patients and 2234 controls.
Results: First, increased plasma levels of Lp(a) associated with increased risk of MI (Lp(a) tertiles, trend: p<0.001). Second, number of KIV-2 repeats inversely associated with Lp(a) levels: mean Lp(a) levels were 56, 31, 20, and 15 mg/dL for the 1st, 2nd, 3rd, and 4th quartile of KIV-2 repeats, respectively (trend, p<0.001, Figure⇓). Third, multifactorially adjusted hazard ratios for MI were 1.6(95% CI:1.3–.2.0), 1.3(1.0 –1.7), and 1.1(0.9 –1.4) for individuals in the 1st, 2nd, and 3rd quartile, respectively, as compared to individuals in the 4th quartile of KIV-2 repeats (Figure⇓). Finally, in the case-control study, multifactorially adjusted odds ratios for MI were 1.5(1.2–1.9), 1.3(1.0 –1.6), and 1.2(1.0 –1.5) for individuals in the 1st, 2nd, and 3rd quartile, respectively, as compared to individuals in the 4th quartile of KIV-2 repeats.
Conclusion: Since Lp(a) levels predict MI, and since Lp(a) KIV-2 genotype predicts both life-long increased Lp(a) levels and MI, increased Lp(a) levels appear to directly cause MI.