Validation and quantification of genetic determinants of lipoprotein-a levels and predictive value for angiographic coronary artery disease

Lipoprotein(a) (Lp[a]) has gained attention as a heritable coronary artery disease (CAD) risk factor and therapeutic target. Two genetic variants in the LPA gene have been reported to influence Lp(a) levels and increase CAD risk. The aim of this study was to prospectively test these variants for their associations with Lp(a) and CAD risk. Participants (n = 1,400) in the Intermountain Heart Collaborative Study Registry who had Lp(a) cholesterol levels determined at coronary angiography were genotyped for rs3798220 and rs1045587 in LPA. Variants were detected by Taqman polymerase chain reaction. Chi-square and linear and logistic regression tests were used as appropriate among genotypes for Lp(a) and angiographic CAD. Age averaged 63 years; 65% were men; and severe CAD was present in 57%, mild CAD in 12%, and no CAD in 31%. Minor allele frequencies were 0.023 for rs3798220 and 0.090 for rs10455872. In multivariate modeling, only rs10455872 (odds ratio [OR] 2.33, 95% confidence interval [CI] 1.67 to 3.33, p = 1.75 × 10⁻⁹) and rs3798220 (OR 1.99, 95% CI 0.99 to 4.00, p = 0.065) contributed to the prediction of elevated Lp(a) cholesterol. Lp(a) cholesterol was weakly associated with CAD (OR 1.17, 95% CI 1.00 to 1.37, p = 0.055). Rs10455872 strongly predicted prevalent CAD (per allele OR 1.43, 95% CI 1.07 to 1.91, p = 0.0172); the effect size for the rare rs3798220 variant was similar (dominant OR 1.47, 95% CI 0.81 to 2.67, p = 0.20), but power was limited to demonstrate significance. The combined genotype explained only a small percentage (≤4%) of variability in Lp(a) cholesterol and prevalence of angiographic CAD. In conclusion, heritable contributions of LPA rs10455872 and rs3798220 to Lp(a) cholesterol levels and to angiographic CAD were prospectively assessed in this study. The percentage of intersubject variability in Lp(a) cholesterol and the percentage of prevalent CAD explained were small.

Cardiovascular risk among patients on clopidogrel anti-platelet therapy after placement of drug-eluting stents is modified by genetic variants in both the CYP2C19 and ABCB1 genes

Long-term (at least one year) dual anti-platelet therapy incorporating aspirin and clopidogrel is currently recommended following percutaneous coronary intervention with placement of a drug-eluting stent (DES). Genetic variants in both the ABCB1 and CYP2C19 genes have been associated with cardiovascular events among patients on clopidogrel. We examined the concurrent contribution of the CYP2C19 *2 and *17 alleles and the ABCB1 3435 alleles to one-year clinical risk among patients (n=1,034 on clopidogrel therapy following the placement of a DES. For CYP2C19*2, event rates were 8.4%, 10.9% and 44.4% for patients with 0, 1 and 2 *2 alleles, respectively (p=0.016). ABCB1 3435 was not associated with events in univariate analysis. However, 72% of patients with a *2 variant also possessed the ABCB1 3435 C allele; among these patients (*2/C genotype) the event rate for myocardial infarction (MI) was 14.2% vs. 6.9% for those lacking both *2 and C alleles (p=0.027) and for MI/death, 16.9% vs. 9.6% (p=0.046). Overall for all genotypes, the presence of the gain-of-function (protective) *17 allele significantly reduced the one-year rate of MI from 11.1% to 7.0% (p=0.045) and trended to reduce the combined rate of MI/death from 13.8% to 10.5% (p=0.182). In conclusion, the ABCB1 3435 locus and the *2 allele combine to impart a significant trend toward increased risk. This trend was largely reversed by the simultaneous carriage of one or two *17 alleles. These findings suggest that assessment of a combined genotype may improve risk assessment.

A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II)

Background—

Warfarin is characterized by marked variations in individual dose requirements and a narrow therapeutic window. Pharmacogenetics (PG) could improve dosing efficiency and safety, but clinical trials evidence is meager.

Methods and Results—

A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II) comprised 2 comparisons: (1) a blinded, randomized comparison of a modified 1-step (PG-1) with a 3-step algorithm (PG-2) (N=504), and (2) a clinical effectiveness comparison of PG guidance with use of either algorithm with standard dosing in a parallel control group (N=1866). A rapid method provided same-day CYP2C9 and VKORC1 genotyping. Primary outcomes were percentage of out-of-range international normalized ratios at 1 and 3 months and percentage of time in therapeutic range. Primary analysis was modified intention to treat. In the randomized comparison, PG-2 was noninferior but not superior to PG-1 for percentage of out-of-range international normalized ratios at 1 month and 3 months and for percentage of time in therapeutic range at 3 months. However, the combined PG cohort was superior to the parallel controls (percentage of out-of-range international normalized ratios 31% versus 42% at 1 month; 30% versus 42% at 3 months; percentage of time in therapeutic range 69% versus 58%, 71% versus 59%, respectively, all P <0.001). Differences persisted after adjustment for age, sex, and clinical indication. There were fewer percentage international normalized ratios ≥4 and ≤1.5 and serious adverse events at 3 months (4.5% versus 9.4% of patients, P <0.001) with PG guidance.

Conclusions—

These findings suggest that PG dosing should be considered for broader clinical application, a proposal that is being tested further in 3 major randomized trials. The simpler 1-step PG algorithm provided equivalent results and may be preferable for clinical application.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00927862.