Lipoprotein(a) Levels, Genotype, and Incident Aortic Valve Stenosis: A Prospective Mendelian Randomization Study and Replication in a Case–Control Cohort

Genome-wide association studies of late-onset cardiovascular disease

Human genetics is a powerful tool for discovering causal mediators of human disease and physiology. Cardiovascular diseases with late onset in the lifecourse have historically not been considered genetic diseases, but in recent years the contribution of a heritable factor has been established. More importantly, over the last decade genome-wide association studies (GWASs) have identified many loci associated with late-onset cardiovascular diseases including coronary artery disease, carotid artery disease, ischemic stroke, aortic aneurysm, peripheral vascular disease, atrial fibrillation, valvular disease and correlates of vascular and myocardial function. Here we review findings from GWASs considered statistically robust with regard to multiple testing (p<5×10(-8)) for late-onset cardiovascular diseases and traits. Although for only a handful of the 92 genetic loci described here have the mechanisms underlying disease association been established, new and previously unsuspected pathways have been implicated for several conditions. Examples include a role for NO signaling in myocardial repolarization and sudden cardiac death and a role for the protein sortilin in lipid metabolism and coronary artery disease. Genetic loci with multiple trait associations have also provided novel biological insights. For example, of the 46 genetic loci associated with coronary artery disease, only 16 are also associated with conventional risk factors for cardiovascular disease whereas the remaining two thirds may reflect novel pathways. Much work remains to functionally characterize genetic loci and for clinical utility, but accruing insights into the biological basis of cardiovascular aging in human populations promise to point to novel therapeutic and preventive strategies. This article is part of a Special Issue entitled 'SI:CV Aging'.

What is the ultimate test that lowering lipoprotein(a) is beneficial for cardiovascular disease and aortic stenosis?

PURPOSE OF REVIEW

Lipoprotein(a) [Lp(a)] is a risk factor for cardiovascular disease (CVD) and calcific aortic valve stenosis. We review recent studies that highlight Lp(a) in CVD and calcific aortic valve stenosis and propose pathways to clinical registration of Lp(a)-lowering agents.

RECENT FINDINGS

Over the last few years, almost irrefutable evidence has accumulated that Lp(a) is a causal, independent, genetic risk factor for CVD. Most recently, new data have emerged that elevated Lp(a) is causally associated with calcific aortic valve stenosis and the need for aortic valve replacement. Three levels of evidence to support these findings: epidemiological studies, Mendelian randomization studies and genetic association studies. A dedicated Lp(a)-lowering trial has not been performed to date. Emerging Lp(a)-lowering therapies with specific and potent lowering of Lp(a) are in phase II clinical trials and provide a tool to test the hypothesis that lowering Lp(a) plasma levels will lead to clinical benefit.

SUMMARY

We provide a rationale for the potential clinical use of Lp(a)-lowering therapies in high-risk patients or patients with established CVD whose major risk factor is elevated Lp(a) levels and propose clinical studies and trials to demonstrate that lowering Lp(a) levels will effectively reduce the risk of calcific aortic valve stenosis and CVD.

Valve tissue characterization by magnetic resonance imaging in calcific aortic valve disease

BACKGROUND

Calcific aortic valve disease affects 10%-15% of the elderly population, causing considerable morbidity and mortality. There is no imaging technique that allows for the assessment of tissue composition of the valve in vivo. We thus investigated whether multiparametric magnetic resonance imaging (MRI) could characterize and quantify lipid, fibrous, and mineralized tissues within aortic valve (AV) cusps.

METHODS

AV leaflets were explanted from patients with severe aortic stenosis at the time of valve replacement surgery. Aortic cusps were imaged ex vivo using 1.5 T MRI using 3 gradient-echo sequences with T1, moderate T2, and proton density weightings (T1w, T2w, and PDw). Histopathologic analysis was performed on coregistered slices to identify and measure mineralized tissue, fibrous tissue, and lipid-rich tissue. Area and mean grey values were measured in all 3 weightings by standardized software.

RESULTS

Four hundred ninety-two regions of interest from 30 AV leaflets were studied. Total leaflet surface and the areas of mineralized (P < 0.0001), fibrous (P = 0.002), and lipid-rich (P = 0.0001) tissues measured by MRI matched closely those measured by histopathologic examination. All 3 weightings provided significant discrimination between median grey values for mineralized, fibrous, and lipid-rich tissues (P < 0.0001 for T1w, moderate T2w, and PDw). A best-fit equation integrating the grey value data from all 3 weightings allowed multiparametric MRI to identify valve leaflet components with areas under the receiver operating characteristic curve of 0.92, 0.81, and 0.72, respectively.

CONCLUSIONS

AV leaflet characteristics, including tissue composition, distribution, and area, may be successfully measured by multiparametric MRI with good to excellent accuracy.

Calcific aortic valve disease: a consensus summary from the Alliance of Investigators on Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is increasingly prevalent worldwide with significant morbidity and mortality. Therapeutic options beyond surgical valve replacement are currently limited. In 2011, the National Heart Lung and Blood Institute assembled a working group on aortic stenosis. This group identified CAVD as an actively regulated disease process in need of further study. As a result, the Alliance of Investigators on CAVD was formed to coordinate and promote CAVD research, with the goals of identifying individuals at risk, developing new therapeutic approaches, and improving diagnostic methods. The group is composed of cardiologists, geneticists, imaging specialists, and basic science researchers. This report reviews the current status of CAVD research and treatment strategies with identification of areas in need of additional investigation for optimal management of this patient population.