Lipoprotein(a) molar concentration, rather than apolipoprotein(a) size, appears to be the factor that drives lipoprotein(a)-based cardiovascular disease, according to research published in the.
The causal association between lipoprotein(a), or Lp(a), and cardiovascular disease has been previously established, but exactly what attribute of Lp(a) is related to cardiovascular risk is not known, Daniel F. Gudbjartsson, PhD, of deCODE genetics and the University of Iceland in Reykjavik, and colleagues wrote in their study. The researchers set out to determine whether Lp(a) molar concentration or apolipoprotein(a), or apo(a), size affects cardiovascular risk. In addition, Dr. Gudbjartsson and colleagues examined the relationship between Lp(a) and type 2 diabetes. While low levels of Lp(a) have been linked to type 2 diabetes, the researchers sought to examine whether low Lp(a) molar concentration levels were also associated with type 2 diabetes risk.
“With Lp(a)-lowering drugs being developed, it is important to understand which attributes of Lp(a) best capture the cardiovascular risk and the consequences of Lp(a) lowering,” noted Dr. Gudbjartsson and colleagues.
Using Mendelian randomization, the researchers assessed Lp(a) molar concentration and kringle IV type 2 (KIV-2) repeat sequence variants to determine a causal relationship between both variants and disease risk. Lp(a) molar concentration serum samples were measured using particle-enhanced turbidimetric immunoassay, while KIV-2 repeats were genotyped with real-time polymerase chain reaction.
Overall, 143,087 participants from Iceland had their genetic information analyzed; of these, 17,715 participants had coronary artery disease, and 8,734 had type 2 diabetes. Lp(a) molecular concentration was analyzed in 12,137 participants and genetically imputed into 130,950 Icelanders, and KIV-2 repeats were estimated in 22,771 Icelanders and genetically imputed into 120,316 Icelanders.
Dr. Gudbjartsson and colleagues found there was a dose-dependent association between Lp(a) molar concentration and risk of coronary artery disease (CAD), peripheral artery disease, aortic valve stenosis, heart failure, and lifespan. In participants in whom Lp(a) molar concentration was at the 79th percentile (50 units of molarity [nM]), the odds ratio was 1.11, and for those in the 99th percentile (250 nM), there was an odds ratio of 2.01 when compared with participants with a median Lp(a) molar concentration of 14 nM. “Lp(a) molar concentration fully explained the Lp(a) association with CAD, and there was no residual association with apo(a) size,” the researchers said.
Participants who were not at increased risk for CAD included those with few KIV-2 repeats and participants with the splice variant G4925A. “This suggested that risk prediction based on Lp(a) should only depend on molar concentration and that treatment of Lp(a) should focus on lowering the molar concentration in subjects with high Lp(a) levels, regardless of the apo(a) size distribution,” Dr. Gudbjartsson and colleagues wrote.
Among participants with type 2 diabetes examined, the 10% of participants with Lp(a) molar concentrations of less than 3.5 nM were at the highest risk of developing type 2 diabetes.
In an accompanying editorial, Benoit J. Arsenault, PhD, of the Quebec Heart and Lung Institute, said that the findings of an association between Lp(a) concentration and atherosclerotic cardiovascular diseases (ASCVD) from Gudbjartsson et al. are important, particularly if they can be replicated in more diverse populations (). “Investigating the association between Lp(a) levels, apo(a) isoform size, and ASCVD risk in different populations is important because the distribution of Lp(a) levels appears to be different across ethnic groups,” he said.
Despite the link between absolute Lp(a) concentrations and cardiovascular disease, cardiovascular outcome trials will need be conducted, Dr. Arsenault noted.
“In the post-statin and post-genomic era, finding much needed therapeutic targets for residual cardiovascular risk can be compared to a gold-digging expedition. Like a map to the location of the gold, GWAS [genome-wide association studies] and Mendelian randomization studies are consistently pointing us in the direction of Lp(a),” he said. “It is time to coordinate our efforts to dig where the map told us, to see once and for all if we will find the golden target of residual cardiovascular risk that we are hoping for and to give hope to high-risk patients with elevated Lp(a) levels.”
Dr. Gudbjartsson and 19 other authors reported being employees of deCODE genetics, owned by Amgen, which is developing Lp(a)-lowering drugs related to the study findings. The other authors reported no relevant conflict of interest. Dr. Arsenault reported being supported by the Fonds de recherche du Québec: Santé and the Canadian Institutes of Health Research; has received research funding from Pfizer, Merck, and Ionis; and was a former consultant for Pfizer and Novartis.
SOURCE: Gudbjartsson DF et al. J Am Coll Cardiol. 2019. .