Author + information
- Pradeep Natarajan, MD, MMSc,
- Puja Kohli, MD,
- Usman Baber, MD,
- Khanh-Dung H. Nguyen, PhD,
- Samantha Sartori, PhD,
- Dermot F. Reilly, PhD,
- Roxana Mehran, MD,
- Pieter Muntendam, PhD,
- Valentin Fuster, MD, PhD,
- Daniel J. Rader, MD and
- Sekar Kathiresan, MD∗ ()
- ↵∗Center for Human Genetic Research and Cardiovascular Research Center, Massachusetts General Hospital, 185 Cambridge Street, CPZN 5.252, Boston, Massachusetts 02114
In 2008, Pollin et al. (1) identified 1 mechanism of lowering triglyceride-rich lipoproteins among the Lancaster Amish, loss of apolipoprotein C-III (APOC3) gene function, which was associated with reduced subclinical atherosclerosis (i.e., coronary arterial calcification on cardiac computed tomography). We recently extended these observations to show that APOC3 loss-of-function mutations also reduce risk for clinical atherosclerotic cardiovascular disease (ASCVD) (2,3). Here, we address 2 questions related to mutations that reduce APOC3 function: 1) do these mutations also associate with lower plasma low-density lipoprotein cholesterol (LDL-C); and 2) do these mutations reduce subclinical atherosclerosis in the general population, particularly in individuals with ancestry outside of Europe?
We studied 6,699 individuals of European, African, Asian, and Hispanic ancestries from the BioImage Study (BioImage Study: A Clinical Study of Burden of Atherosclerotic Disease in an At-Risk Population, NCT00738725), a prospective, observational study aimed at characterizing subclinical atherosclerosis in U.S. adults (55 to 80 years old) at risk for clinical ASCVD (4). We genotyped 4 APOC3 (NM_000040.1) loss-of-function mutations (IVS2+1G→A, A43T, R19X, IVS3+1G→T) using the Illumina HumanExome BeadChip Array v1.1 (Illumina, San Diego, California). Written informed consent was obtained from all study participants according to a protocol approved by the Western Institutional Review Board, Olympia, Washington. Fasting blood lipids were measured at the baseline examination. Blood lipids were adjusted for the presence of statin medications to reflect the observation that statins, on average, reduce total cholesterol by 20% and LDL-C by 30% (5). Noninvasive assessments for subclinical atherosclerosis (coronary arterial calcification [CAC], carotid plaque, and carotid intima media thickness [CIMT]) were performed at the baseline examination on a mobile imaging facility as previously described (4).
A total of 6,395 subjects passed all quality-control measures. Variant calling was performed using GenCall (Illumina) and zCall (5). Sixty-four heterozygous carriers of APOC3 loss-of-function mutations (25 IVS2+1G→A, 25 A43T, 13 R19X, 1 IVS3+1G→T; combined minor allele frequency of 0.5%) were identified. Principal components were derived from a set of high-quality, independent variants on the genotyping array using Eigenstrat as has previously been done (3,5). To minimize confounding from systematic differences in allele frequencies by trait, we reduced the observed genetic variation to the top eigenvectors derived from the sample covariance matrix. To test the association of APOC3 loss-of-function mutation with an outcome, linear regression was used for triglycerides, LDL-C, and high-density lipoprotein cholesterol (HDL-C), and CIMT; triglycerides and CIMT were natural log-transformed. And given the bimodal, skewed distributions of CAC (primary outcome) and carotid plaque, median quantile regression was used for these 2 variables. Age, sex, ethnicity, and principal components of ancestry were used as covariates in all analyses. Given a 2-sided alpha threshold of 0.05, we have >80% power to detect an effect size of 0.16% of variance explained for analyzed traits.
Among carriers and noncarriers of the APOC3 loss-of-function mutations, there were no significant differences in age, sex, hypertension, diabetes mellitus, body mass index, current smoking, aspirin use, or statin use. There were no significant differences in proportions of carriers amongst each ethnicity group (p > 0.20). We replicated the finding that APOC3 loss-of-function mutations were associated with reduced triglycerides (−43.7%; p = 1.83 × 10−21) and increased HDL-C (11.1 mg/dl; p = 3.55 × 10−10), with a larger standardized effect on triglycerides compared with HDL-C (−1.17 SD vs. +0.73 SD). When accounting for statin treatment, carriers did not have different LDL-C concentrations compared with noncarriers (p = 0.75).
APOC3 loss-of-function mutations were associated with decreased median CAC score (−27.9 U; 95% confidence interval [CI]: −51.08 to −4.67; p = 0.019) across all phenotyped participants (n = 5,631); this effect was consistent in those of European ancestry (−27.5 U; 95% CI: −67.1 to 12.1) and of non-European ancestry (−5.62 U; 95% CI: −39.2 to 27.9). Neither carotid plaque (p = 0.79) nor CIMT (p = 0.47) (n = 5,746) differed between carriers and noncarriers (Table 1).
In a multiethnic study of U.S. adults, APOC3 loss-of-function mutation carriers had reduced plasma triglycerides, higher HDL-C, and a decreased burden of coronary arterial calcification. These data support the notion that APOC3 deficiency reduces coronary atherosclerosis in the general population. Whether pharmacological inhibition of APOC3 will reduce ASCVD risk remains to be tested.
(BioImage Study: A Clinical Study of Burden of Atherosclerotic Disease in an At-Risk Population [BioImage Study]; NCT00738725)
Please note: This work was supported by a grant from Harvard Medical School (John S. LaDue Memorial Fellowship in Cardiology, to Dr. Natarajan), grants from the NHLBI (T32HL116275, to Dr. Kohli; R01HL107816, to Dr. Kathiresan), and a grant from the Donovan Family Foundation, an investigator-initiated research grant from Merck & Co. and a grant from Fondation Leducq (all to Dr. Kathiresan). Dr. Nguyen is an employee of Merck & Co. Dr. Reilly is an employee of and holds stock in Merck & Co. Dr. Mehran has received grant support from BG Medicine, Eli Lilly and Company, AstraZeneca, The Medicines Company, and BMS/Sanofi; is a consultant for AstraZeneca, Bayer, CSL Behring, Janssen Pharmaceuticals, Merck & Co., Osprey Medical, and Watermark Research Partners; and is on scientific advisory boards of Abbott Laboratories, Boston Scientific Corporation, Covidien, Janssen Pharmaceuticals, The Medicines Company, and Sanofi. Dr. Muntendam is an employee of and shareholder in scPharmaceuticals. Dr. Kathiresan has received research grants from Regeneron, Bayer, Aegerion; is on the scientific advisory board for Catabasis, Regeneron Genetics Center, Merck, Celera; holds equity in Catabasis, San Therapuetics; and is a consultant for Novartis, Aegerion, Bristol-Myers Squibb, Sanofi, AstraZeneca, Alnylam, Eli Lilly, Leerink Partners, and Merck. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Michael Miller, MD, served as Guest Editor for this paper. The High-Risk Plaque (HRP) Initiative encompassing the BioImage Study is a pre-competitive industry collaboration funded by Abbott, Abbvie, AstraZeneca, BG Medicine, Merck & Co., Philips, and Takeda. HRP Joint Steering Committee: Pieter Muntendam, MD (BG Medicine); Aram Adourian (BG Medicine); Michael Klimas, PhD (Merck); Joel Raichlen, MD (AstraZeneca); Oliver Steinbach (Philips); James Beckett (Philips); Ramon Espaillot (Abbvie); Michael Jarvis (Abbvie); and Tomoyuki Nishimoto (Takeda). The sponsor had no role in the study design; in the collection, analysis, and interpretation of the data; in the writing of this report; or in the decision to submit the paper for publication
- 2015 American College of Cardiology Foundation
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