Supplementary Material for: Causal effect of lipoprotein-associated phospholipase A2 activity on ischemic stroke : a Mendelian randomization study

Background
The relationship between ischemic stroke (IS) and lipoprotein-associated phospholipase A2 (Lp-PLA2) activity is still unclear, and there is a dearth of stratified research on the relationship between Lp-PLA2 activity and different IS subtypes. Therefore, Mendelian randomization was used in this study to examine the relationship between genetically proxied Lp-PLA2 activity and the risks of IS and its subtypes.
Methods
Based on information from a meta-analysis of GWAS, which included 13,664 European people, five single-nucleotide polymorphisms related to Lp-PLA2 activity were chosen as instrumental variables. Summary statistics information about MEGESTROKE consortium with the European group (40,585 cases and 406,111 controls) include any ischemic stroke (AIS) (n = 34,217); large-artery stroke (LAS, n=4,373), cardioembolic stroke (CES, n=7,193) and small vessel stroke (SVS, n=5,386). In order to determine the causal relationships between Lp-PLA2 activity and IS as well as its subtypes, the inverse variance weighted (IVW) approach was chosen as the primary analysis. Significant estimates were then tested by sensitivity analysis to rule out heterogeneity and pleiotropy.
Results
IVW showed Lp-PLA2 activity was causally associated with LAS (OR=3.25, 95% CI=1.65-6.41, p=0.0007), but not with other subtypes of stroke. Sensitivity analysis for causal estimates between Lp-PLA2 activity and LAS showed no significant heterogeneity or pleiotropy.
Conclusions
These MR analyses support a causal effect of Lp-PLA2 activity on LAS but not on AIS, CES or SVS, which suggests that serum Lp-PLA2 activity might be a biomarker for prediction of LAS.

Background
缺血性脑卒中（ischemic stroke, IS）与脂蛋白相关磷脂酶A2（lipoprotein-associated phospholipase A2, Lp-PLA2）活性之间的关联尚未明确，目前针对Lp-PLA2活性与不同IS亚型之间关联的分层研究仍较为匮乏。因此，本研究采用孟德尔随机化（Mendelian randomization）方法，探究经遗传代理的Lp-PLA2活性与IS及其亚型发病风险之间的关联。

Methods
本研究基于一项纳入13664名欧洲人群的全基因组关联研究（Genome-Wide Association Study, GWAS）荟萃分析数据，筛选出5个与Lp-PLA2活性相关的单核苷酸多态性（single-nucleotide polymorphism, SNP）作为工具变量。针对欧洲人群亚组的MEGESTROKE联盟汇总统计数据（包含40585例病例与406111名对照）覆盖急性缺血性脑卒中（acute ischemic stroke, AIS，n=34217）、大动脉粥样硬化型脑卒中（large-artery stroke, LAS，n=4373）、心源性栓塞型脑卒中（cardioembolic stroke, CES，n=7193）以及小血管闭塞型脑卒中（small vessel stroke, SVS，n=5386）。为探究Lp-PLA2活性与IS及其亚型之间的因果关联，本研究以逆方差加权法（inverse variance weighted, IVW）作为主要分析方法，并通过敏感性分析验证所得关联的显著性，以排除异质性与多效性的干扰。

Results
逆方差加权分析结果显示，Lp-PLA2活性与LAS存在因果关联（比值比OR=3.25，95%置信区间CI=1.65~6.41，P=0.0007），但与其他脑卒中亚型无显著关联。针对Lp-PLA2活性与LAS的因果关联估计值进行的敏感性分析未发现显著异质性与多效性。

Conclusions
本项孟德尔随机化分析证实，Lp-PLA2活性对LAS存在因果影响，而与AIS、CES及SVS无显著关联，提示血清Lp-PLA2活性或可作为预测LAS的生物标志物。