The Causal Effect of 179 Plasma Lipid Groups on Immune Thrombocytopenia: A Mendelian Randomized Study

Immune thrombocytopenia (ITP) is a common bleeding disorder. Although global lipidomic analyses have identified a potential role for lipid species in platelet function, there is currently no evidence to support a causal relationship between plasma lipids and ITP. To investigate this further, we conducted a two-sample Mendelian randomization analysis to determine whether there is a genetically predicted causal relationship between 179 plasma lipid groups and ITP.

Genome-wide association data from 179 plasma lipid species from 7,174 Finnish subjects were used in a preliminary analysis of ITP GWAS data from the GWAS catalogue database (GCST90018865, case=675, control=488,749). Causal analyses were performed using random inverse variance weighting (IVW) with MR-Egger and weighted median as complementary analyses. Sensitivity analyses were conducted using the MR-Egger intercept test, MR-PRESSO, and leave-one-out analysis. To assess the association of lipid metabolites with the risk of developing ITP, multivariate MR analysis was performed. Significant correlations were found. The final identification of lipid metabolites was further evaluated using the Steiger test for chain imbalance.

The results of this study showed that six plasma lipid species, sterol esters (27:1/20:2) (SE) (odds ratio [OR]: 1.30, 95% confidence interval [CI]: 1.06-1.60, p=0.013), phosphatidylethanolamine (18:0_0:0) (PE) (OR: 1. 46, 95% CI: 1.10-1.95, p=0.009), phosphatidylcholine (16:0_18:3) (PC) (OR: 1.51, 95% CI: 1.12-2.02, p=0.006), phosphatidylcholine-ether (O-16:0_16:0) (PCO) (OR: 0.64, 95% CI: 0. 47-0.88, p = 0.005), phosphatidylethanolamine-ether (O-18:2_20:4) (PEO) (OR: 0.71, 95% CI: 0.55-0.93, p=0.013), triacylglycerol (49:1) (TAG) (OR: 1.65, 95% CI: 1.21-2.24, p=0.001), and ITP were all significantly correlated. MVMR analysis showed that genetically predicted phosphatidylcholine ethers may independently influence ITP without dependence on other metabolites. Triacylglycerol may be affected by other plasma liposomal metabolites and is a risk factor for the development of ITP.

The current work provides evidence for a causal role of six plasma lipids in ITP and provides new perspectives for combining genomics and metabolomics to explore the biological mechanisms of ITP. These findings may contribute to the screening, prevention, and treatment of ITP.