Objective: To ascertain the role of platelet glycoprotein Ib α-chain (GPIbα) plasma protein levels in cardiovascular, autoimmune, and autoinflammatory diseases and whether its effects are mediated by platelet count.
Methods: We performed a two-sample Mendelian randomization (MR) study, using both a cis-acting protein quantitative trait locus (cis-pQTL) and trans-pQTL near the GP1BA and BRAP genes as instruments. To assess if platelet count mediated the effect, we then performed a two-step MR study. Putative associations (GPIbα/platelet count/disease) detected by MR analyses were subsequently assessed using multiple-trait colocalization analyses.
Results: After correction for multiple testing (Bonferroni-corrected threshold P ≤ 2 × 10-3 ), GPIbα, instrumented by either cis-pQTL or trans-pQTL, was causally implicated with an increased risk of oligoarticular and rheumatoid factor (RF)-negative polyarticular juvenile idiopathic arthritis (JIA). These effects of GPIbα appeared to be mediated by platelet count and were supported by strong evidence of colocalization (probability of all 3 traits sharing a common causal variant ≥0.80). GPIbα instrumented by cis-pQTL did not appear to affect cardiovascular risk, although the GPIbα trans-pQTL was associated with an increased risk of cardiovascular diseases and autoimmune diseases but a decreased risk of autoinflammatory diseases, suggesting that this trans-acting instrument operates through other pathways.
Conclusion: The role of platelets in thrombosis is well-established; however, our findings provide some novel genetic evidence that platelets may be causally implicated in the development of oligoarticular and RF-negative polyarticular JIA, and indicate that GPIbα may serve as a putative therapeutic target for these JIA subtypes.
© 2020 The Authors. Arthritis & Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.