This is the first study of Mendelian randomization to explore the association between lung function and secondary thrombocytopenia. The Mendelian randomization results suggest that the decline of FEV1 and PEF significantly increases the risk of secondary thrombocytopenia. Multiple sensitivity analyses also confirmed the causal relationship between lung function and secondary thrombocytopenia. Several factors may explain its mechanism: firstly, the lung has been reported to be the site of platelet generation and a reservoir of hematopoietic progenitor cells, and the lung can release platelets by capturing megakaryocytes[40]. Thus, lung function decline due to lung injury may lead to abnormalities in pulmonary hematopoietic function[41]. Secondly, diseases that lead to poor lung function, such as COVID-19 and chronic obstructive pulmonary disease, induce activation of the RAS system, abnormalities in endothelial cells and coagulation, platelet adhesion, and aggregation, which depletes platelet amount. Thirdly, ACE2, CD13, and CD66a have been reported to be receptors present in human bone marrow CD34 + cells, monocytes, and platelets[42]. Pulmonary impairment can invade hematopoietic stem/progenitor cells, lymphocytes, and macrophages via ACE2, CD13, or CD66a receptors, leading to apoptosis, inhibition of cell proliferation, and thrombocytopenia[43].
In this study, there are some noted shortcomings. Firstly, the results of other MR analyses, such as those of the MR egger and weighted median methods, are inconsistent with the results of the IVW method in the MR analysis of FEV1, PEF, and secondary thrombocytopenia. However, based on the principle of method selection and the absence of any heterogeneity or pleiotropy, the OR values of the IVW, MR egger, and weighted median methods are in the same direction, and the results of the IVW method can be used in preference. Secondly, the MR study demonstrated secondary thrombocytopenia was correlated with FEV1 and PEF, not lung volume, FVC, or FEV1/FVC. Third, this study only covered European populations, which may limit the application of the findings to other ethnic populations. Fourthly, the participants involved in the two-sample MR analysis of exposure and outcome studies should not be overlapped. Although the extent of overlap in this study was inevitable, the F-statistical tool was used to calculate an F-value for each SNP, minimizing the bias of sample overlap[44]. Finally, the causal relationship between FEV1 and PEF and the risk of developing secondary thrombocytopenia can only be confirmed by bioinformatic analysis, and the underlying biological mechanisms of that should be investigated in further research.
Secondary thrombocytopenia is a very common disease in clinical practice[45], and platelet transfusion is the mainstay of treatment for severe thrombocytopenia, with splenectomy, steroid, and immunoglobulin infusions for other causes[46, 47]. However, these treatments have been reported to be less effective[48]. Our MR study clarified that FEV1 significantly led to secondary thrombocytopenia, and PEF significantly affected the occurrence of secondary thrombocytopenia. Thus, this study provides new ideas for treating secondary thrombocytopenia by testing lung function. Furthermore, the improvement of lung function may prevent the development of secondary thrombocytopenia.