MUC4 mutations promote a thrombotic phenotype in patients with paroxysmal nocturnal haemoglobinuria by increasing the deposition of terminal complement

BACKGROUND: Thrombosis is a common complication in paroxysmal nocturnal haemoglobinuria (PNH) patients, but primary prevention remains controversial. Identifying high-risk individuals could enable risk-stratified prophylactic anticoagulation strategies. METHODS: We analyzed clinical data from PNH patients with or without thrombosis, including MUC4 mutation status and serum complement C5b-9 levels. Complement deposition assays and a murine lower limb deep vein thrombosis model were used to investigate the role of MUC4 mutation in thrombotic risk and explore the underlying mechanism involving terminal complement activation in PNH patients. Therapeutic interventions with low molecular weight heparin (LMWH) were tested in vivo. RESULTS: We found that PNH patients with MUC4 mutations have a higher incidence of thrombotic events (TEs) and MUC4 mutation is an independent risk factor for TE in PNH patients. Additionally, PNH patients with acute thrombosis had elevated serum complement C5b-9 levels, and complement deposition experiments further confirmed the abnormal activation and excessive deposition of C5b-9 as the basis for the thrombotic tendency in PNH patients. By constructing a mouse model of lower limb deep vein thrombosis, we confirmed the thrombotic tendency in a PNH mouse model and that MUC4 deficiency further promoted the thrombotic phenotype of the mice. Moreover, we found that MUC4 knockdown promoted the deposition of C5b-9 on the cell surface, indicating that a lack of MUC4 expression facilitates the deposition of C5b-9. Finally, in vivo drug administration experiments demonstrated that prophylactic anticoagulation with LMWH significantly reduced both the incidence of thrombosis and thrombus length in murine models. CONCLUSION: MUC4 mutations promote the thrombotic phenotype in PNH patients by increasing the deposition of terminal complement. In PNH patients with concomitant MUC4 mutations, the risk of TEs is further elevated. The potential role of early complement inhibitor therapy in reducing this heightened thrombotic risk, as well as the value of prophylactic LMWH therapy as a potential option for patients who are unable to receive complement inhibitor treatment, warrants further study and prospective validation. KEY POINTS: MUC4 gene mutation increases the deposition of abnormally activated terminal complement in patients with PNH, thereby promoting the thrombotic phenotype in these patients. Consequently, the risk of thrombosis is further elevated in PNH patients with concurrent MUC4 mutations. In patients with PNH who have concurrent MUC4 mutations, the potential role of early complement inhibitor therapy in reducing thrombosis risk, as well as the value of prophylactic LMWH therapy as a potential alternative for those who are unable to receive complement inhibitor treatment, may warrant further study and prospective validation.