MRGPRX2 gain-of-function mutation drives enhanced mast cell reactivity in chronic spontaneous urticaria.

Background: Mast cell (MC) activation plays a central role in the pathogenesis of chronic spontaneous urticaria (CSU). Mutations in MC receptors have been suggested as a potential mechanism underlying CSU. MRGPRX2 has been proposed to contribute to the pathogenesis of CSU. However, the relationship between mutations in MRGPRX2 and their impact on disease severity and receptor function remains poorly understood.

Objective: We sought to investigate the prevalence and functional impact of MRGPRX2 mutations in CSU patients.

Methods: The study included 80 patients with CSU. Peripheral blood was collected for DNA sequencing in the coding exon of MRGPRX2. Weekly Urticaria Activity Score and laboratory test results were recorded, and serum MRGPRX2 levels were measured by ELISA. RBL-2H3 cells were transfected with wild-type MRGPRX2 and mutant variants. Flow cytometry and immunofluorescence staining were used to assess MRGPRX2 cell surface expression. Functional assays were performed to measure degranulation by β-hexosaminidase release, calcium mobilization, and cytokine synthesis by quantitative RT-PCR. Additionally, phosphorylation of signaling kinases was detected by Western blotting.

Results: Missense variants of MRGPRX2 185A>G (n = 8, 10%) and 185A>G+46A>C co-mutations (n = 23, 28.75%) were identified in patients with CSU. Patients carrying 185A>G mutation had a significantly higher weekly Urticaria Activity Score and lower circulating basophil and lymphocyte counts than patients with wild-type MRGPRX2. The 185A>G mutation, but not 185A>G+46A>C, was associated with increased MRGPRX2 expression in both patients with CSU and RBL-2H3 cells expressing the 185A>G mutation. Cells transfected with the 185A>G mutation demonstrated increased MC degranulation, calcium mobilization, cytokine synthesis, and extracellular signal-regulated kinase phosphorylation on MRGPRX2 activation, whereas the 46A>C+185A>G co-mutation did not show these changes.

Conclusion: The 185A>G mutation in MRGPRX2 contributes to a gain-of-function phenotype that is associated with enhanced disease activity in patients with CSU.