MYH9 antibodies are autoantibodies targeting the MYH9 protein, a non-muscle myosin heavy chain IIA encoded by the MYH9 gene. This protein plays critical roles in cell motility, cytoskeletal organization, and platelet formation. Initially, MYH9 mutations were linked to rare inherited macrothrombocytopenias (e.g., May-Hegglin anomaly). However, MYH9 antibodies gained attention in autoimmune contexts, particularly in antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE).
In APS, MYH9 antibodies are often detected alongside classic antiphospholipid antibodies (aPL), potentially contributing to thrombotic events or pregnancy complications. Their presence may reflect molecular mimicry or epitope spreading triggered by infections or genetic susceptibility. In SLE, these antibodies correlate with disease activity and thrombocytopenia, though their pathogenic role remains unclear.
Testing for MYH9 antibodies is not routine but may aid in diagnosing atypical autoimmune cases or refining risk stratification. Research suggests they could interfere with MYH9’s function in endothelial cells or platelets, exacerbating inflammation or clotting. However, standardized assays and clinical guidelines are lacking, necessitating further studies to clarify their diagnostic and prognostic value. Understanding MYH9 antibodies bridges gaps between autoimmunity, hematology, and vascular biology.