Altered cytoskeletal integrity underlies impaired platelet shape change and defective thrombus formation in ETV6-related thrombocytopenia.

ratios and diminished alpha-granule pools. Flow cytometry and single-platelet total internal reflection fluorescence imaging demonstrated largely preserved calcium signalling but impaired activation-dependent shape change, dense-granule release and integrin activation. Proteomics showed reduced alpha-granule and lysosomal proteins alongside imbalanced regulators of actin remodelling and β-tubulin. Phalloidin staining confirmed impaired actin cytoskeletal remodelling with reduced lamellipodia formation, while immunofluorescence revealed abnormal β1-tubulin localization with disrupted marginal bands and reduced lysosome-associated membrane protein 1 (LAMP1) expression. Additionally, granulocyte recruitment and migration within thrombi were impaired, suggesting broader thromboinflammatory defects. These findings suggest that combined disruption of cytoskeletal integrity and granule biogenesis underlies impaired thrombus formation in ETV6-RT, providing mechanistic insight into the haemostatic defects associated with this disorder.