Bleeding disorder, platelet-type, 21

An inherited platelet disorder caused by a variation in the FLI1 gene, an ETS-family transcription factor required for megakaryocyte maturation and formation of platelet alpha- and dense granules. Affected individuals typically exhibit mild to moderate thrombocytopenia, enlarged platelets, and characteristic defects in platelet granules, including absent or markedly reduced dense granules and enlarged or fused alpha-granules, leading to abnormal secretion and impaired aggregation responses. The clinical phenotype ranges from asymptomatic to significant mucocutaneous bleeding, menorrhagia, or perioperative bleeding.