Patient B
A 3-year old female with a past medical history of chronic urticaria and reactive airway disease was referred to hematology by allergy & immunology due to low platelet count. She had no history of infection, fever, or sick exposures. She reported easy bruising when active and presented with bilateral leg bruising. CBC results were similar to patient A (Table 1 ).
Family history revealed Patient B is the half-sister of Patient A, both of whom share a father. The father and three of his children have a history of low platelet counts. No other family members were symptomatic or needed treatment for their thrombocytopenia.
While the differential diagnosis for isolated mild thrombocytopenia is broad, family history pointed towards an inherited etiology. Von Willebrand factor (VWF) plasma studies were normal. Platelet transmission electron microscopy (PTEM) showed ultrastructurally normal platelets, with some platelets having large and decreased alpha granules. Bone marrow biopsy/aspirate had normal maturing trilineage hematopoiesis and showed no evidence of leukemia. There were reduced megakaryocytes and few hypolobated forms.
TABLE 1 Laboratory values in members of a family with theETV6 c.1085A>G variant