AbstractBackgroundThe inherited macrothrombocytopenias are rare disorders and the underlying cause can be identified in many cases but in some, this can remain enigmatic. Platelet transfusions are often administered during hemorrhagic events.MethodsA patient with previously unexplained inherited macrothrombocytopenia with a platelet count between 3–20 × 109/L is described in which studies were performed using exome sequencing (ES) and platelet flow cytometry.ResultsBoth the hemoglobin and white cell counts were normal. ES revealed two suspicious variants, one likely pathogenic and one a variant of uncertain significance, in the UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE) gene, and flow cytometry showed diminished expression of surface platelet sialic acid (about 5%) but normal red cell sialic acid. The Thrombopoietin (TPO) level was low, and the patient responded to TPO‐mimetic treatment with an increase in the platelet count.ConclusionTwo variants in the GNE gene were able to be upgraded to pathogenic with apparently restricted expression to the megakaryocyte lineage. Platelet transfusion may be avoided in these patients with TPO‐mimetic treatment.