IntroductionTAM is characterized by a transient proliferation of abnormal myeloid cells in the bone marrow, leading to an excess of immature cells circulating in the peripheral blood [2]. TAM diagnosis is associated with the presence of GATA1 mutations, but other features such as blasts on peripheral blood smear, flow cytometry immunophenotype or cytogenetics can be indicative of TAM. This patient’s case is unusual due to the GATA1 mutation-negative status. The GATA1 gene encodes a transcription factor crucial for normal hematopoiesis and mutations in this gene are associated with myeloid disorders including TAM [3]. TAM leads to a wide range of hematologic abnormalities and clinical complications including hyperviscosity syndrome with potential for thrombosis, hydrops fetalis, pericardial effusion, respiratory distress, hypereosinophilia, pseudohyperkalemia, hyperbilirubinemia with liver failure, multi-organ failure and potential for death [1,2,5,14]. Patients with TAM require timely diagnosis as well as close follow up, as 20-30% of these patients subsequently develop myeloid leukemia associated with Down Syndrome (ML-DS) before the age of four [4]. GATA1 mutations have, to date, been discovered in nearly all patients with TAM and ML–DS [7]. The absence of aGATA1 mutation in this case raises the question of an alternative molecular mechanism contributing to the development of TAM and extreme thrombocytosis in this patient.