The diagnosis of HCL includes studies on peripheral blood showing anemia and thrombocytopenia, flow cytometry showing markers positive for CD19, CD20, CD22, CD123, and CD103, and peripheral smear showing lymphocytes with hair-like cytoplasm projections, termed "hairy cells," that stain positive for tartrate-resistant acid phosphatase (TRAP); bone marrow aspiration is also used as a diagnostic tool where a "dry tap" can be found, meaning an inability to perform the aspiration due to the marrow fibrosis induced by the hairy cells [3,4]. The gene discussed is ACP5; the disease is Thrombocytopenia.