To the Editor, Deficiency of adenosine deaminase 2 (DADA2) was initially described simultaneously in 2014 by two groups [1, 2]. Enzymatic deficiency occurs via autosomal recessive inheritance of CECR1 gene mutations. Early descriptions of the disorder highlighted early-onset stroke, vasculitis presenting as polyarteritis nodosa, livedo reticularis, recurrent fevers, and hypogammaglobulinemia as the predominant clinical manifestations observed in patients [1–5]. The discovery of additional patients with DADA2 has revealed a highly variable clinical presentation with many features responsive to therapy with anti-tumor necrosis factor agents [2, 6–11]. Although not described in the initial cohorts of patients, hematological manifestations now appear to be a significant clinical component of deficiency of adenosine deaminase 2 [6–9, 12]. The pathogenesis underlying the hematologic dysfunction seen in patients has yet to be elucidated, although persistently elevated levels of tumor necrosis factor (TNF)-alpha have been described to be damaging to hematopoiesis within the bone marrow [13, 14]. Here, we describe a case of two adult brothers with DADA2 presenting with cytopenias and bone marrow hypocellularity. We particularly detail the clinical course of one brother with initial partial response to equine anti-thymocyte globulin and cyclosporine with recurrence of cytopenias following withdrawal of immunosuppression. Retreatment was initiated with anti-tumor necrosis factor alpha therapy resulting in clinical symptom improvement and normalization of blood counts. Patient 1 presented at 47 years of age with leukopenia following evaluation for recurrent upper respiratory and allergy symptoms. Complete blood count (CBC) at that time was notable for white blood cell (WBC) count 2.3 K/μL (35% neutrophils, 11% bands, 28% lymphocytes, 25% monocytes, and 1% basophils), hemoglobin 14.3 g/dL, MCV 90.7 fL, and platelets 153,000 K/μL. The patient’s past medical history was notable for Bmyositis^ as a child and right lower extremity cellulitis with associated sepsis as an adult. Family history was significant for a brother with neutropenia. Physical exam was unremarkable other than diffusely dry and vasculitic-appearing darkened skin on his bilateral lower extremities (Fig. 1 a). Within 3 years, he progressed to pancytopenia with hemoglobin falling to 6 g/dL requiring frequent red blood cell transfusions and platelet and absolute neutrophil counts ultimately reaching nadirs of 49,000 and 620/uL, respectively. Initial bone marrow biopsy was hypocellular (range 0–15%) with a patchy distribution of hematopoietic precursors, mild reticulin fibrosis, and an increased proportion of CD3-positive T cells distributed interstitially. Flow cytometric immunophenotyping of the bone marrow disclosed no lymphoid antigen aberrancies and no increase in blasts. Cytogenetic analysis of the bone marrow yielded a normal male karyotype (46, XY). Testing for paroxysmal nocturnal hemoglobinuria was negative. Repeat bone marrow examination performed 6 months later, prior to