Pearson syndrome (PS) is a very rare and often fatal multisystem disease caused by deletions in mitochondrial DNA that result in sideroblastic anemia, vacuolization of marrow precursors, and pancreatic dysfunction. Spontaneous recovery from anemia is often observed within several years of diagnosis. We present the case of a 4-monthold male diagnosed with PS who experienced prolonged severe pancytopenia preceding the emergence of monosomy 7. Whole-exome sequencing identified two somatic mutations, including RUNX1 p.S100F that was previously reported as associated with myeloid malignancies. The molecular defects associated with PS may have the potential to progress to advanced myelodysplastic syndrome. K E Y W O R D S monosomy 7, pearson syndrome, RUNX1 1 INTRODUCTION Pearson syndrome (PS) is a multiorgan system disorder characterized by refractory sideroblastic anemia with vacuolization of bone marrow (BM) precursors, lactic acidosis, and exocrine pancreatic dysfunction that result from the deletion of mitochondrial DNA (mtDNA) Abbreviations: BM, bone marrow; HSCT, hematopoietic stem cell transplantation; IBMFS, inherited bone marrow failure syndrome; MDS, myelodysplastic syndrome; mtDNA, mitochondrial DNA; PS, Pearson syndrome; WES, whole-exome sequencing sequences. Pancreatic dysfunction frequently accompanies PS but it is not critical for the diagnosis. 1,2 The incidence of PS is very low, at approximately one case per million individuals. 3 PS is one of the disorders to be considered in the differential diagnosis of hypocellular BM in young children. 4,5 It is not clear whether PS is associated with malignant transformation; the long-term prognosis of PS is generally poor, as children often succumb to fatal lactic acidosis. 6 Monosomy 7 is a common cytogenetic abnormality identified in inherited BM failure syndromes (IBMFSs) and pediatric

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Hemophagocytic lymphohistiocytosis (HLH) is a severe complication after allogeneic hematopoietic cell transplantation (HCT) and can cause graft failure or multi-organ failure. Here, we report two children with refractory HCT-associated HLH treated with ruxolitinib. In the first patient, ruxolitinib resolved fever, cytopenia and hyperferritinemia. In another patient, although severe hepatic failure, which developed and worsened before the administration of ruxolitinib, was irreversible, rapid improvement in fever, leukopenia and hyperferritinemia was observed. Of note, multiplex cytokine profiling showed amelioration of cytokine storm in both patients. Ruxolitinib may be an encouraging option for HCT-associated HLH.

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