A 24-month-old African-American boy presented to his pediatrician for a well-child check. He had no complaints and an unremarkable physical exam. Complete blood count sent as routine 2-year-old screening showed pancytopenia with hemoglobin 6.1 g/dL, a WBC count 3.6 K/uL, and platelet count of 120 K/uL. Differential was not initially available. Family history was unremarkable. Pennsylvania newborn screen had been normal for hemoglobin screening.

The patient was referred to to the Emergency Department, where he was afebrile with normal vital signs. On targeted questioning, parents noted decreased activity and appetite with increased fatigue. Recent viral symptoms were denied. Exam was notable for pallor and a 2/6 systolic ejection murmur, with no jaundice or hepatosplenomegaly. Repeat blood counts in the ED were essentially the same. White blood cell differential analysis showed 14% neutrophils, 84% lymphocytes, 2% atypical lymphocytes, and calculated absolute neutrophil count of 520 per uL. He received a transfusion of packed red blood cells and was discharged home with Hematology follow-up.

Over the next 2 months, he required two pRBC transfusions for hemoglobin < 8 g/dL. Bone marrow aspirate was performed that showed 15% sideroblasts and 4% blasts.

Have you figured out this diagnosis? The correct answer is single large-scale mitochondrial DNA deletion syndrome (SLSMDS), classically labeled as Pearson syndrome, the subject of the Winter 2019 cover article.

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