LAUSR

Transient abnormal myelopoiesis (TAM) is a myeloid proliferative condition with leukemic potential, almost exclusively seen in infants with trisomy 21 (Down syndrome [DS]). We report here an unusual case of a neonate without DS who presented with a petechial rash and a highly elevated white blood cell (WBC) count with myeloid blasts, initially concerning for acute myeloid leukemia (AML). Trisomy 21 and a GATA1 frameshift mutation were present in the myeloid blast-predominant peripheral blood, leading to the diagnosis of TAM. Trisomy 21 was absent in the lymphocytes and skin fi broblasts, supporting the diagnosis of mosaic DS in this infant. This case highlights the importance of rapid cytogenetic and molecular diagnostic techniques in the evaluation of neonatal leukemia. The patient, a phenotypically normal male infant, was born at 37 weeks via cesarean delivery after an uneventful pregnancy with full prenatal care, including normal prenatal cell-free DNA screening. A petechial rash on face, scalp, and torso was present at He did not have hepatosplenome-galy, and results of a physical examination were otherwise normal. A complete blood count showed a WBC count of 112 3 10 3 cells/ m L with 76% blasts a hemoglobin of 10 g/dL, and a platelet count of