Yuzawa K, Terui K, Toki T, et al. - In order to determine the features of neonates with transient abnormal myelopoiesis (TAM) and nonconstitutional trisomy 21, researchers retrospectively assessed the clinical and cytogenetic findings and GATA1 mutation status of 17 neonates with TAM and nonconstitutional trisomy 21 who had undergone GATA1 mutation testing at the institute, as well as contrasted the findings with those of 64 neonates with TAM and constitutional trisomy 21/Down syndrome (DS). Five of the 17 patients had reported clinical characteristics of DS. Both trisomy 21 and GATA1 mutations were identified in diagnostic samples in all patients. According to findings, TAM and nonconstitutional trisomy 21 patients displayed comparable biology and results to those with TAM and constitutional trisomy 21/DS. The possibility of TAM should be considered for appropriate management, even in phenotypically normal neonates with TAM symptoms.