Transient Myeloproliferative Disorder as the Presenting Feature for Mosaic Trisomy 21

Trisomy 21 is a common congenital disorder with well documented clinical manifestations, including an increased risk for transient myeloproliferative disorder as a neonate and leukemia in childhood and adolescence. Children with mosaic trisomy 21 can have a similar risk for hematological malignancies. We present a non-dysmorphic neonate, with negative noninvasive prenatal screening of maternal blood for trisomy 21, who came to medical attention because of ruddy skin. He was found to have mild polycythemia, thrombocytopenia and developed peripheral blasts. His clinical presentation was concerning for transient myeloproliferative disorder, which is only seen in trisomy 21 patients. Cytogenetic studies were positive for mosaic trisomy 21.