Trisomy 21, transposition of the great arteries and abnormal myelopoiesis.

Down syndrome is a well-recognised genetic condition associated with several comorbidities. Although CHD is common in Down syndrome, transposition of the great arteries is exceptionally rare. We describe a neonate with Down syndrome who presented with transient abnormal myelopoiesis and transposition of the great arteries. Down syndrome may accelerate pulmonary hypertension in transposition of the great arteries and is associated with poor outcomes.