A 4-month-old girl with Down syndrome showed unexpected deterioration of pulmonary hypertension. Despite aggressive pulmonary vasodilation therapy, the patient died at 5 months of age. Lung autopsy showed that the pulmonary veins were obliterated by intimal fibrous thickening, and the media of the veins was arterialised with an increase in elastic fibres. Pulmonary veno-occlusive disease should be considered in the management of individuals with Down syndrome.

We report an infantile case of Loeys–Dietz syndrome prenatally diagnosed with congenital complex heart disease – double outlet right ventricle and interruption of the aortic arch. The patient also showed prominent dilatation of the main pulmonary artery. Emergency bilateral pulmonary artery banding was performed on the 9th day. However, on the 21st day, the patient died of massive bleeding due to rupture of the right pulmonary artery. Subsequently, a mutation of the TGFBR1 gene was detected. As cardiovascular lesions of Loeys–Dietz syndrome appear early and progress rapidly, the prognosis is generally poor. Patients require periodic examination and early intervention with medical therapy such as Losartan administration and surgical therapy. Early genetic screening is thought to be useful for the prediction of complications as well as vascular disease.