Isolated fetal pulmonary artery dilation as the primary presentation of Loeys-Dietz syndrome: a prenatal red flag for a severe TGFBR1 pathogenic variant

Isolated fetal great vessel dilation is rarely reported as the sole prenatal feature of Loeys-Dietz syndrome (LDS). We describe a fetus with isolated main pulmonary artery (PA) dilation detected at 20 weeks’gestation. Postnatal echocardiography and cardiac CT confirmed marked PA aneurysm and mild aortic root enlargement, followed by marked progression from the postnatal baseline. Trio-based whole-exome sequencing identified a de novo pathogenic TGFBR1 variant (c.1460G > A, p.Arg487Gln), confirming LDS. This case establishes isolated fetal PA dilation as an early and severe presenting sign of LDS, expands the prenatal phenotypic spectrum, and highlights the importance of genetic evaluation in cases of apparently isolated great vessel dilation to enable timely surveillance and intervention for potential vascular complications.