Congenital Chylothorax and Hydrops Fetalis: A Novel Neonatal Presentation of RASA1 Mutation.

Mutations in the RASA1 gene are known to cause arteriovenous malformations (AVMs), with evidence of associated lymphatic malformations. We report for the first time, to the best of our knowledge, an infant with RASA1 mutation presenting with hydrops fetalis and chylothorax, but without an associated AVM. Previously, researchers studying rodents have found chylothorax associated with RASA1 mutations, and, in previous case reports, researchers have reported on infants with RASA1 mutations born with hydrops fetalis and AVMs. In this report, we describe the case of a "late preterm" female infant born with nonimmune hydrops fetalis and congenital chylothorax who was detected to have a RASA1 deletion on genetic workup. Although classically described phenotypes of RASA1 mutations present with venous malformations, no such malformations were found in this infant on extensive imaging. This combination is a novel and nonclassic presentation of RASA1 mutation. In cases of congenital chylothorax, especially with nonimmune hydrops fetalis, RASA1 mutations should be considered as part of the differential diagnosis and genetic testing should be included as part of a complete workup to allow for screening for associated vascular anomalies.