SYDE1 (synapse defective Rho GTPase activating protein 1) functions as a GTPase-activating protein (GAP) that regulates cytoskeletal remodeling by controlling the activity of Rho-type GTPases including RHOA, CDC42, and RAC1 1. As a downstream effector of the transcription factor GCM1, SYDE1 plays a critical role in placental development by positively regulating trophoblast cell migration and invasion 1. In endothelial cells, SYDE1 functions as a negative regulator of barrier integrity as part of a CDC42-centered signaling unit that includes the GEF FARP1 and effector PAK7 2. Functionally, SYDE1 promotes cytoskeletal remodeling and cell migration processes 1. Genetic ablation of murine Syde1 results in intrauterine growth restriction (IUGR) with small fetuses and placentas showing defects in placental-yolk sac barriers and vascularization 1. Clinically, decreased SYDE1 expression is associated with IUGR in both preterm and term placentas 1. SYDE1 has also been implicated in epithelial-mesenchymal transition reversal and identified as a candidate gene in familial pulmonary fibrosis 34.