WASHC3 is a component of the WASH complex that functions as a nucleation-promoting factor at endosomal membranes, recruiting and activating the Arp2/3 complex to promote actin polymerization and facilitate endosomal tubule fission during cargo sorting 1. Beyond its canonical role in endosomal trafficking, WASHC3 regulates PTH1R endosomal trafficking and signaling in growth plate chondrocytes, with genetic variants impairing this function causing short stature, distinctive facies, and neurodevelopmental abnormalities 1. WASHC3 also plays an unexpected role in cardiac mitochondrial protein homeostasis; loss of function impairs mitochondrial respiration and oxidative phosphorylation in cardiomyocytes 2. Genetically regulated WASHC3 splicing is associated with endometriosis risk 3, and elevated WASHC3 plasma levels are identified as a risk factor for endometriosis 4. Additionally, genetic variation in WASHC3 influences activation of the mesolimbic reward system, suggesting roles in dopaminergic neurotransmission and reward processing 5. These findings establish WASHC3 as a multifunctional protein with critical roles in skeletal development, cardiac bioenergetics, reproductive disease pathophysiology, and neural reward system function.