Inherited inactivating mutations in EPHB4 and RASA1 are also responsible for the development of lymphatic vascular abnormalities in humans, including lymphedema, chylous ascites and chylothorax, lymphatic-related hydrops fetalis, central conducting lymphatic anomaly, and abnormal lymphatic flow (2, 3, 5–8, 17, 39, 40). The gene discussed is EPHB4; the disease is lymphedema.