Erythrocytosis, Familial, 4, also known as ecyt4, is related to autosomal dominant secondary polycythemia and duodenal somatostatinoma. An important gene associated with Erythrocytosis, Familial, 4 is EPAS1 (Endothelial PAS Domain Protein 1), and among its related pathways/superpathways are Regulation of activated PAK-2p34 by proteasome mediated degradation and Cellular responses to stimuli. Affiliated tissues include bone marrow and bone, and related phenotypes are polycythemia and deep venous thrombosis