Any familial polycythemia in which the cause of the disease is a mutation in the EGLN1 gene. The disease is Monarch Disease Ontology entry MONDO_0012353 (erythrocytosis, familial, 3). Also known as: EGLN1 familial polycythemia, erythrocytosis, familial, type 3, familial polycythemia caused by mutation in EGLN1.