This gene encodes a half of a transcription factor involved in the induction of genes regulated by oxygen, which is induced as oxygen levels fall (hypoxia). The encoded protein contains a basic helix-loop-helix domain protein dimerization domain as well as a domain found in proteins in signal transduction pathways which respond to oxygen levels. EPAS 1 is involved in the development of the embryonic heart and is expressed in the endothelial cells that line the walls of the blood vessels in the umbilical cord. It is essential in maintaining catecholamine homeostasis and protection against heart failure during early embryonic development.
Catecholamines include epinephrine and norepinephrine. It is important for the production of catecholamines to remain in homeostatic conditions so that both the delicate fetal heart and the adult heart do not overexert themselves and induce heart failure. Catecholamine production in the embryo is related to control of cardiac output by increasing the fetal heart rate.
Mutations in EPAS1 gene are related to early onset of neuroendocrine tumors such as paragangliomas, somatostatinomas and/or pheochromocytomas. The mutations are commonly somatic missense mutations that locate in the primary hydroxylation site of HIF-2α, which disrupt the protein hydroxylation/degradation mechanism, and leads to protein stabilization and pseudohypoxic signalging. In addition, these neuroendocrine tumors release erythropoietin (EPO) into circulating blood, and lead to polycythemia.
Mutations in this gene are associated with erythrocytosis familial type 4,pulmonary hypertension and chronic mountain sickness. There is also evidence that certain variants of this gene provide protection for people living at high altitude. EPAS 1 is useful in high altitudes as a short term adaptive response. However, EPAS 1 can also cause excessive production of red blood cells leading to chronic mountain sickness that can lead to death and inhibited reproductive abilities. Some mutations that increase its expression are associated with increased hypertension and stroke at low altitude, with symptoms similar to mountain sickness. People permanently living at high altitudes might experience selection of EPAS 1 to reduce the fitness consequences of excessive red blood cell production.
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