Embryonic hemoglobin

[4] Due to its relative stability compared to hemoglobin Gower 1 and hemoglobin S, it has been proposed as a subject for reactivation in the adult in cases of severe β thalassemia and hemoglobinopathies in subjects for which the reactivation of hemoglobin F is contraindicated due to toxicity concerns.

[4] Hemoglobin Portland I (also referred to as ζ2γ2 or HbE Portland-1) is a form of hemoglobin existing at low levels during embryonic and fetal life, composed of two zeta chains and two gamma chains.

[4] Hemoglobin Portland II (also referred to as ζ2β2 or HbE Portland-2) is a form of hemoglobin existing at low levels during embryonic and fetal life, composed of two zeta chains and two beta chains.

It is quite unstable, more so than even hemoglobin Gower 1, and breaks down very rapidly under stress.

[4] Despite this, it has been proposed as a candidate for reactivation in cases of severe α thalassemia or hemoglobinopathies afflicting the alpha chain.