What is hemoglobin?
Well the first thing to understand about hemoglobin is that there are different kinds of hemoglobin. For most adults, this isn’t too important, but for individuals with globinopathies like major thalassemia or sickle cell disease, knowing the different kinds of hemoglobin and globin chains can be important.
Adult hemoglobin is made up of 2 alpha (α) and 2 beta chains (β). This is referred to as Hb A (α2β2).
Embryonic hemoglobin
But we also have embryonic hemoglobins as well which come in 3 varieties:
- ζ2ε2
- α2ε2
- ζ2γ2
What do all those symbols mean? Let’s break them down.
In early embryo life, there is a form of alpha globin that is expressed that is called zeta ζ
In early embryo life, there is also a form of beta globin that is expressed that is called epsilon (ε)
Fetal hemoglobin
Later in fetal life (~8 weeks after fertilization), there is an increase in the production of a form of beta globin that is called gamma (γ)
When 2 alpha globins and 2 gamma globins combine together, they form Hb F (α2γ2), also known as fetal hemoglobin, the predominant form of hemoglobin in fetuses
- Hb F (α2γ2)
Adult Hemoglobin
Just before birth and continuing shortly after birth, there is an increase in the expression of β-globin and a decrease in the expression of gamma-globin, such that Hb A (α2β2) becomes the predominant form of hemoglobin and surpasses Hb F (α2γ2)
In the context of thalassemias, it is important to mention that there is yet another form of hemoglobin called Hb A2 (α2δ2)
- Hb A2 (α2δ2)
This form of hemoglobin is not too important other than in the context of diagnosing thalassemias.