In thalassemia, there is often an excess production or accumulation of globin chains whose genes are not affected by the deletion.

In beta thalassemia, this may be seen as an increase in gamma chain and delta chain production, leading to increased levels of hemoglobin F and A₂ respectively.

Excess alpha chains may also form tetramers which often lead to red cell membrane damage and decreased red cell deformability. This leads to a hemolytic anemia. Adding to the anemia is a decrease in the total amount of hemoglobin produced in spite of the erythroid hyperplasia of the bone marrow.