There are rare exceptions, notably with beta thalassemia, where globin gene mutations exhibit a dominant pattern of inheritance in which only one gene needs to be altered in order to see disease expression.
This occurs in many diseases, including iron deficiency anemia, thalassemia (an inherited disease in which globin chain production is deficient), and anemias associated with chronic infection or disease.
There are two categories of hemoglobinopathy: in one, abnormal globin chains give rise to abnormal hemoglobin molecules; in the other, normal hemoglobin chains are produced but in abnormal amounts.
Because alpha globin is a necessary component of hemoglobin, absence of all functioning alpha globin genes leads to serious medical consequences that begin even before birth.
Since there are four genes (instead of the usual two) to consider when looking at alpha globin gene inheritance, there are several alpha globin types that are possible.