These conditions are caused by deletions which include the Agamma-globin gene; they are rare and are, with the exception of a few, found in only a few families. The phenotypes are similar to those of the GgammaAgamma(deltabeta)°-thal with a mild anemia in the heterozygote and microcytosis, hypochromia, low-to-normal levels of Hb A2, 10-15% Hb F with Ggamma chains only. Homozygotes have a thalassemia intermedia. Fig. 16 compares the locations and the sizes of the 12 types that have been discovered.
FIG. 16. The locations and sizes of the 12 known deletions causing a Ggamma(Agammadeltabeta)°-thal.
The Indian type is a combination of two small deletions and an inversion. The Black type is likely the most common one observed. The combination of this type with Hb S is often confused with sickle cell anemia (with alpha-thal); family studies and fetal Hb analyses will give some useful data for reaching a differential diagnosis. The original proband of the Thai Ggamma(Agammadeltabeta)°-thal had a most interesting combination of this deletion, a beta°-thal and a gamma-thal.