Six different, large deletions have been described in which all functional globin genes (epsilon, Ggamma, Agamma, delta, beta) have been deleted. The locations and sizes of these deletions are shown in the top section of Fig. 17.
The anomalies are rare occurrences and have only been found in a few, often, single families. Newborns, heterozygous for such a condition, are rather severely affected, sometimes requiring blood transfusions. The condition improves at 3-6 moths after birth; adult heterozygotes have mild anemia with microcytosis and hypochromia and low levels of Hb F (1-3%). In one Dutch family an (epsilongammadeltabeta)°-thal deletion occurred de novo.
FIG. 17. The locations and sizes of the deletions causing an epsilongammadeltabeta-thalassemia.
One deletion has been observed in which the beta-globin gene is intact (Dutch type), a second has intact Agamma, delta, and beta genes (English type), and a third has intact epsilon, Ggamma, Agamma, delta, and beta genes (Hispanic type). All three have in common the deletion of the controlling region HS-1 through HS-4 which is located 5' to the epsilon gene. The absence of this segment of DNA inactivates all globin genes in the 3' location. The locations and sizes of the three deletions are shown at the bottom of Fig. 17.