Hemoglobin E without Hemoglobin A

An individual with hemoglobin E as the principal hemoglobin but no hemoglobin A may have either homozygous hemoglobin E (E/E), or hemoglobin E/beta-thalassemia (E/beta-thal). The best method to distinguish these is to test both parents. It is important to determine the diagnosis accurately since homozygous hemoglobin E (E/E) is an asymptomatic condition and hemoglobin E/beta-thalassemia is a serious life-threatening disease that needs treatment. Hemoglobin E is found mainly in Asians. Viewed worldwide, about 30 million people are Hb E carriers. Carriers are asymptomatic. Hemoglobin E contains lysine substituted for the glutamic acid as amino acid 26 in the beta chain of hemoglobin A. Hemoglobin E has the same electrophoretic mobility (on cellulose acetate at pH 8.6) as hemoglobin A2 and hemoglobin C. The mobility of these hemoglobins differs on agar gel electrophoresis (pH 6.2) and they can be distinguished by this method. The synthesis of hemoglobin E in reticulocytes of A/E heterozygotes and E/E homozygotes appears to be significantly impaired. The impairment seems to be in the production of beta E chains. Therefore the Hb E structural gene may be viewed as a beta-thalassemia-like gene.

Homozygous hemoglobin E: (E/E) Patients who are homozygous for hemoglobin E are usually asymptomatic. They may have a mild to moderate degree of anemia with a slight reduction of red cell survival. The red cells show a significant reduction in MCV with a mean value of 67. Target cells are seen on dried blood smears. No treatment is necessary for patients with homozygous hemoglobin E and no health problems are associated with this diagnosis.

Hemoglobin E/ beta-thalassemia: (E/beta-thal) The combination of HbE and beta⁰-thalassemia (no hemoglobin A present) produces a severe clinical disorder although a great variability of clinical expression is seen. At the severe extreme without treatment, a child with HbE/beta⁰-thalassemia will be small in stature with wasted extremities and poor body development with a protuberant abdomen. As the child grows there are marked skeletal abnormalities and retardation of growth and development. There is an increased incidence of infection and this is the most common cause of death from this disease. The interaction of HbE/beta⁺-thalassemia (some hemoglobin A present) results in a milder condition. The main form of treatment for all forms of symptomatic thalassemia is blood transfusion. For those patients dependent on blood transfusion, iron-chelating agents are required. Early management of complications, in particular infection, and good general medical care are important .

If a child with hemoglobin E and no hemoglobin A cannot be diagnosed because both parents are not available, hemoglobin levels should be monitored closely. If the child becomes anemic, DNA diagnosis is indicated to determine if the diagnosis is Hb E/beta-thalassemia.

References

1. Bunn and Forget: Hemoglobin: Molecular, Genetic and Clinical Aspects. Philadelphia, W.B.Saunders Company, 1986
2. Weatherall and Clegg: The Thalassaemia Syndromes. Third Edition. Oxford, Blackwell Scientific Publications 1981

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