Hemoglobinopathies

Hemoglobinopathies 

conditions caused by the presence of one or more anomalous (pathological) hemoglobins in the red blood cells (erythrocytes).

More than 50 pathological varieties of hemoglobin resulting from a genetically transmitted congenital defect in the formation of the protein constituent of hemoglobin (globin) have been identified. Hemoglobin anomalies impair the physicochemical properties of erythrocytes and their metabolic processes; the erythrocytes become less resistant to various hemolytic factors. Pathological hemoglobins are designated by capital letters of the Latin alphabet from C to Q, combined with the symbol for hemoglobin (Hb). When the hemoglobinopathy is transmitted from one parent only (heterozygous inheritance), the carriers of the pathological hemoglobin trait may in effect appear healthy. When it is transmitted from both parents (homozygous inheritance), the child develops symptoms of severe hemolysis.

Hemoglobinopathies occur mostly in tropical and subtropical regions (equatorial Africa, the Arabian Peninsula, southern India, southern China, the Mediterranean basin, and elsewhere). In the USSR, hemoglobinopathies are found most commonly in Azerbaijan and Georgia. Sickle-cell (drep-anocytic) anemia and thalassemia are the most common and show the most severe symptoms. Sickle-cell anemia (HbS) is caused by the presence of pathological hemoglobin S (so designated for the first letter of the English word “sickle”) in the erythrocytes; the erythrocytes become sickle-shaped when the partial pressure of oxygen in the environment decreases. An increase in the number of sickled erythrocytes makes the blood more viscous and slows the blood flow. The sickled erythrocytes are destroyed and thromboses develop in various organs. In the apparently healthy carriers of HbS the sickling of erythrocytes and the appearance of symptoms of the disease can occur only under hypoxic conditions. Service in aviation is therefore contraindicated for all carriers of HbS, as is all flying on airplanes without sufficient supply of oxygen.

Thalassemia is a disease occurring in Mediterranean countries. It is characterized by a substantial increase of HbF in the blood. This is believed to suppress the formation of normal hemoglobin HbA and to interfere with the formation of heme (the iron-containing constituent of hemoglobin). Thalassemias are described as major, minor, and minimal; the minor or minimal form develops in cases of heterozygous inheritance and the major form, with homozygous inheritance. The presence of “target-like” erythrocytes in the blood is characteristic of all forms of thalassemia, in which the hemoglobin resembles a target in the center of the cell.

The symptoms of sickle-cell anemia and thalassemia (arrested general development, anemia, jaundice, enlarged liver and spleen, and changes in the bones) appear in early childhood. Complications of sickle-cell anemia include thromboses of the intestinal blood vessels and pigmental gallstones. Treatment upon the development of anemia includes blood transfusion and vitamins. In cases of thalassemia slight improvement may follow removal of the spleen. Ovalocytosis is sometimes included among the hemoglobinopathies. There are other hemoglobin anomalies (HbC, HbD, HbE) in addition to the forms described here. Familiarity with the prevalence of hemoglobinopathies and detection of the carriers are of definite value in preventing these diseases.

REFERENCES

Kassirskii, I. A., and G. A. Alekseev. Klinicheskaia gematologiia, 4th ed. Moscow, 1970.
Genetika v gematologii. Edited by I. A. Kassirskii. Leningrad, 1967.

A. M. POLIANSKAIA