Sickle cell anemia and thalassemia are inherited diseases of the blood. Both of these diseases are hemoglobinopathies, which means that hemoglobin is somewhat affected by pathological process. Hemoglobinopathies are rather widespread: about 5% of the world’s population are carriers of a gene mutation for autosomal recessive conditions for a hemoglobinopathy (Metcalfe, Barlow-Stewart, Campbell, ; Emery, 2007, p. 812).
The thalassemias are, according to Weatherall (1997), “a family of inherited disorders of hemoglobin synthesis characterized by a reduced output of one or other of the globin chains of adult hemoglobin” (p. 1675). Thalassemia may result from one of more than 200 different mutations of genes encoding ? or ? chains of hemoglobin (Weatherall, 1997, p. 1675). Spritz ; Forget (1983) discern four groups of thalassemias: ?-thalassemias (p. 335), ?- thalassemias (p. 340), ?-thalassemias (p. 341) and ?-thalassemias (p. 344), whereas Weatherall (1997) mentions only two major groups of thalassemias: ?- and ?-thalassemias (pp. 1676-1677). Spritz ; Forget (1983) also stated the following:
The classical ?-thalassemias are of two general types: ?0- and ?+-thalassemia. In homozygous ?0-thalassemia, ?-globin chains are completely absent, although small quantities of ?-globin mRNA may be either present or absent. In homozygous ?+-thalassemia, however, ?-globin chains are present at 5%-30% of normal levels, and there is a proportional deficiency of ?-globin mRNA in the erythroid cells of affected individuals. (p. 337)
Sickle cell anemia is caused by “a glutamine-to-valine substitution at the sixth residue of the ?-globin polypeptide” (Frenette ; Atweh, 2007, p. 851). This disease has no different forms as thalassemia, and only one mutation is responsible for sickle cell disease. Thalassemias of different forms manifest in different times and through different signs and symptoms. ?-thalassemias may manifest early after birth or even during pregnancy (Metcalfe et al., 2007, p. 812-813). Such early manifestation is possible because ?-globin chains are synthesized both in fetal and subsequent periods of life (Weatherall, 1997, p. 1677).
Forms of thalassemia where ?-globin deficiency is occurred, manifest later than ?-thalassemias: “The common clinical features of ?-thalassaemia manifest after birth, usually within 6–12 months” (Metcalfe et al., 2007, p. 813). This difference in manifestation times is due to presence of fetal hemoglobin in the red blood cells during fetal period of life. Fetal hemoglobin doesn’t contain ?-globin chains and, thus, deficiency of its synthesis doesn’t affect the organism. But when replacement of fetal hemoglobin by adult form of the protein begins, symptoms of thalassemia arise.
Manifestation of sickle cell disease usually occurs at the same time when ?-thalassemias manifest. This similarity in manifestation time is also caused by presence of fetal hemoglobin and its gradual replacement by adult hemoglobin in postpartum period of life. When this replacement is almost complete, polymerization of sickle hemoglobin becomes possible and signs of disease began manifest (Frenette ; Atweh, 2007, p. 851).
Symptoms of ?-thalassemias are dependent upon the extent of mutations of ?-globine genes of affected organism (Metcalfe et al., 2007, p. 813). If all four copies of ?-globine genes are affected by mutations, hydrops fetalis occurs and the fetus or neonate will not survive, and mother’s life will be endangered too due to “high risk of developing early pre-eclampsia, antepartum or postpartum haemorrhage, and preterm delivery” (Metcalfe et al., 2007, p. 813).
Signs of manifesting ?-thalassemias are commonly “pallor, lethargy, poor appetite, failure to thrive, irritability and difficulty settling, developmental delay and haemolytic anaemia. Splenomegaly, hepatomegaly, growth failure with bone changes, fractures and leg ulcers can be seen in childhood” (Metcalfe et al., 2007, p. 813-815). Severity of these symptoms depends of number of mutant copies of ?-globin gene, i.e. of degree of ?-globin deficiency. Full deficiency (which is possible when person is ?0-homozygous) results in severe anemia, and partial deficiencies manifest in moderate or mild symptoms.
Sickle cell anemia is associated with sickle crises which involve “intermittent episodes of vascular occlusion and tissue ischaemia causing pain and resulting in acute and chronic damage to virtually every organ, especially the spleen, brain, lungs and kidneys” (Metcalfe et al., 2007, p. 815). Also intense hemolysis of sickled erythrocytes occurs and this affects spleen and bone marrow greatly. These symptoms manifest only in persons who are homozygous for mutant gene HbS, heterozygous carriers display no symptoms and have very small amounts of HbS in their erythrocytes.
Certain regions exist where thalassemias and sickle cell anemia are prevalent due to high frequency of carriers. These regions are not the same for all diseases mentioned. According to studies of Metcalfe et al. (2007), carriers of ?-thalassemia are common in Middle East, Southern Europe, India, Africa, Central and Southeast Asia. Sickle cell disease has little carriers in Central and Southeast Asian regions, but shares other regions of high carrier density with ?-thalassemia, and is also prevalent among African Americans, in Southern America and on the Caribbean. Carriers of ?-thalassemias are generally less frequent than carriers of other hemoglobinopathies and comprise approximately 1 to 20 in regions of China, Pakistani, Maori, among the Africans, Pacific Islanders, indigenous Australians and population of Southeast Asia, Southern Europe and Middle East (p. 813).
Treatment of all these hemoglobinopathies includes blood transfusions and iron chelation to prevent organ damage from excessive iron in the blood as result of intensive hemolysis (Frenette & Atweh, 2007, p. 853; Weatherall, 1997, p. 1678). But treatment of sickle cell anemia also includes induction of fetal hemoglobin production by hydroxyurea, butyrate and decitabine, and bone marrow transplantations (Frenette & Atweh, 2007, pp. 853-855). Treatment of thalassemias also may include bone marrow transplantations, but on early stages of life only, before damage from iron load becomes significant (Weatherall, 1997, p. 1678).