*2.2.2.2 β-thalassemia*

should be noted that the symptoms of SCD are often serious, substantially reducing life expectancy and often requiring intensive treatment throughout the patient's

**Hemoglobin C** results from a variation in the gene that codes for hemoglobin (β6-Glu ! Lys), the protein in our RBC that helps carry oxygen around the body, It causes hemolytic anemia, splenomegaly in homozygous state and provides a degree of protection against malaria infection [12, 26]. Persons with hemoglobin C trait (Hb AC) are phenotypically normal, with no clinical evident limitations or symptoms. However, their heterozygous status, gives them a degree of protection against developing severe malaria HbC is common in malarious areas of West Africa, especially in Burkina Faso, the prevalence of HbAC is much higher and can reach

**HbS and HbC** caused by point mutations in the beta-globin gene, offer both substantial malaria protection. Despite the fact that the blood disorder caused by homozygosity for HbC is much less severe than that caused by homozygosity for HbS [9, 12, 26, 32], it is the sickle mutation which has come to dominate many oldworld malarious regions, whilst HbC is highly restricted in its geographical distribution [33]. It is probable that this discrepancy (blood disorder between HbC and HbS) may be due to sickle cell heterozygotes enjoying a higher level of malaria protection than heterozygotes for HbC. A probable higher fitness of HbS heterozygotes relative to HbC heterozygotes could certainly have allowed the sickle cell allele to spread more rapidly. However, observations that carrying either HbC or HbS enhances an individual's capacity to transmit malaria parasites to mosquitoes

**Hemoglobin E** results from a glutamate to lysine substitution in codon 26 (β26

HbE is the second commonest abnormal hemoglobin after sickle cell hemoglobin (HbS). HbE is common in South-East Asia, where its prevalence can reach 30–40%

The thalassemia syndromes are inherited disorders characterized by absence or markedly decreased accumulation of one of the globin subunits of hemoglobin. Individuals with thalassemia disease are not able to make enough hemoglobin,

There is two primary types of thalassemia disease: alpha (α) thalassemias and beta (β) thalassemia disease. In the α-thalassemias, there is absent or decreased production of α-globin subunits, whereas, in the β-thalassemias, there is absent or reduced production of β-globin subunits. Thalassemias affecting the production of delta (δ)- or gamma (γ)-globin subunits are also been described but are rare and not

The α-thalassemia syndromes are usually caused by the deletion of one or more α-globin genes and are sub classified according to the number of α-globin genes that

Glu-Lys and GAG-AAG). Besides being a structural variant, the E variant also causes the production of an abnormal mRNA with less b-globin being synthesized. It is synthesized at a slightly reduced rate and has a homozygous phenotype similar

life.

over 21% [26, 28, 30, 31].

could also shed light on this hypothesis [32].

*Human Blood Group Systems and Haemoglobinopathies*

in some parts of Thailand, Cambodia and in Laos [35].

to heterozygous β thalassemia [34].

*2.2.2 Thalassemia syndromes*

which causes severe anemia [24].

clinically significant disorder

are deleted or mutated [24].

There is two primary types of α-thalassemia:

*2.2.2.1 α-thalassemia*

**12**

The β-thalassemias are characterized by a quantitative deficiency of β-globin chains, can be sub classified into those in which there is a total absence of normal bglobin subunit synthesis or accumulation. The βthalassemias are divided into two main varieties (β0-thalassemia, there is no β-chain production and β<sup>+</sup> thalassemia, there is a partial deficiency of β-chain production) [24]. The molecular basis of the β-thalassemias is very heterogeneous, with over 200 different mutations having been described [38]. In general, the mutations causing β-thalassemia are point mutations affecting a single nucleotide, or a small number of nucleotides, in the bglobin gene. The frequency of carriers of β-thalassemia variants is from 5 to 20% in some areas, although not as high as the frequency of α-thalassemia variants [39].
