| Resumo: |
Alpha thalassemia is a syndrome resulting from disturbances in the synthesis of alpha globin chain that forms the tetramer of the hemoglobin molecule. Alpha thalassemia is classified into four types according to the number of alpha genes affected: silent carrier (-α/αα), alpha thalassemia trait (--/αα or -α/-α) Hemoglobin H disease (-- /-α), and fetalis hydrops (--/--). The decrease in synthesis of alpha globin causes inadequate production of hemoglobin resulting in hypochromic and microcytic anaemia. Also it causes accumulation of beta chains, inside the erythrocytes, resulting in formation of beta chain tetramer of hemoglobin called Hb H. Clinically the individual with thalassemia can be asymptomatic or present severe anemia. Asymptomatic forms of thalassemia, silent carrier and alpha thalassemia trait, are more difficult to diagnose because of the inclusions bodies of Hb H are not always present. In these situations it is necessary to research the molecular characterization of the genotype and confirming the presence of alpha thalassemia. This is mainly because the diagnosis by conventional methods, although important, is limited and imprecise. This study evaluated some of the traditional laboratory methods in the detection of alpha thalassemia and associated molecular characterization of the more prevalent deletion forms α3,7 and α4,2. For confirmation and characterization of alpha thalassemia, new oligonucleotides were designed. By conventional PCR technique, using 3.7F/KGB01 primers it was possible to detect the deletion α3,7, differentiating the normal genotype (αα/αα), the heterozygote (-α3,7/αα), and homozygous (-- α3,7/- α3,7). Although it was designed to detect the deletion α3,7, this primers also identified the deletion α4,2 when in homozigose (-α4,2/- α4,2). The primers KGB04/KGB05 detected the deletion α4,2, but without differentiating between the heterozygous and homozygous genotype. The most prevalent deletion founded was the α4,2 (20.0%) which represents 9.2% in the homozygous form (- α4,2/-α4,2). The deletion α3,7 in the heterozygous form was detected in 12.3% of patients. The data demonstrate that the importance of molecular detection for alpha thalassemia is not limited only to the definition of the genotype, but also confirmation of the presence in patients with abnormal erythrogram values, with regular erythrogram values, with values closed to the boundary values and in neonates. |
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