Influence of α and β-Globin Mutations on Ineffective Erythropoiesis in β-Thalassemia Minor Cases.

Introduction: Thalassemia minor is a prevalent genetic disorder around the world. A large number of mutations have been implicated in the development of a β-thalassemia minor phenotype. The diagnosis of β-thalassemia minor is made based on phenotypic parameters: microcytosis and elevated HbA2, with or without elevated HbF. We previously reported (ASH 2004, abstract #3761) that erythrocytic parameters of β-thalassemia minor are significantly different in patients with concomitant α-globin deletions, suggesting a reduction of ineffective erythropoiesis. The goal of the present study is to evaluate the effect of α and β-globin mutations on erythrocytic parameters in β-thalassemia minor patients.

Methods: Diagnosis of β-thalassemia minor was established using Hb HPLC analysis (Variant II, Bio-Rad) with increased HbA2 +/− increased HbF without expression of an abnormal Hb in cases of microcytosis. The DNA of consecutive cases with newly diagnosed β-thalassemia minor was extracted from leucocytes. A m-PCR was used to detect the presence of 7 α-globin gene deletions (-α^3.7, -α^4.2, --^SEA, --^FIL, --^MED, --^THAI, -α^20.5). PCR and automated sequencing using fluorescence-based capillary electrophoresis (ABI PRISM 3100 Genetic Analyser) was performed to identify β-globin mutations causing the thalassemia phenotype. Data on age, sex and erythrocyte indices (Hb, MCV, RBC and RDW) was recorded. Student t-test was used to compare groups on the erythrocytic parameters.

Results: At the time of analysis, 175 samples were fully studied. At least one mutation in the β-globin gene was identified in 172 cases (98.3%, 95%IC: 95–99.5%). Groups were defined for comparison of erythrocytic parameters: mutations causing β⁺ phenotype, mutations causing β⁰ phenotype. Sub-groups were also analysed based on the presence or absence of α-globin gene deletions. Results are presented in Table 1 and 2.

Conclusion: The correlation between β-globin mutation and a β-thalasemia minor phenotype indicates that the phenotypic parameters correctly diagnoses β-thalasemia minor in the great majority of cases. Mutations classified as β⁰ affect more negatively the MCV, probably as a consequence of a reduced β-globin production and a greater level of ineffective erythropoiesis than in the β+ group. Higher MCV values in both β⁺ and β⁰ mutations when paired with an α-globin deletion compared with cases without an α-globin gene deletion could be explained by the concomitant reduction of functional α and β globin chain production, therefore causing less ineffective erythropoiesis.