The -[[alpha].sup.3.7] deletion in [alpha]-globin genes increases the concentration of fetal hemoglobin and hemoglobin [A.sub.2] in a Saudi Arabian population

The regions of Al-Qatif and Al-Ahssa in the Eastern Province of Saudi Arabia are known for their high prevalence of hemoglobinopathies, including [beta]-thalassemia and sickle cell anemia. Previously, the [alpha]-gene deletion has been demonstrated as highly prevalent among populations residing in these two regions. The present study was conducted in order to investigate the implications of the [alpha]-globin gene deletion on fetal hemoglobin (HbF) and hemoglobin [[alpha].sub.2] ([HbA.sub.2]) concentrations in patients with transfusion-dependent [beta]-thalassemia. A total of 166 Saudi patients with transfusion-dependent [beta]-thalassemia and 337 healthy Saudi patients were included in the study. The -[[alpha].sup.3.7], -[[alpha].sup.4.2], [--.sup.FIL], [-- .sup.SEA], [--.sup.MED] and [--.sup.(20.5)] gene deletions were identified using multiplex [alpha]-globin deletion polymerase chain reaction. The present study revealed that the -[[alpha].sup.3.7] gene deletion is the most prevalent (43.5%) in the Saudi populations that were analyzed and is characterized by the deletion of 3,804 base pairs. Numerous genotypes, namely [sup.-3.7][[alpha].sub.2]/[[alpha].sub.1][[alpha].sub.2], [sup.- 3.7][[alpha].sub.2]/[[alpha].sub.1][[alpha].sub.12], [sup.-3.7][[alpha].sub.2]/[sup.-3.7][[alpha].sub.2], [sup.- 3.7][alpha][2.sup.HphI]/[[alpha].sub.1][[alpha].sub.2.sup.HphI], [sup.- 3.7][[alpha].sub.2]/[[alpha].sub.1.sub.-4.2], [sup.-3.7][[alpha].sub.2]/[[alpha].sub.1.sup.polyA-1][[alpha].sub.2], [sup.- 3.7][[alpha].sub.12]/[[alpha].sub.1][[alpha].sub.12], [sup.-FIL]/[sup.- 3.7][[alpha].sub.2] and [sup.- 3.7][[alpha].sub.2]/[sup.-3.7][[alpha].sub.2.sup.Hb Villiers le Bel] were also identified in the investigated population. Furthermore, a gradual increase in the concentration of HbF and [HbA.sub.2] in patients with [beta]-thalassemia and the number of [alpha]-gene deletions was demonstrated; whereas in healthy patients the level of [HbA.sub.2] was demonstrated to decrease as the number of [alpha]-gene deletions increased. Therefore, it can be concluded that the high HbF concentration in the present study is predominantly associated with other mutations associated with [beta]-thalassemia rather than [alpha]-globin deletions. Furthermore, the results of the present study also revealed novel [alpha]-gene deletion genotypes prevalent in the population studied, namely [[alpha].sub.1][[alpha].sub.2]/[[alpha].sub.1][[alpha].sub.2.sup.HphI], [[alpha].sub.1][[alpha].sub.2.sup.HphI]