Balkan Journal of Medical Genetics

RARE AND NEW MUTATIONS OF Β-GLOBIN IN AZARI POPULATION OF IRAN, A CONSIDERABLE DIVERSITY
Abbasali F.H.1, Mahmoud K.Sh.2,3, Hengameh N.3, Mina D.H.3, Setare D.3, Hale D. M3, Sima D.M.2,3*
*Corresponding Author: MD.PhD Sima Mansoori Derakhshan, Department of Medical Genetics, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran, & Ebne Sina Medical Genetics Laboratory, Specialized and Sub-specialized Outpatient Clinics, Tabriz
page: 51

BACKGROUND & OBJECTIVES

The β-thalassemia, as the most common single-gene disorder is found worldwide. It is related to abnormal hemoglobin synthesis, and is more prevalent among the Indian, Mediterranean, and Middle Eastern populations, including Iranians (1, 2). The carrier rate for the β-globin gene mutations is approximately 4-8% in most regions and provinces among the nearly 80 million people living in Iran (3, 4). Thalassemia is a heterogeneous hereditary anemia characterized by the reduced (β+) or lack of (β0) synthesis of the β-globin chains of the hemoglobin (Hb) tetramer composing of two α and two β-globin chains (α2β2) (5, 6). According to a comprehensive review of the studies by Weatherall & Clegg, 2001 and Cao & Galanello, 2011, the disease is diverse at the molecular level (2, 5). More than 200 mutations have been identified worldwide (6-9) resulting in the β-thalassemia major or intermedia. Fortunately, only a subset of the prevalent common mutations is frequently encountered and has been well identified in the at-risk ethnic groups (7). Globally, every high-frequency carrier population has a small number of common mutations that are specific to a particular region, in combination with varying numbers of rare ones (6). Molecular analysis of the patients with β-thalassemia in Iran has led to the identification of 50 various β-globin gene mutations responsible for the disease, thus reflecting the heterogeneity of the Iranian population (10, 11). The diversity of these mutations reflects a historical basis for the admixture of the genes in the country (7, 12). Therefore, it is necessary to determine the frequency and distribution of the β-thalassemia mutations in different regions and provinces. These diverse mutations in the β-globin gene have different frequencies in different regions of Iran and within different ethnicities. In each province, some of these mutations are categorized as common, while others are known to be rare. Collectively, in the 30 provinces of Iran, 13 mutations encompass 70-90% of the patients with β-thalassemia these mutations are classified as common (4, 8, 13-16). The majority of the mutations are single nucleotide substitutions or point mutations. Unlike the α-globin gene, large deletions have been rarely reported in the β-globin gene (11). A geographic distribution with specific mutations could provide information about the place of origin of the genetic change that has generated it. The identification of the particular mutations for prenatal diagnosis during the first trimester of pregnancy is the principal goal for molecular diagnosis of β-thalassemia (17). At the same time, molecular diagnosis of β-thalassemia is more intricate because of the diverse mutations causing defective synthesis of β-globin chain (4).Therefore, the current study was conducted to analyze the rare or lesser known β-globin mutations in the population of Northwestern Iran. The common β-thalassemia mutations in this region have been extensively studied (18). Thus, the purpose of this study was to identify the uncommon and rare β-thalassemia mutations, in order to improve the quality and rate of molecular diagnosis in patients. A timely diagnosis of a mutation in a pregnant woman enrolled in the national prenatal diagnosis (PND) program in Iran is vital, but it is limited to 18 weeks postconception. Awareness of the spectrum of the common and rare mutations would help to detect the responsible mutations in an accurate and timely manner.

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