Prevalence And Molecular Analysidp Of Alpha-and Beta-thalassemia Among Children In Chongqing City

Objective: The α-and β-thalassemias（Thal） are the most commonautosomal recessive disorders in the world. They are a group of hemolyticanemia characterized by decreasing synthesis of α-or β-globin chains. Thehighest prevalence of thalassemia occur in the tropical and subtropicalregions where malaria has been or remains endemic, including areas of thesouth of the Yangtze River in China. It has been estimated by World HealthOrganization that nearly500million people around the world carry thegenes of hemoglobin variant, accouting for about7%of the population inthe world. Of which about260million are α-thalassemia carriers and80-90million are β-thalassemia carriers. Moreover, there are more than300,000children with thalassemia major born. As a deadly disease,thalassemia major caused serious economic burden and society burden inthe whole society and the patient’s families, also threatened the populationquality in the high incidence areas. Thalassemia major currently has noeffective treatment. Previous practice and experience in the developedregions of the world has been confirmed: carrier screening and geneticcounselling are the most effective solutions to prevent the incidences of children with thalassemia major being born in high prevalence areas. Themain purpose of this study is to illustrate the frequency and molecularspectrum of α-and β-thalassemia in Chongqing city, which can providebasis data for the preventive genetic program for controlling thalassemias.Methods: Cluster random sampling was used. Three different districts inChongqing city were chosen to Collect samples, with the help and approvalof Maternal and child health cares where children received healthexamination before Nursery. A total of1057peripheral venous bloodsamples, which was anticoagulated with EDTA, were collected forepidemiology survey of thalassemia, respectively. The children selected forthis study were inquiried basic informations, including gender, age,nationality and native place. The phenotypic analysis was carried out byblood counts and hemoglobin electrophoresis analysis. Samples with Meancorpuscular volume（MCV）<80fL，cell hemoglobin content （MCH）<27pgand hemoglobinA2（HbA2） levels>3.3%, fetal hemoglobin （HbF）>2%forβ-thal phenotypic positive. The phenotype positive samples were detectedand identified by PCR-reverse dot blot method for18common-β-thalmutations in Chinese populations, unknown mutations samples weresubjected to DNA sequencing analysis of the β-globin gene.A total of1057samples were randomly selected for the molecularsurvey of α-thalassemia. Molecular analysis carried out for all the samples. The α-globin gene mutations were identified using the gap-polymerasechain reaction （Gap-PCR） technique for the three common α-thalassemiadeletion defects (--^SEA,-α^3.7and-α^4.2), and two rare α-thalassemia deletiondefects(--^FILand--^THAI). Copy numbers of α-globin genes were detected byQuantitative real-time PCR, and DNA sequencing analysis to identify theα-gene mutations. We used single-tube multiplex-PCR assay to screen forthe presence of α-globin gene triplications.Results:25Cases of β-thal carries were observed from the1754samples,with the β-thal carrier rate being1.43%. A total of7different gene mutationswere detected, the four most common mutations were as the following:CD41-42（-CTTT）, IVS-Ⅱ-654（C→T）, CD17（AAG>TAG）,βE（CD26,GAG>AAG）, accounting for88.00%of all the mutation genes.In addition, one rare mutation of5’UTR;+（43-40） was found, and one caseof the hemoglobin variant of Hb Zurich was reported in Chinese people forthe first time.Of the1057samples,55cases were diagnosed as being carriers ofα-thalassemia, which included80allele genes. Therefore, the frequency ofα-thalassemia carriers for the city of Chongqing was5.20%. Of the55α-thalassemia carriers, five different deletion α-thalassemia were identified,the three most common deletion types and proportions are54.55%for the-α^3.7deletion,18.18%for–SEAdeletion, and9.08%for the-α^4.2deletion; eight types of nondeletion defects were determined, containing one case ofHb Quong Sze and seven novel mutations of a-globin gene. Furthermore,24cases of α-Triplication were detected, with the α-Triplication carrier ratewas2.55%. In addition, in this study we also found two cases of abnormalhemoglobin disorders occurred on α-globin gene, Hb J-Wenchang-Wumingand Hb Arya. Confirmed by literature retrieval, Hb Arya was characterizedin the Chinese population for the first time.Conclusion: In this study, we have clarified the carrier frequency andmolecular spectrum of α-and β-thalassemia in Chongqing, and we firstlyreported the carrier incidence of α-Triplication in Chongqing. In addition,we found seven mutation defects of α-globin gene and two kinds ofabnormal hemoglobin variants which were described in Chinese populationfor the first time. Chongqing region is of the high risk of the thalassemia.All of these defects were enriched the thalassemia and hemoglobin varianttypes in Chinese population. The materials obtained from this study will beof valuable reference for genetic counseling and the examinationinstruction of children in this area. It will also provide foundation in thisregion to establish preventional program for controlling thalassemias in thiscity.