Experimental Study On Prenatal Screening And Diagnosis Of Thalassemia

Background and Purposes:Thalassemia(abbreviated Thal) is most frequent,incomplete dominant,chronic hemolytic anemia among people. Though monogenic inheritance, The expression and regulation of referredα,βgene are multiple and the genes possess higher tissue specificity only expressed hematopoietic cells.They need precise regulation which ensure synthesis ratio ofα/βglobin trends to equilibration.The capacity of required expression is much large.All the characters make it difficult for Thal treat. Bothαallelomorphic globin genes orβallelomorphic globin genes suffer damage,which lead to sick baby with thalassemia major or intermediate,the baby show gradually fatal anaemia of globin dyssynthesis.Patients bring heavy economic consumption and stress for scociety and families.Chongqing is a wide area with high occurrence of Thal. To aim directly at the carriers without overt symptom, prenatal genetic screening is trying to detect recessive pregnant woman even prognoses both Thal heterozygote couple. It makes prenatal consult and antenatal diagnosis possible,offers elective means if or not continue prognancy. To monitor marriage and bearing children,it can come true to prevent intermediate thalassemia,cut off thalassemia major form being born and bread.Our study establishes routine prenatal screening and gene diagnosis method of frequentαthalassemia andβthalassemia by investigating reliable relations of hematologic indexes and various Thal genetypes for pregnant woman, spouse and fetal.We make thalassemia major or intermediate Thal to have laboratory diagnosis after trimenon pregnant fetals, which cut down perinatal period birth with defect,ensure mother and baby health and birth quality.Methods:All antenatal examination crowds in our hospital must have general hematologic routine examination. Then we measure serum iron and hemoglobin electrophoresis with abnor red cell parameters. Positive cases need to be detected globin gene by gap-PCR and PCR-RDB and be carried out prenetal diagnosis. Thal pregnant woman should examine spouse's red cell parameters even gene analysis. When a couple are same genetype thalassemia carriers, we draw cord blood or amniotic fluid for detecting the fetal genetype and obtain conclusive prenatal diagnosis. At the right moment termination of pregnancy occurs to medium Thal and thalassemia major in order to decrease the risk to mother and fetus at early pregnancy period. Finally we have doubtedβThal couples'βglobin gene mutational hot spot sequenced,then detect possible unknown mutation by BLAST and analysis.Results:1,2310 pregnant women were screened. 11 cases of them were final diagnosed asαThal, 58 cases asβThal, 3 cases asα/βThal heterozygote, one case asβ/βThal heterozygote.Two couples respectively were suffering fromαThal orβThal,one couples simultaneously suffering fromαThal,two couples suffering simultaneously fromβThal;Two fetal suffering from gravis type Thal, the coincidence was 100 percent by cord blood gene diagnosis again after artificial labor.In our screened crowd,the incidence rate ofαThal was 0.61%(11+3/2310),βThal rate was 2.68%(58+3+1/2310).2,Red cell parameters as mean corpuscular hemoglobin(MCH)has not statistically significant between each genetype(P>0.05); the variations of hemoglobin(Hb),mean corpuscular volume (MCV),red blood cell count(RBC) have not statistically significant betweenαThal,α/β(αThal compoundβThal heterozygote) andβThal(P>0.05), but the variations between three of them andβ/β(βThal double heterozygote) have statistically significant(P<0.01). The variations of Red cell distribution width(RDW),hemoglobin A2(HbA2) have statistically significant between three ofαThal,α/βThal,βThal andβ/βThal(P<0.01). RDW has statistically significant between bothαThal,α/βThal andβThal(P<0.05). HbA2 has statistically significant betweenαThal andβThal(P<0.01).3,The more common types ofβThal were CD41/42(-CTTT),IVS-Ⅱ-654(C→T),CD17(A→T),CD26(G→A),then CD71/72(+A),CD27-28(+C).The commonαThal was --SEA/αα,non-deletion types ofαThal asααCS andααQS were not a few.4,Among 15 doubtfulβThal samples,11 cases appeared from 2 to 5 pieces of single nucleic acid polymorphism(SNP) at CD2,IVS-Ⅱ-16,IVS-Ⅱ-74,IVS-Ⅱ-654, IVS-Ⅱ-666.The SNP at IVS-Ⅱ-654 C→T can cause shearing mutate ofβ0 Thal,the samples with such SNP were diagnosed again by PCR-RDB,appearing mutate probe colouration,so supplementarily diagnosed as IVS-Ⅱ-654 heterozygote.Conclusions:1,Red cell parameters and quantitated hemoglobin electrophoresis are important indexes of screening Thal. Essential systemic hematologic screen for Thal among Prenatal checked-up pregnant women is the most important steps to monitor homeotype Thal couples conception and to eliminate thalassemia major fetals.2,Gap-PCR,PCR-RDB and gene sequencing may quickly make accurate Thal genetype of mother and fetal,practically prevent Thal birth-defect from being born.3,Chongqing is the region with high incidence rate ofβThal. High risk gravidas need antenatal diagnosis and pregnant deal as early as possible, especially those with the history of dys-fetation or dys-labor,baby or infant decease.