Diagnostic value of fetal hemoglobin Bart’s for evaluation of fetal α-thalassemia syndromes: application to prenatal characterization of fetal anemia caused by undiagnosed α-hemoglobinopathy

To evaluate whether the quantification of fetal hemoglobin (Hb) Bart's is useful for differentiation of α-thalassemia syndromes in the fetus and to characterize the fetal anemia associated with fetal α-hemoglobinopathy.A total of 332 fetal blood specimens collected by cordocentesis were analyzed using capillary electrophoresis and the amount of Hb Bart's was recorded. The result was evaluated against thalassemia genotypes determined based on Hb and DNA analyses. Prenatal Hb and DNA characterization of the fetal anemia observed in two families was done.Among 332 fetuses investigated, Hb and DNA analyses identified 152 fetuses with normal genotypes. The remaining 180 fetuses carried α-thalassemia with several genotypes. Variable amounts of Hb Bart's were identified in all fetuses with α-thalassemia, which could be used for simple differentiation of fetal α-thalassemia genotypes. These included α+- and α0-thalassemia traits, homozygous α+-thalassemia and Hb Constant Spring (CS), Hb H disease, Hb H-CS and Hb H-Quong Sze diseases, homozygous α0-thalassemia causing the Hb Bart's hydrops fetalis and a remain uncharacterized α-thalassemia defect. The previously undescribed interactions of Hb Queens Park and Hb Amsterdam A1 with Hb E were detected in two fetuses with Hb Bart's of 0.5%. The Hb Queens Park-AEBart's disease was also noted in one pregnant woman. Prenatal analysis of the fetuses with severe fetal anemia and cardiomegaly with Hb Bart's of 9.0% and 13.6% revealed unexpectedly the homozygous Hb CS and a compound heterozygosity of Hb CS/Hb Pakse' with Hb E heterozygote, respectively.The usefulness of detecting and differentiation of fetal α-thalassemia syndromes by quantifying of Hb Bart's was demonstrated. Apart from the fatal condition of Hb Bart's hydrops fetalis associated with homozygous α0-thalassemia, homozygous Hb CS and a compound Hb CS/Hb Pakse' could result in severe fetal anemia and fetal complications, prenatal diagnosis is highly recommended. The simple Hb Bart's quantification of fetal blood should prove helpful in this matter.